1. MPI Fundamentals
Myocardial Perfusion Imaging (MPI) is one of the most commonly performed nuclear medicine procedures, providing valuable information about coronary artery disease.
Learning Objectives
- Understand the indications for myocardial perfusion imaging
- Describe proper patient preparation
- Explain the physiologic basis of stress-rest imaging
- Compare 1-day vs 2-day protocols
Indications
Diagnosis of CAD
- Intermediate pre-test probability chest pain
- Evaluation of new symptoms
- Inconclusive exercise ECG
Risk Stratification
- Post-MI evaluation
- Pre-operative assessment (intermediate-high risk surgery)
- Stable CAD assessment
Post-Revascularization
- Evaluation of recurrent symptoms
- Assessment of graft/stent patency
Not Indicated: Asymptomatic patients with low pre-test probability, routine screening in asymptomatic individuals
Patient Preparation
Medication Considerations
| Medication | Hold Period | Reason |
|---|---|---|
| Beta-blockers | 24-48 hours | Blunts heart rate response |
| Calcium channel blockers | 24-48 hours | Affects vasodilation |
| Nitrates | 24 hours | May mask ischemia |
| Caffeine | 12-24 hours | Blocks adenosine receptors |
| Dipyridamole | 48 hours | Interferes with vasodilator stress |
Day of Test
- NPO 4 hours for exercise; light meal OK for pharmacologic
- Avoid caffeine (coffee, tea, chocolate, soda)
- Wear comfortable clothes/shoes for exercise
Stress-Rest Principle
The fundamental concept: coronary flow reserve
Normal arteries: Can increase flow 4-5x during stress
Stenotic arteries: Limited flow reserve → relative hypoperfusion during stress
Key Patterns
| Pattern | Stress | Rest | Interpretation |
|---|---|---|---|
| Normal | Normal | Normal | No significant CAD |
| Reversible | Defect | Normal | Ischemia |
| Fixed | Defect | Defect | Scar/infarct |
| Reverse redistribution | Normal | Defect | Subendocardial ischemia |
Content under development: Protocol details, injection timing, imaging acquisition