Novel Methodology for Measuring Regional Myocardial Efficiency

Our approach differs from the usual global measure of cardiac efficiency by using PET/MRI to measure efficiency of small pieces of cardiac tissue whose limiting size is equal to the spatial resolution of the PET scanner. We initiated a dynamic cardiac PET study immediately prior to the injection of 15.1 mCi of ¹¹C-acetate acquiring data for 25 minutes while simultaneously acquiring MRI cine data. 1) A 3D finite element (FE) biomechanical model of the imaged heart was constructed by utilizing nonrigid deformable image registration to alter the Dassault Systèmes FE Living Heart Model (LHM) to fit the geometry in the cardiac MRI cine data. The patient specific FE cardiac model with estimates of stress, strain, and work was transformed into PET/MRI format. 2) A 1-tissue compartment model was used to calculate wash-in (K₁) and the linear portion of the decay in the PET ¹¹C-acetate time activity curve (TAC) was used to calculate the wash-out k₂(mono) rate constant. K₁ was used to calculate blood flow and k₂(mono) was used to calculate myocardial volume oxygen consumption ( MVO₂ ). 3) Estimates of stress and strain were used to calculate Myocardial Equivalent Minute Work ( MEMW ) and Cardiac Efficiency = MEMW/MVO₂ was then calculated for 17 tissue segments of the left ventricle. The global MBF was 0.96 ± 0.15 ml/min/gm and MVO₂ ranged from 8 to 17 ml/100gm/min. Six central slices of the MRI cine data provided a range of MEMW of 0.1 to 0.4 joules/gm/min and a range of Cardiac Efficiency of 6 to 18%.