Characterization of myocardial and thoracic dimensions in a population of patients undergoing SPECT MPI: Implications for dedicated cardiac imaging systems

Objectives SPECT myocardial perfusion imaging (MPI) is a key tool in the management of coronary artery disease. The demands for improvements in diagnostic performance of MPI, as well as reduction of radiation exposure, can be met by systems designed for the heart’s anatomy. The cardio-centric approach involves systems in which the entire detector images a small field-of-view (FOV) which can enclose the heart. Appropriate application of this approach requires knowledge of relevant anatomic information for the patient population.

Methods We retrospectively examined images from 384 consecutive patients (ages 18-95, 235M/149F) undergoing a Tc-99m SPECT MPI study. For each patient, the cardiac dimensions were characterized by defining two axially oriented cylinders, one enclosing the left ventricle and the other enclosing the entire myocardium. The imaging protocol included transmission imaging with Gd-153 used to derive attenuation maps. These were used to characterize the thoracic dimensions by defining an elliptical cylinder enclosing the thorax.

Results We observe a significant variation in key anatomic dimensions. The diameter of the cylinder encompassing the left ventricle ranged from 82 to 164 mm. The range for the entire myocardium was 88 to 188 mm. Thoracic width ranged from 333 to 602 mm.

Conclusions This extensive dataset of anatomic information has significant implications for cardio-centric systems. The large range of dimensions observed in this work supports an adaptive imaging approach, in which the FOV is varied depending on the results of a scout scan. Such capability is an important step towards optimizing SPECT MPI across the patient population by increasing detector utilization. We show that adding an FOV configuration allows division of the population into two groups to optimize imaging for 72% of the population with a more modest improvement for the rest of the patients. Additional FOV configurations would yield greater benefits.