From the Guidelines
Step artifact in coronary computed tomography angiography (CCTA) is a type of image distortion that appears as stair-step or misalignment between adjacent image slices, primarily caused by inconsistent cardiac motion during image acquisition, as described in the context of CCTA scanning protocols 1.
Causes and Implications
The step artifact is most commonly associated with irregular heart rhythms, variations in heart rate during the scan, or patient movement. This artifact can significantly degrade image quality, potentially leading to misinterpretation of coronary anatomy and resulting in false positive or negative findings. The importance of minimizing such artifacts is underscored by the high negative predictive value of CCTA for detecting atherosclerosis, which is consistently reported in the range of 98% 1.
Minimization Techniques
To mitigate step artifacts, several strategies can be employed:
- Administering beta-blockers before the scan to stabilize heart rate, aiming for less than 65 beats per minute.
- Optimizing ECG-gating techniques.
- Adjusting scan protocols to increase temporal resolution.
- Utilizing newer CT scanners with faster rotation times and wider detector arrays.
Interpretation Considerations
When interpreting CCTA images affected by step artifacts, radiologists must carefully evaluate the impacted segments. They may need to correlate findings with other imaging modalities if diagnostic confidence is compromised. The choice of scanning protocol, such as helical (or spiral) scanning versus axial scanning (step-and-shoot), can influence the presence of artifacts, with axial scanning potentially introducing step artifacts due to its stepwise nature of image acquisition 1.
Clinical Implications
Given the potential of step artifacts to compromise the diagnostic accuracy of CCTA, it is crucial to prioritize techniques that minimize these artifacts, especially in the context of assessing cardiovascular risk in asymptomatic adults, as outlined in guidelines such as the 2010 ACCF/AHA guideline 1. By doing so, the quality of life and outcomes for patients can be improved by providing more accurate diagnoses and appropriate management plans.
From the Research
Definition of Step Artifact in CCTA
- The step artifact, also known as stair-step artifact, is a type of misregistration artifact that occurs in coronary computed tomography angiography (CCTA) images 2, 3, 4.
- This artifact is characterized by a stair-step or misregistered appearance in the transition areas of an acquisition over multiple cardiac cycles.
Causes of Step Artifact
- The occurrence of stair-step artifacts is determined by motion of the entire patient during table travel, particularly in large patients, and by motion of the heart, particularly when heart rates are variable 4.
- Heart rate variability and body mass index (BMI) are significant factors related to the occurrence of stair-step artifacts 3, 4.
Reduction of Step Artifact
- The use of third-generation dual-source CT scanners can reduce the occurrence of misregistration artifacts in CCTA images compared to second-generation scanners 2.
- A novel reconstruction algorithm, such as the ZeeFree algorithm, can significantly reduce the frequency and extent of stair-step artifacts in sequential ultra-high-resolution coronary photon-counting detector CT angiography 3.
- Prospective electrocardiography-gated axial scans with 64-detector CT can also reduce radiation dose and allow diagnostic imaging in most cases, but may show more nonevaluable artifacts than retrospective CCTA 5.