Simulation study on factors affecting the detectability of coronary artery plaques in NaF PET imaging

Positron emission tomography (PET) using F-18 sodium fluoride (NaF) has been investigated as an imaging biomarker for coronary vulnerable plaque. The goal of this work is to study the effects of activity uptake of the plaque, image noise, respiratory and cardiac motion, and respiratory and cardiac gating techniques on the detectability of coronary artery plaques through a realistic simulation study. PET projection data from the 4D XCAT phantom with typical organ uptake and realistic modeling of respiratory and cardiac motion were generated using Monte Carlo simulation methods. Plaques with a fixed size and 4 plaque-to-background uptake ratios were placed at 3 representative locations in the coronary arteries (LAD, LCX, and RCA) of the beating heart of the XCAT phantom. Four respiratory motion amplitudes ranging from 6 to 15 mm and with 6 image noise levels were used in the study. For each projection dataset, reconstructed images without gating, with 6-frame respiratory gating, 8-frame cardiac gating, and dual respiratory and cardiac gating were used to evaluate the detectability of plaque. Without gating, only the LAD plaque was barely visible in the almost noise-free reconstructed images. Although the plaques in all 3 locations were visible in dual respiratory and cardiac gated images in the almost noise-free case, the visibility decreased dramatically with the increase of image noise. The LAD and LCX plaques were barely visible in the almost noise-free respiratory gated images with 71% contrast reduction. The plaques in all 3 locations were visible in the cardiac gated images even with the largest 15 mm respiratory motion amplitude but with 50% contrast reduction. We found that higher plaque-to-background uptake ratio is required to detect the plaque for respiratory motion with larger amplitude. The LAD plaque was least sensitive to respiratory and cardiac motion and was the easiest to detect. Using dual respiratory and cardiac gating, the motion blurring artifacts in the images were reduced at the cost of increased image noise. Cardiac gating provides improved plaque visibility over respiratory gating. Results of this study provide useful guides for coronary artery plaque PET imaging and are useful for optimizing scanning protocols for coronary plaque PET imaging.