Modeling respiratory mechanics in the MCAT and spline-based MCAT phantoms

Respiratory motion can cause artifacts in myocardial SPECT and computed tom ography (CT). We incorporate models of respiratory mechanics into the curre nt 4D MCAT and into the next generation spline-based MCAT phantoms. In orde r to simulate respiratory motion in the current MCAT phantom, the geometric solids for the diaphragm, heart, ribs, and lungs were altered through mani pulation of parameters defining them. Affine transformations were applied t o the control points defining the same respiratory structures in the spline -based MCAT phantom to simulate respiratory motion. The Non-Uniform Rationa l B-Spline (NURBS) surfaces for the lungs and body outline were constructed in such a way as to be linked to the surrounding ribs. Expansion and contr action of the thoracic cage then coincided with expansion and contraction o f the lungs and body. The changes both phantoms underwent were spline-inter polated over time to create time continuous 4D respiratory models. We then used the geometry-based and spline-based MCAT phantoms in an initial simula tion study of the effects of respiratory motion on myocardial SPECT. The si mulated reconstructed images demonstrated distinct artifacts in the inferio r region of the myocardium. We conclude that both respiratory models can be effective tools for researching effects of respiratory motion.