Reduction of Oxygen-Induced CSF Hyperintensity on FLAIR MR Images in Sedated Children: Usefulness of Magnetization-Prepared FLAIR Imaging

BACKGROUND AND PURPOSE:Oxygen-induced CSF hyperintensity on FLAIR MR imaging is often observed in sedated children. This phenomenon can mimic leptomeningeal pathology and lead to a misdiagnosis. The purpose of this study was to investigate whether magnetization-prepared FLAIR MR imaging can reduce oxygen-induced CSF hyperintensity and improve image quality compared with conventional (non-magnetization-prepared) FLAIR MR imaging.MATERIALS AND METHODS:Bloch simulation for magnetization-prepared and non-magnetization-prepared FLAIR sequences was performed for tissue contrast. We retrospectively reviewed 85 children with epilepsy who underwent MR imaging under general anesthesia with supplemental oxygen (41 with non-magnetization-prepared FLAIR and 44 with magnetization-prepared FLAIR). CSF hyperintensity was scored from 0 to 3 points according to the degree of CSF signal intensity and was compared between the 2 sequences. The contrast-to-noise ratios among GM, WM, and CSF were evaluated to assess general image quality from both sequences. To assess the diagnostic accuracy for hemorrhage, we reviewed an additional 25 patients with hemorrhage.RESULTS:Bloch simulation demonstrated that CSF hyperintensity can be reduced on magnetization-prepared FLAIR compared with non-magnetization-prepared FLAIR. CSF hyperintensity scores were significantly lower in magnetization-prepared FLAIR than in non-magnetization-prepared FLAIR (P < .01). The contrast-to-noise ratios for GM-WM, GM-CSF, and WM-CSF were significantly higher in magnetization-prepared FLAIR than in non-magnetization-prepared FLAIR (P < .05). Hemorrhage was clearly demarcated from CSF hyperintensity in the magnetization-prepared group (100%, 12/12) and non-magnetization-prepared group (38%, 5/13).CONCLUSIONS:Magnetization-prepared 3D-FLAIR MR imaging can significantly reduce oxygen-induced CSF artifacts and increase the tissue contrast-to-noise ratio beyond the levels achieved with conventional non-magnetization-prepared 3D-FLAIR MR imaging.

MR imaging is the diagnostic tool of choice in pediatric neurologic diseases because it has no ionizing radiation and is noninvasive. However, sedation is unavoidable if suitable MR images are sought because pediatric patients usually do not cooperate during long-duration scans.CSF hyperintensity on FLAIR MR images is frequently encountered in sedated children.^1–5 These artifacts cause a diagnostic dilemma because they can mimic hemorrhage, infection, and leptomeningeal seeding metastasis, which are all known to generate hyperintense CSF signals on FLAIR MR images.^6–9 Initially, CSF hyperintensity was attributed to anesthetic-induced T1-shortening, protein redistribution due to changes in the intravascular membrane permeability, hyperdynamic CSF pulsation due to altered vascular tone, and supplemental oxygen during anesthesia.^2–4,10 However, several studies have revealed that the most plausible cause of hyperintense CSF artifacts in FLAIR imaging is the administration of supplemental oxygen during anesthesia.^1,2,4,5,10Oxygen is a weak paramagnetic substance, which has 2 unpaired electrons that can cause a moderate increase in the T1 relaxation rate.^11,12 Studies have shown that the diffusional transfer of oxygen from blood to CSF and a consequent FLAIR MR signal increase depend on the inhaled oxygen concentration^1,2,4,13 and oxygen delivery methods.^3,103D-FLAIR imaging is based on the 3D TSE imaging technique that modulates a refocusing flip angle at the TSE echo-train to maintain relatively steady signal levels during a long train of echo signals, which can provide improved image sharpness, helpful in detecting small structures. Consequently, the relaxation-induced image blurring, partial volume effect, and specific absorption rate can be reduced allowing high-resolution 3D data acquisition at isotropic voxels during clinically feasible scan durations.¹⁴ 3D-FLAIR also provides increased SNR and reduces CSF pulsation artifacts compared with 2D FLAIR.^5,15–18 In magnetization-prepared (MP) 3D-FLAIR imaging, a dedicated magnetization preparation is implemented before typical inversion recovery, followed by TSE imaging, which is known to reduce unwanted T1-weighting and image TR.^19,20 Therefore, the purpose of this study was to compare magnetization-prepared 3D-FLAIR imaging with conventional (non-MP) 3D-FLAIR imaging in terms of the ability to reduce oxygen-induced CSF hyperintensity and improve image quality in sedated pediatric patients.     

High-Resolution MRI of the Intraparotid Facial Nerve Based on a Microsurface Coil and a 3D Reversed Fast Imaging with Steady-State Precession DWI Sequence at 3T

BACKGROUND AND PURPOSE:3D high-resolution MR imaging can provide reliable information for defining the exact relationships between the intraparotid facial nerve and adjacent structures. The purpose of this study was to explore the clinical value of using a surface coil combined with a 3D-PSIF-DWI sequence in intraparotid facial nerve imaging.MATERIALS AND METHODS:Twenty-one healthy volunteers underwent intraparotid facial nerve scanning at 3T by using the 3D-PSIF-DWI sequence with both the surface coil and the head coil. Source images were processed with MIP and MPR to better delineate the intraparotid facial nerve and its branches. In addition, the SIR of the facial nerve and parotid gland was calculated. The number of facial nerve branches displayed by these 2 methods was calculated and compared.RESULTS:The display rates of the main trunk, divisions (cervicofacial, temporofacial), and secondary branches of the intraparotid facial nerve were 100%, 97.6%, and 51.4% by head coil and 100%, 100%, and 83.8% by surface coil, respectively. The display rate of secondary branches of the intraparotid facial nerve by these 2 methods was significantly different (P < .05). The SIRs of the intraparotid facial nerve/parotid gland in these 2 methods were significantly different (P < .05) at 1.37 ± 1.06 and 1.89 ± 0.87, respectively.CONCLUSIONS:The 3D-PSIF-DWI sequence combined with a surface coil can better delineate the intraparotid facial nerve and its divisions than when it is combined with a head coil, providing better image contrast and resolution. The proposed protocol offers a potentially useful noninvasive imaging sequence for intraparotid facial nerve imaging at 3T.

3D high-resolution MR imaging can provide reliable information for depicting normal intraparotid facial nerve anatomy and defining the exact relationship of the intraparotid facial nerve and adjacent structures; this information could assist in the planning of parotid tumor surgery.¹ Imaging the intraparotid course of the facial nerve is a challenge due to the fine structure and complex anatomy of the nerve.^1–4 With recent advances in MR imaging technology, especially the use of surface coils combined with 3D high-resolution MR imaging technology, increased attention has been directed to intraparotid facial nerve imaging.^1–4 The inherent resolution of a surface coil itself is significantly better than that of a head coil, ensuring high-quality imaging for fine structures, particularly in superficial organs such as the parotid gland or eye.^1,5 Recently, 3D high-resolution sequences such as 3D gradient-recalled acquisition in the steady state sequence and 3D FIESTA have been applied to intraparotid facial nerve imaging.^2–4 These sequences rely mainly on the fat within the parotid gland as a high signal background to show the facial nerve because both the intraparotid facial nerve and the parotid duct are visualized as linear structures of low intensity.^2–4 In another report, the intraparotid facial nerve showed low signal compared with the high intensity of the parotid duct by using a balanced turbo-field echo, thus avoiding confusion between these 2 structures; however, no volumetric images were obtained,⁶ and MPR or curved planar reconstruction was not available. Thus, although there are several MR imaging sequences that can delineate the intraparotid facial nerve and parotid duct, limitations remain. The aim of this study was to explore the capabilities of simultaneously displaying the intraparotid facial nerve and parotid duct by using a surface coil combined with 3D-PSIF-DWI on a 3T MR imaging scanner.     

Comparison of contrast effect on the cochlear perilymph after intratympanic and intravenous gadolinium injection

BACKGROUND AND PURPOSE:3D-FLAIR imaging 24 hours after intratympanic gadolinium injection (IT-method) or 4 hours after IV injection (IV-method) has been used to visualize the endolymphatic hydrops in Ménière disease. The purpose of this study was to compare the degree of perilymph enhancement with the 2 methods and the perilymph contrast-effect difference with the IV-method in both sides in patients with unilateral Ménière disease.MATERIALS AND METHODS:Sixty-one patients with Ménière disease or sudden SNHL were included in this study. Thirty-nine patients who underwent the unilateral IT-method (Gd-DTPA was diluted 8-fold with saline) and 22 patients who underwent the IV-method (a double-dose of Gd-HP-DO3A; 0.4 mL/kg body weight [ie, 0.2 mmol/kg body weight]) at 3T were analyzed retrospectively. Regions of interest of the cochlear perilymph and the medulla oblongata were determined on each image, and the signal-intensity ratio between the 2 (CM ratio) was subsequently evaluated. The differences in the CM ratio between the 2 methods (Student t test) and the IV-method CM ratio between the affected and unaffected sides in patients with unilateral Ménière disease (paired t test) were evaluated.RESULTS:The IT-method CM ratio (2.98 ± 1.15, n = 39) was higher than the IV-method CM ratio (1.61 ± 0.60, n = 44; P < .001). In patients with unilateral Ménière disease who underwent the IV-method (n = 9), the CM ratio of the affected side (1.86 ± 0.74) was higher than that of the unaffected side (1.29 ± 0.31, P < .05).CONCLUSIONS:In general, the IT-method provides higher perilymph enhancement than the IV-method. In the patients with unilateral Ménière disease who underwent the IV-method, the affected side had a higher contrast effect.

FLAIR imaging is a sensitive technique for the detection of high-protein-content fluid or tissue in the CSF such as in acute meningitis or subarachnoid hemorrhage and various cystic intracranial mass lesions.^1,2 3D-FLAIR imaging can minimize the undesired ghosts of CSF flow³ and enable recognition of the subtle compositional changes in lymph fluid in the inner ear.^4–6 In addition, increased signal intensity of the diseased inner ear can also be observed on 3D-FLAIR imaging shortly after IV gadolinium injection; this technique has been reported to be useful for pathophysiologic analysis of the inner ear in many auditory diseases, such as sudden SNHL, cholesteatoma, cochlear otosclerosis, and vestibular schwannoma.^7–103D-FLAIR imaging 24 hours after intratympanic gadolinium injection (IT-method) has been reported to visualize perilymph and endolymph fluid separately and to enable preliminary prediction of drug distribution to the inner ear, such as gentamicin and steroids.^11–14 The sensitivity of gadolinium-agent detection in perilymph 24 hours after intratympanic gadolinium injection on 3D-FLAIR has been reported to be superior to that on 3D-T1-weighted imaging or on the 3D-constructive interference in steady state sequence,¹⁵ suggesting that 3D-FLAIR would be most suited for signal-intensity- alteration assessment 24 hours after intratympanic gadolinium injection. On the other hand, 3D-FLAIR imaging 4 hours after IV gadolinium injection (IV-method) also has been recently reported to visualize perilymph and endolymph fluid separately, in a less invasive manner than the IT-method, and also enables ascertaining the presence of endolymphatic hydrops in bilateral cochleae.^16,17 Consequently, both the IT-method and IV-method are useful techniques for clarification of the inner ear clinical condition, though a statistical analysis of signal-intensity differences in the perilymph fluid between the 2 methods has not been previously reported, to our knowledge. The principal purpose of the present study was to evaluate the signal intensity of the cochlear perilymph by using both the IT-method and IV-method and to clarify the differences in contrast effect between these 2 techniques. In addition, the contrast effect difference in the cochlear perilymph with the IV-method between affected and unaffected sides in patients with unilateral Ménière disease was also evaluated to infer the condition of the blood-labyrinth-barrier permeability of patients with Ménière disease.     

MS Lesions Are Better Detected with 3D T1 Gradient-Echo Than with 2D T1 Spin-Echo Gadolinium-Enhanced Imaging at 3T

BACKGROUND AND PURPOSE:In multiple sclerosis, gadolinium enhancement is used to classify lesions as active. Regarding the need for a standardized and accurate method for detection of multiple sclerosis activity, we compared 2D-spin-echo with 3D-gradient-echo T1WI for the detection of gadolinium-enhancing MS lesions.MATERIALS AND METHODS:Fifty-eight patients with MS were prospectively imaged at 3T by using both 2D-spin-echo and 3D-gradient recalled-echo T1WI in random order after the injection of gadolinium. Blinded and independent evaluation was performed by a junior and a senior reader to count gadolinium-enhancing lesions and to characterize their location, size, pattern of enhancement, and the relative contrast between enhancing lesions and the adjacent white matter. Finally, the SNR and relative contrast of gadolinium-enhancing lesions were computed for both sequences by using simulations.RESULTS:Significantly more gadolinium-enhancing lesions were reported on 3D-gradient recalled-echo than on 2D-spin-echo (n = 59 versus n = 30 for the junior reader, P = .021; n = 77 versus n = 61 for the senior reader, P = .017). The difference between the 2 readers was significant on 2D-spin-echo (P = .044), for which images were less reproducible (κ = 0.51) than for 3D-gradient recalled-echo (κ = 0.65). Further comparisons showed that there were statistically more small lesions (<5 mm) on 3D-gradient recalled-echo than on 2D-spin-echo (P = .04), while other features were similar. Theoretic results from simulations predicted SNR and lesion contrast for 3D-gradient recalled-echo to be better than for 2D-spin-echo for visualization of small enhancing lesions and were, therefore, consistent with clinical observations.CONCLUSIONS:At 3T, 3D-gradient recalled-echo provides a higher detection rate of gadolinium-enhancing lesions, especially those with smaller size, with a better reproducibility; this finding suggests using 3D-gradient recalled-echo to detect MS activity, with potential impact in initiation, monitoring, and optimization of therapy.

MR imaging is widely used in multiple sclerosis and has become an established tool not only for diagnosis but also for disease monitoring.¹ MR imaging–defined disease activity, in conjunction with clinical status, can be used to ensure treatment optimization by identifying high-risk patients or poor responders during follow-up,^2,3 which is important given that MS is a chronic disease for which expensive treatments are now used. There is an urgent need for an accurate and standardized MR imaging methodology among centers to better characterize and follow intrapatient changes longitudinally in personalized medicine and to facilitate analysis of large standardized datasets, which could help define predictors of disease evolution and long-term effects of therapies. Several attempts to improve and standardize MR imaging protocols have been published,^4–6 and several national cohorts are being developed (MAGNetic resonance Imaging in Multiple Sclerosis centers in Europe,⁷ L''Observatoire Français de la Sclérose en Plaques in France⁸), all sharing the objective of creating a central library documented by using high-quality homogeneous MR imaging examinations with demographic and clinical evaluations.Despite published imaging recommendations,^4–6 recent technical developments suggest a careful re-examination of imaging methods and parameters. One significant development is the successful implementation of single-slab 3D sequences,⁹ which have become more commonplace with stronger field strengths (3T), better gradients, and improved receiver coil arrays. For example, the single-slab version of the 3D-T2-FLAIR has been shown to be better than conventional 2D-T2-FLAIR in terms of contrast-to-noise ratio, lesion detection, and homogeneity of CSF suppression.^10–12 Due to its higher sensitivity for lesion detection, 3D-T2-FLAIR is increasingly being used in MS and it also improves comparison across time points through easier registration of images to be displayed within the same geometric frame.⁶While 3D-T1-weighted imaging sequences such as 3D fast-spoiled gradient recalled (FSPGR) and magnetization-prepared rapid acquisition of gradient echo have been in use for a long time and are widely used in clinical brain imaging,¹³ they are not routinely used in MS for visualization of active lesions after gadolinium injection. This practice is likely a result of theoretic¹⁴ and clinical studies^15–17 that demonstrated that 3D gradient recalled-echo (GRE) sequences could miss contrast enhancement compared with “conventional” 2D spin-echo (SE) images. While it is true that there are fundamental differences in the contrast behavior of the GRE and SE techniques,¹⁴ the dogma favoring 2D-SE over 3D-GRE for contrast enhancement of MS lesions comes from early work by using an older generation of imaging hardware and sequences.^15–18 The increased availability of higher SNR 3T imaging systems and the improved contrast effect of gadolinium agents at 3T compared with 1.5T^19–22 suggest a reconsideration of 2D-versus-3D imaging. High-performance imaging hardware and developments in parallel imaging permit whole-brain coverage with thin-section thickness by using 3D-GRE sequences in relatively short scanning times. The multiplanar reformatting capabilities with high SNR and contrast make 3D sequences appealing. In addition, Kakeda et al²³ found significantly more metastases with contrast-enhanced 3D FSPGR than with 2D-SE imaging at 3T, especially small metastases of <3 mm in diameter. A direct comparison of 3D-GRE and 2D-SE T1-weighted sequences to depict active MS lesions after gadolinium injection has not been conducted, to our knowledge.Consequently, recognizing the need for a standardized optimal detection of MS activity among centers to better guide therapy, we aimed at comparing the detection of gadolinium-enhancing lesions between 3D-GRE and conventional 2D-SE sequences. To achieve this goal, we combined an experimental approach in patients with MS with theoretic models analyzing the contrast-enhancement performance of 3D-GRE versus 2D-SE.     

Comparison of Inner Ear Contrast Enhancement among Patients with Unilateral Inner Ear Symptoms in MR Images Obtained 10 Minutes and 4 Hours after Gadolinium Injection

BACKGROUND AND PURPOSE:Recently 4-hour delayed-enhanced 3D-FLAIR MR imaging has been used in pathophysiologic analysis of the inner ear in many auditory diseases, including sudden sensorineural hearing loss, but comparison among different time points is not clear in patients with unilateral inner ear symptoms. We compared the signal-intensity ratios of the inner ears in patients with unilateral inner ear symptoms on 10-minute delayed-enhanced and 4-hour delayed-enhanced 3D-FLAIR MR images after IV gadolinium injection.MATERIALS AND METHODS:The 10-minute delayed-enhanced and 4-hour delayed-enhanced 3D-FLAIR MR images were retrospectively analyzed. Signal-intensity ratios between the cerebellum and inner ear structures, such as the cochleae, vestibules, and vestibulocochlear nerve were assessed. Multiple comparisons were performed.RESULTS:Signal-intensity ratios of the affected cochleae, vestibules, and vestibulocochlear nerve were higher than those of unaffected sides in both 10-minute delayed-enhanced and 4-hour delayed-enhanced images. At the affected side, signal-intensity ratios of the vestibulocochlear nerve were higher in patients with nonsudden sensorineural hearing loss than in those with sudden sensorineural hearing loss on both 10-minute delayed-enhanced and 4-hour delayed-enhanced images. The signal-intensity ratios of some affected inner ear structures were higher than those of the unaffected sides in a group of 30 patients with sudden sensorineural hearing loss and 20 patients with nonsudden sensorineural hearing loss on 10-minute delayed-enhanced and 4-hour delayed-enhanced images.CONCLUSIONS:Signal-intensity ratios of the inner ear show statistically significant increases in many diseases, especially neuritis, in 10-minute delayed-enhanced and 4-hour delayed-enhanced images. The 4-hour delayed-enhanced images may be superior in neural inflammatory–dominant conditions, while 10-minute delayed-enhanced images may be superior in neural noninflammatory–dominant conditions.

3D fluid-attenuated inversion recovery MR imaging has recently been applied to the inner ear to investigate inner ear pathology. The increased signal intensity of diseased inner ears can also be observed on 3D-FLAIR imaging after intravenous gadolinium injection. This technique is useful for the pathophysiologic analysis of the inner ear in many auditory diseases, such as sudden sensorineural hearing loss (sSNHL), cholesteatoma, cochlear otosclerosis, and vestibular schwannoma.^1–4 Compared with intratympanic gadolinium injection, 3D-FLAIR MR imaging after IV gadolinium injection is less invasive and enables observation of the bilateral cochleae and other inner ear structures.⁵The signal-intensity ratio of the inner ear to other parts of the brain allows semiquantitative expression of the signal intensity and may be useful for comparing results among patients or among ears. Recent articles have reported that the signal-intensity ratio of the inner ear and other parts of the brain is useful in patients with sudden deafness, Ménière disease, and vestibular schwannoma.^4,6–8The signal-intensity ratio of the inner ear and brain stem may indicate disruption of the blood-labyrinthine barrier in patients with inner ear disease with 4-hour enhancement after gadolinium injection.⁷ To our knowledge, the difference in inner ear signal intensity between 10-minute and 4-hour delayed MRI has not been evaluated in most patients with unilateral symptoms, however, including those with sSNHL.The purpose of this study was to compare signal intensities of the inner ear among patients with unilateral symptomatic ear diseases. Comparisons were made between the affected and unaffected sides, between patients with sSNHL and nonsudden sensorineural hearing loss (nsSNHL), and between 10-minute and 4-hour delayed intravenous gadolinium-enhanced 3D-FLAIR MR imaging.     

Evaluation of Ultrafast Wave–Controlled Aliasing in Parallel Imaging 3D-FLAIR in the Visualization and Volumetric Estimation of Cerebral White Matter Lesions

BACKGROUND AND PURPOSE:Our aim was to evaluate an ultrafast 3D-FLAIR sequence using Wave–controlled aliasing in parallel imaging encoding (Wave-FLAIR) compared with standard 3D-FLAIR in the visualization and volumetric estimation of cerebral white matter lesions in a clinical setting.MATERIALS AND METHODS:Forty-two consecutive patients underwent 3T brain MR imaging, including standard 3D-FLAIR (acceleration factor = 2, scan time = 7 minutes 50 seconds) and resolution-matched ultrafast Wave-FLAIR sequences (acceleration factor  = 6, scan time = 2 minutes 45 seconds for the 20-channel coil; acceleration factor = 9, scan time  = 1 minute 50 seconds for the 32-channel coil) as part of clinical evaluation for demyelinating disease. Automated segmentation of cerebral white matter lesions was performed using the Lesion Segmentation Tool in SPM. Student t tests, intraclass correlation coefficients, relative lesion volume difference, and Dice similarity coefficients were used to compare volumetric measurements among sequences. Two blinded neuroradiologists evaluated the visualization of white matter lesions, artifacts, and overall diagnostic quality using a predefined 5-point scale.RESULTS:Standard and Wave-FLAIR sequences showed excellent agreement of lesion volumes with an intraclass correlation coefficient of 0.99 and mean Dice similarity coefficient of 0.97 (SD, 0.05) (range, 0.84–0.99). Wave-FLAIR was noninferior to standard FLAIR for visualization of lesions and motion. The diagnostic quality for Wave-FLAIR was slightly greater than for standard FLAIR for infratentorial lesions (P < .001), and there were fewer pulsation artifacts on Wave-FLAIR compared with standard FLAIR (P < .001).CONCLUSIONS:Ultrafast Wave-FLAIR provides superior visualization of infratentorial lesions while preserving overall diagnostic quality and yields white matter lesion volumes comparable with those estimated using standard FLAIR. The availability of ultrafast Wave-FLAIR may facilitate the greater use of 3D-FLAIR sequences in the evaluation of patients with suspected demyelinating disease.

White matter lesions secondary to demyelination in multiple sclerosis (MS) and related disorders typically present with high T2 signal and are best evaluated with FLAIR imaging, the standard sequence for cerebral white matter lesion detection. FLAIR is a T2-weighted sequence with nulling of the CSF signal, which increases the contrast between lesions and CSF/cerebral sulci and ventricles and improves white matter lesion detection and analysis.¹Quantification of cerebral white matter lesion volume has become increasingly feasible for routine clinical evaluation and use in clinical trials of MS therapies due to the availability of automated segmentation tools and 3D fast spin-echo FLAIR sequences, which delineate cerebral white matter lesions at high isotropic resolution. The Lesion Segmentation Tool (LST; https://www.applied-statistics.de/lst.html), a promising tool for automated segmentation of T2-hyperintense lesions on FLAIR images, was developed for the quantification of MS lesion volumes and has been shown to have good agreement with manual segmentation by expert reviewers.^2-7 However, the high-resolution 3D-FLAIR images required as input for this tool have long acquisition times, limiting the widespread use of automated lesion segmentation in clinical practice.Wave–controlled aliasing in parallel imaging (CAIPI) is a recently developed fast acquisition technology that synergistically combines and extends 2 controlled aliasing approaches, 2D-CAIPI and bunch phase encoding,⁸ to achieve controlled aliasing in all 3 spatial directions (x, y, z). By taking full advantage of the 3D coil sensitivity information, Wave-CAIPI offers high acceleration factors with negligible artifacts and g-factor penalty.^9,10 3D-FLAIR acquired with Wave-CAIPI cuts the scan time down by more than half, possibly facilitating the broader clinical application of 3D-FLAIR in the evaluation of white matter diseases such as MS.The goal of this study was to evaluate an ultrafast Wave-CAIPI 3D-FLAIR sequence (Wave-FLAIR)^11,12 acquired in less than half the time of standard 3D-FLAIR for quantitative and qualitative analyses of cerebral white matter lesions.     

Effectiveness of 3D T2-Weighted FLAIR FSE Sequences with Fat Suppression for Detection of Brain MR Imaging Signal Changes in Children

BACKGROUND AND PURPOSE:T2-weighted FLAIR can be combined with 3D-FSE sequences with isotropic voxels, yielding higher signal-to-noise ratio than 2D-FLAIR. Our aim was to explore whether a T2-weighted FLAIR–volume isotropic turbo spin-echo acquisition sequence (FLAIR-VISTA) with fat suppression shows areas of abnormal brain T2 hyperintensities with better conspicuity in children than a single 2D-FLAIR sequence.MATERIALS AND METHODS:One week after a joint training session with 20 3T MR imaging examinations (8 under sedation), 3 radiologists independently evaluated the presence and conspicuity of abnormal areas of T2 hyperintensities of the brain in FLAIR-VISTA with fat suppression (sagittal source and axial and coronal reformatted images) and in axial 2D-FLAIR without fat suppression in a test set of 100 3T MR imaging examinations (34 under sedation) of patients 2–18 years of age performed for several clinical indications. Their agreement was measured with weighted κ statistics.RESULTS:Agreement was “substantial” (mean, 0.61 for 3 observers; range, 0.49–0.69 for observer pairs) for the presence of abnormal T2 hyperintensities and “fair” (mean, 0.29; range, 0.23–0.38) for the comparative evaluation of lesion conspicuity. In 21 of 23 examinations in which the 3 radiologists agreed on the presence of abnormal T2 hyperintensities, FLAIR-VISTA with fat suppression images were judged to show hyperintensities with better conspicuity than 2D-FLAIR. In 2 cases, conspicuity was equal, and in no case was conspicuity better in 2D-FLAIR.CONCLUSIONS:FLAIR-VISTA with fat suppression can replace the 2D-FLAIR sequence in brain MR imaging protocols for children.

3D (volume) gradient-echo T1-weighted sequences are a well-established part of brain MR imaging protocols due to the intrinsically higher SNR compared with 2D sequences and the ability to obtain optimal MPR.¹ However, abnormalities of the brain are usually detected as nonspecific areas of variably increased signal in T2WI. FLAIR images are preferable to FSE images for detecting such T2 abnormalities because suppression of the CSF high signal results in an improved gray-scale dynamic range.²T2-weighted FLAIR can be combined with 3D-FSE sequences with isotropic voxels that are variably named by different vendors, including volume isotropic turbo spin-echo acquisition (VISTA; Philips Healthcare, Best, the Netherlands), SPACE (sampling perfection with application-optimized contrasts by using different flip angle evolution; Siemens, Erlangen, Germany), Cube (GE Healthcare, Milwaukee, Wisconsin), isoFSE (http://www.hitachimed.com/products/mri/oasis/Neurological/isoFSE), and 3D mVox (Toshiba, Tokyo, Japan). Such T2-weighted FLAIR 3D-FSE sequences have a higher SNR than 2D-FLAIR, enable MPR, and are less affected by CSF flow artifacts,^3–6 which are more prominent in sedated children at a higher field strength 3T magnet.^7–9Theoretically, suppression of fat signal with spectral presaturation could improve the sensitivity of FLAIR-VISTA by further narrowing the gray-scale dynamic range.²The purpose of the present study was to evaluate whether a FLAIR-VISTA sequence with fat suppression shows abnormal brain T2 signal hyperintensities with better conspicuity than a 2D-FLAIR sequence on a single axial plane in children.     

Differentiation between glioblastomas, solitary brain metastases, and primary cerebral lymphomas using diffusion tensor and dynamic susceptibility contrast-enhanced MR imaging

BACKGROUND AND PURPOSE:Glioblastomas, brain metastases, and PCLs may have similar enhancement patterns on MR imaging, making the differential diagnosis difficult or even impossible. The purpose of this study was to determine whether a combination of DTI and DSC can assist in the differentiation of glioblastomas, solitary brain metastases, and PCLs.MATERIALS AND METHODS:Twenty-six glioblastomas, 25 brain metastases, and 16 PCLs were retrospectively identified. DTI metrics, including FA, ADC, CL, CP, CS, and rCBV were measured from the enhancing, immediate peritumoral and distant peritumoral regions. A 2-level decision tree was designed, and a multivariate logistic regression analysis was used at each level to determine the best model for classification.RESULTS:From the enhancing region, significantly elevated FA, CL, and CP and decreased CS values were observed in glioblastomas compared with brain metastases and PCLs (P < .001), whereas ADC, rCBV, and rCBV_max values of glioblastomas were significantly higher than those of PCLs (P < .01). The best model to distinguish glioblastomas from nonglioblastomas consisted of ADC, CS (or FA) from the enhancing region, and rCBV from the immediate peritumoral region, resulting in AUC = 0.938. The best predictor to differentiate PCLs from brain metastases comprised ADC from the enhancing region and CP from the immediate peritumoral region with AUC = 0.909.CONCLUSIONS:The combination of DTI metrics and rCBV measurement can help in the differentiation of glioblastomas from brain metastases and PCLs.

Glioblastomas, brain metastases, and PCLs are common brain malignancies in adults, which may have similar enhancement patterns on MR imaging. Conventional MR imaging is very limited in making the distinction. Contrast enhancement on T1-weighted images reflects areas of blood-brain barrier breakdown regardless of the pathology. FLAIR imaging can depict a large portion of the tumor but also is nonspecific.^1,2 Accurate preoperative diagnosis is often crucial because the management and prognosis of these tumors are substantially different.^3–5 For example, patients with glioblastomas are almost always treated by surgical resection,⁴ while patients with suspected brain metastases without a clinical history of systemic cancer should undergo a complicated systemic staging to determine the site of primary carcinoma and evaluate other distant metastases before any surgical intervention or medical therapy.⁵ PCLs are managed primarily with chemotherapy or radiation therapy after stereotactic biopsy.³DTI has been widely reported in brain tumor classification.^1,6–9 The ADC value, measured from diffusion-weighted imaging or DTI, has been reported to be inversely correlated with cellularity in tumors.^7,8 Prior studies have shown that ADC can help differentiate PCLs from high-grade gliomas^1,6–8,10 and brain metastases⁸; however, other studies have reported a substantial overlap between these tumor types.^11,12 DTI also provides diffusion anisotropy information about the tissue, such as FA, CL, CP, and CS. Of these parameters, FA has been most commonly used in the study of brain neoplasms.^13,14 In contrast to ADC, the relationship between FA and cellularity has not been substantiated. Toh et al¹⁰ reported significantly decreased FA in highly cellular cerebral PCLs compared with glioblastomas, whereas Kinoshita et al¹⁴ demonstrated high FA values in PCLs. Our previous study demonstrated that DTI metrics, including ADC, FA, and CP, from the enhancing region of the tumor can differentiate glioblastomas from brain metastases with 92% sensitivity and 100% specificity.⁹DSC provides maps of CBV, which correlate with tumor vascularity and allow indirect assessment of tumor angiogenesis.^2,15 Vascular proliferation and tumor angiogenesis are among the most important factors in the biologic behavior of malignant brain tumors.¹⁶ An increase in the microvascularity and neovascularity of these tumors leads to increased rCBV. It has been reported that PCLs have lower mean rCBV,^17–19 or lower rCBV_max values^6,20–22 compared with glioblastomas or brain metastases.¹⁷ In the peritumoral region, glioblastomas demonstrate elevated rCBV due to tumor infiltration in the normal brain parenchyma in comparison with brain metastases.²³In this study, we hypothesized that a combination of DTI (FA, ADC, CL, CP, and CS) and DSC (rCBV) parameters can assist in better differentiation of glioblastomas, solitary brain metastases, and PCLs. A 2-level decision tree and a multivariate logistic regression analysis were used to determine the best model for tumor classification.     

Is Contrast Medium Really Needed for Follow-up MRI of Untreated Intracranial Meningiomas?

BACKGROUND AND PURPOSE:Recent concerns relating to tissue deposition of gadolinium are favoring the use of noncontrast MR imaging whenever possible. The purpose of this study was to assess the necessity of gadolinium contrast for follow-up MR imaging of untreated intracranial meningiomas.MATERIALS AND METHODS:One-hundred twenty-two patients (35 men, 87 women) with meningiomas who underwent brain MR imaging between May 2007 and May 2019 in our institution were included in this retrospective cohort study. We analyzed 132 meningiomas: 73 non-skull base (55%) versus 59 skull base (45%), 93 symptomatic (70%) versus 39 asymptomatic (30%). Fifty-nine meningiomas underwent an operation: 54 World Health Organization grade I (92%) and 5 World Health Organization grade II (8%). All meningiomas were segmented on T1 3D-gadolinium and 2D-T2WI. Agreement between T1 3D-gadolinium and 2D-T2WI segmentations was assessed by the intraclass correlation coefficient.RESULTS:The mean time between MR images was 1485 days (range, 760–3810 days). There was excellent agreement between T1 3D-gadolinium and T2WI segmentations (P < .001): mean tumor volume (T1 3D-gadolinium: 9012.15 [SD, 19,223.03] mm³; T2WI: 8528.45 [SD, 18,368.18 ] mm³; intraclass correlation coefficient = 0.996), surface area (intraclass correlation coefficient = 0.989), surface/volume ratio (intraclass correlation coefficient = 0.924), maximum 3D diameter (intraclass correlation coefficient = 0.986), maximum 2D diameter in the axial (intraclass correlation coefficient = 0.990), coronal (intraclass correlation coefficient = 0.982), and sagittal planes (intraclass correlation coefficient = 0.985), major axis length (intraclass correlation coefficient = 0.989), minor axis length (intraclass correlation coefficient = 0.992), and least axis length (intraclass correlation coefficient = 0.988). Tumor growth also showed good agreement (P < .001), estimated as a mean of 461.87 [SD, 2704.1] mm³/year on T1 3D-gadolinium and 556.64 [SD, 2624.02 ] mm³/year on T2WI.CONCLUSIONS:Our results show excellent agreement between the size and growth of meningiomas derived from T1 3D-gadolinium and 2D-T2WI, suggesting that the use of noncontrast MR imaging may be appropriate for the follow-up of untreated meningiomas, which would be cost-effective and avert risks associated with contrast media.

Recent concerns regarding gadolinium (Gd) compounds are fueling a trend to use contrast media in MR imaging less frequently. Notwithstanding the well-established safety profile of Gd compounds, a small number of immediate adverse effects, which may be life-threatening, has been reported^1,2 at a rate of approximately 0.3%.² Furthermore, repeat administration of Gd-based contrast may lead to deposition of Gd in the dentate nucleus and the globus pallidus,^3-7 which seems to be the case with linear rather than macrocyclic Gd compounds,⁴ despite a normal renal function⁷ and an intact blood-brain barrier.⁶ Health care costs should also be considered because they are a heavy burden to modern Western societies,^8-10 and medical imaging accounts for a large proportion of these costs.¹⁰ Gd-based contrast media significantly contribute to the cost of an MR image, due to the price of the contrast medium itself and also because of the prolonged image-acquisition time. Using contrast media more sparingly could, therefore, reduce these costs considerably.The above-mentioned concerns are particularly pertinent to young patients with incidental or asymptomatic meningiomas in which frequent and long-term follow-up MR imaging is usually performed, the current standard-of-care being MR with Gd-based contrast media.¹¹ Intracranial meningiomas are, by and large, benign World Health Organization (WHO) grade I tumors derived from meningothelial cells,^12,13 representing approximately one-third of all primary central nervous system tumors¹⁴ and 15% of symptomatic intracranial masses.¹⁵ They are extra-axial lesions that usually exhibit slow growth (approximately 14%/year for WHO grade I lesions).¹⁶ However, the growth rate can be substantially higher, particularly in WHO grade II and III meningiomas, necessitating frequent MR imaging follow-up. For instance, the European Association of Neuro-Oncology advocates diligent radiologic follow-up of meningiomas. For small asymptomatic meningiomas, the recommendation of this institution is to assess the tumor dynamics with contrast MR imaging at 6 months after the initial diagnosis and then annually as long as the patient remains asymptomatic.¹¹Quantitative MR imaging parameters such as tumor volume¹⁷ are important in predicting tumor growth and behavior. Nakasu and Nakasu,¹⁸ in 2020, identified large tumor size and annual volume change of ≥2.1 cm³ as the strongest predictors of symptomatic tumor progression. Several other parameters may be important in predicting the potential for rapid tumor growth, such as male sex,¹⁸ younger age,¹⁸ absence of calcification,^18-23 peritumoral edema,^21,22,24 and hyperintensity on T2WI.^{18,19,22,25,26}Considering these points, the purpose of this retrospective cohort study was to assess the hypothesis that size and growth of untreated intracranial meningiomas derived from T1 3D-Gd and 2D-T2WI sequences show good agreement, which would, should this be the case, question the added value of Gd-based contrast media for routine follow-up MRIs of intracranial meningiomas.     

How Common Is Signal-Intensity Increase in Optic Nerve Segments on 3D Double Inversion Recovery Sequences in Visually Asymptomatic Patients with Multiple Sclerosis?

BACKGROUND AND PURPOSE:In postmortem studies, subclinical optic nerve demyelination is very common in patients with MS but radiologic demonstration is difficult and mainly based on STIR T2WI. Our aim was to evaluate 3D double inversion recovery MR imaging for the detection of subclinical demyelinating lesions within optic nerve segments.MATERIALS AND METHODS:The signal intensities in 4 different optic nerve segments (ie, retrobulbar, canalicular, prechiasmatic, and chiasm) were evaluated on 3D double inversion recovery MR imaging in 95 patients with MS without visual symptoms within the past 3 years and in 50 patients without optic nerve pathology. We compared the signal intensities with those of the adjacent lateral rectus muscle. The evaluation was performed by a student group and an expert neuroradiologist. Statistical evaluation (the Cohen κ test) was performed.RESULTS:On the 3D double inversion recovery sequence, optic nerve segments in the comparison group were all hypointense, and an isointense nerve sheath surrounded the retrobulbar nerve segment. At least 1 optic nerve segment was isointense or hyperintense in 68 patients (72%) in the group with MS on the basis of the results of the expert neuroradiologist. Student raters were able to correctly identify optic nerve hypersignal in 97%.CONCLUSIONS:A hypersignal in at least 1 optic nerve segment on the 3D double inversion recovery sequence compared with hyposignal in optic nerve segments in the comparison group was very common in visually asymptomatic patients with MS. The signal-intensity rating of optic nerve segments could also be performed by inexperienced student readers.

MR imaging contributes to not only the diagnosis and differential diagnosis of MS but also the monitoring and follow-up of patients.¹ T1-weighted postcontrast, T2-weighted, proton-density, FLAIR, and double inversion recovery (DIR) images are recommended to detect acute and chronic demyelinating lesions in typical locations.^1–9Acute optic neuritis is an inflammatory demyelination of the optic nerve causing acute visual loss.^10–13 After recovery, patients are often visually asymptomatic, but careful visual testing by visually evoked potentials, optical coherence tomography, and visual disability evaluation may reveal persistent slight visual deficits.^14–17 These deficits are also observed in patients without any history of previous acute optic neuritis due to a suspected subclinical disease known as subclinical optic nerve demyelination.^14–17Acute optic neuritis is easily diagnosed on MR imaging by focal nerve swelling and segmental T2-weighted hyperintensity, especially on STIR images or on fat-suppressed T2-weighted images and by segmental gadolinium enhancement on T1-weighted fat-suppressed images.^10,18–22 The enhancement is present for a mean of 30 days after the onset of visual symptoms.^21,23–31Subclinical optic nerve demyelination, however, is not easily visible on MR imaging. Routine T2-weighted images without fat suppression and contrast-enhanced T1-weighted FSE images do not show any signal abnormality in the affected optic nerve. Fat-suppressed T2-weighted FSE images, especially STIR T2-weighted images, may detect a signal-intensity abnormality in subclinical optic nerve demyelination.^23,32,33 The highly diagnostic value of fat-suppressed FLAIR images and fat-suppressed 3D DIR images in the detection of any pathologic signal intensity in the optic nerve has been evaluated in acute optic nerve demyelination.^10,34,35 In a few patients with subclinical optic nerve demyelination, signal-intensity abnormalities have been reported on 3D FLAIR.³⁴ However, there are few data about the use of the 3D DIR sequence in the evaluation of subclinical optic nerve demyelination.³⁶In our department, patients with MS are routinely and regularly monitored for disease progression by a standard protocol with 3D FLAIR, 3D DIR, T2-weighted FSE, and 3D T1-weighted postcontrast images. 3D DIR is added to our standard protocol for improved detection of juxtacortical, cortical, and infratentorial demyelinating lesions.^1–9 On the basis of postmortem and clinical studies having already shown a high percentage of subclinical optic nerve demyelination with ongoing axonal loss in patients with MS,^37–41 we wanted to test 2 hypotheses: first, that it is possible to detect signal-intensity changes in optic nerve segments on the 3D DIR sequence without the additional application of a STIR T2-weighted sequence over the orbits in patients with MS without a history of clinically obvious visual loss and without a history of acute optic neuritis during the previous 3 years; and second, that the signal-intensity changes on 3D DIR are so obvious that even inexperienced readers can detect them. This second hypothesis is important because in our department, MR imaging examinations of patients with MS are evaluated not only by trained neuroradiologists but also general radiologists. Therefore, it is desirable that the lack of neuroradiologic experience be compensated by the application of an easily readable MR image, and the 3D DIR sequence is routinely acquired in our department for the follow-up of patients with MS.For comparison, the signal intensities of normal healthy optic nerve segments in patients evaluated by the identical 3D DIR sequence for different diseases (ie, epileptic seizures and posttraumatic sequelae) were analyzed as well.     

Clinical Significance of an Increased Cochlear 3D Fluid-Attenuated Inversion Recovery Signal Intensity on an MR Imaging Examination in Patients with Acoustic Neuroma

BACKGROUND AND PURPOSE:The increased cochlear signal on FLAIR images in patients with acoustic neuroma is explained by an increased concentration of protein in the perilymphatic space. However, there is still debate whether there is a correlation between the increased cochlear FLAIR signal and the degree of hearing disturbance in patients with acoustic neuroma. Our aim was to investigate the clinical significance of an increased cochlear 3D FLAIR signal in patients with acoustic neuroma according to acoustic neuroma extent in a large patient cohort.MATERIALS AND METHODS:This retrospective study enrolled 102 patients with acoustic neuroma, who were divided into 2 groups based on tumor location; 22 tumors were confined to the internal auditory canal and 80 extended to the cerebellopontine angle cistern. Pure tone audiometry results and hearing symptoms were obtained from medical records. The relative signal intensity of the entire cochlea to the corresponding brain stem was calculated by placing regions of interest on 3D FLAIR images. Statistical analysis was performed to compare the cochlear relative signal intensity between the internal auditory canal acoustic neuroma and the cerebellopontine angle acoustic neuroma_. The correlation between the cochlear relative signal intensity and the presence of hearing symptoms or the pure tone audiometry results was investigated.RESULTS:The internal auditory canal acoustic neuroma cochlea had a significantly lower relative signal intensity than the cerebellopontine angle acoustic neuroma cochlea (0.42 ± 0.15 versus 0.60 ± 0.17, P < .001). The relative signal intensity correlated with the audiometric findings in patients with internal auditory canal acoustic neuroma (r = 0.471, P = .027) but not in patients with cerebellopontine angle acoustic neuroma (P = .427). Neither internal auditory canal acoustic neuroma nor cerebellopontine angle acoustic neuroma showed significant relative signal intensity differences, regardless of the presence of hearing symptoms (P > .5).CONCLUSIONS:The cochlear signal on FLAIR images may be an additional parameter to use when monitoring the degree of functional impairment during follow-up of patients with small acoustic neuromas confined to the internal auditory canals.

The fluid of the inner ear is normally suppressed on 3D fluid-attenuated inversion recovery MR images. Increased signal intensity of the fluid on FLAIR MR images has been reported in various diseases, including sudden sensorineural hearing loss, labyrinthine hemorrhage, otosclerosis, Ramsay Hunt syndrome, and acoustic neuromas (ANs).^1–6 The increased cochlear signal on FLAIR images in patients with ANs is explained by an increased concentration of protein in the perilymphatic space.^7–12FLAIR MR imaging is sensitive to fluids with a high protein content.^13–17 Furthermore, 3D-FLAIR imaging can minimize the undesired inflow artifacts of CSF flow, has a higher signal-to-noise ratio and spatial resolution, and allows recognition of subtle compositional changes of the inner ear fluid.^18–21 Therefore, one can assume that the increased protein content in the cochlear perilymph of patients with ANs can be detected on 3D FLAIR imaging with a high sensitivity and good spatial resolution.Several researchers recently investigated whether there was a correlation between the increased cochlear FLAIR signal in patients with ANs and the degree of their hearing disturbance.^2,5 However, no such correlation was found, nor was there any difference in the cochlear FLAIR signal according to AN extent.Accordingly, the purpose of this study was to investigate the clinical significance of an increased cochlear 3D FLAIR signal in a large number patients with ANs by correlating imaging results with audiometric findings and hearing symptoms according to the extent of ANs after dividing the auditory neuromas into 2 groups: those confined to the internal auditory canal (AN_IAC) and those extending into the cerebellopontine cistern (AN_CPA).     

Appropriate Minimal Dose of Gadobutrol for 3D Time-Resolved MRA of the Supra-Aortic Arteries: Comparison with Conventional Single-Phase High-Resolution 3D Contrast-Enhanced MRA

BACKGROUND AND PURPOSE:The development of nephrogenic systemic fibrosis and neural tissue deposition is gadolinium dose–dependent. The purpose of this study was to determine the appropriate minimal dose of gadobutrol with time-resolved MRA to assess supra-aortic arterial stenosis with contrast-enhanced MRA as a reference standard.MATERIALS AND METHODS:Four hundred sixty-two consecutive patients underwent both standard-dose contrast-enhanced MRA and low-dose time-resolved MRA and were classified into 3 groups; group A (a constant dose of 1 mL for time-resolved MRA), group B (2 mL), or group C (3 mL). All studies were independently evaluated by 2 radiologists for image quality by using a 5-point scale (from 0 = failure to 4 = excellent), grading of arterial stenosis (0 = normal, 1 = mild [<30%], 2 = moderate [30%–69%], 3 = severe to occlusion [≥70%]), and signal-to-noise ratio.RESULTS:The image quality of time-resolved MRA was similar to that of contrast-enhanced MRA in groups B and C, but it was inferior to contrast-enhanced MRA in group A. For the grading of arterial stenosis, there was an excellent correlation between contrast-enhanced MRA and time-resolved MRA (R = 0.957 for group A, R = 0.988 for group B, R = 0.991 for group C). The SNR of time-resolved MRA tended to be lower than that of contrast-enhanced MRA in groups A and B. However, SNR was higher for time-resolved MRA compared with contrast-enhanced MRA in group C.CONCLUSIONS:Low-dose time-resolved MRA is feasible in the evaluation of supra-aortic stenosis and could be used as an alternative to contrast-enhanced MRA for a diagnostic technique in high-risk populations.

Digital subtraction angiography remains the criterion standard for evaluation of supra-aortic steno-occlusive disease, with excellent spatial and temporal resolution. However, it is a time-consuming and invasive technique and is associated with several risks, including transient ischemic attack, permanent neurologic deficit, iodine contrast nephrotoxicity, and exposure to ionizing radiation.^1–3 Consequently, DSA has largely been reserved for interventions for extracranial and intracranial steno-occlusive disease or in cases of uncertain findings on noninvasive imaging studies.⁴ Noninvasive angiography techniques such as CTA and MRA are typically used for routine diagnostic procedures. Recently, 3D high-resolution contrast-enhanced MRA (CE-MRA) has become widely used as an excellent alternative imaging technique for the assessment of supra-aortic steno-occlusive disease.⁵Gadolinium-based contrast agents (GBCAs) were initially thought to be safe in patients with reduced renal function rather than iodine-based contrast agents.⁶ Recently, a positive association between nephrogenic systemic fibrosis and exposure to GBCAs in patients with renal failure has been described.⁷ Several studies showed a relationship between high doses of GBCAs and increased nephrogenic systemic fibrosis risk.^8–11 Also, in the past 2 years, several studies regarding gadolinium retention in intracranial neuronal tissues have been published.^12–14 The development of nephrogenic systemic fibrosis with exposure to GBCAs and gadolinium deposition in neuronal tissue is dose-dependent; therefore, caution has been advised when administering GBCAs.^13,15 There is increasing interest in dose-reduction strategies that maintain diagnostic image quality.¹⁶ Time-resolved MRA (TR-MRA) is used clinically to offer combined anatomic and hemodynamic information of the supra-aortic vessels, and another advantage of TR-MRA is the requirement for low-dose GBCAs.^2,3,16,17 Several studies have demonstrated that TR-MRA with low-dose GBCAs yields comprehensive anatomic and functional information with high sensitivity and negative predictive values.^2,3,17–20The purpose of this study was to determine the appropriate minimal dose for TR-MRA to assess supra-aortic arterial stenosis with CE-MRA as a reference standard.     

Contrast-Enhanced and Time-of-Flight MRA at 3T Compared with DSA for the Follow-Up of Intracranial Aneurysms Treated with the WEB Device

BACKGROUND AND PURPOSE:Imaging follow-up at 3T of intracranial aneurysms treated with the WEB Device has not been evaluated yet. Our aim was to assess the diagnostic accuracy of 3D–time-of-flight MRA and contrast-enhanced MRA at 3T against DSA, as the criterion standard, for the follow-up of aneurysms treated with the Woven EndoBridge (WEB) system.MATERIALS AND METHODS:From June 2011 to December 2014, patients treated with the WEB in our institution, then followed for ≥6 months after treatment by MRA at 3T (3D-TOF-MRA and contrast-enhanced MRA) and DSA within 48 hours were included. Aneurysm occlusion was assessed with a simplified 2-grade scale (adequate occlusion [total occlusion + neck remnant] versus aneurysm remnant). Interobserver and intermodality agreement was evaluated by calculating the linear weighted κ. MRA test characteristics and predictive values were calculated from a 2 × 2 contingency table, by using DSA data as the standard of reference.RESULTS:Twenty-six patients with 26 WEB-treated aneurysms were included. The interobserver reproducibility was good with DSA (κ = 0.71) and contrast-enhanced-MRA (κ = 0.65) compared with moderate with 3D-TOF-MRA (κ = 0.47). Intermodality agreement with DSA was fair with both contrast-enhanced MRA (κ = 0.36) and 3D-TOF-MRA (κ = 0.36) for the evaluation of total occlusion. For aneurysm remnant detection, the prevalence was low (15%), on the basis of DSA, and both MRA techniques showed low sensitivity (25%), high specificity (100%), very good positive predictive value (100%), and very good negative predictive value (88%).CONCLUSIONS:Despite acceptable interobserver reproducibility and predictive values, the low sensitivity of contrast-enhanced MRA and 3D-TOF-MRA for aneurysm remnant detection suggests that MRA is a useful screening procedure for WEB-treated aneurysms, but similar to stents and flow diverters, DSA remains the criterion standard for follow-up.

Endovascular treatment is now the first-line treatment for the management of ruptured and unruptured intracranial aneurysms.^1–4 However, the limitations of standard coiling for complex aneurysms (large, wide-neck, or developed in a bifurcation) have contributed to the development of new endovascular approaches, including balloon-assisted coiling, stent-assisted coiling, flow diversion, and flow disruption.⁵The Woven EndoBridge (WEB) aneurysm embolization system (Sequent Medical, Aliso Viejo, California) is an intrasaccular device designed to disrupt the intra-aneurysmal flow at the level of the neck.^6,7 Initial experience with the WEB–Dual-Layer (DL) showed the clinical utility of this device in wide-neck bifurcation aneurysms with high technical success and low acute morbidity and mortality.^6–16 Several WEB devices are now available, including Single-Layer (WEB-SL), Single-Layer Sphere (WEB-SLS), and WEB-DL subtypes.^12,13 Recently, Enhanced-Visualization (EV) versions were developed to improve fluoroscopic visualization of the devices during treatment.Because of the potential risk of aneurysm recanalization after endovascular treatment, regular imaging follow-up is recommended. Digital subtraction angiography is the criterion standard for the follow-up of intracranial aneurysms after endovascular treatment but has some disadvantages, including potential neurologic complications, iodinated contrast injection, and radiation exposure. With the goal of avoiding DSA drawbacks, several MR angiography techniques have been tested to follow intracranial aneurysms. 3D-TOF-MRA and contrast-enhanced MRA (CE-MRA) at 3T are appropriate techniques for the follow-up of coiled aneurysms but have some limitations for the aneurysms treated with stents or flow diverters.^17–23 Because the WEB is a relatively new device, the value of 3D-TOF-MRA and CE-MRA for the follow-up of WEB-treated intracranial aneurysms has been evaluated in a small number of patients at 1.5T.²⁴The aim of this single-center prospective study was to assess the diagnostic accuracy of 3D-TOF-MRA and CE-MRA at 3T against DSA, as the criterion standard, for the evaluation of aneurysm occlusion after WEB treatment.     

Tractography at 3T MRI of Corpus Callosum Tracts Crossing White Matter Hyperintensities

BACKGROUND AND PURPOSE:The impact of white matter hyperintensities on the diffusion characteristics of crossing tracts is unclear. This study used quantitative tractography at 3T MR imaging to compare, in the same individuals, the diffusion characteristics of corpus callosum tracts that crossed white matter hyperintensities with the diffusion characteristics of corpus callosum tracts that did not pass through white matter hyperintensities.MATERIALS AND METHODS:Brain T2 fluid-attenuated inversion recovery–weighted and diffusion tensor 3T MR imaging scans were acquired in 24 individuals with white matter hyperintensities. Tractography data were generated by the Fiber Assignment by Continuous Tracking method. White matter hyperintensities and corpus callosum tracts were manually segmented. In the corpus callosum, the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts crossing white matter hyperintensities were compared with the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts that did not cross white matter hyperintensities. The cingulum, long association fibers, corticospinal/bulbar tracts, and thalamic projection fibers were included for comparison.RESULTS:Within the corpus callosum, tracts that crossed white matter hyperintensities had decreased fractional anisotropy compared with tracts that did not pass through white matter hyperintensities (P = .002). Within the cingulum, tracts that crossed white matter hyperintensities had increased radial diffusivity compared with tracts that did not pass through white matter hyperintensities (P = .001).CONCLUSIONS:In the corpus callosum and cingulum, tracts had worse diffusion characteristics when they crossed white matter hyperintensities. These results support a role for white matter hyperintensities in the disruption of crossing tracts.

The corpus callosum (CC) is the largest commissural tract with >200 million axons connecting the cerebral hemispheres.¹ Atrophy of the CC is a marker of neurodegeneration and has been reported in cerebrovascular disease.^2–8 White matter hyperintensities (WMH) are high-signal lesions on T2-weighted MR imaging that represent cerebral small vessel disease and have been associated with CC atrophy.^7,9–14 The reason for changes in the corpus callosum with WMH is unclear. Earlier studies have suggested that WMH may be an incidental finding and that CC atrophy results from a coexisting disease process.^7,10–17 For example, WMH are seen with Alzheimer disease, in which CC atrophy can occur by cortical atrophy and subsequent Wallerian degeneration of corpus callosum fibers originating from pyramidal neurons.^{7,10,13,15,16} These studies also suggest that WMH may directly cause CC atrophy by disrupting fibers of the corpus callosum as they are passing through the ischemic lesions in the deep white mater.^7,10–17Diffusion tensor imaging can detect early changes in white matter microstructure before atrophy occurs and could clarify the relationship between WMH and the CC.¹⁸ In DTI, pathologic processes that alter the structural integrity of tracts lead to changes in water diffusion and mean diffusivity (MD) and radial diffusivity (RD) as well as changes in the directionality of diffusion and fractional anisotropy (FA).^18,19 In patients with WMH, decreased FA and increased MD were found in the CC.¹³ Another study demonstrated correlations among CC atrophy, the FA/MD of deep white matter, and the FA/MD of the CC.¹⁷ These results confirm an association between WMH and the entire CC but do not distinguish between the effects of WMH on callosum tracts that cross WMH (CC-WMH) and those that do not cross WMH. If CC-WMH tracts had worse diffusion characteristics than CC tracts not crossing WMH, this feature would support an increased role for WMH in changes in the corpus callosum.Tractography is an application of DTI that allows the reconstruction of white matter tracts.¹⁸ In quantitative tractography, the diffusion characteristics (MD, RD, and FA) along the full trajectory of select fiber tracts can be assessed.¹⁸ This study used quantitative tractography to compare the diffusion characteristics of CC-WMH tracts with those of CC tracts not crossing WMH. For comparison, this study also performed a similar analysis in tracts that crossed WMH (WMH tracts) compared with those that did not cross WMH (lesion-free tracts) in the cingulum, long association fibers, corticospinal/bulbar tracts, and thalamic projection fibers. We hypothesized that CC-WMH tracts would have worse diffusion characteristics (increased MD and RD and decreased FA) compared with CC tracts not crossing WMH.     

Diffusion MRI Microstructural Abnormalities at Term-Equivalent Age Are Associated with Neurodevelopmental Outcomes at 3 Years of Age in Very Preterm Infants

BACKGROUND AND PURPOSE:Microstructural white matter abnormalities on DTI using Tract-Based Spatial Statistics at term-equivalent age are associated with cognitive and motor outcomes at 2 years of age or younger. However, neurodevelopmental tests administered at such early time points are insufficiently predictive of mild-moderate motor and cognitive impairment at school age. Our objective was to evaluate the microstructural antecedents of cognitive and motor outcomes at 3 years'' corrected age in a cohort of very preterm infants.MATERIALS AND METHODS:We prospectively recruited 101 very preterm infants (<32 weeks'' gestational age) and performed DTI at term-equivalent age. The Differential Ability Scales, 2nd ed, Verbal and Nonverbal subtests, and the Bayley Scales of Infant and Toddler Development, 3rd ed, Motor subtest, were administered at 3 years of age. We correlated DTI metrics from Tract-Based Spatial Statistics with the Bayley Scales of Infant and Toddler Development, 3rd ed, and the Differential Ability Scales, 2nd ed, scores with correction for multiple comparisons.RESULTS:Of the 101 subjects, 84 had high-quality DTI data, and of these, 69 returned for developmental testing (82%). Their mean (SD) gestational age was 28.4 (2.5) weeks, and birth weight was 1121.4 (394.1) g. DTI metrics were significantly associated with Nonverbal Ability in the corpus callosum, posterior thalamic radiations, fornix, and inferior longitudinal fasciculus and with Motor scores in the corpus callosum, internal and external capsules, posterior thalamic radiations, superior and inferior longitudinal fasciculi, cerebral peduncles, and corticospinal tracts.CONCLUSIONS:We identified widespread microstructural white matter abnormalities in very preterm infants at term that were significantly associated with cognitive and motor development at 3 years'' corrected age.

Premature birth is associated with a significantly increased risk of brain abnormalities and long-term neurodevelopmental impairment. Injuries or maturational delays affecting the WM are observed in 50%–80% of very preterm infants.^1-3 These abnormalities are associated with serious neurodevelopmental impairment.^1,3,4 However, such abnormalities are challenging to detect using conventional MR imaging techniques alone. Fortunately, DTI, a specialized form of MR imaging that can sensitively query the brain''s microstructure, offers a novel approach for identifying these WM injuries. In preterm brains, the evolution of fractional anisotropy (FA) and mean diffusivity (MD), 2 metrics derived from DTI, varies from that of normative populations, and underlying brain injury may lead to neurodevelopmental impairment later in life.^4-6Functional MR imaging with the FMRIB Tract-Based Spatial Statistics (TBSS; http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/TBSS) tool uses observer-independent voxelwise statistical analysis to process the complex information contained within diffusion-weighted images.^4-16 TBSS can be used to identify specific WM tracts and structures in the infant brain that correlate with later developmental outcomes.^8,10,13-15 Previous studies have used TBSS to objectively assess WM microstructure following clinical events such as infection, sports injury, or preterm brain injury (eg, intraventricular hemorrhage) and to relate the associated WM alterations to outcomes.^9,11,16-19 In addition, studies have used TBSS to identify brain regions and tracts in which FA significantly correlates with cognitive and motor outcomes at 2 years of age or younger.^10,13,15 These studies have consistently concluded that higher FA is associated with better motor, cognitive, and language functioning.Past studies emphasizing the value of TBSS correlated DTI parameters with neurodevelopmental outcomes derived from the Bayley Scales of Infant and Toddler Development, 3rd ed (Bayley-III) collected at 2 years of age or younger. Such standardized assessments are administered between 18 and 24 months of age, representing the earliest time point at which cognitive, language, and motor development can be reliably ascertained. However, assessment at these earliest ages is not necessarily predictive of school age outcomes.^20-22 For example, the Bayley-III Motor subscale at 2 years of age significantly underestimates rates of motor impairment at 4 years of age in preterm infants.²² Spencer-Smith et al²³ showed that cognitive delay, as assessed by the Bayley-III administered at 2 years of age, was not strongly associated with cognitive impairment at 4 years of age as assessed by the Differential Ability Scales, 2nd ed (DAS-II).²⁴ We propose that correlating FA from term-equivalent age MR imaging with 3-year outcomes may provide a more robust understanding of the early changes in WM microstructure that are also significantly associated with cognitive development.Our objective was to test the hypothesis that WM microstructure, assessed using TBSS at term-corrected age (CA), is associated with neurodevelopmental performance at 3 years'' CA in a regional cohort of very preterm infants.     

Identification of the Inflow Zone of Unruptured Cerebral Aneurysms: Comparison of 4D Flow MRI and 3D TOF MRA Data

BACKGROUND AND PURPOSE:The hemodynamics of the inflow zone of cerebral aneurysms may be a key factor in coil compaction and recanalization after endovascular coil embolization. We performed 4D flow MR imaging in conjunction with 3D TOF MRA and compared their ability to identify the inflow zone of unruptured cerebral aneurysms.MATERIALS AND METHODS:This series comprised 50 unruptured saccular cerebral aneurysms in 44 patients. Transluminal color-coded 3D MRA images were created by selecting the signal-intensity ranges on 3D TOF MRA images that corresponded with both the luminal margin and the putative inflow.RESULTS:4D flow MR imaging demonstrated the inflow zone and yielded inflow velocity profiles for all 50 aneurysms. In 18 of 24 lateral-projection aneurysms (75%), the inflow zone was located distally on the aneurysmal neck. The maximum inflow velocity ranged from 285 to 922 mm/s. On 4D flow MR imaging and transluminal color-coded 3D MRA studies, the inflow zone of 32 aneurysms (64%) was at a similar location. In 91% of aneurysms whose neck section plane angle was <30° with respect to the imaging section direction on 3D TOF MRA, depiction of the inflow zone was similar on transluminal color-coded 3D MRA and 4D flow MR images.CONCLUSIONS:4D flow MR imaging can demonstrate the inflow zone and provide inflow velocity profiles. In aneurysms whose angle of the neck-section plane is obtuse vis-a-vis the imaging section on 3D TOF MRA scans, transluminal color-coded 3D MRA may depict the inflow zone reliably.

Although endovascular coil embolization has become a major tactic to address cerebral aneurysms, recanalization or recurrence, which may result in rebleeding, are important problems. Recanalization was reported in 6.1%–39.8% of patients who had undergone endovascular treatment,^1–6 and a meta-analysis found that 20.8% of treated aneurysms recurred.³ The rate of rerupture after endovascular treatment for ruptured aneurysms has ranged from 0.11% to 5.3%,^1,4,6 and the rupture rate in the first year after coil embolization was reported as 2.5%⁷ and 2.2%.⁸ Because hemodynamics acting on the aneurysmal inflow zone may play a key role in the development of coil compaction or recanalization after endovascular coil embolization, the aneurysmal inflow zone must be packed densely to preserve the durability of aneurysm obliteration and to prevent rerupture.^9–15The inflow through the aneurysmal neck into the dome can be seen on 3D TOF MRA images.^13,16,17 Satoh et al,^16,17 who used conventional 3D TOF MRA techniques to select threshold ranges based on the signal intensity of the volume-rendering data, determined the spatial signal-intensity distribution in aneurysms. They developed transluminal color-coded 3D MRA (TC 3D MRA) to improve visualization of the aneurysmal inflow. More recently, 4D flow MR imaging based on time-resolved 3D cine phase-contrast MR imaging techniques was used to evaluate the hemodynamics of cerebral aneurysms.^18–27 However, 4D flow MR imaging requires additional time for data acquisition, and TC 3D MRA may be a convenient alternative to 4D flow MR imaging for identifying the aneurysmal inflow zone.Here, we compared the ability of 4D flow MR imaging and TC 3D MRA to identify the inflow zone of cerebral aneurysms.     

Patient-specific computational hemodynamics of intracranial aneurysms from 3D rotational angiography and CT angiography: an in vivo reproducibility study

BACKGROUND AND PURPOSE:Patient-specific simulations of the hemodynamics in intracranial aneurysms can be constructed by using image-based vascular models and CFD techniques. This work evaluates the impact of the choice of imaging technique on these simulations.MATERIALS AND METHODS:Ten aneurysms, imaged with 3DRA and CTA, were analyzed to assess the reproducibility of geometric and hemodynamic variables across the 2 modalities.RESULTS:Compared with 3DRA models, we found that CTA models often had larger aneurysm necks (P = .05) and that most of the smallest vessels (between 0.7 and 1.0 mm in diameter) could not be reconstructed successfully with CTA. With respect to the values measured in the 3DRA models, the flow rate differed by 14.1 ± 2.8% (mean ± SE) just proximal to the aneurysm and 33.9 ± 7.6% at the aneurysm neck. The mean WSS on the aneurysm differed by 44.2 ± 6.0%. Even when normalized to the parent vessel WSS, a difference of 31.4 ± 9.9% remained, with the normalized WSS in most cases being larger in the CTA model (P = .04). Despite these substantial differences, excellent agreement (κ ≥ 0.9) was found for qualitative variables that describe the flow field, such as the structure of the flow pattern and the flow complexity.CONCLUSIONS:Although relatively large differences were found for all evaluated quantitative hemodynamic variables, the main flow characteristics were reproduced across imaging modalities.

Degradative biologic processes in the arterial wall that lead to growth and rupture of intracranial aneurysms¹ have been related to intra-aneurysmal hemodynamics.^2–4 CFD simulations have been used to gain insight into the patient-specific hemodynamics and could potentially assist rupture-risk assessment^5–9 and treatment planning.^10–16Vascular models can be constructed through segmentation of 3DRA and CTA images. Compared with CTA, 3DRA produces images with higher contrast, higher spatial resolution, and lower visibility of bone,^17–19 which lead to better segmentation results²⁰ and superior anatomic accuracy.^21–23 However, acquisition of 3DRA images involves the introduction of a catheter into the cerebral vasculature to locally inject contrast agent, making it more invasive than CTA, in which contrast is injected in a peripheral vein.^24,25 As a result of this trade-off, 3DRA is often used before and during treatment, whereas CTA is often used for diagnosis and follow-up studies.²⁶To the best of our knowledge, the reproducibility of hemodynamic simulations based on in vivo images from different modalities is yet unknown. Previous studies did show that among all input parameters of the modeling pipeline, the vascular geometry has the greatest impact on its output.^27,28 Because the choice of imaging technique may affect the vascular geometry, it could give rise to differences in hemodynamic predictions. To investigate this issue, we conducted a study comparing simulations with 3DRA- and CTA-based vascular models of 10 aneurysms.     

Benign Miliary Osteoma Cutis of the Face: A Common Incidental CT Finding

BACKGROUND AND PURPOSE:Osteoma cutis of the face represents a primary or secondary formation of ossific foci in the facial skin. Its primary form has been sparsely described in the plastic surgery and dermatology literature. As radiologists, we routinely encounter incidental, very small facial calcified nodules on CT studies performed for a variety of unrelated reasons. We hypothesized that this routinely encountered facial calcification represents primary miliary osteoma cutis and is a common, benign, age-related finding.MATERIALS AND METHODS:We retrospectively reviewed 1315 consecutive sinus CTs obtained during an 8-month period and their associated demographics. The number of dermal radiopaque lesions with Hounsfield units of >150 was counted, and we analyzed the association between the prevalence of these lesions and patients'' demographics with logistic regression methods.RESULTS:Five hundred ninety-nine males and 716 females from 4 to 90 years of age were included in the study (mean, 52 versus 51 years; P = .259). Among these, 252 males and 301 females had small facial calcified nodules (42.1% versus 42.0%, P = .971). The patient''s age was a statistically significant predictor for having facial calcified nodules (odds ratio = 1.02, P < .001), while the patient''s sex was not (P = .826).CONCLUSIONS:Facial calcified nodules, observed in routine head and face CT imaging, are common, benign, age-related findings, which have been largely overlooked in the radiology literature. It is a manifestation of primary miliary osteoma cutis.

Osteoma cutis (cutaneous ossification) represents primary or secondary formation of ossific foci in the skin. It was first described by Martin Wilckens in 1858.¹ It is distinguished radiographically and pathologically from calcinosis cutis by the deposition of organized bone matrix, while the latter is characterized by the deposition of amorphous calcium salts within the skin.^2–4 Some consider calcinosis cutis a precursor or the early manifestation of osteoma cutis.⁵ Similar to secondary cutaneous calcification, the etiologies of secondary osteoma cutis have been well-described in the radiology and dermatopathology literature and are attributed to iatrogenic, traumatic, metabolic (eg, Albright hereditary osteodystrophy), inflammatory (eg, acne or dermatomyositis), and neoplastic (eg, basal cell carcinoma) processes.^2,5–7 However, primary or idiopathic osteoma cutis has been sparsely described as a rare disease entity in the plastic surgery and dermatology literature, mostly in the form of case reports.^4,6,8–11The most frequently reported subclass of primary osteoma cutis occurs in the face and scalp soft tissues. It is reported as “miliary osteoma cutis of the face.”^4,10,12,13 Current literature agrees on its idiopathic etiology and its benign, noninvasive, and asymptomatic nature.^4,6,10,12,13 However, there have been varying reports regarding its epidemiology. While several authors describe it as a very rare disease^6,9,12 with slightly increased incidence in elderly or middle-aged women,^2,14,15 other authors report it as a very common entity in the general population,¹⁶ without sex or age predilection.⁶As radiologists, we routinely encounter incidental, punctate facial hypodermal calcifications on CT studies performed for a variety of reasons in patients without clinically recognized underlying dermatopathology (Fig 1). Due to their benign and asymptomatic nature, these incidental facial calcified nodules have been largely overlooked in the imaging literature. We performed a retrospective review of a large CT dataset. Our imaging technique extended the results of a previously reported large, radiographic, cadaveric case series,¹⁶ in an effort to establish that routinely encountered facial dermal calcification/ossification is primary miliary osteoma cutis, a common, benign, age-related finding.Open in a separate windowFig 1.Axial (A), sagittal (B), and coronal (C) CT images of 3 different representative patients demonstrate multiple millimetric scattered facial and scalp hypodermal calcified nodules with varying degrees of severity. A 3D bone window reconstruction of a patient''s sinus CT (D) also demonstrates a relatively large, 4- to 5-mm facial calcified nodule within the right premaxillary skin.     

Visualization of the Peripheral Branches of the Mandibular Division of the Trigeminal Nerve on 3D Double-Echo Steady-State with Water Excitation Sequence

BACKGROUND AND PURPOSE:Although visualization of the extracranial branches of the cranial nerves has improved with advances in MR imaging, only limited studies have assessed the detection of extracranial branches of the mandibular nerve (V3). We investigated the detectability of the branches of V3 on a 3D double-echo steady-state with water excitation sequence.MATERIALS AND METHODS:We retrospectively evaluated the detectability of the 6 branches of the V3, the masseteric, buccal, auriculotemporal, lingual, inferior alveolar, and mylohyoid nerves, by using a 5-point scale (4, excellent; 3, good; 2, fair; 1, poor; and 0, none) in 86 consecutive patients who underwent MR imaging with the 3D double-echo steady-state with water excitation sequence. Weighted κ analysis was used to calculate interobserver variability among the 3 readers.RESULTS:The detection of the lingual and inferior alveolar nerves was the most successful, with excellent average scores of 3.80 and 3.99, respectively. The detection of the masseteric, the buccal, and the auriculotemporal nerves was good, with average scores of 3.31, 2.67, and 3.11, respectively. The mylohyoid nerve was difficult to detect with poor average scores of 0.62. All nerves had excellent interobserver variability across the 3 readers (average weighted κ value, 0.95–1.00).CONCLUSIONS:The 3D double-echo steady-state with water excitation sequence demonstrated excellent visualization of the extracranial branches of V3 in most patients. The 3D double-echo steady-state with water excitation sequence has the potential for diagnosing V3 pathologies and preoperatively identifying peripheral cranial nerves to prevent surgical complications.

Cranial nerve deficits are not uncommon, and there are many pathologic processes that can affect the cranial nerves.^1–10 Unfortunately, the physical examination findings are often nonspecific for differentiating among these pathologic causes, and imaging plays a crucial role in diagnosing pathologic processes affecting the cranial nerves. With increasing spatial and contrast resolution of cross-sectional imaging, better visualization of the cranial nerves and their major branches has become possible, but the delineation of the entire course of the extracranial segments of the cranial nerves still remains a diagnostic challenge.^11–17The trigeminal nerve has the largest distribution of innervation among all the cranial nerves in the suprahyoid neck. Even though the mandibular nerve (V3) is the largest division of the trigeminal nerve, there have been only limited studies investigating the visualization of the extracranial segments of V3 with MR imaging. Several prior studies have focused on imaging the extracranial segments of V3 by using a T1-weighted fast-spoiled gradient recalled-echo sequence with fat suppression,⁹ a T1-weighted MPRAGE sequence with water excitation fat suppression,¹⁸ or a diffusion tensor tractography sequence,¹⁹ but these studies evaluated only the inferior alveolar nerve. Another study used FIESTA and fast-spoiled gradient recalled-echo sequences to evaluate the entire V3 nerve, but the extracranial peripheral V3 branches were not well-demonstrated, with the exception of the inferior alveolar and lingual nerves.¹³The 3D double-echo steady-state with water excitation (3D-DESS-WE) sequence is a recently introduced MR imaging technique that can delineate the peripheral cranial nerves as high-signal-intensity structures.²⁰ At our institution, this sequence has been added to our standard MR imaging protocol of the salivary glands and has been used routinely to evaluate the intraparotid facial nerve and salivary ducts within the salivary glands since October 2012. The purpose of this study was to investigate the detectability of the extracranial peripheral branches of V3 on the 3D-DESS-WE sequence.     

Usefulness of Subtraction of 3D T2WI-DRIVE from Contrast-Enhanced 3D T1WI: Preoperative Evaluations of the Neurovascular Anatomy of Patients with Neurovascular Compression Syndrome

BACKGROUND AND PURPOSE:High-resolution 3D MR cisternography techniques such as 3D T2WI–driven equilibrium radiofrequency reset pulse (DRIVE) are used preoperatively to assess neurovascular anatomy in patients with neurovascular compression syndrome, but contrast between vessels and cranial nerves at the point of neurovascular contact is limited. The postprocessing technique subtraction of 3D T2WI-driven equilibrium radiofrequency reset pulse from contrast-enhanced 3D T1WI (sDRICE) provides both high spatial resolution and excellent contrast in depicting the neurovascular contact. We evaluated the usefulness of sDRICE compared with 3D T2WI-DRIVE.MATERIALS AND METHODS:Twelve patients who underwent microvascular decompression for hemifacial spasm or trigeminal neuralgia were examined preoperatively with 3D T2WI-DRIVE and sDRICE. Two neuroradiologists retrospectively analyzed and scored lesion conspicuity, defined as the ease of discrimination between offending vessels and compressed nerves or the brain stem at the neurovascular contact. They also quantitatively analyzed the contrast and contrast-to-noise ratio at the neurovascular contact.RESULTS:The lesion conspicuity scores of sDRICE images were significantly higher than those of 3D T2WI-DRIVE for all 12 patients (P = .006) and the 6 cases of hemifacial spasm (P = .023) but were not significantly higher in the 6 trigeminal neuralgia cases alone (P = .102). For all 12 patients, the contrast-to-noise ratio between the offending vessels and the brain stem and between the vessels and nerves on sDRICE images was significantly higher than that on 3D T2WI-DRIVE (P = .003 and P = .007, respectively). Among these structures, the contrast values were also significantly higher on the sDRICE than on the 3D T2WI-DRIVE (P < .001) images.CONCLUSIONS:The postprocessing technique sDRICE is useful to evaluate neurovascular anatomy and to improve contrast and the contrast-to-noise ratio in patients with neurovascular compression syndrome.

Neurovascular compression syndromes such as trigeminal neuralgia (TN) and hemifacial spasm (HFS) are characterized by hyperactive cranial nerve dysfunction. The most effective and standard treatment for this syndrome is microvascular decompression, which is capable of providing complete resolution of symptoms in most cases.^1–4 A preoperative determination of microvascular anatomy in terms of the exact localization and direction of the compressing vessel and the anatomic relationship between cranial nerves and vessels is of great value to neurosurgeons. Some authors have proposed that the presence of clear-cut and marked vascular compression is a factor in good long-term prognosis^5,6; thus, the accurate preoperative radiologic evaluation of the neurovascular anatomy is crucial to achieve an excellent clinical outcome. High-resolution 3D MR cisternography, such as 3D T2-weighted imaging driven equilibrium radiofrequency reset pulse (3D T2WI-DRIVE),^7,8 3D FIESTA^9,10 and 3D CISS,^11–13 is the method of choice to evaluate preoperative neurovascular anatomy in patients with neurovascular compression syndrome.Although these sequences have excellent spatial resolution, the contrast between vessels and cranial nerves at the point of neurovascular contact (NVC) is limited in general; this poor contrast is a major drawback of these sequences for preoperative evaluations of vascular compression syndromes.^14,15 On 3D TOF-MRA^8,16–18 or 3D gadolinium-enhanced T1WI,^8,13,18 vessels are clearly depicted but the nerves are too poorly seen to be depicted at the point of NVC. Fused images of 3D CTA or 3D TOF-MRA and 3D MR cisternography have been used to evaluate the NVC to solve this problem,^19–23 but making these fusion images is technically challenging and too time-consuming for daily clinical practice.We report a simple postprocessing technique that we named subtraction of 3D T2WI-DRIVE from contrast-enhanced 3D T1WI (sDRICE), which provides both high spatial resolution and excellent contrast between vessels and cranial nerves. It is easy and simple to create sDRICE images on a console without the need for any fusion technique or special software. We evaluated the utility of sDRICE imaging for the radiologic evaluation of patients with neurovascular compression syndrome, and we compared its efficacy with that of 3D T2WI-DRIVE, which is used in standard 3D MR cisternography.