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A new digital radiographic system (Matrix Laser Rad) employing a filmless photostimulable reusable phosphor (PSP) was evaluated for spatial resolution and high and low contrast object detectability. Receiver operator characteristic curve (ROC) comparisons were made to film images using equal or lower exposure factors. The low and high contrast test objects for the ROC evaluation were respectively a 5/32 inch diameter hemispheric depression filled with mineral oil and 250-500 micrometer diameter silicon carbide granules, both in a 2 inch thick plexiglass block. These object sizes were shown to be at thresh-old of detectability for either the film or PSP system at the exposure factors used. The ROC curves were generated from data obtained by radiologists viewing multiple film radiographs and CRT displays of both the digitized film radiographs and PSP images with the test objects in random locations. There were 90 images generated for each system, 45 with test objects and 45 without. Each observer had 15 seconds at a fixed distance to view each image presented at random at standard view box intensities (140 foot-lamberts) on either a light view box or CRT. The unenhanced filmless PSP radiographs had a reduced detectability threshold for the test objects, however with the use of windowing, level manipulations and appropriate filtering, detectability could be improved for the low contrast objects with the digital system surpassing unenhanced film radiographs. In addition, a dose reduction could be achieved with the PSP filmless system without loss of significant detectability. Enhanced film radiographs demonstrated the highest detectability characteristics. To achieve similar detectability for high contrast objects with the PSP system, a significant increase in object size was necessary.
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