INVESTIGATION OF CORONARY VESSELS IN MICROSCOPIC DIMENSIONS BY 2-DIMENSIONAL AND 3-DIMENSIONAL NMR MICROSCOPIC IMAGING IN THE ISOLATED RAT-HEART - VISUALIZATION OF VASOACTIVE EFFECTS OF ENDOTHELIN-1

Background Nuclear magnetic resonance (NMR) imaging of macroscopic cor onary vessels is rapidly advancing, whereas little attention has focus ed on development of NMR techniques for investigation of coronary micr ovessels. Such techniques would be of particular importance, since con ventional methods to visualize coronary microvessels have specific lim itations. The aim of our study was to develop two- and three-dimension al (2D and 3D) high-resolution imaging of coronary microvessels. Quant itative analysis of vessel size was performed in tomograms and applied to evaluate the vasoconstrictor effect of endothelin 1. Methods and R esults Angiographic imaging was performed on an 11.75-T magnet by 2D a nd 3D gradient-echo pulse sequences. In tomograms, the validity of thi s method in providing correct vessel size was tested by phantom experi ments. Experiments were carried out in the isolated constant-pressure- perfused rat heart with continuous registration of coronary flow and l eft ventricular pressure. NMR pulse sequences were pressure-triggered in mid diastole. Four groups of hearts were studied. In group 1 (n=20) , 2D imaging perpendicular and parallel to the long axis of the heart was performed. Cross sections of vessels with diameter >140 mu m were clearly detectable. In group 2 (control, n=5) and group 3 (n=13), tomo grams perpendicular to the long axis were obtained before and after ad ministration of vehicle (group 2) and 200 pmol endothelin 1 bolus (gro up 3). Vehicle had no effect on vessel cross section. Endothelin 1, wh ich decreased global coronary flow by 47%, reduced vessel cross sectio n by 38+/-19%. A weak but, on average, significant inverse correlation between area of cross section and vessel size was found. In group 4 ( n=10), 3D imaging was performed in 7 normal hearts and 3 hearts with a nterior myocardial infarction. a 3D image of the entire coronary arter y tree was obtained, revealing excellent agreement with anatomic studi es. In infarcted rat hearts, occlusion of the left coronary artery was demonstrated. Conclusions Visualization and quantification of coronar y microvessels are feasible by NMR microscopy. NMR microscopy bears th e potential of becoming a powerful tool for the investigation of the c oronary microcirculation.