What are the indications, patient preparation, procedure, and interpretation of a technetium‑99m (Tc‑99m) sestamibi scan?

Technetium-99m Sestamibi Scan: Clinical Overview

Primary Indications

Tc-99m sestamibi scanning is primarily indicated for myocardial perfusion imaging to detect coronary artery disease, with additional applications in parathyroid adenoma localization and breast imaging in select populations. 1

Cardiac Applications

• Coronary artery disease detection: Sestamibi demonstrates sensitivity of 93% and specificity of 70% for detecting myocardial infarction 1, 2
• Risk stratification post-myocardial infarction: Identifies areas at risk and guides management decisions 1
• Acute chest pain evaluation: Particularly valuable in emergency department settings with non-diagnostic ECG, showing 100% sensitivity for ruling out acute MI in multiple studies 1
• Assessment of myocardial viability: Distinguishes viable from infarcted tissue 1

Non-Cardiac Applications

• Parathyroid adenoma localization: Achieves high accuracy (11 of 16 solitary adenomas detected) when combined with I-123 thyroid subtraction imaging 3, 4
• Supplemental breast cancer screening: Used in molecular breast imaging (MBI) for women with dense breast tissue, showing incremental cancer detection rate of 7.7-9.3 per 1,000 1

Patient Preparation

Pre-Procedure Requirements

• Fasting status: 4-6 hours fasting recommended for cardiac studies to minimize hepatobiliary uptake that can obscure inferior wall 1
• Medication management: Beta-blockers and calcium channel blockers may need to be held 24-48 hours before stress testing (coordinate with referring physician) 1
• Caffeine restriction: Avoid for 12-24 hours if pharmacologic stress with adenosine agents planned 2
• Pregnancy screening: Must be excluded in women of childbearing age; fetal dose is minimal (0.013 mSv) but procedure should only proceed if benefit outweighs risk 5

Contraindications to Stress Testing

• Acute myocardial infarction within 48 hours 1
• Unstable angina not stabilized with medical therapy 1
• Severe aortic stenosis or hypertrophic cardiomyopathy 1

Procedure Protocol

Radiopharmaceutical Administration

Standard adult dosing for cardiac imaging is 20-30 mCi per injection, with stress-first/stress-only protocols preferred to minimize radiation exposure. 2, 5

Dosing Protocols

• Adult cardiac imaging: 20-30 mCi for single injection; 1-day rest-stress protocol delivers 9.8-16.3 mSv effective dose 2, 5
• Pediatric cardiac imaging: 0.15 mCi/kg (minimum 2 mCi, maximum 10 mCi) using weight-based adjustment 1
• Two-injection protocol: Requires stress injection followed by rest injection on separate day (same dose) or 3-4 times higher rest dose if same-day imaging 1

Imaging Acquisition

SPECT imaging is superior to planar imaging and should be the standard approach, with acquisition beginning 15-60 minutes post-injection. 1

Technical Parameters

• Timing: Imaging can be delayed several hours after injection due to minimal redistribution—a key advantage over thallium-201 1, 2
• Acquisition time: Approximately 40 minutes for SPECT acquisition 1, 2
• Patient positioning: Multiple-position imaging (supine and prone) increases normalcy rate and reduces need for rest imaging in pediatric patients 1

Stress Testing Options

• Exercise stress: Preferred when patient can achieve adequate workload (≥85% maximum predicted heart rate) 1
• Pharmacologic stress: Regadenoson, adenosine, or dipyridamole for patients unable to exercise adequately 2
• Injection timing: Administer sestamibi at peak stress (exercise) or 3 minutes into pharmacologic infusion 1

Image Interpretation

Normal Findings

• Homogeneous myocardial uptake: Uniform distribution throughout left ventricular myocardium on both stress and rest images 1
• Expected biodistribution: Myocardium, liver, gallbladder, kidneys, and bowel show physiologic uptake 6

Abnormal Patterns

Reversible defects (present on stress, absent on rest) indicate ischemia; fixed defects (present on both) indicate infarction or scar. 1

Perfusion Defect Classification

• Reversible defects: Stress-induced ischemia in viable myocardium; requires two separate injections to distinguish from fixed defects 1
• Fixed defects: Prior myocardial infarction or scar tissue 1
• Partially reversible defects: Mixed ischemia and infarction in same territory 1

Quantitative Analysis

• Circumferential profile analysis: Compares regional uptake to normal database, improving sensitivity to 90% 1
• SPECT superiority: Achieves 89% sensitivity and 76% specificity versus 85% sensitivity and 88% specificity for planar imaging 1

Critical Interpretation Pitfalls

Common Artifacts

• Attenuation artifacts: Breast tissue in women, diaphragm in inferior wall—prone imaging helps differentiate 1
• Hepatic uptake: Can obscure inferior wall; upright positioning or delayed imaging may help 1
• Balanced ischemia: Severe three-vessel disease may appear falsely normal due to globally reduced uptake 1

Technical Limitations

• Flow underestimation: Sestamibi uptake plateaus at coronary flow >2.0-2.5 times baseline, potentially underestimating severity of high-grade stenosis during maximal stress 1
• Small infarcts: May be missed on planar imaging; SPECT significantly improves detection 1

Radiation Safety Considerations

The effective radiation dose from cardiac sestamibi imaging (9.8-16.3 mSv) is comparable to 3-5 years of natural background radiation but well below thresholds for deterministic effects. 5

Dose Context

• Adult cardiac study: 9.8-16.3 mSv for 1-day protocol 2, 5
• Pediatric considerations: Age-dependent; 1-year-old receives 16.7 mSv from 10 mCi dose versus 2.9 mSv in adults—emphasizing need for weight-based dosing 1
• Safety threshold: Non-cancer effects not detectable below 50 mSv; deterministic effects do not occur below 100-200 mSv 5
• Lactation: Breastfeeding discontinuation recommended temporarily 5

Dose Optimization Strategies

• Stress-first/stress-only protocol: Eliminates rest imaging if stress images normal, reducing radiation by 50% 1
• Advanced technology: Cadmium-zinc-telluride cameras allow dose reduction to ≤5 mCi while maintaining image quality 1

Special Clinical Scenarios

Emergency Department Use

Sestamibi can be injected during active chest pain with imaging delayed until patient stabilizes—a unique advantage over thallium-201. 1, 2

• Negative predictive value of 99% for ruling out acute MI 1
• Cost savings of 10-17% projected versus routine admission 1
• Must inject during or immediately after symptoms to capture ischemic territory 1

Post-Thrombolytic Therapy

• Sestamibi injected before reperfusion therapy demonstrates initial "risk area" even if subsequent reperfusion occurs 1
• Allows assessment of myocardium salvaged by intervention 1