DIGITAL CHEST RADIOGRAPHY WITH PHOTOSTIMULABLE STORAGE PHOSPHORS - SIGNAL-TO-NOISE RATIO AS A FUNCTION OF KILOVOLTAGE WITH MATCHED EXPOSURE RISK

A photostimulable storage phosphor (PSP) digital radiography system was evaluated regarding the signal-to-noise ratio (S/N) on chest images acquired at differing peak kilovoltage settings but with matched risk from radiation exposure. Images of two chest phantoms were acquired by using bedside (portable) imaging equipment at tube voltages ranging from 60 to 120 kV. Exposure factors were set so that the effective dose equivalent, a risk estimator weighted for various organs, was approximately equal in all exposures. The S/N in the lung-equivalent regions was found to be slightly higher (maximum, 15%) in the low-energy exposures, while the S/N values in the mediastinum- and subdiaphragm-equivalent regions were approximately equal at all kilovoltage settings. The absence of a high sensitivity of S/N to kilovoltage in risk-matched PSP images should enable institutions to select x-ray beam quality on the basis of other imaging criteria.