What process involves applying radiation dose before and after the acquisition volume in helical CT?

Overranging is the process where radiation is applied before and after the acquisition volume in helical computed tomography (CT). This technique is implemented to ensure that the entire area of interest is adequately covered during the scanning process. Helical CT acquires images in a continuous spiral motion, which can cause some portion of the anatomy to be irradiated both before the actual start of the imaging (the scout or pre-scan) and after the end of the intended imaging area. This overlap helps in minimizing the risk of missing any anatomical structures at the edges of the scanned volume, providing a more complete dataset for image reconstruction.

In contrast, overbeaming refers to the phenomenon where radiation is directed at a larger area than necessary due to beam width or angle, which can lead to increased patient exposure without improving image quality. Pitch adjustment relates to the ratio of table movement to the beam width during a helical scan; altering this can change the amount of radiation used but does not directly pertain to the application of radiation before and after the acquisition volume. Reconstruction is the process of creating images from the data collected during the scan but does not involve the radiation delivery process itself.