Tc-99m DMSA Renal Cortical Scintigraphy

Tc-99m DMSA renal cortical scintigraphy binds to proximal tubular cells and images functioning renal cortex, making it the reference test for renal scarring and for measuring differential renal function. A defensible study depends on correct geometric-mean quantification with background subtraction, SPECT or pinhole imaging in children, weight-based pediatric activity, and documented dose-calibrator and radiochemical-purity quality control.

Technetium-99m dimercaptosuccinic acid (DMSA) occupies a specific niche in pediatric and adult nephro-urology. Unlike the dynamic agents used to assess drainage and obstruction, DMSA is a static cortical agent: it is retained in the functioning proximal tubules, so the image is a map of viable renal parenchyma. That is exactly what a clinician needs to detect acute pyelonephritis, chronic scarring, dysplasia, and ectopic tissue, and to quantify how function is divided between the two kidneys.¹²

This article explains the tracer mechanism, the quantification math that turns counts into a differential renal function, why SPECT or pinhole imaging is now standard, the dosimetry, and the QC and regulatory framework a defensible program needs. DRPS supports these programs through its PET/CT and nuclear medicine physics and medical physics consulting services.

Introduction

DMSA answers a different question than a dynamic renogram: it shows where functioning cortex is, not how urine drains. After intravenous injection, roughly 40–50% of Tc-99m DMSA is taken up and retained by the proximal convoluted tubular cells of the renal cortex over several hours, with slow blood clearance and low urinary excretion during the imaging window. Imaging at 2–4 hours (commonly ~3 hours) therefore produces a high-contrast image of functioning parenchyma against a low soft-tissue background.¹²

Two clinical products come from that image. First, a qualitative map of cortical defects — focal photopenia from acute pyelonephritis or permanent scars. Second, a quantitative differential (split) renal function, the percentage of total functioning cortex contributed by each kidney. Both depend on careful acquisition, quantification, and quality control; small processing errors change the reported split and can change management.²³

This guide walks through the tracer, the quantification method with a worked example, the planar-versus-SPECT decision, the clinical impact of getting the numbers right, practical tips, the dosimetry, and the regulatory context under 10 CFR Part 35 and ICRP Publication 128.

Topic Explanation

What Tc-99m DMSA measures

Tc-99m DMSA is a cortical retention agent: its distribution reflects the mass of functioning proximal tubular tissue. Because uptake depends on both cortical blood flow and tubular function, a region of acute pyelonephritis or an established scar appears as a focal area of reduced tracer — a cortical defect. Global reduction on one side reduces that kidney's share of the differential function.

Compared with the dynamic agents covered in our companion post on renal scintigraphy, split function, and GFR, DMSA trades information about drainage for a cleaner picture of parenchyma:

For facilities building or auditing these protocols, cortical and dynamic renography should be reviewed together with radiation safety training and the physics QC program so acquisition and processing are standardized across technologists.

Acquisition: planar, oblique, and cross-sectional

A standard DMSA study acquires high-count static planar images — posterior and both posterior-oblique projections — using a low-energy high-resolution (LEHR) collimator and a 140 keV Tc-99m photopeak window. In infants and small children, pinhole magnification views sharpen cortical detail. Current SNMMI and EANM guidance recommends that SPECT (or pinhole in the youngest patients) be a routine part of the protocol, because tomographic imaging detects cortical defects that overlapping planar projections can hide.²⁴ For the tomographic QC that underlies quantitative cortical imaging, see SPECT/CT quality control.

Key Technical Principles

Depth correction with the geometric mean

Planar counts from a posterior view underestimate an anteriorly positioned kidney because of attenuation. When both anterior and posterior projections are acquired, the geometric mean combines them to reduce this depth dependence. For a kidney with background-subtracted anterior counts $C_{\text{ant}}$ and posterior counts $C_{\text{post}}$:

$$C_{\text{GM}}=\sqrt{C_{\text{ant}}\times C_{\text{post}}}$$

The geometric mean is far less sensitive to kidney depth than either single view, which matters when one kidney is ectopic or malrotated.

Background subtraction and differential renal function

Each kidney region of interest (ROI) contains counts from overlying and underlying soft tissue. A perirenal background ROI is used to subtract this contribution before quantification. For a kidney ROI with gross counts $C_{\text{gross}}$, area $A_{\text{kidney}}$, and a background ROI with count density $b$ (counts per pixel):

$$C_{\text{net}}=C_{\text{gross}}-\left(b\times A_{\text{kidney}}\right)$$

The differential (split) renal function for the left kidney is then its net (geometric-mean) counts as a fraction of the total:

$${\text{DRF}}_{\text{L}}=\frac{C_{\text{net,L}}}{C_{\text{net,L}}+C_{\text{net,R}}}\times 100\%$$

Worked example. Suppose the background-subtracted geometric-mean counts are $C_{\text{net,L}}=82,000$ and $C_{\text{net,R}}=118,000$. Then:

$${\text{DRF}}_{\text{L}}=\frac{82,000}{82,000+118,000}\times 100\%=\frac{82,000}{200,000}\times 100\%=41\%$$

A left kidney at 41% (right at 59%) falls below the roughly 45–55% symmetric range and is flagged as reduced left-sided function. Because the denominator is the sum of both kidneys, an error in one ROI or in the background region shifts both reported percentages — a reminder that consistent ROI and background placement is the single most important processing discipline in DMSA quantification.²³

Dosimetry: activity in, effective dose out

The administered activity is measured in a dose calibrator and converted to effective dose with published biokinetic coefficients. Using ICRP Publication 128, the adult effective-dose coefficient for Tc-99m DMSA is:

$$e=8.8\times 10^{-3}\text{mSv/MBq}$$

For a typical adult administration of $A=185\text{MBq}$ (5 mCi):

$$E=A\times e=185\text{MBq}\times 8.8\times 10^{-3}\frac{\text{mSv}}{\text{MBq}}\approx 1.6\text{mSv}$$

The kidneys receive the highest absorbed dose per unit activity, consistent with the cortical retention mechanism. Pediatric administrations are reduced and weight-based; the per-MBq effective-dose coefficient is higher in children, which is why activity is scaled down rather than held constant.⁵⁶

Clinical Impact

Getting the split right changes management

Differential renal function is not an academic number. In a child with a duplex system, an obstructed moiety, or reflux nephropathy, the split can influence whether a kidney or moiety is watched, treated medically, or considered for surgery. Studies of DMSA grading in vesicoureteral reflux show that the presence and extent of cortical changes — not reflux grade alone — track with the treatment ultimately chosen, so an accurately quantified and read DMSA study feeds directly into the clinical decision.⁷ A processing error that moves a 45% kidney to 40%, or that misses a cortical defect visible only on SPECT, can nudge that decision in the wrong direction.

Why SPECT detection matters

Overlapping tissue on planar projections can obscure small cortical defects. Comparative work has shown that SPECT detects cortical defects that high-resolution planar imaging misses, improving sensitivity for scarring — the reason current guidance folds SPECT or pinhole imaging into the routine protocol rather than treating it as an add-on.³⁴ The trade is modestly longer acquisition and the need for rigorous tomographic QC, discussed below.

The pediatric imperative

DMSA is a heavily pediatric study, and children are more radiosensitive than adults. That places two obligations on the physics program: weight-based activity that follows the EANM pediatric dosage card and SNMMI harmonized guidance, and acquisition optimized for the lowest activity that still yields a diagnostic, quantifiable image. The connection to pediatric nuclear medicine dosing is direct: the dosage card is how the department turns a weight into a defensible administered activity.⁵

Practical Optimization Tips

A reliable, reproducible DMSA program follows a consistent workflow.

1. Standardize the administered activity

Use the SNMMI/EANM weight-based schedule for children and a documented reference activity for adults, with a defined minimum activity so the smallest patients still get a diagnostic count density. Measure every dose in a calibrated dose calibrator and record it.

2. Verify radiochemical purity

DMSA labeling can degrade; free pertechnetate or hydrolyzed-reduced technetium changes biodistribution and can bias the cortical image and the split. Confirm radiochemical purity by thin-layer chromatography before injection, as covered in radiochemical purity and TLC quality control.

3. Fix the imaging window and geometry

Image at a consistent time post-injection (commonly ~3 hours), with a LEHR collimator, a properly peaked 140 keV window, high total counts, and reproducible patient positioning. Consistency here is what makes the differential function comparable across serial studies.

4. Standardize processing

Use a written ROI and background protocol — same background region shape and placement, geometric mean when anterior and posterior views are acquired — so the split does not depend on which technologist processed the study.

5. Keep the camera and SPECT QC current

Uniformity, energy-peak, and, for SPECT, center-of-rotation and reconstruction QC directly affect quantitative cortical imaging. See gamma camera uniformity QC and dose calibrator quality control.

Common pitfalls to avoid

• Inconsistent background ROIs. Because both kidney percentages share a denominator, a sloppy background region shifts both numbers.
• Posterior-only quantification for an ectopic or malrotated kidney. Without the geometric mean, depth differences bias the split.
• Skipping SPECT/pinhole in children. Small cortical defects can hide on planar projections.
• Fixed activity for all children. Pediatric activity must be weight-based, with a diagnostic minimum.
• Ignoring radiochemical purity. Poor labeling degrades the cortical image and the quantification.
• Off-peak energy window. A mis-set 140 keV window adds scatter and noise that degrade cortical contrast.

Regulatory Considerations

A DMSA program operates under the medical-use rules for byproduct material and the biokinetic/dosimetric conventions used to report dose. The imaging protocol, activity determination, and QC are documented so the program is defensible at inspection.

Key frameworks to reference:

• 10 CFR Part 35 — Medical Use of Byproduct Material. Governs authorized users, dosage determination, and radiation safety for Tc-99m administrations. A diagnostic DMSA study does not require a written directive (those apply to therapy and to I-131 sodium iodide above threshold), but it must follow the authorized user's directions and license conditions.⁸
• 10 CFR 35.63 — Determination of dosages. Requires that the licensee measure or otherwise determine each patient dosage before administration, which for DMSA means a calibrated dose-calibrator measurement recorded per procedure.⁸
• ICRP Publication 128. The current compilation of radiopharmaceutical biokinetics and dose coefficients, the source for the Tc-99m DMSA effective-dose coefficient used above.⁶
• SNMMI/EANM pediatric renal cortical scintigraphy guidance and the EANM pediatric dosage card, which define the acquisition, processing, and weight-based activity conventions.⁴⁵

Radioactive material for nuclear medicine is regulated by the NRC under 10 CFR Parts 20 and 35, or by an Agreement State administering an equivalent program. Of the states DRPS serves, Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey are NRC Agreement States, while Washington, DC and Delaware are regulated directly by the NRC for byproduct material. A facility must confirm which authority issues its license and which dosage-determination and recordkeeping requirements apply. Program-specific expectations for medical-use licensees are described in NRC NUREG-1556, Volume 9. Coordinate the DMSA QC and dosimetry review with medical physics consulting and radioactive material license support.⁸⁹

Frequently Asked Questions (FAQs)

What is Tc-99m DMSA renal cortical scintigraphy?

It is a nuclear medicine study using technetium-99m dimercaptosuccinic acid (DMSA), a radiopharmaceutical that binds to proximal renal tubular cells and is retained in the functioning renal cortex. Imaging a few hours after injection maps functioning cortex, which makes it the reference test for renal scarring and for measuring differential (split) renal function.

How is differential renal function calculated on a DMSA scan?

Regions of interest are drawn around each kidney and a background region is subtracted. When anterior and posterior images are both acquired, the geometric mean of the two counts is used to correct for depth. Each kidney's percentage is its background-subtracted (geometric-mean) counts divided by the sum for both kidneys; a normal split is roughly 45 to 55 percent per kidney.

Is SPECT or planar imaging preferred for DMSA?

Current SNMMI and EANM guidance recommends that SPECT, or pinhole imaging in infants and small children, be a routine part of the DMSA protocol because it detects cortical defects that planar imaging can miss. Planar posterior and oblique views remain part of the study, particularly for differential-function quantification.

What is the radiation dose from a DMSA scan?

Using ICRP Publication 128 coefficients, the adult effective dose from Tc-99m DMSA is about 0.0088 mSv per MBq, so a typical adult administration of roughly 185 MBq gives an effective dose on the order of 1.6 mSv. The kidneys are the organ receiving the highest absorbed dose. Pediatric activity is reduced and weight-based using the EANM dosage card and SNMMI guidance.

Why is DMSA used instead of a dynamic renogram?

DMSA and dynamic renography answer different questions. DMSA is a static cortical study that shows functioning parenchyma, scars, and differential function. Dynamic agents such as Tc-99m MAG3 or Tc-99m DTPA assess perfusion, drainage, and obstruction. For suspected pyelonephritis or renal scarring, cortical DMSA imaging is the reference test.

What quality control supports a reliable DMSA study?

Key QC includes dose-calibrator accuracy, constancy, and linearity for measuring the administered activity, radiochemical-purity testing of the DMSA preparation, gamma-camera uniformity and, for SPECT, center-of-rotation and reconstruction QC. Correct energy windowing on the 140 keV Tc-99m photopeak and consistent processing protocols are also essential for reproducible quantification.

Does a diagnostic DMSA scan require a written directive?

No. Under 10 CFR Part 35, a written directive is required for therapeutic administrations and for I-131 sodium iodide above the regulatory threshold, not for a diagnostic Tc-99m DMSA study. The administration must still follow the authorized user's directions, dosage determination under 10 CFR 35.63, and the facility's license conditions.

Key Takeaways

• DMSA images functioning cortex. Proximal-tubule binding makes it the reference test for scarring, pyelonephritis, and differential renal function.
• Quantification discipline drives the result. Geometric-mean depth correction and consistent background subtraction determine the reported split; both kidney percentages share a denominator, so one bad ROI moves both.
• SPECT or pinhole is now routine. Tomographic imaging detects cortical defects planar views can miss.
• Dose is small but the patients are radiosensitive. About 0.0088 mSv/MBq (adult) means ~1.6 mSv for a typical adult study; pediatric activity must be weight-based per the EANM dosage card.
• QC underpins the numbers. Dose-calibrator accuracy, radiochemical purity, energy-window and uniformity/SPECT QC all feed the quantification.
• Document against 10 CFR Part 35 and ICRP 128 so activity determination and dosimetry are defensible at inspection.

Conclusion

Tc-99m DMSA renal cortical scintigraphy is deceptively simple: inject, wait a few hours, image. The value — and the risk — is in the quantification. A differential renal function is only as good as the ROI and background discipline behind it, the depth correction, and the decision to image tomographically in children where small defects hide on planar views.

For a heavily pediatric study, the physics program carries a double duty: keep activity weight-based and as low as reasonably achievable, and keep the quantification reproducible enough that a serial change in the split reflects the kidney, not the processing. A DMSA program built on documented acquisition, standardized processing, and current camera and dose-calibrator QC gives clinicians a number they can act on.

How DRPS Can Help

Diagnostic Radiation Physics Services helps nuclear medicine departments build and audit renal cortical imaging programs: acquisition and processing protocol review, differential-function quantification standardization, SPECT and gamma-camera QC, dose-calibrator accuracy and linearity, radiochemical-purity procedures, and pediatric weight-based dosing aligned with SNMMI and EANM guidance. This is delivered through PET/CT and nuclear medicine physics, medical physics consulting, and radioactive material license support.

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

A defensible DMSA study is not just a pretty cortical image — it is a differential function a clinician can trust enough to act on.

Related Resources

• Renal scintigraphy: split function and GFR
• Pediatric nuclear medicine dosing
• SPECT/CT quality control
• Gamma camera uniformity QC
• Dose calibrator quality control
• Radiochemical purity and TLC quality control
• PET/CT and nuclear medicine physics
• Medical physics consulting

References

1. Bar-Sever Z, Shammas A, Gheisari F, Vali R. Pediatric Nephro-Urology: Overview and Updates in Diuretic Renal Scans and Renal Cortical Scintigraphy. Semin Nucl Med. 2022;52(4):419-431. doi:10.1053/j.semnuclmed.2021.12.002. doi.org
2. Tahlili R, Mardanshahi A, Abedi SM, Mohammadjafari H. The Role of Quantitative DMSA Scan Analysis in Assessing Prognosis of Acute Pyelonephritis in Children. Clin Pediatr (Phila). 2025;64(7):979-986. doi:10.1177/00099228241307441. doi.org
3. Brenner M, Bonta D, Eslamy H, Ziessman HA. Comparison of 99mTc-DMSA dual-head SPECT versus high-resolution parallel-hole planar imaging for the detection of renal cortical defects. AJR Am J Roentgenol. 2009;193(2):333-337. doi:10.2214/AJR.08.1788. doi.org
4. Society of Nuclear Medicine and Molecular Imaging. Pediatric [99mTc]Tc-DMSA Renal Cortical Scintigraphy Procedure Standard (SNMMI/EANM harmonized guideline). snmmi.org
5. Lassmann M, Treves ST; EANM/SNMMI Paediatric Dosage Harmonization Working Group. Paediatric radiopharmaceutical administration: harmonization of the 2007 EANM paediatric dosage card and the 2010 North American consensus guidelines. Eur J Nucl Med Mol Imaging. 2014;41(5):1036-1041. doi:10.1007/s00259-014-2731-9. doi.org
6. 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
7. Chroustová D, Trnka J, Langer J, Urbanová I, Lambert L, Kočvara R. How the Tc-DMSA scintigraphy findings are reflected in the adopted treatment of primary vesicoureteral reflux: One centre experience. J Pediatr Urol. 2023;19(4):456-462. doi:10.1016/j.jpurol.2023.01.017. doi.org
8. U.S. Nuclear Regulatory Commission. 10 CFR Part 35: Medical Use of Byproduct Material. ecfr.gov
9. U.S. Nuclear Regulatory Commission. NUREG-1556, Volume 9, Revision 3: Program-Specific Guidance About Medical Use Licenses. nrc.gov