Bowtie and spectral filtration in CT for radiographic practice

Abstract

This review connects CT bowtie and spectral filtration with radiographic practice through a common framework linking patient geometry, exposure control, dose endpoints and task-specific image performance. A targeted narrative synthesis combined web and Europe PMC searches with reference follow-up. Evidence was compared by mechanism, study design, comparator and endpoint, without pooling or formal risk-of-bias assessment. The synthesis identified two interacting pathways through which off-centring affects exposure: mismatch between patient geometry and the bowtie-shaped beam, and changes in localiser information used by automatic exposure control. Scanner and endpoint differences prevent a universal off-centring penalty. Camera assistance can improve positioning or workflow without consistent downstream dose benefits. Spectral filtration changes attenuation and dose-conversion relationships, requiring task-specific assessment. Photon-counting studies identify additional calibration and scatter-correction requirements; adaptive attenuators remain a research perspective. Centring should be judged against the intended anatomical target and scanner protocol. Positioning accuracy, scanner dose indices, organ dose and diagnostic performance are distinct outcomes that do not necessarily improve together. Interpreting them together offers a more defensible basis for practice than applying a universal off-centring penalty. Radiographers should assess camera recommendations against the intended anatomy and localiser geometry. Protocol changes affecting quantitative CT require joint validation with radiologists and medical physicists. Local audits should examine positioning, dose and image quality separately.