Experimental spectral measurements of heavy K-edge filtered beams for X-ray computed mammotomography
A compact, dual modality computed mammotomography (CmT) and single photon emission computed tomography (SPECT) system for dedicated 3D breast imaging is in development. The CmT component utilizes novel, heavy K-edge filtration to practicably narrow the energy spectrum of the cone-shaped x-ray beam incident on the patient's pendant, uncompressed breast. This quasi-monochromatic beam in CmT is expected to improve discrimination of tissue with very similar attenuation coefficients while restraining dose levels to below that of existing dual view mammography. Our previous extensive simulation studies showed the optimal energy range that provides maximum dose efficiency for a 50/50 adipose/glandular breast is in the 35-40keV range. This current study aims to experimentally validate previous simulation results. Here, experimental pre-breast and post-breast collimated x-ray beam spectral measurements are made under tube operating voltages between 40-100kVp using filter materials from Z= 13-74, with K-edge values spanning that of Ce (K=40.4keV), and using different attenuating thicknesses of filter material, approximately equivalent to the 200 th and 500 th attenuating value layer (VL) thickness. Ce-filtered post breast spectra for 8cm to 18cm breasts are measured for a range of breast adipose/glandular compositions. Evaluated figures of merit include mean beam energy, spectral full-width at tenth-maximum, beam hardening and dose for the range of breast sizes. Measurements are shown to corroborate the simulations, and both indicate that for a given dose a 200 th VL of Ce filtration may have the most optimal performance in the dedicated mammotomography paradigm.
Crotty, DJ; McKinley, RL; Tornai, MP
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