title: Quantitation of cell number by a positron emission tomography reporter gene strategy.
abstract: OBJECTIVE
  An important potential of positron emission tomography (PET) is the capacity for quantitation of cell signals in an anatomic regions of interest. However, little is known about the constraints and parameters for using PET signal detection to establish cell numbers in regions of interest. In this study, we determined the correlation of PET signal to cell number, and characterized the cellular limit of detection for PET imaging.
  
  
  METHODS
  Cells expressing the herpes simplex virus type I thymidine kinase PET reporter gene (HSV1-sr39TK) were detected following accumulation of [(18)F]FHBG (9-[4-[(18)F]-fluoro-3-(hydroxymethyl) butyl]guanine) by microPET scanning and quantitation.
  
  
  RESULTS
  When cells were cultured with [(18)F]FHBG in vitro, and then transferred to a model vascularized site, 73% retention was observed one hour post-transfer. Using this information, and the measured attenuation of PET signal in whole mouse scans, we assessed the per-cell uptake of [(18)F]FHBG in the vascularized site following standard parenteral administration of the substrate. We observed a cell number-dependent signal, with a limit of detection calculated as 10(6) cells in a region of interest of 0.1 mL volume. Quantitatively similar parameters were observed with stably tranfected N2a glioma cells and retrovirally transduced primary T lymphocytes.
  
  
  CONCLUSIONS
  These methods and findings provide a strategy for quantitation of cellularity using PET imaging that has implications for both experimental models and clinical diagnosis.
authors.affiliation: Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
authors.forename: Helen
authors.initials: H
authors.lastname: Su
authors.forename: Ashley
authors.initials: A
authors.lastname: Forbes
authors.forename: Sanjiv S
authors.initials: SS
authors.lastname: Gambhir
authors.forename: Jonathan
authors.initials: J
authors.lastname: Braun
mesh_terms: D000818:Animals; D002452:Cell Count / Q000379:methods*; D002460:Cell Line; D005260:Female; D017930:Genes, Reporter; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis; D008214:Lymphocytes / Q000201:enzymology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D049268:Positron-Emission Tomography; D018139:Simplexvirus / Q000201:enzymology; D013937:Thymidine Kinase / Q000032:analysis / Q000235:genetics
chemical_list: C113308:9-(4-fluoro-3-hydroxymethylbutyl)guanine; D006147:Guanine; D013937:Thymidine Kinase