Transactions of the American Nuclear Society, 1993
The technique of imaging neutron activation analysis (NAA) is being developed at the University o... more The technique of imaging neutron activation analysis (NAA) is being developed at the University of Michigan in collaboration with Charles Evans Associates, who built the prototype instrument. A 20-[mu]m lateral resolution has been achieved for imaging element distributions in heterogeneous solids. There are applications in such fields as material sciences, biology, geology, and particle analysis. Results obtained using the prototype instrument indicate that chromium is an ideal candidate for imaging NAA.
International Journal of Radiation Oncology Biology Physics, Aug 1, 2019
PURPOSE Predictive 3D dosimetry requires spatial concordance between diagnostic and therapeutic a... more PURPOSE Predictive 3D dosimetry requires spatial concordance between diagnostic and therapeutic activity distributions. We assess similarity between theranostic pairs (99mTc-MAA SPECT/ 90Y microsphere PET) in patients using criteria that account for spatial resolution differences and mis-registration. METHODS Phantom-based acceptance criteria were determined using a liver phantom filled with 99mTc and 90YCl3 scanned with SPECT/CT and PET/CT, respectively. Gaussian blurring was applied to PET to match 99mTc phantom scan image quality. Following rigid registration between SPECT/CT and PET/CT, perturbations up to ± 3 voxels were applied to determine similarity metrics (SM) sensitivity. 99mTc-MAA SPECT/CT and 90Y microsphere PET/CT image pairs/patients (n=23) were processed analogously. SM calculated include Pearson's (ρr), Lin's concordance(ρc)and Spearman's rank(ρs), mean squared difference (MSD), and Dice similarity coefficient (DSC). Patient-specific acceptance criteria were determined by evaluating SM of the blurred PET compared with itself mis-registered. RESULTS After transforming PET to SPECT resolution, high similarity was found in phantom, withρc, ρr, ρs > 0.98 ± 0.01, MSD of(4.1±0.3)×10-4 , and DSC > 0.85 ± 0.01 for investigated thresholds (5,30,50%). SM for patients varied from poor to good. A small percentage (13-30%) of patient scans were acceptable using phantom-based acceptance criteria. The percentage increased slightly (17-35%) using patient-specific acceptance criteria. DSC for most patients were substantially lower (average 0.95 vs 0.61 for 5% threshold) than phantom values. CONCLUSIONS At best 35% of patients had a SM within the acceptance criteria established to account for imaging-related effects impacting spatial concordance between 99mTc-MAA SPECT and 90Y PET. Additional clinical factors should be evaluated in the future. The procedure of accounting for image related effects when assessing spatial concordance can be applied to other theranostic pairs.
Most existing PET image reconstruction methods impose a nonnegativity constraint in the image dom... more Most existing PET image reconstruction methods impose a nonnegativity constraint in the image domain that is natural physically, but can lead to biased reconstructions. This bias is particularly problematic for Y-90 PET because of the low probability positron production and high random coincidence fraction. We propose a new PET reconstruction formulation that enforces nonnegativity of the projections instead of the voxel values. This formulation allows some negative voxel values thereby potentially reducing bias. To relax the non-negativity constraint embedded in the standard methods for PET reconstruction, we used an Alternating Direction Method of Multipliers (ADMM). Because choice of ADMM parameters can greatly influence convergence rate, we applied an automatic parameter selection method to improve the convergence speed. We investigated several variants differentiated by the base model and the constraint condition using lung to liver slices of XCAT phantom. We simulated low true coincidence count-rates with high random fractions corresponding to the typical values from patient imaging in Y-90 microsphere radioembolization. We compared our new methods with standard reconstruction algorithms. As the proposed algorithm iterates, the new method reduces the bias in cold spot while yielding lower noise than the standard method. The new model improves the quantification in all regions of interest when the methods achieve similar level of noise in the liver. The improvements with the new method are especially notable when simulating conditions corresponding to patients with lower activity administration (i.e., higher random fractions).
43 Objectives: Quantitative yttrium-90 (Y90) bremsstrahlung SPECT imaging in radionuclide therapy... more 43 Objectives: Quantitative yttrium-90 (Y90) bremsstrahlung SPECT imaging in radionuclide therapy is challenging. Recently proposed joint spectral reconstruction (JSR) with wide energy windows yielded promising improvements in quantitative image qualities with low noise over single spectral reconstruction (SSR). In this work, based on our observations of the contrast and noise trade-offs over iterations, we propose guided filtering (GF)-aided reconstruction methods to reduce noise level while maintaining other image qualities and details. Methods: Reconstructed images at early iterations often contain low noise and rough image details (e.g., low contrast), while reconstructed images at later iterations usually contain high noise and better image details. The guided filter yields the output by considering the content of a guidance image based on a local linear model and can be used as an edge-preserving smoothing operator. We conjecture that images at early iterations are perfect candidates to be guide images of GF and proposed GF-aided image reconstruction methods for both SSR and JSR in Y90 bremsstrahlung SPECT. Assuming that one cycle consists of k iterations, GF was performed every cycle (k = 4 in our case) using the guided filtered image at the previous cycle as a guide image. The output of GF was used for both an initial image for the next k iterations of 3D OS-EM as well as a guide image for the next cycle. Our proposed scheme was applied to both SSR (called SSR-GF) with a 105-135keV energy window and JSR (called JSR-GF) with six 30keV-width energy windows on 105-285keV with phantom simulation and experimental measurement using high-energy collimators on SPECT/CT. MC scatter correction was used for reconstructions with experimental measurement. Results: Qualitatively, in both simulation and phantom experiment (2 to 100 mL spheres in warm background), our proposed SSR-GF and JSR-GF yielded significantly reduced noise levels compared to SSR and JSR. Quantitatively, for simulation, SSR-GF, JSR-GF yielded 126.5%, 71.5% higher contrast-to-noise ratio (CNR) than SSR, JSR, respectively. Note that JSR-GF still yielded 15.2% better CNR than SSR-GF. Similarly, in phantom measurements, SSR-GF, JSR-GF yielded 60.9%, 46.1% higher CNR than SSR, JSR, respectively. Note also that JSR-GF still yielded 31.2% better CNR than SSR-GF. Our proposed GF scheme yielded substantially lower root mean square error (RMSE) as follows: for simulation from 4.41 to 3.80, from 4.00 to 3.75 for SSR, JSR, respectively, and for measurement from 3.94 to 3.74, from 3.63 to 3.54 for SSR, JSR, respectively. For given average recovery coefficient, JSR-GF yielded the lowest noise level among all methods for both simulation and experiment. Conclusions: We propose Y90 single and joint spectral reconstructions using guided filtering with reconstructed images at lower iterations as guidance images. Our proposed methods yielded the highest CNR, the lowest RMSE, the best averaged recovery coefficient - noise level trade-offs, and enhanced visual quality images. Research support: This work was supported in part by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1B05035810) and in part by grant R01 EB022075, awarded by National Institute of Biomedical Imaging and Bioengineering, National Institute of Health, U.S. Department of Health and Human Services.
Most existing fully automatic or semi-automatic medical imaging segmentation methods start from r... more Most existing fully automatic or semi-automatic medical imaging segmentation methods start from reconstructed images. However, a framework for joint segmentation and image reconstruction can be beneficial because both tasks can be mutually dependent. Better segmentation can improve image reconstruction and vice-versa. We propose to perform joint PET image reconstruction and fully automatic PET image segmentation, using the CT image from a PET-CT scanner as a given input. Within a unified framework, our proposed method generates a PET image and a segmentation mask utilizing two connected trained networks: 1) a network dedicated to denoising the PET image with boundary information from the segmentation network. While reconstructing the PET image, the algorithm exploits the denoised image recovered from the trained network. 2) a segmentation network dedicated to estimating the lesion and background (e.g., liver) masks using PET/CT information. A boundary indicator image is generated based on the gradients of segmentation masks. We simulated extremely low-count PET, typical for Y-90 imaging, where traditional segmentation and reconstruction methods tend to perform poorly. For PET reconstruction, proposed method using true boundary improves CNR (RMSE) by 28.9 % (49.1%) and 16.8 % (13.2%) compared to EM and proposed method without using boundary. For multi-modal segmentation, our proposed method improved global Dice score in tumor by 70.6% compared to our proposed segmentation framework using only CT information.
Transactions of the American Nuclear Society, 1993
The technique of imaging neutron activation analysis (NAA) is being developed at the University o... more The technique of imaging neutron activation analysis (NAA) is being developed at the University of Michigan in collaboration with Charles Evans Associates, who built the prototype instrument. A 20-[mu]m lateral resolution has been achieved for imaging element distributions in heterogeneous solids. There are applications in such fields as material sciences, biology, geology, and particle analysis. Results obtained using the prototype instrument indicate that chromium is an ideal candidate for imaging NAA.
International Journal of Radiation Oncology Biology Physics, Aug 1, 2019
PURPOSE Predictive 3D dosimetry requires spatial concordance between diagnostic and therapeutic a... more PURPOSE Predictive 3D dosimetry requires spatial concordance between diagnostic and therapeutic activity distributions. We assess similarity between theranostic pairs (99mTc-MAA SPECT/ 90Y microsphere PET) in patients using criteria that account for spatial resolution differences and mis-registration. METHODS Phantom-based acceptance criteria were determined using a liver phantom filled with 99mTc and 90YCl3 scanned with SPECT/CT and PET/CT, respectively. Gaussian blurring was applied to PET to match 99mTc phantom scan image quality. Following rigid registration between SPECT/CT and PET/CT, perturbations up to ± 3 voxels were applied to determine similarity metrics (SM) sensitivity. 99mTc-MAA SPECT/CT and 90Y microsphere PET/CT image pairs/patients (n=23) were processed analogously. SM calculated include Pearson's (ρr), Lin's concordance(ρc)and Spearman's rank(ρs), mean squared difference (MSD), and Dice similarity coefficient (DSC). Patient-specific acceptance criteria were determined by evaluating SM of the blurred PET compared with itself mis-registered. RESULTS After transforming PET to SPECT resolution, high similarity was found in phantom, withρc, ρr, ρs > 0.98 ± 0.01, MSD of(4.1±0.3)×10-4 , and DSC > 0.85 ± 0.01 for investigated thresholds (5,30,50%). SM for patients varied from poor to good. A small percentage (13-30%) of patient scans were acceptable using phantom-based acceptance criteria. The percentage increased slightly (17-35%) using patient-specific acceptance criteria. DSC for most patients were substantially lower (average 0.95 vs 0.61 for 5% threshold) than phantom values. CONCLUSIONS At best 35% of patients had a SM within the acceptance criteria established to account for imaging-related effects impacting spatial concordance between 99mTc-MAA SPECT and 90Y PET. Additional clinical factors should be evaluated in the future. The procedure of accounting for image related effects when assessing spatial concordance can be applied to other theranostic pairs.
Most existing PET image reconstruction methods impose a nonnegativity constraint in the image dom... more Most existing PET image reconstruction methods impose a nonnegativity constraint in the image domain that is natural physically, but can lead to biased reconstructions. This bias is particularly problematic for Y-90 PET because of the low probability positron production and high random coincidence fraction. We propose a new PET reconstruction formulation that enforces nonnegativity of the projections instead of the voxel values. This formulation allows some negative voxel values thereby potentially reducing bias. To relax the non-negativity constraint embedded in the standard methods for PET reconstruction, we used an Alternating Direction Method of Multipliers (ADMM). Because choice of ADMM parameters can greatly influence convergence rate, we applied an automatic parameter selection method to improve the convergence speed. We investigated several variants differentiated by the base model and the constraint condition using lung to liver slices of XCAT phantom. We simulated low true coincidence count-rates with high random fractions corresponding to the typical values from patient imaging in Y-90 microsphere radioembolization. We compared our new methods with standard reconstruction algorithms. As the proposed algorithm iterates, the new method reduces the bias in cold spot while yielding lower noise than the standard method. The new model improves the quantification in all regions of interest when the methods achieve similar level of noise in the liver. The improvements with the new method are especially notable when simulating conditions corresponding to patients with lower activity administration (i.e., higher random fractions).
43 Objectives: Quantitative yttrium-90 (Y90) bremsstrahlung SPECT imaging in radionuclide therapy... more 43 Objectives: Quantitative yttrium-90 (Y90) bremsstrahlung SPECT imaging in radionuclide therapy is challenging. Recently proposed joint spectral reconstruction (JSR) with wide energy windows yielded promising improvements in quantitative image qualities with low noise over single spectral reconstruction (SSR). In this work, based on our observations of the contrast and noise trade-offs over iterations, we propose guided filtering (GF)-aided reconstruction methods to reduce noise level while maintaining other image qualities and details. Methods: Reconstructed images at early iterations often contain low noise and rough image details (e.g., low contrast), while reconstructed images at later iterations usually contain high noise and better image details. The guided filter yields the output by considering the content of a guidance image based on a local linear model and can be used as an edge-preserving smoothing operator. We conjecture that images at early iterations are perfect candidates to be guide images of GF and proposed GF-aided image reconstruction methods for both SSR and JSR in Y90 bremsstrahlung SPECT. Assuming that one cycle consists of k iterations, GF was performed every cycle (k = 4 in our case) using the guided filtered image at the previous cycle as a guide image. The output of GF was used for both an initial image for the next k iterations of 3D OS-EM as well as a guide image for the next cycle. Our proposed scheme was applied to both SSR (called SSR-GF) with a 105-135keV energy window and JSR (called JSR-GF) with six 30keV-width energy windows on 105-285keV with phantom simulation and experimental measurement using high-energy collimators on SPECT/CT. MC scatter correction was used for reconstructions with experimental measurement. Results: Qualitatively, in both simulation and phantom experiment (2 to 100 mL spheres in warm background), our proposed SSR-GF and JSR-GF yielded significantly reduced noise levels compared to SSR and JSR. Quantitatively, for simulation, SSR-GF, JSR-GF yielded 126.5%, 71.5% higher contrast-to-noise ratio (CNR) than SSR, JSR, respectively. Note that JSR-GF still yielded 15.2% better CNR than SSR-GF. Similarly, in phantom measurements, SSR-GF, JSR-GF yielded 60.9%, 46.1% higher CNR than SSR, JSR, respectively. Note also that JSR-GF still yielded 31.2% better CNR than SSR-GF. Our proposed GF scheme yielded substantially lower root mean square error (RMSE) as follows: for simulation from 4.41 to 3.80, from 4.00 to 3.75 for SSR, JSR, respectively, and for measurement from 3.94 to 3.74, from 3.63 to 3.54 for SSR, JSR, respectively. For given average recovery coefficient, JSR-GF yielded the lowest noise level among all methods for both simulation and experiment. Conclusions: We propose Y90 single and joint spectral reconstructions using guided filtering with reconstructed images at lower iterations as guidance images. Our proposed methods yielded the highest CNR, the lowest RMSE, the best averaged recovery coefficient - noise level trade-offs, and enhanced visual quality images. Research support: This work was supported in part by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1B05035810) and in part by grant R01 EB022075, awarded by National Institute of Biomedical Imaging and Bioengineering, National Institute of Health, U.S. Department of Health and Human Services.
Most existing fully automatic or semi-automatic medical imaging segmentation methods start from r... more Most existing fully automatic or semi-automatic medical imaging segmentation methods start from reconstructed images. However, a framework for joint segmentation and image reconstruction can be beneficial because both tasks can be mutually dependent. Better segmentation can improve image reconstruction and vice-versa. We propose to perform joint PET image reconstruction and fully automatic PET image segmentation, using the CT image from a PET-CT scanner as a given input. Within a unified framework, our proposed method generates a PET image and a segmentation mask utilizing two connected trained networks: 1) a network dedicated to denoising the PET image with boundary information from the segmentation network. While reconstructing the PET image, the algorithm exploits the denoised image recovered from the trained network. 2) a segmentation network dedicated to estimating the lesion and background (e.g., liver) masks using PET/CT information. A boundary indicator image is generated based on the gradients of segmentation masks. We simulated extremely low-count PET, typical for Y-90 imaging, where traditional segmentation and reconstruction methods tend to perform poorly. For PET reconstruction, proposed method using true boundary improves CNR (RMSE) by 28.9 % (49.1%) and 16.8 % (13.2%) compared to EM and proposed method without using boundary. For multi-modal segmentation, our proposed method improved global Dice score in tumor by 70.6% compared to our proposed segmentation framework using only CT information.
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Papers by Yuni Dewaraja