Functional Imaging in Cardiology

Functional Imaging in Cardiology

Functional Imaging in Cardiology

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Basics & Goals - Cardiac Function Unveiled

  • Assesses dynamic cardiac physiology, moving beyond static anatomical views.
  • Core Goals:
    • Evaluate myocardial perfusion (coronary blood flow adequacy).
    • Determine myocardial viability (distinguishing live, stunned, or hibernating tissue from scar).
    • Quantify global and regional ventricular function (e.g., LVEF, RVEF, wall motion).
    • Detect, localize, and assess extent of myocardial ischemia and infarction.
    • Guide patient selection for revascularization procedures (PCI, CABG).
    • Assess hemodynamic consequences of valvular heart disease.

⭐ Functional imaging is pivotal in identifying hibernating myocardium, which can recover function after revascularization.

Nuclear Techniques - Radionuclide Revelations

  • Core Principle: Detects radiation from tracers for myocardial perfusion, viability & function.
  • Key Modalities:
    • SPECT (Single Photon Emission Computed Tomography):
      • Tracers: $^{201}$Tl (Thallium), $^{99m}$Tc-Sestamibi/Tetrofosmin (↓radiation, better images).
      • Detects: Ischemia (reversible defect), Infarction (fixed). Gated for LVEF.
    • PET (Positron Emission Tomography):
      • Tracers: Perfusion ($^{82}$Rb, $^{13}$N-Ammonia); Metabolism ($^{18}$F-FDG for viability).
      • Pros: ↑Resolution, quantitative flow (MBFR). 📌 "FDG Finds Good (viable) myocardium."
  • Stress: Exercise or Pharmacological (Adenosine, Dipyridamole, Dobutamine, Regadenoson).
  • Viability ($^{18}$F-FDG PET):
    • Hibernating: ↓Perfusion, normal/↑FDG (mismatch).
    • Scar: ↓Perfusion, ↓FDG (match).

⭐ PET with $^{18}$F-FDG is gold standard for myocardial viability, guiding revascularization in severe LV dysfunction.

Cardiac SPECT Myocardial Perfusion Bullseye Plot

Cardiac MRI (CMR) - Magnetic Heartbeats

  • Versatile, radiation-free imaging for comprehensive cardiac assessment.
  • Gold standard for:
    • Left Ventricular (LV) & Right Ventricular (RV) volumes, mass.
    • Ejection Fraction (EF).
  • Key Sequences & Utility:
    • Cine (SSFP): Cardiac function, regional wall motion abnormalities.
    • T1 & T2 Mapping: Quantitative tissue characterization (e.g., diffuse fibrosis, edema).
    • Late Gadolinium Enhancement (LGE): Identifies myocardial scar/fibrosis (infarct, non-ischemic).
    • Stress Perfusion: Detects inducible ischemia.
  • Broad applications: Ischemic heart disease (IHD), cardiomyopathies (DCM, HCM, ARVC), myocarditis, pericardial disease, congenital heart defects. LGE patterns in ischemic vs non-ischemic cardiomyopathy

⭐ LGE is typically subendocardial or transmural in ischemic cardiomyopathy, while non-ischemic patterns (e.g., mid-myocardial, epicardial, or diffuse) suggest other etiologies like myocarditis or amyloidosis respectively.

Stress Echocardiography & CT - Echoes & Angio Insights

  • Stress Echocardiography (SE):
    • Detects inducible ischemia by assessing regional wall motion abnormalities (RWMA) with stress (exercise/dobutamine).
    • Key for CAD diagnosis, risk stratification, viability.
    • Positive: New/worsening RWMA, fall in LVEF.
  • CT Functional Insights:
    • CT-FFR: Non-invasive hemodynamic stenosis assessment from CTA data.
    • CT Perfusion (CTP): Evaluates myocardial blood flow, identifies perfusion defects.
    • Coronary Artery Calcium (CAC) Score: Important prognostic marker. Stress Echocardiography: Rest vs. Post-Exercise Views

⭐ Dobutamine Stress Echocardiography (DSE) is valuable for ischemia and viability assessment, especially in patients unable to exercise effectively or with LBBB an ECG confounder for treadmill test interpretation for ischemia detection .

High‑Yield Points - ⚡ Biggest Takeaways

  • SPECT MPI: Widely used for ischemia detection (Tc-99m agents, rest-stress).
  • PET MPI: Superior for viability (FDG) & perfusion quantification; higher resolution.
  • Cardiac MRI (CMR): Gold standard for ventricular function; LGE for scar/viability.
  • Stress Echocardiography: Detects ischemia via stress-induced wall motion abnormalities.
  • FDG-PET identifies hibernating myocardium (perfusion-metabolism mismatch).
  • Dobutamine Stress CMR: Assesses ischemia via wall motion and perfusion.
  • MUGA scans: Accurate LVEF, key for cardiotoxicity monitoring.

Practice Questions: Functional Imaging in Cardiology

Test your understanding with these related questions

A 45-year-old man presents with intermittent pain in the chest, radiating to the left arm, aggravated by exertion, and relieved by rest. What is the most appropriate initial investigation?

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Flashcards: Functional Imaging in Cardiology

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The application of MR to imaging was first done by _____

TAP TO REVEAL ANSWER

The application of MR to imaging was first done by _____

Paul Lauterbur.

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