Analysis of patient doses for myelogram and discogram examinations and their reduction through changes in equipment set-up

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Abstract
Patient doses for myelogram and discogram examinations performed on two C-arm X-ray units have been measured using dose-area product meters. Contributions to the dose from fluoroscopy and radiography have been obtained from analysis of results for a selection of examinations. Information was recorded about the individual beam projections used, in order to allow estimates of effective dose. Effective doses for lumbar myelograms were 3-4 mSv and for cervical myelograms and discograms were 1 mSv. The doses on the two units were similar, but contributions from the various parts of the examinations were different. Quality assurance (QA) measurements of dose variables were used to determine reasons for these differences in performance. Fluoroscopic doses are influenced by image intensifier dose rate and by the way in which exposure factor selection has been set up for the automatic exposure control (AEC) system. Doses from digital fluorography on units for specialized applications may be greater than those with standard film/screen systems. Recommendations have been made concerning ways in which doses on each unit might be reduced. Detailed assessments of doses resulting from AEC set-up options, made during QA tests, can help to ensure that the optimum balance between patient dose and image quality is achieved.