Evaluation of MR Contrast Agents with High Relaxivity and Reduced Interstitial Diffusion for Contrast Material–enhanced MRA and Myocardial Perfusion Studies

Abstract

For perfusion imaging and contrast material–enhanced magnetic resonance angiography (MRA) of small vessels, quality of information is highly dependent on the characteristics of the selected contrast agents. Performance of MRA has been greatly improved by the use of contrast agents (1,2). With fast, three-dimensional (3D) gradient echo T1-weighted sequences combined with bolus injection of contrast agent, visualization of arteries can be performed at the arterial phase of contrast agent, provided a good timing procedure is established. Because small-molecular-weight gadolinium chelates diffuse rapidly in the interstitium, the examination must be performed in a very narrow acquisition window (2). To improve visualization of vessels without time constraints, different blood pool agents have been investigated (1,3–10). The main drawback of intravascular contrast agents is their slow elimination rate, which precludes the possibility of a second injection and may increase toxicity. As the quality of MRA is improved by the r1 efficiency of the contrast agent, new blood pool agents with a high r1 relaxivity have been developed. These agents are characterized by fast renal elimination and low interstitial diffusion (11). In perfusion imaging with the so-called first-pass technique, the quantitative approach by kinetic modeling is made quite simple with an intravascular agent (12,13). To detect abnormal perfusion pattern encountered with myocardial ischemia, different intravascular contrast agents have been evaluated (12,14–18). For the follow-up of coronary diseases, it is important to evaluate perfusion parameters such as myocardial perfusion reserve (19). Because these protocols require a second injection of contrast agent to perform rest and stress imaging, a contrast agent with fast elimination rate would be preferred. With high relaxivity contrast agents, it should be possible to reduce the dose with the same enhancement. Moreover, because these agents have a low interstitial diffusion and yet a relatively fast clearance, they theoretically present the advantages of intravascular contrast agents for quantitative perfusion studies without their drawbacks. In summary, contrast agents for MRA and myocardial perfusion studies should fulfill the following criteria: a high T1 efficiency, a low interstitial diffusion during firstpass but yet a relatively fast clearance. The purpose of this study was to evaluate in vivo a new class of MR blood pool agents, compared to gadolinium chelates for MRA and myocardial perfusion studies.