What is sestamibi (Technetium-99m sestamibi)?

What is Sestamibi (Technetium-99m sestamibi)?

Sestamibi (Technetium-99m sestamibi) is a radiopharmaceutical agent that accumulates in viable myocardial tissue and various tumor tissues, used primarily for cardiac perfusion imaging and parathyroid localization. 1

Chemical Composition and Properties

Technetium-99m sestamibi (also known as MIBI) consists of:

• A technetium-99m radioisotope bound to six methoxyisobutylisonitrile (MIBI) molecules, forming a Tc-99m[MIBI]₆⁺ complex 1
• It has a physical half-life of 6.02 hours 1
• The radiopharmaceutical emits gamma rays with a mean energy of 140.5 keV, ideal for imaging 1

Physiological Mechanism

Sestamibi functions through several key mechanisms:

• It accumulates in viable myocardial tissue similar to thallium-201 chloride 1
• Cellular retention occurs specifically within the mitochondria through electrostatic interactions 1
• Blood clearance occurs rapidly with a half-life of 4.3 minutes at rest and 1.6 minutes during exercise 1
• The myocardial biological half-life is approximately 6 hours 1
• The liver biological half-life is approximately 30 minutes 1
• It undergoes minimal redistribution compared to thallium-201 1

Clinical Applications

1. Cardiac Imaging

• Detection of coronary artery disease by localizing myocardial ischemia (reversible defects) and infarction (non-reversible defects) 1, 2
• Evaluation of myocardial function for patient management decisions 1
• Assessment of myocardial viability in patients with mechanical dysfunction 2
• Risk stratification in patients with unstable angina that has been stabilized with medical therapy 2

2. Parathyroid Imaging

• Localization of parathyroid adenomas using either:
  • Dual-phase imaging protocols that take advantage of differential washout from thyroid and parathyroid tissue 3
  • Subtraction imaging techniques using iodine-123 or Tc-99m sodium pertechnetate 3
• Particularly valuable for detecting ectopic parathyroid glands and in cases of recurrent disease 4

3. Other Applications

• Detection of recurrent gliomas after radiation therapy 5
• Breast cancer imaging, particularly in molecular breast imaging (MBI) 2

Advantages Over Other Imaging Agents

• Superior imaging characteristics compared to thallium-201 due to higher photon energy 2
• Lower radiation exposure to patients compared to thallium-201 2
• Minimal redistribution, allowing delayed imaging up to several hours after injection 2
• Can be used with SPECT (Single Photon Emission Computed Tomography) for improved diagnostic accuracy 2

Radiation Safety Considerations

• The effective dose varies by patient size and age, with children receiving proportionally higher doses 2
• For a 10 mCi dose of Tc-99m sestamibi at exercise:
  • Adult: 2.9 mSv
  • 15-year-old: 3.7 mSv
  • 10-year-old: 5.9 mSv
  • 5-year-old: 8.5 mSv
  • 1-year-old: 16.7 mSv 2
• Dose optimization strategies should be employed, particularly in pediatric patients 2

Administration Protocol

• Administered intravenously for diagnostic use 1
• For cardiac imaging, typically injected during peak stress or at rest 2
• Imaging is usually performed 15-60 minutes after injection 2
• For parathyroid imaging, early (10 minutes) and delayed (120 minutes) imaging is effective 4

Sestamibi has revolutionized nuclear cardiology and parathyroid imaging with its favorable pharmacokinetic properties and lower radiation exposure compared to previous agents, making it the radiopharmaceutical of choice for these applications.