title: The washout rate of a subcutaneous 99mTc-HSA depot in lower extremity lymphoedema.
abstract: OBJECTIVE
  Lymphoscintigraphy is currently the leading diagnostic modality of lower extremity lymphoedema but has been criticized for being unreliable. Washout rate constants have been investigated and proven to be of diagnostic value in several studies of breast-cancer-related lymphoedema; however, the applicability in lower extremity lymphoedema needs further evaluation. The aim of the study was to verify if washout of (99m) Tc-human serum albumin ((99m) Tc-HSA) is a reliable diagnostic tool in lower extremity lymphoedema.
  
  
  METHODS
  Twenty healthy volunteers and eight patients (11 legs) with lymphoscintigraphy verified lower extremity lymphoedema participated in the study. A depot consisting of 0.1 ml 10 MBq/ml (99m) Tc-HSA was injected subcutaneously into the dorsum of each foot. The depot washout rate was measured using a portable scintillation detector system and time-activity curves were generated. After 30 min of supine rest and 10 min of standardized ergometric exercise, measurements were recorded for 20 min. Following correction for physical decay of (99m) Tc, the depot washout rate constant was calculated using linear regression analysis. Finally depot half-life was calculated from the washout rate constant.
  
  
  RESULTS
  Median half-life for healthy volunteers was 9.4 h (range 2.5-28.3 h). Median half-life for lymphoedema patients was 10.7 h (range 1.5-35.1 h). No statistical significant difference could be detected between healthy volunteers and lymphoedema patients (P = 0.78).
  
  
  CONCLUSIONS
  The washout rate of a subcutaneous (99m) Tc-HSA depot is not a reliable diagnostic tool in examination of lower extremity lymphoedema. Additional examinations revealed in vivo instability of the utilized (99m) Tc-HSA as the likely reason.
authors.affiliation: Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, University Hospital of Copenhagen, Copenhagen, Denmark. mjen0221@bbh.regionh.dk
authors.forename: Mads R
authors.initials: MR
authors.lastname: Jensen
authors.forename: Lene
authors.initials: L
authors.lastname: Simonsen
authors.forename: Tonny
authors.initials: T
authors.lastname: Karlsmark
authors.forename: Jens
authors.initials: J
authors.lastname: Bülow
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D003718:Denmark; D015444:Exercise; D005260:Female; D006207:Half-Life; D006801:Humans; D007279:Injections, Subcutaneous; D016014:Linear Models; D035002:Lower Extremity; D008209:Lymphedema / Q000000981:diagnostic imaging* / Q000378:metabolism; D061305:Lymphoscintigraphy; D008297:Male; D008875:Middle Aged; D015609:Organotechnetium Compounds / Q000008:administration & dosage / Q000493:pharmacokinetics*; D056888:Patient Positioning; D011237:Predictive Value of Tests; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000493:pharmacokinetics*; D015203:Reproducibility of Results; D012709:Serum Albumin / Q000008:administration & dosage / Q000493:pharmacokinetics*; D040521:Subcutaneous Tissue / Q000378:metabolism*; D016683:Supine Position; D014018:Tissue Distribution
chemical_list: D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D012709:Serum Albumin; C107869:technetium Tc 99m serum albumin