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Submitted on 30 Apr 2020
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Clinical brain QSM acquisition and automated processing at 3T and 7T for routine use
Ludovic de Rochefort, Olivier Girard, Arnaud Le Troter, Pascal Spincemaille, Lauriane Pini, Patrick Viout, Alexandre Eusébio, Soraya Gherib, Adil
Maarouf, W Zaaraoui, et al.
To cite this version:
Ludovic de Rochefort, Olivier Girard, Arnaud Le Troter, Pascal Spincemaille, Lauriane Pini, et al.. Clinical brain QSM acquisition and automated processing at 3T and 7T for routine use. ESM-RMB 2017, 34th Annual Scientific Meeting, Oct 2017, Barcelona, Spain. 30 (S1), pp.446, 2017, �10.1007/s10334-017-0635-y�. �hal-02559487�
Quantitative susceptibility mapping (QSM) is a recent MRI technique that measures tissue magnetic susceptibility mostly influenced by iron, myelin and calcium content in the brain that may provide additional biomarkers [1-3]. QSM involves advanced numerical methods designed to solve the complex inverse problem from the measured magnetic field inhomogeneity (derived from phase) to the spatial distribution of susceptibility. The reconstruction algorithms now become sufficiently robust to be implemented in routine brain exams. We present here the installation of an online reconstruction solution and initial in vivo results at high 3 T and ultra-high 7 T clinical fields.
Purpose
L. de Rochefort1, O. Girard1, A. Le Troter1, P. Spincemaille2, L. Pini1, P. Viout1, A. Eusébio3, S. Gherib1, A. Maarouf1,W. Zaaraoui1, S. Confort-Gouny1, M. Guye1, J. P. Ranjeva1, and Y. Wang1,2
1CRMBM-CEMEREM, UMR 7339 CNRS-Aix-Marseille Univ, Marseille, France; 2Radiology, Weill Medical College of Cornell University, New York, NY, United States; 3Service Neurologie,
Pathologie du Mouvement CHU Timone, Marseille, France
Clinical brain QSM acquisition and automated processing at 3T and 7T for routine use
MRI systems and sequences: Siemens Verio 3T and Magnetom 7T were used (VB17 revision) with 32 channel head coils. A 3D
multi-echo gradient echo sequence was applied. At 3T, the R2* mapping protocol designed for multicenter studies [4] was used (1 mm resolution, Tacq=10min); at 7T, isotropic 600 µm resolution were targeted (Tacq=12.5min). A modified reconstruction software (ICE functor) was used to generate proper combined phase images for QSM in which the first-echo individual coil images are used as a reference to solve the known issue in coil combination [5].
QSM reconstruction: The amplitude and phase DICOM images were sent to a separate DICOM server based on dicom toolkit
(dcmtk open source software). Additional scripts were automatically triggered on reception to start the QSM post-processing. QSM reconstruction involved a field inhomogeneity calculation and unwrapping step from the multiple echoes, followed by a brain extraction (BET) step, an estimation of the internal field and the final MEDI reconstruction [2]. The BET algorithm was modified at 7T for an enhanced brain coverage. Images were then sent automatically back to the MRI when completed.
Methods
Conclusion
References: 1. de Rochefort et al., MRM 2010;63:194. 2. Liu et al., MRM 2011;66:777 3. Eskreis-Winkler et al., NMR Biomed 2016. 4. D. Gay et al., ISMRM 2016,
5. Bernstein MA et al., MRM 1994; 32: 330–33.
QSM can be readily applied to on-going protocols involving 3D or 2D–multislice multi-echo gradient echo data providing additional quantitative information as compared to previously available qualitative SWI and quantitative R2* mapping. QSM seems more sensitive than R2*, with the possibility to easily separate diamagnetic and paramagnetic structures and with less sensitivity to magnetic field strength. 7T QSM should provide a significant gain in terms of achievable spatial resolution and sensitivity in routine clinical studies at our site.
Results
Fig.1 and 2 present typical results obtained at 3T in on-going Parkinson and Multiple Sclerosis (MS) protocols, respectively, and Fig. 3 display 7T volunteer data. QSM images appeared on scanners within 10min with consistent image quality. Two-to-four cases per week in research protocols are currently performed.
Figure 1 - 1-mm isotropic images obtained on a patient with Parkinson disease at 3T. The MEDIC image (square root of the squared magnitude over echoes) displays a limited T2* weighting. On the R2* map, CSF has low R2* as expected, WM/GM R2* and close to 20 s-1, vessels, deep grey nuclei, calcifications then have higher R2* values. The QSM map, while cropping some brain boundaries, clearly separates paramagnetic structures (vessels, deep grey nuclei) from diamagnetic calcifications, and displays some WM/GM susceptibility differences.
Figure 2 – MEDIC, R2* map and QSM acquired at 3T on a 56 y.o. male MS patient on which MS lesions are easily identifiable by their paramagnetic values (the view is centered on one of them). While some reduction in R2* values can also be seen at the same location, the contrast is higher on the QSM maps.
Figure 3 - 600-µm isotropic images obtained on a volunteer at 7T. The MEDIC image displays a limited T2* weighting. On the R2* map, CSF has low R2* as expected, WM/GM R2* and close to 40 s-1, vessels, deep grey nuclei, calcifications have higher R2* values. The window level has been multiplied by 2 as compared to 3T, indicating the trend for linear increase of R2* with B0. The QSM map clearly separates paramagnetic structures (vessels, deep grey nuclei) from diamagnetic calcifications, and displays some WM/GM susceptibility differences with finer details as compared to 3T.
