16 March 2011 Noise reduction in dual-source CT scanning
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With dual source CT, special attention has to be paid to scattered radiation. X-ray quanta from the second source (tube B) get scattered from the object in the scan field and are registered by the first detector (detector A) and vice versa ("cross scattered radiation"). Depending on object and CT scan parameters, the ratio of scattered radiation intensity s over primary radiation intensity p can even exceed unity. In order to restore contrast and to avoid artifacts, the scattered radiation signal needs to be determined and subtracted from the measured signal. However, the thus corrected projections experience a noise increase proportional to √(1+s/p). In CT, line integrals are often redundantly measured. With dual source CT, the rays within redundant projection data can be differently affected by cross-scattered radiation. Typically, rays which are complementary to those that experience maximum scattered intensity are affected by rather low scattered intensity. The current work presents a noise-weighted reconstruction scheme, depending on the scatter-to-primary ratio s/p, which leads to a minimal noise increase in these situations. The proposed weighting scheme can also be combined with other means of noise reduction in the case of scattered radiation correction, e.g. a subsequent spatial signal filtering. The effect of the weighting scheme is evaluated with phantom scans using typical dual energy CT parameter settings. For a water cylinder of 40 cm diameter, the weighting scheme leads to a pixel noise reduction of up to 16%. For a semi-anthropomorphic liver phantom a noise decrease of up to 5% was observed.
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M. Petersilka, M. Petersilka, B. Krauss, B. Krauss, K. Stierstorfer, K. Stierstorfer, } "Noise reduction in dual-source CT scanning", Proc. SPIE 7961, Medical Imaging 2011: Physics of Medical Imaging, 79613Q (16 March 2011); doi: 10.1117/12.878282; https://doi.org/10.1117/12.878282

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