Myocardial Perfusion Imaging — SPECT

Myocardial perfusion SPECT images regional myocardial blood flow at stress and rest using Tc-99m-labelled agents (sestamibi or tetrofosmin) or thallium-201, which distribute in proportion to perfusion and viable myocyte uptake. Comparison of stress and rest images distinguishes reversible ischaemia (defect present on stress, resolving at rest) from fixed infarct/scar (defect on both). ECG-gated acquisition adds left-ventricular wall motion, thickening and ejection fraction. It is a cornerstone for detecting and risk-stratifying coronary artery disease.

Indications

Detection of coronary artery disease in patients with intermediate pre-test probability of chest pain
Risk stratification and prognosis in known or suspected coronary disease
Differentiation of myocardial ischaemia from infarction/scar and assessment of viability
Pre-operative cardiac risk assessment before intermediate/high-risk non-cardiac surgery
Evaluation of the functional significance of known coronary stenoses and post-revascularisation assessment

Contraindications & Cautions

Pregnancy is a relative contraindication; justify and minimise dose, favouring the lower-dose or pharmacologic option
Breastfeeding: brief interruption for Tc-99m agents per local guidance; Tl-201 requires longer precautions
Vasodilator stress (adenosine/regadenoson/dipyridamole) is contraindicated in high-grade AV block without pacemaker, active bronchospasm/severe asthma, and recent use of caffeine/theophylline (adenosine antagonists)
Dobutamine is avoided in significant arrhythmia, severe hypertension, or dynamic outflow obstruction; exercise is contraindicated in unstable angina, acute MI, severe aortic stenosis and decompensated heart failure
Withhold caffeine for 12-24 h and methylxanthines before vasodilator stress

Patient Preparation

Withhold caffeine and methylxanthine-containing foods/drugs for 12-24 hours before vasodilator stress
Withhold nitrates, beta-blockers and calcium-channel blockers per protocol when maximal ischaemia detection is required
Fast for several hours; a light fatty meal after Tc-99m injection promotes hepatobiliary clearance and reduces subdiaphragmatic activity
Establish IV access; obtain baseline ECG, blood pressure and heart rate; screen for contraindications to the chosen stressor
Confirm pregnancy/lactation status and recent caffeine intake

Technique & Parameters

Use Tc-99m sestamibi or tetrofosmin (or Tl-201); common one- or two-day rest/stress protocols
Stress by exercise treadmill or pharmacologic agent (regadenoson, adenosine, dipyridamole, or dobutamine) with continuous ECG and blood-pressure monitoring
Inject the tracer at peak stress; acquire ECG-gated SPECT of the left ventricle, then a separate rest acquisition
Reconstruct short-axis, vertical and horizontal long-axis slices; assess perfusion on a 17-segment model with summed scores
Derive gated LV ejection fraction, volumes and regional wall motion/thickening; apply attenuation correction where available

Systematic Review

Confirm adequacy of stress (target heart rate/haemodynamic response) and image quality/attenuation
Compare stress and rest perfusion segment by segment across the three axes
Classify each defect as reversible (ischaemia), fixed (scar) or partially reversible
Localise defects to coronary territories (LAD, LCx, RCA) and estimate extent and severity
Review gated wall motion, thickening, ejection fraction and any transient ischaemic dilatation

Key Findings & Significance

Reversible defect (present at stress, normalises at rest) indicates inducible ischaemia
Fixed defect (present on stress and rest) indicates infarction/scar; preserved wall thickening suggests viability or attenuation artefact
Transient ischaemic dilatation of the LV cavity on stress images is a marker of severe/multivessel disease
Increased summed stress score reflects greater ischaemic burden and adverse prognosis
Reduced gated ejection fraction and regional wall-motion abnormality corroborate significant disease and stratify risk

Differential Considerations

Reversible defect: myocardial ischaemia versus balanced ischaemia (may under-call multivessel disease)
Fixed defect: prior infarction versus soft-tissue attenuation artefact (breast, diaphragm)
Apparent inferior wall defect: diaphragmatic attenuation versus true RCA territory ischaemia/infarct
Apparent anterior defect: breast attenuation versus LAD disease
Non-coronary causes of abnormal perfusion/function: cardiomyopathy, left bundle branch block (septal artefact), microvascular disease

Pearls & Pitfalls

Gated imaging distinguishes attenuation artefact (normal wall thickening) from true scar (absent thickening)
Transient ischaemic dilatation and lung uptake (with Tl-201) are high-risk markers even without large defects
Balanced (three-vessel) ischaemia can appear falsely normal — correlate with clinical, ECG and haemodynamic stress response
Prone or attenuation-corrected imaging reduces inferior (diaphragmatic) and anterior (breast) attenuation artefacts
Avoid caffeine before adenosine/regadenoson — it blocks the vasodilator response and blunts ischaemia detection

Structured Report

State tracer, protocol, stressor and haemodynamic/ECG response with reason for terminating stress
Describe perfusion defects by location, extent, severity and reversibility on the 17-segment model
Report gated LV ejection fraction, volumes, wall motion and any transient ischaemic dilatation
Give summed stress/rest/difference scores and relate them to coronary territories and prognosis
Conclude on the presence, extent and severity of ischaemia versus infarction with management implications

References

Henzlova MJ, et al. ASNC imaging guidelines for SPECT nuclear cardiology procedures: stress, protocols, and tracers. J Nucl Cardiol 2016
Dorbala S, et al. SNMMI/ASNC/SCCT guideline for cardiac SPECT/CT and PET/CT 1.0. J Nucl Med 2013
Verberne HJ, et al. EANM procedural guidelines for radionuclide myocardial perfusion imaging. Eur J Nucl Med Mol Imaging 2015
Garcia EV, et al. Quantification of myocardial perfusion SPECT. RadioGraphics / J Nucl Cardiol

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

Myocardial Perfusion Imaging — SPECT

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References