Experimental demonstration of a dynamic bowtie for region-based CT fluence optimization

Technology development in Computed Tomography (CT) is driven by clinical needs, for example the need for image quality sufficient for the clinical task, and the need to obtain the required image quality using the lowest possible radiation dose to the patient. One approach to manage dose without compromising image quality is to spatially vary the X-ray flux such that regions of high interest receive more radiation while regions of low interest or regions sensitive to radiation receive less dose. If the region of interest (ROI) is centered at the CT system's axis of rotation, a simple stationary bowtie mounted between the X-ray tube and the patient is sufficient to reduce the X-ray flux outside the central region. If the ROI is off center, then a dynamic bowtie that can track the ROI as the gantry rotates is preferred. We experimentally demonstrated the dynamic bowtie using a design that is relatively simple, low cost, requires no auxiliary power supply, and can be retrofitted to an existing clinical CT scanner. We installed our prototype dynamic bowtie on a clinical CT scanner, and we scanned a phantom with a pre-selected off-center ROI. The dynamic bowtie reduced the X-ray intensity outside the targeted ROI tenfold. As a result, the reconstructed image shows significantly lower noise within the dynamic bowtie ROI compared to regions outside it. Our preliminary results suggest that a dynamic bowtie could be an effective solution for further reducing CT radiation dose.