Correlation between exposure indicators and image quality in chest radiographs

Abstract

The exposure index (EI) and its deviation (DI) convert the amount of X-rays received by the detector into a numerical value in radiography. A DI of 0 indicates ideal exposure, while higher values indicate overexposure and lower values indicate underexposure. This experimental study evaluated the influence of exposure indicators (EI and DI) on image quality (IQ) in chest radiographs. A fixed radiographic device, a semi-anatomic chest phantom, and a computed radiography (CR) system were used. During image digitization, twenty combinations of exposure techniques were tested, ten for each incidence: posteroanterior (PA) and lateral (LAT). The voltage value was kept constant at 120 kV, while the current-time product (mAs) was varied. EI and DI values were obtained at the CR system workstation, while IQ was assessed using the “histogram” tool of the ImageJ software, calculating the signal-to-noise ratio (SNR) based on the mean signal and noise values. The results indicated that images 5, 6, and 7 in PA and 8, 9, and 10 in LAT had DI within the recommended range (-1 to 1). Image 5 (120 kV/5 mAs) and image 8 (120 kVp/16 mAs) had DI values of -0.3 and -0.5 for PA and LAT, respectively, and higher SNR values compared to other images, exemplifying the effective application of the ALARA principle. It was concluded that adjustments in exposure techniques affect the exposure indicators (EI and DI) more than the IQ (SNR) in chest exams with CR systems.