Radiation Dose and Image Quality in Spiral Computed Tomography: Results of a Multi-Centre Study at Eight Radiological Institutions

Abstract

To evaluate radiation dose (expressed as PCTDI or D AVE ) in correlation to image quality, seven clinical protocols were measured in eight radiological departments provided with six different types of high-end spiral CT scanners of the latest generation. Central and surface PCTDI for seven clinically applied protocols and one standardised liver protocol were determined with a dedicated phantom and ionisation chamber. For low contrast measurements, a cylindrical 3D phantom (different sized spheres of defined contrast) was tiled. Image noise was measured with a cylindrical water phantom, high contrast resolution with a Perspex hole phantom. Images were randomised, made anonymous and read by eight radiologists (one from each institution). Radiation output (PCTDI per 100 mA.s) for six different scanners varied by a factor between 1.7 (central PCTDI) and 2.0 (surface PCTDI) for the standardised protocol and by a factor of 4.3 for the 1 mm inner ear protocol. For seven clinically applied protocols of six radiological departments doses (expressed as D AVE /pitch) varied by factors between 1.7 (head protocol) and 8.3 (abdomen paediatric protocol). Low contrast detectability correlated closely with dose. An improvement in detection from 8 mm to 4 mm sized spheres needed approximately a tenfold increase in dose. Differences of modern CT scanner technology seem to he of minor importance for radiation exposure compared with selection of protocol parameters in different radiological institutes. Future discussion on guidelines, e.g. reference doses, should consider optimisation of tube current according to the individual patient and the clinical indication.