Molecular imaging scored two victories in studies that assessed its usefulness as a tool with added quantitative coronary flow reserve (CFR) measurements in patients with coronary disease. One study gave quantitative CFR a thumbs up for identifying elderly patients who are at low risk for developing coronary artery disease (CAD) while the other found that adding CFR improves the diagnostic accuracy of PET myocardial perfusion imaging (MPI) for detecting CAD.

In the first study, Venkatesh Murthy, MD, PhD, a cardiovascular medicine and imaging fellow at Brigham and Women's Hospital and Harvard Medical School in Boston, and colleagues sought to evaluate the prognostic value of quantitative CFR in patients 75 years and older using PET. They identified 704 consecutive elderly patients who were referred for rest and stress Rubidium-82 (Rb-82) PET and followed them for 1.2 years. They analyzed the extent and severity of PET perfusion abnormalities with a semi-quantitative visual analysis and calculated rest and stress myocardial blood flows to determine CFR.

Based on medical records and the National Death and Social Security indices, they found that 9.4 percent of patients had died. Patients categorized as normal, mild-moderate and severely abnormal in the semi-quantitative visual analysis had annualized cardiac mortality rates of 3.5 percent, 5.6 percent and 11.3 percent, respectively. Based on further adjustments and analyses, they found that reduced CFR was associated with increased mortality and that global CFR added incremental prognostic value in addition to clinical and PET variables.  

“We demonstrate that many older adults have preserved coronary vascular function and that this group has an extremely favorable prognosis,” Murthy said in a press release. “They are much less likely to die from cardiac causes compared to those with abnormal coronary vascular function. This work suggests that loss of vascular function may not be an inevitable consequence of aging.”

In the second analysis, Michael Fiechter, MD, of the department of radiology at University Hospital Zurich in Switzerland, and colleagues looked at the added diagnostic value of CFR over PET MPI to predict angiographic CAD. Their study was based on 73 patients who underwent N-13 ammonia PET/CT MPI to evaluate quantitative CFR as an indicator of CAD. They used invasive coronary angiography as a standard of reference.  

They found that sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MPI for detecting significant CAD was 79 percent, 80 percent, 91 percent, 59 percent and 79 percent, respectively. Adding CFR significantly improved the values to 96 percent, 80 percent, 93 percent, 89 percent and 92 percent, respectively.

“The quantification of CFR with molecular imaging provides a substantial advantage for unmasking coronary artery disease, even in patients who would otherwise be considered healthy with normal myocardial perfusion imaging,” Fiechter said in a press release.

The two studies were presented as scientific papers June 11 at the annual meeting of the Society of Nuclear Medicine and Molecular Imaging in Miami.