Characterization of PET partial volume corrections for variable myocardial wall thicknesses

Limited scanner resolution and cardiac motion contribute to partial volume (PV) averaging of PET images. An extravascular (EV) density image, created from the subtraction of a blood pool (BP) from a transmission (TX) image can be used to estimate PV losses in the myocardium (MYO). A phantom emulating the left ventricle myocardium, with a variable wall thickness (5 mm to 25 mm), was used to characterize the method for use in 3D PET ¹⁸FDG studies. Myocardial activity showed largest PV losses, of 60%, at a wall thickness of 5 mm. Prior to EV creation, the morphological operators dilation/erosion were applied to the BP and TX images to account for the presence of the phantom´s plastic walls, which would otherwise bias the EV values. Dividing MYO by the EV values improved the recovery to within 15% at 5 mm, however, TX ring artifacts and the anisotropic nature of dilation/erosion contributed to errors in the EV image. Instead of using dilation/erosion, a second method, involving placement of adjusted ROIs on the BP and TX images, was investigated use of these new EV values, as well as placement of the cardiac phantom in a chest phantom to reduce TX ring artifacts, allowed for 90% recovery of the activity at 5 mm. These results show that the EV density image can correct for PV averaging with 3D PET over a range of myocardial thicknesses applicable to patient studies. However, in the thinnest regions, the method was found to be sensitive to errors in both the blood pool and transmission images.