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Managing Dose in PET and SPECT Myocardial Perfusion Imaging
By Dave Fornell
New technologies and stress-only imaging can help cut nuclear imaging dose rates below 10 mSv
Nuclear myocardial perfusion imaging (MPI) with positron emission tomography (PET) and single-photon emission computed tomography (SPECT) have been the gold standard for noninvasive detection of coronary ischemia and infarcts. However, the high radiation doses patients receive are making some providers think twice before referring their patients for nuclear MPI.
Public concern over radiation risks from medical imaging have been brought to the forefront with numerous mainstream media articles in recent years. Newer dose lowering technologies have helped reduce radiation dose by more than 50 percent for cardiac computed tomography angiography (CTA) scans, making it much more attractive as a diagnostic imaging modality. New CT technology — including perfusion imaging with advanced visualization software and CT-fractional flow reserve (FFR) imaging, recently cleared by the U.S. Food and Drug Administration (FDA) — may lead to increased use of CT.
When 64-slice scanners were first introduced nearly 10 years ago, CTA dose was 20-30 mSv, but new reconstruction software, more sensitive detectors and other technologies have reduced this below 10 mSv. With the newest scanners and software, it is now possible to perform CTA with about 1 mSv of dose. This new dose profile has made CTA much more attractive, and nuclear imaging now finds itself in the position as the high radiation dose technology being called into question.
The average background radiation dose in 1985 was around 3.5 mSv, but this has risen to about 6.1 mSv in 2015, due to the expanded use of medical imaging, said Gary Heller, M.D., Ph.D., FACC, FASNC, consultant to nuclear cardiology at Morristown Medical Center, New Jersey. He said nuclear imaging and CT account for the majority of this rise in patient exposure. The American Society of Nuclear Cardiology (ASNC), of which Heller is past-president, recognized this trend and created guidelines in 2010 to achieve the goal of doses of 9 mSv or below using Tc99m. He cited several advances to help achieve this goal.