C. Trauernicht

Filtration to reduce paediatric dose for a linear slot-scanning digital X-ray machine

This paper describes modelling, application and validation of a filtration technique for a linear slot-scanning digital X-ray system to reduce radiation dose to paediatric patients while preserving diagnostic image quality. A dose prediction model was implemented, which calculates patient entrance doses using variable input parameters. Effective dose is calculated using a Monte Carlo simulation. An added filter of 1.8-mm aluminium was predicted to lower the radiation dose significantly. An objective image quality study was conducted using detective quantum efficiency (DQE). The PTW Normi 4FLU test phantom was used for quantitative assessment, showing that image contrast and spatial resolution were maintained with the proposed filter. A paediatric cadaver full-body imaging trial assessed the diagnostic quality of the images and measured the dose reduction using a 1.8-mm aluminium filter. Assessment by radiologists indicated that diagnostic quality was maintained with the added filtration, despite a reduction in DQE. A new filtration technique for full-body paediatric scanning on the Lodox Statscan has been validated, reducing entrance dose for paediatric patients by 36 % on average and effective dose by 27 % on average, while maintaining image quality.

Dose Optimisation in CT Colonography

There is a growing awareness that radiation dose originating from medical diagnostic procedures in radiology is contributing an increasing proportion of the total population dose, especially for examinations using computed tomography (CT). In response to the heightened awareness of the importance of patient dose contributed by radiology procedures, there has been a general trend to optimise CT examinations to obtain the required diagnostic outcome while minimising the dose to the patient. This chapter describes various options for dose optimisation in CT colonography (CTC). These techniques are not necessarily unique to CTC and can be applied for optimisation of CT-scan protocols for other sites as well. Dose-reduction tools discussed include tube current reduction and automatic tube current modulation, tube voltage, iterative reconstruction, filtration, active collimation, CT detectors, shielding and other factors such as pitch and slice thickness.

Principles of Radiation Dose in Computed Tomography and Computed Tomography Colonography

Radiation dose in X-ray computed tomography (CT) has become a topic of high interest due to the increasing numbers of CT examinations performed worldwide. Computed tomography has its own dose quantities, including the computed tomography dose index (CTDI) and its variations, as well as the dose-length product (DLP). The measurement and use of these quantities is described in this chapter. The CTDI is often substituted as the patient dose, but in reality it is only the dose to a particular phantom and not the patient dose. In addition, the latest CT scanners have scan widths that are wider than the scan widths that the scanners had when the CTDI was introduced; this potentially makes the CTDI an inaccurate dose measure and correction factors have to be applied. The concepts of effective dose and diagnostic reference levels (DRLs) are introduced.