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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.