磁共振弥散张量成像在神经疾病中的应用

磁共振弥散张量成像（DT）是近几年发展起来的水弥散成像技术，它通过脑水分子的弥散性定量反映脑白质纤维束的完整性。文章简要介绍了DTI的基本概念及其在脑梗死、多发性硬化、癫痫、Alzheimer病和颅内肿瘤等多种神经疾病中的应用。     

磁共振成像对高血压性心脏病左心室肥厚的诊断价值

对 2 5例原发性高血压、血压≥ 16 0 /90mmHg ,且经过心电图、心脏远达距离摄片、超声心动图检查 ,其中至少一项符合左心室肥厚 (LVH)标准的患者 ,进行磁共振扫描成像 (MRI) ,并与上述检测结果对比 ,以估价MRI对高血压性心脏病LVH的诊断价值。结果表明 ,MRI对LVH的诊断率 (96 % )明显高于超声心动图(5 6 % )、X线 (40 % )和心电图 (2 8% )对LVH的诊断率 (P均 <0 .0 1)。且MRI可测定收缩及舒张期室壁厚度 ,可对LVH准确分型 ,可对比心脏大小、心室容量及心肌重量。MRI对LVH是一种极好的诊断方法     

Relative Utility of Magnetic Resonance Imaging and Right Ventricular Angiography to Diagnose Arrhythmogenic Right Ventricular Cardiomyopathy

INTRODUCTION: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by fibrofatty replacement of the RV myocardium. Two imaging techniques used to assess patients suspected of having ARVC are magnetic resonance imaging (MRI) and right ventricular angiography (RVA). Traditionally, RVA has played a central role in the diagnosis of ARVC, but the non-invasive nature of MRI and its unique ability to detect fatty tissue infiltration has increased its popularity as a diagnostic tool. The objective of this study was to assess the relative diagnostic accuracy of MRI and RVA for ARVC. METHODS AND RESULTS: Seventeen patients (9 men, 8 women; ages 42 +/- 17 [range 16-78] years) with documented ventricular arrhythmias were investigated for ARVC. A positive diagnosis of ARVC was based on criteria set forth by the ISFC Working Group on Cardiomyopathies and Dysplasia. ECG-gated spin-echo and gradient-echo MR images in multiple planes and RAO/LAO RV angiograms were compared for diagnostic concordance. Based on working group criteria, 7 patients were diagnosed with ARVC. In ten patients, MRI suggested ARVC. The remaining 7 patients had no MRI findings suggestive of the disease. Four patients with MRI findings of ARVC were incorrectly diagnosed based on Task Force criteria. Conversely, 1 patient with a normal MRI met Task Force criteria for the diagnosis of ARVC. Based on RV angiograms, 7 patients had findings suggestive of ARVC. The 10 patients without AVRD (based on RVA) also did not meet the necessary criteria for diagnosis of ARVC using Task Force standards. RVA was 100% specific and 100% sensitive compared to MRI that was only 86% sensitive and 60% specific. MRI proved to be most reliable when the images demonstrated gross, lipomatous infiltration, evidenced by a large area of hyperintensity. When the results of MRI and RVA were congruent, the diagnosis was always accurate. CONCLUSION: RVA is more sensitive and specific to diagnose ARVC diagnosis than MRI, at least until MRI protocols are better developed. MRI results are most robust when indicators of ARVC are grossly apparent. False-positive diagnosis by MRI was primarily related to perceived motion abnormalities that were not seen by RVA. One of its greatest potential assets (fat detection) did not enhance diagnostic specificity.     

Three-Dimensional Muscular Architecture of the Human Tongue Determined In Vivo With Diffusion Tensor Magnetic Resonance Imaging

The myoarchitecture of the tongue is believed to consist of a complex network of interwoven fibers, which function together to produce a near limitless array of functional deformations. These deformations contribute mechanically to speech production and to oral cavity food handling during swallowing. We have previously imaged the 3D myoarchitecture of the mammalian tongue in excised tissue with diffusion tensor MRI, a technique which derives the 3D orientation of intramural fibers as a function of the extent to which a direction-specific MR signal attenuates under diffusion-encoding magnetic gradients. The resulting 3D diffusion tensor defines the relative orientations of the myofiber populations within a region of tissue. In this study, we have extended the use of this method to assess lingual myoarchitecture in normal human subjects in vivo. Subjects were imaged using a diffusion-sensitive stimulated-echo pulse sequence with single-shot echo-planar spatial encoding in the midsagittal plane. Differences in lingual fiber orientation were manifested by graduated changes in fiber direction throughout the tissue, without clear anatomical demarcations between regions of the tissue. The anterior tissue was composed generally of orthogonally oriented fibers surrounded by an axially oriented ring of tissue, whereas the posterior portion of the tissue was composed mostly of fibers projecting in the superior and posterior directions. The bulk of the tissue displayed a highly homogeneous, vertically oriented set of fibers, including the anteroinferior region of the tissue and extending nearly to the superior surface. Further analysis of the tissue in terms of diffusion anisotropy demonstrated that the tissue could be represented by varying degrees of anisotropy, with a tendency toward high anisotropy in the dorsal and anteroventral periphery and low anisotropy in the central region of the tissue. These findings demonstrate that the muscular anatomy of the tongue can be displayed as a continuous array of structural units, or tensors, representing fibers of varying orientations throughout the tissue.     

Semiautomatic Quantification of Left Ventricular Function by Two‐Dimensional Feature Tracking Imaging Echocardiography. A Comparison Study with Cardiac Magnetic Resonance Imaging

Objective: To evaluate the accuracy of a semiautomatic quantification of left ventricular (LV) volumes and ejection fraction (EF) using two‐dimensional (2D) feature tracking imaging (FTI). Methods: Thirty‐four consecutive subjects (11 patients with dilated cardiomyopathy, 13 with hypertrophic cardiomyopathy, and 10 subjects with no cardiac disease) underwent, on the same day, trans‐thoracic echocardiography (TTE) examination, FTI, and cardiac magnetic resonance imaging (MRI), as gold standard, in order to quantify LV volumes and EF. The echocardiographic quantification of LV volumes and EF was determined from four‐ and two‐chamber views using both standard TTE Biplane Simpson's method and a semiautomatic border detection based on FTI. Furthermore, the time for data analysis for each method was measured. Results: The time required for semiautomatic analysis of volumes and EF was significantly lower (P < 0.0001) by FTI (71 seconds) in comparison with standard biplane Simpson's method (93 seconds). LV volumes obtained by FTI were significant underestimated (P < 0.001) in comparison with MRI. Bland‐Altman analysis of EDV and ESV using FTI and cardiac MRI showed a low level of agreement for EDV (mean difference = 40.8; SD = 39) and ESV (mean difference = 38.1; SD = 42). On the contrary, no significant difference between FTI and MRI in assessing the LVEF was found; furthermore, a very low bias (2 ± 12) by Bland‐Altman analysis was found between FTI and cardiac MRI for the quantification of EF. Conclusion: Semiautomatic quantification of LV volumes using FTI allows an accurate, rapid, easy and reliable assessment of LV EF and a rough estimation of LV volumes. (Echocardiography 2010;27:791‐797)     

Non-Invasive Cardiac Evaluation in Heart Failure Patients Using Magnetic Resonance Imaging: A Feasibility Study

Background: To assess the feasibility of a fast, flow-insensitive magnetic resonance imaging (MRI) protocol in heart failure patients for the evaluation of cardiac function, cardiovascular anatomy, and myocardial viability. Methods and Results: Thirty-two consecutive patients with left ventricular (LV) systolic dysfunction and 13 control subjects were prospectively evaluated with MRI. The exam consisted of cine imaging with a steady-state free precession sequence, followed by time-resolved, three-dimensional angiography and delayed, contrast-enhanced imaging. Multiple LV parameters were evaluated, and the heart failure and control results were compared. In 12 patients, MRI-determined ejection fractions were compared to echocardiographic values. Additionally, a qualitative analysis of the cine images was performed. The cardiac MR evaluation yielded diagnostic-quality images in all subjects. Mean imaging time was 37 min. MRI demonstrated significant differences between the heart failure and control subjects in all parameters assessed (p < 0.05). MRI-determined ejection fractions correlated strongly with echocardiographic values (R = 0.75), although the limits of agreement were wide (−17.3%–18.3%). Conclusions: Using fast, flow-insensitive imaging techniques, MRI is feasible in heart failure for the derivation of more independent indices of cardiac status than any other non-invasive test. Although further investigation is warranted, MRI may prove uniquely helpful in heart failure diagnosis and management.     

Myocardial Ischemia Evaluation With Dual-source Computed Tomography: Comparison With Magnetic Resonance Imaging

Introduction and objectives

Computed tomography does not accurately determine which coronary lesions lead to myocardial ischemia and consequently further tests are required to evaluate ischemia induction. The aim of this study was to compare diagnostic accuracy between dual-energy computed tomography and magnetic resonance imaging in the assessment of myocardial perfusion and viability in patients suspected of coronary artery disease.

Methods

A prospective study was performed in 56 consecutive patients (39 men [69.6%]; mean age [standard deviation], 63 [10]; range, 23-81). Computed tomography was performed with the following protocol: 1, adenosine stress perfusion; 2, coronary angiography; and 3, delayed enhancement. Magnetic resonance imaging for the evaluation of stress perfusion and delayed enhancement was performed within 30 days. Two observers in consensus analyzed the perfusion and delayed enhancement images.

Results

We studied 952 myocardial segments and 168 vascular territories. In a per-segment analysis, the sensitivity, specificity, and positive and negative predictive values of computed tomography compared with magnetic resonance were 76%, 99%, 89%, and 98% for perfusion defects, and 64%, 99%, 82%, and 99% for delayed enhancement, respectively. In a per-vascular territory analysis, the same measures were 78%, 97%, 86%, and 95% for perfusion defects, and 72%, 99%, 93%, and 97% for delayed enhancement, respectively. The mean radiation dose was 8.2 (2) mSv.

Conclusions

Dual-source computed tomography may allow accurate and concomitant evaluation of perfusion defects and myocardial viability and analysis of coronary anatomy.     

Unipolar Mapping and Magnetic Resonance Imaging of "Idiopathic" Right Ventricular Outflow Tract Ectopy

Unipolar Mapping and MRI of Ventricular Ectopy. Radiofrequency catheter ablation of symptomatic ventricular ectopy guided by bipolar mapping was successfully accomplished at the right ventricular outflow tract in a patient who did not exhibit apparent structural heart disease. A "QS" morphology with a fast slope of the downstroke deflection at the successful ablation site was observed on the unipolar electrogram. Focal thinning of the lateral wall of the right ventricular outflow tract was shown in the magnetic resonance image, similar to that reported in patients with "idiopathic" right ventricular outflow tract tachycardia.     

Cardiac Magnetic Resonance: One Slice,Two Different LGE Patterns

A 56-years-old man with previous myopericarditis (10 months earlier, coronary angiography not performed) was admitted because of pericarditis pain and ST segment elevation, together with myocardial necrosis markers rise. Electrocardiogram (EKG) showed negative T waves in lateral and inferior leads; echocardiogram showed mild pericardial effusion and inferior and lateral basal hypokinesis. Cardiac magnetic resonance imaging (CMRI) on day 7 post-admission showed increased T2-short tau inversion recovery (T2-STIR) signal of inferior wall and two different noncontiguous late gadolinium enhancement (LGE) areas: Ischemic-like with about 75% transmural extension (inferior wall) and subepicardial (inferolateral wall) along with pericardial LGE (inferior and inferolateral wall). Coronary angiography showed three vessel disease. Pathogenetic hypothesis of these unexpected findings are discussed. This case shows again the ability of CMRI to unreveal unusual and unexpected pathologic patterns.