Both PET and CT are excellent cardiac imaging modalities, but how does their individual value play out when combined in a hybrid scanner? Is hybrid imaging poised to upstage cardiology’s imaging workhorse, SPECT?
PET/CT has carved a niche, albeit a somewhat limited one, in cardiology. “Compared to classical pure PET, PET/CT has the advantages of detecting coronary calcium, slightly higher resolution, and minimally faster throughput, but the disadvantages of significantly higher radiation dose to the patient and more frequent misregistration artifacts that require correction for adequate clinical interpretation,” explains K. Lance Gould, MD, professor of cardiovascular medicine at University of Texas Medical School in Houston.
Most cardiology departments that have invested in hybrid technology use the system for sequential studies rather than simultaneous exams. The clinical and operational benefits of the model are fairly clear.
Hybrid cameras acquire perfusion information, along with the coronary artery calcium (CAC) score without the need for contrast and with an average of 1 mSv of additional radiation exposure for the CAC study. Many larger practices leverage the hybrid scanner in a comprehensive manner: half the day for PET imaging and the other half for CT imaging.
Flexibility represents half of the PET/CT equation. The economics of cardiac PET improved with the release of the 2010 Medicare Physician Fee Schedule, which raised myocardial PET perfusion reimbursement 24 percent and slashed SPECT reimbursement 36 percent. The differential may make the $1.5 million price tag of PET/CT slightly more palatable.
“At Cedars-Sinai Medical Center, we have a dedicated cardiac PET/CT scanner that is used for simultaneous rest/stress myocardial perfusion imaging and coronary calcium scanning,” says Daniel S. Berman, MD, director of cardiac imaging and nuclear cardiology at Cedars-Sinai in Los-Angeles. The PET/CT scanner is not used for simultaneous PET myocardial perfusion and coronary CT angiography studies, since it is not known prior to testing with either of these examinations if the other test will be indicated, Berman says.
One of the two tests should suffice to answer the clinical question in most cases, agrees Vasken Dilsizian, MD, professor of medicine and radiology at the University of Maryland Medical Center in Baltimore.
PET/CT in evolution
The ongoing technetium shortage has thrust cardiac PET into a more prominent role at many hybrid cardiology sites. For example, since the technetium shortage, PET has pinch hit for SPECT at Brigham and Women’s Hospital. “All patients who require pharmacological perfusion studies are being scanned on the PET scanner. On days of no SPECT isotope, we have sometimes used PET instead of SPECT, especially if the test results are needed right away. For patients who can reschedule their test, we have rescheduled the exercise SPECT scans to days of isotope availability,” explains Sharmila Dorbala, MD, director of nuclear cardiology at Brigham and Women’s Hospital in Boston.
The current market reality, however, is that most cardiology practices do not have the flexibility to substitute PET for SPECT. “There are almost 12,000 SPECT cameras available for screening patients for coronary diseases vs. only 1,600 PET cameras,” explains Dilsizian.
The upshot? Although cardiac PET has gained traction in the last year due to the SPECT isotope shortage and better PET reimbursement, a wholesale switch from SPECT to either PET or PET/CT in the near future is unlikely. First, cardiac SPECT has decades of research behind it and cardiologists are comfortable with the technology. Second, a SPECT camera is much less expensive than a PET scanner. And third, technological advancements in SPECT imaging have made this diagnostic workhorse competitive. For now, the use of cardiac PET/CT has found a small niche delivering perfusion and CAC data, which could change in a heartbeat as medical imaging continues to evolve.