Measurement of regional myocardial perfusion using collimated miniature radiation detectors and the method of 133-Xenon washout

A new approach to the measurement of local myocardial perfusion based on the application of highly-collimated miniature cadmium telluride radiation detectors to measure washout of 133-Xenon from well-defined tissue volumes is presented. Single-hole collimators with length/diameter ratios of 1 (L=4 mm, D=4 mm) and 4 (L=12 mm, D=3 mm) were employed as prototype designs. The probe field of view was characterized theoretically using a spherical model of the myocardium in conjunction with experimental point source response measurements for each collimator. Method evaluation using two medium resolution collimators (L/D=1) was effected by performing left main and circumflex coronary artery perfusion studies at controlled but variable flows in the dog heart. An excellent correlation (r>0.99) between actual and estimated perfusion determined from 65 washout curves over the flow range 0.38 to 3.18 ml/min/gm was demonstrated. The ability to resolve regional flow differences was verified by measuring tracer washout from circumflex and left anterior descending regions of the myocardium, using two high resolution collimators (L/D=4), in a preparation where the left main coronary artery was cannulated and a snare was placed around the circumflex coronary artery to selectively reduce flow to that region.