Will CT overtake nuclear medicine in myocardial perfusion?

It’s not enough that sidelined nuclear reactors are restricting the supply of technetium for cardiac SPECT. Or that reimbursements for SPECT procedures are falling. Now the besieged modality has to contend with a challenge from CT.

Researchers at the Medical University of South Carolina say CT can do myocardial perfusion just as well as the nuclear procedure-or better. As proof, they point to data slated for the March/April issue of the Journal of Cardiovascular Computed Tomography that demonstrate the potential of CT as a one-stop shop for cardiac assessment.

“In my mind, of all the tests that are currently available for the assessment of coronary artery disease, CT has the greatest potential to bring it all together in one modality,” said Dr. U. Joseph Schoepf, a radiologist and director of cardiovascular imaging at MUSC.

All the information needed to evaluate heart patients at MUSC are acquired in single 20-minute exams that expose the patient to less radiation than if the data had been obtained by competing modalities. Recent reports from The New York Times have galvanized public fears about medical radiation. The FDA has responded by proposing initiatives to rein in patient exposure. The protocol at MUSC could help.

“This exam creates the kind of synergy that would make tests less invasive, expose patients to less radiation, and be more cost-effective than the current combination of tests that is thrown at patients to obtain similar information,” Schoepf said.

The MUSC protocol records calcium score while performing coronary CT angiography, stress perfusion, and delayed enhancement exams. Together they can be used to determine whether coronary artery disease is present and, if so, which parts, if any, of the heart muscle are underperfused. They can also establish the viability of tissue affected and the likelihood that interventional procedures will remedy the problems. The CT-only protocol could replace SPECT/CT and cardiac cath as diagnostic studies in the workup of patients suspected of coronary artery disease, he said.

“You can detect stenosis and determine the hemodynamic significance of myocardial perfusion,” Schoepf told me. “If an infarct has occurred, it can be detected, and in that way you can predict the success of revascularization therapy.”

Reducing dependence on cardiac SPECT also cuts the medical community’s need for technetium, which has been in short supply due to the shutdown last spring of the Chalk River reactor in Canada. The recent six-month shutdown of the High Flux Reactor in Petten, the Netherlands, has worsened the problem.

While myocardial perfusion with CT may sound like the ideal solution to multiple problems, the modality still has a ways to go before it reaches routine clinical use. Schoepf and colleagues have assessed only 20 patients with the protocol. (Data from the first three will be published in next month’s Journal of Cardiovascular Computed Tomography.) The protocol can be done only on very sophisticated CT scanners. (Schoepf used a Siemens’ dual-source CT, the Somatom Definition Flash.) And, even with the best equipment handy, CT faces an uphill battle.

“We are running up against an established front of nuclear cardiology that has decades of data to show its usefulness and predictive value (in myocardial perfusion),” Schoepf said. “For CT to replace nuclear studies will take many years of research and a huge patient population to garner the kind of data that would match the existing data supporting nuclear perfusion imaging.”

So it may be only a matter of time until CT overtakes nuclear medicine in myocardial perfusion, but it looks like it’s going to be a very long time.