Advanced Intravascular MRI for Assessing Atherosclerosis

描述（由申请人提供）：动脉粥样硬化及其并发症是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射线导管插入术的管腔狭窄来诊断。由于X射线成像不能显示血管壁，因此无法评估晚期斑块形成之前的过程或斑块破裂的脆弱性。其他当前的成像方法难以区分斑块成分并且具有空间和时间分辨率。NHLBI将这些问题确定为图像引导干预的核心问题。血管内磁共振成像（IVMRI）承诺在无电离辐射的情况下对狭窄和血管壁病理进行精确的高对比度评估。以前，在我们的实验室中开发了直径约1 mm的生物相容性血管内导丝作为临床1.5特斯拉（T）扫描仪的主动MRI探测器，但尚未得到广泛使用。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 MRI已成为新的临床研究标准，提供比现有1.5T扫描仪更高的信噪比（SNR），但IVMRI探测器仅限于1.5T，因此无法从任何3T SNR增益中受益。一个问题是在3T与1.5T下引入的金属器械的潜在发热增加了4倍，所有其他因素都是恒定的。我们提供了新的初步实验和理论数据，证明在3T与1.5T下，等效血管内天线的SNR增益超过3倍，灵敏度或视场面积（显示相同SNR的面积）增加超过10倍。我们表明，在3T MRI期间，加热可以保持在安全水平内。这样的性能增益提供了巨大的潜力，高对比度，高分辨率IVMRI动脉粥样硬化的体内评估。目的1开发和测试用于3T MRI的活性、生物相容性高SNR、高FOV血管内导丝。图像引导设备跟踪需要高速MRI。然而，常规MRI被锁定到扫描仪的参考系（FoR），需要耗时的设备位置的“读出”来为新位置规定MRI梯度。目标2开发了一种新的MRI方法，该方法使用天线本身进行激励，将图像FoR内在地锁定到探头的有源端。天线变成了一个“MR眼”，当它像内窥镜一样穿过动脉时，会产生它“看到”的图像。由于MRI激发体积在探头附近大大减小，因此加热电位大大降低。目标3在体内兔动脉粥样硬化模型中测试这些新技术，其中主动脉的直径与人类冠状动脉相当。这些发展将成为未来人类使用的基础。

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.