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PET Perfusion Takes New Approach to Quantify
Coronary Artery Disease

Using PET myocardial perfusion imaging to quantify coronary flow reserve (CFR) may provide better diagnosis of heart disease than traditional angiography, according to information presented this month at the SNM annual meeting in Miami.

“Although different studies revealed a prognostic value of CFR, this study is the first that systematically assessed the diagnostic value of CFR against invasive coronary angiography as a standard of reference for detection of coronary artery disease,” said Philipp Kaufmann, MD, a lead study author from the department of radiology and cardiac imaging at University Hospital Zurich in Switzerland.

The study, presented at a press conference during the SNM annual meeting in June, was one of two that examined aspects of using PET and CFR to assess coronary artery disease. The second was led by researchers from Brigham and Women’s Hospital in Boston.

“The primary message of our study is that aging does not always imply decline in vascular function and that the many people with preserved vascular function have far better prognosis—about half the risk of dying from heart disease,” said Venkatesh Murthy, MD, PhD, a cardiovascular medicine and imaging fellow at Brigham and Women’s Hospital and Harvard Medical School.

When an active heart needs more oxygen, blood vessels naturally dilate to increase blood flow. CFR represents the vessels’ maximum possible dilation. Diseased coronary arteries cannot dilate as fully as healthy blood vessels, potentially limiting oxygen supply to the heart muscle, making reduced CFR one of the earliest signs of coronary artery disease.

In the two studies presented at the meeting, investigators examined quantitative imaging data to help them assess the true extent of coronary artery disease. In the Zurich study, researchers examined a stress test conducted with PET. They then measured the CFR and calculated the precise dilation of blood vessels at rest and under stress. The objective of the study was to compare this technique’s ability to predict arterial disease to the more conventional imaging method, angiography. At Brigham and Women’s, researchers used a PET stress test and measured CFR to determine whether age is always a risk factor for arterial disease.

“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,” said Michael Fiechter, MD, a lead investigator of one study from the department of radiology at University Hospital Zurich.

Measuring CFR using PET goes beyond traditional SPECT perfusion imaging’s visual interpretation of the differences between blood flow at rest and under stress and quantifies coronary artery disease using imaging data acquired during scanning.

In the two presented studies, a total of 777 elderly participants underwent myocardial perfusion imaging with PET and either Rb-82 or N-13-ammonia as an imaging biomarker to evaluate quantitative CFR as an indicator for coronary artery disease. One study of 73 participants concluded significant improvements across five different reference points, including sensitivity, positive predictive value, and accuracy of myocardial perfusion imaging, compared with imaging studies without CFR measurements.

Results of the research revealed that myocardial perfusion imaging with PET and either Rb-82 or N-13-ammonia with added quantitative CFR measurements significantly improved sensitivity and diagnostic value of stress testing over myocardial perfusion imaging alone and may provide more information for identifying coronary vascular disease and exploring why some people develop the disease and others do not, according the Zurich study.

In a separate study of 704 patients over the age of 75, researchers using similar methods discovered that age was not necessarily a risk factor for developing coronary artery disease, as was once thought.

“This is the first large study of the effects of aging on coronary vascular function in patients,” Murthy said. “Aging has been previously shown in small studies to affect vascular performance, but these have generally used less accurate methodologies. We demonstrate that many older adults have preserved coronary vascular function and that this group has an extremely favorable prognosis. 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.”

— Source: SNM