Evaluation of the hepatobiliary excretion of technetium-99m-MAG3 and reconstitution factors affecting radiochemical purity.

UNLABELLED: Technetium-99-MAG3 is a renal tubular function agent. However, sporadic liver and gallbladder visualization have raised questions about kit stability, impurities and nonrenal routes of excretion. To address these issues, studies were conducted to optimize the labeling efficiency of the TechneScan MAG3 kit and to evaluate the hepatobiliary excretion of the MAG3 complex. METHODS: Thirty-six vials of the commercial formulation of 99mTc-MAG3 were prepared according to manufacturer's instructions and evaluated for radiochemical purity using two methods: a combination of high-performance liquid chromatography and paper chromatography (HPLC/PC); and the manufacturer's miniature chromatography system (Sep-Pak procedure). RESULTS: The labeling efficiency was significantly higher when the kit was reconstituted with 10 ml (96.6%) of saline versus 5 ml (91.4%) (p < 0.01). The radiochemical purity of the kits remained stable for up to 6 hr, but the purity determined by Sep-Pak averaged 2.5% higher than that determined by HPLC procedures (p < 0.01). Rat studies to evaluate renal and hepatobiliary elimination of MAG3 showed no difference in the %ID excreted into the urine by 60 min in all groups of animals studied. However, the %ID excreted into the bile was significantly higher for the kit formulation than the HPLC-purified MAG3, 9.9% versus 6.6% (p = 0.0475). CONCLUSION: The radiochemical purity of the TechneScan MAG3 kit can be improved by reconstituting with larger volumes. In addition, the studies in rats suggest that fasting or kit impurities may be a contributing factor to increased hepatobiliary visualization in patient studies.

Early stage melanoma: lymphoscintigraphy, reproducibility of sentinel node detection, and effectiveness of the intraoperative gamma probe.

PURPOSE: To assess the influence of lymphoscintigraphic and intraoperative gamma probe findings on the surgical management of melanoma and to test reproducibility of lymphoscintigraphic findings. MATERIALS AND METHODS: After lymphoscintigraphic identification of the sentinel node, intraoperative gamma probe localization and sentinel lymph node excision were performed in 25 patients. To assess reproducibility, 13 patients underwent lymphoscintigraphy twice within 2-17 days. A modified preparation of technetium-99m sulfur colloid with smaller particles than routinely obtained was injected intradermally around the lesion. Dynamic flow images were obtained at 10 seconds per frame followed by a series of static images obtained every 5 minutes for 30 minutes. RESULTS: A sentinel node was identified in all patients. In eight patients, multiple drainage pathways were seen and surgical management was changed. In 11 of the 13 who underwent lymphoscintigraphy twice, sentinel node identification was reproducible. CONCLUSION: Lymphoscintigraphy is reproducible in detection of the sentinel node and with the surgical probe helps effectively guide surgical management.