The washout rate of a subcutaneous 99mTc‐HSA depot in lower extremity lymphoedema

Summary Purpose:  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 99mTc-Human Serum Albumin (99mTc-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 99mTc-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 99mTc, 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 99mTc-HSA depot is not a reliable diagnostic tool in examination of lower extremity lymphoedema. Additional examinations revealed in vivo instability of the utilized 99mTc-HSA as the likely reason.