Cardiac PET/CT: Measuring calcification via low-dose CT

Low-dose CT has become a mainstay for PET attenuation correction, but why not take it a step further by quantifying coronary artery calcium without adding any extra dose, asks an Ottawa Heart Institute study published ahead of print Nov. 20 in the Journal of Nuclear Cardiology.  

Coronary artery calcification is predictive of adverse cardiac events and mortality and can add useful information to clinical case management, but it is usually measured with a dedicated CT scan. Researchers including Tyler S. Kaster, MD, from the Ottawa Heart Institute in Ontario, Canada, took advantage of low-dose CT already being used for attenuation correction to gain additional coronary artery calcium scores.

For this study, researchers assessed a small cohort of patients in two sequential phases of study: one to test the viability of using CT attenuation correction during rest to reconstruct Rb-82 stress PET perfusion. The other phase looked at how the scan could be optimized to provide calcium measurements and how the low-dose scan compared to standard coronary artery calcium scans.

By the end of the study, all patients had undergone both conventional coronary artery calcium scan on a cardiac CT scanner and modified myocardial perfusion scan via PET/CT. Researchers optimized the post-stress CT scan during PET/CT to approximate the calcium CT without going above a 0.5 mSv dose.

Results of the study showed that the calcium CT attenuation correction (Ca-CTAC) protocol achieved perfect accuracy without exposing patients to any additional dose.

“A single low-dose CT scan was used for accurate attenuation correction of rest and stress PET perfusion images, allowing a second low-dose CT scan to be optimized for improved quantification of coronary artery calcium,” wrote Kaster et al. “The categorical classification of coronary artery calcium of the 23 patients in the attenuation cohort was 100 percent accurate using the modified Ca-CTAC protocol.”

The only downside was a potential 5 percent underestimation of calcium and a less than 3.5 percent reduction in PET anterior wall perfusion during Ca-CTAC. This protocol could be a boon for cardiac patients undergoing PET/CT, but further study is needed in larger patient populations before researchers can determine the added benefit of a low-dose calcium CT scan during PET/CT imaging.