In the recent past, a number of MR-guided vascular interventions have been performed, evaluating MR-compatible and MR-safe instruments that make use of passive visualization techniques. The catheter-only image (second echo) can be threshold and overlaid in color on the vascular image (first echo) ( 3). The image based on the short echo renders both the vasculature and the catheter bright, whereas the image based on the long echotime (TE) renders only the catheter bright. By filling the catheter with a Gd-based contrast agent, both vascular system and instruments can be visualized separately with a double-echo gradient-echo sequence. Strategies for reducing venous opacification have been explored by using contrast agents based on superparamag-netic iron oxides with both T 1– and T 2-shortening effects ( 3). Intravascular MR contrast agents have a prolonged intra-vascular presence but equally opacify both arteries and veins ( 1, 2). Target vessel and potentially reduces catheter visualization. This alters the signal characteristics of the Gadolinium diethylenetriaminepentaacetate (DTPA) allows the acquisition of high-resolution MR angiograms that could be used for tracking vascular instruments relative to arterial morphologic background “road maps.” However, commercially available contrast agents rapidly leak out of the vascular space, resulting in increased signal in the background tissues. This can be achieved with administration of a vascular contrast agent. The first is to alter the blood signal relative to the catheter signal. Two approaches to passive catheter guidance exist. The additional capabilities of MRI could potentially open up new applications within the purview of vascular interventions beyond those currently performed under x-ray fluoroscopic guidance. These images can provide the capability to distinguish and identify various plaque components. In addition, the ability to introduce an RF coil mounted on a catheter presents the opportunity to obtain high-resolution images of the vessel wall. Passive techniques depend on contrast agents or susceptibility artifacts that enhance the appearance of the catheter in the image itself, whereas active techniques rely on supplemental hardware built into the catheter, such as a radiofrequency (RF) coil. Several approaches for rendering instruments visible in an MR environment have been developed, including both passive and active techniques. ![]() For MR guidance of vascular interventions to be safe, the interventionist must be able to visualize catheters and guidewires relative to the vascular system and surrounding tissues. Several attributes make magnetic resonance imaging (MRI) attractive for guidance of intravascular therapeutic procedures, including high soft tissue contrast, imaging in arbitrary oblique planes, lack of ionizing radiation, and the ability to provide functional information, such as flow velocity or flow volume per unit time, in conjunction with morphologic information.
0 Comments
Leave a Reply. |