Added value of double inversion recovery magnetic resonance sequence in detection of cortical and white matter brain lesions in multiple sclerosis

Objective

The aim of this study was to evaluate the value of double inversion recovery (DIR) magnetic resonance (MR) sequence in the detection of brain cortical and white matter lesions in multiple sclerosis (MS).

Patients and methods

Fifteen patients with remitting relapsing MS were included in this study. Imaging was performed on a 1.T MR system using DIR, fluid-attenuated inversion-recovery (FLAIR), and T2-weighted image (T2WI) sequences. The sensitivity of DIR was compared with the corresponding sensitivity of FLAIR and T2WI sequences. The contrast between lesions and normal-appearing gray matter (NAGM), normal-appearing white matter (NAWM), and cerebrospinal fluid (CSF) was determined for all sequences.

Results

DIR showed significantly more MS lesion load overall when compared to T2WI or FLAIR. Significantly higher number of lesions was seen in the supra- and infratentorial locations. DIR detected higher periventricular white matter lesions when compared to FLAIR, but did not detect significantly higher lesions when compared to T2WI. Significantly higher deep white matter, juxtacortical, and intracortical lesions were seen on DIR when compared to both T2WI and FLAIR. The image contrast measurements between the MS lesions and the NAWM in all anatomical locations were significantly higher in DIR sequence compared to both T2WI and FLAIR sequences. However, there was no significant statistical difference between the DIR and both T2WI and FLAIR sequences regarding the contrast of intracortical lesions compared to NAGM.

Conclusion

DIR sequence is valuable in the imaging workup of MS as it can detect more MS lesions compared to the T2W and FLAIR sequences in all anatomical locations. DIR showed better delineation between the white matter, gray matter, and the MS lesions due to its high image contrast. DIR sequence should be included in the routine MR protocol of MS patients especially to answer the question about intra-cortical and juxta-cortical MS lesions.     

Improved differentiation between MS and vascular brain lesions using FLAIR* at 7 Tesla

Objectives

To investigate whether a new magnetic resonance image (MRI) technique called T2*-weighted fluid attenuation inversion recovery (FLAIR*) can differentiate between multiple sclerosis (MS) and vascular brain lesions, at 7 Tesla (T).

Methods

We examined 16 MS patients and 16 age-matched patients with (risk factors for) vascular disease. 3D-FLAIR and T2*-weighted images were combined into FLAIR* images. Lesion type and intensity, perivascular orientation and presence of a hypointense rim were analysed.

Results

In total, 433 cerebral lesions were detected in MS patients versus 86 lesions in vascular patients. Lesions in MS patients were significantly more often orientated in a perivascular manner: 74 % vs. 47 % (P?<?0.001). Ten MS lesions (2.3 %) were surrounded by a hypointense rim on FLAIR*, and 24 MS lesions (5.5 %) were hypointense on T2*. No lesions in vascular patients showed any rim or hypointensity. Specificity of differentiating MS from vascular lesions on 7-T FLAIR* increased when the presence of a central vessel was taken into account (from 63 % to 88 %), most obviously for deep white matter lesions (from 69 % to 94 %). High sensitivity remained (81 %).

Conclusion

7-T FLAIR* improves differentiation between MS and vascular lesions based on lesion location, perivascular orientation and presence of hypointense (rims around) lesions.

Key Points

? A new MRI technique T2*-weighted fluid attenuation inversion recovery (FLAIR*) was investigated. ? FLAIR* at 7-T MRI combines FLAIR and T2* images into a single image. ? FLAIR* at 7 T does not require enhancement with contrast agents. ?High-resolution 7-T FLAIR* improves differentiation between MS and vascular brain lesions. ? FLAIR* revealed a central vessel more frequently in MS than vascular lesions.     

Anterior temporal lobe white matter abnormal signal (ATLAS) as an indicator of seizure focus laterality in temporal lobe epilepsy: comparison of double inversion recovery, FLAIR and T2W MR imaging

Objectives

To investigate the diagnostic capability of anterior temporal lobe white matter abnormal signal (ATLAS) for determining seizure focus laterality in temporal lobe epilepsy (TLE) by comparing different MR sequences.

Methods

This prospective study was approved by the institutional review board and written informed consent was obtained. Three 3D sequences (double inversion recovery (DIR), fluid-attenuated inversion recovery (FLAIR) and T2-weighted imaging (T2WI)) and two 2D sequences (FLAIR and T2WI) were acquired at 3?T. Signal changes in the anterior temporal white matter of 21 normal volunteers were evaluated. ATLAS laterality was evaluated in 21 TLE patients. Agreement of independent evaluations by two neuroradiologists was assessed using ?? statistics. Differences in concordance between ATLAS laterality and clinically defined seizure focus laterality were analysed using McNemar??s test with multiple comparisons.

Results

Pre-amygdala high signals (PAHS) were detected in all volunteers only on 3D-DIR. Inter-evaluator agreement was moderate to almost perfect for each sequence. Correct diagnosis of seizure laterality was significantly more frequent on 3D-DIR than on any other sequences (P????0.031 for each evaluator).

Conclusions

The most sensitive sequence for detecting ATLAS laterality was 3D-DIR. ATLAS laterality on 3D-DIR can be a good indicator for determining seizure focus localization in TLE.

Key Points

? Magnetic resonance imaging is widely used to investigate temporal lobe epilepsy. ? Numerous MR sequences can show anterior temporal lobe white matter abnormal signal. ? ATLAS on 3D-DIR can frequently indicate seizure focus laterality in TLE. ? 3D-DIR is more sensitive about ATLAS laterality than T2WI or FLAIR.     

Comparison of 3D double inversion recovery and 2D STIR FLAIR MR sequences for the imaging of optic neuritis: pilot study

Objectives

We compared the three-dimensional (3D) double inversion recovery (DIR) magnetic resonance imaging (MRI) sequence with the coronal two-dimensional (2D) short tau inversion recovery (STIR) fluid-attenuated inversion recovery (FLAIR) for the detection of optic nerve signal abnormality in patients with optic neuritis (ON).

Methods

The study group consisted of 31 patients with ON (44 pathological nerves) confirmed by visual-evoked potentials used as the reference. MRI examinations included 2D coronal STIR FLAIR and 3D DIR with 3-mm coronal reformats to match with STIR FLAIR. Image artefacts were graded for each portion of the optic nerves. Each set of MR images (2D STIR FLAIR, DIR reformats and multiplanar 3D DIR) was examined independently and separately for the detection of signal abnormality.

Results

Cisternal portion of optic nerves was better delineated with DIR (p?p?Conclusions Our study showed a high sensitivity and specificity of 3D DIR compared with STIR FLAIR for the detection of ON. These findings suggest that the 3D DIR sequence may be more useful in patients suspected of ON.

Key points

? 3D DIR is increasingly used in neuroradiology ? Compared with STIR FLAIR, 3D DIR improves detection of optic neuritis ? Multiplanar analysis had the best diagnostic performance for optic nerve signal abnormalities ? Sensitivity was 95?% and specificity 94?% ? Findings support the use of 3D DIR instead of 2D sequences     

FLAIR2: A Combination of FLAIR and T2 for Improved MS Lesion Detection

BACKGROUND AND PURPOSE:FLAIR and double inversion recovery are important MR imaging scans for MS. The suppression of signal from CSF in FLAIR and the additional suppression of WM signal in double inversion recovery improve contrast between lesions, WM and GM, albeit at a reduced SNR. However, whether the acquisition of double inversion recovery is necessary is still debated. Here, we present an approach that allows obtaining CSF-suppressed images with improved contrast between lesions, WM and GM without strongly penalizing SNR.MATERIALS AND METHODS:3D T2-weighted and 3D-FLAIR data acquired from September 2014 to April 2015 in healthy volunteers (23.4 ± 2.4 years of age; female/male ratio, 3:2) and patients (44.1 ± 14.0 years of age; female/male ratio, 4:5) with MS were coregistered and multiplied (FLAIR²). SNR and contrast-to-noise measurements were performed for focal lesions and GM and WM. Furthermore, data from 24 subjects with relapsing-remitting and progressive MS were analyzed retrospectively (52.7 ± 8.1 years of age; female/male ratio, 14:10).RESULTS:The GM-WM contrast-to-noise ratio was by 133% higher in FLAIR² than in FLAIR and improved between lesions and WM by 31%, 93%, and 158% compared with T2, DIR, and FLAIR, respectively. Cortical and juxtacortical lesions were more conspicuous in FLAIR². Furthermore, the 3D nature of FLAIR² allowed reliable visualization of callosal and infratentorial lesions.CONCLUSIONS:We present a simple approach for obtaining CSF suppression with an improved contrast-to-noise ratio compared with conventional FLAIR and double inversion recovery without the acquisition of additional data. FLAIR² can be computed retrospectively if T2 and FLAIR scans are available.

MR imaging is important for the diagnosis and monitoring of MS. Formation of MS lesions creates a hydrophilic environment, resulting in an increase in the T2 and proton density–weighted MR signal and a signal reduction on T1-weighted scans.¹ Ovoid hyperintense areas on T2-weighted MR imaging are therefore a radiologic hallmark of MS. Lesion conspicuity is often affected by the bright CSF signal, for instance, close to the ventricles or cortical sulci. FLAIR is a T2-weighted scan that suppresses CSF selectively with an inversion pulse.² Yet, the CSF signal suppression comes at the cost of reduced SNR. Usually, FLAIR scans are acquired in 2D with sections parallel to the subcallosal line. Additional sagittal FLAIR scans are required to reliably detect corpus callosum lesions.^2,3 Furthermore, 2D-FLAIR has artifacts due to CSF and blood inflow and often provides insufficient T2-weighting,⁴ requiring additional proton density/T2-weighted images for the detection of lesions in infratentorial areas. The brain MR imaging protocol for MS studies⁵ includes proton density and T2-weighted spin-echo, axial, and sagittal FLAIR and recommends pre- and postcontrast T1-weighted spin-echo MR imaging.Apart from diagnosis, conventional MR images play an important role as outcome measures in clinical trials of new MS therapies.^5,6 New lesion activity (eg, gadolinium-enhancing lesions and new or enlarging T2-lesions) and estimates of disease burden (eg, total T2-lesion volume or count; T1-hypointense lesion volume; brain atrophy) are typical imaging end points in clinical trials.⁵ These scans are directed toward lesion identification in WM. Demyelination and the appearance of lesions is, however, not limited to the WM; it also involves the deep and cortical GM.⁷ Focal GM lesions appear in the earliest stages of MS^8,9 and are associated with physical and cognitive disability.^10,11 Moreover, cortical lesion load was shown to be a predictor of progression of clinical disability during 5 years¹² and to improve predictions for the conversion from relapsing-remitting to secondary-progressive MS compared with assessing WM lesions alone.¹³ Given the importance of cortical lesions in MS, there is great interest in their visualization. However, the cortex is thin, its myelin content is low, and inflammation is low in cortical lesions. Contrast between lesions and healthy tissue is therefore low, making the detection of cortical damage challenging.In double inversion recovery (DIR),¹⁴ both CSF and the WM signal are suppressed; this suppression results in enhanced contrast between lesions, GM and WM. T1-relaxation times of GM and WM are similar. Therefore, both tissues are affected by the inversion pulse, resulting in reduced SNR. Long data-acquisition times further limit the spatial resolution of DIR to 1 mm³ isotropic at 3T. In a postmortem study, the specificity of 3D-DIR was found to be 90%, whereas sensitivity was only 18%.¹⁵ DIR detected most leukocortical lesions; however, intracortical and subpial lesions were still missed.¹⁵ Intracortical and subpial lesions are the most common cortical lesions in patients with chronic MS, yet subpial lesions are rarely detected with DIR or other techniques.^16,17 More recently, 3D versions of MR imaging sequences for MS have become available¹⁸ but are not yet used widely in clinical imaging of MS.¹⁹ 3D sequences with isotropic voxels of 1 mm³ volume or smaller are particularly suitable for the assessment of the cortex. Moreover, these scans allow simultaneous assessment of all 3 orthogonal image planes. A drawback is the increased acquisition time per scan, in particular for DIR. Lesion detection, especially within the cortex, would benefit from a rapid 3D imaging approach with high spatial resolution, suppressed CSF, higher SNR than DIR, and a good contrast-to-noise ratio (CNR) between lesions, GM and WM.This study aims to develop and test a method that combines the good SNR of T2-weighted images with the CSF suppression of FLAIR to achieve GM-WM contrast similar to that in DIR and good contrast between lesions, healthy tissue. We compared SNR and CNR of this new approach with conventional FLAIR, T2, and DIR; and we present images acquired in patients with relapsing-remitting and progressive MS.     

Arterial hyperintensity on BLADE fluid-attenuated inversion recovery images (FLAIR) in hyperacute territorial infarction: comparison with conventional FLAIR

Objectives

To evaluate the utility of BLADE fluid-attenuated inversion recovery images (FLAIR) magnetic resonance (MR) imaging compared to conventional FLAIR for the detection of arterial hyperintensity (AH) in hyperacute territorial infarction.

Methods

We retrospectively analysed MR images of patients with hyperacute (<6 h) territorial infarction over a 9-month study period. Special attention was paid to the presence or absence of AH in the frontal, parietal and temporal lobes and the number of AHs in the sylvian fissure. We also evaluated the presence of three kinds of artefacts on BLADE FLAIR and conventional FLAIR images.

Results

AH was seen in 41 (91 %) patients with conventional FLAIR and 45 (100 %) patients with BLADE FLAIR images. More instances of AH were detected in the frontal, parietal and temporal lobes and within the sylvian fissure using BLADE FLAIR. Motion artefacts, pulsation artefacts from the sigmoid sinus and incomplete cerebrospinal fluid (CSF) nulling that reduced image quality were observed more frequently on conventional FLAIR images than on BLADE FLAIR images.

Conclusions

BLADE FLAIR sequences are more sensitive than conventional FLAIR for the detection of AH in hyperacute territorial infarctions and provide better image quality by reducing artefacts. They may be used in place of conventional FLAIR for patients with hyperacute stroke.

Key points

? Arterial hyperintensity is an important sign in patients with acute territorial infarctions. ? BLADE FLAIR sequences are sensitive for the detection of AH. ? BLADE FLAIR sequences provide better image quality by reducing artefacts.     

Axial 3D gradient-echo imaging for improved multiple sclerosis lesion detection in the cervical spinal cord at 3T

Introduction

In multiple sclerosis (MS), spinal cord imaging can help in diagnosis and follow-up evaluation. However, spinal cord magnetic resonance imaging (MRI) is technically challenging, and image quality, particularly in the axial plane, is typically poor compared to brain MRI. Because gradient-recalled echo (GRE) images might offer improved contrast resolution within the spinal cord at high magnetic field strength, both without and with a magnetization transfer prepulse, we compared them to T2-weighted fast-spin-echo (T2-FSE) images for the detection of MS lesions in the cervical cord at 3T.

Methods

On a clinical 3T MRI scanner, we studied 62 MS cases and 19 healthy volunteers. Axial 3D GRE sequences were performed without and with off-resonance radiofrequency irradiation. To mimic clinical practice, all images were evaluated in conjunction with linked images from a sagittal short tau inversion recovery scan, which is considered the gold standard for lesion detection in MS. Two experienced observers recorded image quality, location and size of focal lesions, atrophy, swelling, and diffuse signal abnormality independently at first and then in consensus.

Results

The number and volume of lesions detected with high confidence was more than three times as high on both GRE sequences compared to T2-FSE (p?<?0.0001). Approximately 5 % of GRE scans were affected by artifacts that interfered with image interpretation, not significantly different from T2W-FSE.

Conclusions

Axial 3D GRE sequences are useful for MS lesion detection when compared to 2D T2-FSE sequences in the cervical spinal cord at 3T and should be considered when examining intramedullary spinal cord lesions.     

Isolated cerebral susceptibility artefacts in patients with malignant melanoma: metastasis or not?

Objective

While staging patients with malignant melanoma, cerebral susceptibility artefacts on T2*-weighted/susceptibility-weighted imaging (SWI) sequences without a correlate on contrast-enhanced T1-weighted images can be confusing. Without intravenous contrast enhancement, cavernomas, microhaemorrhages and melanin-containing metastases represent possible differential diagnoses for these findings. The purpose of this study was to find out, how often such lesions correspond to metastases.

Methods

Brain MR images (1.5 T) of 408 patients with malignant melanoma but without cerebral metastases in the initial staging by MRI were reviewed retrospectively. Eighteen patients (5 female, 13 male) with malignant melanoma and signal intensity loss on T2*/SWI were included in our study. The average observation period was 19.6 months (6–46 months, 2006–2009).

Results

In each of these 18 patients between one and seven hypointense lesions on T2*/SWI were found. None of these lesions developed into metastasis.

Conclusion

Focal areas of susceptibility artefacts in the brain parenchyma without corresponding abnormalities in contrast-enhanced T1 weighted images are unlikely to represent brain metastases.

Key Points

? In melanoma patients early diagnosis of metastatic brain lesions is mandatory. ? Melanin content and haemorrhage are potential reasons for MRI characteristics of melanoma metastases. ? Susceptibility-weighted MRI visualises melanin and blood products. ? Isolated cerebral susceptibility artefacts do not convert into melanoma metastases. ? SWI/T2* sequences cannot replace Gd-enhanced sequences.     

Image quality and cancer visibility of T2-weighted Magnetic Resonance Imaging of the prostate at 7 Tesla

Objectives

To assess the image quality of T2-weighted (T2w) magnetic resonance imaging of the prostate and the visibility of prostate cancer at 7 Tesla (T).

Materials & methods

Seventeen prostate cancer patients underwent T2w imaging at 7T with only an external transmit/receive array coil. Three radiologists independently scored images for image quality, visibility of anatomical structures, and presence of artefacts. Krippendorff’s alpha and weighted kappa statistics were used to assess inter-observer agreement. Visibility of prostate cancer lesions was assessed by directly linking the T2w images to the confirmed location of prostate cancer on histopathology.

Results

T2w imaging at 7T was achievable with ‘satisfactory’ (3/5) to ‘good’ (4/5) quality. Visibility of anatomical structures was predominantly scored as ‘satisfactory’ (3/5) and ‘good’ (4/5). If artefacts were present, they were mostly motion artefacts and, to a lesser extent, aliasing artefacts and noise. Krippendorff’s analysis revealed an α?=?0.44 between three readers for the overall image quality scores. Clinically significant cancer lesions in both peripheral zone and transition zone were visible at 7T.

Conclusion

T2w imaging with satisfactory to good quality can be routinely acquired, and cancer lesions were visible in patients with prostate cancer at 7T using only an external transmit/receive body array coil.

Key Points

? Satisfactory to good T2-weighted image quality of the prostate is achievable at 7T. ? Periprostatic lipids appear hypo-intense compared to healthy peripheral zone tissue at 7T. ? Prostate cancer is visible on T2-weighted MRI at 7T.     

Pre- and Postcontrast 3D Double Inversion Recovery Sequence in Multiple Sclerosis: A Simple and Effective MR Imaging Protocol

BACKGROUND AND PURPOSE:The double inversion recovery sequence is known to be very sensitive and specific for MS-related lesions. Our aim was to compare the sensitivity of pre- and postcontrast images of 3D double inversion recovery and conventional 3D T1-weighted images for the detection of contrast-enhancing MS-related lesions in the brain to analyze whether double inversion recovery could be as effective as T1WI.MATERIALS AND METHODS:A postcontrast 3D double inversion recovery sequence was acquired in addition to the standard MR imaging protocol at 3T, including pre- and postcontrast 3D T1WI sequences as well as precontrast double inversion recovery of 45 consecutive patients with MS or clinically isolated syndrome between June and December 2013. Two neuroradiologists independently assessed precontrast, postcontrast, and subtraction images of double inversion recovery as well as T1WI to count the number of contrast-enhancing lesions. Afterward, a consensus reading was performed. Lin concordance was calculated between both radiologists, and differences in lesion detectability were assessed with the Student t test. Additionally, the contrast-to-noise ratio was calculated.RESULTS:Significantly more contrast-enhancing lesions could be detected with double inversion recovery compared with T1WI (16%, 214 versus 185, P = .007). The concordance between both radiologists was almost perfect (ρ_c = 0.94 for T1WI and ρ_c = 0.98 for double inversion recovery, respectively). The contrast-to-noise ratio was significantly higher in double inversion recovery subtraction images compared with T1-weighted subtraction images (double inversion recovery, 14.3 ± 5.5; T1WI, 6.3 ± 7.1; P < .001).CONCLUSIONS:Pre- and postcontrast double inversion recovery enables better detection of contrast-enhancing lesions in MS in the brain compared with T1WI and may be considered an alternative to the standard MR imaging protocol.

Since the introduction of the double inversion recovery (DIR) sequence in 1994 by Redpath and Smith,^1,2 many studies have investigated the usefulness of DIR for the detection of inflammatory lesions in the brain in multiple sclerosis. In this sequence, the signals from both the CSF and normal white matter are suppressed simultaneously; thus, differentiation between gray matter and white matter is facilitated. Additionally, inflammatory lesions remain unsuppressed and appear hyperintense. The studies concluded that DIR is very sensitive and specific for MS lesions in the brain,^3–5 especially for intracortical lesions.^6–8 One group could also show that DIR provides the highest sensitivity in the detection of MS lesions in the infratentorial region compared with FLAIR and T2WI.⁴ A similar benefit was found for an adapted DIR sequence in the spinal cord.⁹ Due to the high sensitivity and specificity as well as the increasing availability of the DIR sequence, it is more often included in routine MR imaging protocols.The standard MR imaging protocol for the examination of patients with MS commonly includes the intravenous administration of gadolinium-based contrast agents (GBCAs). The presence of contrast-enhancing lesions is important for the diagnosis and therapeutic strategies of MS and is listed in the revised McDonald criteria from 2010¹⁰ and the magnetic resonance imaging in multiple sclerosis consensus guidelines¹¹ for the criteria of dissemination in time. Because the best sensitivity for enhancing lesions is achieved about 5–10 minutes after injection of a GBCA,¹² further sequences, usually T2WI, are performed for bridging the waiting time. However, these sequences should be carefully selected because the signal of contrast-enhancing lesions might be changed in modified T2WI sequences such as FLAIR^13,14 or DIR.^15,16One group found that contrast-enhancing parts of tumors appear hypointense in postcontrast DIR.¹⁵ Furthermore, it has been shown recently that there is an altered signal intensity of active enhancing inflammatory MS lesions in postcontrast DIR of the brain.¹⁶ This observation led to the recommendation to acquire DIR sequences before GBCA administration.Here, we test the hypothesis that the signal loss on DIR images after GBCA administration can be used to detect active enhancing lesions. In particular, the aim was to compare the sensitivity of pre- and postcontrast images of 3D double inversion recovery and conventional 3D T1WI for the detection of contrast-enhancing MS-related lesions in the brain to analyze whether DIR could be as effective as T1WI.     

Comparison between gadolinium-enhanced 2D T1-weighted gradient-echo and spin-echo sequences in the detection of active multiple sclerosis lesions on 3.0T MRI

Objectives

To compare the sensitivity of enhancing multiple sclerosis (MS) lesions in gadolinium-enhanced 2D T1-weighted gradient-echo (GRE) and spin-echo (SE) sequences, and to assess the influence of visual conspicuity and laterality on detection of these lesions.

Methods

One hundred MS patients underwent 3.0T brain MRI including gadolinium-enhanced 2D T1-weighted GRE and SE sequences. The two sets of contrast-enhanced scans were evaluated in random fashion by three experienced readers. Lesion conspicuity was assessed by the image contrast ratio (CR) and contrast-to-noise ratio (CNR). The intracranial region was divided into four quadrants and the impact of lesion location on detection was assessed in each slice.

Results

Six hundred and seven gadolinium-enhancing MS lesions were identified. GRE images were more sensitive for lesion detection (0.828) than SE images (0.767). Lesions showed a higher CR in SE than in GRE images, whereas the CNR was higher in GRE than SE. Most misclassifications occurred in the right posterior quadrant.

Conclusions

The gadolinium-enhanced 2D T1-weighted GRE sequence at 3.0T MRI enables detection of enhancing MS lesions with higher sensitivity and better lesion conspicuity than 2D T1-weighted SE. Hence, we propose the use of gadolinium-enhanced GRE sequences rather than SE sequences for routine scanning of MS patients at 3.0T.

Key Points

? 2D SE and GRE sequences are useful for detecting active MS lesions. ? Which of these sequences is more sensitive at high field remains uncertain. ? GRE sequence showed better sensitivity for detecting active MS lesions than SE. ? We propose GRE sequence for detecting active MS lesions at 3.0T.

     

Detecting hepatocellular carcinoma in gadoxetic-acid-enhanced hepatobiliary-phase MR imaging at 3T: comparing high and low flip angle

Purpose

We evaluated the diagnostic performance of fat-suppressed 3D T1-weighted gradient-echo magnetic resonance imaging (MRI) sequences for the hepatobiliary phase of gadoxetic-acid-enhanced liver MRI between low and high flip angle (FA) at 3T.

Materials and methods

Forty-six patients with 62 HCCs were enrolled in this retrospective study from among 267 consecutive patients who underwent 3T MRI with low and high FA (10° and 25°) sequences at the hepatobiliary phase. A radiologist measured signal intensities and standard deviations (SD) of lesion, liver, and spleen and calculated signal-to-noise ratio, liver–spleen contrast, and liver–lesion contrast. Two reviewers assessed both image sequences using a five-point rating scale focusing on detecting hypointense lesions.

Results

The high FA sequence showed significantly higher liver–spleen and liver–lesion contrast compared with those of low FA (p < 0.05, p < 0.05, respectively). Per-lesion sensitivities of high FA were higher than those of low FA (p < 0.05, p < 0.05, respectively), and per-person sensitivities were elevated on high FA (p < 0.05 in a reviewer). There were statistically significant differences for detecting HCCs larger than 1 cm (p < 0.05, p < 0.05, respectively).

Conclusion

Increasing FA in T1-weighted hepatobiliary-phase liver MRI may help in detecting HCC at 3T.     

3 Tesla and 7 Tesla MRI of multiple sclerosis cortical lesions

Cortical lesions are prevalent in multiple sclerosis but are poorly detected using MRI. The double inversion recovery (DIR) sequence is increasingly used to explore the clinical relevance of cortical demyelination. Here we evaluate the agreement between imaging sequences at 3 Tesla (T) and 7T for the presence and appearance of individual multiple sclerosis cortical lesions. Eleven patients with demyelinating disease and eight healthy volunteers underwent MR imaging at 3T (fluid attenuated inversion recovery [FLAIR], DIR, and T(1)-weighted magnetization prepared rapid acquisition gradient echo [MP-RAGE] sequences) and 7T (T(1)-weighted MP-RAGE). There was good agreement between images for the presence of mixed cortical lesions (involving both gray and white matter). However, agreement between imaging sequences was less good for purely intracortical lesions. Even after retrospective analysis, 25% of cortical lesions could only be visualized on a single MRI sequence. Several DIR hyperintensities thought to represent cortical lesions were found to correspond to signal arising from extracortical blood vessels. High-resolution 7T imaging appeared useful for confidently classifying the location of lesions in relation to the cortical/subcortical boundary. We conclude that DIR, FLAIR, and MP-RAGE imaging sequences appear to provide complementary information during the detection of multiple sclerosis cortical lesions. High resolution 7T imaging may facilitate anatomical localization of lesions in relation to the cortical boundary.     

Manual Segmentation of MS Cortical Lesions Using MRI: A Comparison of 3 MRI Reading Protocols

BACKGROUND AND PURPOSE:Double inversion recovery has been suggested as the MR imaging contrast of choice for segmenting cortical lesions in patients with multiple sclerosis. In this study, we sought to determine the utility of double inversion recovery for cortical lesion identification by comparing 3 MR imaging reading protocols that combine different MR imaging contrasts.MATERIALS AND METHODS:Twenty-five patients with relapsing-remitting MS and 3 with secondary-progressive MS were imaged with 3T MR imaging by using double inversion recovery, dual fast spin-echo proton-density/T2-weighted, 3D FLAIR, and 3D T1-weighted imaging sequences. Lesions affecting the cortex were manually segmented by using the following 3 MR imaging reading protocols: Protocol 1 (P1) used all available MR imaging contrasts; protocol 2 (P2) used all the available contrasts except for double inversion recovery; and protocol 3(P3) used only double inversion recovery.RESULTS:Six hundred forty-three cortical lesions were identified with P1 (mean = 22.96); 633, with P2 (mean = 22.6); and 280, with P3 (mean = 10). The counts obtained by using P1 and P2 were not significantly different (P = .93). The counts obtained by using P3 were significantly smaller than those obtained by using either P1 (P < .001) or P2 (P < .001). The intraclass correlation coefficients were P1 versus P2 = 0.989, P1 versus P3 = 0.615, and P2 versus P3 = 0.588.CONCLUSIONS:MR imaging cortical lesion segmentation can be performed by using 3D T1-weighted and 3D FLAIR images acquired with a 1-mm isotropic voxel size, supported by conventional T2-weighted and proton-density images with 3-mm-thick sections. Inclusion of double inversion recovery in this multimodal reading protocol did not significantly improve the cortical lesion identification rate. A multimodal approach is superior to using double inversion recovery alone.

Multiple sclerosis is an inflammatory and neurodegenerative disease that affects both the white matter and gray matter of the central nervous system. Postmortem immunohistochemical characterization of cortical lesions (CLs) has allowed the identification of a substantial burden of cortical GM lesions in patients with long-standing MS.^1–5 However, the prevalence of cortical lesions at earlier stages of MS is underexplored.⁶ As a result, an efficient, standardized MR imaging protocol for segmentation of CLs in early-stage MS has become an important research goal. Double inversion recovery (DIR) MR imaging has generally been selected because it enhances the conspicuity of GM by suppressing unwanted signal from both WM and CSF. However, DIR images have a low signal-to-noise ratio due to the application of 2 inversion pulses. They are also prone to hyperintense vascular artifacts, which can confound CL identification.^7–14In 2011, an international panel of experts formulated consensus recommendations for scoring CLs at 1.5T and 3T by using DIR.¹¹ As part of the recommendations, they noted that in the future, the additional use of other MR imaging contrasts (T1-weighted, T2-weighted, or fluid-attenuated inversion recovery images) in combination with DIR could improve the detection of cortical lesions by reducing the number of false-positives and false-negatives. Several groups have since reported on such multicontrast approaches for segmenting CLs. Examples include the following: 1) CL segmentation performed by using a single MR imaging contrast followed by subsequent verification of lesion labels on other contrasts¹³; 2) CL segmentation performed independently by using 2 different MR imaging contrasts, where a tight correlation between the counts is considered evidence that each MR imaging contrast yields counts proportional to the real lesion load¹⁵; 3) CL segmentation performed by using a single MR imaging contrast with the results subsequently reviewed by a second (more experienced) rater who uses other contrasts to resolve ambiguities/potential false-positives¹⁶; and 4) CL segmentation performed independently for each independent contrast, and then each count compared with the counts obtained from the other MR imaging contrasts to determine which one detects the highest number of lesions.¹⁷ The variability among these methods has led to difficulty in developing a standardized CL segmentation protocol.¹¹ Consequently, a major goal of this work was to identify a robust, multicontrast CL segmentation protocol that could be used with more generally available MR imaging pulse sequences at clinically accessible magnetic field strengths.According to the consensus recommendations, only type I leukocortical and type II intracortical lesions should be considered for radiologic scoring¹¹ in MS. However, type I lesions affecting both the cortex and the juxtacortical white matter are often difficult to differentiate from purely juxtacortical lesions. Consequently, these lesions can be misclassified. Type II lesions are the smallest and affect the cortex without reaching either the pial or white matter boundaries. These lesions are also challenging to detect visually by using 1.5T or 3T MR imaging. Subpial lesions (type III and IV), extending from the pial boundary down to the white matter surface, are not considered within the consensus guidelines for MR imaging at 1.5 and 3T due to their low detectability at these clinical field strengths. Even with these simplifying assumptions in place, CL identification has been highly variable.^10,13,18,19 The prevalence of MR imaging–identified intracortical lesions ranges from 8.2% to 46% across different published reports.^{10,12,13,18,19} This variability may partially reflect the variable sensitivity of current MR imaging protocols but also may indicate the inherent variability of cortical lesion involvement across MS disease stages and individual patients. Support for this hypothesis is provided by histology studies in which the percentage of intracortical lesions (type II) also shows a wide range: 7%–31% and 17%–71% when we consider types I and type II combined.^{1–6,19,20,21}A significant aim of our study was to simplify and improve the process of manual cortical lesion segmentation when using multiple MR imaging contrasts derived from 3T MR imaging. We specifically strived to identify a lesion-segmentation method with reduced variability and reduced false-positive identifications. To do this, we avoided classification of cortical lesions into subtypes.     

Fluid-attenuated inversion recovery vascular hyperintensities are not visible using 3D CUBE FLAIR sequence

Objective

Fluid-attenuated inversion recovery (FLAIR) vascular hyperintensities (FVH), initially described on 2D FLAIR images, are a useful imaging marker in patients with acute ischaemic stroke. We aimed to compare the sensitivity of the 3D CUBE FLAIR sequence with 2D FLAIR for the detection of FVH.

Methods

Forty-seven consecutive patients admitted for a suspected stroke were explored by 2D and 3D CUBE FLAIR MR sequences at 1.5 and 3 T. Three blinded readers assessed FVH defined as hyperintensities within cerebral arteries. Location of FVH, acute brain infarct and arterial stenosis were also assessed. 2D images were compared with 3D images for the detection of FVH. Agreement between readers was assessed.

Results

Of the 47 patients, 21 FVHs were observed on 2D FLAIR images of 15 patients (11 with acute brain infarct and 11 with an arterial stenosis). No FVH was visualised on 3D CUBE FLAIR images for either proximal or distal locations. Agreement between readers was excellent.

Conclusion

FVHs are not visible using 3D CUBE FLAIR images. This study suggests that, in suspected acute ischaemic stroke, the assessment of FVH should only be performed on conventional 2D FLAIR images.

Key Points

? Fluid-attenuated inversion recovery (FLAIR) vascular hyperintensities (FVH) are of neuroradiological importance. ? FVHs are useful imaging markers in patients with an acute ischaemic stroke. ? FVHs are not visible using 3D CUBE FLAIR images. ? Assessment of FVH should be performed on conventional 2D FLAIR images.     

Detection of focal hepatic lesions with 3-T MRI: comparison of two-dimensional and three-dimensional T2-weighted sequences

Purpose

To evaluate whether incorporation of a 3D turbo spin-echo sequence during T2-weighted MR imaging improves the detection of focal hepatic lesions by 3T MR imaging.

Materials and methods

Seventy-nine consecutive patients including 67 patients with 62 malignant and 71 benign lesions and 12 patients having no hepatic lesion underwent respiratory-triggered fat-suppressed axial T2-weighted turbo spin-echo imaging using two-dimensional (2D-TSE) and 3D (3D-TSE) sequences. Coronal multiplanar reformatted images (MPR-3D-TSE) were generated from 3D-TSE images. Breath-hold fat-suppressed 2D axial T2-weighted half-Fourier turbo spin-echo (HF-2D-TSE) images were combined for reading. Two independent radiologists reviewed three imaging sets, (1) 2D-TSE and HF-2D-TSE, (2) 3D-TSE and HF-2D-TSE, and (3) 3D-TSE, HF-2D-TSE and MPR-3D-TSE, for detection of malignant and benign lesions. Lesion-to-liver contrast ratio (CR) and the conspicuity of anatomical boundaries were assessed.

Results

For benign lesions, lesion-to-liver CRs with 3D-TSE (2.77?±?1.91, p?=?.0002) and MPR-3D-TSE (2.47?±?1.42, p?=?.012) were higher than with 2D-TSE (2.13?±?1.80). Sensitivity for lesions of???10-mm was higher with 3D-TSE (86?%, p?=?.0039) and MPR-3D-TSE (84?%, p?=?.0078) than with 2D-TSE (72?%). However, the edge of left lateral lobe was less conspicuous with 3D-TSE (p?< .0001) and MPR-3D-TSE (p?=?.0003) than with 2D-TSE because of susceptibility artifacts.

Conclusion

Incorporation of 3D T2-weighted sequence may incrementally improve the detection of focal hepatic lesions.     

Uterine cervical carcinoma: a comparison of two- and three-dimensional T2-weighted turbo spin-echo MR imaging at 3.0 T for image quality and local-regional staging

Objective

To compare three-dimensional (3D) T2-weighted turbo spin-echo (TSE) with multiplanar two-dimensional (2D) T2-weighted TSE for the evaluation of invasive cervical carcinoma.

Methods

Seventy-five patients with cervical carcinoma underwent MRI of the pelvis at 3.0 T, using both 5-mm-thick multiplanar 2D (total acquisition time?=?12 min 25 s) and 1-mm-thick coronal 3D T2-weighted TSE sequences (7 min 20 s). Quantitative analysis of signal-to-noise ratio (SNR) and qualitative analysis of image quality were performed. Local-regional staging was performed in 45 patients who underwent radical hysterectomy.

Results

The estimated SNR of cervical carcinoma and the relative tumour contrast were significantly higher on 3D imaging (P?<?0.0001). Tumour conspicuity was better with the 3D sequence, but the sharpness of tumour margin was better with the 2D sequence. No significant difference in overall image quality was noted between the two sequences (P?=?0.38). There were no significant differences in terms of the diagnostic accuracy, sensitivity, and specificity of parametrial invasion, vaginal invasion, and lymph node metastases.

Conclusion

Multiplanar reconstruction 3D T2-weighted imaging is largely equivalent to 2D T2-weighted imaging for overall image quality and staging accuracy of cervical carcinoma with a shorter MR data acquisition, but has limitations with regard to the sharpness of the tumour margin.

Key Points

? 3D T2-weighted MR sequence is equivalent to 2D for cervical carcinoma staging. ? Coronal 3D acquisitions can reduce the examination time. ? SNR and relative tumour conspicuity were significantly higher on 3D sequences. ? Reformatted 3D T2-weighted imaging had limitations in sharpness of tumour margin.     

Application of variable threshold intensity to segmentation for white matter hyperintensities in fluid attenuated inversion recovery magnetic resonance images

Introduction

White matter hyperintensities (WMHs) are regions of abnormally high intensity on T2-weighted or fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI). Accurate and reproducible automatic segmentation of WMHs is important since WMHs are often seen in the elderly and are associated with various geriatric and psychiatric disorders.

Methods

We developed a fully automated monospectral segmentation method for WMHs using FLAIR MRIs. Through this method, we introduce an optimal threshold intensity (I _O ) for segmenting WMHs, which varies with WMHs volume (V _WMH), and we establish the I _O –V _WMH relationship.

Results

Our method showed accurate validations in volumetric and spatial agreements of automatically segmented WMHs compared with manually segmented WMHs for 32 confirmatory images. Bland–Altman values of volumetric agreement were 0.96 ± 8.311 ml (bias and 95 % confidence interval), and the similarity index of spatial agreement was 0.762 ± 0.127 (mean ± standard deviation). Furthermore, similar validation accuracies were obtained in the images acquired from different scanners.

Conclusions

The proposed segmentation method uses only FLAIR MRIs, has the potential to be accurate with images obtained from different scanners, and can be implemented with a fully automated procedure. In our study, validation results were obtained with FLAIR MRIs from only two scanner types. The design of the method may allow its use in large multicenter studies with correct efficiency.     

Diagnostic performance of 64-MDCT and 1.5-T MRI with highresolution sequences in the T staging of gastric cancer: a comparative analysis with histopathology

Purpose

This study was undertaken to compare the accuracy of magnetic resonance (MR) imaging and 64-slice multidetector computed tomography (64-MDCT) in the T staging of gastric carcinoma in comparison with histopathology.

Materials and methods

Forty patients with an endoscopic diagnosis of gastric carcinoma underwent preoperative MR imaging and 64-MDCT, both of which were performed after i.v. injection of scopolamine and water distension of the stomach. In the MR imaging protocol, we acquired T2-weighted turbo spin-echo (TSE) sequences, true fast imaging steady-state free precession (true-FISP) and gadolinium-enhanced T1-weighted volumetric interpolated breath-hold examination (VIBE) 3D sequences. Contrastenhanced CT scans were obtained in the arterial and venous phases. Two groups of radiologists independently reviewed the MR and 64-MDCT images. The results were compared with pathology findings.

Results

In the evaluation of T stage, 64-MDCT had 82.5% and MR imaging had 80% sensitivity. Accuracy of MR imaging was slightly higher than that of 64-MDCT in identifying T1 lesions (50% vs 37.5%), whereas the accuracy of 64-MDCT was higher in differentiating T2 lesions (81.2% vs 68.7%). The accuracy of MR imaging and 64-MDCT did not differ significantly in the evaluation of T3-T4 lesions (p>0.05). Understaging was observed in 20% of cases with MR imaging and in 17.5% with 64-MDCT.

Conclusions

MR imaging and 64-MDCT accuracy levels did not differ in advanced stages of disease, whereas MR imaging was superior in identifying early stages of gastric cancer and can be considered a valid alternative to MDCT in clinical practice.     

MR imaging of the knee in patients with medial unicompartmental arthroplasty: comparison among sequences at 1.5 T

Purpose

This study was done to test a series of magnetic resonance (MR) imaging sequences of the knee after medial unicompartmental arthroplasty.

Materials and methods

Four patients who had undergone Oxford III medial unicompartmental arthroplasty underwent 1.5-T MR imaging of the operated knee using coronal sequences: T1-weighted spin-echo (SE), T1-weighted turbo SE (TSE), proton-density (PD)- and T2-weighted TSE, T1-weighted gradient echo (GE), short-tau inversion recovery (STIR), multi echo data image combination (MEDIC), T2*-weighted GE, volumetric interpolated breath-hold examination (VIBE), and dual-echo steady state (DESS). For each sequence, we evaluated the visibility of the anatomical structures of the central pivot, lateral compartment, and anterior compartment using a semiquantitative score (0=total masking; 1=insufficient visibility; 2=sufficient visibility; 3=optimal visibility). The sum of the scores given to each sequence was divided by the maximal sum, obtaining a percentage visibility index. Friedman and sign tests were used for statistical analysis.

Results

MR examination time was 30–32 min. No patients reported pain, heat or other local discomfort. The visibility index ranged between 83% and 89% for the first four sequences without significant differences among them, 58% for STIR and 11%–36% for the last five sequences. Significant differences were found between each of the four first sequences and the remaining sequences (p<0.004) and between STIR and the last five sequences (p<0.008).

Conclusions

MR imaging of the knee after medial unicompartmental arthroplasty was not associated with adverse events. An imaging protocol including SE, TSE and STIR sequences could be used to study the knee with unicompartmental arthroplasty.