DOCTORAL THESIS Basic And Clinical Research Of MRS And MRI In Reperfused-ischemic Myocardium

Magnetic resonance spectroscopy (MRS) is a method for non-invasive detection of various aspects of cardiac metabolism in humen. The MR spectroscopic technique allows for study of a number of nuclei, such as 1H, 13C, 19F, 23N, 31P and 39K. At present, 'H and 31P nucleus are often used. 31P MRS allows the non-invasive study of cardiac high-energy phosphate metabolites and its largest field for potential clinical applications is of coronary artery disease.Two applications of them have good perspective: (1) "biochemical engometry": It is clear that such a biochemical test would find its way into routine cardiological practice as a way to non-invasively study the direct biochemical consequences of exercise on the heart. The biochemical engometry allow to non-invasively study the effectiveness of revascularization procedures or variousantianginal therapies. (2) Evaluation of myocardial viability: The potential area for the application of 31P MRS in coronary artery disease is the evaluation of myocardial viability. Akinetic myocardium that is supplied by a stenotic coronary artery may be non-viable, in which case revascularization by PICA or bypass grafting will not restore contractility. Alternatively, such myocardium may also be viable, biochemically and morphologically largely intact, but has down-regulated contractility in order to reduce its energetic needs.However, the report about 31P MRS applied studies on reperfused myocardium is sparse. Magnetic resonance spectroscopy, which can be combined with MRI analysis of cardiac morphology and function, has the advantages of non-invasive study of basic mechanism of coronary artery disease. On the other hand, based on the systematic experimental study of reperfused-ischemic myocardium in dogs, the present research, which is a pioneering work in China, is undertaken as a clinical investigation of reperfused-ischemic myocardium.1 Objectives:(1) To investigate the characteristics of the changes in high-energy phosphates during reperfused myocardium using 31P MRS.(2) To observe the dynamics changs of the energy metabolism instunned myocardium using 31P MRS and MRI in a canine model, and to establish their relationship between the function and the energy metabolism.(3) To evaluate the ability and accuray of 31P MRS to distinguish reperfused viable (stunned) myocardium from reperfused-infarcted myocardium in vivo at 6h, 30h, and 54h hours following coronary artery occlusion in a canine models, and to examine the accuracy of 31P MRS for distinguishing reperfused-infarcted from reperfused-viable myocardium at times of up to 54h following coronary reperfusion.(4) To study the value of 31P MRS as a passable tool to distinguish viable from non-viable tissue after myocardial infarction in humen.(5) To evaluate the clinical utility of 31P MRS combined with MRI.(6) To evaluate the characteristics of myocardial perfusion using first-pass perfusion MR imaging.2 Materials and Methods:(1) Establishing a canine model of reperfused myocardium by occluding LAD followed by reperfusion. A 15-minute occlusion produced reperfused-viable (stunned) mycecordium in 7 dogs and a 120-minute occlusion produced reperfused-imfarcted myocardium in 6 dogs, performing MRI of heart and 31P MRS of myocardium at regular intervals.(2) Performing MRI and 31P MRS on 12 healthy volunteers who served as controls.(3) Conducting heart MRI and 31P MRS studies on 10 selected patients with MI, whose diagnosis of MI has been confirmed by coronary angiographies and some other tests.(4) Gd-DTPA enhanced myocardial perfusion and delayed imagings was performed in a 90-minute occlusion produced reperfused infracted canine model.3 Results:(1) Postreperfusion risk zone myocardial phosphocreatine (PCr) level measured by 31P MRS was significantly decreased throughout the 6-54h study period in infracted but not in viable myocardium (stunned myocardium in 30...