SPECT MPI: The Lowdown on Lowering Dose

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 - Lowering

Advancements in hardware, software and protocols now allow nuclear medicine groups to lower both dose and acquisition time when performing SPECT MPI studies. For some labs, though, folding new technologies into routine practice may require some sacrifice.

Balancing cost & benefit

In 2010, the American Society of Nuclear Cardiology (ASNC) set a goal for the nuclear imaging community to lower patient radiation exposure in SPECT myocardial profusion imaging (MPI) to less than 9 mSv in half of patients by 2014 (J Nucl Cardiol 2010;17:709-718). ASNC encouraged nuclear cardiology specialists to consider technologies and techniques that allowed them to reduce the injected radiopharmaceutical dose and consequently reduce the radiation dose absorbed by the patient—all while maintaining, or even improving, image quality. To meet ASNC’s challenge, nuclear cardiologists, radiologists and technologists may need to modernize.

According to a survey by ASNC and the consulting company MedAxiom, only 3 percent of cardiology practices that provided the age of their cameras reported having equipment that was less than a year old. About four in five cameras were six years old or older, and one in five were 11 years or older. The survey was conducted in 2011 and included 111 cardiology practices in the U.S.  

Age of Cameras
<1 year 3%
1–5 years 18%
6–10 years 58%
11–15 years 18%
16–20 years 3%
>20 years 0%
Source: American Society of Nuclear Cardiology and MedAxiom, "2012 Nuclear Trending" report

Purchasing a state-of-the-art dedicated cardiac camera solves the sometimes competing issues of time and dose. Typically, longer imaging time allows for lower dose and shorter time requires higher dose to ensure images with diagnostic accuracy to detect ischemia in patients with coronary artery disease. Some of today’s instruments can accomplish both.

But dose typically trumps time, says E. Gordon DePuey, MD, director of nuclear medicine at St. Luke’s-Roosevelt Hospital in New York City. Guidelines such as Image Wisely, Choosing Wisely and ASNC’s patient-centered initiative emphasize minimizing patient exposure and tailoring imaging plans to best serve each patient. Time becomes a factor in scenarios when the patient cannot or will not remain still for the needed duration or where efficiency and throughput are a priority.

“The issue of reducing time is attractive but not overwhelmingly attractive,” DePuey says. “The issue of dose, however, is very important. We really want to reduce dose.”

And money may trump all. While the price of a new, state-of-the-art camera varies, it still falls at a minimum in the six-digit range. The supply contracting company Novation placed the cost of a single-head gamma camera at $200,000 and a SPECT/CT system at $600,000 in its 2012 Diagnostic Imaging Watch report. Other estimates for a new camera suggest $750,000 or higher. Labs may not be able to justify the price, despite the equipment’s technical wizardry.

“Money is tight now,” DePuey says. “Not all labs have enough volume to have a dedicated cardiac camera. They instead might want to use a general nuclear medicine camera for that purpose and other purposes as well. In that case, they can reduce the injected dose and, thus, patient radiation exposure by incorporating new software.”   

Ernest V. Garcia, PhD, director of nuclear cardiology research and development at Emory University School of Medicine in Atlanta, includes value in the equation. The dedicated cardiac SPECT hardware in his lab has allowed a fivefold increase in counts, he says, at no loss in quality. Increased count sensitivity in solid-state cameras means scans can be completed in less time, or physicians can sacrifice some count sensitivity and lower the injected dose.

“Solid-state [cameras] in general do cost more than the conventional cameras but the question is how do you measure cost?” Garcia says. “You pay more but it is more efficient and at a lower dose.” With the ability to perform scans on more patients, the program at Emory also was able consolidate patient flow to one camera and one site.   

His group found that new software let them goose efficiencies by an additional factor of two, for a tenfold improvement. “The other beauty is not only an increase in efficiency, or a reduction in dose, but in fact the images have higher quality,” he says. Their goal is to further reduce dose by another factor of three.  

Alternative routes

Nuclear cardiologists and radiologists also have less