A framework to simulate CT images with tube current modulation

Tube current modulation (TCM) is routinely implemented in clinical CT imaging. By modifying the x-ray tube current as a function of patient attenuation, image quality can be made more consistent and radiation dose can be better managed. Optimal TCM settings depend on the scan protocol and the physical characteristics of the patient. This study was undertaken to develop a realistic TCM model and integrate it into a scanner-specific CT simulation platform, allowing for faithful emulation of CT scans with TCM and optimization of TCM methods. The developed model adjusts the mAs for each projection based on attenuation estimated from two localizers, a strength parameter similar to the implementation of one major CT manufacturer (Siemens CARE Dose 4D), and imposed tube power limits. To demonstrate the utility of this framework, a virtual imaging trial was conducted to characterize image quality as a function of TCM strength. Three XCAT phantoms (BMIs at 25th, 50th, and 75th percentile) were imaged at five TCM strengths, using a CT configuration based on the geometry and physics of a commercial scanner (Siemens Definition Flash). Noise magnitude was measured in each reconstructed CT slice, average noise magnitude was calculated in lungs and bones, and RMSE, PSNR, SSIM, and contrast were computed in the lungs. The TCM strength which minimized noise increased with phantom BMI, suggesting that optimal TCM settings will differ for patients of different sizes. This study demonstrates the first incorporation of TCM into a scanner-specific virtual imaging trial platform and its application to patient-specific optimization.