Radiation can be reduced without harming image quality

Steps can be taken by cardiologists to reduce radiation without sacrificing image quality, according to a presentation from the American Society of Nuclear Cardiology Annual Meeting.

James A. Case, PhD, chief scientific officer of Cardiovascular Imaging Technologies in Kansas City, Missouri, and the department of nuclear cardiology at the University of Missouri, said during his presentation that physicians should make radiation exposure as low as reasonably achievable (ALARA), but the word “reasonably” is something that is often overlooked.

“We all know that the leading cause of death in the U.S. is not diagnostic radiation, it’s heart disease,” Case said. “Failure to identify heart disease is a much greater risk than any amount of radiation that you can produce out of a CT, PET or SPECT study. We have to keep in mind that ALARA never means sacrificing image quality to minimize dose.”

According to the presentation, physicians can reduce radiation dose for CT, PET and SPECT single-photon emission CT by using better software techniques, better protocols and better instrumentation.

Replacing older systems, such as single-head systems and analog detectors, with digital detectors, fixed 90° or equivalent, cadmium zinc telluride (CZT) systems or low-dose attenuation correction are efficient ways of reducing dose for SPECT.

In terms of software reduction for SPECT, Case said, the use of the filtered back projection for the processing of data should be avoided. New processes such as iterative reconstruction and 3-D imaging should be considered for modeling to reduce dose.

Dosing strategies and protocols can be improved by avoiding the use of thallium, according to Case. He said many practices do not have access to technetium tracers, but moving toward technetium tracers is an ideal way to reduce dosage.

Although PET scans are at a major advantage due to their low radiation dose, shorter half-life tracers and efficiency detectors, allowing physicians to operate at much lower doses, steps can still be taken to reduce patient dose.

According to Case, one of the most beneficial qualities of PET scans is that they do not need collimation to make a picture, increasing the sensitivity of the system. Taking advantage of this quality is one of the simplest ways of reducing radiation dose in patients.

Perhaps the most important way of reducing radiation dose in PET scans is the use of 3-D imaging, which can reduce radiation dose by up to a factor of three without reducing image quality, Case said.

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The reduction of radiation is important for patients and physicians. Case said the most important ways to reduce radiation doses for staff are time, distance and shielding. Since there are different sources of radiation, certain strategies will be more effective than others.

Because of the level of penetrance in SPECT procedures, radiation can be most effectively reduced in staff through distance and dosage, he said.

Due to the short duration, the intensity and low photon beam, CT operators can best protect themselves with time, distance and shielding, according to Case.

Shielding for staff conducting PET scans, however, is highly ineffective, and should rely heavily on lab layout to protect against radiation exposure.

In his concluding slides, Case said there are many ways to reduce radiation dose without sacrificing image quality, such as resolution recovery, the use of CZT systems, advanced protocols, replacing outdated software and equipment, considering individual risk and considering all sources of radiation in the laboratory.

Although there are many different strategies for the reduction of radiation exposure for patients and staff in PET, CT and SPECT scans, Case said filtered back projection is the most important single strategy that physicians can do in a laboratory.

“These are the strategies that you need to do to reduce radiation in your patients,” he said. – by Dave Quaile

Reference:

Case J. Nuclear Cardiology Laboratory in 2017. Presented at: American Society of Nuclear Cardiology Annual Meeting; Sept. 14-17, 2017; Kansas City, Mo.

Disclosure: Case reports he receives royalties from and is an owner of Cardiovascular Imaging Technologies.