High-resolution whole-body magnetic resonance imaging applications at 1.5 and 3 Tesla: a comparative study

OBJECTIVES: To analyze the impact of altered magnetic field properties on image quality and on potential artifacts when an established whole-body magnetic resonance imaging (WB-MRI) protocol at 1.5 Tesla (T) is migrated to 3 T. MATERIALS AND METHODS: Fifteen volunteers underwent noncontrast magnetic resonance imaging (MRI) on 32-channel whole body-scanners at 1.5 and 3 T with the use of parallel acquisition techniques (PAT). Coronal T1-weighted TSE- and short tau inversion recovery (STIR)-sequences at 4 body levels including sagittal imaging of the whole spine were performed. Additional axial HASTE-imaging of lung and abdomen, T1-/T2-weighted-TSE- and EPI-sequences of the brain and T2-weighted respiratory-triggered imaging of the liver was acquired. Both data sets were compared by 2 independent readers in respect to artifacts and image quality using a 5-point scale. Regions of pronounced artifacts were defined. RESULTS: Overall image impression was both qualitatively rated as "good" at 1.5 and 3 T for T1-w-TSE- and STIR-imaging of the whole body and spine. At 1.5 T, significantly better quantitative values for overall image quality were found for WB-STIR, T2-w-TSE imaging of the liver and brain (Wilcoxon Mann-Whitney U Test; P < 0.05), overall rated as good at 3 T. Significantly higher dielectric effects at 3 T were affecting T1-w- and STIR-WB-MRI, and HASTE of the abdomen and better image homogeneity at 1.5 T was observed for T1-weighted-/STIR-WB-MRI and T1-w-TSE-imaging of the spine. Pulsation artifacts were significantly increased at 3 T for T1-w WB-MRI. Significantly higher susceptibility artifacts were found for GRE-sequences of the brain at 3 T. Motion artifacts, Gibbs-Ringing, and image distortion was not significantly different and showed slightly higher quantitative values at 3 T (except for HASTE imaging of the abdomen). Overall scan time was 45 minutes and 44 seconds at 1.5 T and 40 minutes and 28 seconds at 3 T at identical image resolution. CONCLUSION: Three Tesla WB-MRI is feasible with good image quality comparable to 1.5 T. 3.0 T WB-MRI shows significantly more artifacts with a mild to moderate impact on image assessment. Therefore 1.5 T WB-MRI is the preferred image modality. Overall scan time at 3 T is reduced with the use of parallel imaging at a constant image resolution.     

Neural correlates of telling lies: a functional magnetic resonance imaging study at 4 Tesla

RATIONALE AND OBJECTIVE: Intentional deception (ie, lying) is a complex cognitive act, with important legal, moral, political, and economic implications. Prior studies have identified activation of discrete anterior frontal regions, such as the ventrolateral prefrontal cortex (VLPFC), dorsolateral prefrontal cortex (DLPFC), dorsal medial prefrontal cortex (DMPFC), and anterior cingulate cortex (ACC) during deception. To extend these findings, we used novel real-time functional magnetic resonance imaging (fMRI) technology to simulate a polygraph experience in order to evoke performance anxiety about generating lies, and sought to ascertain the neural correlates of deception. MATERIALS AND METHODS: In this investigational fMRI study done with a 4-T scanner, we examined the neural correlates of lying in 14 healthy adult volunteers while they performed a modified card version of the Guilty Knowledge Test (GKT), with the understanding that their brain activity was being monitored in real time by the investigators conducting the study. The volunteers were instructed to attempt to generate Lies that would not evoke changes in their brain activity, and were told that their performance and brain responses were being closely monitored. RESULTS: Subjects reported performance anxiety during the task. Deceptive responses were specifically associated with activation of the VLPFC, DLPFC, DMPFC, and superior temporal sulcus. DISCUSSION: These findings suggest the involvement of discrete regions of the frontal cortex during lying, and that the neural substrates responsible for cognitive control of behavior may also be engaged during deception.     

Analysis of cardiac function--comparison between 1.5 Tesla and 3.0 Tesla cardiac cine magnetic resonance imaging: preliminary experience

PURPOSE: We sought to assess the feasibility of magnetic resonance imaging to evaluate cardiac function at 3.0 T compared with 1.5 T. MATERIAL AND METHODS: In a prospective intraindividual comparative study, 12 volunteers (range, 18-54 years), and 2 patients (range, 43-53 years) underwent cardiac cine magnetic resonance at both 3.0 T and 1.5 T. Data were acquired both with a steady-state free precession sequence (SSFP) and a spoiled gradient echo (SGE) sequence. If necessary, a frequency scout was used to correct for off-resonance artifacts. For both SSFP and SGE imaging, 6-mm thick retrospectively EKG-gated short axis views were acquired with equal matrix size (192 x 163) and comparable repetition time (TR). Cardiac function parameters were determined manually by a single investigator. Cardiac function parameters, signal to noise ratio (SNR), contrast to noise ratio (CNR), and the presence of artifacts were compared between the 2 magnetic field strengths. For statistical analysis, a Pearson's correlation coefficient was calculated, and a paired Student t test was used to test statistical significance. RESULTS: Very good correlations between cardiac function parameters at 1.5 T and 3.0 T (r > 0.84, P < 0.0011) were obtained. Compared with SGE, SSFP more frequently was prone to artifacts. With SSFP/SGE at 3.0 T, a SNR gain of 9.4/16% was achieved compared with 1.5 T. CONCLUSION: Functional cardiac cine magnetic resonance imaging can be regarded as equally accurate at 3.0 T compared with 1.5 T. Compared with SSFP imaging, the SGE sequence benefits more from higher field strengths and is less affected by artifacts.     

Fast 3D functional magnetic resonance imaging at 1.5 T with spiral acquisition

A new method to perform rapid 3D fMRI in human brain is introduced and evaluated in normal subjects, on a standard clinical scanner at 1.5 Tesla. The method combines a highly stable gradient echo technique with a spiral scan method, to detect brain activation related changes in blood oxygenation with high sensitivity. A motor activation paradigm with a duration of less than 5 min, performed on 10 subjects, consistently showed significant changes in signal intensity in the area of the motor cortex. In all subjects, these changes survived high statistical thresholds.     

Magnetic resonance angiography in infrapopliteal arterial disease: prospective comparison of 1.5 and 3 Tesla magnetic resonance imaging

PURPOSE: To prospectively determine the accuracy of 1.5 Tesla (T) and 3 T magnetic resonance angiography (MRA) versus digital subtraction angiography (DSA) in the depiction of infrageniculate arteries in patients with symptomatic peripheral arterial disease. PATIENTS AND METHODS: A prospective 1.5 T, 3 T MRA, and DSA comparison was used to evaluate 360 vessel segments in 10 patients (15 limbs) with chronic symptomatic peripheral arterial disease. Selective DSA was performed within 30 days before both MRAs. The accuracy of 1.5 T and 3 T MRA was compared with DSA as the standard of reference by consensus agreement of 2 experienced readers. Signal-to-noise ratios (SNR) and signal-difference-to-noise ratios (SDNRs) were quantified. RESULTS: No significant difference in overall image quality, sufficiency for diagnosis, depiction of arterial anatomy, motion artifacts, and venous overlap was found comparing 1.5 T with 3 T MRA (P > 0.05 by Wilcoxon signed rank and as by Cohen k test). Overall sensitivity of 1.5 and 3 T MRA for detection of significant arterial stenosis was 79% and 82%, and specificity was 87% and 87% for both modalities, respectively. Interobserver agreement was excellent k > 0.8, P < 0.05) for 1.5 T as well as for 3 T MRA. SNR and SDNR were significantly increased using the 3 T system (average increase: 36.5%, P < 0.032 by t test, and 38.5%, P < 0.037 respectively). CONCLUSIONS: Despite marked improvement of SDNR, 3 T MRA does not yet provide a significantly higher accuracy in diagnostic imaging of atherosclerotic lesions below the knee joint as compared with 1.5 T MRA.     

The magnetic resonance imaging appearance at 1.5 Tesla of cartilaginous tumors involving the epiphysis

Three cases of lytic, calcified epiphyseal lesions with plain film and computed tomography features suggestive of chondroblastoma were imaged by magnetic resonance imaging. Histopathologic correlation was obtained in each case. Two cases of chondroblastoma showed low signal intensity on both short (TR600/TE20ms) and long (TR2500/TE80ms) spin echo (SE) images. The third case, a clear cell chondrosarcoma, demonstrated increased signal intensity on moderately T2 weighted (TR2500/TE40ms) images. These findings suggest that magnetic resonance imaging may be helpful in distinguishing these lesions.     

Myocardial tagging and strain analysis at 3 Tesla: comparison with 1.5 Tesla imaging

PURPOSE: To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole. MATERIALS AND METHODS: Normal volunteers (N = 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG-triggered, segmented k-space, spoiled-gradient-echo grid-tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNR(tag)). Matched short-axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)). RESULTS: The average CNR(tag) over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 +/- 12.1, 1.5 T: 9.8 +/- 8.4; P < 0.0001). This difference remained significant at cycle initiation, end-systole, and the end R-R interval (at cycle termination: 3 T = 14.0 +/- 11.0 vs. 1.5 T = 4.4 +/- 3.5; P < 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R-R interval for 3 T images. CONCLUSION: Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole.     

High-resolution magnetic resonance imaging of the temporomandibular joint: image quality at 1.5 and 3.0 Tesla in volunteers

PURPOSE: To assess the image quality of a high-resolution imaging protocol for the temporomandibular joint (TMJ) at 3.0 T and to compare it with our standard 1.5 T protocol. MATERIALS AND METHODS: Fifteen volunteers without history of TMJ dysfunction underwent bilateral magnetic resonance imaging (MRI) of the TMJ with the jaw in closed and open position. MRI was performed with using a 1.5 T (standard TMJ coil) and 3.0 T (purpose build phased array coil) MR system (Gyroscan Intera 1.5 T and 3.0 T; Philips Medical Systems, Best, the Netherlands). Imaging protocols consisted of a parasagittal PDw-TSE sequence and a coronal PDw-TSE sequence in closed mouth position and a sagittal PDw-TSE sequence in open mouth position. Acquisition parameters were adjusted for 3.0 T and voxel size was reduced from 0.29 x 0.29 x 3.0 mm (1.5 T) to 0.15 x 0.15 x 1.5 mm (3.0 T). Total examination time (15 minutes) was similar for both systems. Two observers assessed in consensus delineation, image quality, and artifacts of anatomic landmarks (disk, bilaminar zone, capsular attachment, cortical bone) and ranked them qualitatively on a 5-point scale from 1 (optimal) to 5 (nondiagnostic). Disk position and motility was noted. For CNR analysis, signal intensity from disk and retrodiscal tissue was measured. RESULTS: Disk position and mobility was identical at both field strengths. All anatomic landmarks were visualized significantly better at 3.0 T. In particular, the capsular attachment was depicted in more detail. Overall image quality was ranked significantly higher at 3.0 T, whereas artifact score was similar. Quantitative evaluation showed significantly higher CNR for 3.0 T (10.23 vs. 8.08, P < 0.0001). CONCLUSION: Depiction of the normal anatomy of the TMJ benefits significantly when investing the higher SNR at 3.0 T into better spatial resolution. We anticipate that this advantage of 3.0 T MRI will also permit a more detailed analysis of capsular and disk pathology.     

Multicontrast-weighted magnetic resonance imaging of atherosclerotic plaques at 3.0 and 1.5 Tesla: ex-vivo comparison with histopathologic correlation

The purpose was to analyze magnetic resonance (MR) plaque imaging at 3.0 Tesla and 1.5 Tesla in correlation with histopathology. MR imaging (MRI) of the abdominal aorta and femoral artery was performed on seven corpses using T1-weighted, T2-weighted, and PD-weighted sequences at 3.0 and 1.5 Tesla. Cross-sectional images at the branching of the inferior mesenteric artery and the profunda femoris were rated with respect to image quality. Corresponding cross sections of the imaged vessels were obtained at autopsy. The atherosclerotic plaques in the histological slides and MR images were classified according to the American Heart Association (AHA) and analyzed for differences. MRI at 3.0 Tesla offered superior depiction of arterial wall composition in all contrast weightings, rated best for T2-weighted images. Comparing for field strength, the highest differences were observed in T1-weighted and T2-weighted techniques (both P< or =0.001), with still significant differences in PD-weighted sequence (P< or =0.005). The majority of plaques were histologically classified as calcified plaques. In up to 21% of the cases, MRI at both field strengths detected signal loss characteristic of calcification although calcified plaque was absent in histology. MRI at 3.0 Tesla offers superior plaque imaging quality compared with 1.5 Tesla, but further work is necessary to determine whether this translates in superior diagnostic accuracy.     

1.5T与3.0T32通道接收线圈膝关节MRI的影像质量比较

比较3.0T与1.5T多通道射频(RF)接收线圈人膝关节MRI,探讨膝关节解剖结构显示的提高程度。对20个膝关节进行了1.5T和3.0TMRI检查,采用32通道RF线圈进     

Comparison of image quality in magnetic resonance imaging of the knee at 1.5 and 3.0 Tesla using 32-channel receiver coils

We examined to what degree the visualization of anatomic structures in the human knee is improved using 3.0-T magnetic resonance imaging (MRI) and many element RF receive coils as compared to 1.5 T. We imaged 20 knees at 1.5 and 3.0 T using T2-weighted STIR, T2-weighted gradient echo, T1-weighted spin-echo, true-FISP and T2-weighted fast spin echo techniques in conjunction with 32-element RF coil arrays. The 3.0-T examination was considerably faster than its 1.5-T counterpart. A superior subjective visibility at 3.0 T vs 1.5 T was found in 27 of 50 evaluated structures (meniscus, ligaments) with the exception of true-FISP techniques. The 3.0-T examination provided a better visibility (evaluated by blinded consensus-reading by two radiologists) of small structures such as the ligamentum transversum genu. Also, cartilage was better delineated at 3.0 T. A 23% increased average signal-to-noise ratio as assessed using a temporal filter was observed at 3.0 T as compared to 1.5 T. At 3.0 T, imaging of the human knee is faster and results in a subjective visibility of anatomic structures that is superior to and competitive with 1.5 T.     

Age-related changes in locus ceruleus on neuromelanin magnetic resonance imaging at 3 Tesla.

PURPOSE: To investigate age-related changes in the locus ceruleus (LC) in healthy subjects using neuromelanin magnetic resonance (MR) imaging at 3 Tesla. METHODS: We examined 64 healthy volunteers (aged 23 to 80 years) using neuromelanin-sensitive T1-weighted images and measured the contrast of areas of high signal intensity corresponding to the LC. RESULTS: A pair of punctate areas of high signal intensity that represented neuromelanin within the noradrenergic neurons of the LC was easily recognized in all subjects. The contrast ratio of the LC to the adjacent pontine tegmentum increased to the age of 40 to 59 years and gradually and significantly decreased in elderly subjects. This correlates well with pathologically proven age-related changes in neuromelanin content within the LC. CONCLUSION: Age-related variance should be considered when determining the existence of abnormalities in the LC.     

Recording of the event-related potentials during functional MRI at 3.0 Tesla field strength.

The feasibility of recording event-related potentials (ERP) during functional MRI (fMRI) scanning was studied. Using an alternating checkerboard stimulus in a blocked presentation, visually evoked potentials were obtained with their expected configuration and latencies. A clustered echoplanar imaging protocol was applied to observe the hemodynamic response due to the visual stimulus interleaved with measuring ERPs. Influences of the electrode/amplifier set up on MRI scanning and the scanning process on the recording of electrophysiological signals are reported and discussed. Artifacts overlaid on the electrophysiological recordings were corrected by post hoc filtering methods presented here. Implications and limitations of conducting combined ERP/fMRI experiments using higher-level cognitive stimuli are discussed. Magn Reson Med 44:277-282, 2000.     

Analysis of MR image quality of echo planar diffusion-weighted imaging: investigations at 1.5 Tesla with higher gradient field strength

PURPOSE: Single-shot echo planar Diffusion-weighted-Imaging (EPI DWI) requires extended gradient facilities with strong, fast switching gradients. Up to now the image quality of EPI DWI is enormously influenced by some kinds of artifacts. Therefore we evaluated the image quality of EPI DWI in demonstrating anatomical structures using a 1.5 T MR scanner with a higher gradient field strength of 40 mt/m, a risetime of 200 micros and a slewrate of 200T/m/s. MATERIALS AND METHODS: Using an evaluation scale with four categories two independent readers evaluated 12 different infra- and supratentorial anatomic regions of the brain on 50 DWI images and compared them with the corresponding T2 turbospin echo image. RESULTS: No region was judged to be undistinguishable. On axial DWI images the assessment of the brain stem was poor. In the level of the putamen and thalamus the image quality of DWI was judged to be from adequate to excellent. The central sulcus and the boundary of the white and grey matter was assessed to be adequately visible. The interobserver variability showed a good agreement between the two readers. CONCLUSION: The image quality of EPI DWI improves from a higher gradient field strength. The shortening rise time of 200 micros and the slewrate of 200 T/m/s will lead to a faster gradient switching. Single shot EPI DWI is less influenced by image artefacts and the presentation of different anatomical structures profits when a MR scanner with higher gradient field strength is used.     

FAIR-TrueFISP imaging of cerebral perfusion in areas of high magnetic susceptibility differences at 1.5 and 3 Tesla

PURPOSE: To estimate cerebral blood perfusion in areas of strong magnetic susceptibility changes with high spatial and temporal resolution using a flow-sensitive alternating inversion recovery (FAIR) arterial spin labeling (ASL) method. MATERIALS AND METHODS: We implemented an ASL method that is capable of imaging perfusion in areas of high magnetic susceptibility changes by combining a FAIR spin preparation with a true fast imaging in steady precession (TrueFISP) data acquisition strategy. A TrueFISP readout sequence was applied especially in regions with magnetic field inhomogeneities and compared with corresponding FAIR measurements obtained with a standard echo-planar imaging (EPI) readout. Quantitative perfusion images were obtained at 1.5 Tesla (1.5T) from eight healthy volunteers (24-42 years old) and one patient (23 years old). FAIR-TrueFISP perfusion images were compared with FAIR echo-planar images. T1 maps, which are necessary for quantitative perfusion estimation, were obtained with inversion recovery (IR) TrueFISP and IR EPI. Additionally, high-resolution perfusion measurements were performed on four volunteers at 3T. RESULTS: The two ASL perfusion imaging modalities yielded comparable diagnostic image quality in brain areas with low susceptibility differences at 1.5T. Cerebral perfusion of gray matter (GM) areas was 105.7 +/- 5.2 mL/100 g/minute for FAIR-TrueFISP and 88.8 +/- 14.6 mL/100 g/minute for FAIR-EPI at 1.5T, and 70.4 +/- 7.1 mL/100 g/minute for FAIR-TrueFISP and 63.5 +/- 6.9 mL/100 g/minute for FAIR-EPI at 3.0T. Higher perfusion values at 1.5T were due to more pronounced partial-volume effects from fast moving spins at lower spatial resolution. The FAIR-TrueFISP sequence showed no significant distortions and markedly reduced signal void artifacts in areas of high susceptibility changes (e.g., near brain-bone transitions and close to metallic clips) compared to FAIR-EPI. At 3T, highly resolved FAIR-TrueFISP perfusion images were acquired with an in-plane resolution of up to 1.3 mm. CONCLUSION: FAIR-TrueFISP allows for assessment of cerebral perfusion in areas of critically high susceptibility changes with conventional ASL methods.     

A review of the safety implications of magnetic resonance imaging at field strengths of 3 Tesla and above

RationaleDiagnostic imaging is being driven by technological developments particularly so in the field of Magnetic Resonance Imaging (MRI). Electromagnetic fields used to produce images are becoming much stronger and switched more rapidly and it is essential that safety advice remains appropriate and current. Using a systematic methodology, this review aims to identify the clinical safety implications in performing MRI at field strengths of 3 Tesla (T) and above and determine whether the current clinical safety guidelines are appropriate.MethodReferences were sourced from The Cochrane Library, Centre for Reviews and Dissemination Science Direct, PubMed and Google Scholar. Related websites searched included The British Institute of Radiology, Society of Radiographers, Royal College of Radiologists, The Institution of Engineering and Technology, IMRSER (Institute for Magnetic Resonance Safety, Education, and Research), MagNet (NHS PASA). References supplied in retrieved papers were also checked for potential relevance. The use of consistent search terminology and inclusion and exclusion criteria ensured quality and provided rigour to conclusions drawn.ConclusionAccording to the literature retrieved, the current body of knowledge has allowed safety guidelines to be established for patient safety and these are both appropriate and valid at field strengths of 3 T.     

Endorectal magnetic resonance imaging at 1.5 Tesla to assess local recurrence following radical prostatectomy using T2-weighted and contrast-enhanced imaging

To evaluate diagnostic performance of endorectal magnetic resonance (eMR) for diagnosing local recurrence of prostate cancer (PC) in patients with previous radical prostatectomy (RP) and to assess whether contrast-enhanced (CE)-eMR improved diagnostic accuracy in comparison to unenhanced study. Unenhanced eMR data of 72 male patients (mean of total PSA: 1.23 ± 1.3 ng/ml) with previous RP were interpreted retrospectively and classified either as normal or suspicious for local recurrence. All eMR examinations were re-evaluated also on CE-eMR 4 months after the first reading. Images were acquired on a 1.5-T system. These data were compared to the standard of reference for local recurrence: prostatectomy bed biopsy results; choline positron emission tomography results; PSA reduction or increase after pelvic radiotherapy; PSA modification during active surveillance. Sensitivity, specificity, predictive positive value, negative predictive value and accuracy were 61.4%, 82.1%, 84.4%, 57.5% and 69.4% for unenhanced eMR and 84.1%, 89.3%, 92.5%, 78.1% and 86.1% for CE-eMR. A statistically significant difference was found between accuracy and sensitivity of the two evaluations (χ² = 5.33; p = 0.02 and χ² = 9.00; p = 0.0027). EMR had great accuracy for visualizing local recurrence of PC after RP. CE-eMR improved diagnostic performance in comparison with T2-weighted imaging alone.     

In vivo magnetic resonance imaging of the human cervical spinal cord at 3 Tesla

PURPOSE: To demonstrate the feasibility of obtaining high-quality magnetic resonance (MR) images of the human cervical spinal cord in vivo at a magnetic field strength of 3 T and to optimize the signal contrast between gray matter, white matter, and cerebrospinal fluid (CSF) on 2D gradient recalled echo (GRE) images of the cervical spinal cord. MATERIALS AND METHODS: Using a custom-built, anatomically molded radio frequency (RF) surface coil, the repetition time and flip angle of a 2D GRE sequence were systematically varied in five volunteers to assess tissue contrast in the cervical spinal cord. RESULTS: The 2D GRE parameters for an optimal balance between gray-white matter and CSF-white matter contrast at 3 T were determined to be a time-to-repetition (TR) of 2000 msec and a flip angle of 45 degrees, with the constant short time-to-echo (TE) of 12 msec used in this study. Excellent tissue contrast and visualization of the internal anatomy of the spinal cord was demonstrated reproducibly in eight subjects using these optimal parameters. CONCLUSION: This study demonstrates that imaging the cervical spinal cord and delineating internal spinal cord structures such as gray and white matter is feasible at 3 T.