Brown fat uptake of 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG) on a positron emission tomography (PET) scan limits the ability to assess for cancer. Drugs such as benzodiazepine, propranolol, and reserpine have been proposed to reduce this uptake, but the studies have been either small clinical or preclinical trials. As an alternative, we evaluated the effect of controlling the patient's environmental temperature on brown fat uptake of FDG.
Method: From January 1, 2002 to November 30, 2004, patients were identified who had (1) a pattern of FDG uptake in the neck/paravertebral areas suggestive of brown fat, (2) a repeat FDG-PET scan after control of the patient's environmental temperature, and (3) no evidence of cancer in the neck/paravertebral areas by other diagnostic methods. For the follow-up PET scan, all patients wore warm clothing and avoided exposure to cold air during their transit to our facility. After arrival, patients were kept in a separate temperature-controlled room (at least 75 degrees F) for 15 minutes to two hours before FDG injection as well as during the uptake phase. Four physicians blindly and retrospectively assessed the FDG uptake in the neck and paravertebral regions on all initial and temperature-controlled PET scans by visually grading the radioactivity on a semiquantitative scale (0 = background, 1+ = background but <liver, 2+ = equal to liver, 3+ >liver). The changes in maximal SUVs were determined in the left and right neck region. Data were evaluated using a two-tail t-test.
Results: Ten patients met the above criteria. The median age was 32 years with a range of 11-58 years. In comparing the semiquantitative uptake and the SUVs of FDG in the neck and paravertebral areas on the initial PET scan to the temperature-controlled PET scan, the mean decrease and the standard deviation of the decrease demonstrated a statistically significant decrease in with P values range from <0.02 to <0.001.
Conclusion: Controlling the patient's environmental temperature prior to the dosing and during the uptake phase can significantly reduce FDG uptake in brown fat in the neck and paravertebral areas. Further studies are warranted to determine the most effective protocol to control the patient's environmental temperature in order to minimize brown fat uptake.