Dynamic MRM: Source of Specificity Errors and Solutions

描述(由申请人提供)： 磁共振乳腺摄影(MRM)是一种正在开发中的成像技术，旨在克服X射线乳腺摄影的局限性。一种方法使用来自动态对比增强(DCE)数据的渗透性表面积(PS)产品来提高特异性。通过这项技术获得的特异性，37%到97%是有争议的。DCE需要较高的时间分辨率来采集动力学信息，但需要牺牲空间分辨率。还没有人报道由部分体积效应引起的PS产物的平均化是否限制了使用PS产物对肿瘤进行鉴别和分级的有效性。我们正在测试的假设是，人类DCE-MRM中使用的空间分辨率导致部分体积平均，这显著减少了从DCE-MRM数据计算的PS产品可获得的预后信息，并且基于一个参考图像重建图像的简化编码方法产生具有部分体积平均的PS产品。然后，我们演示了一种获得高时间和空间分辨率图像的技术。我们将通过研究Gd(III)-DTPA在N-乙基-N-亚硝脲诱发的大鼠乳腺肿瘤感兴趣区的PS产物作为平面内分辨率和切片厚度的函数来实现这些目标。PS值在平面分辨率下用两室模型计算，包括临床上使用的6.25mm2，以及用于分析血管密度的体外“显微视野”大小，0.74mm2和0.152 mm2。PS值与肿瘤分级、血管密度和体外组织化学方法获得的血管通透因子相关。我们采用一种简化的编码方法获得了高时间和空间分辨率的DCE MRM数据，并证明了由这些图像计算的PS乘积相对于标准的高空间分辨率技术得到的PS乘积是准确的。该算法使用了一种广义级数方法，该方法具有前后对比增强的参考图像TRIGR。利用TRIGR将低平面分辨率的动态数据重建到高空间分辨率。这保持了较高的时间分辨率。然后将该方案与DCE MRM和树枝状大分子造影剂一起用于区分良、恶性肿瘤，并与组织学方法进行比较。

DESCRIPTION (provided by applicant): Magnetic resonance mammography (MRM) is an imaging technique under development to overcome the limitations of X-ray mammography. One method uses permeability-surface area (PS) products derived from dynamic contrast enhancement (DCE) data to improve specificity. The specificity, 37 to 97%, obtained by this technique is controversial. DCE requires high temporal resolution to collect the kinetic information at the expense of spatial resolution. No one has reported if the averaging of the PS product, induced by partial volume effects, limits the effectiveness in using PS products to differentiate and grade tumors. We are testing the hypothesis that the spatial resolution used in human DCE MRM results in partial volume averaging that significantly reduces the prognostic information obtainable with PS products calculated from DCE-MRM data, and that reduced encoding methods that reconstruct images based on one reference image produce PS-products with partial volume averaging. We then demonstrate a technique to obtain images with both high temporal and spatial resolutions. We will accomplish these goals by studying the PS product of Gd(III)-DTPA in tumor region of interests in N-ethyI-N-nitrosourea induced rat mammary tumors as a function of both the in plane resolution and slice thickness. The PS values are calculated with a two compartment model at in plane resolutions that include those used clinically, 6.25 mm2, and at the "microscopic field" sizes used to analyze vascular density, 0.74 and 0.152 mm2, in vitro. PS values are correlated to tumor grade, vascular density, and vascular permeability factor obtained by in vitro histochemical methods. We apply a reduced encoding method to obtain DCE MRM data with both high temporal and spatial resolutions, and show that the PS product calculated from these images are accurate relative to those obtained with standard high spatial resolution techniques. The algorithm uses a generalized series method with both pre and post contrast enhanced reference images, TRIGR. The dynamic data obtained with low in plane resolution is reconstructed to high spatial resolution with TRIGR. This maintains the high temporal resolution. The protocol is then used with DCE MRM and a dendrimer based contrast agent to differentiate benign from malignant tumors and compared against histological methods.