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PLANET: An ellipse fitting approach for simultaneous T1 and T2 mapping using phase-cycled balanced steady-state free precession.

ABSTRACT: To demonstrate the feasibility of a novel, ellipse fitting approach, named PLANET, for simultaneous estimation of relaxation times T1 and T2 from a single 3D phase-cycled balanced steady-state free precession (bSSFP) sequence.A method is presented in which the elliptical signal model is used to describe the phase-cycled bSSFP steady-state signal. The fitting of the model to the acquired data is reformulated into a linear convex problem, which is solved directly by a linear least squares method, specific to ellipses. Subsequently, the relaxation times T1 and T2 , the banding free magnitude, and the off-resonance are calculated from the fitting results.Maps of T1 and T2 , as well as an off-resonance and a banding free magnitude can be simultaneously, quickly, and robustly estimated from a single 3D phase-cycled bSSFP sequence. The feasibility of the method was demonstrated in a phantom and in the brain of healthy volunteers on a clinical MR scanner. The results were in good agreement for the phantom, but a systematic underestimation of T1 was observed in the brain.The presented method allows for accurate mapping of relaxation times and off-resonance, and for the reconstruction of banding free magnitude images at realistic signal-to-noise ratios. Magn Reson Med 79:711-722, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

SUBMITTER: Shcherbakova Y

PROVIDER: S-EPMC5811804 | biostudies-other | 2018 Feb

REPOSITORIES: biostudies-other

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PLANET: An ellipse fitting approach for simultaneous T<sub>1</sub> and T<sub>2</sub> mapping using phase-cycled balanced steady-state free precession.

Shcherbakova Yulia Y van den Berg Cornelis A T CAT Moonen Chrit T W CTW Bartels Lambertus W LW

Magnetic resonance in medicine 20170522 2

<h4>Purpose</h4>To demonstrate the feasibility of a novel, ellipse fitting approach, named PLANET, for simultaneous estimation of relaxation times T<sub>1</sub> and T<sub>2</sub> from a single 3D phase-cycled balanced steady-state free precession (bSSFP) sequence.<h4>Methods</h4>A method is presented in which the elliptical signal model is used to describe the phase-cycled bSSFP steady-state signal. The fitting of the model to the acquired data is reformulated into a linear convex problem, which ...[more]

PMID: 28543430

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Project description:The objectives of this study were to acquire ultra-high resolution images of the brain using balanced steady-state free precession (bSSFP) at 7 T and to identify the potential utility of this sequence.Eight volunteers participated in this study after providing informed consent. Each volunteer was scanned with 8 phase cycles of bSSFP at 0.4-mm isotropic resolution using 0.5 number of excitations and 2-dimensional parallel acceleration of 1.75 × 1.75. Each phase cycle required 5 minutes of scanning, with pauses between the phase cycles allowing short periods of rest. The individual phase cycles were aligned and then averaged. The same volunteers underwent scanning using 3-dimensional (3D) multiecho gradient recalled echo at 0.8-mm isotropic resolution, 3D Cube T2 at 0.7-mm isotropic resolution, and thin-section coronal oblique T2-weighted fast spin echo at 0.22 × 0.22 × 2.0-mm resolution for comparison. Two neuroradiologists assessed image quality and potential research and clinical utility.The volunteers generally tolerated the scan sessions well, and composite high-resolution bSSFP images were produced for each volunteer. Rater analysis demonstrated that bSSFP had a superior 3D visualization of the microarchitecture of the hippocampus, very good contrast to delineate the borders of the subthalamic nucleus, and relatively good B1 homogeneity throughout. In addition to an excellent visualization of the cerebellum, subtle details of the brain and skull base anatomy were also easier to identify on the bSSFP images, including the line of Gennari, membrane of Liliequist, and cranial nerves. Balanced steady-state free precession had a strong iron contrast similar to or better than the comparison sequences. However, cortical gray-white contrast was significantly better with Cube T2 and T2-weighted fast spin echo.Balanced steady-state free precession can facilitate ultrahigh-resolution imaging of the brain. Although total imaging times are long, the individually short phase cycles can be acquired separately, improving examination tolerability. These images may be beneficial for studies of the hippocampus, iron-containing structures such as the subthalamic nucleus and line of Gennari, and the basal cisterns and their contents.

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Dataset Information

PLANET: An ellipse fitting approach for simultaneous T1 and T2 mapping using phase-cycled balanced steady-state free precession.

Publications

PLANET: An ellipse fitting approach for simultaneous T<sub>1</sub> and T<sub>2</sub> mapping using phase-cycled balanced steady-state free precession.

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