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Volume isotropic 3D myelin weighted Imaging using broadband IR-prepared FLORET UTE: comparison with myelin water fraction1Department of Radiology, Faculty of Medicine, University of Miyazaki, Miyazaki, Japan, 2Division of Radiology, Miyazaki University Hospital, Miyazaki, Japan, 3Philips Japan, Tokyo, Japan, 4Philips Healthcare, Rochester, MN, United States
Synopsis
Keywords: Multiple Sclerosis, Neurodegeneration
Motivation: Myelin water fraction (MWF) is a promising method for quantitative evaluation of myelin in the brain. FLORET MR bone imaging using UTE sequences has possibility to show brain myelin structure because myelin also has quite short T2 relaxation times.
Goal(s): To demonstrate the feasibility of FLORET MyelinVIEW in comparison with MWF.
Approach: We evaluated the FLORET MyelinVIEW and MWF based on the distribution of myelin in the brain structures.
Results: FLORET MyelinVIEW may be useful for evaluating the distribution of myelin.
Impact: FLORET MyelinVIEW showed comparable distribution of brain myelin to MWF, it may be useful to visualize the myelin distribution with the 3D isotropic images.
INTRODUCTION
Myelin water fraction (MWF), the fraction of signal contribution from myelin water, is a promising method for quantitative evaluation of myelin function in the brain. MFW has been histopathologically validated as a biomarker for myelin and has demonstrated significant variation in myelination between different brain structures1,2.MR bone imaging, using ultrashort echo-time (UTE) sequences, has gained more attention for detecting and assessing bone pathology as an alternative to CT imaging3. Recently, we have demonstrated the feasibility of a new scheme for 3D volumetric isotropic MR bone imaging by using broadband IR-prepared Fermat looped, orthogonally encoded trajectories (FLORET) UTE4. Since this technique enhances the short T2 signals, such as bone, while suppressing long T2 signals, we realized that it sometimes also shows brain myelin structure because myelin also has quite short T2 relaxation times. We hypothesized that 3D IR-FLORET UTE can be extended for whole-brain 3D isotropic myelin weighted imaging by slightly modifying the sequence.
In this study, we attempted to evaluate the usefulness of IR-FLORET UTE bone imaging for myelin detection (FLORET MyelinVIEW). The purpose of this study was to evaluate the feasibility of FLORET MyelinVIEW by comparing with MWF.
METHODS
A total of eight healthy volunteers were included in this study. Age and sex demographic information was collected for all subjects (mean age 32.7 years, range 24 – 50 years, 3 female/5 male). The local IRB approved the study, and written informed consent was obtained from all subjects. All subjects were examined with a 3.0T whole-body clinical system (Ingenia CX, Philips Healthcare) and underwent 3D MyelinVIEW and MWF.3D MyelinVIEW is based on BoneVIEW sequence, which includes broadband adiabatic IR-prepared UTE FLORET sequence with Fibonacci ordering. The broadband offset independent trapezoid (OIT) inversion pulses selectively invert long-T2 species and fat simultaneously. To suppress the background signals sufficiently, we used a long-duration OIT inversion pulse (≥20ms). By using a long pulse duration, long T2 species are inverted whereas short T2 species are saturated. Myelin signal can be saturated because the T2 of myelin is shorter than the duration of the RF pulse. We used slightly long inversion time (TI) compared to bone imaging to maximize the myelin and background signal contrast (Figure 1).
For the MWF, 3D multi-echo (48 echoes) gradient and spin-echo (GraSE) sequence5 is used. The Sparsity Promoting Iterative Joint NNLs (non-negative least squares) (SPIJN)6 algorithm is used for generating MWF map.
For image analysis, one radiologist manually placed three 5-mm2 regions of interest (ROI) on MWF map and 3D MyelinVIEW images of the bilateral 8 areas: genu/body/splenium of corpus callosum (CC), anterior/posterior/superior corona radiata (CR), anterior/posterior internal capsule (IC) (Figure 2). The ROIs on MWF map were copied onto the 3D MyelinVIEW images. The mean signal intensity values of the 3D MyelinVIEW images were divided by the mean values of the CSF, and the normalized mean relative signal intensity value of FLORET MyelinVIEW (nMyelinVIEW) was calculated. For statistical analysis, Friedman test and Wilcoxon test were used for the comparison of MWF and nMyelinVIEW among different areas. The regression analysis between MWF and nMyelinVIEW was performed.
Scan parameters are shown in Table 1.
RESULTS and DISCUSSION
MWF and nMyelinVIEW showed similar tendencies on CC, CR, and IC: MWF and nMyelinVIEW were significantly higher for the genu of CC, superior CR, and posterioa IC (Figure 3). In these three areas, MWF and nMyelinVIEW showed significant positive correlation (Figure 4). Previous studies have reported that the MWF of the CC, superior CR, and posterior IC is higher than other brain structures, and our results are consistent with this2. FLORET MyelinVIEW could evaluate the distribution of myelin similar to MWF, and it may be useful for the clinical situation in the futureCONCLUSION
In our study, we demonstrated the feasibility of FLORET MyelinVIEW, it showed comparable distribution of brain myelin to MWF, it may be useful to visualize the myelin distribution with the 3D isotropic images.Acknowledgements
No acknowledgement found.References
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4. Yoneyama M, et al. Volume isotropic 3D bone Imaging with broadband IR-prepared FLORET UTE and Fibonacci interleaved trajectory ordering. Proc Intl Soc Mag Reson Med. 2023;0632.
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6. Nagtegaal M, et al. Myelin water imaging from multi-echo T2 MR relaxometry data using a joint sparsity constraint. Neuroimage 2020 Oct 1;219:117014. doi: 10.1016/j.neuroimage.2020.117014.
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