SU-F-BRCD-07: Experimental Validation of Fluence Field Modulation for Noise and Dose Management in CT

Dose management in CT is a growing concern as the number of CT scans per capita rises. Fluence field modulated computed tomography (FFMCT) is a proposed approach for more optimal dose management, where the incident fluence pattern can change independently for each projection in order to minimize dose while meeting prescribed image quality metrics. This work studies the application of FFMCT for dose and noise management to a small cylindrical phantom.

Experiments were carried out on an experimental CT system using a small cylindrical phantom comprised of acrylic spheres, water and teflon rods as the object of interest. Modulation of the incident fluence was optimized using a simulated annealing algorithm that attempts to achieve user-prescribed, regionally varying SNR criteria while limiting dose. The modulated projections were synthesized from projection sets taken at various tube current settings. SNR patterns and predicted dose outcomes were compared to the prescribed values as well as against expected results using a bowtie filter.

FFMCT resulted in SNR outcomes with greater agreement to the prescribed regionally varying SNR criteria than achieved by the bowtie filter. Dose reductions were observed for the majority of the object, and reached as high as 60%. Limited regions, coinciding with lower noise, observed dose increases less than 20%. Integral dose reduction over the entire object was greater than 40% when compared to a bowtie filter with comparable image quality in the region of interest.

The results support the hypothesis that FFMCT has the potential to meet user-prescribed, regionally varying image quality objectives, while decreasing radiation dose to the patient. These results suggest that given a suitable collimator approach, fluence field modulated computed tomography could reap significant benefits in terms of reducing dose and optimizing image quality. NSERC.