Imaging description

Misregistration is a CT artifact caused by both gross patient or physiologic motion during helical or axial acquisition [1, 2]. Motion artifacts can cause a variety of appearances on CT, including shading, streaking and double contours [1]. The appearance and severity of CT motion artifacts varies depending on the magnitude, speed, and direction of patient movement, as well as on the speed of the CT scanner itself. Slight patient motion, such as from cardiac motion, peristalsis, or tremor, can cause misregistration during image reconstruction, and is detected as bands and streaks on the axial image at the level of motion [1]. This motion is most problematic for evaluation of soft tissues and rarely causes significant diagnostic dilemmas in the skeleton. Gross patient motion, which occurs in intoxicated patients who cannot lie still, or can be due to respiratory motion, can cause step-off between axial images that may be confused for fracture or dislocation (Figures 78.1–78.3). In this case, the step-off will involve not only the cortex but also overlying soft tissue planes, such as the posterior wall of the pharynx in the neck or the skin overlying the sternum (Figure 78.4). Blurring may also be seen in the adjacent soft tissues, confirming the presence of motion (Figure 78.5).