Cardiac Disease in the Adult: MR Evaluation

Angiographic assessment of coronary stenoses: a review of the techniques

This article reviews the fundamental techniques to quantify the physiological severity of (coronary) stenoses. Although a wide survey of different techniques and applications is provided, the focus of this review is on: 1) the assessment of the immediate effect of the stenoses on blood flow (i.e., the hemodynamic severity), and not on the assessment of the pathology of the vessel itself; 2) the flow reserve methods to defining the physiological severity of stenoses; and 3) the determination of blood flow and tissue perfusion by X-ray angiography (a short survey of other imaging modalities is provided as well). Although the practical implementation of the techniques is illustrated by applying them to coronary stenoses, most of the issues involved are of interest in other application areas (using other imaging modalities) as well. This review consists of four parts. The first part deals with the definition of stenoses severity; the second part with tracer kinetic theory necessary to determine flows by imaging; the third part focusses on (cardiac) imaging modalities, with an emphasis on X-ray angiography; and the last part illustrates the practical implementation of the techniques in cardiology.

MRI-guided coronary catheterization and PTCA: A feasibility study on a dog model

The aim of this work was to demonstrate the feasibility of MRI-guided coronary artery catheterization and intervention in a dog model. Experiments were performed on 10 healthy dogs. A 9F introducer sheath was placed through a right carotid artery cutdown. A prototype 0.014-inch coronary MRI guidewire, a prototype 7 French MRI-guiding catheter, and two flexible surface coils were connected to a GE 1.5 T CV/i scanner for simultaneous visualization of the guidewire, guiding catheter, and chest anatomy. Images were displayed in real time on an in-room monitor. A nongated, single-slice fast gradient-echo sequence was used to obtain real-time images of the catheters and background anatomy during the intervention. Fifteen selective catheterizations were attempted in the coronary arteries, and all were successful. Selective injection of diluted gadolinium into the MRI-guiding catheter provided dynamic 2D projection coronary angiography in all cases, confirming successful catheterization. Percutaneous transluminal coronary angioplasty (PTCA) was attempted after two catheterizations, and all attempts were successful. Inflation of the balloon angioplasty catheter was performed successfully in the left anterior and circumflex arteries. Our results indicate that coronary artery catheterization and intracoronary balloon angioplasty are feasible with MRI guidance only. MRI guidance may be used as an alternative to X-ray guidance in coronary artery interventions in the future.