Digitally subtracted images may require remasking due to which of the following?

Digitally subtracted images may require remasking primarily due to motion artifacts, which can occur if the patient moves between the pre- and post-contrast images used for subtraction. In digital subtraction angiography or similar imaging modalities, the process relies on the two images being perfectly aligned and the objects remaining stationary. Any movement can create discrepancies, resulting in unwanted artifacts that obscure or distort the final image. Therefore, remasking—adjusting the digital mask applied—becomes necessary to accurately represent the anatomical structures of interest.

Though noise artifacts and underexposure can impact image quality and interpretation, they do not specifically necessitate remasking in the same way that motion artifacts do. Noise typically affects the clarity of the image but does not disrupt the alignment of the two images used for subtraction, and underexposure deals primarily with the overall exposure level rather than misalignment or misregistration of the images. Thus, remasking is most critically tied to the dynamics of motion during imaging rather than these other factors.