Program Information
Self-Navigated, Respiratory-Correlated 4D-MRI with Switchable Contrast Modes
E Paulson*, N Mickevicius , Radiation Oncology, Radiology, and Biophysics, Medical College of Wisconsin, Milwaukee, WI
Presentations
TH-EF-605-11 (Thursday, August 3, 2017) 1:00 PM - 3:00 PM Room: 605
Purpose: Respiratory-correlated 4D-MRI is a promising motion management approach for radiotherapy. While many 4D-MRI techniques have been developed to leverage a particular pulse sequence, certain tumor sites may benefit more or less from a particular image contrast. We demonstrate here a self-navigated, respiratory-correlated, 4D-MRI pulse sequence with switchable contrast modes.
Methods: Patients with abdominal or thoracic tumors were imaged on a Siemens 3T using a hybrid, 3D golden angle radial stack of stars sequence of our own design. The sequence supports switchable FLASH, FISP, True-FISP, and PSIF (reversed FISP) modes for T1 and mixed T2/T1-weighted contrasts. A 3-point Dixon readout, integrated into the sequence, is available for FLASH and FISP modes. Typical 4D-MRI scan parameters included: axial prescription, field of view: 330 mm, base resolution: 192, readout bandwidth: 200 kHz, TE/TR: 1.3/3.5-6 msec, flip angle: 10 deg, slab thickness: 240 mm, total acquisition time: 2 minutes. The raw k-space data were transferred offline to a 40-core linux workstation. A motion navigator, extracted from the k-space data, was used to reshuffle the acquired data into one of 6-8 respiratory phase bins. Reconstruction was then performed using the XD-GRASP algorithm parallelized over partitions.
Results: All patients successfully completed the 2-minute 4D-MRI acquisition. By parallelizing the image reconstruction over partitions, the radial stack of star trajectory permitted reconstructions in 8 minutes for T1 and mixed T2/T1 contrasts. However, the reconstruction time lengthened considerably for fat/water separation of Dixon 4D-MR images. Compared with True-FISP, the PSIF contrast mode provided similar T2/T1 contrast but without banding artifacts. The XD-GRASP algorithm was effective at minimizing undersampling artifacts in the reshuffled k-space data.
Conclusion: A self-navigated, respiratory-correlated 4D-MRI sequence with switchable contrast modes permits high quality 4D-MR images for motion management with optimized contrasts tailored to specific tumor sites.
Funding Support, Disclosures, and Conflict of Interest: Advancing a Healthier Wisconsin
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