| 1. | Srujan Singh, Ethan L. Nyberg, Aine N. O'Sullivan, Ashley Farris, Alexandra N.Rindone, Nicholas Zhang, Emma C. Whitehead, Yuxiao Zhou, Eszter Mihaly, Chukwuebuka C. Achebe, Wojciech Zbijewski, Will Grundy, David Garlick, Nicolette D. Jackson, Takashi Taguchi, Catherine Takawira, Joseph Lopez, Mandi J. Lopez, Michael P.Grant, Warren L. Grayson Point-of-care treatment of geometrically complex midfacial critical-sized bone defects with 3D-Printed scaffolds and autologous stromal vascular fraction Journal Article In: Biomaterials, vol. 282, no. 121392, 2022, ISSN: 0142-9612. @article{Singh2022,
title = {Point-of-care treatment of geometrically complex midfacial critical-sized bone defects with 3D-Printed scaffolds and autologous stromal vascular fraction},
author = {Srujan Singh and Ethan L. Nyberg and Aine N. O'Sullivan and Ashley Farris and Alexandra N.Rindone and Nicholas Zhang and Emma C. Whitehead and Yuxiao Zhou and Eszter Mihaly and Chukwuebuka C. Achebe and Wojciech Zbijewski and Will Grundy and David Garlick and Nicolette D. Jackson and Takashi Taguchi and Catherine Takawira and Joseph Lopez and Mandi J. Lopez and Michael P.Grant and Warren L. Grayson},
url = {https://www.sciencedirect.com/science/article/pii/S014296122200031X},
doi = {doi.org/10.1016/j.biomaterials.2022.121392},
issn = {0142-9612},
year = {2022},
date = {2022-03-01},
urldate = {2022-03-01},
journal = {Biomaterials},
volume = {282},
number = {121392},
abstract = {Abstract: Critical-sized midfacial bone defects present a unique clinical challenge due to their complex three-dimensional shapes and intimate associations with sensory organs. To address this challenge, a point-of-care treatment strategy for functional, long-term regeneration of 2 cm full-thickness segmental defects in the zygomatic arches of Yucatan minipigs is evaluated. A digital workflow is used to 3D-print anatomically precise, porous, biodegradable scaffolds from clinical-grade poly-ε-caprolactone and decellularized bone composites. The autologous stromal vascular fraction of cells (SVF) is isolated from adipose tissue extracts and infused into the scaffolds that are implanted into the zygomatic ostectomies. Bone regeneration is assessed up to 52 weeks post-operatively in acellular (AC) and SVF groups (BV/DV = 0.64 ± 0.10 and 0.65 ± 0.10 respectively). In both treated groups, bone grows from the adjacent tissues and restores the native anatomy. Significantly higher torque is required to fracture the bone-scaffold interface in the SVF (7.11 ± 2.31 N m) compared to AC groups (2.83 ± 0.23 N m). Three-dimensional microcomputed tomography analysis reveals two distinct regenerative patterns: osteoconduction along the periphery of scaffolds to form dense lamellar bone and small islands of woven bone deposits growing along the struts in the scaffold interior. Overall, this study validates the efficacy of using 3D-printed bioactive scaffolds with autologous SVF to restore geometrically complex midfacial bone defects of clinically relevant sizes while also highlighting remaining challenges to be addressed prior to clinical translation.
Keywords: 3D printing; Yucatan pigs; Decellularized bone; Stromal vascular fraction; Critical-sized bone defects},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract: Critical-sized midfacial bone defects present a unique clinical challenge due to their complex three-dimensional shapes and intimate associations with sensory organs. To address this challenge, a point-of-care treatment strategy for functional, long-term regeneration of 2 cm full-thickness segmental defects in the zygomatic arches of Yucatan minipigs is evaluated. A digital workflow is used to 3D-print anatomically precise, porous, biodegradable scaffolds from clinical-grade poly-ε-caprolactone and decellularized bone composites. The autologous stromal vascular fraction of cells (SVF) is isolated from adipose tissue extracts and infused into the scaffolds that are implanted into the zygomatic ostectomies. Bone regeneration is assessed up to 52 weeks post-operatively in acellular (AC) and SVF groups (BV/DV = 0.64 ± 0.10 and 0.65 ± 0.10 respectively). In both treated groups, bone grows from the adjacent tissues and restores the native anatomy. Significantly higher torque is required to fracture the bone-scaffold interface in the SVF (7.11 ± 2.31 N m) compared to AC groups (2.83 ± 0.23 N m). Three-dimensional microcomputed tomography analysis reveals two distinct regenerative patterns: osteoconduction along the periphery of scaffolds to form dense lamellar bone and small islands of woven bone deposits growing along the struts in the scaffold interior. Overall, this study validates the efficacy of using 3D-printed bioactive scaffolds with autologous SVF to restore geometrically complex midfacial bone defects of clinically relevant sizes while also highlighting remaining challenges to be addressed prior to clinical translation.
Keywords: 3D printing; Yucatan pigs; Decellularized bone; Stromal vascular fraction; Critical-sized bone defects |
| 2. | Chumin Zhao, Magdalena Herbst, Thomas Weber, Christoph Luckner, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, Jeffrey H. Siewerdsen, Wojciech Zbijewski Slot-scan dual-energy bone densitometry using motorized X-ray systems Journal Article In: Medical Physics, vol. 48, iss. 11, 2021, ISSN: 0094-2405. @article{Zhao2022,
title = {Slot-scan dual-energy bone densitometry using motorized X-ray systems},
author = {Chumin Zhao and Magdalena Herbst and Thomas Weber and Christoph Luckner and Sebastian Vogt and Ludwig Ritschl and Steffen Kappler and Jeffrey H. Siewerdsen and Wojciech Zbijewski},
url = {https://aapm.onlinelibrary.wiley.com/doi/full/10.1002/mp.15272},
doi = {doi.org/10.1002/mp.15272},
issn = {0094-2405},
year = {2021},
date = {2021-10-10},
urldate = {2021-10-10},
journal = {Medical Physics},
volume = {48},
issue = {11},
abstract = {Purpose
We investigate the feasibility of slot-scan dual-energy (DE) bone densitometry on motorized radiographic equipment. This approach will enable fast quantitative measurements of areal bone mineral density (aBMD) for opportunistic evaluation of osteoporosis.
Methods
We investigated DE slot-scan protocols to obtain aBMD measurements at the lumbar spine (L-spine) and hip using a motorized x-ray platform capable of synchronized translation of the x-ray source and flat-panel detector (FPD). The slot dimension was 5 × 20 cm2. The DE slot views were processed as follows: (1) convolution kernel-based scatter correction, (2) unfiltered backprojection to tile the slots into long-length radiographs, and (3) projection-domain DE decomposition, consisting of an initial adipose–water decomposition in a bone-free region followed by water–CaHA decomposition with adjustment for adipose content. The accuracy and reproducibility of slot-scan aBMD measurements were investigated using a high-fidelity simulator of a robotic x-ray system (Siemens Multitom Rax) in a total of 48 body phantom realizations: four average bone density settings (cortical bone mass fraction: 10–40%), four body sizes (waist circumference, WC = 70–106 cm), and three lateral shifts of the body within the slot field of view (FOV) (centered and ±1 cm off-center). Experimental validations included: (1) x-ray test-bench feasibility study of adipose–water decomposition and (2) initial demonstration of slot-scan DE bone densitometry on the robotic x-ray system using the European Spine Phantom (ESP) with added attenuation (polymethyl methacrylate [PMMA] slabs) ranging 2 to 6 cm thick.
Results
For the L-spine, the mean aBMD error across all WC settings ranged from 0.08 g/cm2 for phantoms with average cortical bone fraction wcortical = 10% to ∼0.01 g/cm2 for phantoms with wcortical = 40%. The L-spine aBMD measurements were fairly robust to changes in body size and positioning, e.g., coefficient of variation (CV) for L1 with wcortical = 30% was ∼0.034 for various WC and ∼0.02 for an obese patient (WC = 106 cm) changing lateral shift. For the hip, the mean aBMD error across all phantom configurations was about 0.07 g/cm2 for a centered patient. The reproducibility of hip aBMD was slightly worse than in the L-spine (e.g., in the femoral neck, the CV with respect to changing WC was ∼0.13 for phantom realizations with wcortical = 30%) due to more challenging scatter estimation in the presence of an air–tissue interface within the slot FOV. The aBMD of the hip was therefore sensitive to lateral positioning of the patient, especially for obese patients: e.g., the CV with respect to patient lateral shift for femoral neck with WC = 106 cm and wcortical = 30% was 0.14. Empirical evaluations confirmed substantial reduction in aBMD errors with the proposed adipose estimation procedure and demonstrated robust aBMD measurements on the robotic x-ray system, with aBMD errors of ∼0.1 g/cm2 across all three simulated ESP vertebrae and all added PMMA attenuator settings.
Conclusions
We demonstrated that accurate aBMD measurements can be obtained on a motorized FPD-based x-ray system using DE slot-scans with kernel-based scatter correction, backprojection-based slot view tiling, and DE decomposition with adipose correction.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Purpose
We investigate the feasibility of slot-scan dual-energy (DE) bone densitometry on motorized radiographic equipment. This approach will enable fast quantitative measurements of areal bone mineral density (aBMD) for opportunistic evaluation of osteoporosis.
Methods
We investigated DE slot-scan protocols to obtain aBMD measurements at the lumbar spine (L-spine) and hip using a motorized x-ray platform capable of synchronized translation of the x-ray source and flat-panel detector (FPD). The slot dimension was 5 × 20 cm2. The DE slot views were processed as follows: (1) convolution kernel-based scatter correction, (2) unfiltered backprojection to tile the slots into long-length radiographs, and (3) projection-domain DE decomposition, consisting of an initial adipose–water decomposition in a bone-free region followed by water–CaHA decomposition with adjustment for adipose content. The accuracy and reproducibility of slot-scan aBMD measurements were investigated using a high-fidelity simulator of a robotic x-ray system (Siemens Multitom Rax) in a total of 48 body phantom realizations: four average bone density settings (cortical bone mass fraction: 10–40%), four body sizes (waist circumference, WC = 70–106 cm), and three lateral shifts of the body within the slot field of view (FOV) (centered and ±1 cm off-center). Experimental validations included: (1) x-ray test-bench feasibility study of adipose–water decomposition and (2) initial demonstration of slot-scan DE bone densitometry on the robotic x-ray system using the European Spine Phantom (ESP) with added attenuation (polymethyl methacrylate [PMMA] slabs) ranging 2 to 6 cm thick.
Results
For the L-spine, the mean aBMD error across all WC settings ranged from 0.08 g/cm2 for phantoms with average cortical bone fraction wcortical = 10% to ∼0.01 g/cm2 for phantoms with wcortical = 40%. The L-spine aBMD measurements were fairly robust to changes in body size and positioning, e.g., coefficient of variation (CV) for L1 with wcortical = 30% was ∼0.034 for various WC and ∼0.02 for an obese patient (WC = 106 cm) changing lateral shift. For the hip, the mean aBMD error across all phantom configurations was about 0.07 g/cm2 for a centered patient. The reproducibility of hip aBMD was slightly worse than in the L-spine (e.g., in the femoral neck, the CV with respect to changing WC was ∼0.13 for phantom realizations with wcortical = 30%) due to more challenging scatter estimation in the presence of an air–tissue interface within the slot FOV. The aBMD of the hip was therefore sensitive to lateral positioning of the patient, especially for obese patients: e.g., the CV with respect to patient lateral shift for femoral neck with WC = 106 cm and wcortical = 30% was 0.14. Empirical evaluations confirmed substantial reduction in aBMD errors with the proposed adipose estimation procedure and demonstrated robust aBMD measurements on the robotic x-ray system, with aBMD errors of ∼0.1 g/cm2 across all three simulated ESP vertebrae and all added PMMA attenuator settings.
Conclusions
We demonstrated that accurate aBMD measurements can be obtained on a motorized FPD-based x-ray system using DE slot-scans with kernel-based scatter correction, backprojection-based slot view tiling, and DE decomposition with adipose correction.
|
| 3. | Nicolas Charon, Asef Islam, Wojciech Zbijewski Landmark-free morphometric analysis of knee osteoarthritis using joint statistical models of bone shape and articular space variability Journal Article In: J. Med. Imag, vol. 8, iss. 4, 2021. @article{Charon2021,
title = {Landmark-free morphometric analysis of knee osteoarthritis using joint statistical models of bone shape and articular space variability},
author = { Nicolas Charon and Asef Islam and Wojciech Zbijewski },
url = {https://doi.org/10.1117/1.JMI.8.4.044001},
doi = {doi.org/10.1117/1.JMI.8.4.044001},
year = {2021},
date = {2021-07-05},
journal = {J. Med. Imag},
volume = {8},
issue = {4},
abstract = { Purpose: Osteoarthritis (OA) is a common degenerative disease involving a variety of structural changes in the affected joint. In addition to narrowing of the articular space, recent studies involving statistical shape analysis methods have suggested that specific bone shapes might be associated with the disease. We aim to investigate the feasibility of using the recently introduced framework of functional shapes (Fshape) to extract morphological features of OA that combine shape variability of articular surfaces of the tibia (or femur) together with the changes of the joint space.
Approach: Our study uses a dataset of three-dimensional cone-beam CT volumes of 17 knees without OA and 17 knees with OA. Each knee is then represented as an object (Fshape) consisting of a triangulated tibial (or femoral) articular surface and a map of joint space widths (JSWs) measured at the points of this surface (joint space map, JSM). We introduce a generative atlas model to estimate a template (mean) Fshape of the sample population together with template-centered variables that model the transformations from the template to each subject. This approach has two potential advantages compared with other statistical shape modeling methods that have been investigated in knee OA: (i) Fshapes simultaneously consider the variability in bone shape and JSW, and (ii) Fshape atlas estimation is based on a diffeomorphic transformation model of surfaces that does not require a priori landmark correspondences between the subjects. The estimated atlas-to-subject Fshape transformations were used as input to principal component analysis dimensionality reduction combined with a linear support vector machine (SVM) classifier to identify the morphological features of OA.
Results: Using tibial articular surface as the shape component of the Fshape, we found leave-one-out cross validation scores of ≈91.18 % for the classification based on the bone surface transformations alone, ≈91.18 % for the classification based on the residual JSM, and ≈85.29 % for the classification using both Fshape components. Similar results were obtained using femoral articular surfaces. The discriminant directions identified in the statistical analysis were associated with medial narrowing of the joint space, steeper intercondylar eminence, and relative deepening of the medial tibial plateau.
Conclusions: The proposed approach provides an integrated framework for combined statistical analysis of shape and JSPs. It can successfully extract features correlated to OA that appear consistent with previous studies in the field. Although future large-scale study is necessary to confirm the significance of these findings, our results suggest that the functional shape methodology is a promising new tool for morphological analysis of OA and orthopedics data in general.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Purpose: Osteoarthritis (OA) is a common degenerative disease involving a variety of structural changes in the affected joint. In addition to narrowing of the articular space, recent studies involving statistical shape analysis methods have suggested that specific bone shapes might be associated with the disease. We aim to investigate the feasibility of using the recently introduced framework of functional shapes (Fshape) to extract morphological features of OA that combine shape variability of articular surfaces of the tibia (or femur) together with the changes of the joint space.
Approach: Our study uses a dataset of three-dimensional cone-beam CT volumes of 17 knees without OA and 17 knees with OA. Each knee is then represented as an object (Fshape) consisting of a triangulated tibial (or femoral) articular surface and a map of joint space widths (JSWs) measured at the points of this surface (joint space map, JSM). We introduce a generative atlas model to estimate a template (mean) Fshape of the sample population together with template-centered variables that model the transformations from the template to each subject. This approach has two potential advantages compared with other statistical shape modeling methods that have been investigated in knee OA: (i) Fshapes simultaneously consider the variability in bone shape and JSW, and (ii) Fshape atlas estimation is based on a diffeomorphic transformation model of surfaces that does not require a priori landmark correspondences between the subjects. The estimated atlas-to-subject Fshape transformations were used as input to principal component analysis dimensionality reduction combined with a linear support vector machine (SVM) classifier to identify the morphological features of OA.
Results: Using tibial articular surface as the shape component of the Fshape, we found leave-one-out cross validation scores of ≈91.18 % for the classification based on the bone surface transformations alone, ≈91.18 % for the classification based on the residual JSM, and ≈85.29 % for the classification using both Fshape components. Similar results were obtained using femoral articular surfaces. The discriminant directions identified in the statistical analysis were associated with medial narrowing of the joint space, steeper intercondylar eminence, and relative deepening of the medial tibial plateau.
Conclusions: The proposed approach provides an integrated framework for combined statistical analysis of shape and JSPs. It can successfully extract features correlated to OA that appear consistent with previous studies in the field. Although future large-scale study is necessary to confirm the significance of these findings, our results suggest that the functional shape methodology is a promising new tool for morphological analysis of OA and orthopedics data in general. |
| 4. | Danny Poinapen, Tadashi Yoshizawa, Yuan Zhou, Nicolas Charon, Stephanie Mou, Kiyoko Oshima, Laura Wood, Ralph H Hruban, Wojciech Zbijewski Three-dimensional shape and topology analysis of tissue-cleared tumor samples Conference vol. 11603, Medical Imaging 2021: Digital Pathology International Society for Optics and Photonics, 2021. @conference{Poinapen2021,
title = {Three-dimensional shape and topology analysis of tissue-cleared tumor samples},
author = {Danny Poinapen, Tadashi Yoshizawa, Yuan Zhou, Nicolas Charon, Stephanie Mou, Kiyoko Oshima, Laura Wood, Ralph H Hruban, Wojciech Zbijewski},
url = {https://doi.org/10.1117/12.2582601},
doi = {10.1117/12.2582601},
year = {2021},
date = {2021-02-15},
volume = {11603},
pages = {1160316},
publisher = {International Society for Optics and Photonics},
organization = {Medical Imaging 2021: Digital Pathology},
abstract = {Purpose: We developed a semi-automated framework to obtain numerical descriptors of surface morphology and topology from volumetric microscopy of human cleared cancer tissues to enable quantitative studies of 3D tumor microarchitecture. Methods: Individual slices of immunolabeled confocal or light-sheet microscopic images of cleared cancer tissue samples are first segmented using the Chan-Vese morphological snake method. Then, the Marching Cubes algorithm is used to generate 3D models of the tumors. Surface area-volume ratio (SAV) of the 3D models is computed using the discrete divergence theorem. Geometries of model centerlines (obtained as shortest paths of maximal inscribed spheres) are quantified in terms of their curvature, torsion, and bifurcations angles. Topological analysis is performed on 3D point clouds generated by uniformly sampling the 3D models. Vietoris-Rips (VR) simplicial complexes of the point clouds are constructed, and their persistent diagrams are used to compute the lifetime of homological features such as connected components, loops, and voids. The framework is applied to cleared samples of extrahepatic cholangiocarcinoma labeled with CK19. Specifically, we investigate whether the proposed quantitative descriptors of tumor microarchitecture can differentiate cancers showing low-grade (LG) tumor budding (TB) from those presenting high-grade (HG) TB. Results: The proposed framework yielded 3D surface models of the tumors that retained the major morphological features (e.g., glands and protrusions) observable in the microscopic image stacks. Initial evidence from quantitative analysis of the 3D models (3 samples each of HG and LG tumors) indicates quantitative differences in the microarchitecture of HG and LG cancer tissues. The average SAV ratio of HG tumors was 0.153±0.0036 μm-1 compared to 0.235±0.0089 μm-1 for LG samples. Analysis of centerline geometries found less curvature in HG samples compared to LG (average curvature of 15.87±0.122 mm-1 vs. 20.87±0.122 mm-1), less torsion (51.54±1.077 mm-1 vs. 62.73±1.120 mm-1), and narrower bifurcation angles (0.543±0.0303 rads vs. 0.671±0.0281 rads). Persistent homology, via VR filtration, indicated that the connected components (homological dimension H0) have longer lifetime in LG tumors (mean lifetime 0.0349 ±0.00297) than in HG ones (mean lifetime 0.0284 ±0.00307). Conclusion: The proposed quantitative analysis framework yields potential geometrical and topological descriptors for statistical analysis of the rich 3D imaging data made available by the application of tissue clearing to human tumor samples.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Purpose: We developed a semi-automated framework to obtain numerical descriptors of surface morphology and topology from volumetric microscopy of human cleared cancer tissues to enable quantitative studies of 3D tumor microarchitecture. Methods: Individual slices of immunolabeled confocal or light-sheet microscopic images of cleared cancer tissue samples are first segmented using the Chan-Vese morphological snake method. Then, the Marching Cubes algorithm is used to generate 3D models of the tumors. Surface area-volume ratio (SAV) of the 3D models is computed using the discrete divergence theorem. Geometries of model centerlines (obtained as shortest paths of maximal inscribed spheres) are quantified in terms of their curvature, torsion, and bifurcations angles. Topological analysis is performed on 3D point clouds generated by uniformly sampling the 3D models. Vietoris-Rips (VR) simplicial complexes of the point clouds are constructed, and their persistent diagrams are used to compute the lifetime of homological features such as connected components, loops, and voids. The framework is applied to cleared samples of extrahepatic cholangiocarcinoma labeled with CK19. Specifically, we investigate whether the proposed quantitative descriptors of tumor microarchitecture can differentiate cancers showing low-grade (LG) tumor budding (TB) from those presenting high-grade (HG) TB. Results: The proposed framework yielded 3D surface models of the tumors that retained the major morphological features (e.g., glands and protrusions) observable in the microscopic image stacks. Initial evidence from quantitative analysis of the 3D models (3 samples each of HG and LG tumors) indicates quantitative differences in the microarchitecture of HG and LG cancer tissues. The average SAV ratio of HG tumors was 0.153±0.0036 μm-1 compared to 0.235±0.0089 μm-1 for LG samples. Analysis of centerline geometries found less curvature in HG samples compared to LG (average curvature of 15.87±0.122 mm-1 vs. 20.87±0.122 mm-1), less torsion (51.54±1.077 mm-1 vs. 62.73±1.120 mm-1), and narrower bifurcation angles (0.543±0.0303 rads vs. 0.671±0.0281 rads). Persistent homology, via VR filtration, indicated that the connected components (homological dimension H0) have longer lifetime in LG tumors (mean lifetime 0.0349 ±0.00297) than in HG ones (mean lifetime 0.0284 ±0.00307). Conclusion: The proposed quantitative analysis framework yields potential geometrical and topological descriptors for statistical analysis of the rich 3D imaging data made available by the application of tissue clearing to human tumor samples. |
| 5. | Chumin Zhao, Stephen Z Liu, Wenying Wang, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, J Webster Stayman, Jeffrey H Siewerdsen, Wojciech Zbijewski Effects of x-ray scatter in quantitative dual-energy imaging using dual-layer flat panel detectors Conference no. 11595, Medical Imaging 2021: Physics of Medical Imaging International Society for Optics and Photonics, 2021. @conference{Zhao2021b,
title = {Effects of x-ray scatter in quantitative dual-energy imaging using dual-layer flat panel detectors},
author = {Chumin Zhao, Stephen Z Liu, Wenying Wang, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, J Webster Stayman, Jeffrey H Siewerdsen, Wojciech Zbijewski},
url = {https://doi.org/10.1117/12.2581822},
doi = {10.1117/12.2581822},
year = {2021},
date = {2021-02-15},
number = {11595},
pages = {115952A},
publisher = {International Society for Optics and Photonics},
organization = {Medical Imaging 2021: Physics of Medical Imaging},
abstract = {Purpose: We compare the effects of scatter on the accuracy of areal bone mineral density (BMD) measurements obtained using two flat-panel detector (FPD) dual-energy (DE) imaging configurations: a dual-kV acquisition and a dual-layer detector. Methods: Simulations of DE projection imaging were performed with realistic models of x-ray spectra, scatter, and detector response for dual-kV and dual-layer configurations. A digital body phantom with 4 cm Ca inserts in place of vertebrae (concentrations 50 - 400 mg/mL) was used. The dual-kV configuration involved an 80 kV low-energy (LE) and a 120 kV high-energy (HE) beam and a single-layer, 43x43 cm FPD with a 650 μm cesium iodide (CsI) scintillator. The dual-layer configuration involved a 120 kV beam and an FPD consisting of a 200 μm CsI layer (LE data), followed by a 1 mm Cu filter, and a 550 μm CsI layer (HE data). We investigated the effects of an anti-scatter grid (13:1 ratio) and scatter correction. For the correction, the sensitivity to scatter estimation error (varied ±10% of true scatter distribution) was evaluated. Areal BMD was estimated from projection-domain DE decomposition. Results: In the gridless dual-kV setup, the scatter-to-primary ratio (SPR) was similar for the LE and HE projections, whereas in the gridless dual layer setup, the SPR was ~26% higher in the LE channel (top CsI layer) than in the HE channel (bottom layer). Because of the resulting bias in LE measurements, the conventional projection-domain DE decomposition could not be directly applied to dual-layer data; this challenge persisted even in the presence of a grid. In contrast, DE decomposition of dual-kV data was possible both without and with the grid; the BMD error of the 400 mg/mL insert was -0.4 g/cm2 without the grid and +0.3 g/cm2 with the grid. The dual-layer FPD configuration required accurate scatter correction for DE decomposition: a -5% scatter estimation error resulted in -0.1 g/cm2 BMD error for the 50 mg/mL insert and a -0.5 g/cm2 BMD error for the 400 mg/mL with a grid, compared to <0.1 g/cm2 for all inserts in a dual-kV setup with the same scatter estimation error. Conclusion: This comparative study of quantitative performance of dual-layer and dual-kV FPD-based DE imaging indicates the need for accurate scatter correction in the dual-layer setup due to increased susceptibility to scatter errors in the LE channel.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Purpose: We compare the effects of scatter on the accuracy of areal bone mineral density (BMD) measurements obtained using two flat-panel detector (FPD) dual-energy (DE) imaging configurations: a dual-kV acquisition and a dual-layer detector. Methods: Simulations of DE projection imaging were performed with realistic models of x-ray spectra, scatter, and detector response for dual-kV and dual-layer configurations. A digital body phantom with 4 cm Ca inserts in place of vertebrae (concentrations 50 - 400 mg/mL) was used. The dual-kV configuration involved an 80 kV low-energy (LE) and a 120 kV high-energy (HE) beam and a single-layer, 43x43 cm FPD with a 650 μm cesium iodide (CsI) scintillator. The dual-layer configuration involved a 120 kV beam and an FPD consisting of a 200 μm CsI layer (LE data), followed by a 1 mm Cu filter, and a 550 μm CsI layer (HE data). We investigated the effects of an anti-scatter grid (13:1 ratio) and scatter correction. For the correction, the sensitivity to scatter estimation error (varied ±10% of true scatter distribution) was evaluated. Areal BMD was estimated from projection-domain DE decomposition. Results: In the gridless dual-kV setup, the scatter-to-primary ratio (SPR) was similar for the LE and HE projections, whereas in the gridless dual layer setup, the SPR was ~26% higher in the LE channel (top CsI layer) than in the HE channel (bottom layer). Because of the resulting bias in LE measurements, the conventional projection-domain DE decomposition could not be directly applied to dual-layer data; this challenge persisted even in the presence of a grid. In contrast, DE decomposition of dual-kV data was possible both without and with the grid; the BMD error of the 400 mg/mL insert was -0.4 g/cm2 without the grid and +0.3 g/cm2 with the grid. The dual-layer FPD configuration required accurate scatter correction for DE decomposition: a -5% scatter estimation error resulted in -0.1 g/cm2 BMD error for the 50 mg/mL insert and a -0.5 g/cm2 BMD error for the 400 mg/mL with a grid, compared to <0.1 g/cm2 for all inserts in a dual-kV setup with the same scatter estimation error. Conclusion: This comparative study of quantitative performance of dual-layer and dual-kV FPD-based DE imaging indicates the need for accurate scatter correction in the dual-layer setup due to increased susceptibility to scatter errors in the LE channel. |
| 6. | Stephen Z Liu, Jeffrey H Siewerdsen, J Webster Stayman, Wojciech Zbijewski Quantitative dual-energy imaging in the presence of metal implants using locally constrained model-based decomposition Conference vol. 11595, Medical Imaging 2021: Physics of Medical Imaging International Society for Optics and Photonics, 2021. @conference{Liu2021,
title = {Quantitative dual-energy imaging in the presence of metal implants using locally constrained model-based decomposition},
author = {Stephen Z Liu, Jeffrey H Siewerdsen, J Webster Stayman, Wojciech Zbijewski},
url = {https://doi.org/10.1117/12.2582277},
doi = {10.1117/12.2582277},
year = {2021},
date = {2021-02-15},
volume = {11595},
pages = {115951C},
publisher = {International Society for Optics and Photonics},
organization = {Medical Imaging 2021: Physics of Medical Imaging},
abstract = {Purpose: To mitigate effects of metal artifacts in Dual-Energy (DE) CT imaging, we introduce a constrained optimization algorithm to enable simultaneous reconstruction-decomposition of three materials: two tissues-of-interest and the metal. Methods: The volume conservation principle and nonnegativity of volume fractions were incorporated as a pair of linear constraints into the Model-Based Material Decomposition (MBMD) algorithm. This enabled solving for three unknown material concentrations from DE projection data. A primal-dual Ordered Subsets Predictor-Corrector Interior-Point (OSPCIP) algorithm was derived to perform the optimization in the proposed constrained-MBMD (CMBMD). To improve computational efficiency and monotonicity of CMBMD, we investigated an approach where the constraint was applied locally onto a small region containing the metal (identified from a preliminary reconstruction) during initial iterations, followed by final iterations with the constraint applied globally. Validation studies involved simulations and test bench experiments to assess the quantitative accuracy of bone concentration measurements in the presence of fracture fixation hardware. In all studies, DE data was acquired using a kVp-switching protocol with the 60 kVp low-energy beam and the 140 kVp high-energy beam. The system geometry emulated the extremity Cone-Beam CT (CBCT). Simulation studies included: i) a cylindrical phantom (80 mm diameter) with a 30 mm long Ti screw and an insert of varying cortical bone concentrations (3 – 13%), and ii) a realistic tibia phantom created from patient CBCT data with Ti fixation hardware of increasing complexity. The test bench experiment involved a 100 mm diameter water bath containing four Ca inserts (6.5 – 39.1% bone concentration) and a Ti plate. Results: CMBMD substantially reduced artifacts in DE decompositions in the presence of metal. The sequentially localglobal constraint strategy resulted in more monotonic convergence than using a global constraint for all iterations. In the simulation studies, CMBMD achieved quantitative accuracy within ~12% of nominal bone concentration in areas adjacent to metal, and within ~5% in areas further away from the metal, compared to ~80% error for the two-material MBMD. In the test bench study, CMBMD generated ~40% reduction in the error of bone concentration estimates compared to MBMD for nominal insert concentrations of <250 mg/mL, and ~12% reduction for concentrations <250 mg/mL. Conclusion: Proposed CMBMD enables accurate DE decomposition in the presence of metal implants by incorporating the metal as an additional base material. Proposed method will be particularly useful in quantitative orthopedic imaging, which is often challenged by metal fracture fixation and joint replacement hardware.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Purpose: To mitigate effects of metal artifacts in Dual-Energy (DE) CT imaging, we introduce a constrained optimization algorithm to enable simultaneous reconstruction-decomposition of three materials: two tissues-of-interest and the metal. Methods: The volume conservation principle and nonnegativity of volume fractions were incorporated as a pair of linear constraints into the Model-Based Material Decomposition (MBMD) algorithm. This enabled solving for three unknown material concentrations from DE projection data. A primal-dual Ordered Subsets Predictor-Corrector Interior-Point (OSPCIP) algorithm was derived to perform the optimization in the proposed constrained-MBMD (CMBMD). To improve computational efficiency and monotonicity of CMBMD, we investigated an approach where the constraint was applied locally onto a small region containing the metal (identified from a preliminary reconstruction) during initial iterations, followed by final iterations with the constraint applied globally. Validation studies involved simulations and test bench experiments to assess the quantitative accuracy of bone concentration measurements in the presence of fracture fixation hardware. In all studies, DE data was acquired using a kVp-switching protocol with the 60 kVp low-energy beam and the 140 kVp high-energy beam. The system geometry emulated the extremity Cone-Beam CT (CBCT). Simulation studies included: i) a cylindrical phantom (80 mm diameter) with a 30 mm long Ti screw and an insert of varying cortical bone concentrations (3 – 13%), and ii) a realistic tibia phantom created from patient CBCT data with Ti fixation hardware of increasing complexity. The test bench experiment involved a 100 mm diameter water bath containing four Ca inserts (6.5 – 39.1% bone concentration) and a Ti plate. Results: CMBMD substantially reduced artifacts in DE decompositions in the presence of metal. The sequentially localglobal constraint strategy resulted in more monotonic convergence than using a global constraint for all iterations. In the simulation studies, CMBMD achieved quantitative accuracy within ~12% of nominal bone concentration in areas adjacent to metal, and within ~5% in areas further away from the metal, compared to ~80% error for the two-material MBMD. In the test bench study, CMBMD generated ~40% reduction in the error of bone concentration estimates compared to MBMD for nominal insert concentrations of <250 mg/mL, and ~12% reduction for concentrations <250 mg/mL. Conclusion: Proposed CMBMD enables accurate DE decomposition in the presence of metal implants by incorporating the metal as an additional base material. Proposed method will be particularly useful in quantitative orthopedic imaging, which is often challenged by metal fracture fixation and joint replacement hardware. |
| 7. | Alejandro Sisniega, Heyuan Huang, Wojciech Zbijewski, Joseph Webster Stayman, Clifford R Weiss, Tina Ehtiati, Jeffrey H Siewerdsen Deformable image-based motion compensation for interventional cone-beam CT with learned autofocus metrics Conference vol. 11595, Medical Imaging 2021: Physics of Medical Imaging International Society for Optics and Photonics, 2021. @conference{Sisniega2021,
title = {Deformable image-based motion compensation for interventional cone-beam CT with learned autofocus metrics},
author = {Alejandro Sisniega, Heyuan Huang, Wojciech Zbijewski, Joseph Webster Stayman, Clifford R Weiss, Tina Ehtiati, Jeffrey H Siewerdsen},
url = {https://doi.org/10.1117/12.2582140},
doi = {10.1117/12.2582140},
year = {2021},
date = {2021-02-15},
volume = {11595},
pages = {115950W},
publisher = {International Society for Optics and Photonics},
organization = {Medical Imaging 2021: Physics of Medical Imaging},
abstract = {Cone-beam CT is used for 3D guidance in interventional radiology, but its long acquisition time results in motion. Multi-region autofocus showed successful compensation of deformable motion, but conventional metrics might be limited. This work presents a learning-based approach to design autofocus metrics. A deep CNN was used to quantify the local motion severity and as the core of the cost function for deformable autofocus. Predicted local motion amplitude showed a linear relationship (R2 = 0.95) with truth and errors < 2 mm. Deformable motion compensation with the learned metric showed compensation of motion artifacts proving feasibility of the proposed approach.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Cone-beam CT is used for 3D guidance in interventional radiology, but its long acquisition time results in motion. Multi-region autofocus showed successful compensation of deformable motion, but conventional metrics might be limited. This work presents a learning-based approach to design autofocus metrics. A deep CNN was used to quantify the local motion severity and as the core of the cost function for deformable autofocus. Predicted local motion amplitude showed a linear relationship (R2 = 0.95) with truth and errors < 2 mm. Deformable motion compensation with the learned metric showed compensation of motion artifacts proving feasibility of the proposed approach. |
| 8. | Chumin Zhao, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, Jeffrey H Siewerdsen, Wojciech Zbijewski Image-domain cardiac motion compensation in multidirectional digital chest tomosynthesis Conference vol. 11595, Medical Imaging 2021: Physics of Medical Imaging International Society for Optics and Photonics, 2021. @conference{Zhao2021,
title = {Image-domain cardiac motion compensation in multidirectional digital chest tomosynthesis},
author = {Chumin Zhao, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, Jeffrey H Siewerdsen, Wojciech Zbijewski},
url = {https://doi.org/10.1117/12.2581287},
doi = {10.1117/12.2581287},
year = {2021},
date = {2021-02-05},
volume = {11595},
pages = {1159525},
publisher = {International Society for Optics and Photonics},
organization = {Medical Imaging 2021: Physics of Medical Imaging},
abstract = {We investigate an image-based strategy to compensate for cardiac motion-induced artifacts in Digital Chest Tomosynthesis (DCT). We apply the compensation to conventional unidirectional vertical “↕” scan DCT and to a multidirectional circular trajectory "O" providing improved depth resolution. Propagation of heart motion into the lungs was simulated as a dynamic deformation. The studies investigated a range of motion propagation distances and scan times. Projection-domain retrospective gating was used to detect heart phases. Sparsely sampled reconstructions of each phase were deformably aligned to yield a motion compensated image with reduced sampling artifacts. The proposed motion compensation mitigates artifacts and blurring in DCT images both for “↕” and "O" scan trajectories. Overall, the “O” orbit achieved the same or better nodule structural similarity index in than the conventional “↕” orbit. Increasing the scan time improved the sampling of individual phase reconstructions.
Conference Presentation
},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We investigate an image-based strategy to compensate for cardiac motion-induced artifacts in Digital Chest Tomosynthesis (DCT). We apply the compensation to conventional unidirectional vertical “↕” scan DCT and to a multidirectional circular trajectory "O" providing improved depth resolution. Propagation of heart motion into the lungs was simulated as a dynamic deformation. The studies investigated a range of motion propagation distances and scan times. Projection-domain retrospective gating was used to detect heart phases. Sparsely sampled reconstructions of each phase were deformably aligned to yield a motion compensated image with reduced sampling artifacts. The proposed motion compensation mitigates artifacts and blurring in DCT images both for “↕” and "O" scan trajectories. Overall, the “O” orbit achieved the same or better nodule structural similarity index in than the conventional “↕” orbit. Increasing the scan time improved the sampling of individual phase reconstructions.
Conference Presentation
|
| 9. | Stephen Z Liu, Qian Cao, Matthew Tivnan, Steven Tilley II, Jeffrey H Siewerdsen, J Webster Stayman, Wojciech Zbijewski Model-based dual-energy tomographic image reconstruction of objects containing known metal components Journal Article In: Physics in Medicine & Biology, vol. 65, no. 24, pp. 245046, 2020. @article{Liu2021b,
title = {Model-based dual-energy tomographic image reconstruction of objects containing known metal components},
author = {Stephen Z Liu, Qian Cao, Matthew Tivnan, Steven Tilley II, Jeffrey H Siewerdsen, J Webster Stayman, Wojciech Zbijewski},
url = {https://iopscience.iop.org/article/10.1088/1361-6560/abc5a9/meta},
doi = {10.1088/1361-6560/abc5a9/meta},
year = {2020},
date = {2020-12-20},
journal = {Physics in Medicine & Biology},
volume = {65},
number = {24},
pages = {245046},
abstract = {Abstract
Dual-energy (DE) decomposition has been adopted in orthopedic imaging to measure bone composition and visualize intraarticular contrast enhancement. One of the potential applications involves monitoring of callus mineralization for longitudinal assessment of fracture healing. However, fracture repair usually involves internal fixation hardware that can generate significant artifacts in reconstructed images. To address this challenge, we develop a novel algorithm that combines simultaneous reconstruction-decomposition using a previously reported method for model-based material decomposition (MBMD) augmented by the known-component (KC) reconstruction framework to mitigate metal artifacts. We apply the proposed algorithm to simulated DE data representative of a dedicated extremity cone-beam CT (CBCT) employing an x-ray unit with three vertically arranged sources. The scanner generates DE data with non-coinciding high- and low-energy projection rays when the central source is operated at high tube potential and the peripheral sources at low potential. The proposed algorithm was validated using a digital extremity phantom containing varying concentrations of Ca-water mixtures and Ti implants. Decomposition accuracy was compared to MBMD without the KC model. The proposed method suppressed metal artifacts and yielded estimated Ca concentrations that approached the reconstructions of an implant-free phantom for most mixture regions. In the vicinity of simple components, the errors of Ca density estimates obtained by incorporating KC in MBMD were ~1.5–5× lower than the errors of conventional MBMD; for cases with complex implants, the errors were ~3–5× lower. In conclusion, the proposed method can achieve accurate bone mineral density measurements in the presence of metal implants using non-coinciding DE projections acquired on a multisource CBCT system.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract
Dual-energy (DE) decomposition has been adopted in orthopedic imaging to measure bone composition and visualize intraarticular contrast enhancement. One of the potential applications involves monitoring of callus mineralization for longitudinal assessment of fracture healing. However, fracture repair usually involves internal fixation hardware that can generate significant artifacts in reconstructed images. To address this challenge, we develop a novel algorithm that combines simultaneous reconstruction-decomposition using a previously reported method for model-based material decomposition (MBMD) augmented by the known-component (KC) reconstruction framework to mitigate metal artifacts. We apply the proposed algorithm to simulated DE data representative of a dedicated extremity cone-beam CT (CBCT) employing an x-ray unit with three vertically arranged sources. The scanner generates DE data with non-coinciding high- and low-energy projection rays when the central source is operated at high tube potential and the peripheral sources at low potential. The proposed algorithm was validated using a digital extremity phantom containing varying concentrations of Ca-water mixtures and Ti implants. Decomposition accuracy was compared to MBMD without the KC model. The proposed method suppressed metal artifacts and yielded estimated Ca concentrations that approached the reconstructions of an implant-free phantom for most mixture regions. In the vicinity of simple components, the errors of Ca density estimates obtained by incorporating KC in MBMD were ~1.5–5× lower than the errors of conventional MBMD; for cases with complex implants, the errors were ~3–5× lower. In conclusion, the proposed method can achieve accurate bone mineral density measurements in the presence of metal implants using non-coinciding DE projections acquired on a multisource CBCT system. |
