Christos Papageorgakis^{1}, Eleni Firippi^{1}, Benoit Gy^{1}, Timothé Boutelier^{1}, Ibrahim Khormi^{2,3,4}, Oun Al-iedani^{2,3}, Bryan Paton^{3,5}, Jeannette Lechner-Scott ^{3,6,7}, Amir Fazlollahi^{8}, Anne-Louise Ponsonby^{9,10}, Patrick Liebig^{11}, Saadallah Ramadan^{2,3}, Moritz Zaiss^{12}, and Stefano Casagranda^{1}

^{1}Department of Research & Innovation, Olea Medical, La Ciotat, France, ^{2}School of Health Sciences, College of Health, Medicine and Wellbeing,, University of Newcastle, Newcastle, Australia, ^{3}Hunter Medical Research Institute, Newcastle, Australia, ^{4}College of Applied Medical Sciences, University of Jeddah, Jeddah, Saudi Arabia, ^{5}School of Psychology, College of Engineering, Science and Environment, University of Newcastle, Newcastle, Australia, ^{6}Department of Neurology, John Hunter Hospital, New Lambton Heights, Australia, ^{7}School of Medicine and Public Health, College of Health, Medicine and Wellbeing, University of Newcastle, Newcastle, Australia, ^{8}CSIRO Health and Biosecurity, Brisbane, Australia, ^{9}The Florey Institute of Neuroscience and Mental Health, Victoria, Australia, ^{10}Murdoch Children's Research Institute, Royal Children's Hospital, University of Melbourne, Victoria, Australia, ^{11}Siemens Healthcare GmbH, Erlangen, Germany, ^{12}Department of Neuroradiology, University Clinic Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Erlangen, Germany

This work provides a new method for
fast post-processing of MRI data acquired using the WASAB1 sequence for
simultaneous B_{0} and B_{1} mapping, used in CEST imaging for field inhomogeneity corrections. We are proposing a new
processing method with outstanding acceleration of the parameter estimation
procedure, without compromising the stability of the estimation. The stability
of the method is demonstrated on phantom data and in vivo 3 Tesla clinical
data.

Some sequences have been proposed for separate B

Sampling of several frequency offsets $$$\Delta(\omega)$$$ around the water resonance frequency, a WASAB1-Spectrum is acquired and normalized using a M

$$ Z(\Delta\omega)=|c-d\cdot f(B_0,B_1,\Delta(\omega))| \;\;\;\;\;\;\;\;\;\; (1)$$

with

$$f(B_0,B_1,\Delta(\omega))=\sin^2\left(\tan^{-1}\left(\frac{\bar\gamma \cdot B_1}{freq\cdot(\Delta\omega-B_0)}\right)\right) \cdot sin^2\left(\left(\left ( \frac{\bar\gamma \cdot B_1}{freq}\right)+(\Delta\omega-B_0)^2\right)^{\frac{1}{2}} \cdot\frac{t_p}{2}\right) \;\;\;\;\;\;\;\;\;\;(2)$$

where parameters

B

The classical WASAB1 postprocessing method proposed in

Our proposed method is divided in two steps. For each voxel: i) retrieve the sign of some data points of the WASAB1-Spectra to generate a polarized dataset, ii) knowing the sign of the signal, the absolute value in Equation1 can be removed and the model becomes linear in parameters

The polarized dataset is constructed by removing the data points that are unlikely to be positive (Figure1C). It is an iterative process that starts at the extremities of the WASAB1-Z-spectra. Moving toward the central frequency offsets of the spectrum, it extrapolates the WASAB1-Z-spectra at the next frequency offset and checks if the predicted value is likely to be positive or negative. The extrapolated value at the i

To evaluate the robustness of the proposed method, WASAB1-Z-Spectra were generated applying

The WASAB1 data were acquired on a 3 Tesla MRI scanner (Prisma, Siemens Healthineers, Germany) equipped with a 64-channel head and neck coil, on 10 persons with relapsing-remitting multiple sclerosis (pw-RRMS), in the framework of a clinical CEST study (Figure2). The WASAB1 sequence (WIP816B) used a 3D snapshot-GRE with the following parameters: FOV=220×180mm

The acquired WASAB1 sequences were motion-corrected using SimpleElastix

Figure5 shows a clinical Amide Proton Transfer weighted (APTw)

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2-Togao, O., Keupp, J., Hiwatashi, A., Yamashita, K., Kikuchi, K., Yoneyama, M., & Honda, H. (2017). Amide proton transfer imaging of brain tumors using a self-corrected 3D fast spin-echo dixon method: Comparison with separate B0 correction. Magnetic Resonance in Medicine, 77(6), 2272–2279.

3-Kim, M., Gillen, J., Landman, B. A., Zhou, J., & van Zijl, P. C. M. (2009). Water saturation shift referencing (WASSR) for chemical exchange saturation transfer (CEST) experiments. Magnetic Resonance in Medicine, 61(6), 1441–1450.

4-Insko, E. K., & Bolinger, L. (1993). Mapping of the Radiofrequency Field. Journal of Magnetic Resonance, Series A, 103(1), 82–85.

5-Schuenke, P., Windschuh, J., Roeloffs, V., Ladd, M. E., Bachert, P., & Zaiss, M. (2017). Simultaneous mapping of water shift and B 1 (WASABI)—Application to field-Inhomogeneity correction of CEST MRI data. Magnetic Resonance in Medicine, 77(2), 571–580.

6-https://www.cest-sources.org/doku.php

7-Golub G, Pereyra V. Separable nonlinear least squares: the variable projection method and its applications. Inverse problems. 2003 Feb 14;19(2):R1.

8-Marstal, K., Berendsen, F., Staring, M., & Klein, S. (2016). SimpleElastix: A user-friendly, multi-lingual library for medical image registration. Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition Workshops, 134–142.

9-Windschuh J, Zaiss M, Meissner JE, Paech D, Radbruch A, Ladd ME, Bachert P. Correction of B1‐inhomogeneities for relaxation‐compensated CEST imaging at 7 T. NMR in biomedicine. 2015 May;28(5):529-37.

APTw map was corrected

DOI: https://doi.org/10.58530/2022/2717