Dose optimization for myocardial perfusion CZT-SPECT imaging: Why and how?

Abstract

Myocardial perfusion SPECT imaging (MPI) is able to provide a physiological assessment during physical exercise and is widely used for diagnosing coronary artery disease and assessing cardiac risk. Until recently, however, MPI needed to provide a lower radiation exposure, especially for the growing number of patients referred for repeated ionizing procedures throughout the course of their life. This goal has been partly attained with the advent of new imaging systems dedicated to nuclear cardiology and equipped with semiconductor cadmium zinc telluride (CZT) detectors, new collimation systems, and novel reconstruction software. Two CZT cameras are currently commercially available and when compared with conventional Anger cameras, they offer much higher energy resolutions and count sensitivities, allowing image quality to be improved as well as acquisition times and injected activities to be markedly reduced. Low-dose protocols have already been assessed with these CZT cameras, leading to a mean effective dose not exceeding 9 mSv per patient and thus, at a much lower level than that currently achieved with single-day protocols on conventional cameras (around 14 mSv). These doses can furthermore be reduced to less than 4 mSv, on average, owing to the use of a stress-first protocol, where the normality of stress images may lead to avoiding rest imaging. In the near future, effective doses will likely be further decreased to a lower level with technical improvements leading to minimizing the reconstructed noise and attenuation artifacts while at the same time optimizing and better tailoring the injection protocols to the individual patient.