Information loss in visual assessments of medical images.
We applied information theory to quantify information losses in assessing contrast-detail (C-D) analysis. Images of a C-D phantom were acquired with a flat panel detector (FPD) and a computed radiography (CR) by changing surface entrance doses. Six phantom radiographs (FPD: five images; CR: one image) were prepared for visual evaluations. Thirteen radiographers and two radiologists participated in the observation test. Detectability was defined as the shortest length of the cylinders of which border the observers could recognize from the background, and was recorded using row number. Information content was defined as the entropy summation operatorp(i)log(1/p(i)) with detection probabilities p(i), which were calculated from distribution of detection rate of the ith column. Information loss, in unit of bits, was calculated as the difference between information obtained and information content when all the columns were detected. The information losses decreased with the increase in cylinder diameters and with the increase in surface entrance dose. Because the information loss varies depending on distribution of detection rate, this method of using the information theory was expected to be more sensitive in evaluating the C-D image quality than using the averaged values of detectability.
Niimi
Takanaga
T
Department of Radiological Technology, Nagoya University School of Health Sciences, 1-1-20 Daiko-minami, Higashi-ku, Nagoya 461-8673, Japan. takanaga213@ybb.ne.jp
Imai
Kuniharu
K
Maeda
Hisatoshi
H
Ikeda
Mitsuru
M
D015350:Contrast Sensitivity; D006801:Humans; D007257:Information Theory; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement; D014963:X-Ray Intensifying Screens