A study of possible causes of artifactual decreases in the left ventricular apex with SPECT cardiac perfusion imaging.

The objectives of this investigation were to determine the impact on appare nt localization of perfusion agents in the apex of the left ventricle (LV) of cardiac and respiratory motion, extra-cardiac uptake, the anisotropic sp atial resolution associated with imaging, and thinning of the LV wall at th e apex. The ability of attenuation compensation (AC), and of combined atten uation and spatial resolution correction (ARC) to alter the impact of these factors on apparent apex counts was also investigated. The MCAT phantom wa s used to simulate cardiac gated radionuclide perfusion imaging both with a nd without apical thinning of the LV wall. Simple respiratory motion of the heart was included in the simulation. After reconstruction using filtered backprojection (FBP) with no correction for physical degradation (NC) and u sing the maximum likelihood ordered subset expectation maximization (OSEM) algorithm with AC, and with ARC, polar maps were generated. Results show th at cardiac motion had no impact on apex counts other than an increase in co unts with myocardial thickening. Respiratory motion of a magnitude similar to that observed clinically does not influence the apex, but does have some effect on adjacent regions. A small decrease in apical counts was observed with body-contouring as opposed to imaging with a circular camera orbit. C ounts in the apex varied greatly with extent of the thinning. AC increased the visibility of the apparent decrease in apical counts over NC with apica l thinning, as did ARC over AC.