Salivary gland scintigraphy: the use of semiquantitative analysis for uptake and clearance

OBJECTIVE: Quantitative analysis of (99m)Tc-pertechnetate salivary gland scintigraphy has been used in the evaluation of salivary gland function, but so far no one method can be considered optimal for this task. In this study, a semiquantitative method providing 2 functional parameters for objective assessment of salivary gland function by scintillation camera imaging was tested. METHODS: Twenty-one patients referred for (99m)Tc-pertechnetate thyroid scanning were studied. Two patients with salivary complaints were also included. Dynamic imaging of the anterior head using a scintillation camera was started after a bolus intravenous injection of 185 MBq (5 mCi) (99m)Tc-pertechnetate at 1 frame per 30 s for 30 min. At 15 min after injection, diluted lemon juice was administered orally. Analysis of the dynamic study included time-activity curves of 4 salivary glands (right and left parotid and right and left submandibular). Two parameters of function were defined: uptake rate, taken as the value of the initial slope of the time-activity curve, and washout fraction, which was the relative mobilizable radioactivity from each salivary gland after ingestion of the sialogogue. A parametric image of the washout fraction was also generated. RESULTS: The images showed gradual uptake in the parotid and submandibular glands. Washout was noted immediately after ingestion of the lemon juice. The pattern of the time-activity curve in all glands showed an early fast-rising part followed by a slow-rising component to nearly a plateau within 6-10 min after injection. The mean value of the uptake rate parameter was 0.10 +/- 0.09 cps/s. There was no significant difference between the parotid and submandibular glands or the right and left sides. Uptake in the parotid gland was 1.5-2 times that in the submandibular gland. The washout fraction was 1.40 +/- 1.60 for the parotid glands and 0.77 +/- 0.41 for the submandibular glands (P = 0.005). CONCLUSION: The quantitative analysis method including the uptake rate and the washout fraction parameters would enable objective assessment of salivary function and provide a reproducible means for follow-up of functional impairment in certain diseases.