Warm Blankets Reduce the Chance of Cancer False Positives in PET Scans
By Zosia Chustecka
Medscape Medical News 2006.
False-positive results on positron emission tomography (PET) with computed tomography (CT) scans, which may suggest that there is a malignancy when in fact there is none, can be reduced by asking patients to wrap up in a warm blanket while they wait for the scan, US researchers have shown.
This measure is about twice as effective as the current option of pretreating with diazepam or beta-blockers, they reported at the Society of Nuclear Medicine 2006 annual meeting earlier this month. The study won third prize in the technologist section of the meeting.
Offering heated blankets to patients is a solution that "not only is effective but is also low cost and extremely easy for any PET facility to implement," said lead researcher Medhat Osman, MD, PhD, assistant professor of nuclear medicine at Saint Louis University School of Medicine in Missouri.
False-positive results occur when the radiotracer used for the scan is taken up by brown adipose tissue. "The resultant image looks like an area of increased metabolic activity, which is the same as what we see when there is a malignancy," Dr. Osman explained in an interview.
The same phenomenon can also lead to false negatives; for example, brown fat uptake (BFU) in the lymph nodes can cause a blending in the image that masks the tumor. Ambiguous results like these occur in as many as 9% of patients, he added.
Simple, Noninvasive Measure
Dr. Osman and colleagues studied 400 consecutive patients undergoing scans on a Gemini PET/CT scanner (Philips Medical Systems, Andover, Massachusetts) 1 hour after having an intravenous injection of the radiotracer, 18F-fluorodeoxyglucose, administered in a weight-adjusted dose of 0.14 mCi/kg.
The patients were undergoing scans for known or suspected cancer of various types.
One group of patients was given a warm blanket and remained covered during the 1-hour uptake phase. The blanket had been heated in a Pedigo (Vancouver, Washington) P-2010 blanket warmer at an internal temperature of 77ºC.
Retrospective reviews of the scans showed that 5 of 164 patients (3.04%) in the blanket group had BFU of the radiotracer, compared with 19 of 236 patients (8.05%) in the nonblanket group. Hence, use of the warm blanket decreased the frequency of BFU by 62.2%, the researchers conclude.
Current measures used to try to reduce BFU include the use of diazepam and beta-blockers, and other studies have shown that they do so by about 30%. "So our finding shows a considerable improvement over this," Dr. Osman said.
"A warm blanket is more than twice as effective, and patients don't have to worry about negative drug interactions — or how they are going to get home after their scan," he said.
Previous research conducted by the same group has shown that strenuous activity can increase the chance of a false-positive result on a PET/CT scan. "We always call our patients 24 hours before their appointments as a reminder," Dr. Osman said. "Now we can advise them to take it easy and tell them to bundle up and stay warm to ensure the most accurate scan."
He added that his team is now conducting a further study in which patients are advised to dress warmly for 24 hours before the scan as well as use a heated blanket to see whether this will reduce the BFU of the radiotracer even further.
Society for Nuclear Medicine 2006 annual meeting: Abstract 2022. June 3 – 7, 2006.
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