Differences In Motion Amplitude Research Articles

Time-resolved magnetic resonance fingerprinting for radiotherapy motion management.

This study aims to develop a novel time-resolved magnetic resonance fingerprinting (TR-MRF) technique for respiratory motion imaging applications. The TR-MRF technique consists of repeated MRF acquisitions using an unbalanced steady-state free precession sequence with spiral-in-spiral-out trajectory. Time-resolved magnetic resonance fingerprinting was first tested via computer simulation using a four-dimensional (4D) extended cardiac-torso (XCAT) phantom for both regular and irregular breathing profiles, and was tested in three healthy volunteers. Parametric TR-MRF maps at different respiratory phases were subsequently estimated using our TR-MRF sorting and reconstruction techniques. The resulting TR-MRF maps were evaluated using a set of metrices related to radiotherapy applications, including absolute difference in motion amplitude, error in the amplitude of diaphragm motion (ADM), tumor volume error (TVE), signal-to-noise ratio (SNR), and tumor contrast. TR-MRF maps with regular and irregular breathing were successfully generated in XCAT phantom. Numerical simulations showed that the TVE were 1.6±2.7% and 1.3±2.2%, the average absolute differences in tumor motion amplitude were 0.3±0.7mm and 0.3±0.6mm, and the ADM were 4.1±0.9% and 3.5±0.9% for irregular and regular breathing, respectively. The SNR of the T1 and T2 maps of the liver and the tumor were generally higher for regular breathing compared to irregular breathing, whereas tumor-to-liver contrast is similar between the two breathing patterns. The proposed technique was successfully implemented on the healthy volunteers. We have successfully demonstrated in both digital phantom and healthy subjects a novel TR-MRF technique capable of imaging respiratory motions with simultaneous quantification of MR multiparametric maps.

MO‐G‐18C‐04: Improved Synthetic 4D‐MRI Using Linear Polynomial Fitting Model

Purpose:To reduce deformable image registration error by fitting the displacement vector field (DVF) to smooth the motion trajectory of each pixel in synthetic 4D‐MRI.Methods:Five patients with cancers in the liver were enrolled in this study. For a 4D MR image data set, the DVF matrices relative to a specific reference phase were calculated using an in‐house deformable image registration based on b‐spline. The displacement trajectory of each voxel throughout the respiratory cycle was constituted by concatenating the corresponding displacement values from all DVF matrices. A linear polynomial fitting model was then used to fit the DVFs in three spatial and the temporal dimension, respectively. By warpping the source MR images using the remodeled DVFs, we synthesized MR images at selected phases. Tumor motion trajectories were derived from source 4DMRI, original synthetic images and improved synthetic images. These were analyzed in the superior‐inferior (SI), anterior‐posterior (AP), and mediallateral (ML) directions, respectively. Correlation coefficients (CC) and differences in motion amplitude (D) were calculated for comparison.Results:For all patients, tumor motion trajectories were strongly correlated between source 4D‐MRI images and improved synthetic 4D‐MRI (mean CC 0.98±0.01). Differences in motion amplitude were small (mean D 0.46±0.14 mm) in all directions. Correlation between source 4D‐MRI and original synthetic 4D‐MRI was slightly less strong (mean CC 0.97±0.01) and motion amplitude differences were slightly larger (0.55±0.19 mm).Conclusion:The feasibility of synthesizing T2w 4D‐MRI using remodeled DVFs has been investigated in this study. Preliminary results in oncologic patients demonstrated the potential of reducing inaccuracies in original synthetic 4DMRI caused by registration errors using the linear polynomial fitting model without much loss of respiratory motion information.NIH (1R21CA165384‐01A1), Golfers Against Cancer (GAC) Foundation, The China Scholarship Council (CSC)

An Integrated Simulation System Based on Digital Human Phantom for 4D Radiation Therapy of Lung Cancer

Purpose: To develop and test an integrated simulation system based on the digital Extended Cardio Torso (XCAT) phantom for 4-dimensional (4D) radiation therapy of lung cancer. Methods: A computer program was developed to facilitate the characterization and implementation of the XCAT phantom for 4D radiation therapy applications. To verify that patient-specific motion trajectories are reproducible with the XCAT phantom, motion trajectories of the diaphragm and chest were extracted from previously acquired MRI scans of five subjects and were imported into the XCAT phantom. The input versus the measured trajectories was compared. Simulation methods of 4D-CT and 4D-cone-beam CT (CBCT) based on the XCAT phantom were developed and tested for regular and irregular respiratory patterns. Simulation of 4D dose delivery was illustrated in a simulated lung stereotactic-body radiation therapy (SBRT) case based on the XCAT phantom. Dosimetric comparison was performed between the planned dose and simulated delivered dose. Result: The overall mean (±standard deviation) difference in motion amplitude between the input and measured trajectories was 1.19 (±0.79) mm for the XCAT phantoms with voxel size of 2 mm. 4D-CT and 4D-CBCT images simulated based on the XCAT phantom were validated using regular respiratory patterns and tested for irregular respiratory patterns. Comparison between simulated 4D dose delivery and planned dose for the lung SBRT case showed comparable results in all dosimetric matrices: the relative differences were 0.3%, 4.0%, 0%, and 2.8%, respectively, for max cord dose, max esophagus dose, mean heart dose, and V20Gy of the lungs. 97.5% of planning target volume (PTV) received prescription dose in the simulated 4D delivery, as compared to 95% of PTV received prescription dose in the plan. Conclusion: We developed an integrated simulation system based on the XCAT digital phantom and illustrated its utility in 4D radiation therapy of lung cancer. This simulation system is potentially a useful tool for quality control and development of imaging and treatment techniques for 4D radiation therapy of lung cancer.

WE-C-116-07: Tumor Enhancement Using Deformable Image Registration for Four-Dimensional Magnetic Resonance Imaging (4D-MRI): A Feasibility Study

Purpose: We have previously developed a 4D‐MRI technique using the fast imaging sequence employing steady‐state acquisition (FIESTA) sequence, which has suboptimal tumor‐to‐tissue contrast‐to‐noise ratio (CNR) due to its T2*/T1 weighting. This study investigated the feasibility of enhancing the tumor‐to‐tissue CNR using deformable image registration (DIR). Methods: Five patients with cancers in the liver were included in an IRB‐approved study. 4D‐MRI images were acquired on a 1.5T GE scanner and reconstructed off line using in‐house developed program. All patients were also imaged with a T2‐w fast recovery fast spin‐echo (FRFSE) sequence at the end‐of‐exhalation phase. Deformation vectors between respiratory phases of the 4D‐MRI were determined using commercial software. Pseudo ‘enhanced’ 4D‐MRI was then generated by applying the deformation vectors to the T2‐w FRFSE MR images. Motion trajectories of tumor and diaphragm and tumor‐to‐tissue CNR were compared between the original T2*/T1‐w 4D‐MRI and the ‘enhanced’ T2‐w 4D‐MRI. To validate our method, we performed a simulation study based on a 4D digital human phantom. MR images with T2*/T1‐w and T2‐w with were generated by assigning organ intensities corresponding to those in FIESTA and FRFSE images, respectively. Results: In the phantom study, motion trajectories of the hypothesized ‘tumor’ matched excellently between the original T2*/T1‐w 4D‐MRI and the ‘enhanced’ T2‐w 4D‐MRI. Mean(±SD) absolute difference in motion amplitude was 0.66 (±0.62) mm. In the patient study, tumor and diaphragm motion trajectories closely matched between the two 4D‐MRIs: mean correlation coefficient was great than 0.97 in all directions; the mean (±SD) absolute difference in motion amplitude was smaller than 0.55(±0.19) mm. Tumor‐to‐tissue CNR was significantly improved from 7.57(±5.6) in the original 4D‐MRI to 23.75(±15.8) in the ‘enhanced’ 4D‐MRI. Conclusion: It is feasible to improve tumor‐to‐tissue CNR of T2*/T1‐w 4D‐MRI using the DIR method. The ‘enhanced’ 4D‐MRI retained comparable tumor motion information as the original 4D‐MRI. This work is partly supported by funding from NIH (1R21CA165384‐01A1) and a research grant from the Golfers Against Cancer (GAC) Foundation.

TH‐C‐141‐07: T2‐Weighted 4D‐MRI with Combined Phase and Amplitude Sorting

Purpose: T2‐weighted MR provides excellent delineation of malignant liver lesions due to its superior tumor‐to‐tissue contrast. This study aims to develop a novel T2‐weighted retrospective 4D‐MRI technique for imaging organ/tumor respiratory motion with improved soft‐tissue contrast. Method and Materials: Determine the number of repeated scans (NR) required obtaining sufficient phase information for each slice is the critical component in developing this technique and needs substantial testing with many samples. To do that, computer simulations using RPM respiratory signals of 29 cancer patients were performed to derive the relationships between NR and the following factors: number of slice to scanned (Ns), number of respiratory phases of the 4D‐MRI (Np), and starting phase at image acquisition (P0). Assuming T2‐w HASTE/SSFSE MR sequence to be used to acquire raw images for 4D‐MRI, frame rate of 2 frames/s was used in the simulation. To validate our technique, 4D‐MRI acquisition and reconstruction were simulated on a 4D digital human phantom using parameters derived from the above studies. Retrospective sorting of 4D‐MRI was achieved using a novel phase and amplitude hybrid sorting algorithm by effectively utilizing redundant images. Result: Percentage of complete acquisition of all required phases (Cp) increased as NR increased in an inverse‐exponential (Cp=100*[1‐exp(−0.11*NR)],when Ns=50,Np=10) fashion. NR to achieve 95% completion (Cp=95%) of all required phases, defined as the NR needed for 4D‐MRI, is linearly proportional to Np (Nr∼2.86*Np, r=1.0) but independent of NS and P0. Simulated 4D‐MRI on the digital phantom showed clear pattern of respiratory motion. Tumor motion trajectories measured on 4D‐MRI were comparable to the average input signal, with a mean relative difference in motion amplitude of 16%, presumably due to breathing irregularity. Conclusions: A novel T2‐weighted 4D‐MRI technique based on HASTE/SSFSE sequence have been developed and validated. Future evaluation on patients is desired. This work is partly supported by funding from NIH (1R21CA165384‐01A1) and a research grant from the Golfers Against Cancer (GAC) Foundation.

SU-E-J-145: Implementing 4D XCAT Phantom for 4D Radiotherapy Research.

To characterize and implement the 4D Integrated Extended Cardiac Torso (XCAT) digital phantom for 4D radiotherapy (RT) application. A computer program was developed to facilitate the characterization and implementation of the 4D XCAT phantom. The program can (1) generate 4D XCAT images with customized parameter files; (2) review 4D XCAT images; (3) generate composite images from 4D XCAT images; (4) track motion of selected region-of-interested (ROI); (5) convert XCAT raw binary images into DICOM format; (6) analyze clinically acquired 4DCT images and Real-time Position Management (RPM) respiratory signal. Validation of the motion tracking algorithm was made by comparing to manual method. Major characteristics of the 4D XCAT phantom were studied including the dependence of lesion motion on its location/size and inputted diaphragm profile. An end-to-end test from image generation to treatment planning was also performed. The comparison between motion tracking and manual measurements of lesion motion trajectory showed a small difference between the two (mean difference in motion amplitude: 1.2 mm). The maximum lesion motion decreased nearly linearly (R2=0.97) as its distance to the diaphragm (DD) increased. At any given DD, lesion motion amplitude increased nearly linearly (R2 range: 0.89 to 0.95) as the inputted diaphragm motion increased. For a given diaphragm motion, the lesion motion is independent f the lesion size at any given DD. The 4D XCAT phantom can closely reproduce irregular breathing profile: the mean difference in motion amplitude between the inputted and the measured motion profile was 1.4 mm. The end-to-end test showed that clinically comparable treatment plans can be generated successfully based on 4D XCAT images. An integrated computer program has been developed to generate, review, analyze, process, and export the 4D XCAT images. A robust workflow has been established to implement the 4D XCAT phantom for 4D RT application.

SU-D-218-02: 4D-MRI Based on Body Area (BA) Surrogate and Sagittal Image Acquisition.

4D-MRI based on body area (BA) surrogate using axial image acquisition has been demonstrated. Since respiratory motion mostly occurs in the superior-inferior (SI) direction, it is expected that sagittal acquisition may provide more robust and accurate breathing signal than axial acquisition. The aim of this study was to investigate the feasibility of extracting breathing signals from sagittal images using BA surrogate and its application in 4D-MRI. 7 human subjects were imaged continuously in a single (n=5) or multiple (n=2) sagittal planes using a steady-state precession sequence. Imaging parameters were: TR/TE, 3.7ms/1.21ms; Matrix, 256×166; FOV, 350×300mm; flip angle, 52°; slice thickness, 5mm; frame rate: ∼3 frames/s. Imaging time per slice is 2 minutes for single slice acquisition and ∼10 seconds for multi-slice acquisition. Breathing signals were generated for all subjects by tracking the change of BA. The multi-slice sagittal acquisition was performed on a MRI- compatible motion phantom with a cylindrical gel target and was simulated on a 4D digital human phantom. Breathing signals were extracted from the sagittal images using the BA surrogate. Respiratory phases were calculated. 4D-MRI of both phantoms were retrospectively reconstructed based on the respiratory phases. Breathing signals extracted from both single slice and multi-slice sagittal acquisitions showed stable and well- characterized patterns. 4D-MRI of the physical phantom showed clear sinusoidal motion of the gel target in all three planes with minimal artifacts. Simulated '4D-MRI' of the 4D digital phantom matched well with original images: the mean absolute difference in motion amplitude of the 'tumor' was 0.4±0.3mm. Small artifacts of discontinuity were observed in the SI direction in certain phases. It is feasible to extract breathing signals from sagittal images for 4D-MRI application. Further investigation is needed to test whether sagittal acquisition is more robust and accurate than axial acquisition for breathing signal extraction.

Establishing a framework to implement 4D XCAT Phantom for 4D radiotherapy research

To establish a framework to implement the 4D integrated extended cardiac torso (XCAT) digital phantom for 4D radiotherapy (RT) research. A computer program was developed to facilitate the characterization and implementation of the 4D XCAT phantom. The program can (1) generate 4D XCAT images with customized parameter files; (2) review 4D XCAT images; (3) generate composite images from 4D XCAT images; (4) track motion of selected region-of-interested (ROI); (5) convert XCAT raw binary images into DICOM format; (6) analyse clinically acquired 4DCT images and real-time position management (RPM) respiratory signal. Motion tracking algorithm was validated by comparing with manual method. Major characteristics of the 4D XCAT phantom were studied. The comparison between motion tracking and manual measurements of lesion motion trajectory showed a small difference between them (mean difference in motion amplitude: 1.2 mm). The maximum lesion motion decreased nearly linearly (R 2 = 0.97) as its distance to the diaphragm (DD) increased. At any given DD, lesion motion amplitude increased nearly linearly (R 2 range: 0.89 to 0.95) as the inputted diaphragm motion increased. For a given diaphragm motion, the lesion motion is independent of the lesion size at any given DD. The 4D XCAT phantom can closely reproduce irregular breathing profile. The end-to-end test showed that clinically comparable treatment plans can be generated successfully based on 4D XCAT images. An integrated computer program has been developed to generate, review, analyse, process, and export the 4D XCAT images. A framework has been established to implement the 4D XCAT phantom for 4D RT research.

Four‐dimensional magnetic resonance imaging (4D‐MRI) using image‐based respiratory surrogate: A feasibility study

Four-dimensional computed tomography (4D-CT) has been widely used in radiation therapy to assess patient-specific breathing motion for determining individual safety margins. However, it has two major drawbacks: low soft-tissue contrast and an excessive imaging dose to the patient. This research aimed to develop a clinically feasible four-dimensional magnetic resonance imaging (4D-MRI) technique to overcome these limitations. The proposed 4D-MRI technique was achieved by continuously acquiring axial images throughout the breathing cycle using fast 2D cine-MR imaging, and then retrospectively sorting the images by respiratory phase. The key component of the technique was the use of body area (BA) of the axial MR images as an internal respiratory surrogate to extract the breathing signal. The validation of the BA surrogate was performed using 4D-CT images of 12 cancer patients by comparing the respiratory phases determined using the BA method to those determined clinically using the Real-time position management (RPM) system. The feasibility of the 4D-MRI technique was tested on a dynamic motion phantom, the 4D extended Cardiac Torso (XCAT) digital phantom, and two healthy human subjects. Respiratory phases determined from the BA matched closely to those determined from the RPM: mean (± SD) difference in phase: -3.9% (± 6.4%); mean (± SD) absolute difference in phase: 10.40% (± 3.3%); mean (± SD) correlation coefficient: 0.93 (± 0.04). In the motion phantom study, 4D-MRI clearly showed the sinusoidal motion of the phantom; image artifacts observed were minimal to none. Motion trajectories measured from 4D-MRI and 2D cine-MRI (used as a reference) matched excellently: the mean (± SD) absolute difference in motion amplitude: -0.3 (± 0.5) mm. In the 4D-XCAT phantom study, the simulated "4D-MRI" images showed good consistency with the original 4D-XCAT phantom images. The motion trajectory of the hypothesized "tumor" matched excellently between the two, with a mean (± SD) absolute difference in motion amplitude of 0.5 (± 0.4) mm. 4D-MRI was able to reveal the respiratory motion of internal organs in both human subjects; superior-inferior (SI) maximum motion of the left kidney of Subject #1 and the diaphragm of Subject #2 measured from 4D-MRI was 0.88 and 1.32 cm, respectively. Preliminary results of our study demonstrated the feasibility of a novel retrospective 4D-MRI technique that uses body area as a respiratory surrogate.