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Abstract
Reaching the full potential of X-ray nanotomography, in particular for biological samples, is limited by many factors, of which one of the most serious is radiation damage. Although sample deformation caused by radiation damage can be partly mitigated by cryogenic protection, it is still present in these conditions and, as we exemplify here using a specimen extracted from scales of the Cyphochilus beetle, it will pose a limit to the achievable imaging resolution. We demonstrate a generalized tomographic model, which optimally follows the sample morphological changes and attempts to recover the original sample structure close to the ideal, damage-free reconstruction. Whereas our demonstration was performed using ptychographic X-ray tomography, the method can be adopted for any tomographic imaging modality. Our application demonstrates improved reconstruction quality of radiation-sensitive samples, which will be of increasing relevance with the higher brightness of 4th generation synchrotron sources. Radiation induced sample deformation can be a limiting factor for X-ray imaging resolution at the nanoscale. The authors report a tomographic model that estimates and accounts for morphological changes during data acquisition and enables reconstruction of a high-resolution image ab initio.
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Guo M, Chee G, O'Connell D, Dhou S, Fu J, Singhrao K, Ionascu D, Ruan D, Lee P, Low DA, Zhao J, Lewis JH. Reconstruction of a high-quality volumetric image and a respiratory motion model from patient CBCT projections. Med Phys 2019; 46:3627-3639. [PMID: 31087359 DOI: 10.1002/mp.13595] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 04/10/2019] [Accepted: 05/08/2019] [Indexed: 12/25/2022] Open
Abstract
PURPOSE To develop and evaluate a method of reconstructing a patient- and treatment day- specific volumetric image and motion model from free-breathing cone-beam projections and respiratory surrogate measurements. This Motion-Compensated Simultaneous Algebraic Reconstruction Technique (MC-SART) generates and uses a motion model derived directly from the cone-beam projections, without requiring prior motion measurements from 4DCT, and can compensate for both inter- and intrabin deformations. The motion model can be used to generate images at arbitrary breathing points, which can be used for estimating volumetric images during treatment delivery. METHODS The MC-SART was formulated using simultaneous image reconstruction and motion model estimation. For image reconstruction, projections were first binned according to external surrogate measurements. Projections in each bin were used to reconstruct a set of volumetric images using MC-SART. The motion model was estimated based on deformable image registration between the reconstructed bins, and least squares fitting to model parameters. The model was used to compensate for motion in both projection and backprojection operations in the subsequent image reconstruction iterations. These updated images were then used to update the motion model, and the two steps were alternated between. The final output is a volumetric reference image and a motion model that can be used to generate images at any other time point from surrogate measurements. RESULTS A retrospective patient dataset consisting of eight lung cancer patients was used to evaluate the method. The absolute intensity differences in the lung regions compared to ground truth were 50.8 ± 43.9 HU in peak exhale phases (reference) and 80.8 ± 74.0 in peak inhale phases (generated). The 50th percentile of voxel registration error of all voxels in the lung regions with >5 mm amplitude was 1.3 mm. The MC-SART was also applied to measured patient cone-beam projections acquired with a linac-mounted CBCT system. Results from this patient data demonstrate the feasibility of MC-SART and showed qualitative image quality improvements compared to other state-of-the-art algorithms. CONCLUSION We have developed a simultaneous image reconstruction and motion model estimation method that uses Cone-beam computed tomography (CBCT) projections and respiratory surrogate measurements to reconstruct a high-quality reference image and motion model of a patient in treatment position. The method provided superior performance in both HU accuracy and positional accuracy compared to other existing methods. The resultant reference image and motion model can be combined with respiratory surrogate measurements to generate volumetric images representing patient anatomy at arbitrary time points.
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Affiliation(s)
- Minghao Guo
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.,Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Geraldine Chee
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Dylan O'Connell
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Salam Dhou
- Department of Computer Science and Engineering, American University of Sharjah, Sharjah, 26666, United Arab Emirates
| | - Jie Fu
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Kamal Singhrao
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Dan Ionascu
- Department of Radiation Oncology, College of Medicine, University of Cincinnati, Cincinnati, OH, 45221, USA
| | - Dan Ruan
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Percy Lee
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Daniel A Low
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Jun Zhao
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - John H Lewis
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
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