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Hybrid radial-cones trajectory for accelerated MRI.

ABSTRACT: To design and develop a series of ultrashort echo time k-space sampling schemes, termed radial-cones, which enables high sampling efficiency while maintaining compatibility with parallel imaging and compressed sensing reconstructions.Radial-cones is a trajectory that samples three-dimensional (3D) k-space using a single base cone distributed along radial dimensions through a cost function-based optimization. Trajectories were generated for highly undersampled, short readout sampling and compared with 3D radial sampling in point spread function (PSF) analysis, digital and physical phantoms, and initial human volunteers. Parallel imaging reconstructions were evaluated with and without the use of compressed sensing-based regularization.Compared with 3D radial sampling, radial-cones reduced the peak value and energy of PSF aliasing. In both digital and physical phantoms, this improved sampling behavior corresponded to a reduction in the root mean square error with a further reduction using compressed sensing. A slight increase in noise and a corresponding increase in apparent resolution was observed with radial-cones. In in vivo feasibility testing, radial-cones reconstructed images have a markedly lower number of apparent artifacts. Ultimate gains in imaging performance were limited by off-resonance blurring.Radial-cones is an efficient non-Cartesian sampling scheme enabling short echo readout with a high level of compatibility with parallel imaging and compressed sensing. Magn Reson Med 77:1068-1081, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Johnson KM

PROVIDER: S-EPMC5040626 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Hybrid radial-cones trajectory for accelerated MRI.

Johnson Kevin M KM

Magnetic resonance in medicine 20160328 3

<h4>Purpose</h4>To design and develop a series of ultrashort echo time k-space sampling schemes, termed radial-cones, which enables high sampling efficiency while maintaining compatibility with parallel imaging and compressed sensing reconstructions.<h4>Theory and methods</h4>Radial-cones is a trajectory that samples three-dimensional (3D) k-space using a single base cone distributed along radial dimensions through a cost function-based optimization. Trajectories were generated for highly unders ...[more]

PMID: 27017991

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Project description:BackgroundT2 * mapping can characterize tumor hypoxia, which may be associated with resistance to therapy. Acquiring T2 * maps during MR-guided radiotherapy could inform treatment adaptation by, for example, escalating the dose to resistant sub-volumes.PurposeThe purpose of this work is to demonstrate the feasibility of the accelerated T2 * mapping technique using model-based image reconstruction with integrated trajectory auto-correction (TrACR) for MR-guided radiotherapy on an MR-Linear accelerator (MR-Linac).Materials and methodsThe proposed method was validated in a numerical phantom, where two T2 * mapping approaches (sequential and joint) were compared for different noise levels (0,0.1,0.5,1) and gradient delays ([1, -1] and [1, -2] in units of dwell time for x- and y-axis, respectively). Fully sampled k-space was retrospectively undersampled using two different undersampling patterns. Root mean square errors (RMSEs) were calculated between reconstructed T2 * maps and ground truth. In vivo data was acquired twice weekly in one prostate and one head and neck cancer patient undergoing treatment on a 1.5 T MR-Linac. Data were retrospectively undersampled and T2 * maps reconstructed, with and without trajectory corrections were compared.ResultsNumerical simulations demonstrated that, for all noise levels, T2 * maps reconstructed with a joint approach demonstrated less error compared to an uncorrected and sequential approach. For a noise level of 0.1, uniform undersampling and gradient delay [1, -1] (in units of dwell time for x- and y-axis, respectively), RMSEs for sequential and joint approaches were 13.01 and 9.32 ms, respectively, which reduced to 10.92 and 5.89 ms for a gradient delay of [1, 2]. Similarly, for alternate undersampling and gradient delay [1, -1], RMSEs for sequential and joint approaches were 9.80 and 8.90 ms, respectively, which reduced to 9.10 and 5.40 ms for gradient delay [1, 2]. For in vivo data, T2 * maps reconstructed with our proposed approach resulted in less artifacts and improved visual appearance compared to the uncorrected approach. For both prostate and head and neck cancer patients, T2 * maps reconstructed from different treatment fractions showed changes within the planning target volume (PTV).ConclusionUsing the proposed approach, a retrospective data-driven gradient delay correction can be performed, which is particularly relevant for hybrid devices, where full information on the machine configuration is not available for image reconstruction. T2 * maps were acquired in under 5 min and can be integrated into MR-guided radiotherapy treatment workflows, which minimizes patient burden and leaves time for additional imaging for online adaptive radiotherapy on an MR-Linac.

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Hybrid radial-cones trajectory for accelerated MRI.

Publications

Hybrid radial-cones trajectory for accelerated MRI.

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