Four CT Scanner Generations

From historical perspective, four scanner generations are known in CT. Head scanners, which the patient by translation and rotation of the measurement system with pencil beam(a) or a small fan beam(b) and fan beam system. The “3^rd Generation” featuring a rotating detector(c)has clearly outdistance the “4^th generation” ,which utilizes stationary detector rings(d)

 Most commercial translation scanner offered a field of measurement for head examinations only. The first attempt to scan typical body cross sections by CT was also based on translation rotation principle. The ACTA scanner (automatic Computerized Axial Scanner) sampled a field of measurement with 48 cm diameter in a six minutes scans taken during a single brathhold. The instruction of fan beam scanning was the solution to this problem.

Instead of sampling a transmission profile, i.e a projection , by pencil beam with translator motion, a fan beam and a larger detector are were used to measure a complete projection simultaneously. In this approach, the available x ray power is utilized much more efficiently. The translator motion becomes obsolete and the system only executes a rotatory motion. The first whole body scanner with fan beam system came to market

 In 1976 and with this envisaged goal of 20 second per image scan time was achieved. In the first scanners of this type both the x ray tube and the detector rotated around the patient demanding  higher technical efforts but offering advantages with respect a component cost and image quality and image quality (3^rd generation). Only a little later scanner followed with a ring like stationary detector fully encircling the patient, so that only the x ray tube rotated (fourth generation). Only a little later scanner followed with a ring like stationary detector fully encircling the patient, so that quickly accepted, and translation rotation systems meanwhile disappeared almost type is over, both with respect to numbers installed and more importantly, with respect to development of multi row detectors, which will be discussed below, the third generation has prevailed