A method for optimizing the x-ray tube current in ROI imaging using a simulation framework for radiation dose and image quality calculation for arbitrary fluence distributions

Sascha Manuel Huck; George S. K. Fung; Katia Parodi; Karl Stierstorfer

doi:10.1117/12.2580828

15 February 2021 A method for optimizing the x-ray tube current in ROI imaging using a simulation framework for radiation dose and image quality calculation for arbitrary fluence distributions

Sascha Manuel Huck, George S. K. Fung, Katia Parodi, Karl Stierstorfer

Author Affiliations +

Proceedings Volume 11595, Medical Imaging 2021: Physics of Medical Imaging; 1159505 (2021) https://doi.org/10.1117/12.2580828
Event: SPIE Medical Imaging, 2021, Online Only

Abstract

In previous works, we have presented concepts for dynamic beam attenuators (DBAs) allowing for substantial dose reductions. So far, we have used a tube current modulation (TCM) scheme where the tube current is proportional to the square root of the maximum object attenuation in each projection. As DBAs show particularly beneficial behavior in region-of-interest (ROI) imaging, the question arose whether the employed TCM method would still be the most meaningful in this case. We present a simulation framework calculating i) the dose distribution in the object and ii) the image quality in the ROI of the reconstructed images for a given primary fluence: The dose to every voxel was calculated from individual Monte- Carlo simulations for every beamlet. From this we can approximate the effective dose, that incorporates tissue-specific weighting factors describing the stochastic health risk, for any fluence distribution. Using the same fluence distribution, the image variance according to the propagated fluence can be calculated for a given ROI. We employed a homogeneous phantom with a centered ROI and a female thorax phantom where the ROI is described by either the heart or the spine. Eventually, we optimized the tube current according to the product of mean image variance in the ROI and patient dose. Furthermore, the tube current obtained was compared with a heuristic square root TCM (hsqTCM) method. In result, the optimized TCM matches the hsqTCM well for the idealized case of a central ROI in an elliptical, homogeneous phantom. For a more complex case with an off-center ROI, the optimized TCM differs substantially from the hsqTCM rule, offering an additional dose reduction of up to 30%.

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Sascha Manuel Huck, George S. K. Fung, Katia Parodi, and Karl Stierstorfer "A method for optimizing the x-ray tube current in ROI imaging using a simulation framework for radiation dose and image quality calculation for arbitrary fluence distributions", Proc. SPIE 11595, Medical Imaging 2021: Physics of Medical Imaging, 1159505 (15 February 2021); https://doi.org/10.1117/12.2580828

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