title: CT Hounsfield units of brown adipose tissue increase with activation: preclinical and clinical studies.
abstract: Brown adipose tissue (BAT) densities assessed as CT Hounsfield units (HUs) were evaluated in a rodent model and in patients to determine whether HUs changed in relation to BAT activity.
  
  
  METHODS
  Serial (18)F-FDG PET/CT was performed on rats under both room temperature control conditions and after 4 h of cold-stimulation, which is known to activate BAT. The maximum standardized uptake values and CT HUs of BAT were measured, and tissues were examined in the laboratory. Image records from cancer patients who underwent PET/CT were reviewed, and 23 patients were identified who displayed both high and low (18)F-FDG uptake into BAT on serial (18)F-FDG PET/CT scans. The maximum standardized uptake values and CT HUs of BAT were compared in these scans.
  
  
  RESULTS
  The mean (+/-SD) CT HUs of cold-activated BAT (-12.4 +/- 22.4) were significantly higher than those (-27.9 +/- 9.6) of the controls in the rat model. The CT HUs of BAT (-71.6 +/- 18.0) in the patients with high (18)F-FDG uptake were significantly higher than those (-104.4 +/- 16.8) of the patients with low (18)F-FDG uptake . A decrease in relative lipid content is seen in activated BAT in rats on histology.
  
  
  CONCLUSIONS
  The CT HUs of BAT increased in activated conditions in both animals and patients, likely because of lipid consumption by activated BAT.
authors.affiliation: Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287-0817, USA.
authors.forename: Shingo
authors.initials: S
authors.lastname: Baba
authors.forename: Heather A
authors.initials: HA
authors.lastname: Jacene
authors.forename: James M
authors.initials: JM
authors.lastname: Engles
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Honda
authors.forename: Richard L
authors.initials: RL
authors.lastname: Wahl
mesh_terms: D002001:Adipose Tissue, Brown / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000818:Animals; D003080:Cold Temperature; D005260:Female; D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18; D006801:Humans; D066298:In Vitro Techniques; D050356:Lipid Metabolism; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D051381:Rats; D011917:Rats, Inbred Lew; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18