Are the target exposure index and deviation index used efficiently?

Exposure index (EI) is important to evaluate correct exposure in radiography and thus important for image quality. The purpose of this study was to evaluate whether the target exposure index (EI_T) and deviation index (DI) were used efficiently.

Radiography departments in Iceland, using <10 years old equipment, were invited to participate. For each x-ray unit, admin users were asked about the use of EI_T and data was gathered on EI_T for five body parts (BP); lumbar spine, chest, hip, knee and hand. For each of the five BP, 100 examinations from the past year were selected randomly (or all, if < 100). The EI from one predefined view was recorded and the corresponding DI calculated.

A total of ten x-ray units, from four manufacturers and located at eight departments, were included in the study. The departments involved are comprised of a university hospital, smaller hospitals, and miscellaneous private departments. Two departments (25%) had not set EI_T, five (62.5%) used default values and only one had revised EI_T values. In four departments (50%) radiographers favored "acceptable EI range" over DI. The mean EI was significantly different (p < 0.05) from the EI_T in the majority of the five BP, in four out of the six departments that had defined EI_T. In total 30% of images from all departments combined had DI outside the range of -3.0 < DI < +3.0. The standard deviation of DI was from 1.4 to 2.7.

The study shows that the EI_T and DI are not used efficiently, regardless of equipment vendor or department characteristics.

Current recommendations on targeting the mean DI of 0 need to be reinforced. Theoretical knowledge and training need to be improved.