In our previous study we successfully built a novel sheet-based dynamic beam attenuator (sbDBA) for fluence field modulation in X-ray computed tomography (CT) and performed a first-time experimental validation. In this work, we focus on the optimization of the DBA transmission properties for a given object. In clinical routine, CT scanners must cope with various attenuation properties differing from patient to patient. Typically, the attenuation of patients is high in the center of the fan beam, decreasing towards the periphery. The attenuation profiles of an object can also change for different X-ray tube positions. These variations cause unfavorable imbalances of image quality in the reconstructed object. Typically, the peripheral region, which is generally of minor diagnostically relevance, has relatively lower noise than the central region because the rays contributing to the peripheral region are less attenuated. This imbalance can be reduced by using beam-shaping prefilters, e.g. bowtie filters, attenuating the propagated intensity towards the periphery in a predefined, static profile. Bowtie filters, however, are not capable of dynamically adapting their attenuation to the attenuation profile of the patient. This can be accomplished by using dynamic beam attenuators (DBA) where the fan beam intensity can dynamically be modulated on a view-by-view basis, reducing noise inhomogeneities and enabling region-of-interest (ROI) imaging. Different scenarios (no attenuator, tube current modulation, conventional bowtie filter, the sbDBA and an ideal DBA) are compared in terms of image quality. The optimized sbDBA with tube current modulation (TCM) not only reduces the total radiation dose but also allows for spatial selection of intensity as required for ROI imaging.
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Applying Laser-driven Particle Acceleration Workshop: Using Distinctive Energetic Particle and Photon Sources