Room: Room 202
Purpose: To shape measured energy spectrum using different k-edge filters and determine minimum of energy overlapping in spectral CT imaging approach.
Methods: A CdTe x-ray detector (3x3mm) calibrated with â?µâ?·Co source was used to measure the energy spectrum at 80kVp and 140kVp from 64 slices CT scanner equipped with x-ray tube: beam quality 5.41 mm Al equivalent at 80kVp. An ACR approved phantom with elliptical extension and k-edge filters: Sn, Ag, W, Au, Pt and Ta of thicknesses ranging from 25 Âµm to 500 Âµm were used to shape the energy spectrum. Emitted energy spectrum, exit energy spectrum (attenuated by the phantom) and exit energy spectrum shaped with appropriate k-edge filters were obtained such that the same level of image noise at the selected kVps were maintained.The CdTe detector was aligned with the x-ray tube focal spot. To reduce the detectorâ€™s dead-time to <30%, a 1000 Âµm hole Tungsten collimator (1cm in diameter and 2mm in thickness) was positioned closed to the x-ray tube focal spot. Additional, 400 Âµm and 100 Âµm tungsten collimators were positioned at the top of the x-ray detector crystal.
Results: The percentage of overlapped region was calculated for the measured energy spectrums. The overlap of 89% in exit energy spectrum was chosen as the reference point. Combination of different k-edge filters showed different reduction percentage for overlapping regions with the maximum reduction up-to 29.4% was obtained when 50 Âµm thick Au filter used with 80kVp and 508 Âµm thick Sn filter used with 140kVp.
Conclusion: A 29% reduction in the overlapping region is substantial achievement. However, this reduced overlapping is still significant and will lead to considerable inaccuracy in the processed spectral CT images. Hence, using a wider energy range (such as 60kVp and 160kVp) will be the right choice in spectral CT imaging.