What causes S-distorsion in imaging?

S-distortion, also known as pincushion distortion, typically occurs in imaging systems due to external factors or inherent characteristics of the equipment. In this case, the correct answer regarding the cause of S-distortion is linked to external magnetic fields. When imaging systems, especially those involving magnetic fields (like some fluoroscopic systems), are affected by external magnetic fields, this interference can disrupt the flow of electrons. This results in a distortion of the image as the path of the electrons is altered, causing the S-shaped artifacts in the imaging.

Understanding the mechanisms of distortion is crucial for optimizing imaging quality and ensuring accurate diagnostics. Proper calibration and contamination from external sources like magnetic fields must be accounted for in imaging protocols to minimize such distortions. The other choices, while related to imaging issues, do not fundamentally address the specific phenomenon of S-distortion.