Master of Science (MS)
Physics and Astronomy
Purpose: Adaptive filtration facilitates spectral breast CT by decreasing count rate and dynamic range requirements of photon counting detectors. This project investigated the effect of adaptive filtration on beam hardening, CT numbers, noise, and dose in dedicated breast CT. Methods: Adaptive filters were simulated to provide a flat fluence at the detector surface when used with a 14 cm breast phantom at 120 kVp. Beam hardening with each filter type was measured against increasing x-ray beam half-fan angle.. Breast CT images were simulated with and without an adaptive filter in the beam at multiple tube voltages. CT number, noise, and contrast to noise ratio (CNR) were measured for contrast elements inside the phantom. Finally, dose measurements were performed with and without an adaptive filter to determine its effect on breast dose. Results: Acrylic filters, while larger in size, provided a more uniform spectral distribution across the detector field of view compared to other filters tested. Without the adaptive filter in the beam, CT numbers, noise and CNR of the contrast elements were non-uniform across the CT images, and became uniform when the adaptive filter was used. When combining an adaptive filter and scaled x-ray exposure, the CNR increased and became comparable to or higher than the CNR without using an adaptive filter. Measurements showed breast dose distributions were more spatially uniform with an adaptive filter than without. Furthermore, the dose distribution across the phantom with the adaptive filter was more uniform at lower tube voltages than at higher tube voltages. Conclusion: We concluded the filter material should be similar to breast tissue with respect to the attenuation coefficients and density. Acrylic adaptive filters provided the flattest intensity with minimal beam hardening for the 14 cm breast phantom. Finally, breast dose uniformity with filter was comparable or better than without filter.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Silkwood, Justin, "Spectral breast CT : effect of adaptive filtration on CT numbers, CT noise, and CT dose" (2013). LSU Master's Theses. 1332.