Why does CT-scan require a prep but a CAT -scan doesn't?

Actually, a CT scan and a CAT scan refer to the same imaging technique; "CAT scan" stands for "Computed Axial Tomography," which is an earlier term for CT scanning. The preparation required for a CT scan often depends on the specific type of scan being performed and the area of the body being examined. Certain scans may necessitate fasting or other preparations to ensure clear imaging, especially if contrast dye is used, while others may not require any prep.