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Extracting Breathing Signal from Image Fourier Transform for Developing 4D-MRI
Proceedings of the 52nd Annual ASTRO Meeting available metal-shadow-excluded projection data, with image non-negativity enforced. The constrained minimization problem is optimized through the combination of projection onto convex sets (POCS) and steepest descent of smoothness measure objective. Once the optimizer is found, same optimization algorithm is applied to the second sinogram, with the initial image set to be the optimal solution of previous optimization. We constantly alternating these two optimization processes until the pre-defined termination criteria are met. The algorithm is evaluated using two numerical phantoms (shepp-logan and QA, 350x350 (in pixels)) and experimental CatPhan 600 phantom. The experimental projection data was acquired using cone-beam CT lose dose protocol (10mA/10ms), including 680 views for a full 360o rotation. Results: Both simulation and experimental studies showed that the proposed algorithm has superior performance compared with other widely-used analytical and iterative algorithms. It also improved the image quality compared with constrained optimization for a single scan. Metal artifacts were significantly suppressed even in the presence of noise and system imperfections. The FWHM comparisons on CatPhan 600 suggested that reconstructed image has a higher resolution than FDK reconstruction. Conclusions: The proposed dual optimization algorithm can be used to significantly reduce metal artifacts and produce clinically acceptable images in low dose protocol. The proposed algorithm can also be generated to other incomplete/missing data problems in systems involving x-ray source trajectories. Author Disclosure: X. Zhang, None; L. Xing, None; J. Wang, None.
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Extracting Breathing Signal from Image Fourier Transform for Developing 4D-MRI
J. Cai, Z. Chang, Z. Wang, F. Yin Duke University Medical Center, Durham, NC Purpose/Objective(s): According to the theory of Fast Fourier Transform (FFT), shifts in the spatial domain result in phase change in the frequency domain. The objective of this study is to investigate the feasibility of exacting breathing signals from the FFT of continuous acquired images and applying them in the development of 4D-MRI. Materials/Methods: This technique was developed using previously acquired data and validated using a phantom study. 10 subjects were imaged continuously for 2-min during free breathing on a 1.5T Siemens MR scanner using a true fast imaging with steady-state precession (TrueFISP). Imaging parameters (TR/TE, 3.7/1.21ms; Matrix, 256x166; FOV, 350x300 mm; flip angle, 52 ; slice thickness, 5 mm) were used to achieve a frame rate of 3 frames/s. The study was approved by local IRB and consents were obtained before the study. All images were acquired in a single coronal (n = 5) or sagittal (n = 5) plane. For each subject, breathing signals were determined 1) by tracking the motion of a selected internal structure, and 2) as the phase change of the image FFT. Respiratory phases were then calculated from breathing signals and compared between two methods. Pearson correlation was performed. To test the feasibility of using FFT for 4D-MRI, a self built MR-compatible motion phantom was imaged on a 1.5T GE MR scanner using a fast imaging employed steady-state acquisition (FIESTA, equivalent to TrueFISP) with similar parameters as above. The phantom consists of a cylinder object and a piece of bolus to mimic tumor and body surface respectively. During experiment the object moved superior-inferiorly and the bolus moved anterior-posteriorly with a sinusoid curve (period 5s, amplitude 2cm). Multi-slice images of the phantom were acquired in sagittal planes with each slice imaged for 6s. Number of slices was chosen to cover entire interested volume. 4D-MRI were retrospectively reconstructed using breathing signals determined with the FFT method. Motions of the objective determined from 4D-MRI were compared against the sinusoid curve. Results: Breathing signals determined using the FFT method matched well with those determined using the tracking method. On average of 10 subjects, the mean difference in respiratory phase between two methods is -3.13 ± 4.85%, and the mean correlation coefficient is 0.97 ± 0.02. In the phantom study, sinusoidal motions of object were clearly revealed with minimal artifacts in all three planes of 4D-MRI. Motion measured from 4D-MRI are consistent with the sinusoid curve (mean difference in amplitude: -0.5 ± 0.6 mm). Conclusions: Preliminary results demonstrated that breathing signals can be extracted from image FFT with accurate respiratory phase information, and can be used as respiratory surrogate for retrospective reconstruction of 4D-MRI. Author Disclosure: J. Cai, None; Z. Chang, None; Z. Wang, None; F. Yin, None.
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Evaluation of Dosimetric Effects of Use of Deformably-Mapped Contours for Lung IMRT Treatment Planning
N. Dogan1, W. Sleeman1, M. Fatyga1, W. Lehman1, E. Weiss1, G. Christensen1,2, J. Williamson1 1
Virginia Commonwealth University, Richmond, VA, 2The University of Iowa, Iowa City, IA
Purpose/Objective(s): To evaluate the dosimetric differences in IMRT treatment plans using deformably-mapped and physiciandrawn contours in lung cancer patients. Materials/Methods: Twelve lung cancer patients who had 4D-CTs were included. Small Deformation Inverse Consistent Linear Elastic (SICLE) and a viscous-fluid based deformable image registration (DIR) algorithms were used to generate deformably-mapped contours on respiratory phases. The GTvs., right and left lungs, heart, cord, and esophagus were also manually delineated by the same physician for all ten respiratory phases. For both physician-drawn and deformably-mapped contours at each phase, CTvs. and PTvs. were created. The prescription dose to PTvs. for all plans was 74 Gy /37fx. IMRT plans based on both set of contours were generated on respiratory phase 5 since it has the largest motion trajectory. Plans based on physician-drawn contours were also generated on phase 0 (reference) image set and doses from phase 0 were deformed to phase 5 image sets using the displacement vector fields generated by two DIR algorithms. Plans on phase 5 images were compared for their coverage of physician-drawn contours which were used as a benchmark. Plans were evaluated using the differences in PTV D95, D2, lungs-GTV D30 cord and non-PTV tissue D2, heart D50 and esophagus D30. Results: Differences in GTV volumes between physician-drawn and deformably-mapped contours were $ 10% in 5 patients. For PTV, on average, differences in D2 for physician-drawn and deformably-mapped contour plans on phase 5 and plans based on warping dose from phase 0 to 5 were \ 1.0 Gy. For PTV D95, mean differences were -1.8 ± 2.95 Gy, -4.8 ± 7.6 Gy, -3.5 ±
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3168
Extracting Breathing Signal from Image Fourier Transform for Developing 4D-MRI
J. Cai, Z. Chang, Z. Wang, F. Yin Duke University Medical Center, Durham, NC Purpose/Objective(s): According to the theory of Fast Fourier Transform (FFT), shifts in the spatial domain result in phase change in the frequency domain. The objective of this study is to investigate the feasibility of exacting breathing signals from the FFT of continuous acquired images and applying them in the development of 4D-MRI. Materials/Methods: This technique was developed using previously acquired data and validated using a phantom study. 10 subjects were imaged continuously for 2-min during free breathing on a 1.5T Siemens MR scanner using a true fast imaging with steady-state precession (TrueFISP). Imaging parameters (TR/TE, 3.7/1.21ms; Matrix, 256x166; FOV, 350x300 mm; flip angle, 52 ; slice thickness, 5 mm) were used to achieve a frame rate of 3 frames/s. The study was approved by local IRB and consents were obtained before the study. All images were acquired in a single coronal (n = 5) or sagittal (n = 5) plane. For each subject, breathing signals were determined 1) by tracking the motion of a selected internal structure, and 2) as the phase change of the image FFT. Respiratory phases were then calculated from breathing signals and compared between two methods. Pearson correlation was performed. To test the feasibility of using FFT for 4D-MRI, a self built MR-compatible motion phantom was imaged on a 1.5T GE MR scanner using a fast imaging employed steady-state acquisition (FIESTA, equivalent to TrueFISP) with similar parameters as above. The phantom consists of a cylinder object and a piece of bolus to mimic tumor and body surface respectively. During experiment the object moved superior-inferiorly and the bolus moved anterior-posteriorly with a sinusoid curve (period 5s, amplitude 2cm). Multi-slice images of the phantom were acquired in sagittal planes with each slice imaged for 6s. Number of slices was chosen to cover entire interested volume. 4D-MRI were retrospectively reconstructed using breathing signals determined with the FFT method. Motions of the objective determined from 4D-MRI were compared against the sinusoid curve. Results: Breathing signals determined using the FFT method matched well with those determined using the tracking method. On average of 10 subjects, the mean difference in respiratory phase between two methods is -3.13 ± 4.85%, and the mean correlation coefficient is 0.97 ± 0.02. In the phantom study, sinusoidal motions of object were clearly revealed with minimal artifacts in all three planes of 4D-MRI. Motion measured from 4D-MRI are consistent with the sinusoid curve (mean difference in amplitude: -0.5 ± 0.6 mm). Conclusions: Preliminary results demonstrated that breathing signals can be extracted from image FFT with accurate respiratory phase information, and can be used as respiratory surrogate for retrospective reconstruction of 4D-MRI. Author Disclosure: J. Cai, None; Z. Chang, None; Z. Wang, None; F. Yin, None.
3169
Evaluation of Dosimetric Effects of Use of Deformably-Mapped Contours for Lung IMRT Treatment Planning
N. Dogan1, W. Sleeman1, M. Fatyga1, W. Lehman1, E. Weiss1, G. Christensen1,2, J. Williamson1 1
Virginia Commonwealth University, Richmond, VA, 2The University of Iowa, Iowa City, IA
Purpose/Objective(s): To evaluate the dosimetric differences in IMRT treatment plans using deformably-mapped and physiciandrawn contours in lung cancer patients. Materials/Methods: Twelve lung cancer patients who had 4D-CTs were included. Small Deformation Inverse Consistent Linear Elastic (SICLE) and a viscous-fluid based deformable image registration (DIR) algorithms were used to generate deformably-mapped contours on respiratory phases. The GTvs., right and left lungs, heart, cord, and esophagus were also manually delineated by the same physician for all ten respiratory phases. For both physician-drawn and deformably-mapped contours at each phase, CTvs. and PTvs. were created. The prescription dose to PTvs. for all plans was 74 Gy /37fx. IMRT plans based on both set of contours were generated on respiratory phase 5 since it has the largest motion trajectory. Plans based on physician-drawn contours were also generated on phase 0 (reference) image set and doses from phase 0 were deformed to phase 5 image sets using the displacement vector fields generated by two DIR algorithms. Plans on phase 5 images were compared for their coverage of physician-drawn contours which were used as a benchmark. Plans were evaluated using the differences in PTV D95, D2, lungs-GTV D30 cord and non-PTV tissue D2, heart D50 and esophagus D30. Results: Differences in GTV volumes between physician-drawn and deformably-mapped contours were $ 10% in 5 patients. For PTV, on average, differences in D2 for physician-drawn and deformably-mapped contour plans on phase 5 and plans based on warping dose from phase 0 to 5 were \ 1.0 Gy. For PTV D95, mean differences were -1.8 ± 2.95 Gy, -4.8 ± 7.6 Gy, -3.5 ±
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