THERMOGRAPHIC IMAGING IN THE BEATING HEART - A METHOD FOR CORONARY FLOW ESTIMATION BASED ON A HEAT-TRANSFER MODEL

Intraoperative thermographic imaging in open-chest conditions can prov ide the surgeon with important qualitative information regarding coron ary flow by utilizing heat transfer analysis following injection of co ld saline into the aortic root. The beat transfer model is based on th e assumption that the epicardial temperature changes are mainly due to convection of heat by the blood flow, which may, therefore, be estima ted by measuring the temperature variations. Hearts of eight dogs were exposed and imaged by a thermographic camera. Flow in the left arteri al descending (LAD) coronary branch was measured by a transit-time flo wmeter. 20 ml of cold saline were injected into the aortic root (just after the aortic valve) and the epicardial temperature images were rec orded at end-diastole, for 20-30 s. Different flow rates were achieved by 1 min occlusion of the LAD, which affected a reactive hyperemic re sponse. The dynamics of the temperature in the arterial coronary tree was obtained by averaging the temperature over an edge-detected arteri al segment for each frame. The heat transfer equation was curve-fitted , and the flow-dependent heat transfer index was correlated with the e xperimentally determined coronary flow (r = 0.69, p(-) < 0.001). In su mmary: a method for quantitative estimation of coronary blood flow by thermography and heat transfer analysis was developed and tested in an imal experiments. This method can provide important information regard ing coronary blood flow during open-chest surgical procedures. (C) 199 8 IPEM. Published by Elsevier Science Ltd. All rights reserved.