CONCEPTS OF MYOCARDIAL PERFUSION IMAGING IN MAGNETIC-RESONANCE-IMAGING

Based on the major innovations in ultrafast magnetic resonance (MR) im aging in recent years, myocardial perfusion imaging with MR has become the focus of many investigators. Two major approaches to myocardial p erfusion imaging involve either exogenous or endogenous contrast agent s. For the first category of perfusion experiments, we review the char acteristics of the common contrast agents and MR techniques for experi mental and clinical first-pass studies and in particular address the q uestion of extracting quantitative estimates for myocardial blood flow (milliliters per minute per gram) and volume (milliliters per gram). We demonstrated quantitative perfusion analysis using intravascular re laxation agents and heavily T1-weighted ultrafast gradient echo sequen ces. Signal time curves need to be transformed to content time curves and the resulting residue functions were analyzed with a multiple-path way, axially distributed perfusion model. These preliminary results su ggest that quantitative assessment of myocardial perfusion is feasible , but additional studies should provide further confidence for this no vel MR approach. The exact sensitivity and specificity of MR first-pas s imaging in conjunction with extracellular contrast agents in patient studies and its diagnostic accuracy as judged against coronary angiog raphy and scintigraphic perfusion imaging remain yet undefined. The se cond category of perfusion experiments does not require exogenous cont rast agents and has not yet been tested in patient studies. Progress i s reported on several MR perfusion-sensitive methods that use the tiss ue water as an endogenous contrast agent in combination with magnetiza tion transfer techniques as well as paramagnetic deoxyhemoglobin for m easuring tissue oxygenation using heavily T2-weighted sequences for b lood oxygen-level-dependent contrast. Possible future directions and d evelopments toward further improvements for MR myocardial perfusion me asurements and contraction-perfusion matching are also addressed.