Digital Radiography Best Practices: Dose, Quality and Workflow

Why digital radiography needs active dose control

With film, an over-exposed image was visibly too dark and was repeated. With a digital detector the software normalises brightness, so over-exposure can produce a pleasant, low-noise image without any visible warning. The result can be a slow rise in average exposure over time, known as dose creep, driven by the natural preference for cleaner images.

Professional bodies, including ASRT, publish guidance for digital radiography, and national and international standards exist for exposure indicators. Use those documents as the basis for your protocols and confirm what your local regulator and health authority expect.

Exposure index in digital radiography

The exposure index (EI) tells you how much radiation reached the detector for a given image. Most manufacturers also provide a target EI and a deviation index showing how far the exposure is from the target. Following the standard framework (IEC 62494-1), a deviation index near zero means the exposure matched the target, positive values mean over-exposure and negative values under-exposure.

Make the EI and deviation index visible to the radiographer at the console, set target values for each body part with your physicist, and review the values regularly. Check that the detector is calibrated, because incorrect calibration makes the index misleading; see flat panel detector care.

• Define target EI per examination and detector
• Review deviation index trends monthly
• Investigate repeated high values, not only low ones
• Recalibrate after repairs or if the index looks inconsistent

Preventing dose creep: technique and collimation

Use technique charts and the automatic exposure control where appropriate, apply the lowest exposure that gives diagnostic quality, and train radiographers to accept slightly noisier images when the diagnostic information is adequate. Review technique charts when detectors are changed, since sensitivity differs between models.

Collimate to the area of interest and avoid repeated use of a larger field than required: it lowers dose, reduces scatter and improves contrast. Use a grid only when body-part thickness and technique justify it, as explained in our guide to anti-scatter grids and bucky devices, and consider virtual grid software for portable examinations.

Special groups need special attention. Paediatric examinations should use child-specific techniques and positioning aids, and the same detector sensitivity that suits an adult may be wrong for an infant. Bariatric patients may need higher exposure, and the target EI should reflect this rather than being forced to the standard value.

Image processing and presets

Image processing improves visibility but should not hide a poor exposure. Use the anatomical presets provided for each examination and avoid manually adjusting contrast and brightness repeatedly. Villa's Moviplan iC DR, for example, uses VDX Next software with anatomical presets and advanced image processing, plus optional Software Grid, Bone Suppression and Boost Lines. Evaluate such options on your own cases with the radiologist before routine use.

Standardise display settings and monitors so that images are read under consistent conditions. Make sure DICOM output, annotation and image orientation are correct, since these determine downstream use; our article on digital radiography and PACS covers integration.

Reject analysis and ongoing quality assurance

Reject analysis counts and classifies repeated images by cause: positioning, exposure, motion, artefact, wrong patient or equipment fault. A rate that is tracked by room, shift and examination points to the areas where training or equipment changes will help. Many departments review rejects every month and set a target rate with their radiologists and physicist.

Combine reject analysis with the technical checks in X-ray quality control tests. For a broader overview of how DR works, see DR systems in radiology. To discuss workflow and software options for your department, request a consultation from Beckfinity.

Finally, make training continuous. New staff, new detectors and software updates all change behaviour, so schedule short refresher sessions that use real reject and EI data from your own department.