Purpose: Twin-beam dual-energy CT (TB-DECT) provides a cost-effective DECT platform. However, its performance in material specific imaging is known to be inferior to other major platforms. The purpose of this work is to optimize the spectra in TB-DECT using k-edge filters for three clinical tasks: virtual un-enhanced imaging with iodine, biphasic liver imaging with iodine and gadolinium, and small bowel imaging with iodine and bismuth.
Methods: A two-step scheme was proposed to optimize three parameters in TB-DECT, including x-ray tube potential, k-edge filter material (Ce/Gd/Er/Lu/W/Au/Bi), and filter thickness. First, all possible tube potential and filter pairs were used to form the â€œlow-energyâ€? beam. The thickness of each filter was fixed in this step to provide radiation output values equivalent to that of 0.05 mm Au with 100/120/140 kV (original TB-DECT design), and 0.025 mm Au with 80 kV. The â€œhigh-energyâ€? beam was formed by 100/120/140 kV pre-filtered with 0.6 mm Sn, and 80 kV with 0.3 mm Sn. Second, for each tube potential, the thickness of the filter material determined to be optimal in step 1 was gradually increased until achieving a radiation output value equal to the â€œhigh-energyâ€? beam. Three cylindrical water phantoms were designed, one for each imaging task, and virtually scanned with TB-DECT using the same total radiation dose. After material decomposition, noise in each basis material image was used to determine optimal parameters for TB-DECT.
Results: Optimal spectra were achieved with 0.184mm-W, 0.6mm-Sn, 120kV; 0.264mm-Gd, 0.3mm-Sn, 80kV; and 0.401mm-Bi, 0.6mm-Sn, 120kV for iodine, iodine/gadolinium, and iodine/bismuth imaging, respectively. Noise reduction of 40-90% was achieved with the optimized spectra compared to the original TB-DECT design. Optimized TB-DECT showed slightly inferior or comparable noise performance to dual-source DECT.
Conclusion: With optimized spectra, TB-DECT performance for two- and three-material decomposition tasks approaches that of current dual-source DECT scanners.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Institutes of Health under award numbers R21 EB024071. Dr. McCollough receives industry grant support from Siemens. No other potential conflicts of interest were declared.