Salivary Gland Scintigraphy: Tc-99m Pertechnetate

Q: What does salivary gland scintigraphy measure?

It measures the function of the four major salivary glands — both parotid and both submandibular glands — simultaneously after a single intravenous injection of Tc-99m pertechnetate. The study captures two phases: uptake (trapping) of the tracer by the glands, and excretion (washout) of saliva after a sialagogue such as lemon juice stimulates secretion. From the resulting time-activity curves, semiquantitative parameters such as an uptake ratio and an ejection (excretion) fraction are derived.

Q: What is the role of lemon juice or citric acid in the study?

The sialagogue — usually lemon juice, citric acid, or vitamin C given partway through the acquisition — stimulates the glands to secrete saliva. The sudden washout of tracer this produces is what allows the excretion (ejection) fraction to be measured. Without stimulation, the study would show only trapping, not the secretory response that often distinguishes a healthy gland from an impaired one.

Q: How is salivary gland function quantified?

From dynamic images, regions of interest are drawn over each gland and a background region. The uptake ratio compares gland counts to background, and the ejection or excretion fraction is the drop in gland counts after the sialagogue divided by the pre-stimulation maximum. Scoring systems grade each gland by its excretion rate, and the summed score across all four glands gives a semiquantitative index of overall salivary function.

Q: What is salivary gland scintigraphy used for clinically?

The most common indication is the evaluation of dry mouth (xerostomia) and suspected Sjögren's syndrome, where reduced trapping and excretion correlate with gland damage and disease severity. It is also used to assess salivary function before and after radioiodine therapy, after radiotherapy to the head and neck, and to evaluate obstruction or the effect of drugs or procedures on gland function.

Q: Is salivary gland scintigraphy safe, and what is the radiation dose?

Yes. Tc-99m pertechnetate is a diagnostic radiopharmaceutical with a low radiation dose; the effective dose for a typical administered activity is in the low-single-digit millisievert range, and the gland, thyroid, stomach wall, and bladder receive the higher organ doses. Dose coefficients are published by the ICRP, and the study follows the facility's radioactive material license, 10 CFR Part 20 dose limits, and ALARA practices.

Salivary gland scintigraphy uses Tc-99m pertechnetate — a radioactive analog of iodide — to image how the salivary glands trap tracer and then release it when stimulated, quantifying the function of all four major glands from a single injection. Because pertechnetate is handled by the same transporter the glands use to move iodide, the study turns a physiological process into time-activity curves and numbers a physician can follow over time in dry mouth, Sjögren's syndrome, and after radioiodine or radiotherapy. ^{1, 2}

Most imaging of the salivary glands is anatomic: ultrasound, CT, MRI, and sialography show structure, stones, and masses. Scintigraphy is different because it shows function — whether the glandular tissue is still trapping and secreting — and it does so for the right and left parotid and the right and left submandibular glands at the same time. That functional, whole-gland view is its unique contribution, and the physics of the tracer and the acquisition are what make it quantitative. ²

This guide explains the tracer and its trapping mechanism, the dynamic acquisition and the sialagogue step, how uptake and ejection-fraction parameters are calculated, how the results are scored and used clinically, and the dosimetry and regulatory framework. DRPS supports nuclear medicine programs with this work through PET/CT and nuclear medicine physics and accreditation support across Florida, Maryland, Virginia, Washington DC, California, Nevada, and our other service areas.

Introduction

The study works because pertechnetate mimics iodide. The pertechnetate ion (TcO₄⁻) is a monovalent anion of similar size and charge to iodide, and it is concentrated by the sodium-iodide symporter (NIS) that the thyroid, gastric mucosa, choroid plexus, and salivary ductal epithelium all express. Injected intravenously, Tc-99m pertechnetate is trapped by functioning salivary tissue and later discharged into the mouth with stimulated saliva. ^{5, 9}

That two-step behavior — trap, then secrete — is exactly what the imaging protocol is designed to capture. A dynamic acquisition records the gradual accumulation of tracer in each gland, a sialagogue is administered partway through to provoke secretion, and the resulting washout is recorded. The shape of each gland's time-activity curve, and the parameters derived from it, carry the functional information. ^{1, 2}

Tc-99m is almost ideal for this task: it is eluted from a molybdenum-99/technetium-99m generator, emits a single 140 keV gamma photon well matched to a gamma camera, and has a physical half-life of about six hours — long enough for the roughly 30-minute study and short enough to keep the patient dose low. ⁶

Topic Explanation

What is salivary gland scintigraphy?

Salivary gland scintigraphy is a dynamic nuclear medicine study of salivary gland trapping and secretory function using intravenous Tc-99m pertechnetate. After injection, the gamma camera records a series of images of the face and neck over roughly half an hour. The acquisition has two functional phases:

Uptake (trapping) phase. Over the first several minutes, functioning gland tissue traps pertechnetate from the blood. Activity in each gland rises, typically with an early fast component followed by a slower rise toward a plateau within about 6–10 minutes. ¹
Excretion (secretory) phase. A sialagogue — lemon juice, citric acid, or vitamin C — is given partway through the study to stimulate secretion. A healthy gland rapidly discharges tracer-laden saliva into the mouth, producing a sharp drop in gland counts. ^{1, 2}

A background region (usually over the cerebral region or skull) is used to correct the gland measurements, and four regions of interest are placed over the parotid and submandibular glands. ²

The tracer and the trapping mechanism

Pertechnetate is trapped but not organified; unlike radioiodine in the thyroid, it is concentrated and then released rather than incorporated into a larger molecule. In the salivary glands, the ductal epithelium concentrates it, and secretion moves it into the oral cavity. This is also why the same mechanism explains salivary side effects of radioiodine therapy: the glands that concentrate iodide for imaging also concentrate therapeutic I-131, which is the basis for using sialagogues to reduce salivary dose during thyroid cancer treatment. ^{5, 10}

Acquisition parameters

A representative protocol, following the semiquantitative methods validated in the literature, is:

Radiopharmaceutical: Tc-99m pertechnetate, typically 185 MBq (5 mCi) intravenously, with some protocols using somewhat higher activity. ¹
Collimator and window: a low-energy, high-resolution or all-purpose parallel-hole collimator with the 140 keV photopeak and a 15–20% energy window.
Positioning: anterior view of the face and neck, patient supine with the head immobilized.
Dynamic framing: for example 1 frame every 30 seconds for about 30 minutes. ¹
Sialagogue: administered at a defined time, commonly around 10–15 minutes after injection. ¹

Because the measurement is count-based and relies on consistent region-of-interest placement and a reproducible sialagogue step, a standardized protocol with a normal database substantially improves reproducibility — the central message of the quantitative-protocol work by Klutmann and colleagues. ²

Key Technical Principles

From counts to parameters

The analysis starts with the time-activity curve of each gland. Two families of parameters are derived:

Uptake parameters describe trapping. A simple uptake ratio compares background-corrected gland counts to a background region:

UR = \frac{C _{gland} - C _{bkg}}{C _{bkg}}

Loutfi and colleagues instead used the initial slope of the time-activity curve as an uptake-rate parameter, reporting a mean uptake rate of about $0.10 \pm 0.09$ counts per second per second, with no significant difference between parotid and submandibular glands, and parotid uptake roughly 1.5–2 times that of the submandibular glands. ¹

Excretion parameters describe the secretory response to the sialagogue. The ejection (excretion) fraction is the fractional drop in gland counts after stimulation:

EF = \frac{C _{m a x} - C _{m i n}}{C _{m a x}} \times 100%

where $C_{m a x}$ is the maximum (pre-stimulation) gland counts and $C_{m i n}$ is the minimum after the sialagogue. This is the most widely used functional index because it directly reflects the gland's ability to secrete. ^{3, 4}

Accounting for decay

The raw counts also decline because Tc-99m decays. Over a 30-minute study this is modest but should be understood when comparing phases. For physical half-life $T_{1/2}$ and decay constant $λ = ln 2/ T_{1/2}$ ,

A (t) = A_{0} e^{- λ t}, λ = \frac{ln 2}{T _{1/2}} = \frac{0.693}{6.0 h} \approx 0.116 h^{- 1}

Over 30 minutes (0.5 h), the decay factor is $e^{- 0.116 \times 0.5} \approx 0.944$ , so physical decay alone reduces counts by about 6% across the study. Because the ejection fraction is computed from the sharp, sialagogue-driven change over a few minutes, physical decay has only a small effect on it, but decay correction matters for absolute uptake comparisons. ⁶

A grading table

Scoring systems convert the ejection/excretion fraction of each gland into an ordinal grade and sum the grades to give an overall index. The widely cited excretion-rate scoring of Shizukuishi and colleagues uses four grades per gland:

Grade	Excretion rate	Interpretation
0	≥ 50%	Normal function
1	40% to under 50%	Mild dysfunction
2	25% to under 40%	Moderate dysfunction
3	under 25%	Severe dysfunction

Summing the grade of all four glands gives a total score from 0 to 12. In the validation study, the total scintigraphic score showed a strong inverse linear correlation with a sialometric reference test (the Saxon test), with $R^{2} = 0.95$ in the abnormal range, supporting the score as an objective, reproducible index of salivary function. ⁴

Worked example

Suppose the right parotid gland reaches a maximum of $C_{m a x} = 8200$ background-corrected counts before the sialagogue, and falls to $C_{m i n} = 4100$ counts at its minimum after lemon juice. The ejection fraction is:

EF = \frac{8200 - 4100}{8200} \times 100% = 50%

An ejection fraction of 50% sits at the boundary between normal and mild dysfunction, so it would score a grade of 0 (normal) on the Shizukuishi scale. If the same gland had fallen only to 6560 counts, the ejection fraction would be $(8200 - 6560) /8200 = 20%$ , a grade of 3 (severe). The worked numbers show how a single reproducible ROI measurement maps onto a clinically meaningful grade — and why consistent technique matters, because a difference of a few hundred counts can move a gland across a grade boundary. ⁴

Clinical Impact

The main clinical question salivary gland scintigraphy answers is whether the glands still work. That makes it most useful where function, not anatomy, is the issue.

Xerostomia and Sjögren's syndrome. Dry mouth from autoimmune destruction of exocrine glands is the classic indication. Reduced trapping and a blunted ejection fraction correlate with gland damage and disease severity. In a large quantitative series, scintigraphic parameters decreased with increasing histopathologic grade on labial gland biopsy, and a pre-stimulatory oral-activity index above a derived cutoff identified Sjögren's syndrome with a sensitivity of about 79% and a specificity of about 86% — a performance level that makes quantitative scintigraphy a useful objective adjunct to clinical and serologic criteria. ³
Before and after radioiodine therapy. Because the salivary glands concentrate iodide, patients treated with I-131 for thyroid cancer are at risk of sialadenitis and permanent dry mouth. Scintigraphy can document baseline function, and the same sialagogue physics that the study exploits is used therapeutically: lemon juice produces a rapid but transient washout of radioiodine from the parotid glands — on the order of 84% washout in one series — supporting sialagogue strategies to reduce salivary radiation dose. ¹⁰
Head-and-neck radiotherapy. External-beam radiation to the head and neck damages salivary tissue; scintigraphy can quantify the loss and the benefit of gland-sparing techniques.
Obstruction and drug effects. A gland that traps but does not excrete after stimulation suggests ductal obstruction, and the study can show the functional impact of medications or procedures.

The value in all of these is the same: a repeatable number. A single qualitative image is hard to compare over time, but an ejection fraction or a summed score lets a clinician track progression or response, provided the acquisition and analysis are standardized. ^{2, 4}

Practical Optimization Tips

1. Standardize the protocol

Reproducibility is the whole game. Fix the administered activity, the timing of the sialagogue, the framing, the patient positioning, and the ROI method. A normal database acquired on the same system makes individual results interpretable. ²

2. Place regions of interest consistently

Gland and background ROIs should be drawn the same way every time. Small, inconsistent ROIs are a major source of variability in the uptake ratio and ejection fraction; the worked example shows how a few hundred counts can change a grade.

3. Give the sialagogue the same way every time

The ejection fraction depends entirely on a reproducible secretory stimulus. The type (lemon juice, citric acid, vitamin C), amount, and timing should be standardized and documented, because the washout it produces is the measurement.

4. Correct for background and decay

Background subtraction using a cerebral/skull region is essential, and decay correction matters when comparing absolute uptake across the study or between patients. The ejection fraction is relatively robust to decay because it is a short-interval ratio, but do not assume raw counts are decay-free. ⁶

5. Read uptake and excretion together

A gland can fail to trap, fail to excrete, or both. Reporting only one parameter misses half the picture. The combination — trapping (uptake) and secretory response (ejection fraction) — is what localizes the functional defect.

Common pitfalls to avoid

Skipping the sialagogue or giving it inconsistently, which makes the ejection fraction meaningless.
Comparing results across different protocols or cameras without a matching normal database.
Over-interpreting a single value. The literature cautions that some indices are variable; trends and the combination of parameters are more robust than any one number. ^{1, 2}
Ignoring the thyroid and gastric activity that also appear because of shared trapping — useful context, not an artifact.

Regulatory Considerations

Tc-99m pertechnetate is byproduct material, so salivary gland scintigraphy is performed under a radioactive material license and the medical-use rules for diagnostic imaging. The framework is federal (NRC) or the equivalent Agreement State program.

10 CFR Part 35 — Medical Use of Byproduct Material. Diagnostic imaging and localization studies using generator-produced radionuclides such as Tc-99m fall under the medical-use rules, with authorized-user and radiation safety officer responsibilities and recordkeeping. ⁷
10 CFR Part 20 — Standards for Protection Against Radiation. Sets occupational and public dose limits and the ALARA framework that govern tracer handling, administration, and waste. ⁸
Dosimetry (ICRP Publication 128). Tc-99m pertechnetate is a low-dose diagnostic agent; the effective dose for a typical administered activity is in the low-single-digit millisievert range, with the salivary glands, thyroid, stomach wall, and bladder among the organs receiving higher dose. Published ICRP dose coefficients are the basis for patient-dose estimates. ⁵
FDA labeling. Sodium pertechnetate Tc-99m injection is an approved radiopharmaceutical; administered activity and handling follow the prescribing information and the facility's procedures. ⁹

Of the states DRPS serves, radioactive material is regulated by the NRC in Washington, DC and Delaware (direct-NRC, non-Agreement States) and by the Agreement State program in Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey. A board-certified medical physicist supports the imaging physics, quantification, and quality control, while the authorized user and radiation safety officer own the medical-use and radiation safety requirements. For related functional-imaging quantification, see our guides to radiopharmaceutical dosimetry and ICRP 128 and thyroid uptake measurement.

Frequently Asked Questions (FAQs)

What does salivary gland scintigraphy measure?

It measures the function of all four major salivary glands simultaneously after a single intravenous injection of Tc-99m pertechnetate, capturing both the uptake (trapping) of tracer and the excretion (washout) after a sialagogue stimulates secretion. Semiquantitative parameters such as an uptake ratio and an ejection fraction are derived from the time-activity curves.

Why is Tc-99m pertechnetate used instead of another tracer?

Pertechnetate is a monovalent anion that behaves like iodide and is trapped by the same sodium-iodide symporter that concentrates iodide in the thyroid, stomach, and salivary ductal epithelium. That shared mechanism makes it a natural salivary functional tracer, and it is readily available from a generator with a 140 keV photon and a six-hour half-life. ^{6, 9}

What is the role of lemon juice or citric acid in the study?

The sialagogue stimulates the glands to secrete saliva. The washout of tracer it produces is what allows the excretion (ejection) fraction to be measured. Without stimulation, the study would show only trapping, not the secretory response. ^{1, 10}

How is salivary gland function quantified?

Regions of interest are drawn over each gland and a background region. The uptake ratio compares gland to background, and the ejection fraction is the drop in gland counts after the sialagogue divided by the pre-stimulation maximum. Scoring systems grade each gland by excretion rate and sum the grades for an overall index. ⁴

What is salivary gland scintigraphy used for clinically?

Most often for dry mouth and suspected Sjögren's syndrome, where reduced trapping and excretion correlate with disease severity; also for assessing function before and after radioiodine therapy or head-and-neck radiotherapy, and for evaluating obstruction or drug effects. ^{3, 10}

Is salivary gland scintigraphy safe, and what is the radiation dose?

Yes. Tc-99m pertechnetate is a low-dose diagnostic agent; the effective dose for a typical administered activity is in the low-single-digit millisievert range, with the glands, thyroid, stomach wall, and bladder receiving higher organ doses. The study follows the facility's license, 10 CFR Part 20 dose limits, and ALARA. ⁵

Key Takeaways

The tracer mimics iodide. Tc-99m pertechnetate is trapped by the sodium-iodide symporter in salivary ductal epithelium, which is why it images gland function. ^{5, 9}
The study has two phases. Uptake (trapping) and sialagogue-stimulated excretion are both recorded, and both carry functional information. ^{1, 2}
Quantification is the point. Uptake ratio and ejection fraction turn a functional process into reproducible numbers; scoring systems summarize overall function. ^{1, 4}
Standardization drives reliability. A fixed protocol, consistent ROIs, a reproducible sialagogue, and a normal database are what make results comparable over time. ²
The main use is dry mouth and Sjögren's syndrome, with additional roles around radioiodine and radiotherapy. ^{3, 10}
The dose is low and the study is well regulated under 10 CFR Parts 20 and 35, with ICRP dose coefficients for patient-dose estimates. ⁵

Conclusion

Salivary gland scintigraphy is a small study with a clear physical logic: a tracer that the glands handle like iodide, an acquisition built around trapping and a stimulated washout, and a handful of parameters that make function measurable. Its strength is the functional, whole-gland, quantitative view that anatomic imaging cannot provide — and its reliability depends almost entirely on doing the same thing the same way each time, with consistent regions of interest, a reproducible sialagogue, and a matching normal database. Done that way, it gives clinicians an objective number to follow in xerostomia, Sjögren's syndrome, and the salivary consequences of radioiodine and radiotherapy. A board-certified medical physicist helps keep the acquisition, quantification, and quality control defensible. ^{1, 2, 4}

How DRPS Can Help

Diagnostic Radiation Physics Services supports nuclear medicine facilities with the physics behind functional studies like this one: camera and collimator selection, energy-window and uniformity quality control, dynamic-acquisition and quantification review, dose assessment, and accreditation support. Our PET/CT and nuclear medicine physics and medical physicist consulting services help programs keep quantitative studies reproducible and compliant.

DRPS supports facilities across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware.

Related Resources

References

Loutfi I, Nair MK, Ebrahim AK. Salivary gland scintigraphy: the use of semiquantitative analysis for uptake and clearance. J Nucl Med Technol. 2003;31(2):81-85. PubMed
Klutmann S, Bohuslavizki KH, Kröger S, et al. Quantitative salivary gland scintigraphy. J Nucl Med Technol. 1999;27(1):20-26. PubMed
Huang J, Wu J, Zhao L, et al. Quantitative evaluation of salivary gland scintigraphy in Sjögren's syndrome: comparison of diagnostic efficacy and relationship with pathological features of the salivary glands. Ann Nucl Med. 2020;34(4):289-298. doi:10.1007/s12149-020-01448-9. PubMed
Shizukuishi K, Nagaoka S, Kinno Y, et al. Scoring analysis of salivary gland scintigraphy in patients with Sjögren's syndrome. Ann Nucl Med. 2003;17(8):627-631. doi:10.1007/BF02984967. PubMed
International Commission on Radiological Protection. ICRP Publication 128: Radiation Dose to Patients from Radiopharmaceuticals — A Compendium of Current Information Related to Frequently Used Substances. Ann ICRP. 2015;44(2S). icrp.org
National Institute of Standards and Technology. Technetium-99m decay data (140 keV photon; 6.0 h half-life). nist.gov
U.S. Nuclear Regulatory Commission. 10 CFR Part 35: Medical Use of Byproduct Material. nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR Part 20: Standards for Protection Against Radiation. nrc.gov
U.S. Food and Drug Administration. Sodium Pertechnetate Tc 99m Injection — prescribing information. accessdata.fda.gov
Van Nostrand D, Bandaru V, Chennupati S, et al. Radiopharmacokinetics of radioiodine in the parotid glands after the administration of lemon juice. Thyroid. 2010;20(10):1113-1119. doi:10.1089/thy.2009.0429. PubMed