Vulnerable plaque detection by 3.0 tesla magnetic resonance imaging

RATIONALE AND OBJECTIVES: A clinical case report is presented on a 76-year-old man who volunteered for a 3.0 T magnetic resonance (MR) carotid protocol. The subject was referred for carotid endarterectomy and histology was performed on the ex vivo specimen and compared with the in vivo images. METHODS: The 3.0 and 1.5 T (obtained for comparison) MR protocol consisted of 2-dimensional (2D) and 3-dimensional (3D) multicontrast bright and black blood imaging for detecting the lumen and vessel wall. RESULTS: The combination of multicontrast black blood transverse images and the 3D time of flight transverse images provided visualization of a narrowed internal carotid artery lumen 4 mm above of the bifurcation and the presence of a complex atherosclerotic plaque containing a large lipid pool, calcification, and intact fibrous cap. Quantitative comparisons including vessel lumen and plaque area, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were obtained for 1.5 and 3.0 T image data. Plaque composition was verified with histology. Macrophages were also detected in the shoulders of the plaque as demonstrated by CD68 staining and corresponded with a small hyperintense area in the T2W images at 3.0 T, but not observed in comparable 1.5 T images. CONCLUSIONS: High field 3.0 T multicontrast MRI of atherosclerotic plaque has been validated with histology comparison and provides improved detection of complex atherosclerotic plaque with increased SNR and CNR compared with 1.5 T. Further studies validating contrast mechanisms of plaque at 3.0 T are required, but atherosclerotic plaque imaging has clear benefit from application at the higher magnetic field strength.     

Multislice dark-blood carotid artery wall imaging: a 1.5 T and 3.0 T comparison

PURPOSE: To compare two multislice turbo spin-echo (TSE) carotid artery wall imaging techniques at 1.5 T and 3.0 T, and to investigate the feasibility of higher spatial resolution carotid artery wall imaging at 3.0 T. MATERIALS AND METHODS: Multislice proton density-weighted (PDW), T2-weighted (T2W), and T1-weighted (T1W) inflow/outflow saturation band (IOSB) and rapid extended coverage double inversion-recovery (REX-DIR) TSE carotid artery wall imaging was performed on six healthy volunteers at 1.5 T and 3.0 T using time-, coverage-, and spatial resolution-matched (0.47 x 0.47 x 3 mm3) imaging protocols. To investigate whether improved signal-to-noise ratio (SNR) at 3.0 T could allow for improved spatial resolution, higher spatial resolution imaging (0.31 x 0.31 x 3 mm3) was performed at 3.0 T. Carotid artery wall SNR, carotid lumen SNR, and wall-lumen contrast-to-noise ratio (CNR) were measured. RESULTS: Signal gain at 3.0 T relative to 1.5 T was observed for carotid artery wall SNR (223%) and wall-lumen CNR (255%) in all acquisitions (P < 0.025). IOSB and REX-DIR images were found to have different levels of SNR and CNR (P < 0.05) with IOSB values observed to be larger. Normalized to a common imaging time, the higher spatial resolution imaging at 3.0 T and the lower spatial resolution imaging at 1.5 T provided similar levels of wall-lumen CNR (P = NS). CONCLUSION: Multislice carotid wall imaging at 3.0 T with IOSB and REX-DIR benefits from improved SNR and CNR relative to 1.5 T, and allows for higher spatial resolution carotid artery wall imaging.     

Comparison between 2D and 3D high-resolution black-blood techniques for carotid artery wall imaging in clinically significant atherosclerosis

PURPOSE: To compare two- (2D) and three-dimensional (3D) black-blood imaging methods for morphological measurements of the carotid artery wall and atherosclerotic plaque. MATERIALS AND METHODS: A total of 18 subjects with 50% to 79% carotid stenosis were scanned with 2D (2-mm slice thickness) and 3D (1-mm/0.5-mm actual/interpolated slice thickness) T1-weighted fast spin-echo (FSE) black-blood imaging sequences with double inversion-recovery (DIR) blood suppression. Morphological measurements (lumen area, wall area, vessel area, mean wall thickness, and maximal wall thickness), signal-to-noise ratio (SNR) in the wall and lumen, and wall-lumen contrast-to-noise ratio (CNR) were compared between 2D and 3D images. The effect of improved slice resolution in 3D imaging was evaluated for visualization of small plaque components. RESULTS: Lumen SNR (P = 0.16), wall SNR (P = 0.65), and CNR (P = 0.94) were comparable between 2D/3D. There was no difference in average lumen area (P = 0.16), average wall area (P = 0.99), average vessel area (P = 0.0.58), mean wall thickness (P = 0.09), and maximum wall thickness (P = 0.06) between 2D/3D. Distributions of small plaque components such as calcification were better characterized by the 3D acquisition. There was a higher sensitivity to motion artifacts with 3D imaging, resulting in three examinations with low image quality. CONCLUSION: 2D and 3D protocols provided comparable morphometric measurements of the carotid artery. The major advantage of 3D imaging is improved small plaque component visualization, while the 2D technique provides higher reliability for image quality.     

Improved suppression of plaque-mimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium (MSDE) turbo spin-echo (TSE) sequence

In this study, a turbo spin-echo (TSE) based motion-sensitized driven-equilibrium (MSDE) sequence was used as an alternative black-blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast-to-noise ratio (CNR_eff) and residual signal-to-noise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion-recovery (DIR) images. Statistically significant higher CNR_eff and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery (CA) imaging. Magn Reson Med 58:973–981, 2007. © 2007 Wiley-Liss, Inc.     

Atherosclerosis imaging using 3D black blood TSE SPACE vs 2D TSE

AIM: To compare 3D Black Blood turbo spin echo (TSE) sampling perfection with application-optimized contrast using different flip angle evolution (SPACE) vs 2D TSE in evaluating atherosclerotic plaques in multiple vascular territories.METHODS: The carotid, aortic, and femoral arterial walls of 16 patients at risk for cardiovascular or atherosclerotic disease were studied using both 3D black blood magnetic resonance imaging SPACE and conventional 2D multi-contrast TSE sequences using a consolidated imaging approach in the same imaging session. Qualitative and quantitative analyses were performed on the images. Agreement of morphometric measurements between the two imaging sequences was assessed using a two-sample t-test, calculation of the intra-class correlation coefficient and by the method of linear regression and Bland-Altman analyses.RESULTS: No statistically significant qualitative differences were found between the 3D SPACE and 2D TSE techniques for images of the carotids and aorta. For images of the femoral arteries, however, there were statistically significant differences in all four qualitative scores between the two techniques. Using the current approach, 3D SPACE is suboptimal for femoral imaging. However, this may be due to coils not being optimized for femoral imaging. Quantitatively, in our study, higher mean total vessel area measurements for the 3D SPACE technique across all three vascular beds were observed. No significant differences in lumen area for both the right and left carotids were observed between the two techniques. Overall, a significant-correlation existed between measures obtained between the two approaches.CONCLUSION: Qualitative and quantitative measurements between 3D SPACE and 2D TSE techniques are comparable. 3D-SPACE may be a feasible approach in the evaluation of cardiovascular patients.     

不同MR扫描序列在SPIO增强大鼠肝癌模型的对比研究

目的：比较多种扫描序列超顺磁氧化铁（SPIO）增强扫描对显示大鼠肝癌病灶的能力，找出最佳扫描方案。TSE T2WI、SE双回波的T2WI＋PDWI、GRE T1WI、T2^＊WI，分析增强前后大鼠肝癌病灶的强化特征，并进行病理学检查对照分析。结果：注射SPIO对比剂后，所有扫描序列均显示肝脏的信号强度较增强前有不同程度的下降，肝癌病灶CNR均分别高于平扫。增强后GRE T2^＊WI中病灶的CNR明显高于其它序列，但增强后TSE T2WI和常规SE T2WI在显示病变的SNR、CNR方面没有显著性差异。结论：SPIO增强后检测肝癌病灶的各种序列中，以GRE T2^*WI最为敏感，其次是双回波的T2WI＋PDWI序列。     

质子加权预饱和脂肪抑制序列在肛瘘中的应用价值

目的评价质子加权预饱和脂肪抑制序列(PDW PFS)对肛瘘显示的准确性及图像质量的清晰性,探讨PDW PFS在肛瘘中的应用价值。资料与方法 20例经手术证实的肛瘘患者术前进行MRI检查,序列包括T1WI、T2W频谱选择性衰减反转恢复序列(SPAIR)和PDW PFS。MRI检查前均向患者肛管直肠内置入肛肠水囊以撑开肛管和直肠。获得图像后,观察患者的瘘管、内口和肛周脓肿,评估和比较MRI各序列显示的瘘管、内口、脓腔,并对PDW PFS和T2W SPAIR序列瘘管的信号强度(SI)、信噪比(SNR)及瘘管与周围肌肉的对比噪声比(CNR)进行测量及比较。结果 PDW PFS序列显示瘘管(100%)、内口(95.7%)、肛周脓肿(100%)的准确率较T1WI及T2WSPAIR序列为高。Kruskal Wallis检验显示上述各序列对瘘管(χ2=6.95,P<0.05)及内口(χ2=31.53,P<0.05)的显示具有显著统计学差异,PDW PFS序列显示瘘管及内口最多。PDW PFS序列SI、SNR值和CNR值均显著高于T2W SPAIR序列(P<0.05)。结论 PDW PFS成像技术具有较高的图像SNR和CNR,更易认识辨别瘘管和内口,可以作为一种新的无创性磁共振成像技术应用于肛瘘成像。     

Evaluation of optimised 3D turbo spin echo and gradient echo MR pulse sequences of the knee at 3T and 1.5T

IntroductionTo investigate the impact of parameter optimisation for novel three-dimensional 3D sequences at 1.5T and 3T on resultant image quality.MethodsFollowing institutional review board approval and acquisition of informed consent, MR phantom and knee joint imaging on healthy volunteers (n = 16) was performed with 1.5 and 3T MRI scanners, respectively incorporating 8- and 15-channel phased array knee radiofrequency coils. The MR phantom and healthy volunteers were prospectively scanned over a six-week period. Acquired sequences included standard two-dimensional (2D) turbo spin echo (TSE) and novel three-dimensional (3D) TSE PDW (SPACE) both with and without fat-suppression, and T21W gradient echo (TrueFISP) sequences. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured for knee anatomical structures. Two musculoskeletal radiologists evaluated anatomical structure visualisation and image quality. Quantitative and qualitative findings were investigated for differences using Friedman tests. Inter- and intra-observer agreements were determined with κ statistics.ResultsPhantom and healthy volunteer images revealed higher SNR for sequences acquired at 3T (p-value <0.05). Generally, the qualitative findings ranked images acquired at 3T higher than corresponding images acquired at 1.5T (p < 0.05). 3D image data sets demonstrated less sensitivity to partial volume averaging artefact (PVA) compared to 2D sequences. Inter- and intra-observer agreements for evaluation across all sequences ranged from 0.61 to 0.79 and 0.71 to 0.92, respectively.ConclusionBoth 2D and 3D images demonstrated higher image quality at 3T than at 1.5T. Optimised 3D sequences performed better than the standard 2D PDW TSE sequence for contrast resolution between cartilage and joint fluid, with reduced PVA artefact.Implications for practiceWith rapid advances in MRI scanner technology, including hardware and software, the optimisation of 3D MR pulse sequences to reduce scan time while maintaining image quality, will improve diagnostic accuracy and patient management in musculoskeletal MRI.     

Comparison of 3T and 7T MRI clinical sequences for ankle imaging

The purpose of this study was to compare 3T and 7T signal-to-noise and contrast-to noise ratios of clinical sequences for imaging of the ankles with optimized sequences and dedicated coils. Ten healthy volunteers were examined consecutively on both systems with three clinical sequences: (1) 3D gradient-echo, T(1)-weighted; (2) 2D fast spin-echo, PD-weighted; and (3) 2D spin-echo, T(1)-weighted. SNR was calculated for six regions: cartilage; bone; muscle; synovial fluid; Achilles tendon; and Kager's fat-pad. CNR was obtained for cartilage/bone, cartilage/fluid, cartilage/muscle, and muscle/fat-pad, and compared by a one-way ANOVA test for repeated measures. Mean SNR significantly increased at 7T compared to 3T for 3D GRE, and 2D TSE was 60.9% and 86.7%, respectively. In contrast, an average SNR decrease of almost 25% was observed in the 2D SE sequence. A CNR increase was observed in 2D TSE images, and in most 3D GRE images. There was a substantial benefit from ultra high-field MR imaging of ankles with routine clinical sequences at 7T compared to 3T. Higher SNR and CNR at ultra-high field MR scanners may be useful in clinical practice for ankle imaging. However, carefully optimized protocols and dedicated extremity coils are necessary to obtain optimal results.     

Multicontrast black-blood MRI of carotid arteries: comparison between 1.5 and 3 tesla magnetic field strengths

PURPOSE: To compare black-blood multicontrast carotid imaging at 3T and 1.5T and assess compatibility between morphological measurements of carotid arteries at 1.5T and 3T. MATERIALS AND METHODS: Five healthy subjects and two atherosclerosis patients were scanned in 1.5T and 3T scanners with a similar protocol providing transverse T1-, T2-, and proton density (PD)-weighted black-blood images using a fast spin-echo sequence with single- (T1-weighted) or multislice (PD-/T2-weighted) double inversion recovery (DIR) preparation. Wall and lumen signal-to-noise ratio (SNR) and wall/lumen contrast-to-noise ratio (CNR) were compared in 44 artery cross-sections by paired t-test. Interscanner variability of the lumen area (LA), wall area (WA), and mean wall thickness (MWT) was assessed using Bland-Altman analysis. RESULTS: Wall SNR and lumen/wall CNR significantly increased (P < 0.0001) at 3T with a 1.5-fold gain for T1-weighted images and a 1.7/1.8-fold gain for PD-/T2-weighted images. Lumen SNR did not differ for single-slice DIR T1-weighted images (P = 0.2), but was larger at 3T for multislice DIR PD-/T2-weighted images (P = 0.01/0.03). The LA, WA, and MWT demonstrated good agreement with no significant bias (P 0.5), a coefficient of variation (CV) of < 10%, and intraclass correlation coefficient (ICC) of > 0.95. CONCLUSION: This study demonstrated significant improvement in SNR, CNR, and image quality for high- resolution black-blood imaging of carotid arteries at 3T. Morphologic measurements are compatible between 1.5T and 3T.     

Signal-to-noise ratio increase in carotid atheroma MRI: a comparison of 1.5 and 3 T

Objectives

This study reports quantitative comparisons of signal-to-noise ratio (SNR) at 1.5 and 3 T from images of carotid atheroma obtained using a multicontrast, cardiac-gated, blood-suppressed fast spin echo protocol.

Methods

18 subjects, with carotid atherosclerosis (>30% stenosis) confirmed on ultrasound, were imaged on both 1.5 and 3 T systems using phased-array coils with matched hardware specifications. T₁ weighted (T₁W), T₂ weighted (T₂W) and proton density-weighted (PDW) images were acquired with identical scan times. Multiple slices were prescribed to encompass both the carotid bifurcation and the plaque. Image quality was quantified using the SNR and contrast-to-noise ratio (CNR). A phantom experiment was also performed to validate the SNR method and confirm the size of the improvement in SNR. Comparisons of the SNR values from the vessel wall with muscle and plaque/lumen CNR measurements were performed at a patient level. To account for the multiple comparisons a Bonferroni correction was applied.

Results

One subject was excluded from the protocol owing to image quality and protocol failure. The mean improvement in SNR in plaque was 1.9, 2.1 and 2.1 in T₁W, T₂W and PDW images, respectively. All plaque SNR improvements were statistically significant at the p<0.05 level. The phantom experiment reported an improvement in SNR of 2.4 for PDW images.

Conclusions

Significant gains in SNR can be obtained for carotid atheroma imaging at 3 T compared with 1.5 T. There was also a trend towards increased CNR. However, this was not significant after the application of the Bonferroni correction.Carotid MRI has been in use since the mid-1990s for detecting atherosclerosis [1], with advances being driven by a greater understanding of the pathophysiology of plaque development and progression [2]. This has in turn led to a desire to be able to distinguish characteristics of carotid atheroma (such as a large lipid-rich necrotic core or a thin fibrous cap) that put an individual at a significantly greater risk of a future stroke [3]. MRI has been repeatedly validated against the gold standard of histology for the characterisation of carotid atheroma and measurement of plaque components [1,2,4,5]. The capacity for MRI to demonstrate plaque characteristics has been applied to assess the long-term pathogenesis of atherosclerosis and to monitor the effects of therapeutic interventions [6-9].The current limiting factors for multicontrast MRI in atheroma are image resolution and scan time, but the advent of higher field strengths has provided the opportunity to advance the quality of carotid imaging. The requirement for high-resolution imaging at small fields of view places high demands on the hardware being used, and current protocols typically use signal averaging to improve signal-to-noise ratio (SNR). In theory, SNR should increase linearly with field strength; thus, a 1.5 vs 3 T comparison experiment should produce an approximate doubling of the SNR [10]. This expected increase in SNR could be used either to improve spatial resolution or to reduce the number of averages, and hence reduce the scan time in future protocols.Initial studies have indicated the benefit of 3 T MRI of the carotid artery wall. One of the early studies, in 2005, used a double inversion recovery (DIR) prepared turbo spin echo (TSE) sequence to image a phantom and healthy volunteers [11]. The phantom experiments demonstrated an SNR increase of a factor of 2.5 for 3 T over 1.5 T, compared with 2.1 in vivo. A separate image with a larger field of view (FOV; 24×12 cm as opposed to 12×12 cm) but the same bandwidth/pixel size was used to define the background regions of interest (ROI) for the SNR calculation. The superlinear increase in the phantom was ascribed to the differential noise contribution of the small coil elements at the different field strengths. In addition to this, the lower SNR gain in vivo was attributed to the differences in T₁ and T₂ at the higher field strength, as well as the need to use a lower refocusing flip angle at 3 T (160°) in two of the subjects owing to specific absorption rate (SAR) limitations.A study published in 2006 performed multicontrast fast spin echo (FSE) imaging with DIR preparation and fat suppression without cardiac gating [12]. A cohort of five healthy volunteers and two atheroma-affected subjects were imaged at both field strengths, and SNR and contrast-to-noise ratio (CNR) values increased by 1.5–1.8 times at 3 T. Noise levels were determined from four ROIs drawn in an artefact-free background area in a rectangular FOV (16×12 cm), and the wall/luminal signal intensities were corrected for the mean noise contribution.A 2007 study using a small cohort (five healthy volunteers, five with atherosclerosis) produced comparable results [13], albeit with different coils (eight-element at 3 T and four-element at 1.5 T) and slightly different pixel sizes used at the two field strengths. A two-fold increase in SNR for the vessel wall (in sections unaffected by plaque) was reported after adjustment for the larger voxel size used at 1.5 T. However, differences in SNR enhancement between the different contrast weightings were not described.A single case report considering multicontrast imaging in a patient with moderate carotid stenosis using 1.5 and 3 T systems from different manufacturers found a significant improvement in SNR across T₁ weighted (T₁W), T₂ weighted (T₂W) and proton density weighted (PDW) images at 3 T, varying from a 64% to 83% increase [14].While the majority of these studies confirm the expected increase in SNR with field strength, they are based upon small sample sizes (mainly normal volunteers) and varying numbers of sequences, and they utilise a range of SNR measurement methodologies, as well as differences in coil design/manufacture and MRI system manufacturers at the two field strengths.In comparison with the previous studies, the current work provides a substantially more detailed and standardised comparative analysis of SNR at 1.5 and 3.0 T for the widely used multicontrast imaging using, as far as possible, identical pulse sequences, coil designs and MRI systems. Unlike the previous studies, rather than using normal volunteers, a larger cohort of patients with confirmed carotid atheroma of varying degrees of severity was used, as would be seen in clinical practice.     

Water-saturated three-dimensional balanced steady-state free precession for fast abdominal fat quantification

PURPOSE: To compare the performance of a novel water-saturated b-SSFP sequence with that of a conventional T1-weighted turbo spin echo (T1W TSE) sequence for abdominal fat quantification. MATERIALS AND METHODS: A water-saturated, segmented, three-dimensional balanced steady-state free precession (b-SSFP) sequence and a traditional T1W TSE sequence were both employed on phantom and human studies. For phantom studies, a dual-layered phantom with known internal/external oil volumes was imaged using the two sequences. Images obtained by the two sequences were both processed using a computer-aided semiautomatic program for oil volume quantification. For human studies, six volunteers were scanned axially, centered at L2-L3 levels. Signal-to-noise ratio (SNR)(fat), contrast-to-noise ratio (CNR)(fat-muscle), CNR(fat-large bowel), and CNR(fat-small bowel) were calculated on hand-drawn regions of interest (ROIs), and averaged over all six slices for each subject. Statistical analyses were then performed to determine the SNR and CNR differences between images obtained by the two techniques. RESULTS: The phantom studies show that water-saturated b-SSFP offers a significantly closer estimation of true oil volumes compared with that of T1W TSE (P < 0.0001), as well as a more accurate internal/external volume ratio (P = 0.0001). In human studies, three-dimensional water-saturated b-SSFP images demonstrated higher CNR than that of T1W TSE (P < 0.0005), and very close SNR(fat) (P = 0.045). CONCLUSION: The proposed three-dimensional water-saturated b-SSFP sequence can generate high quality fat-only abdominal images with high CNR and SNR in shorter scan duration than the conventional T1W TSE approach. As images generated by this sequence suffer from no flow artifacts, and are less sensitive to bulk, respiratory, and bowel motion, three-dimensional water-saturated b-SSFP is a faster and more robust method for improving abdominal fat quantification using MRI.     

颈动脉粥样硬化斑块的MR成像

目的：探讨MR成像技术在颈动脉粥样硬化斑块检测中的应用，及其对斑块内成份进行定性分析的可能性。方法：采用3D-TOF、Double-IR(DIR)T1WI、T2WI、PDWI序列对11位高度疑诊颈动脉粥样硬化的患者及9位健康志愿者进行颈动脉成像。部分患者行彩超对照。结果：11例患者中9例可见明显颈动脉粥样硬化改变。TOF上表现为管腔内高信号血流中见低信号充盈缺损。DIR T1WI、T2WI、PDWI表现为管壁增厚，斑块呈等、低均匀信号或等、低、高混杂信号。与多普勒彩超对比，MRI对颈动脉粥样硬化的检出准确率较高。结论：MRI对颈动脉粥样硬化可达到满意的诊断，并提示MRI能分析斑块内成份，分析斑块成份及性质为临床选择治疗方案及估计预后提供有力的帮助。     

Black-blood steady-state free precession (SSFP) coronary wall MRI for cardiac allografts: a feasibility study

Purpose:

To assess the hypothesis that steady‐state free procession (SSFP) allows for imaging of the coronary wall under the conditions of fast heart rate in heart transplantation (HTx) patients.

Materials and Methods:

With the approval of our Institutional Review Board, 28 HTx patients were scanned with a 1.5T scanner. Cross‐sectional black‐blood images of the proximal portions of the left main artery, left anterior descending artery, and right coronary artery were acquired with both a 2D, double inversion recovery (DIR) prepared turbo (fast) spin echo (TSE) sequence and a 2D DIR SSFP sequence. Image quality (scored 0–3), vessel wall area, thickness, signal‐to‐noise ratio (SNR, vessel wall), and contrast‐to‐noise ratio (CNR, wall‐lumen) were compared between TSE and SSFP.

Results:

The overall image quality of SSFP was higher than TSE (1.23 ± 0.95 vs. 0.88 ± 0.69, P < 0.001). SSFP had a higher coronary wall SNR (20.1 ± 8.5 vs. 14.9 ± 4.8, P < 0.001) and wall‐lumen CNR (8.2 ± 4.6 vs. 6.8 ± 3.7, P = 0.005) than TSE.

Conclusion:

Black‐blood SSFP coronary wall MRI provides higher image quality, SNR, and CNR than traditional TSE does in HTx recipients. It has the potential to become an alternative means to noninvasive imaging of cardiac allografts. J. Magn. Reson. Imaging 2012;35:1210‐1215. © 2012 Wiley Periodicals, Inc.     

Three‐dimensional flow‐independent balanced steady‐state free precession vessel wall MRI of the popliteal artery: Preliminary experience and comparison with flow‐dependent black‐blood techniques

Purpose:

To examine the feasibility of flow‐independent T2‐prepared inversion recovery (T2IR) black‐blood (BB) magnetization preparation for three‐dimensional (3D) balanced steady‐state free precession (SSFP) vessel wall MRI of the popliteal artery, and to evaluate its performance relative to flow‐dependent double inversion recovery (DIR), spatial presaturation (SPSAT), and motion‐sensitizing magnetization preparation (MSPREP) BB techniques in healthy volunteers.

Materials and Methods:

Eleven subjects underwent 3D MRI at 1.5 Tesla with four techniques performed in a randomized order. Wall and lumen signal‐to‐noise ratio (SNR), wall‐to‐lumen contrast‐to‐noise ratio (CNR), vessel wall area, and lumen area were measured at proximal, middle, and distal locations of the imaged popliteal artery. Image quality scores based on wall visualization and degree of intraluminal artifacts were also obtained.

Results:

In the proximal region, DIR and SPSAT had higher wall SNR and wall‐to‐lumen CNR than both MSPREP and T2IR. In the middle and distal regions, DIR and SPSAT failed to provide effective blood suppression, whereas MSPREP and T2IR provided adequate black blood contrast with comparable wall‐to‐lumen CNR and image quality.

Conclusion:

The feasibility of 3D SSFP imaging of the popliteal vessel wall using flow‐independent T2IR was demonstrated with effective blood suppression and good vessel wall visualization. Although DIR and SPSAT are effective for thin slab imaging, MSPREP and T2IR are better suited for 3D thick slab imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Segmentation of carotid plaque using multicontrast 3D gradient echo MRI

Purpose:

To evaluate the performance of automatic segmentation of atherosclerotic plaque components using solely multicontrast 3D gradient echo (GRE) magnetic resonance imaging (MRI).

Materials and Methods:

A total of 15 patients with a history of recent transient ischemic attacks or stroke underwent carotid vessel wall imaging bilaterally with a combination of 2D turbo spin echo (TSE) sequences and 3D GRE sequences. The TSE sequences included T1‐weighted, T2‐weighted, and contrast‐enhanced T1‐weighted scans. The 3D GRE sequences included time‐of‐flight (TOF), magnetization‐prepared rapid gradient echo (MP‐RAGE), and motion‐sensitized driven equilibrium prepared rapid gradient echo (MERGE) scans. From these images, the previously developed morphology‐enhanced probabilistic plaque segmentation (MEPPS) algorithm was retrained based solely on the 3D GRE sequences to segment necrotic core (NC), calcification (CA), and loose matrix (LM). Segmentation performance was assessed using a leave‐one‐out cross‐validation approach via comparing the new 3D‐MEPPS algorithm to the original MEPPS algorithm that was based on the traditional multicontrast protocol including 2D TSE and TOF sequences.

Results:

Twenty arteries of 15 subjects were found to exhibit significant plaques within the coverage of all imaging sequences. For these arteries, between new and original MEPPS algorithms, the areas per slice exhibited correlation coefficients of 0.86 for NC, 0.99 for CA, and 0.80 for LM; no significant area bias was observed.

Conclusion:

The combination of 3D imaging sequences (TOF, MP‐RAGE, and MERGE) can provide sufficient contrast to distinguish NC, CA, and LM. Automatic segmentation using 3D sequences and traditional multicontrast protocol produced highly similar results. J. Magn. Reson. Imaging 2012;35:812–819. © 2011 Wiley Periodicals, Inc.     

ACUT2E TSE-SSFP: a hybrid method for T2-weighted imaging of edema in the heart.

ACUT(2)E TSE-SSFP is a hybrid between steady state free precession (SSFP) and turbo spin echo (TSE) for bright-blood T2-weighted imaging with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) similar to dark-blood TSE. TSE-SSFP uses a segmented SSFP readout during diastole with 180 degrees pulses following a 90 degrees preparation. The 180 degrees refocusing pulses make TSE-SSFP similar to TSE but TSE-SSFP uses gradient moment nulling, whereas TSE uses gradient crushing. TSE-SSFP produced T2-weighted images with minimal T1 weighting. TSE-SSFP and TSE had similar SNR (155.9 +/- 6.0 vs 160.9 +/- 7.0; P = NS) for acute myocardial infarction (MI) and twice the SNR of T2-prepared SSFP (73.1 +/- 3.4, P < 0.001). TSE-SSFP and TSE had approximately double the CNR of T2-prepared SSFP for differentiating acute MI from normal myocardium. Imperfect blood suppression, present in all animals on some TSE images, was a problem eliminated by TSE-SSFP and T2-prepared SSFP.     

In vivo detection of hemorrhage in human atherosclerotic plaques with magnetic resonance imaging

PURPOSE: To investigate the performance of high-resolution T1-weighted (T1w) turbo field echo (TFE) magnetic resonance imaging (MRI) for the identification of the high-risk component intraplaque hemorrhage, which is described in the literature as a troublesome component to detect. MATERIALS AND METHODS: An MRI scan was performed preoperatively on 11 patients who underwent carotid endarterectomy because of symptomatic carotid disease with a stenosis larger than 70%. A commonly used double inversion recovery (DIR) T1w turbo spin echo (TSE) served as the T1w control for the T1w TFE pulse sequence. The MR images were matched slice by slice with histology, and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the MR images were calculated. Additionally, two readers, who were blinded for the histological results, independently assessed the MR slices concerning the presence of intraplaque hemorrhage. RESULTS: More than 80% of the histological proven intraplaque hemorrhage could be detected using the TFE sequence with a high interobserver agreement (Kappa = 0.73). The TFE sequence proved to be superior to the TSE sequence concerning SNR and CNR, but also in the qualitative detection of intraplaque hemorrhage. The false positive TFE results contained fibrous tissue and were all located outside the main plaque area. CONCLUSION: The present study shows that in vivo high-resolution T1w TFE MRI can identify the high-risk component intraplaque hemorrhage with a high detection rate in patients with symptomatic carotid disease. Larger clinical trials are warranted to investigate whether this technique can identify patients at risk for an ischemic attack.     

Magnetic resonance imaging of hyaline cartilage defects at 1.5T and 3.0T: comparison of medium T2-weighted fast spin echo, T1-weighted two-dimensional and three-dimensional gradient echo pulse sequences

PURPOSE: To evaluate and compare the diagnostic accuracy of appropriate magnetic resonance (MR) sequences in the detection of cartilage lesions at 1.5T and 3.0T. MATERIAL AND METHODS: Twelve chondral defects of varying depths, widths, and locations were created in the retropatellar hyaline cartilage in six sheep cadaver limbs. Axial images employing three fat-suppressed imaging sequences--(1) a T2-weighted fast spin-echo (FSE) sequence, (2) a two-dimensional (2D) and (3) three-dimensional (3D) gradient-echo (GE) sequence at 1.5T and 3.0T using an extremity quadrature coil--were evaluated by three experienced radiologists. Statistical analysis of the results consisted of receiver operating characteristics (ROC) and significant testing using the bivariate chi-square test. In addition, signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were evaluated with significance testing using the Wilcoxon test. RESULTS: The 3D GE sequence compared favorably with other sequences at 3.0T and 1.5T (Az=0.88 at 3.0T and Az=0.85 at 1.5T) missing only one small grade 2 lesion. 2D GE imaging was inferior to 3D imaging at both field strengths (P<0.05) in general. However, compared to 1.5T, lesion detectability was improved at the higher magnetic field of 3.0T (Az=0.81 and 0.73 at 3.0T and 1.5T, respectively). FSE images showed significantly inferior sensitivity and less anatomical detail compared to the GE sequences at both field strengths (Az=0.64 and 0.72 at 3.0T and 1.5T, respectively; P<0.05). However, compared to 1.5T, lesion detectability SNR and CNR values were superior in all sequences tested at 3.0T. CONCLUSION: MRI at 3.0T improves SNR and CNR significantly in the most common sequences for cartilage MRI, resulting in an improvement in chondral lesion detection. GE imaging therefore allows resolution to be increased in an acceptable time manner for patient comfort, and the 3D GE fat-suppressed sequence at 3.0T appears to be best suited for cartilage imaging in a clinical setting.     

Application of turbo fluid-attenuated inversion-recovery MRI in evaluation of intraspinal tumors

PURPOSE: Although fluid-attenuated inversion-recovery (FLAIR) magnetic resonance imaging (MRI) is widely applied to diagnose central nervous system diseases, its role in diagnosis of intraspinal tumors is unclear. In this study, we evaluated the potential clinical application of a turbo FLAIR sequence for imaging of intraspinal tumors. MATERIALS AND METHODS: Forty-eight consecutive patients with intraspinal tumors underwent MRI with turbo FLAIR and turbo spinal echo (TSE) sequences. Turbo FLAIR images were then qualitatively and quantitatively compared with T2-weighted TSE images. RESULTS: Turbo FLAIR images were evaluated as superior to T2-weighted TSE images for image artifact, extradural tumor conspicuity, and intradural extramedullary tumor conspicuity and detection. Intramedullary tumor conspicuity with turbo FLAIR was less than T2-weighted TSE. Similar capabilities in detection of extradural and intramedullary tumors were found between turbo FLAIR and T2-weighted TSE. Turbo FLAIR and T2-weighted TSE displayed similar normal spinal cord signal-noise ratio (SNR) and tumor-to-cerebrospinal fluid (CSF) contrast-to-noise ratio (CNR). In addition, turbo FLAIR yielded significantly higher tumor-to-CSF contrast than T2-weighted TSE. However, tumor SNR, tumor-to-normal spinal cord contrast and CNR with turbo FLAIR images were lower than those with T2-weighted TSE images. CONCLUSION: This study demonstrated (a) a superiority of turbo FLAIR to T2-weighted TSE in displaying and detecting intradural extramedullary tumors, (b) a superiority of turbo FLAIR to T2-weighted TSE in demonstrating extradural tumors, and (c) less usefulness in displaying intramedullary tumors with turbo FLAIR than with T2-weighted TSE.