title: Autoradiographic quantification of 18F-FDG uptake in experimental soft-tissue abscesses in rats.
abstract: OBJECTIVE
  To use semiquantitative autoradiography to investigate fluorodeoxyglucose (FDG) uptake, distribution, and cellular localization in acute, early chronic, and late chronic soft-tissue infections.
  
  
  METHODS
  Unilateral calf-muscle abscesses were induced in 12 Sprague-Dawley rats by means of intramuscular inoculation of 0.1 mL of bacterial suspension (Staphylococcus aureus, 1.2 x 10(9) CFU/mL). Following injection of 130-180 MBq of fluorine 18 FDG, autoradiography of the abscess and contralateral muscle was performed (10-microm section thickness) on days 2, 5, and 9 after infection. Detailed spatial correlation of autoradiographs and histopathologic samples was performed by means of image fusion. Regions of interest were placed in the abscess wall, and measured gray values were converted to kilobecquerels per cubic centimeter according to kilobecquerels of injected activity per gram of body weight, which yielded standardized uptake values (SUVs).
  
  
  RESULTS
  Acute abscess formation was characterized by central necrosis predominantly surrounded by neutrophils and a second necrotic tissue layer that bordered neutrophil infiltrates peripherally. Areas with increased FDG uptake corresponded to cellular inflammatory infiltrates, mainly granulocytes. The corresponding SUV was calculated to be 4.08 +/- 0.65 (mean +/- SD). Early chronic phase showed mixed cellular infiltrate of granulocytes and macrophages that surrounded central necrosis with interspersed fibroblasts and only residual muscle necrosis layer within the abscess wall. FDG uptake was located where granulocytes and macrophages were present, as in acute infection (SUV = 5.32 +/- 2.30). Late chronic infection was characterized by a prominent layer of macrophages around residual central necrosis and fibroblast-enriched granulation tissue delineating the infection from muscle tissue. FDG uptake clearly coincided with the macrophages, and no substantial increase of FDG uptake was detected within fibroblast-enriched granulation tissue. The SUV was calculated as 7.97 +/- 0.21. Results of Kruskal-Wallis ANOVA demonstrated that the change in SUV with time was statistically significant (chi(2) = 7.42, P <.05).
  
  
  CONCLUSIONS
  The highest FDG uptake coincides with areas of inflammatory cell infiltrates, predominantly in neutrophils in the acute phase and in macrophages in the chronic phase of soft-tissue infection.
authors: Division of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland. achim.kaim@dmr.usz.ch
authors: Achim H
authors: AH
authors: Kaim
authors: Bruno
authors: B
authors: Weber
authors: Michael O
authors: MO
authors: Kurrer
authors: Jochen
authors: J
authors: Gottschalk
authors: Gustav K
authors: GK
authors: Von Schulthess
authors: Alfred
authors: A
authors: Buck
mesh_terms: D000038:Abscess / Q000000981:diagnostic imaging*; D000818:Animals; D001345:Autoradiography; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D007249:Inflammation / Q000000981:diagnostic imaging*; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D019788:Fluorodeoxyglucose F18