What artefacts occur in SPECT imaging?

SPECT artefacts are image distortions that arise from physical limitations, acquisition errors, or reconstruction inaccuracies. Common artefacts include attenuation artefacts, patient motion artefacts, centre-of-rotation errors, ring artefacts, and streak artefacts from limited angular sampling.

SPECT artefacts arise from attenuation, motion, misalignment, and reconstruction limitations, and understanding their origin is essential for accurate interpretation.

Because SPECT reconstruction integrates data from multiple projections, even small inconsistencies can produce visible artefacts in reconstructed slices. Understanding their physical origin is essential for accurate interpretation.

Understanding the physics

SPECT relies on accurate projection data and correct modelling of photon behaviour. Artefacts occur when assumptions made during reconstruction are violated.

Attenuation artefacts occur because photons emitted from deeper structures are absorbed within the body. If attenuation is not corrected, these regions may appear falsely reduced in activity. This is particularly important in myocardial perfusion imaging, where diaphragmatic or breast attenuation can simulate perfusion defects.

Motion artefacts arise when the patient moves during acquisition. Because projections are acquired sequentially over several minutes, movement between angles leads to misalignment between projections. During reconstruction, this inconsistency produces blurring or duplication of structures.

Centre-of-rotation errors occur when the assumed rotational axis differs from the true mechanical axis. This leads to circular misregistration and ring artefacts in reconstructed slices.

Ring artefacts may also result from detector non-uniformity. Small variations in detector response become amplified during reconstruction.

Streak artefacts can occur when angular sampling is insufficient. If too few projections are acquired, reconstruction may produce star-like streaking patterns, particularly with filtered back projection.

Because SPECT uses mechanical collimation and single-photon detection, it is more susceptible to attenuation and scatter artefacts than PET.

Where this matters clinically

Recognising artefacts prevents false-positive diagnoses. For example, distinguishing attenuation artefacts from true perfusion defects is critical in cardiac imaging. Routine quality control and appropriate reconstruction methods reduce artefact incidence.