When CT scanners were first developed, the X-ray tube that rotated around the patient's body was attached to the machine by the powering electrical cables. The limited length of the cables prevented the X-ray tube from continuously revolving around the patient. Instead, the machine's head would make one 360-degree loop (generating the information needed to construct one image) and then stop. The patient would be advanced forward a bit, and the X-ray head would rotate backward 360 degrees, generating the next image as the power cable unwound.

Then engineers devised a way to send power to the X-ray as it rotated through a sliding ring, thus disconnecting it from a fixed cable and allowing it to rotate around the patient as he or she was eased forward through the machine. This "low-dose spiral CT scanner" generates a spiral "cut" through the patient that approximates a long series of sliced images. The method speeds the scanning process and decreases the radiation dose to the patient.