Segmental cardiac function computed from ECG-gated SPECT images through solution of equations of continuity for...

Segmental contractions were quantified from images of electrocardiographic-gated single-photon emission computed tomography. Counts were integrated in 64 angles about the centre on short-axis images and projected onto a cylindrical screen. Changes in the projected count were shown to obey the equation of continuity for two-dimensional fluids (the Poisson equation). Displacements of each pixel point were calculated from the velocity field to quantify the amount of dislocation. Changes in the configuration of the pixel points were projected back on the cardiac wall, and finally segmental contractions were evaluated as a percentage reduction of the area. Computer simulations were performed for numerical models of circumferential and long-axial contractions, uneven eccentric contractions and rotations. These models were blurred with a three-dimensional Gaussian function. The results obtained using this method (quantification of segmental function by solving the Poisson equation (QSFP)) were compared with the wall-thickening method (WTM) and the maximum-count method. Both QSFP and WTM yielded good agreement with predicted values for circumferential and long-axial contractions. Only QSFP gave satisfactory results for uneven eccentric contractions, and rotation models. QSFP should provide a useful tool for in vivo quantification of contraction tangential to the cardiac wall by eliminating errors due to displacements.