Storage Phosphor Digital Radiography in Portable Chest Imaging : Comparison of Image Quality with ConventionalFilm-Screen System with Variation of mAs

Abstract

Purposes : To compare image quality of storage phosphor digital radiography(DR) with film-screen radiographyin portable chest imaging, and to assess the minimum X-ray dose that can be applied to DR in adults without imagedegradation, and also to compare image qualities of low dose and standard dose DR. Materials and Methods : Ageometrical phantom similar to the human thorax was imaged by a portable radiographic unit with fixed kVp andvariable mAs in both film-screen and DR systems. Three radiologists scored the images by four grades in fourcategories of 1)contrast between mediastinum and lung, 2)definition of the nodule in the lung, 3)definition ofanother nodule through the mediastinal shadow, and 4)grainess(noise: assessed only in DR). Additionally, portablechest images were obtained in 10 patients in a intensive care unit by film-screen, standard dose and half dose DRin consequtive days. The same readers scored the images by four grades in six categories of 1)the lungs and hila,2)the mediastinum, 3)subphrenic area. 4)musculoskeletal shadow, 5)tubes and lines, and 6)grainess(only in DR). Theimages with superior quality were assessed by paired t-test. Results : In phantom study, the minimum dose ofdigital images scored 3 or more by all readers was 39% of the standard dose. In patient study, DR was superior tofilm-screen radiography in all categories except tube and line. Low dose DR was not inferior to standard dose DRin five categories other than grainess to two readers or more. Conclusion : In portable chest imaging, storagephosphor DR image was superior to conventional film-screen radiography and half dose DR was comparable to standarddose DR despite of more noise.