Normal Biodistribution of Common Radiopharmaceuticals

Nuclear medicine interpretation depends as much on knowing what is normal as on identifying what is abnormal. Every radiopharmaceutical has a predictable physiologic distribution pattern. When you understand this baseline, you instantly recognize when something is off, whether it’s unexpected uptake in an organ, missing activity where it should be, or a shift caused by disease, artifact, or timing error.

Accurate interpretation starts with pattern memory. For example, a bright bowel focus on FDG PET might be physiologic, but if you don’t know FDG’s tendency for variable bowel uptake, you may overcall it as pathology. Likewise, recognizing that Tc-99m sulfur colloid accumulates in the liver, spleen, and bone marrow in fixed ratios prevents false diagnoses of “hepatic cold spots” that are actually physiologic variations.

This reference consolidates the normal biodistribution patterns of the most widely used diagnostic radiopharmaceuticals — Tc-99m, In-111, Ga-67, Tl-201, and F-18 — drawn from the Society of Nuclear Medicine and Molecular Imaging (SNMMI) Procedure Standards and leading textbooks.
It’s designed for daily clinical use, teaching, and board exam review.

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Tc-99m Radiopharmaceuticals

Agent	Mechanism	Normal Uptake Sites
Tc-99m Pertechnetate	Active transport (iodide analog)	Thyroid, salivary glands, gastric mucosa, choroid plexus, nasopharynx, esophagus, testes, bladder
Tc-99m MDP / HDP	Chemisorption to hydroxyapatite	All bones (especially axial skeleton), growth plates, joints, bladder
Tc-99m DTPA	Glomerular filtration	Kidneys (cortex), ureters, bladder
Tc-99m MAG3	Tubular secretion	Kidneys (parenchyma), ureters, bladder
Tc-99m Sulfur Colloid	Phagocytosis by RES	Liver (homogeneous), spleen, bone marrow
Tc-99m HMPAO (WBC)	Leukocyte labeling	Liver, spleen, bone marrow (no bowel activity)
Tc-99m DISIDA / HIDA	Hepatic excretion	Liver, gallbladder, biliary tree, small bowel
Tc-99m RBC (tagged)	Intravascular compartment	Heart, blood pool, liver, spleen
Tc-99m Sestamibi	Passive diffusion, mitochondrial uptake	Myocardium, salivary glands, thyroid, liver, kidneys, bowel, bladder
Tc-99m Tetrofosmin	Passive diffusion	Myocardium, liver, kidneys, bladder

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In-111 Radiopharmaceuticals

Agent	Mechanism	Normal Uptake Sites
In-111 WBC (oxine)	Phagocytosis by neutrophils	Liver, spleen, bone marrow (no bowel or kidney activity)
In-111 DTPA	CSF distribution	CSF spaces (ventricles, cisterns), bladder
In-111 Polyclonal IgG	Fc receptor binding	Liver, spleen, bone marrow, blood pool
In-111 Octreotide	Somatostatin receptor binding	Spleen, liver, kidneys, thyroid, pituitary, bowel, bladder

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Ga-67 Citrate

Mechanism	Normal Uptake Sites
Binds to transferrin, lactoferrin, siderophores	Liver, spleen, bone marrow, salivary glands, nasopharynx, lacrimal glands, breasts, lungs (mild), bowel (variable), kidneys (early), bladder (early)

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Tl-201 Thallous Chloride

Mechanism	Normal Uptake Sites
Na⁺/K⁺ ATPase pump (potassium analog)	Myocardium, skeletal muscle, liver, kidneys, testes, salivary glands, thyroid, spleen, bowel (mild), bladder

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F-18 Radiopharmaceuticals

Agent	Mechanism	Normal Uptake Sites
F-18 FDG	Glucose analog via GLUT transporters	Brain (high), myocardium (variable), liver, kidneys, bladder, salivary glands, thymus (children), GI tract (variable), brown fat (neck, supraclavicular), testes, endometrium (cyclical), breasts (lactating), muscles (active), vocal cords (talking), lymphoid tissue
F-18 NaF	Chemisorption to bone	Skeleton, bladder
F-18 DOPA	Amino acid transport	Brain, pancreas, adrenal medulla
F-18 PSMA	Binds to PSMA receptor	Salivary glands, kidneys, liver, bowel, bladder
F-18 Fluciclovine	Amino acid transport	Liver, pancreas, muscle, bladder

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Clinical Tip

• Recognize asymmetric or unexpected intensity in a physiologic site; it’s often your first clue for pathology.
• Always correlate biodistribution with patient preparation, injection site, and timing.
• Reviewing these patterns regularly improves speed and accuracy in board and clinical reporting.

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References:

1. Mettler FA, Guiberteau MJ. Essentials of Nuclear Medicine and Molecular Imaging. 7th ed. Philadelphia: Elsevier; 2019.
2. Cherry SR, Sorenson JA, Phelps ME. Physics in Nuclear Medicine. 4th ed. Philadelphia: Elsevier Saunders; 2012.
3. Society of Nuclear Medicine and Molecular Imaging. Procedure Standards and Guidelines. [Internet]. SNMMI; 2025 [cited 2025 Oct 20]. Available from: https://www.snmmi.org/ClinicalPractice
4. Palestro CJ. Radionuclide imaging of infection: In search of the grail. J Nucl Med. 2009;50(5):671–673.
5. Love C, Palestro CJ. Radionuclide imaging of infection. J Nucl Med Technol. 2004;32(2):47–57.
6. Hoffer PB. Gallium: mechanisms. J Nucl Med. 1980;21(7):667–670.
7. Kostakoglu L, Goldsmith SJ. 18F-FDG PET evaluation of the response to cancer therapy. Semin Nucl Med. 2003;33(4):328–341.
8. Delbeke D, Coleman RE, Guiberteau MJ, et al. Procedure guideline for tumor imaging with 18F-FDG PET/CT 1.0. J Nucl Med. 2006;47(5):885–895.
9. Silberstein EB, Ryan J. Prevalence of physiologic and benign variants on whole-body FDG PET imaging. Radiographics. 2001;21(2):545–559.
10. Bombardieri E, Aktolun C, Baum RP, et al. 111In-pentetreotide scintigraphy: procedure guidelines for tumor imaging. Eur J Nucl Med Mol Imaging. 2003;30(5):BP146–BP155.

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