Rubidium PET edges SPECT in diagnosing coronary artery disease

PET imaging with the rubidium-82 (Rb-82) radiotracer can accurately detect obstructive coronary artery disease and is superior to technetium-99m (Tc-99m) SPECT imaging, according to a meta-analysis published online October 3 by the Journal of the American College of Cardiology.

The study by Canadian researchers found that Rb-82 PET demonstrated sensitivity of 90%, compared with 85% for Tc-99m SPECT, and specificity of 88%, compared with 85% for Tc-99m SPECT, in detecting obstructive coronary disease. In addition, despite the greater initial cost for the procedure, Rb-82 PET is as cost-effective as invasive coronary angiography when subsequent follow-up treatment expenses are considered.

Lead study author is Dr. Brian McArdle from the Molecular Function and Imaging Program at the National Cardiac PET Centre in Ottawa, Ontario.

The researchers noted that myocardial perfusion imaging is commonly used to assess patients with known or suspected coronary artery disease. PET imaging with Rb-82 potentially is more accurate than SPECT and can reduce radiation exposure to patients, but costs more than SPECT. In addition, studies comparing PET with other modalities such as SPECT are limited and don't incorporate recent technological advances like attenuation correction.

In their search of previously research, McArdle and colleagues found 15 PET studies and eight SPECT studies published between January 2006 and January 2012 that met their search criteria. The Rb-82 PET papers covered 1,344 patients, while the Tc-99m SPECT studies included 1,755 patients.

The criteria for inclusion in the study included prospective, observational, and retrospective studies, as well as case series from peer-reviewed journals that involved humans who received either Rb-82 PET or Tc-99m SPECT with both electrocardiography (ECG) gating and attenuation correction. In addition, the studies used invasive coronary angiography as the reference standard to diagnose obstructive coronary artery disease.

The majority of patients in the 15 Rb-82 PET studies were male with an overall mean age of 61.7 years, ranging from 58.9 years to 64.4 years. In the eight Tc-99m SPECT studies, the predominantly male patients had an overall mean age of 61.1 years, ranging from 51.9 years to 63.2 years. The majority of SPECT studies used both exercise and pharmacological stress, and both forms of testing were included in the analysis.

Better sensitivity

The analysis by McArdle and colleagues calculated a combined sensitivity of 90% for Rb-82 PET for detecting obstructive coronary artery disease, compared with a sensitivity of 85% for Tc-99m SPECT. Specificity for Rb-82 PET was 88%, compared with 85% for Tc-99m SPECT.

Excluding some 1,170 patients who had a low likelihood of coronary artery disease had no significant effect on overall accuracy of Rb-82 PET, and only a small decrease in specificity to 86%. In a comparison of studies in which there was stenosis of greater than 50% on invasive coronary angiography, Rb-82 PET also showed no significant difference in diagnostic accuracy.

When researchers included only studies of patients with no documented coronary artery disease (n = 297), again they found no significant increase in overall accuracy when compared with studies that included patients with previous myocardial infarction or revascularization. However, specificity increased from 87% to 91%.

Cost considerations

The study authors also broached the issue of cost for the imaging procedures, stating that one disadvantage of Rb-82 PET is its greater cost compared with SPECT myocardial perfusion imaging. A 2007 study by researchers from the Heart Center of Niagara in Niagara Falls, NY, estimated the cost for a Rb-82 PET scan at approximately $1,850, compared with approximately $1,000 for SPECT (Journal of Nuclear Medicine, July 2007, Vol. 48:7, pp. 1069-1076).

However, McArdle and colleagues noted that the use of rubidium PET led to a decrease in false-positive scans, from 15.6% to 5.2%, which in turn led to a 50% decrease in subsequent referrals for invasive coronary angiography among patients in the Rb-82 PET group.

"This, in turn, led to the overall costs of patient management using both modalities being identical when the cost of increased use of [invasive coronary angiography] was considered," the authors wrote. "Moreover, there was a trend toward better short-term outcomes in the Rb-82 PET cohort."

The current study findings suggest "more widespread use of Rb-82 PET may be beneficial to improve the accuracy of noninvasive detection of obstructive [coronary artery disease]," McArdle and colleagues concluded.

Study disclosures

Two study authors are consultants with Jubilant DraxImage and have received grant funding from a government/industry program, which includes GE Healthcare, Nordion, Lantheus Medical Imaging, and DraxImage. One of those two study authors receives revenues from rubidium generator technology licensed to Jubilant DraxImage, while the other author is a consultant for Lantheus and has received grant funding from Genentech.
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