How do you interpret images in a nuclear stress test?

Nuclear Stress Test Image Interpretation

The proper interpretation of nuclear stress test images requires systematic evaluation of perfusion defects, their location, extent, severity, and reversibility, along with ventricular function parameters, using a standardized 17-segment model to assess for coronary artery disease and determine patient prognosis. 1

Key Components of Image Interpretation

1. Perfusion Defect Assessment

• Identification and Characterization:

  • Examine for presence/absence of perfusion defects
  • Determine location using standardized 17-segment model
  • Relate defects to specific coronary artery territories
  • Assess extent (percentage of left ventricle affected)
  • Evaluate severity (mild, moderate, or severe reduction in tracer uptake)
  • Determine reversibility (reversible defects indicate stress-induced ischemia; fixed defects suggest myocardial infarction or scar) 1

• Quantification Methods:

  • Calculate summed stress score (SSS), summed rest score (SRS), and summed difference score (SDS)
  • Determine percentage of left ventricle affected by perfusion defects
  • Use automated quantification software to support visual interpretation 2

2. Ventricular Function Assessment

• Evaluate global and regional function:
  • Left ventricular ejection fraction (LVEF) - normal is >50%
  • End-systolic and end-diastolic volumes
  • Wall motion abnormalities that may indicate ischemia or infarction 1
  • Transient ischemic dilation (TID) of the left ventricle (high-risk feature)

3. Stress Test Protocol Documentation

• Record type of stress used:
  • Exercise stress (treadmill or bicycle)
  • Pharmacological stress (vasodilator agents like regadenoson/adenosine or dobutamine)
• Document exercise capacity in METs, peak heart rate, blood pressure, and ECG changes for exercise tests
• For pharmacological stress, document agent used, dosage, timing, and any adverse reactions 1

Systematic Interpretation Approach

1. Review raw data for quality issues:

   • Patient motion
   • Attenuation artifacts
   • Subdiaphragmatic tracer activity
   • Apical thinning

2. Examine stress and rest perfusion images:

   • Compare stress and rest images side by side
   • Review short-axis, vertical long-axis, and horizontal long-axis slices
   • Use both non-attenuation corrected and attenuation corrected images when available 3

3. Analyze gated SPECT data:

   • Assess wall motion and thickening
   • Calculate LVEF and volumes
   • Look for post-stress stunning (worsening of wall motion on stress images)

4. Integrate findings:

   • Compare perfusion defects with wall motion abnormalities
   • Correlate with clinical information and stress test results
   • Determine if defects represent true ischemia or artifacts

Reporting Findings

The comprehensive report should include:

1. Patient demographics and clinical indication
2. Stress test protocol and findings
3. Tracer administration details
4. Perfusion findings:
   • Location, extent, severity, and reversibility of defects
   • Quantification when possible (percentage of myocardium affected)
5. Left ventricular function parameters
6. Overall impression with clinical implications
7. Comparison to prior studies if available 3

High-Risk Features to Identify

• Multiple perfusion defects in different coronary territories
• Large defect size (>10% of left ventricle)
• Transient ischemic dilation of the left ventricle
• Significant drop in ejection fraction with stress
• Increased lung uptake of tracer 1

Common Pitfalls and Artifacts

• Attenuation artifacts:

  • Breast attenuation (anterior/anterolateral wall)
  • Diaphragmatic attenuation (inferior wall)
  • Solution: Use attenuation correction, prone imaging, or gated SPECT to differentiate artifacts from true defects

• Patient motion:

  • Can create artificial defects
  • Solution: Review raw data and consider repeat acquisition if severe

• Subdiaphragmatic tracer activity:

  • Can create artifacts in the inferior wall
  • Solution: Delayed imaging or use of prone positioning

• Technical factors:

  • Left bundle branch block can cause septal perfusion defects
  • Apical thinning can mimic apical defects
  • Solution: Correlate with ECG and other clinical information 1

By following this systematic approach to nuclear stress test image interpretation, clinicians can accurately identify coronary artery disease, assess its severity, and guide appropriate management decisions to reduce morbidity and mortality in patients with suspected or known cardiac disease.