Researchers from Emory School of Medicine have performed a first-of-its-kind cardiac imaging procedure that they hope will help better assess coronary blockage and prevent future cardiac events. First performed in October 2021, the procedure is known as dynamic myocardial CT perfusion imaging, or cardiac CTP imaging for short, according to a statement from the university. The imaging scan is performed in conjunction with CT angiography.
Carlo De Cecco, MD, PhD, Professor of Radiology and Imaging Sciences at the university and Director of the Translational Lab for Cardiothoracic Imaging and Artificial Intelligence, explained how the procedure is performed and how it works with CT angiography to provide an improved image of the heart.
"With dynamic CT perfusion, we capture multiple images over time to capture the [inflow] and outflow of contrast in the myocardium," said De Cecco, noting that the examination is done under pharmacological stress using regadenoson. "This allows us to visualize and quantify which part of the heart muscle receives normal or lower amounts of blood, and thereby receives less oxygen. We perform the dynamic CT perfusion in conjunction with CT angiography, which is used to see if there is blockage of the coronary arteries."
However, "we know that a blockage of the arteries doesn't always mean that the heart muscle is affected (yet). By adding dynamic CT perfusion, we can see whether the coronary artery blockage is causing blood flow and oxygen shortages to the heart muscle, and hopefully determine if better intervention is needed. By relating the coronary stenosis to the myocardial perfusion, we can see whether any perfusion impairment is most likely caused by a coronary stenosis and, therefore, [can see whether] intervention should or should not be considered."
As De Cecco and his colleagues point out, more conventional CT angiography provides information about partial or complete blockage, or stenosis, and which arteries are involved, which aids in planning future treatment and therapy. CT angiography is currently used for the evaluation of stenosis severity and is accurate in excluding disease, but often overestimates the severity of stenosis.
Studies have historically shown that functional information better predicts disease severity and helps guide decision-making about invasive interventions, such as stenting or bypass surgery. Procedures such as fractional flow reserve measurement were typically necessary to provide accurate functional information, and were performed during cardiac catheterization.
Going forward, the Emory researchers foresee dynamic myocardial CT enhancing the way cardiac imaging is done.
"By adding a quantitative measure of myocardial blood flow, we can see the effect a coronary blockage has on the heart muscle and guide further therapy," said De Cecco, adding that this is currently done by using cardiac PET perfusion (nuclear stress testing).
That modality, however, does not have the option to evaluate the coronaries, he added. "By using CT for both coronary and myocardial evaluation, we can assess the full cardiac status in one examination. By better assessing whether a coronary stenosis results in impaired blood flow, CT perfusion could help to optimize treatment and avoid unnecessary interventions while preventing future adverse cardiac events such as myocardial infarction."
Researchers at Emory are also conducting a study that compares cardiac CTP imaging to nuclear stress testing (positron emission tomography, PET) myocardial perfusion imaging. The study's goal is to include 30 patients, including those who are referred for a clinically indicated myocardial PET perfusion scan, according to De Cecco.
Primary indications for participating patients are cardiac-related complaints and abnormal results in initial testing, such that functional testing is required to assess for myocardial ischemia or infarction, according to Emory researchers.
As the research team pointed out, a catheter is not introduced into the body in cardiac CTP imaging, but vasodilator drugs such as regadenoson and iodine contrast agents are used. In addition, cardiac CTP imaging is similar to PET-based myocardial perfusion imaging, except that radioactive probes are not introduced into the patient's body, the researchers noted, adding that PET-based myocardial perfusion imaging "is currently the gold standard for quantitatively assessing cardiac blood flow, but it does not allow assessment of the coronary arteries."
The actual CTP imaging exam lasts about 30 seconds. In combination with CT angiography, it can be performed in 30-40 minutes total, reducing radiation dose compared to PET-based procedures.
While noting that PET perfusion imaging is currently the clinical standard to quantify blood flow in the heart muscle, "CT allows simultaneous evaluation of the coronaries and myocardium," De Cecco stated. "Using dynamic CT perfusion could be a one-stop shop method to evaluate cardiac status in coronary artery disease patients and [could ultimately help] optimize patient management."
Mark McGraw is a contributing writer.