TISSUE CHARACTERIZATION WITH SLAB SCAN DIFFUSIION MRI

在医学成像中，组织定征是评估脑肿瘤病理和形态的基础。在没有对比剂的T1或T2加权MR图像上，病变组织与正常组织的区别往往有限。然而，在急性中风病例中，弥散加权磁共振成像的结果是极好的对比度。此外，张量扩散加权比通常使用的范围要大得多，已经证明用两个扩散分量来描述脑组织中的扩散更好。这一发现称为多成分扩散，可能是由于分开的水箱，如细胞外和细胞内的水池，或由于微结构特征，通过线扫描扩散成像(LSDI)获得的初步数据显示，脑肿瘤的两个表观扩散系数(ADC)及其各自的幅度可以明显区分肿瘤、周围水肿和正常组织。基于这些参数的图像，结合扩散张量成像对纤维束的详细描绘，提供了非常适合于评估脑肿瘤病理和形态的组织定征。这项研究的一个主要目标是实现一种快速扩散成像技术，称为平板扫描扩散成像(SSDI)，用于在几分钟的扫描时间内对整个大脑体积的张量和多分量ADC组织进行表征。所提出的扩散成像技术不需要心脏选通或后处理来抑制运动伪影。与单次激发回波平面扩散加权成像相比，SSDI在磁化率变化较大的区域的失真伪影最小。将收集正常志愿者和不同脑肿瘤患者的扩散张量和多分量ADC数据。正常组织值和它们各自的方向变异性(各向异性)将通过正常受试者获得的ADC数据来建立。具有扩散张量数据和多分量ADC参数的组织分离可以与使用造影剂和常规T1加权磁共振成像建立的肿瘤边缘进行比较。该计划是将扩散张量数据和多分量ADC参数与特定的肿瘤病理、恶性肿瘤指南和肿瘤的不同成分(即坏死部分、边缘和浸润性周围组织)相关联。因此，这项研究建议将基础研究直接应用于临床情况，要求尽可能高的敏感性和特异性，用于其他治疗决策的侵入性治疗。

In medical imaging, tissue characterization is fundamental for the assessment of brain tumor pathology and morphology. On T1 or T2- weighted MR images obtained without contrast agents., distinction of pathologic tissue from normal tissue often is limited. Excellent contrast, however, results from diffusion weighted MR imaging in the case of acute stroke. Moreover, tensor diffusion weighting over a considerable wider range than typically used, it has been demonstrated that diffusion in brain tissue is described better with two diffusion components. This finding, referred to as multi--component diffusion, may be due to separate water compartments, such as the extra- and intra-cellular water pools, or due to micro-structural features Preliminary data obtained with line scan diffusion imaging (LSDI) in brain tumors indicates that the two apparent diffusion co-efficients (ADC) and their respective amplitudes permit a clear differentiation among tumor, surrounding edema, and normal tissue. Images based on these parameters, together with the detailed mapping of the fiber tracts through diffusion tensor imaging, provide a tissue characterization that is very suitable for the assessment of brain tumor pathology and morphology. A principal goal of the research proposed here is to implement a fast diffusion imaging technique, referred to as slab scan diffusion imaging (SSDI), for tensor and multi-component ADC tissue characterization of the entire brain volume in a scan time of a few minutes. The proposed diffusion imaging technique does not require cardiac gating or post processing for the suppression of motion artifacts. With SSDI, contrary to single-shot echo planar diffusion-weighted imaging, distortion artifacts in areas of large susceptibility variations are minimal. Diffusion tensor and multi-component ADC data will be collected in normal volunteers and in patients with different brain tumors. Normal tissue values and their respective direction variability (anisotropy) will be established with the ADC data obtained in normal subjects. Tissue separations with diffusion tensor data and multi- component ADC parameters can be compared with tumor margins established by the use of contrast agents and conventional T1-weighted MR imaging. The plan is to correlate the diffusion tensor data and multi- component ADC parameters with the specific tumor pathologies, malignancy guide, and different components of a tumor, i.e., necrotic part, margin, and infiltrated surrounding tissue. The study, therefore, proposes direct applications of basic research to clinical situations demanding the highest possible sensitivity and specific for invasive treatment of other therapeutic decisions.