MR‐guided balloon angioplasty: In vitro demonstration of the potential of MRI for guiding, monitoring, and evaluating endovascular interventions

Abstract

The purpose of this study was to demonstrate the potential of MRI for guiding, monitoring, and evaluating endovascular interventions. This was done by investigating the feasibility of MR-guided balloon angioplasty in a stenosed vessel model. Catheters and guidewires were prepared for susceptibility-based MR visualization by incorporating paramagnetic markers into their walls. Near real-time monitoring (up to 1 image/sec) of the interventional procedure was achieved by using a dynamic two-dimensional gradient-echo technique. Devices were localized by on-the-fly subtraction of a baseline image from consecutive dynamic images and by merging the subtraction images with a previously acquired road map. All steps involved in balloon angioplasty, from the introduction and placement of a guidewire to the positioning of a catheter across the stenosis, inflation of the balloon, and dilatation of the stenosis could adequately be monitored with MR fluoroscopy. The beneficial effect of dilatation could be substantiated by a reduction of stenosis-related hypointensities and hyperintensities in the posttreatment MR angiogram as compared to the pretreatment angiogram and by a posttreatment increase of the volumetric flow rate.

Improved lumen visualization in metallic vascular implants by reducing RF artifacts

“…The effect such a change in the effective excitation angle has on the signal intensity depends on the shape of the signal intensity vs. flip angle profile as determined by the values of T 1 and TR in Eq. [6]. With the parameters used in this experiment, the excitation angle of 30°lies beyond the Ernst angle, which can be calculated to be 13°.…”

“…[7] reduces to Eq. [6], is shown as a reference. The Ernst angle E for the gadolinium solution at a TR of 23 ms in this "unscaled" situation was calculated to be 87°.…”

“…Furthermore, MRI is gaining interest for the guidance of endovascular interventional procedures and posttreatment evaluations (5)(6)(7)(8). For all these applications the imaging of regions of the body containing metallic vascular implants, like stents and vena cava filters, is troublesome because of the artifacts provoked by these implants.…”

MR‐guided intravascular interventions: Techniques and applications

“…To detect interventional instruments on MR images, markers can be attached that either amplify or reduce the MR signal. To create a negative contrast small paramagnetic rings or magnetite mixtures have been applied (28,29) (Fig. 2), whereas a positive contrast has been achieved with paramagnetic contrast agents in the catheter lumen (30) or on the surface of the catheter (31,32).…”

“…Any of the measures mentioned above to reduce coupling between the RF transmitting coil and the intravascular device that causes heating of the intravascular device would result in fundamental device modifications that could change the mechanical properties and would require new certification of approval. The safety problems with metallic wires have led to the development of MR-visible guidewires made of fiberglass (29) or PEEK (36) by several groups. Recently, a 0.019Љ guidewire prototype was presented that was manufactured by a micro-pultrusion technique using glassfiber-reinforced plastics materials (Fig.…”