Image quality and its evaluation

The medical doctors and technicians engaged in CT (computed tomography) need to know the picture characteristics of CT apparatuses prior to the clinical applications. The evaluation of CT image quality, which is extremely important, is currently in a confused state, as it is entrusted to the manufacturers or made by the diversified method of individual personnel. The practices of CT picture quality evaluation are explained on the basis of the results reported by an ad hoc committee: noise, contrast scale, spatial resolving power, contrast resolving power, exposure dosage, artifact, dimensional dependency, positional dependency, edge effect, absorption coefficient and CT value linearity, geometrical and contrast image distortion in display devices, and reproducibility. CT picture evaluation requires the standardization; so, the unification of ideas, the determination of the evaluation items and the trial making of standard phantoms are necessary. (J.P.N.)