Fletchers were built in two visually distinctive variations: Round-bridge (also known as high-bridge ) had a curved pilot house ; square-bridge (or low-bridge ) has a more angular pilot house that was roomier, had better visibility and was easier to fabricate; no round-bridge examples remain. In addition, after World War II the mainmasts on most Fletchers were converted to tripods to better support heavier radar antennas. Photos of Fletcher-class destroyers can usually be dated by the mainmast style and the camouflage paint scheme .
CT is regarded as a moderate- to high- radiation diagnostic technique. The improved resolution of CT has permitted the development of new investigations, which may have advantages; compared to conventional radiography, for example, CT angiography avoids the invasive insertion of a catheter. CT colonography (also known as virtual colonoscopy or VC for short) is far more accurate than a barium enema for detection of tumors, and uses a lower radiation dose. CT VC is increasingly being used in the UK and US as a screening test for colon polyps and colon cancer and can negate the need for a colonoscopy in some cases.