What is the recommended protocol for a patient undergoing salivary scintigraphy?

Salivary Scintigraphy Protocol

Salivary gland scintigraphy should be performed using 370-925 MBq (10-25 mCi) of Tc-99m pertechnetate with dynamic imaging for 25-40 minutes, followed by administration of a sialogogue (typically 3 mL lemon juice or carbachol) approximately 15 minutes post-injection to assess excretory function. 1, 2, 3

Pre-Procedure Preparation

Patient Instructions

• Schedule the study at a standardized time (ideally 9-11 AM) to minimize diurnal variation in salivary gland function 4
• Fasting is not required, but patients should avoid eating for at least 1 hour before the procedure 4
• Avoid oral hygiene products (including tooth brushing) for 1-2 hours prior to the study 4
• No smoking for 4 hours and no alcohol consumption for 12 hours before the examination 4
• Avoid vigorous exercise for at least 24 hours (ideally 48 hours) prior to the study 4

Baseline Assessment

• Measure unstimulated whole salivary flow rate before the scintigraphic study, as this correlates with submandibular uptake and excretion parameters 3
• Rinse mouth with water 10 minutes before radiopharmaceutical injection 4

Imaging Protocol

Radiopharmaceutical Administration

• Inject 370-925 MBq (10-25 mCi) of Tc-99m pertechnetate intravenously as a single bolus 1, 2, 3
• The uptake of Tc-99m pertechnetate reflects intact salivary gland parenchyma and allows simultaneous evaluation of all four major salivary glands (bilateral parotid and submandibular glands) 1, 2

Dynamic Imaging Sequence

Phase 1: Uptake Phase

• Begin dynamic acquisition immediately after radiopharmaceutical injection 2, 5
• Acquire sequential images for 12-15 minutes (typically 12 × 1-minute frames) in anterior projection 2, 5
• Patient should be positioned supine with the gamma camera positioned anteriorly to include all major salivary glands in the field of view 1

Phase 2: Stimulation Phase

• Administer sialogogue at 15 minutes post-injection (3 mL lemon juice orally or carbachol injection) 1, 5
• Continue dynamic imaging for an additional 16-25 minutes (typically 16 × 1-minute frames) to assess excretory function 2, 5

Optional SPECT Acquisition

• SPECT imaging may be performed after the planar dynamic sequences (4-minute acquisition) to assess intra-glandular dose-function relationships, particularly useful in post-radiotherapy patients 5
• SPECT should be acquired both before and after sialogogue administration if performed 5

Quantitative Analysis

Essential Parameters to Calculate

• Parotid uptake ratio (PU): Reflects parenchymal function of parotid glands 3
• Submandibular uptake ratio (SU): Reflects parenchymal function of submandibular glands; correlates with unstimulated salivary flow 3
• Percentage parotid excretion (%PE): Measures excretory function after stimulation 3
• Percentage submandibular excretion (%SE): Measures excretory function; correlates with unstimulated salivary flow 3
• Salivary excretion fraction (SEF): Can be calculated from geometric mean of planar images or from SPECT data for each transverse plane 5

Image Analysis Method

• Use geometric mean of anterior and posterior planar images for accurate quantification when biplanar imaging is performed 5
• Draw regions of interest (ROI) over each major salivary gland and background regions 2
• Generate time-activity curves to assess both uptake and excretion phases 1, 2

Clinical Applications

Diagnostic Utility

• Sjögren's syndrome: All parameters (PU, SU, %PE, %SE) are significantly reduced compared to normal controls 3, 6
• Post-radioiodine therapy: Primarily affects %PE, with less impact on uptake parameters 3
• Post-radiotherapy for head/neck cancer: SPECT can demonstrate dose-dysfunction relationships within individual glands 5
• Sialolithiasis: Can assess parenchymal damage beyond mechanical obstruction 1

Key Advantages

• Simultaneous functional assessment of all four major salivary glands with a single injection 1, 2
• Quantifies both parenchymal function and excretion fraction, unlike morphological imaging (ultrasound, CT, MRI) 1, 2
• Non-invasive, reproducible, and well-tolerated by patients 1, 2, 6
• Accepted diagnostic criterion for Sjögren's syndrome by the American-European consensus group 6

Common Pitfalls to Avoid

• Do not rely solely on visual interpretation: Schall's categorical classification is subjective with limited capacity to discriminate borderline results; always perform quantitative analysis 6
• Ensure adequate stimulation: The sialogogue must be administered at the appropriate time (15 minutes post-injection) to properly assess excretory function 1, 5
• Account for diurnal variation: Standardize timing of studies to the same time window for serial examinations 4
• Consider SPECT for radiation therapy patients: When large variations in radiation dose exist within the glands (>20 Gy), SPECT provides superior assessment of regional dysfunction 5