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Artifacts and Pitfalls

Artifacts should be suspected when the perfusion pattern does not match coronary anatomy, gated function, raw data, or the clinical presentation.

Rapid Approach

When a defect appears abnormal:

  1. Inspect the raw projection images.
  2. Check patient motion and positioning.
  3. Review extracardiac activity.
  4. Confirm reconstruction and axis selection.
  5. Compare gated wall motion and thickening.
  6. Review attenuation-corrected or prone images when available.
  7. Decide whether the defect follows a coronary territory.

Soft-Tissue Attenuation

Artifact Typical appearance Helpful clues
Diaphragmatic attenuation Fixed inferior defect Normal inferior motion; more common in men
Breast attenuation Anterior or anterolateral defect Breast shadow on raw images; normal motion
Lateral chest-wall attenuation Lateral defect Obesity or arm position
Apical thinning Small fixed apical defect Preserved apical motion and otherwise normal study

Changing breast position between stress and rest can create apparent reversibility or reverse redistribution.

Solutions: attenuation correction, prone imaging, repeat positioning, and correlation with gated function.

Subdiaphragmatic Activity

Hepatic, gastric, or bowel activity may:

  • Obscure the inferior wall
  • Artificially increase adjacent counts
  • Suppress adjacent myocardial counts during reconstruction
  • Create an apparent inferior defect

This is more common after vasodilator stress.

Solutions: delayed imaging, hydration, ambulation, repeat acquisition, or iterative reconstruction.

Patient Motion

Motion may produce:

  • Noncoronary defects
  • Opposing count abnormalities
  • Misregistration
  • A swirling or “hurricane” appearance

Vertical motion may sometimes be corrected. Complex horizontal or rotational motion often requires repeat acquisition.

LBBB and Ventricular Pacing

LBBB may cause a septal or anteroseptal defect without obstructive LAD disease, especially with exercise or dobutamine.

Best approach: vasodilator stress rather than exercise-based MPI.

Gating Errors

Arrhythmia or incorrect R-wave detection can cause:

  • Artificially low LVEF
  • Distorted LV volumes
  • Apparent wall-motion abnormalities
  • Flickering or inconsistent gated frames

Always inspect the beat histogram and gated cine images.

Small-Heart Effect

A small LV cavity may produce:

  • Underestimated end-systolic volume
  • Artificially elevated LVEF
  • Reduced spatial resolution
  • Apparent apical abnormality

This is particularly relevant in smaller patients and with older reconstruction methods.

Processing Errors

Error Consequence
Incorrect myocardial axis False perfusion defect
Inappropriate normalization Under- or overestimation of a defect
Incorrect LV contours False EF or volume measurement
Stress/rest misregistration Apparent reversibility
Attenuation-map misregistration New defect on corrected images
Camera nonuniformity Ring artifact
Center-of-rotation error Blurring or skewed reconstruction

Transient Ischemic Dilation

\[ \text{TID ratio} = \frac{\text{stress LV cavity size}} {\text{rest LV cavity size}} \]

The abnormal threshold is protocol-, tracer-, camera-, and software-specific.

TID with abnormal perfusion suggests extensive ischemia. Isolated TID may also occur with hypertensive heart disease, LVH, microvascular dysfunction, or technical differences between acquisitions.

Balanced Ischemia

SPECT normalization may conceal diffuse flow reduction in left main or three-vessel CAD.

Clues include:

  • TID
  • Stress-induced LV dysfunction
  • Increased lung uptake
  • Severe coronary calcification
  • Marked ischemic ECG changes
  • Typical angina despite normal perfusion

PET myocardial blood-flow quantification, CCTA, or angiography may be needed when suspicion remains high.

Artifact vs True Defect

Feature Artifact favored True disease favored
Coronary distribution No Yes
Wall motion Normal Abnormal with scar
Wall thickening Normal Reduced with scar
Attenuation pattern Present Absent
Position dependence Changes Persists
Seen in two planes Less consistent More consistent
Raw-data abnormality Often present Usually absent

Board Pearls

  • Fixed inferior defect + normal motion → diaphragmatic attenuation.
  • Fixed anterior defect + normal motion → breast attenuation.
  • LBBB + septal defect → consider conduction artifact.
  • Hot liver or bowel adjacent to the heart → suspect reconstruction artifact.
  • Normal perfusion + multiple high-risk markers → consider balanced ischemia.
  • Never interpret SPECT without reviewing the raw projections and gated images.

References