Advanced Intravascular MRI for Assessing Atherosclerosis

描述(申请人提供)：动脉粥样硬化及其并发症是导致发病率和死亡率的主要原因。疾病的存在和严重程度通常通过X射线导管术中的管腔狭窄来诊断。由于X射线成像不能显示血管壁，它不能评估晚期斑块形成之前的过程，也不能评估斑块破裂的脆弱性。其他目前的成像方法很难区分斑块成分以及空间和时间分辨率。这些问题被NHLBI确定为图像引导干预的中心问题。血管内磁共振成像(IVMRI)承诺在没有电离辐射的情况下对狭窄和血管壁病理进行精确、高对比度的评估。以前，我们实验室开发了直径约1 mm的生物兼容血管内导丝作为临床1.5T扫描仪的有源MRI探测器，但尚未得到广泛应用。最大限度地提高速度、灵敏度和空间分辨率是临床应用的关键。虽然全身3T磁共振成像已经成为一种新的临床研究标准，提供了比现有1.5T扫描仪更高的信噪比(SNR)，但IVMRI探测器被限制在1.5T，因此没有从任何3T信噪比增益中受益。一个问题是，在其他条件不变的情况下，引入的金属器件在3T比1.5T时的潜在发热增加了4倍。我们给出了新的初步实验和理论数据，证明了在3T和1.5T时，等效血管内天线的信噪比提高了3倍以上，灵敏度或视场面积(表现出相同信噪比的区域)增加了10倍以上。我们证明，在3T磁共振成像过程中，加热可以保持在安全水平内。这种性能的提高为高对比度、高分辨率的IVMRI在体内评估动脉粥样硬化提供了巨大的潜力。目的1开发和测试用于3T磁共振成像的活性、生物兼容的高信噪比、高视场血管内导丝。图像引导的设备跟踪需要高速磁共振成像。然而，传统的MRI被锁定在扫描仪的参照系(FOR)上，需要耗时的设备位置读出来规定新位置的MRI梯度。Aim 2开发了一种新的磁共振成像方法，它使用天线本身进行激励，本质上将图像锁定在探头的活动端。天线变成了“磁共振眼”，当它像内窥镜一样穿过一条动脉时，生成它所“看到”的图像。由于MRI激发的体积大大减少到探头附近，加热电势大大降低。Aim 3在活体兔动脉粥样硬化模型中测试了这些新技术，在该模型中，主动脉的直径与人类冠状动脉相当。这些发展将为人类未来的使用奠定基础。

DESCRIPTION (provided by applicant): Atherosclerosis and its complications are leading causes of morbidity and mortality. The presence and severity of disease is typically diagnosed by luminal narrowing at X-ray catheterization. Because X-ray imaging does not visualize vessel walls, it does not allow assessment of processes that precede advanced plaque formation, or the vulnerability of plaques to rupture. Other current imaging approaches have difficulty distinguishing plaque components and with spatial and temporal resolution. Such issues are identified by NHLBI as central problems for image-guided intervention. Intravascular magnetic resonance imaging (IVMRI) promises precise, high-contrast assessment of stenoses and vessel wall pathology without ionizing radiation. Previously, ~1 mm diameter biocompatible intravascular guidewires were developed as active MRI detectors for clinical 1.5 Tesla (T) scanners in our laboratories, but have not gained wide use. Maximizing speed, sensitivity and spatial resolution are key to clinical use. While whole-body 3T MRI has emerged as a new clinical research standard, delivering higher signal-to-noise ratio (SNR) than existing 1.5T scanners, IVMRI detectors are limited to 1.5T, and thus have not benefited from any 3T SNR gain. One problem is a 4-fold increase in potential heating of introduced metallic devices at 3T vs 1.5T, all else being constant. We present new preliminary experimental and theoretical data demonstrating an over 3-fold gain in SNR and over 10-fold increase in the area of sensitivity or field-of-view (area exhibiting the same SNR) for equivalent intravascular antennae at 3T vs 1.5T. We show that heating can be kept within safe levels during 3T MRI. Such performance gains offer huge potential for high-contrast, high-resolution IVMRI for the in vivo assessment of atherosclerosis. Aim 1 develops and tests active, biocompatible high-SNR, high-FOV intravascular guidewires for 3T MRI. Image-guided device tracking requires high-speed MRI. However, conventional MRI is locked to the scanner's frame-of-reference (FoR), requiring time-consuming "read-out" of device location to prescribe MRI gradients for new locations. Aim 2 develops a new MRI approach that uses the antenna itself for excitation, intrinsically locking the image FoR to the active end of the probe. The antenna becomes an "MR-eye", generating images of what it "sees" as it courses through an artery like an endoscope. Because the MRI-excited volume is vastly reduced to the vicinity of the probe, heating potential is greatly reduced. Aim 3 tests these new technologies in an in vivo rabbit atherosclerosis model, where the aorta is of comparable diameter to human coronary arteries. These developments will form a basis for future human use.