- Email: [email protected]
Initial Evaluation of Four Dimensional Diffusion-Weighted MR Imaging (4D-DWI) in Phantom and Human Subject
E604
International Journal of Radiation Oncology Biology Physics
and surface structures have been observed. This problem may be less prominent under computer-assisted deep inspiration breathhold (DIBH) due to less degrees of freedom of relative movement of surface and internal structures. We propose a method to study the correlation of surface and internal assess the clinical feasibility. Materials/Methods: Based on the geometrical relationship of CBCT rotational isocenter and the diaphragm dome (DD) in the transversal plane, a cosinus-function for the correction of projection conditions of the DD in the planar frames acquired for CBCT reconstruction was parametrized. This allowed the calculation of absolute diaphragm position along the patient longitudinal axis. In 5 patients that underwent CA-CBCT before SBRT (start-and-stop CBCT with frames only acquired during 10-20sbreathhold phases), the percentage of frames usable for DD detection was assessed. In a pilot patient, correlation of the movement of a surface gating point (SGP) and the position of DD was quantified. Results: Unequivocal DD detection was possible over 62.8% 12.8% of all frames (for right DD with an isocenter on the left side of the thorax, typically 270 - 221 , 219 - 170 , 168 - 119 and 116 - 67 ) and therefore allowed the correlation of DD and SGP for a sufficient part of all breathhold phases. In the pilot patient, a standard deviation of the SGPmovement of 0.61 mm corresponded with a standard deviation of 0.44 mm for DD position along the patient longitudinal axis. Conclusion: Detection of inspiration depth by determining DD position during breathhold phases of a DIBH-only CBCTacquisition is possible using a cosinus-fit based on geometrical patient parameters. Under computerassisted DIBH induction, initial results show excellent correlation of surfacescanning trigger-point position and diaphragm position. Author Disclosure: A.O. Simeonova: Travel Expenses; Elekta. J. Hofmann: None. L. Jahnke: Honoraria; Elekta. Travel Expenses; Elekta. D. Hauck: None. C. Roß: None. J. Boda-Heggemann: Travel Expenses; Elekta. F. Wenz: Research Grant; Elekta, Zeiss. Honoraria; Elekta, Roche, Lilly, Ipsen. Consultant; Elekta. Advisory Board; Elekta, Celgene. Travel Expenses; Elekta, Zeiss, Celgene, Roche, Lilly. Patent/License Fees/ Copyright; Zeiss. Chairman; University Medical Center Mannheim, Department Radiation Oncology. Director; University Medical Center Mannheim. F. Lohr: Honoraria; Elekta, IBA, CRAD. Advisory Board; CRAD. Travel Expenses; Elekta, IBA, C-RAD. Vice-Chair; University Medical Center Mannheim, University of Heidelberg. Board Member; CRAD. F. Stieler: Honoraria; Elekta. Travel Expenses; Elekta.
Motion trajectories of the region of interests (ROI) were extracted from 4D-DWI and compared with that from MRI cine (reference). The mean motion trajectory amplitude differences (D) between the two was calculated. Since the 4D-DWI reconstruction method was different from the other 4D-MRI reconstruction methods, we compared the image volume inconsistency artifacts shown on healthy volunteer 4D-DWI with T2-w 4D-MRI, which was acquired during the same MRI scan. To quantify the artifacts, amplitude variance between different slice locations (Var) was calculated for each phase bin as an indication. Results: Tumor trajectory extracted from simulated 10-phase bin 4D-DWI on the XCAT phantom showed clear respiratory motion pattern, consistent with the input signal (reference): D for the tumor were 1.9 mm and 0.4 mm in the SI and AP directions, respectively. Reconstructed 6-phase bin 4DDWI of the motion phantom and healthy volunteer also revealed the respiratory motion clearly. D of the selected ROI was 1.7mm and 2.0 mm, respectively. The image volume inconsistency artifacts were less on 4DDWI (Var Z 4.6%) than T2-w 4D-MRI (Var Z 7.3%). This indicated that 4D-DWI showed less amplitude variance, leading to less image volume inconsistency artifacts. Conclusion: A respiratory correlated 4D-DWI technique has been developed and initially evaluated in phantoms and a human subject. This has significant potential to improve the visualization and delineation of mobile cancers for radiation therapy. Author Disclosure: Y. Liu: None. F. Yin: None. B. Czito: None. M.R. Bashir: None. J. Cai: None.
3514 Initial Evaluation of Four Dimensional Diffusion-Weighted MR Imaging (4D-DWI) in Phantom and Human Subject Y. Liu, F.F. Yin, B. Czito, M.R. Bashir, and J. Cai; Duke University Medical Center, Durham, NC Purpose/Objective(s): Diffusion-weighted imaging (DWI) has been shown to have superior tumor-to-tissue contrast as compared to CT, T1-w and T2-w MR images for cancer detection. Current 4D imaging technique for radiation therapy, 4D-CT, is insufficient in providing high tumor-totissue contrast for abdominal cancers. The existing breathing-hold, rapid imaging technique helps but not provides comprehensively respiratory motion information. This study aims at developing and evaluating a respiratory correlated four dimensional Diffusion-Weighted MR Imaging (4D-DWI) technique using retrospective sorting method for imaging respiratory motion for radiation therapy. Materials/Methods: Image acquisition of 4D-DWI was achieved by repeatedly imaging a volume of interest using interleaf-mode single-shot 2D DWI sequence in axial planes. Each 2D-DWI image were acquired in x, y and z directions with a high b-value (bZ500s/mm2). The respiratory motion was simultaneously recorded using an external respiratory surrogate: Physiologic Monitoring Unit (PMU). Retrospective phase sorting algorithm was applied to respectively re-sort x-, y- and z-DWI images. Then the sorted x-, y- and z-DWI images were combined to reconstruct 4D-DWI. The technique was evaluated using a computer simulated 4D digital human phantom (XCAT), a motion phantom and a healthy volunteer. The healthy volunteer was involved in an IRB-approved study.
3515 Feasibility of Diffusion Weighted MR Lymphography for Cervical Lymph Node Delineation in Head and Neck Cancer E.S. Paulson, W.A. Hall, and J.R. Robbins; Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): Cervical lymph node delineation in head and neck cancer (HNC) can be challenged by the poor soft tissue contrast inherent in CT. The goal of this work was to investigate whether lymph nodes can be visualized using non-contrast advanced MR imaging. Materials/Methods: One volunteer with lymphadenopathy and two HNC patients were scanned at 3T. One patient underwent a left-sided Mohs resection and skin flap reconstruction, resulting in atypical lymph node anatomy. The patients were set up and imaged in treatment position. A vendor-provided single-shot, echo-planar imaging sequence with STIR preparation (TI Z 220 msec) and water excitation was employed in the study. A long echo time (TEZ80 msec) was used to suppress signal from muscle and a small amount of diffusion weighting (bZ50 s/mm2) was applied to suppress signal from fast intravascular spins. The combination of parallel imaging (GRAPPA, RZ2), partial Fourier encoding, and optimized readout bandwidth was employed to reduce the length of the echo train to minimize geometric distortions. Remnant geometric distortions were corrected using a separately acquired B0 map. Eighty contiguous, interleaved, axial 2D slices were acquired with voxel sizes of 2 x 2 x 2 mm. Total scan time was approximately 3 minutes. The axial images were subsequently reformatted as thin coronal MIPs. Images were loaded into a commercially available deformable registration algorithm and lymph node signal-to-background ratios were calculated between CT and MRI. Results: Level I e VII cervical lymph nodes were adequately visualized on coronal MIPs for the volunteer with lymphadenopathy. As expected, discernable differences in left and right side lymph nodes were detected in the patient with Mohs resection. Increasing the diffusion weighting from bZ50 s/mm2 to bZ300 s/mm2 did not improve lymph node contrast. Lymph node signal-to-background ratio improved from nearly 1 on CT to 6.2 using the proposed method. Conclusion: Visualization of lymph nodes using diffusion-weighted MR lymphography is feasible. Future work will investigate generating apparent diffusion coefficient (ADC) maps from serial MR lymphography measurements to differentiate benign from malignant lymph nodes. Author Disclosure: E.S. Paulson: Research Grant; Advancing a Healthier Wisconsin. W.A. Hall: None. J.R. Robbins: None.
International Journal of Radiation Oncology Biology Physics
and surface structures have been observed. This problem may be less prominent under computer-assisted deep inspiration breathhold (DIBH) due to less degrees of freedom of relative movement of surface and internal structures. We propose a method to study the correlation of surface and internal assess the clinical feasibility. Materials/Methods: Based on the geometrical relationship of CBCT rotational isocenter and the diaphragm dome (DD) in the transversal plane, a cosinus-function for the correction of projection conditions of the DD in the planar frames acquired for CBCT reconstruction was parametrized. This allowed the calculation of absolute diaphragm position along the patient longitudinal axis. In 5 patients that underwent CA-CBCT before SBRT (start-and-stop CBCT with frames only acquired during 10-20sbreathhold phases), the percentage of frames usable for DD detection was assessed. In a pilot patient, correlation of the movement of a surface gating point (SGP) and the position of DD was quantified. Results: Unequivocal DD detection was possible over 62.8% 12.8% of all frames (for right DD with an isocenter on the left side of the thorax, typically 270 - 221 , 219 - 170 , 168 - 119 and 116 - 67 ) and therefore allowed the correlation of DD and SGP for a sufficient part of all breathhold phases. In the pilot patient, a standard deviation of the SGPmovement of 0.61 mm corresponded with a standard deviation of 0.44 mm for DD position along the patient longitudinal axis. Conclusion: Detection of inspiration depth by determining DD position during breathhold phases of a DIBH-only CBCTacquisition is possible using a cosinus-fit based on geometrical patient parameters. Under computerassisted DIBH induction, initial results show excellent correlation of surfacescanning trigger-point position and diaphragm position. Author Disclosure: A.O. Simeonova: Travel Expenses; Elekta. J. Hofmann: None. L. Jahnke: Honoraria; Elekta. Travel Expenses; Elekta. D. Hauck: None. C. Roß: None. J. Boda-Heggemann: Travel Expenses; Elekta. F. Wenz: Research Grant; Elekta, Zeiss. Honoraria; Elekta, Roche, Lilly, Ipsen. Consultant; Elekta. Advisory Board; Elekta, Celgene. Travel Expenses; Elekta, Zeiss, Celgene, Roche, Lilly. Patent/License Fees/ Copyright; Zeiss. Chairman; University Medical Center Mannheim, Department Radiation Oncology. Director; University Medical Center Mannheim. F. Lohr: Honoraria; Elekta, IBA, CRAD. Advisory Board; CRAD. Travel Expenses; Elekta, IBA, C-RAD. Vice-Chair; University Medical Center Mannheim, University of Heidelberg. Board Member; CRAD. F. Stieler: Honoraria; Elekta. Travel Expenses; Elekta.
Motion trajectories of the region of interests (ROI) were extracted from 4D-DWI and compared with that from MRI cine (reference). The mean motion trajectory amplitude differences (D) between the two was calculated. Since the 4D-DWI reconstruction method was different from the other 4D-MRI reconstruction methods, we compared the image volume inconsistency artifacts shown on healthy volunteer 4D-DWI with T2-w 4D-MRI, which was acquired during the same MRI scan. To quantify the artifacts, amplitude variance between different slice locations (Var) was calculated for each phase bin as an indication. Results: Tumor trajectory extracted from simulated 10-phase bin 4D-DWI on the XCAT phantom showed clear respiratory motion pattern, consistent with the input signal (reference): D for the tumor were 1.9 mm and 0.4 mm in the SI and AP directions, respectively. Reconstructed 6-phase bin 4DDWI of the motion phantom and healthy volunteer also revealed the respiratory motion clearly. D of the selected ROI was 1.7mm and 2.0 mm, respectively. The image volume inconsistency artifacts were less on 4DDWI (Var Z 4.6%) than T2-w 4D-MRI (Var Z 7.3%). This indicated that 4D-DWI showed less amplitude variance, leading to less image volume inconsistency artifacts. Conclusion: A respiratory correlated 4D-DWI technique has been developed and initially evaluated in phantoms and a human subject. This has significant potential to improve the visualization and delineation of mobile cancers for radiation therapy. Author Disclosure: Y. Liu: None. F. Yin: None. B. Czito: None. M.R. Bashir: None. J. Cai: None.
3514 Initial Evaluation of Four Dimensional Diffusion-Weighted MR Imaging (4D-DWI) in Phantom and Human Subject Y. Liu, F.F. Yin, B. Czito, M.R. Bashir, and J. Cai; Duke University Medical Center, Durham, NC Purpose/Objective(s): Diffusion-weighted imaging (DWI) has been shown to have superior tumor-to-tissue contrast as compared to CT, T1-w and T2-w MR images for cancer detection. Current 4D imaging technique for radiation therapy, 4D-CT, is insufficient in providing high tumor-totissue contrast for abdominal cancers. The existing breathing-hold, rapid imaging technique helps but not provides comprehensively respiratory motion information. This study aims at developing and evaluating a respiratory correlated four dimensional Diffusion-Weighted MR Imaging (4D-DWI) technique using retrospective sorting method for imaging respiratory motion for radiation therapy. Materials/Methods: Image acquisition of 4D-DWI was achieved by repeatedly imaging a volume of interest using interleaf-mode single-shot 2D DWI sequence in axial planes. Each 2D-DWI image were acquired in x, y and z directions with a high b-value (bZ500s/mm2). The respiratory motion was simultaneously recorded using an external respiratory surrogate: Physiologic Monitoring Unit (PMU). Retrospective phase sorting algorithm was applied to respectively re-sort x-, y- and z-DWI images. Then the sorted x-, y- and z-DWI images were combined to reconstruct 4D-DWI. The technique was evaluated using a computer simulated 4D digital human phantom (XCAT), a motion phantom and a healthy volunteer. The healthy volunteer was involved in an IRB-approved study.
3515 Feasibility of Diffusion Weighted MR Lymphography for Cervical Lymph Node Delineation in Head and Neck Cancer E.S. Paulson, W.A. Hall, and J.R. Robbins; Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): Cervical lymph node delineation in head and neck cancer (HNC) can be challenged by the poor soft tissue contrast inherent in CT. The goal of this work was to investigate whether lymph nodes can be visualized using non-contrast advanced MR imaging. Materials/Methods: One volunteer with lymphadenopathy and two HNC patients were scanned at 3T. One patient underwent a left-sided Mohs resection and skin flap reconstruction, resulting in atypical lymph node anatomy. The patients were set up and imaged in treatment position. A vendor-provided single-shot, echo-planar imaging sequence with STIR preparation (TI Z 220 msec) and water excitation was employed in the study. A long echo time (TEZ80 msec) was used to suppress signal from muscle and a small amount of diffusion weighting (bZ50 s/mm2) was applied to suppress signal from fast intravascular spins. The combination of parallel imaging (GRAPPA, RZ2), partial Fourier encoding, and optimized readout bandwidth was employed to reduce the length of the echo train to minimize geometric distortions. Remnant geometric distortions were corrected using a separately acquired B0 map. Eighty contiguous, interleaved, axial 2D slices were acquired with voxel sizes of 2 x 2 x 2 mm. Total scan time was approximately 3 minutes. The axial images were subsequently reformatted as thin coronal MIPs. Images were loaded into a commercially available deformable registration algorithm and lymph node signal-to-background ratios were calculated between CT and MRI. Results: Level I e VII cervical lymph nodes were adequately visualized on coronal MIPs for the volunteer with lymphadenopathy. As expected, discernable differences in left and right side lymph nodes were detected in the patient with Mohs resection. Increasing the diffusion weighting from bZ50 s/mm2 to bZ300 s/mm2 did not improve lymph node contrast. Lymph node signal-to-background ratio improved from nearly 1 on CT to 6.2 using the proposed method. Conclusion: Visualization of lymph nodes using diffusion-weighted MR lymphography is feasible. Future work will investigate generating apparent diffusion coefficient (ADC) maps from serial MR lymphography measurements to differentiate benign from malignant lymph nodes. Author Disclosure: E.S. Paulson: Research Grant; Advancing a Healthier Wisconsin. W.A. Hall: None. J.R. Robbins: None.