Optimising image quality and radiation dose with a focus on geometry and attenuation

Optimisation in medical imaging ensures an appropriate balance is achieved between acquiring images of diagnostic quality and the radiation dose received by the patient. Pragmatic, simple and effective methods are essential to ensure that optimisation techniques are adopted into clinical practice.The six papers presented within this thesis explore geometry and/or attenuation for various imaging techniques in order to optimise image quality and radiation dose. The first paper explores the impact of SID and magnification on image quality and radiation dose for AP pelvis on the x-ray tabletop. The next two papers explore SID for AP pelvis trolley work. The additional geometry and attenuation considerations from the mattresses and image receptor holder, as well as the lack of AEC, reinforced the importance of optimising this examination. The final three papers focus on neonatal chest imaging within incubators, which presents similar challenges to trolley imaging in terms of geometry (SID, OID and magnification) and attenuation. The overall aim was to establish optimal acquisition parameters for these imaging techniques.To demonstrate the collective contribution of the six papers, the thesis is spilt into sections that critically evaluate new and novel findings. The first section demonstrates the methods used to evaluate image quality and radiation dose with certain areas highlighted as requiring improvements, such as the standardisation of the methods used to derive SNR/CNR and their correlation to visual image quality. Geometry and attenuation are then considered individually to highlight their impact on image quality and radiation with numerous recommendations made for clinical practice. These include the use of maximum achievable SID for AP pelvis (tabletop and trolley) to reduce patient radiation dose but to also ensure reduction in magnification especially from the increased OID associated with trolley imaging. Maximum achievable SID is also advocated for neonatal chest imaging when using the image receptor holder, with a 100cm SID at lower mAs found to be optimal for direct neonatal chest imaging. The use of maximum achievable SID for trolley and incubator imaging requires a corresponding increase in mAs to compensate for the combined effect of increasing SID and the additional attenuation. Using maximum achievable SID will also result in some magnification variation within images and therefore it is recommended that images are annotated with the SID used, and whether an image receptor holder is used, to help with image interpretation. The impact of the work is considered through evaluating educational impact, citation analysis, training opportunities, implementation, influence on procurement, and manufacturer collaboration. Overall, the work demonstrates developments and new knowledge when optimising image quality and radiation dose for AP pelvic imaging (tabletop and trolley) and neonatal chest imaging with the main findings related to geometry and attenuation. Increasing SID is advocated for all examinations explored, with the exception of direct neonatal chest imaging. The recommended increase in SID may require a corresponding increase in mAs to compensate for geometry (SID and OID) and attenuation from the mattresses and image receptor holder of trolleys and incubators. The difference in OID for the various techniques, in combination with the maximum achievable SID, will cause variation in image magnification and this should be made transparent to those interpreting the images