MR-Guided Endovascular Intervention Using Off-Resonance Contrast Angiography

描述(申请人提供)：我们建议使用一种新的对比剂机制，非共振对比剂血管造影术(ORCA)，以促进MR引导的血管内手术。ORCA依赖于观察到顺磁造影剂(如Gd-DTPA)由于Gd的整体磁化率效应而诱导频率漂移。从本质上讲，ORCA在“调谐”所需结构的同时“调谐”了来自其他组织的信号。该方法在血管造影导管的可视化和实时跟踪方面具有很大的应用前景。ORCA对于MR引导的血管内手术特别有吸引力，原因有几个：(1)标准的血管造影导管含有低浓度的Gd螯合物，在投影图像上具有高清晰度；(2)它能够使用滑动窗径向采集实现实时导管跟踪，而不会出现采样不足伪影；(3)即使反复注入造影剂，背景组织也可以完全被抑制。在这项计划中，我们将使用“现成”造影剂评估BMS引起的频移，开发利用ORCA效应的新型导管设计和涂层，并实施包含实时频率调节的超快MRI脉冲序列，用于导管跟踪。我们的目标如下：具体目标1：对ORCA效应进行参数化，并确定在1.5特斯拉的情况下，使MRI兼容导管具有足够可见度的最低造影剂浓度。任务包括：(1)系统地改变两种磁共振造影剂(Gd-DTPA和阿魏酸甘油)的浓度，以确定哪种造影剂最有希望提高介入性磁共振导管的显着性，(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进的导管设计，最大限度地提高导管的显着性。任务涉及：(1)测量含有顺磁性造影剂稀溶液的尼龙导管管腔内和管腔周围自旋的共振频率；(2)在导丝表面涂覆球对称移频涂层，以最大限度地减少频移和导管显着性的方向依赖性；(3)通过体内模型，比较非共振和依赖T1的被动导管跟踪方法的有效性。任务将包括：(1)使用高帧速率、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。(2)展示促进肾动脉插管的能力，比较以有效性和安全性为终点的技术之间的结果。公共卫生相关性我们开发了一种新的磁共振技术，可以在血管疾病的诊断和治疗中有广泛的应用。这项研究将导致更好地了解基本的对比机制，并将导致使用MR引导的介入操作改进肾血管性高血压的治疗策略。

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.