Comparison of diffusion tensor imaging by cardiovascular magnetic resonance and gadolinium enhanced 3D image intensity approaches to investigation of structural anisotropy in explanted rat hearts

Background

Cardiovascular magnetic resonance (CMR) can through the two methods 3D FLASH and diffusion tensor imaging (DTI) give complementary information on the local orientations of cardiomyocytes and their laminar arrays.

Methods

Eight explanted rat hearts were perfused with Gd-DTPA contrast agent and fixative and imaged in a 9.4T magnet by two types of acquisition: 3D fast low angle shot (FLASH) imaging, voxels 50 × 50 × 50 μm, and 3D spin echo DTI with monopolar diffusion gradients of 3.6 ms duration at 11.5 ms separation, voxels 200 × 200 × 200 μm. The sensitivity of each approach to imaging parameters was explored.

Results

The FLASH data showed laminar alignments of voxels with high signal, in keeping with the presumed predominance of contrast in the interstices between sheetlets. It was analysed, using structure-tensor (ST) analysis, to determine the most (v₁^ST), intermediate (v₂^ST) and least (v₃^ST) extended orthogonal directions of signal continuity. The DTI data was analysed to determine the most (e₁^DTI), intermediate (e₂^DTI) and least (e₃^DTI) orthogonal eigenvectors of extent of diffusion. The correspondence between the FLASH and DTI methods was measured and appraised. The most extended direction of FLASH signal (v₁^ST) agreed well with that of diffusion (e₁^DTI) throughout the left ventricle (representative discrepancy in the septum of 13.3 ± 6.7°: median ± absolute deviation) and both were in keeping with the expected local orientations of the long-axis of cardiomyocytes. However, the orientation of the least directions of FLASH signal continuity (v₃^ST) and diffusion (e₃^ST) showed greater discrepancies of up to 27.9 ± 17.4°. Both FLASH (v₃^ST) and DTI (e₃^DTI) where compared to directly measured laminar arrays in the FLASH images. For FLASH the discrepancy between the structure-tensor calculated v₃^ST and the directly measured FLASH laminar array normal was of 9 ± 7° for the lateral wall and 7 ± 9° for the septum (median ± inter quartile range), and for DTI the discrepancy between the calculated v₃^DTI and the directly measured FLASH laminar array normal was 22 ± 14° and 61 ± 53.4°. DTI was relatively insensitive to the number of diffusion directions and to time up to 72 hours post fixation, but was moderately affected by b-value (which was scaled by modifying diffusion gradient pulse strength with fixed gradient pulse separation). Optimal DTI parameters were b = 1000 mm/s² and 12 diffusion directions. FLASH acquisitions were relatively insensitive to the image processing parameters explored.

Conclusions

We show that ST analysis of FLASH is a useful and accurate tool in the measurement of cardiac microstructure. While both FLASH and the DTI approaches appear promising for mapping of the alignments of myocytes throughout myocardium, marked discrepancies between the cross myocyte anisotropies deduced from each method call for consideration of their respective limitations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12968-015-0129-x) contains supplementary material, which is available to authorized users.     

脊髓损伤的弥散张量成像研究进展

MR DTI作为目前唯一能显示水分子运动方向和强度的成像技术,可以动态反应中枢神经系统白质的超微结构及相应病理生理改变,为研究脊髓损伤提供了新的方法。近年来脊髓DTI已应用于临床。本文对脊髓DTI技术的应用、发展趋势进行综述。     

Probing dynamic myocardial microstructure with cardiac magnetic resonance diffusion tensor imaging

This article is an invited editorial comment on the paper entitled “In vivo cardiovascular magnetic resonance diffusion tensor imaging shows evidence of abnormal myocardial laminar orientations and mobility in hypertrophic cardiomyopathy” by Ferreira et al., and published as Journal of Cardiovascular Magnetic Resonance 2014; 16:87.     

Cuprizone诱导的C57BL/6小鼠脱髓鞘模型的T2WI及DTI研究

目的探讨T2WI及扩散张量成像（DTI）在探测cuprizone（CPZ）诱导的C57BL/6小鼠脑白质脱髓鞘损伤中的应用价值,并观察CPZ诱导的脑白质脱髓鞘损伤是否具有区域选择性。材料与方法 C57BL/6小鼠各10只,分别喂养常规饲料（正常组）及喂养均匀混有0.2%CPZ的饲料（CPZ组）,4周后进行T2WI及DTI检查（所有检查均在安捷伦7.0 T动物MR仪上完成）。利用体视觉分区分析法对脑白质区标准化T2信号强度（相应部位T2信号强度与侧脑室信号强度之比）、部分各向异性指数（FA值）、平均扩散率（MD）、轴向扩散系数（AD）及径向扩散系数（RD）进行测量。感兴趣区（ROIs）包括大脑皮层（CTX）、海马（HP）、尾状核（CP）、丘脑（TH）。上述5组数据均使用独立样本t检验进行统计学分析。结果与正常组相比,CPZ组标准化T2信号强度在大脑皮层、海马、尾状核出现明显下降（P〈0.01）,在丘脑呈下降趋势,但无统计学意义（P=0.119）。CPZ组大脑皮层、海马、尾状核FA值明显下降（P〈0.05）,丘脑FA值呈下降趋势,但无统计学意义（P=0.178）。在FA值出现明显下降的三个部位（大脑皮层、海马以及尾状核）,MD值及径向扩散系数RD均出现明显升高（P〈0.05）;轴向扩散系数AD均呈下降趋势,但仅在大脑皮层出现明显下降（P〈0.05）。结论基于7.0 T的扩散张量成像对探测CPZ诱导的C57BL/6小鼠脱髓鞘损伤均十分敏感,能反映脑白质纤维束完整性。另外,大脑皮层、海马以及尾状核较丘脑对CPZ的诱导可能更敏感。研究结果也在一定程度上说明相对于轴向扩散系数的下降,此动物模型FA值的下降更依赖于径向扩散系数的升高。     

3.0T 1H-MRS及DTI诊断脑胶质瘤: AA值与FA值的相关性

目的 探讨脑胶质瘤肿瘤外周至肿瘤中心3.0T磁共振氢质子波谱(¹H-MRS)的N-乙酰天门冬氨酸(NAA)值及弥散张量成像(DTI)的各向异性(FA)值的相关性,评价¹H-MRS及DTI对脑胶质瘤的诊断价值。方法 回顾性分析经组织病理学证实的9例低级别(Ⅰ~Ⅱ级)胶质瘤、16例高级别(Ⅲ~Ⅳ级)胶质瘤的常规MRI、DTI及¹H-MRS资料,分析肿瘤不同感兴趣区的部分FA值、NAA与肌酸(Cr)比值、胆碱(Cho)与肌酸(Cr)比值及胆碱(Cho)与NAA的比值,并观察NAA值与FA值的相关性。结果 从肿瘤中心到外周(包括肿瘤邻近脑白质和对侧大脑半球白质)FA和NAA数值持续升高,且两者呈正相关(r=0.90,P<0.05)。低级别、高级别胶质瘤组瘤体的NAA/Cr无明显差异,FA、Cho/Cr和Cho/NAA差异均有统计学意义(P均<0.05)。结论 脑胶质瘤中,从肿瘤外周至肿瘤中心脑胶质瘤对周围组织的浸润程度逐渐增加,而NAA值及FA数值表现为降低趋势,反映了神经元结构和白质纤维的完整性的破坏。肿瘤中心FA、Cho/Cr和Cho/NAA数值对鉴别低级别、高级别胶质瘤具有一定意义。     

7.0 T MR扩散张量成像技术对大鼠肥厚心肌纤维特性的研究

目的采用7.0 T MR扩散张量成像(DT-MRI)技术从心肌纤维水分子扩散、心肌纤维微结构及心肌力学单元角度综合定量研究心肌肥厚模型大鼠的心肌纤维特性。材料与方法 20只健康雄性SD大鼠随机分为正常组(n=10)与心肌肥厚组(n=10),正常组大鼠离体心脏并固定,心肌肥厚组大鼠行胸主动脉缩窄手术12周后离体心脏并固定,采用扩散张量成像技术获取图像,并使用Diffusion Toolkit、Trackvis及Matlab软件进行图像后处理。观察两组大鼠心脏三维整体观、乳头肌层面心肌纤维和张量图以及心肌组织HE染色的特点,使用独立样本t检验统计分析两组大鼠左心室心肌纤维平均ADC值、FA值及螺旋角的差异。结果心脏三维整体观显示,两组大鼠心肌纤维由心外膜向心内膜均呈致密、规则的螺旋排布。乳头肌层面心肌纤维示踪图以及张量图显示正常组心肌纤维走行规则、排布均匀,心肌肥厚组左心室壁较正常组增厚,像素内的张量显示较正常组增加,心外膜向心内膜过渡的三层结构较正常组更明显;心肌肥厚组大鼠较正常组大鼠左心室心肌纤维平均ADC值下降(P0.01),FA值上升(P0.05),两组间均有统计学差异。心肌肥厚组大鼠左心室由心外膜至心内膜的平均螺旋角透壁范围较正常组增大(P0.01),两组间均具有统计学差异。结论扩散张量成像及图像后处理技术可三维可视化定量综合评价大鼠心肌肥厚模型心肌纤维特性较正常大鼠的变化,为将来实现心肌纤维结构、力学、电生理特性的在体研究奠定基础。     

In vivo cardiovascular magnetic resonance diffusion tensor imaging shows evidence of abnormal myocardial laminar orientations and mobility in hypertrophic cardiomyopathy

Background

Cardiac diffusion tensor imaging (cDTI) measures the magnitudes and directions of intramyocardial water diffusion. Assuming the cross-myocyte components to be constrained by the laminar microstructures of myocardium, we hypothesized that cDTI at two cardiac phases might identify any abnormalities of laminar orientation and mobility in hypertrophic cardiomyopathy (HCM).

Methods

We performed cDTI in vivo at 3 Tesla at end-systole and late diastole in 11 healthy controls and 11 patients with HCM, as well as late gadolinium enhancement (LGE) for detection of regional fibrosis.

Results

Voxel-wise analysis of diffusion tensors relative to left ventricular coordinates showed expected transmural changes of myocardial helix-angle, with no significant differences between phases or between HCM and control groups. In controls, the angle of the second eigenvector of diffusion (E2A) relative to the local wall tangent plane was larger in systole than diastole, in accord with previously reported changes of laminar orientation. HCM hearts showed higher than normal global E2A in systole (63.9° vs 56.4° controls, p = 0.026) and markedly raised E2A in diastole (46.8° vs 24.0° controls, p < 0.001). In hypertrophic regions, E2A retained a high, systole-like angulation even in diastole, independent of LGE, while regions of normal wall thickness did not (LGE present 57.8°, p = 0.0028, LGE absent 54.8°, p = 0.0022 vs normal thickness 38.1°).

Conclusions

In healthy controls, the angles of cross-myocyte components of diffusion were consistent with previously reported transmural orientations of laminar microstructures and their changes with contraction. In HCM, especially in hypertrophic regions, they were consistent with hypercontraction in systole and failure of relaxation in diastole. Further investigation of this finding is required as previously postulated effects of strain might be a confounding factor.

Electronic supplementary material

The online version of this article (doi:10.1186/s12968-014-0087-8) contains supplementary material, which is available to authorized users.     

磁共振扩散张量成像数据分析中基于统一计算设备架构的高速行处理求解超定线性方程组方法

目的提出一种运行于普通个人电脑平台上的并行方法,用于求解MR DTI中的超定线性方程组。方法利用统一计算设备架构(CUDA)使中央处理器(CPU)与图形处理器(GPU)协同求解超定线性方程组。CPU用于数据准备与生成扩散矩阵,GPU中的大量流处理器并行用于迭代计算。结果 CUDA模式下行处理运算速度远快于CPU串行计算,图像矩阵增大时这一优势更加明显。结论与CPU串行模式相比,CUDA模式可显著提高DTI数据处理速度。     

A diffusion tensor magnetic resonance imaging study of corpus callosum from adult patients with migraine complicated with depressive/anxious disorder

(Headache 2011;51:237‐245) Objective.— The aim of this study was to investigate the possible microstructural abnormalities of the corpus callosum (CC) in adult patients with migraine without aura complicated with depressive/anxious disorder. Background.— Emotional disorders, especially depression and anxiety, are with relatively higher incidence in migraine population. However, the mechanism of migraine complicated with depressive/anxious disorder remains unclear. Methods.— Diffusion tensor magnetic resonance imaging was carried out in 12 adult patients with simple migraine (without aura and without depressive/anxious disorder) (S‐M group), 12 adult patients with complicated migraine (without aura but complicated with depressive/anxious disorder) (Co‐M group), and 12 age‐ and sex‐matched healthy subjects (Control group). Fractional anisotropy (FA) and apparent diffusion coefficient were measured at genu, body, and splenium of the CC, respectively. Results.— There were significant differences in FA values at all locations of the CC among the 3 groups. The FA values from both the SM and Co‐M groups were significantly lower than the control (P < .05 and P < .01, respectively). The FA values from Co‐M group were significantly lower than the SM group (P < .01). The apparent diffusion coefficient values of the above regions had no significant differences among these groups (P > .05). There were negative correlations between FA value of genu of the CC and disease course as well as FA value of genu and body of the CC and headache frequency (P < .05). Negative correlations were also found between FA values at all locations of the CC and Hamilton anxiety and Hamilton depression scores (both P < .05). Conclusions.— There might be an integrity change of neurofibrotic microstructures existing as a possible neuroanatomical basis in the CC of migraine patients complicated with depressive/anxious disorder.     

MRI T2加权像与扩散张量成像量化指标对脊髓型颈椎病术后脊髓功能恢复的预测价值

目的 探讨MRI T2加权像(T2WI)量化指标与扩散张量成像（DTI）量化参数对脊髓型颈椎病（CSM）患者术后脊髓功能恢复的预测价值。 方法 收集2014年4月至2016年4月期间在天津医院术前行MRI及DTI检查并完成术后随访的140例CSM患者资料,所有患者术后均行系统康复治疗。采用日本骨科学会评分系统（JOA）评估患者脊髓神经功能恢复情况。根据术后1年随访时JOA评分改善率将上述患者分为恢复良好组（其JOA评分改善率≥50%）和恢复不良组（其JOA评分改善率<50%）。比较2组患者MRI T2WI量化指标［包括脊髓受压百分比（MSCC）、脊髓信号强度比值（SCR）和脊髓横截面积（TA）］和DTI量化参数［包括脊髓表观弥散系数（ADC）和各向异性分数（FA）］,并绘制受试者工作特征曲线（ROC）,评价MRI T2WI与DTI各量化指标对CSM术后脊髓功能恢复不良的预测价值。将单因素分析中有统计学差异的临床与影像学指标行多因素Logistic回归分析,确定CSM恢复不良的独立危险因素。 结果 MSCC、SCR、TA、ADC及FA预测CSM术后脊髓功能恢复不良的曲线下面积（AUC）分别为0.593、0.682、0.706、0.719和0.749,其预测界值分别为44.85%、1.561、0.46cm2、1.339×10-3mm2/s和0.386。DTI各量化参数的AUC均大于T2WI量化指标。MSCC与SCR的预测价值较低（其AUC均小于0.7）;TA、ADC和FA具有中等预测价值（其AUC 0.7~0.9）。多因素Logistic回归分析显示,低JOA评分、TA≤0.46cm2和FA≤0.386均为CSM术后恢复不良的独立危险因素（P<0.05）,并据此建立预测模型;该模型预测CSM术后预后不良的AUC（0.871）明显高于JOA评分的AUC（0.760）,其间差异具有统计学意义（P<0.05）。该模型以0.360为预测界值,敏感度为80.39％,特异度为77.53％。 结论 将JOA评分、MRI T2WI与DTI量化指标相结合,可更准确地预测CSM术后脊髓功能恢复情况,同时也为术后康复方案制订提供参考。     

Ex vivo cardiovascular magnetic resonance measurements of right and left ventricular mass compared with direct mass measurement in excised hearts after transplantation: a first human SSFP comparison

Background

CMR is considered the ‘gold standard’ for non-invasive LV and RV mass quantitation. This information is solely based on gradient-recalled echo (GRE) sequences while contrast dependent on intrinsic T1/T2 characteristics potentially offers superior image contrast between blood and myocardium. This study aims, for the first time in humans, to validate the SSFP approach using explanted hearts obtained from heart transplant recipients. Our objective is establish the correlation between and to validate steady-state free precession (SSFP) derived LV and RV mass vs. autopsy mass of hearts from cardiac transplants patients.

Methods

Over three-years, 58 explanted cardiomyopathy hearts were obtained immediately upon orthotopic heart transplantation from the OR. They were quickly cleaned, prepared and suspended in a saline-filled container and scanned ex vivo via SSFP-SA slices to define LV/RV mass. Using an automatic thresholding program, segmentation was achieved in combination with manual trimming (ATMT) of extraneous tissue incorporating 3D cardiac modeling performed by independent and blinded readers. The explanted hearts were then dissected with the ventricles surgically separated at the interventricular septum. Weights of the total heart not excluding papillary and trabecular myocardium, LV and RV were measured via high-fidelity scale. Linear regression and Bland-Altman plots were used to analyze the data. The intra-class correlation coefficient was used to assess intra-observer reliability.

Results

Of the total of 58 explanted hearts, 3 (6%) were excluded due to poor image quality leaving 55 patients (94%) for the final analysis. Significant positive correlations were found between total 3D CMR mass (450 ± 111 g) and total pathology mass (445 ± 116 g; r = 0.99, p < 0.001) as well as 3D CMR measured LV mass (301 ± 93 g) and the pathology measured LV mass (313 ± 96 g; r = 0.95, p < 0.001). Strong positive correlations were demonstrated between the 3D CMR measured RV mass (149 ± 46 g) and the pathology measured RV mass (128 ± 40 g; r = 0.76, p < 0.001). The mean bias between 3D-CMR and pathology measures for total mass, LV mass and RV mass were: 3.0 g, -16 g and 19 g, respectively.

Conclusions

SSFP-CMR accurately determines total myocardial, LV and RV mass as compared to pathology weighed explanted hearts despite variable surgical removal of instrumentation (left and right ventricular assist devices, AICD and often apical core removals). Thus, this becomes the first-ever human CMR confirmation for SSFP now validating the distinction of ‘gold standard’.     

A prospective evaluation of cardiovascular magnetic resonance measures of dyssynchrony in the prediction of response to cardiac resynchronization therapy

Background

Many patients with electrical dyssynchrony who undergo cardiac resynchronization therapy (CRT) do not obtain substantial benefit. Assessing mechanical dyssynchrony may improve patient selection. Results from studies using echocardiographic imaging to measure dyssynchrony have ultimately proved disappointing. We sought to evaluate cardiac motion in patients with heart failure and electrical dyssynchrony using cardiovascular magnetic resonance (CMR). We developed a framework for comparing measures of myocardial mechanics and evaluated how well they predicted response to CRT.

Methods

CMR was performed at 1.5 Tesla prior to CRT. Steady-state free precession (SSFP) cine images and complementary modulation of magnetization (CSPAMM) tagged cine images were acquired. Images were processed using a novel framework to extract regional ventricular volume-change, thickening and deformation fields (strain). A systolic dyssynchrony index (SDI) for all parameters within a 16-segment model of the ventricle was computed with high SDI denoting more dyssynchrony. Once identified, the optimal measure was applied to a second patient population to determine its utility as a predictor of CRT response compared to current accepted predictors (QRS duration, LBBB morphology and scar burden).

Results

Forty-four patients were recruited in the first phase (91% male, 63.3 ± 14.1 years; 80% NYHA class III) with mean QRSd 154 ± 24 ms. Twenty-one out of 44 (48%) patients showed reverse remodelling (RR) with a decrease in end systolic volume (ESV) ≥ 15% at 6 months. Volume-change SDI was the strongest predictor of RR (PR 5.67; 95% CI 1.95-16.5; P = 0.003). SDI derived from myocardial strain was least predictive. Volume-change SDI was applied as a predictor of RR to a second population of 50 patients (70% male, mean age 68.6 ± 12.2 years, 76% NYHA class III) with mean QRSd 146 ± 21 ms. When compared to QRSd, LBBB morphology and scar burden, volume-change SDI was the only statistically significant predictor of RR in this group.

Conclusion

A systolic dyssynchrony index derived from volume-change is a highly reproducible measurement that can be derived from routinely acquired SSFP cine images and predicts RR following CRT whilst an SDI of regional strain does not.