High-efficiency SPECT system works, even in morbidly obese

A high-efficiency SPECT system provided high quality and diagnostically accurate images for detecting coronary artery disease in obese patients, even morbidly obese patients, researchers reported in the April issue of the Journal of Nuclear Cardiology.

Obesity increases the risk of cardiovascular disease and it also poses challenges for cardiologists and radiologists who want to evaluate these patients because soft tissue may create artifacts. Ryo Nakazato, PhD, of Cedars-Sinai Medical Center in Los Angeles, and colleagues wanted to assess the image quality and diagnostic value of new high-efficiency SPECT cameras using multiple pinhole collimation with cadmium-zinc-telluride (CZT) semiconductor detectors in this patient population.

The system already has been validated by coronary angiography for detecting coronary artery disease, they pointed out. The pinhole collimation design also “is relatively easily positioned, even in the severely obese patients.”

Nakazato et al enrolled 118 consecutive patients at three centers between 2008 and 2013 with a body mass index (BMI) of 35 kg/m² or greater with suspected CAD. The patients underwent rest/stress high-efficiency SPECT myocardial perfusion imaging (MPI) in upright and supine positions. Their mean BMI was 43.6 kg/m² with the heaviest at 79.7 kg/m².

For validation, they compared high-efficiency SPECT with invasive coronary angiography in 67 obese patients who had angiography within six months of the SPECT test.

For the quantitative analysis, they assessed total perfusion deficit using upright images, supine images and a combination of both (U-TPD, S-TPS and C-TPD). For U-TPD, S-TPS and C-TPD, respectively, they calculated the receiver-operating characteristic curve was 0.8, 0.8 and 0.87; sensitivity/specificity was 82/57 percent, 74/71 percent and 80/82 percent; accuracy was 72 percent, 73 percent and 81 percent; and normalcy rates were 75 percent, 78 percent and 88 percent.

Image quality for stress and rest was similar when patients were stratified into three different BMI groups. “Image quality with this parallel hole CZT SPECT system was high in this population of consecutively selected obese patients, including 60 patients in the morbidly obese group. … Remarkably, none of the patients had a nondiagnostic stress SPECT study.”

They wrote that accuracy was highest using combined imaging, as was specificity and normalcy rates. They also stressed that they used quantitative and visual assessment to interpret the studies and that the interpreters in their group were very experienced with studies using the camera system. They suggested centers without that expertise might employ quantitative analysis to achieve similar results.