Advanced Technology & Protocols Steer SPECT Imaging

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 - Nuclear Medicine
Results from a high-speed SPECT camera are comparable to those of conventional SPECT, but with greatly reduced imaging time, in a 46-year-old woman.
Office-based nuclear cardiology practices are currently re-prioritizing, primarily due to reimbursement cuts called for in the 2010 Medicare Physician Fee Schedule. To keep their practices afloat, nuclear cardiologists are paying attention to several factors, including appropriate patient selection, improved lab management and cautious investment in technology.

Hardware, software & dose

Generally, SPECT myocardial perfusion imaging (MPI) uses a prescribed isotope dosage and SPECT has come under fire recently for its relatively high patient radiation exposure. Advances in hardware and software, however, have made it possible to use less radioisotope, feasibly delivering an effective dose under 10 mSv, says Howard Lewin, MD, medical director for Cardiac Imaging Associates in Los Angeles.

Advanced software services are economically friendly, ranging in price from $20,000 to $30,000, compared with purchasing a new camera, with a price tag ranging from $300,000 to $750,000. Most vendor software upgrades are applicable only for their cameras. Some software-only vendors offer a turnkey solution that can fit on most SPECT cameras, according to Lewin, who uses a turnkey upgrade (UltraSPECT) on a Philips Healthcare camera. The software relies primarily on employing advanced reconstruction algorithms that improve resolution and increase the speed of imaging.

Newer nuclear cameras have smaller footprints and they each have various permutations of detector technology that reduce scatter and improve energy resolution, thus allowing for faster image acquisition, Lewin says. With both hardware and software upgrades, imagers can choose to administer the full isotope dosage in one-half or one-fourth the imaging time, or they can reduce the isotope dosage while imaging at full-time duration. In some select patients, a combination protocol of half-time and reduced isotope is possible.

“Ideally, we’d like to have the radiation exposure below 10 mSv. With half-time imaging, we can get within that low range,” Lewin says. He adds that a one-time fee for the software add-on is cost effective as the improved efficiency can lead to increased throughput, without necessarily extending hours of existing technologists or adding another technologist.

It also is possible with some systems to conduct a single-day rest/stress protocol or a dual-isotope single-day protocol. However, while the improved image quality from these newer technologies has been validated, the accuracy has not. Studies are ongoing to determine whether the improved quality leads to better outcomes compared with the reference standard of catheter angiography.

Nevertheless, the option of half-time acquisition duration with full-dose isotope is particularly appealing for imaging older patients who have difficulty remaining still for long periods. An imaging protocol of three to five minutes for these patients will result in fewer motion artifacts than if they had to remain still for 20 to 25 minutes. Younger patients, who have more tolerance for longer scans and more of a long-term risk for developing cancer from repeated exposure to medical imaging radiation, can undergo SPECT scans at the normal duration but with lower isotope dosages.

Researchers at Mount Sinai Medical Center in New York City conducted a study where they divided patients into three groups based on isotope dose: low-dose stress-only, high-dose stress-only and full-dose rest-stress (reported at ACC.10). Using the Discovery NM 530c SPECT camera (GE Healthcare), they found that the proportion of patients with excellent or good image quality was similar in all three groups, with an average imaging time of three to five minutes. However, compared to the full-dose rest-stress group (41.7 mCi), radiation was decreased on average by 70 percent in the low-dose stress-only group (12.5 mCi) and by 30 percent (29.2 mCi) in the high-dose stress-only group.

While the cost of advanced cameras could be steep for some, they could allow for savings on isotope dosage, as well as increased throughput, which could feasibly allow a facility to shed one or two older cameras and attending staff, says Milena J. Henzlova, MD, a professor of medicine at Mount Sinai and senior author of the study. She and colleagues are designing a study to determine the accuracy of the imaging.

In a multicenter trial, Berman et al reported that high-speed SPECT technology (Spectrum Dynamics) provided quantitative measures of myocardial perfusion and function comparable to those with conventional SPECT in one-seventh of the acquisition (see image) (J Am Coll Cardiol 2010;55:1965–74). There were important differences between the images and further studies must be performed to gauge the accuracy, wrote Frans J. Th. Wackers, MD, from Yale University, in an accompanying editorial.

While these technological advances have been available for about two to three years, they are just now piquing the interest of more practices, Lewin says. The isotope shortage is helping to drive the interest, but he expects the decrease in radiation exposure  to become a significant factor in the next few years.

Appropriate patients  

Once validated for accuracy, the newer generation of cameras and software has the potential to deliver better patient care, according to David Wolinsky, MD, director of nuclear cardiology and the clinical research department at Albany Associates in Cardiology and a clinical assistant professor of medicine at Albany Medical College in New York.

“A report stating that the patient has a ‘mildly abnormal stress test’ is not necessarily helpful in terms of patient management. These patients will most likely undergo further testing, particularly catheterization,” Wolinsky explains. “In these cases, false positives are bound to happen. If we can determine a more definitive diagnosis—meaning a study that is neither technically limited nor equivocal—we are truly acting in the patient’s best interest.” He says the newer generation of hardware and software will be able to better quantify the amount of ischemia, thereby resulting in fewer unnecessary tests.

But practices need more than technology to survive; they also need savvy practice management. Like many practices across the U.S., Wolinsky’s group of 16 cardiologists has seen a drop in its SPECT MPI volume—in their case, a decrease of about 20 percent. In response to the decreased volume, the practice has folded its exercise stress testing into its nuclear lab and is able share nurses and techs between the two testing techniques, as well as with stress echocardiography. “By having fewer tests, we can handle them more efficiently,” he says.

Patient selection is another area that Wolinsky says is critical to maintaining a healthy throughput. “If patients are selected appropriately, there will be less equivocal exams and fewer downstream tests as a result of a suboptimal test,” he says. “Imaging the right patient with the right test with the right protocols leads to better patient care and increased throughput, which is especially important in these times of declining reimbursement and staff cuts.”

SPECT imaging has a proven track record for stratifying patients who are at immediate risk of coronary artery disease, but it doesn’t tell clinicians much about a patient’s longer-term risk. That is where the combination of SPECT with a CT coronary artery calcium (CAC) score might prove beneficial. Chang et al found that asymptomatic patients with normal SPECT results but a CAC score greater than 400 have nearly a four-fold increased risk of cardiac events and death (J Am Coll Cardiol 2009;54;1872-1882).

“Typically, when a patient presents with chest pain and the SPECT test result is normal, we tell them everything looks fine, but this may not be the case,” says senior author John J. Mahmarian, MD, a cardiologist at the Methodist DeBakey Heart and Vascular Center in Houston. “Our most provocative finding was that although a normal SPECT result predicts excellent short-term event-free survival, long-term outcome is significantly worse if the CAC score is severe.”

The combined tests may not be for every patient, but in certain circumstances, there is clinical utility to doing both, says Wolinsky. “Clinicians need to know what they’re going to do with the results. If the tests will guide treatment and stratify the risk, then perform them.”

As practices are challenged to do more with less, advanced technology could play an important role. It also is important to choose patients in accordance with appropriateness criteria and to optimize lab resources as volumes fluctuate among the various stress techniques.