Imaging description

Stair-step reconstruction artifacts occur with ECG-gated CT scanning techniques. Bands of data in the z-direction are acquired at sequential heart beats in the cardiac cycle as the patient moves through the scanner and are reconstructed into a single image. If there is an irregular heart rhythm, the coronary arteries are not in the exact same location for the acquisition of each band of data, and then a phase misregistration, or stair-step artifact will be seen at the interface between these bands (Figure 31.1) These artifacts have a horizontal orientation and can range from mild to severe, rendering images non-diagnostic in the worst cases. Mild cases of stair-step artifact can be quite misleading, and may result in artifactual appearance of significant stenoses (Figures 31.1 and 31.2). However, on multiphase reconstructions acquired at different points in the cardiac cycle, these artifacts generally disappear or change in location (Figure 31.2). Routine confirmation of any significant coronary stenoses using these additional reconstructed phases is recommended to avoid misdiagnosis. Additionally, the absence of visible atherosclerotic plaque in association with a stenosis should serve as a clue that the lesion may be an artifact.

Importance

Stair-step artifacts are common and can be quite misleading. Inadvertent overestimation of coronary artery stenosis due to these artifacts may lead to unnecessary additional tests such as catheter angiography or stress testing and the risks and costs associated with these procedures.

Typical clinical scenario

Stair-step artifacts can be seen in nearly any coronary CT examination; however, they are particularly problematic in patients with irregular heart rates. Beta blockade may help educe heart rate variability during coronary CT. ECG-editing may help improve quality of examinations if patients have ventricular ectopy. If the arrhythmia is limited to one or several ectopic beats, the image data related to these ectopic beats can be deleted from the image dataset and may be able to salvage the examination.