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Tilted-CAIPI for highly accelerated distortion-free EPI with point spread function (PSF) encoding.

ABSTRACT: PURPOSE:To develop a method for fast distortion- and blurring-free imaging. THEORY:EPI with point-spread-function (PSF) mapping can achieve distortion- and blurring-free imaging at a cost of long acquisition time. In this study, an acquisition/reconstruction technique, termed "tilted-CAIPI," is proposed to achieve >20× acceleration for PSF-EPI. The proposed method systematically optimized the k-space sampling trajectory with B0 -inhomogeneity-informed reconstruction, to exploit the inherent signal correlation in PSF-EPI and take full advantage of coil sensitivity. Susceptibility-induced phase accumulation is regarded as an additional encoding that is estimated by calibration data and integrated into reconstruction. Self-navigated phase correction was developed to correct shot-to-shot phase variation in diffusion imaging. METHODS:Tilted-CAIPI was implemented at 3T, with incorporation of partial Fourier and simultaneous multislice to achieve further accelerations. T2 -weighted, T2 * -weighted, and diffusion-weighted imaging experiments were conducted to evaluate the proposed method. RESULTS:The ability of tilted-CAIPI to provide highly accelerated imaging without distortion and blurring was demonstrated through in vivo brain experiments, where only 8 shots per simultaneous slice group were required to provide high-quality, high-SNR imaging at 0.8-1 mm resolution. CONCLUSION:Tilted-CAIPI achieved fast distortion- and blurring-free imaging with high SNR. Whole-brain T2 -weighted, T2 * -weighted, and diffusion imaging can be obtained in just 15-60 s.

SUBMITTER: Dong Z

PROVIDER: S-EPMC6258292 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Tilted-CAIPI for highly accelerated distortion-free EPI with point spread function (PSF) encoding.

Dong Zijing Z Wang Fuyixue F Reese Timothy G TG Manhard Mary Katherine MK Bilgic Berkin B Wald Lawrence L LL Guo Hua H Setsompop Kawin K

Magnetic resonance in medicine 20180905 1

<h4>Purpose</h4>To develop a method for fast distortion- and blurring-free imaging.<h4>Theory</h4>EPI with point-spread-function (PSF) mapping can achieve distortion- and blurring-free imaging at a cost of long acquisition time. In this study, an acquisition/reconstruction technique, termed "tilted-CAIPI," is proposed to achieve >20× acceleration for PSF-EPI. The proposed method systematically optimized the k-space sampling trajectory with B<sub>0</sub> -inhomogeneity-informed reconstruction, to ...[more]

PMID: 30229562

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Project description:BACKGROUND:Rapid volumetric imaging protocols could better utilize limited scanner resources. PURPOSE:To develop and validate an optimized 6-minute high-resolution volumetric brain MRI examination using Wave-CAIPI encoding. STUDY TYPE:Prospective. POPULATION/SUBJECTS:Ten healthy subjects and 20 patients with a variety of intracranial pathologies. FIELD STRENGTH/SEQUENCE:At 3?T, MPRAGE, T2 -weighted SPACE, SPACE FLAIR, and SWI were acquired at 9-fold acceleration using Wave-CAIPI and for comparison at 2-4-fold acceleration using conventional GRAPPA. ASSESSMENT:Extensive simulations were performed to optimize the Wave-CAIPI protocol and minimize both g-factor noise amplification and potential T1 /T2 blurring artifacts. Moreover, refinements in the autocalibrated reconstruction of Wave-CAIPI were developed to ensure high-quality reconstructions in the presence of gradient imperfections. In a randomized and blinded fashion, three neuroradiologists assessed the diagnostic quality of the optimized 6-minute Wave-CAIPI exam and compared it to the roughly 3× slower GRAPPA accelerated protocol using both an individual and head-to-head analysis. STATISTICAL TEST:A noninferiority test was used to test whether the diagnostic quality of Wave-CAIPI was noninferior to the GRAPPA acquisition, with a 15% noninferiority margin. RESULTS:Among all sequences, Wave-CAIPI achieved negligible g-factor noise amplification (gavg ???1.04) and burring artifacts from T1 /T2 relaxation. Improvements of our autocalibration approach for gradient imperfections enabled increased robustness to gradient mixing imperfections in tilted-field of view (FOV) prescriptions as well as variations in gradient and analog-to-digital converter (ADC) sampling rates. In the clinical evaluation, Wave-CAIPI achieved similar mean scores when compared with GRAPPA (MPRAGE: ØW ?=?4.03, ØG ?=?3.97; T2 w SPACE: ØW ?=?4.00, ØG ?=?4.00; SPACE FLAIR: ØW ?= 3.97, ØG ?=?3.97; SWI: ØW ?=?3.93, ØG ?=?3.83) and was statistically noninferior (N?=?30, P?<?0.05 for all sequences). DATA CONCLUSION:The proposed volumetric brain exam retained comparable image quality when compared with the much longer conventional protocol. LEVEL OF EVIDENCE:2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:961-974.

Project description:PurposeIn echo-planar diffusion-weighted imaging, correcting for susceptibility-induced artifacts typically requires acquiring pairs of images, known as blip-up blip-down acquisitions, to create an undistorted volume as a target to correct distortions that are often focal where regions with differences in magnetic susceptibility interface, such as the frontal and temporal areas. However, blip-up blip-down acquisitions are not always available, and distortion effects may not be specifically localized to such areas, with subtle effects potentially extending throughout the brain. Here, we apply a deep learning technique to generate an undistorted volume to correct susceptibility-induced artifacts and demonstrate implications for image fidelity and diffusion-based inference outside of areas where high focal distortion is present.MethodsTo demonstrate differences due to susceptibility artifact correction, uncorrected baseline images were compared to identical images where correction was performed using an undistorted target volume produced by the deep learning tool "PreQual". Widespread geometric distortion was assessed visually by referencing diffusion-weighted images to T1-weighted images. Tract-based spatial statistics (TBSS) were utilized to perform whole brain analysis of fractional anisotropy (FA) values to assess differences between subject groups (depressed vs. non-depressed) via permutation-based, voxel-wise testing. Multivariate regression models were then used to contrast TBSS results between corrected and non-corrected diffusion images.ResultsSusceptibility artifact correction resulted in visible, widespread improvement in image fidelity when referenced to T1-weighted images. TBSS results were dependent on susceptibility artifact correction with correction resulting in widespread structural alterations of the mean FA skeleton, changes in skeletal FA, and additional positive tests of significance of regression coefficients in subsequent regression models.ConclusionOur results indicated that EPI distortion effects are not purely focal, and that reducing distortion can result in significant differences in the interpretation of diffusion data, even in areas remote from high distortion.

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Dataset Information

Tilted-CAIPI for highly accelerated distortion-free EPI with point spread function (PSF) encoding.

Publications

Tilted-CAIPI for highly accelerated distortion-free EPI with point spread function (PSF) encoding.

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