CLINICAL CARDIAC MAGNETIC-RESONANCE SPECTROSCOPY - PRESENT STATE AND FUTURE-DIRECTIONS

MR spectroscopy opens a window to the non-invasive evaluation of vario us aspects of cardiac metabolism. Experimentally, the method has exten sively been used since 1970's. P-31-MR allows the registration of card iac high-energy phosphate metabolism to non-invasively estimate the en ergetic state of the heart: ATP, phosphocreatine, inorganic phosphate, monophosphate esters and intracellular pH can all be quantitated. In conjunction with extracellular shift reagents such as [DyTTHA](3-) or [TmDOTP](5-), Na-23- and K-39-MR allow the measurement of intra- and e xtra-cellular cation pools. H-1-MR spectroscopy allows the detection o f a large number of metabolites such as, e.g. creatine, lactate, or ca rnitine. Human cardiac spectrocsopy has so far been confined to the P- 31 nucleus. Localization techniques (DRESS, ISIS, 3D-CSI etc.) are req uired to confine the acquired signal to the heart region. Relative qua ntification is straightforward (phosphocreatine/ATP ratio), absolute q uantification (mM) is under development. Cardiac P-31-MR spectroscopy has research application in at least three clinical areas: (1) Coronar y artery disease: A biochemical stress test for non-invasive ischemia detection (decrease of phosphocreatine with exercise) and viability as sessment via quantification of ATP may become feasible. (2) Heart fail ure: The phosphocreatine / ATP ratio may provide an independent index for grading of heart failure, allow to monitor the longterm effects of different forms of drug therapy on cardiac energy metabolism in heart failure, and may also hold prognostic information on survival. (3) Va lve disease: It is possible that the decrease of phosphocreatine/ATP c an be used to guide the timing for the valve replacement. At the prese nt time, no routine clinical applications can be defined for the use o f human cardiac spectroscopy in patients with cardiac disease. However , the technique holds great potential for the future as a non-invasive approach to cardiac metabolism, and in coming years routine applicati ons may become reality.