Motion-insensitive rapid configuration relaxometry

114

PurposeTo 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.MethodsA 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.ResultsMaps 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.ConclusionThe 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.

Section: Discussionsupporting

confidence: 82%

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

Shcherbakova

Berg

Moonen

et al. 2017

114

“…Another method using 1 single scan based on a triple echo steady‐state (TESS) sequence makes use of modeling the relation between the echoes and an iterative numerical solution for obtaining the T 2 map. MIRACLE is similar to TESS and merges TESS with a balanced acquisition scheme for motion‐insensitive rapid configuration relaxometry. All these methods can be used to decrease T 2 mapping time to 5–10 min.…”

Section: Discussionmentioning

confidence: 99%

bSSFP phase correction and its use in magnetic resonance electrical properties tomography

Ozdemir

Ider

2018

Purpose Balanced steady‐state free precession (bSSFP) sequence is widely used because of its high SNR and high speed. However, bSSFP images suffer from “banding artifact” caused by B0 inhomogeneity. In this article, we propose a method to remove this artifact in bSSFP phase images and investigate the usage of the corrected phase images in phase‐based magnetic resonance electrical properties tomography (MREPT). Theory and Methods Two bSSFP phase images, obtained with different excitation frequencies, are collaged to get rid of the regions containing banding artifacts. Phase of the collaged bSSFP image is the sum of the transceive phase of the RF system and an error term that depends on B0 and T2. By using B0 and T2 maps, this error is eliminated from bSSFP phase images by using pixel‐wise corrections. Conductivity maps are obtained from the uncorrected and the corrected phase images using the phase‐based cr‐MREPT method. Results Phantom and human experiment results of the proposed method are illustrated for both phase images and conductivity maps. It is shown that uncorrected phase images yield unacceptable conductivity images. When only B0 information is used for phase correction conductivity, reconstructions are substantially improved, and yet T2 information is still needed to fully recover accurate and undistorted conductivity images. Conclusions With the proposed technique, B0 sensitivity of the bSSFP phase images can be removed by using B0 and T2 maps. It is also shown that corrected bSSFP phase images are of sufficient quality to be used in conductivity imaging.

“…Balanced SSFP (bSSFP) sequences deserve special attention due to their rapid acquisition time and high SNR efficiency. Despite sensitivity to local off‐resonance, bSSFP has been successfully used for quantitative relaxometry, especially for simultaneous T 1 and T 2 quantification …”

Section: Introductionmentioning

confidence: 99%

“…Despite sensitivity to local off-resonance, bSSFP has been successfully used for quantitative relaxometry, [12][13][14] especially for simultaneous T 1 and T 2 quantification. 15,16 We recently proposed a method named PLANET 17 to simultaneously map the relaxation parameters T 1 and T 2 , to the local off-resonance ∆f 0 , the RF phase, and the banding free magnitude image using a phase-cycled bSSFP sequence. Linear least-squares fitting of an ellipse to the complexvalued bSSFP data acquired with an RF phase incrementing scheme is first applied.…”

mentioning

confidence: 99%

On the accuracy and precision of PLANET for multiparametric MRI using phase‐cycled bSSFP imaging

Shcherbakova

Berg

Moonen

et al. 2018

Purpose In this work we demonstrate how sequence parameter settings influence the accuracy and precision in T 1 , T 2 , and off‐resonance maps obtained with the PLANET method for a single‐component signal model. In addition, the performance of the method for the particular case of a two‐component relaxation model for white matter tissue was assessed. Methods Numerical simulations were performed to investigate the influence of sequence parameter settings on the accuracy and precision in the estimated parameters for a single‐component model, as well as for a two‐component white matter model. Phantom and in vivo experiments were performed for validation. In addition, the effects of Gibbs ringing were investigated. Results By making a proper choice for sequence parameter settings, accurate and precise parameter estimation can be achieved for a single‐component signal model over a wide range of relaxation times at realistic SNR levels. Due to the presence of a second myelin‐related signal component in white matter, an underestimation of approximately 30% in T 1 and T 2 was observed, predicted by simulations and confirmed by measurements. Gibbs ringing artifacts correction improved the precision and accuracy of the parameter estimates. Conclusion For a single‐component signal model there is a broad “sweet spot” of sequence parameter combinations for which a high accuracy and precision in the parameter estimates is achieved over a wide range of relaxation times. For a multicomponent signal model, the single‐component PLANET reconstruction results in systematic errors in the parameter estimates as expected.