CTA and MRA equally accurate for coronary imaging

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First direct comparison of newer imaging modalities shows equal accuracy in diagnosing coronary artery stenosis.

Newer MRI and CT-angiography proved nearly equal in identifying significant stenosis, and were equally accurate in predicting the need for revascularization in patients with known coronary artery disease (CAD), in the first direct comparison of MRA and CTA, say German researchers.

32-channel MRI offers equal accuracy in diagnosing stenosis with CTA, and is less invasive than conventional angiography.In their study, the researchers led by Dr. Ashraf Hamdan, of the German Heart Institute, compared the diagnostic accuracy of 32-channel, 3.0-T MRI and 64-slice CT scan before conventional x-ray angiography. Their report appeared in the January, 2011, issue of the Journal of the American College of Cardiology: Cardiovascular Imaging.

“Thirty-two channel 3.0-T MRI and 64-slice CT angiography similarly identify significant coronary stenosis in patients with suspected or known coronary artery disease scheduled for elective coronary angiography,” the authors wrote, “however, CT angiography showed a favorable trend toward higher diagnostic performance.”

The prospective study involved 120 consecutive patients with known or suspected CAD, all of whom underwent both MRI and CT scans before elective x-ray angiography. They compared the ability of either modality to detect stenosis of 50 percent or greater in artery segments greater than 1.5 mm in diameter. A total of 322 coronary vessels were imaged.

Conventional catheter angiogram using dye remains the gold standard for diagnosing coronary artery stenosis.MRI accurately diagnosed stenosis in 83 percent of the patients with 87 percent sensitivity. That compared to an accurate diagnosis rate of 87 percent for the CT scans with 90 percent sensitivity.  Both methods were 100 percent accurate in diagnosing three-vessel and left main disease, although numbers of these were very small, with two patients having left main disease and 11 with three-vessel disease.

The authors also reported that both methods provided equally accurate predictions of the need for revascularization, but that conventional angiography was significantly better. Angiography via an arterial catheter is accepted as the gold standard for the diagnosis of coronary artery stenosis, but it is an invasive procedure requiring threading a catheter through arteries to areas of interest, where a dye is injected and an x-ray is taken. The procedure carries rare, but serious risks and takes one to three hours.

Hamdan told The Hub that MRI and CT both hold advantages and disadvantages that make them useful in addition to conventional angiography in certain situations.

MRI can be used in diagnosing heart disease, particularly when examining ventricular function, myocardial viability, and myocardial ischemia,” Hamdan said via e-mail. “In addition, MRI can be used to differ(entiate) between ischemic and non-ischemic cardiomyopathy.”

The advantage of conventional catheter angiography is that treatment with a stent can be done immediately at the time of diagnosis, whereas patients with stenosis diagnosed by MRI or CT will likely need to schedule catheterization for treatment on another day. In addition, CT angiography requires exposure to radiation and potentially toxic dyes. Hamdan thinks that combining MRI with coronary angiography might provide a significant advantage for certain types of patients.

“In the future a combined use of MRI stress testing and coronary angiography or CT stress testing and coronary angiography in the same imaging session would provide incremental and crucial benefit for the evaluation of coronary artery disease,” he said.

In an editorial accompanying the study, Dr. Paul Schoenhagen, of the Cleveland Clinic, and Dr. Eike Nagel, of King's College in London, pointed out that although coronary angiography remains the preferred approach for patients at high risk, it is a more invasive procedure that carries risks.

In an interview with The Hub, Schoenhagen said that the choice of one modality over another is not about which is better, but which is best for the individual patient.

“The main difference/advantage is the non-invasive nature of CT and MRI (with lower examination time, higher patient comfort, etc.” Schoenhagen said. “However, risk-benefit must be considered for individual patient and depends on both patient characteristics and the clinical scenario. In experienced centers, the physicians will direct the individual patient to the most appropriate test.”

By: Michael O'Leary, contributing editor Health Imaging Hub

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