MR-Guided Endovascular Intervention Using Off-Resonance Contrast Angiography

描述（由申请人提供）：我们建议使用一种新的造影机制，即非共振造影血管造影（ORCA），以促进MR引导的血管内手术。ORCA依赖于顺磁性造影剂（如钆-DTPA）由于钆的体磁化率效应而引起频率偏移的观察结果。从本质上讲，ORCA“调谐”所需的结构，同时“调谐”来自其他组织的信号。该方法显示了很大的前景可视化和实时跟踪血管造影导管。ORCA对于MR引导的血管内手术特别有吸引力，原因如下：（1）在投影图像上，含有低浓度钆螯合物的标准血管造影导管具有高清晰度;（2）它能够使用滑动窗口径向采集实现实时导管跟踪，而不会出现欠采样伪影;（3）即使在重复输注造影剂后，背景组织也可以完全抑制。在本提案中，我们将使用“现成”造影剂评估BMS诱导的频率偏移，开发利用ORCA效应的新型导管设计和涂层，并实施超快MRI脉冲序列，该序列包含用于导管跟踪的实时频率调整。我们的目标如下：具体目标1：参数化ORCA效应，并确定允许MRI兼容导管在1.5 T下充分可见的造影剂最低浓度。任务包括：（1）系统地改变两种MRI造影剂（钆-DTPA和ferumoxytol）的浓度，以确定哪种最有希望改善介入MRI导管的显著性，（2）设计具有优化导管与背景对比度的特性的射频脉冲。具体目标2：使用非共振成像和改良的导管设计最大限度地提高导管的显著性。任务包括：（1）测量含有顺磁性造影剂的稀溶液的尼龙导管的内腔内和周围的自旋的共振频率;（2）将球对称频移涂层施加到导丝的表面，以最小化频移和导管显著性的取向依赖性。使用体内模型比较非共振和T1依赖方法在被动导管跟踪中的效用。任务将包括：（1）使用高帧率非共振和基于T1的方法测量可视化导管长度和空间保真度。静态、高分辨率3D TrueFISP采集将作为参考标准;（2）证明促进肾动脉导管插入术的能力，使用有效性和安全性作为终点比较技术之间的结局。公共卫生相关性我们开发了一种新型磁共振技术，可广泛应用于血管疾病的诊断和治疗。这项研究将导致更好地了解基本的对比机制，并将导致改进的治疗策略，肾血管性高血压使用MR引导介入手术。

DESCRIPTION (provided by applicant): We propose the use of a new contrast mechanism, Off Resonance Contrast Angiography (ORCA), to facilitate MR-guided endovascular procedures. ORCA relies on the observation that a paramagnetic contrast agent (such as gadolinium-DTPA) induces a frequency shift due to the bulk magnetic susceptibility effect of gadolinium. In essence, ORCA "tunes in" the desired structures while "tuning out" signals from other tissues. The method shows great promise for visualization and real-time tracking of angiographic catheters. ORCA is particularly attractive for MR-guided endovascular procedures for several reasons: (1) standard angiographic catheters containing low concentrations of gadolinium chelate are depicted with high conspicuity on projection images; (2) it enables real-time catheter tracking using a sliding window radial acquisition without undersampling artifact; (3) background tissues can be completely suppressed even after repeated infusions of contrast agent. In this proposal, we will evaluate BMS-induced frequency shifts using "off the shelf" contrast agents, develop novel catheter designs and coatings that exploit the ORCA effect, and implement an ultra-fast MRI pulse sequence that incorporates real-time frequency adjustment for catheter tracking. Our aims are as follows: Specific Aim 1: Parameterize the ORCA effect and determine the lowest concentration of contrast agent that allows adequate visibility of an MRI compatible catheter at 1.5 Tesla. Tasks involve: (1) systematically varying the concentrations of two MRI contrast agents, gadolinium-DTPA and ferumoxytol, to determine which holds the most promise for improving the conspicuity of catheters for interventional MRI, (2) designing radiofrequency pulses with properties that optimize catheter-to-background contrast. Specific Aim 2: Maximize catheter conspicuity using off-resonance imaging and modified catheter designs. Tasks involve: (1) measuring the resonance frequency of spins within and surrounding the lumen of a nylon catheter containing a dilute solution of paramagnetic contrast agent; (2) applying spherically-symmetrical frequency-shifting coatings to the surface of the guidewire in order to minimize orientation-dependence of the frequency shift and catheter conspicuity Specific Aim 3: Compare the utility of off-resonance and T1-dependent methods for passive catheter tracking using an in vivo model. Tasks will involve: (1) measurement of visualized catheter length and spatial fidelity using high frame-rate off-resonance and T1-based methods. A static, high-resolution 3D trueFISP acquisition will be the reference standard; (2) demonstrate capability for facilitating renal artery catheterization, comparing outcomes between the techniques using efficacy and safety as endpoints. PUBLIC HEALTH RELEVANCE We have developed a novel magnetic resonance technology that could have broad applications to the diagnosis and therapy of vascular disorders. This study will result in a better understanding of the basic contrast mechanisms and will lead to improved treatment strategies for renovascular hypertension using MR-guided interventional procedures.