🫀 Myocardial Perfusion Imaging (MPI) relies on stressing the heart to unmask regions with impaired blood flow. By raising oxygen demand—through 🏃 exercise or 💊 pharmacological stress—ischemic areas supplied by stenotic coronary arteries appear underperfused (“cold”) compared to normal myocardium. This contrast helps detect coronary artery disease (CAD) before overt infarction.

🔎 About

Based on the principle that stenoses >70% limit flow during stress, but not always at rest.
Well-perfused myocardium = normal uptake/motion ✅; Ischemic myocardium = reduced uptake or abnormal contraction ❌.
Techniques vary (nuclear, echo, angiography), but all test the supply-demand mismatch.

📡 Common Diagnostic Modalities

🏃 Exercise Stress Test: ECG monitoring looks for ST depression as a marker of ischemia. Non-invasive, but less sensitive/specific than imaging modalities.
💉 Dobutamine Stress Echocardiography: Dobutamine ↑ HR and contractility → ↑ O₂ demand. New wall motion abnormalities = ischemia.
☢️ Technetium Radionuclide Imaging: Radioactive tracer (e.g., Tc-99m sestamibi) injected → distribution imaged. “Cold spots” after stress = ischemic myocardium.
🧪 Thallium / MIBI / Myoview Scans: Thallium behaves like potassium → taken up by viable cells. Reversible ischemia = stress defect that fills in on delayed imaging. Technetium agents → sharper images, shorter half-life.
💊 Adenosine or Dipyridamole Stress: Potent vasodilators → normal vessels dilate, stenotic ones do not. Creates “steal phenomenon,” highlighting perfusion defects. Preferred if patient cannot exercise.
🩻 Coronary Angiography: Gold standard → direct contrast imaging of coronary lumen. Invasive, but defines exact location/severity of stenosis.
📊 MUGA Scan: Radionuclide ventriculography assessing LV function. Provides EF and wall motion info but not perfusion directly.

📊 Comparison Table

Test	Principle	Strengths	Limitations
🏃 Exercise ECG	ST depression with stress	Cheap, simple, widely available	Lower sensitivity/specificity, not for those unable to exercise
💉 Dobutamine Stress Echo	Wall motion changes	No radiation, assesses LV function	Operator dependent, contraindicated in arrhythmias
☢️ Tc-99m Radionuclide	Tracer uptake = perfusion	Good image quality, quantitative	Radiation exposure, cost
🧪 Thallium Scan	Redistribution of thallium	Shows reversible vs fixed defects	Lower resolution, more radiation
💊 Adenosine/Dipyridamole	Vasodilation → flow mismatch	Useful if cannot exercise	Bronchospasm risk (avoid in asthma/COPD)
🩻 Angiography	Direct lumen visualization	Gold standard, can stent simultaneously	Invasive, contrast nephropathy risk
📊 MUGA	Radioisotope EF + wall motion	Accurate EF measurement	No perfusion data

💡 Teaching Pearls: - MPI detects flow-limiting stenosis, not early plaque. - Reversible defect = ischemia; Fixed defect = infarct. - Adenosine stress = beware in asthmatics (bronchospasm). - Always check renal function before angiography due to contrast.

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Myocardial perfusion

🔎 About

📡 Common Diagnostic Modalities

📊 Comparison Table

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