Lumbar spine radiography--poor collimation practices after implementation of digital technology

The transition from analogue to digital radiography may have reduced the motivation to perform proper collimation, as digital techniques have made it possible to mask areas irradiated outside the area of diagnostic interest (ADI). We examined the hypothesis that collimation practices have deteriorated since digitalisation.

After defining the ADI, we compared the proportion of the irradiated field outside the ADI in 86 digital and 86 analogue frontal lumbar spine radiographs using the Mann-Whitney test. 50 digital images and 50 analogue images were from a Norwegian hospital and the remainder from a Danish hospital. Consecutive digital images were compared with analogue images (from the hospitals' archives) produced in the 4 years prior to digitalisation. Both hospitals' standard radiographic procedures remained unchanged during the study. For digital images, the irradiated field was assessed using non-masked raw-data images.

The proportion of the irradiated field outside the ADI was larger in digital than in analogue images (mean 61.7% vs 42.4%, p<0.001), and also in a subsample of 39 image pairs that could be matched for patient age (p<0.001). The mean total field size was 46% larger in digital than in analogue images (791 cm(2) vs 541 cm(2)).

Following the implementation of digital radiography, considerably larger areas were irradiated. This causes unnecessarily high radiation doses to patients.