Nuclear imaging of vulnerable plaque: Contrast improvements through multi-labeling of nanoparticles

Vulnerable plaque is now recognized as the major cause of sudden cardiac death and acute cardiovascular events in the population of at-risk but asymptomatic patients. Nuclear medicine can potentially localize and determine disease extent or response to treatment. Multi-labeling of nanoparticles, a molecular imaging technique, can improve contrast-to-noise ratio (CNR) and overcome the partial volume effect that afflicts conventional nuclear medicine. First, we describe a general mechanism for CNR improvement using multi-labeling of nanoparticles. Applying the analysis to a simplified geometrical model yields a closed-form solution for the dependence of first-order CNR in a planar image on the number of atoms per interacting particle. We then created a computer simulation capable of providing an accurate estimation for more complicated geometries, particularly when taking advantage of a SPECT/CT dual modality scanner. Results from the simulation of the geometrical model agree with the closed-form solution for CNR. Finally, cardiac torso phantom images verified the correctness of the CNR estimation results for small multi-labeling ratios. CNR increases supra-linearly with the number of radioactive atoms per molecule, indicating potential improvement in vulnerable plaque visibility through the use of high-payload nanoparticles.