Purpose: There are many clinical situations where diagnostic CT is used for an initial diagnosis or treatment planning,
followed by one or more CBCT scans that are part of an image-guided intervention. Because the high-quality diagnostic
CT scan is a rich source of patient-specific anatomical knowledge, this provides an opportunity to incorporate the prior
CT image into subsequent CBCT reconstruction for improved image quality. We propose a penalized-likelihood method
called reconstruction of difference (RoD), to directly reconstruct differences between the CBCT scan and the CT prior.
In this work, we demonstrate the efficacy of RoD with clinical patient datasets.
Methods: We introduce a data processing workflow using the RoD framework to reconstruct anatomical changes
between the prior CT and current CBCT. This workflow includes processing steps to account for non-anatomical
differences between the two scans including 1) scatter correction for CBCT datasets due to increased scatter fractions in
CBCT data; 2) histogram matching for attenuation variations between CT and CBCT; and 3) registration for different
patient positioning. CBCT projection data and CT planning volumes for two radiotherapy patients – one abdominal study
and one head-and-neck study – were investigated.
Results: In comparisons between the proposed RoD framework and more traditional FDK and penalized-likelihood
reconstructions, we find a significant improvement in image quality when prior CT information is incorporated into the
reconstruction. RoD is able to provide additional low-contrast details while correctly incorporating actual physical
changes in patient anatomy.
Conclusions: The proposed framework provides an opportunity to either improve image quality or relax data fidelity
constraints for CBCT imaging when prior CT studies of the same patient are available. Possible clinical targets include
CBCT image-guided radiotherapy and CBCT image-guided surgeries.
Hao Zhang, Grace J. Gang, Junghoon Lee, John Wong, and J. Webster Stayman, "Integration of prior CT into CBCT reconstruction for improved image quality via reconstruction of difference: first patient studies," Proc. SPIE 10132, Medical Imaging 2017: Physics of Medical Imaging, 1013211 (Presented at SPIE Medical Imaging: February 15, 2017; Published: 9 March 2017); https://doi.org/10.1117/12.2255513.
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