Potential for unnecessary patient exposure from the use of storage phosphor imaging systems

Abstract

It is possible to use storage phosphor radiography (SR) devices in a manner that results in excess exposure to the patient without the operators knowledge. Because these SR systems have an automatic correction for the final optical density (OD) of the image, the technologist and radiologist will not be able to use excessive blackness of the image as a sign of overexposure. Tests reported here demonstrate that it is possible to obtain images of a chest phantom that appear acceptable with a 32 times difference in exposure (maximal exposure .86 R). It is possible to obtain exposures of a pelvis phantom that appear acceptable up to the tube limit of our machine (4.8R). Tests of the Fuji AC-i demonstrate that it will accept a much wider range of exposures than the AGFA ADC prototype which permits only a 7 times difference in exposure before The image is degraded.Exposure estimates, based on the dosimetry of the phantom, of the exposures actually used by our technologist when they obtain bedside chest radiographs initially demonstrated a range of estimated exposure of 8.5 TO 289 mR with an average exposure of 33 mR. When the exposure data was evaluated by the exposure techniques used by each individual technologist, the average exposure estimated to be used by each technologist ranged from 10 TO 289 mR, a 29 times difference in exposure. Based on this data, an educational program was commenced. Six months after the conclusion of the educational program, the range of average exposures used by the technologists on bedside chest radiographs varied from 24 to 121 mR, a 5 times range, with a mean of 55 mR. The 5 fold range of variation in exposure of beside chest radiographs is similar to that expected in conventional bedside chest radiographs.

One Year’s Results from a Server-Based System for Performing Reject Analysis and Exposure Analysis in Computed Radiography

“…While this has resulted in fewer repeats due to overexposed images, [9][10][11]16 it has also resulted in a phenomenon known as dose creep. 17,18 Because of the automatic adjustment of grayscale in digital imaging, until the limit of adjustment is reached, overexposed images have a more pleasing appearance than underexposed images. Technologists respond to feedback from radiologists who naturally prefer less noisy images.…”

Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI

“…Accordingly, in digital imaging modalities there is a tendency to increase the amount of radiation used to avoid this problem (dose creep) (92,93). Increasing doses in this manner does not necessarily improve diagnostic performance, but will always increase the patient dose.…”

The HVL in soft tissue and the AAPM and IEC exposure indices

“…Computed radiography and digital radiography systems have substantial exposure latitude, which, combined with modern reliable AEC systems, should always result in optimum images at doses that are as low as reasonably achievable, with minimal repeat rates. However, in the absence of counter-measures, such systems actually exhibit the phenomenon of exposure creep [4][5][6][7]. In addition, historical studies of exposure settings and patient doses have shown that there is a wide spread in these quantities [8][9][10].…”

“…Furthermore, each 15% change in kVp was equivalent to a factor of two in mAs, or in mA or time individually. The 15% value is derived from the reasonable approximation that the energy absorbed by the image receptor is proportional to kVp 5 and noting that 1.15 5 = 2.0 [2], leading to the well-known 15% rule [3].…”