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Making your pet scan more accurate
Warm blankets may improve accuracy of PET/CT scans
Anthony J. Brown, MD
Reuters Health
Posting Date: June 23, 2006
Last Updated: 2006-06-23 16:23:34 -0400 (Reuters Health)
NEW YORK (Reuters Health) - Simply providing a warm blanket to patients undergoing PET/CT can dramatically reduce brown fat uptake (BFU), an important cause of both false-positive and false-negative readings when looking for malignancy, according to a new report.
Unlike its better-known (and more abundant) cousin white fat, brown fat protects the body from cold temperatures by taking up metabolites and converting them into heat, rather than ATP. Unfortunately, brown fat can accumulate the glucose tracer used in PET/CT, resulting in scans that either falsely appear to have cancer or ones that have a malignancy masked by BFU.
In agreement with other studies, "our findings suggest that BFU affects roughly 8% of patients in the general PET/CT population," lead author Dr. Medhat Osman, from St. Louis University School of Medicine, told Reuters Health. "Giving a warm blanket to these patients can cut the frequency of BFU by 62%."
Various pharmacologic agents have also shown some efficacy in reducing BFU, most notably propranolol and benzodiazepines. However, many clinicians are uncomfortable giving these drugs to patients for a problem that most likely will not happen.
This led Dr. Osman's team to consider other methods of cutting BFU. They reasoned that giving a warm blanket to patients during PET/CT would help eliminate the heat-producing job for brown fat, resulting in less uptake of the glucose tracer.
The study involved 400 consecutive patients who underwent PET/CT and were randomized to receive or not receive a warm blanket. The blanket, which was heated using a standard hospital blanket warmer (77 degrees Celsius), was applied before the glucose tracer was injected and remained in place through the rest of the uptake phase. Readers blinded to the group assignments evaluated the PET/CT images.
Dr. Osman presented his team's findings earlier this month at the annual meeting of the Society of Nuclear Medicine in San Diego.
As noted, BFU was seen in 8.05% of subjects who did not receive a warm blanket. With blanket use, the rate fell markedly to just 3.04%. The warm blankets were well tolerated by all patients.
"The 62% reduction in BFU seen with warm blankets is more than double the reduction typically reported with pharmacologic agents," Dr. Osman noted. "Whether the reduction in BFU actually translates into improved diagnostic accuracy remains to be determined, but in my own personal experience I believe it does."
Dr. Osman said that even before the imaging period, body temperature as well as other factors, such as drinking coffee or exercising, can affect BFU. For this reason, he said that his group is now calling patients 24 hours before their scheduled appointments to advise them to stay warm, refrain from coffee drinking, and reduce physical activity.
Dr. Osman is hopeful that the use of this calling service in combination with a warm blanket at the time of scanning will completely eliminate BFU. A study investigating this is currently in the works, he added.
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