title: Modeling of temperature mapping for quantitative dynamic infrared coronary angiography for intraoperative graft patency control.
abstract: OBJECTIVE
  Intraoperative application of thermal coronary angiography based on dynamic infrared imaging leads to useful qualitative information concerning coronary artery bypass graft flow and anatomy. Additional quantitative flow estimation is desirable to detect graft failures. The aim of this study was to develop a heat-transfer model for quantitative flow estimation in an experimental setup. The first clinical results in coronary artery bypass grafting are reported.
  
  
  METHODS
  Dynamic infrared imaging was applied in pig hearts to collect video data of the rewarming process of the left anterior descending artery supplied by antegrade perfusion. For mathematic description, we used the dynamic enthalpy balance for open systems, and a Laplace transformation was carried out. Therefore the time constant tau was calculated by performing a nonlinear fit procedure on the averaged dynamic temperature curves recorded over a left anterior descending artery segment. Subsequently, left internal thoracic artery-left anterior descending artery bypass graft flow was assessed intraoperatively. Effective left anterior descending artery flow was determined by using a transit-time flowmeter.
  
  
  RESULTS
  Tau is a system constant and changes depending on the flow and the system capacity. Assuming system capacity to be constant, tau only depends on the flow. It follows from the differential equation that there is a potential relation between tau and the flow. An excellent comparison (R2 = 0.968, P <.005) was demonstrated. By using the algorithms, quantitative flow estimation in pig hearts was possible. For clinical application, the formulas were applied to intraoperatively derived dynamic temperature curves with a good comparison to the actual left internal thoracic artery-left anterior descending artery flow.
  
  
  CONCLUSIONS
  The developed heat-transfer model allows for precise measurement of graft flow by using dynamic infrared imaging and can be applied for noninvasive graft flow estimation in beating-heart surgery.
authors.affiliation: Department of Cardiac Surgery, Heart Center, University of Leipzig, Leipzig, Germany. jgmed93@hotmail.com
authors.forename: Jens
authors.initials: J
authors.lastname: Garbade
authors.forename: Cris
authors.initials: C
authors.lastname: Ullmann
authors.forename: Marcus
authors.initials: M
authors.lastname: Hollenstein
authors.forename: Markus Johannes
authors.initials: MJ
authors.lastname: Barten
authors.forename: Stephan
authors.initials: S
authors.lastname: Jacobs
authors.forename: Stefan
authors.initials: S
authors.lastname: Dhein
authors.forename: Thomas
authors.initials: T
authors.lastname: Walther
authors.forename: Jan Fritz
authors.initials: JF
authors.lastname: Gummert
authors.forename: Volkmar
authors.initials: V
authors.lastname: Falk
authors.forename: Friedrich-Wilhelm
authors.initials: FW
authors.lastname: Mohr
mesh_terms: D000818:Animals; D017023:Coronary Angiography / Q000379:methods*; D007259:Infrared Rays; D007430:Intraoperative Care / Q000379:methods; D008954:Models, Biological; D013552:Swine; D014654:Vascular Patency