Even with the high degree of technology used in CAT scan imaging, sometimes anomalies show up in the pictures. The list provided below provides descriptions and reasons for anomalies to occur.
Streak Artifact: Streaks will show up in images around objects that block x-rays. These are caused by metal objects, motion, beam hardening, photon starvation, and under sampling.
Partial Volume Effect: Appears as blurred edges of structures, and are often found near areas where bone and cartilage converge. May be possible to overcome by using thinner slices of picture.
Ring Artifact: Image will contain one or multiple rings. This occurs when the machine is not calibrated correctly or is broken.
Noise: The image shows up granulated. This may due to insufficient power to the machine or due to picture slices being to thin.
Motion Artifact: Shows up as a blurred or streaked image. This is caused by motion of the object at the time the image is taken.
Windmill: This looks like wide streaking in a circular pattern and occurs when the reconstruction plane and detectors intersect. Filters and pitch adjustment can correct this.
Beam Hardening: Shows a cupped image. Happens because of a large attenuation path passing through an objects center. This can be corrected with filters and software.