Radiology, Vol 181, 273-276, Copyright © 1991 by Radiological Society of North America
Quantitative assessment of quality of digitized portal images: receiver operating characteristic analysis applied to imaging in radiation therapy
K Okajima, M Nakata, S Yano, Y Nagata, I Kimura, Y Nakano and M Abe
Department of Radiology, Faculty of Medicine, Kyoto University, Japan.
An objective and quantitative method for the evaluation of the quality of
megavoltage portal images was developed by applying receiver operating
characteristic analysis. On the basis of therapeutic use of portal images,
setup errors were employed as "signals" in this experimental study that
compared the original portal films with digitized images. Six readers
observed 104 portal images of a chest phantom, half of which were
"abnormal" (ie, had setup errors). Digital images (2,048 x 2,048 matrix)
were enhanced by means of histogram equalization and then printed with a
laser printer for observation. The readers showed a higher discrimination
capacity with the digitally enhanced images, although a statistically
significant improvement was not demonstrated. The present method of
assessment of image quality proved to be both simple and clinically
reasonable.
