Tc-99m-Sestamibi / Tetrofosmin⁹⁹ᵐTc-sestamibi · ⁹⁹ᵐTc-tetrofosmin
Lipophilic cationic myocardial perfusion agents (also used for parathyroid and other imaging)
Quick Answer
Tc-99m-sestamibi and tetrofosmin are lipophilic monovalent cations taken up by myocardium in proportion to blood flow and retained in mitochondria, making them the standard SPECT myocardial perfusion agents. Because uptake also occurs in metabolically active parathyroid adenomas and some tumors, sestamibi is additionally used for parathyroid localization and molecular breast imaging. Unlike thallium, it shows minimal redistribution, so imaging timing is flexible.
Mechanism
The lipophilic cation diffuses across membranes driven by transmembrane potentials and is sequestered in mitochondria of viable cells. Myocardial uptake tracks perfusion; parathyroid-adenoma and tumor uptake reflects high mitochondrial density and metabolic activity. Efflux is mediated by P-glycoprotein (MDR) — the basis of investigational multidrug-resistance imaging. Minimal redistribution distinguishes it from thallium (which redistributes).
Biodistribution
Myocardium, plus liver and gallbladder (hepatobiliary clearance), gut, kidneys, and skeletal muscle. Breast and diaphragm cause cardiac attenuation; intense subdiaphragmatic (liver/bowel) activity can obscure the inferior wall.
Clinical Indications
- Myocardial perfusion imaging (stress/rest) — the primary use.
- Parathyroid adenoma localization (dual-phase and/or SPECT/CT).
- Molecular breast imaging (MBI)/scintimammography — problem-solving (dense breasts, equivocal mammography).
- Investigational MDR/P-glycoprotein tumor imaging.
Protocol Notes
- Cardiac: same-day rest/stress or stress/rest, or two-day (larger patients); image ~15–60 min post-injection; gated for function; attenuation correction/prone imaging for artifacts.
- Parathyroid dual-phase: early (~10–15 min) and delayed (~1.5–2.5 h) images — adenomas retain tracer as thyroid washes out; SPECT/CT localizes ectopic (mediastinal/retroesophageal) glands.
Interpretation Highlights
- Cardiac: reversible defect = ischemia; fixed = scar (see MPI pages); gating disambiguates attenuation from scar.
- Parathyroid: a focus of persistent uptake on delayed images (or SPECT/CT) localizes the adenoma; coexisting thyroid nodules are a false-positive source.
Reporting Checklist
- Cardiac: report as in the MPI protocol (perfusion + gated function, attenuation-correction method).
- Parathyroid: describe the focus of retained uptake and its SPECT/CT localization (including ectopic sites).
- Note attenuation/subdiaphragmatic-activity limitations.
Common Pitfalls
- Breast/diaphragm attenuation artifacts on cardiac images (use AC, prone/upright, gating).
- Intense adjacent liver/bowel activity mimicking/masking inferior-wall findings.
- Coexisting thyroid nodules causing parathyroid false positives.
Board Pearls
Sestamibi is a lipophilic cation retained in mitochondria in proportion to blood flow and cell viability — the basis of both jobs: myocardial perfusion imaging (uptake tracks coronary flow) and parathyroid localization (mitochondria-rich adenomas retain it longer than thyroid).
Minimal redistribution (unlike thallium) lets imaging start ~15–60 min post-injection without losing defect information and allows flexible same-day/two-day sequencing; hepatobiliary clearance means subdiaphragmatic activity can obscure the inferior wall (timing, positioning, hydration help).
The same retention property drives the dual-phase parathyroid technique (adenoma retains, thyroid washes out) and SPECT/CT localization of ectopic glands, while P-glycoprotein-mediated efflux underlies investigational MDR imaging. Coexisting thyroid nodules are the classic parathyroid false positive; breast/diaphragm attenuation is the classic cardiac one.
Related Pages
- Protocol: MPI SPECT, disease: parathyroid imaging.
- Contrast tracer: thallium-201 (redistribution/viability).
- Pitfalls: Pearls, pitfalls & normal variants.
Figure / Diagram Suggestions
- A mitochondrial-retention mechanism cartoon (potential-driven uptake).
- A dual-phase parathyroid washout sequence (thyroid clears, adenoma retains).
- An attenuation-artifact cardiac plate (breast/diaphragm) with gating rescue.
Self-Check (Board-Style)
Q1. What single cellular property underlies both sestamibi's cardiac and parathyroid uses?
Answer: Mitochondrial retention of the lipophilic cation — proportional to blood flow/viability in myocardium and to high mitochondrial density in metabolically active parathyroid adenomas.
Q2. How does sestamibi differ from thallium in redistribution, and what practical advantage does this give?
Answer: Sestamibi shows minimal redistribution, so imaging timing is flexible (~15–60 min post-injection) and stress/rest can be sequenced same-day or two-day, unlike thallium's redistribution-dependent protocols.
Q3. In dual-phase parathyroid imaging, what distinguishes an adenoma from thyroid?
Answer: The adenoma retains tracer on delayed images while thyroid washes out; SPECT/CT localizes it, including ectopic mediastinal/retroesophageal glands.
Q4. Why can the inferior wall be hard to assess on sestamibi cardiac images?
Answer: Hepatobiliary clearance produces intense adjacent liver/bowel activity that can obscure the inferior wall — timing, positioning, and hydration mitigate it.
Evidence & sources
https://nuc.med/sestamibi/ Report an issue