著者

Toru Shirai Ryota Sato Yasuo Kawata Yoshitaka Bito Hisaaki Ochi

出版者

Japanese Society for Magnetic Resonance in Medicine

雑誌

Magnetic Resonance in Medical Sciences (ISSN:13473182)

巻号頁・発行日

pp.mp.2021-0043, (Released:2022-11-12)

参考文献数

26

被引用文献数

2

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Purpose: Quantitative susceptibility mapping (QSM) is useful for obtaining biological information. To calculate susceptibility distribution, it is necessary to calculate the local field caused by the differences of susceptibility between the tissues. The local field can be obtained by removing a background field from a total field acquired by MR phase image. Conventional approaches based on spherical mean value (SMV) filtering, which are widely used for background field calculations, fail to calculate the background field of the brain surface region corresponding to the radius of the SMV kernel, and consequently cannot calculate the QSM of the brain surface region. Accordingly, a new method calculating the local field by expansively removing the background field is proposed for whole brain QSM.Methods: The proposed method consists of two steps. First, the background field of the brain surface is calculated from the total field using a locally polynomial approximation of spherical harmonics. Second, the whole brain local field is calculated by SMV filtering with a constraint term of the background field of the brain surface. The parameters of the approximation were optimized to reduce calculation errors through simulations using both a numerical phantom and a measured human brain. Performance of the proposed method with the optimized parameters was quantitatively and visually compared with conventional methods in an experiment of five healthy volunteers.Results: The proposed method showed the accurate local field over the expanded brain region in the simulation studies. It also showed consistent QSM with conventional methods inside of the brain surface and showed clear vein structures on the brain surface.Conclusion: The proposed method enables accurate calculation of whole brain QSM without eroding the brain surface region while maintaining same values inside of the brain surface as the conventional methods.

著者

Yoshitaka Bito Hisaaki Ochi Ryuji Shirase Wataru Yokohama Kuniaki Harada Kohsuke Kudo

出版者

Japanese Society for Magnetic Resonance in Medicine

雑誌

Magnetic Resonance in Medical Sciences (ISSN:13473182)

巻号頁・発行日

pp.mp.2023-0081, (Released:2023-10-27)

参考文献数

33

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Purpose: Analysis of cerebrospinal fluid (CSF) dynamics may be beneficial for understanding the mechanisms and diagnosis of several neurological diseases. Low b-value diffusion tensor imaging (low-b DTI) is useful for observing the slow and complex motion of the CSF. Theoretically, a mathematical framework suggests that low-b DTI provides the variance of the pseudorandom motion of the CSF. Furthermore, low-b DTI could provide comprehensive information on fluid dynamics. Accordingly, we proposed an analysis technique that resolves intravoxel pseudorandom motion into ordered (linear) and disordered (random) motions based on the mathematical framework.Methods: The proposed analysis technique helps measure low-b DTI with multiple diffusion times and linearly fits its mean diffusivity (MD) with the diffusion time to obtain two parameters, double-slope Vv and y-intersect Dr, which represent the variance of the velocity distribution of linear motion and the diffusion coefficient of random motion, respectively. Seven healthy subjects were scanned to evaluate the proposed technique and investigate fluid dynamics in several representative ROIs.Results: The obtained data showed the validity of the technique, repeatability, and consistency across the subjects in ROIs, such as the lateral ventricle (LV), third ventricle (3V), fourth ventricle (4V), and Sylvian fissure (SF). The obtained parameters Vv and Dr highlighted different characteristics of fluid dynamics in the representative ROIs: low Vv and low Dr in the LV, high Vv and moderate Dr in the 3V, and moderate Vv and moderate Dr in the 4V and SF.Conclusion: The proposed analysis technique will facilitate a comprehensive investigation of the complex dynamics of the CSF using resolved parameters representing ordered and disordered motions.

著者

Yo Taniguchi Suguru Yokosawa Toru Shirai Ryota Sato Tomoki Amemiya Yoshihisa Soutome Yoshitaka Bito Hisaaki Ochi

出版者

Japanese Society for Magnetic Resonance in Medicine

雑誌

Magnetic Resonance in Medical Sciences (ISSN:13473182)

巻号頁・発行日

pp.mp.2021-0045, (Released:2022-07-30)

参考文献数

21

被引用文献数

3

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Purpose: MR parameter mapping is a technique that obtains distributions of parameters such as relaxation time and proton density (PD) and is starting to be used for disease quantification in clinical diagnoses. Quantitative susceptibility mapping is also promising for the early diagnosis of brain disorders such as degenerative neurological disorders. Therefore, we developed an MR quantitative parameter mapping (QPM) method to map four tissue-related parameters (T1, T2*, PD, and susceptibility) and B1 simultaneously by using a 3D partially RF-spoiled gradient echo (pRSGE). We verified the accuracy and repeatability of QPM in phantom and volunteer experiments.Methods: Tissue-related parameters are estimated by varying four scan parameters of the 3D pRSGE: flip angle, RF-pulse phase increment, TR and TE, performing multiple image scans, and finding a least-squares fit for an intensity function (which expresses the relationship between the scan parameters and intensity values). The intensity function is analytically complex, but by using a Bloch simulation to create it numerically, the least-squares fitting can be used to estimate the quantitative values. This has the advantage of shortening the image-reconstruction processing time needed to estimate the quantitative values than with methods using pattern matching.Results: A 1.1-mm isotropic resolution scan covering the whole brain was completed with a scan time of approximately 12 minutes, and the reconstruction time using a GPU was approximately 1 minute. The phantom experiments confirmed that both the accuracy and repeatability of the quantitative values were high. The volunteer scans also confirmed that the accuracy of the quantitative values was comparable to that of conventional methods.Conclusion: The proposed QPM method can map T1, T2*, PD, susceptibility, and B1 simultaneously within a scan time that can be applied to human subjects.

著者

Akinori Yamaguchi Kohsuke Kudo Ryota Sato Yasuo Kawata Niki Udo Masaaki Matsushima Ichiro Yabe Makoto Sasaki Masafumi Harada Noriyuki Matsukawa Toru Shirai Hisaaki Ochi Yoshitaka Bito

出版者

Japanese Society for Magnetic Resonance in Medicine

雑誌

Magnetic Resonance in Medical Sciences (ISSN:13473182)

巻号頁・発行日

pp.mp.2021-0015, (Released:2022-03-10)

参考文献数

28

被引用文献数

3

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Purpose: Studies on quantitative susceptibility mapping (QSM) have reported an increase in magnetic susceptibilities in patients with Alzheimer’s disease (AD). Despite the pathological importance of the brain surface areas, they are sometimes excluded in QSM analysis. This study aimed to reveal the efficacy of QSM analysis with brain surface correction (BSC) and/or vein removal (VR) procedures.Methods: Thirty-seven AD patients and 37 age- and sex-matched, cognitively normal (CN) subjects were included. A 3D-gradient echo sequence at 3T MRI was used to obtain QSM. QSM images were created with regularization enabled sophisticated harmonic artifact reduction for phase data (RESHARP) and constrained RESHARP with BSC and/or VR. We conducted ROI analysis between AD patients and CN subjects who did or did not undergo BSC and/or VR using a t-test, to compare the susceptibility values after gray matter weighting.Results: The susceptibility values in RESHARP without BSC were significantly larger in AD patients than in CN subjects in one region (precentral gyrus, 8.1 ± 2.9 vs. 6.5 ± 2.1 ppb) without VR and one region with VR (precentral gyrus, 7.5 ± 2.8 vs. 5.9 ± 2.0 ppb). Three regions in RESHARP with BSC had significantly larger susceptibilities without VR (precentral gyrus, 7.1 ± 2.0 vs. 5.9 ± 2.0 ppb; superior medial frontal gyrus, 5.7 ± 2.6 vs. 4.2 ± 3.1 ppb; putamen, 47,8 ± 16.5 vs. 40.0 ± 15.9 ppb). In contrast, six regions showed significantly larger susceptibilities with VR in AD patients than in CN subjects (precentral gyrus, 6.4 ± 1.9 vs. 4.9 ± 2.7 ppb; superior medial frontal gyrus, 5.3 ± 2.7 vs. 3.7 ± 3.3 ppb; orbitofrontal cortex, –2.1 ± 2.7 vs. –3.6 ± 3.2 ppb; parahippocampal gyrus, 0.1 ± 3.6 vs. –1.7 ± 3.7 ppb; putamen, 45.0 ± 14.9 vs. 37.6 ± 14.6 ppb; inferior temporal gyrus, –3.4 ± 1.5 vs. –4.4 ± 1.5 ppb).Conclusion: RESHARP with BSC and VR showed more regions of increased susceptibility in AD patients than in CN subjects. This study highlights the efficacy of this method in facilitating the diagnosis of AD.