Image Evaluation and Quality Assurance
Evaluation
Assess against explicit criteria: correct patient and marker, all required anatomy included, no rotation, adequate inspiration or positioning, exposure index within range, acceptable contrast and sharpness, no artefact, and no avoidable collimation of essential anatomy. Reject analysis should classify cause - patient, equipment, technique or processing - and feed a cycle of improvement rather than blame. Dose reference levels and exposure index trends are audit tools.
Quality assurance programme
Acceptance testing by a medical physicist precedes first clinical use. Routine testing covers tube output, kVp accuracy, automatic exposure control performance, collimation alignment, grid performance, detector uniformity, monitor calibration to the DICOM grey-scale display function, and printer output. Frequency varies: some tests daily, others monthly, quarterly or annually. Radiographers perform many routine tests and must record and escalate failures; physicists perform performance testing; the operator or owner is accountable overall.
Artefacts
Grid cut-off from off-level, off-centre or wrong-distance positioning; CR plate scratches and ghosting; detector dead pixels; motion; clothing and jewellery; backscatter; CR line artefacts; CT beam-hardening streaks.
Traps
Confusing quality assurance with quality control; failing to document results; deleting rather than flagging a rejected image; describing an image as poor without naming a criterion and a cause.
Rule of thumb
If exposure indices are consistently high or low across many patients in one room, suspect equipment calibration rather than every radiographer's technique. Check the automatic exposure control and tube output before re-educating staff.