Yoshitaka Bito

Data processing method to reduce truncation artifacts in nuclear magnetic resonance apparatus

A data processing method for image reconstruction in an NMR apparatus for use in the medical field which reduces a computation quantity relating to data extrapolation when truncation artifacts are reduced by data extrapolation. The data processing method is utilized with an inspection apparatus including a magnetic field generation apparatus for generating each of a static magnetic field, gradient magnetic field and RF magnetic field, a signal detection device for detecting NMR signals from an inspection object, a computer for computing detection signals of the signal detection device and for outputting the result of computation by the computer, for obtaining an image by effecting inverse Fourier transform for a measurement signal row representing data of spatial frequency space. An evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in the spatial frequency space is utilized for comparison with a threshold value and signals are extrapolated into spatial frequency domains which are located outside of a measured spatial frequency domain by use of coefficients computed from the signals of the measured spatial frequency domain only when the evaluation is greater than the threshold value so that an image in which the ringing thereof is corrected is obtained.

Inspection method and inspection apparatus using nuclear magnetic resonance

In an inspection method which generates a static magnetic field, a gradient magnetic field and a radio frequency magnetic field, detects nuclear magnetic resonance signals from an inspection object, computes and processes the nuclear magnetic resonance signals so detected and outputs the result of computation processing, a gradient magnetic field for generating signal attenuation by diffusion and an oscillating gradient magnetic field for generating chemical shift information and spatial information of the materials contained in the inspection object are applied, separation and acquisition of spatial information of each material contained in the inspection object are simultaneously conducted, and a measurement time is shortened.

Optimization of Scan Parameters to Reduce Acquisition Time for Diffusion Kurtosis Imaging at 1.5T

PURPOSE To shorten acquisition of diffusion kurtosis imaging (DKI) in 1.5-tesla magnetic resonance (MR) imaging, we investigated the effects of the number of b-values, diffusion direction, and number of signal averages (NSA) on the accuracy of DKI metrics. METHODS We obtained 2 image datasets with 30 gradient directions, 6 b-values up to 2500 s/mm(2), and 2 signal averages from 5 healthy volunteers and generated DKI metrics, i.e., mean, axial, and radial kurtosis (MK, K∥, and K⊥) maps, from various combinations of the datasets. These maps were estimated by using the intraclass correlation coefficient (ICC) with those from the full datasets. RESULTS The MK and K⊥ maps generated from the datasets including only the b-value of 2500 s/mm(2) showed excellent agreement (ICC, 0.96 to 0.99). Under the same acquisition time and diffusion directions, agreement was better of MK, K∥, and K⊥ maps obtained with 3 b-values (0, 1000, and 2500 s/mm(2)) and 4 signal averages than maps obtained with any other combination of numbers of b-value and varied NSA. Good agreement (ICC > 0.6) required at least 20 diffusion directions in all the metrics. CONCLUSION MK and K⊥ maps with ICC greater than 0.95 can be obtained at 1.5T within 10 min (b-value = 0, 1000, and 2500 s/mm(2); 20 diffusion directions; 4 signal averages; slice thickness, 6 mm with no interslice gap; number of slices, 12).

Lactate discrimination incorporated into echo-planar spectroscopic imaging

A technique for discriminating a lactate signal from overlapping lipid signals in 1H spectroscopic imaging is presented. It is based on J‐coupling between lactate protons and on the broad spectral bandwidth of lipid signal. Measurement parameters used in the technique are determined so that TE is separated from n/J (n: a natural number, J: J‐coupling constant) enough to suppress the lipid signal at the time when the lactate signal is strongest. Data processing is used to calculate the lactate signal intensity from the reconstructed spectra. This technique enables lactate to be discriminated in a single measurement and enables spectra of other metabolites to be acquired simultaneously. However, it necessitates a homogeneous magnetic field, long TE, and supplementary lipid suppression. Discrimination of the lactate signal is demonstrated by applying lactate‐discriminating echo‐planar spectroscopic imaging (EPSI), which combines this discrimination technique with the standard EPSI, to rat focal cerebral ischemia models. Magn Reson Med 45:568–574, 2001.

Quantitative Susceptibility Mapping Using the Multiple Dipole-Inversion Combination with k-space Segmentation Method

Quantitative susceptibility mapping (QSM) is a new magnetic resonance imaging (MRI) technique for noninvasively estimating the magnetic susceptibility of biological tissue. Several methods for QSM have been proposed. One of these methods can estimate susceptibility with high accuracy in tissues whose contrast is consistent between magnitude images and susceptibility maps, such as deep gray-matter nuclei. However, the susceptibility of small veins is underestimated and not well depicted by using the above approach, because the contrast of small veins is inconsistent between a magnitude image and a susceptibility map. In order to improve the estimation accuracy and visibility of small veins without streaking artifacts, a method with multiple dipole-inversion combination with k-space segmentation (MUDICK) has been proposed. In the proposed method, k-space was divided into three domains (low-frequency, magic-angle, and high-frequency). The k-space data in low-frequency and magic-angle domains were obtained by L1-norm regularization using structural information of a pre-estimated susceptibility map. The k-space data in high-frequency domain were obtained from the pre-estimated susceptibility map in order to preserve small-vein contrasts. Using numerical simulation and human brain study at 3 Tesla, streaking artifacts and small-vein susceptibility were compared between MUDICK and conventional methods (MEDI and TKD). The numerical simulation and human brain study showed that MUDICK and MEDI had no severe streaking artifacts and MUDICK showed higher contrast and accuracy of susceptibility in small-veins compared to MEDI. These results suggest that MUDICK can improve the accuracy and visibility of susceptibility in small-veins without severe streaking artifacts.

Diffusion-weighted Line-scan Echo-planar Spectroscopic Imaging Technique to Reduce Motion Artifacts in Metabolite Diffusion Imaging

Metabolite diffusion is expected to provide more specific microstructural and functional information than water diffusion. However, highly accurate measurement techniques have still not been developed, especially for reducing motion artifacts caused by cardiac pulsation and respiration. We developed a diffusion-weighted line-scan echo-planar spectroscopic imaging (DW-LSEPSI) technique to reduce such motion artifacts in measuring diffusion-weighted images (DWI) of metabolites. Our technique uses line-scan and echo-planar techniques to reduce phase errors induced by such motion during diffusion time. The phase errors are corrected using residual water signals in water suppression for each acquisition and at each spatial pixel specified by combining the line-scan and echo-planar techniques. We apply this technique to a moving phantom and a rat brain in vivo to demonstrate the reduction of motion artifacts in DWI and apparent diffusion coefficient (ADC) maps of metabolites. DW-LSEPSI will be useful for investigating a cellular diffusion environment using metabolites as probes.

B1-control receive array coil (B-RAC) for reducing B1+ inhomogeneity in abdominal imaging at 3T-MRI

B1+ inhomogeneity in the human body increases as the nuclear magnetic resonance (NMR) frequency increases. Various methods have thus been developed to reduce B1+ inhomogeneity, such as a dielectric pad, a coupling coil, parallel transmit, and radio-frequency (RF) shimming. However, B1+ inhomogeneity still remains in some cases of abdominal imaging. In this study, we developed a B1-control receive array coil (B-RAC). Unlike the conventional receive array coil, B-RAC reduces B1+ inhomogeneity by using additional PIN diodes to generate the inductive loop during the RF transmit period. The inductive loop can generate dense and sparse regions of the magnetic flux, which can be used to compensate for B1+ inhomogeneity. First, B-RAC is modeled in the numerical simulation, and the spatial distributions of B1+ in a phantom and a human model were analyzed. Next, we fabricated a 12-channel B-RAC and measured receive sensitivity and B1+ maps in a 3T-MRI experiment. It was demonstrated that B-RAC can reduce B1+ inhomogeneity in the phantom and human model without increasing the maximum local specific absorption rate (SAR) in the body. B-RAC was also found to have almost the same the receive sensitivity as the conventional receive coil. Using RF shimming combined with B-RAC was revealed to more effectively reduce B1+ inhomogeneity than using only RF shimming. Therefore, B-RAC can reduce B1+ inhomogeneity while maintaining the receive sensitivity.

A high-speed MRI simulator using the transition matrix method and periodicity of magnetization

An MRI simulator is a tool for understanding MR phenomena and developing new pulse sequences, which determine picture quality and information included in MR signals. Conventional simulators calculate the Bloch equations approximately to reduce the computation time. This paper presents a technique for solving the equations exactly at high speed and for creating images. The processing time is made practical by using the transition matrix method and the periodicity of the magnetization.

EARLY STAGE METABOLITE DIFFUSION IN A MOUSE MODEL OF ALZHEIMER’S DISEASE

cerebral small vessel health, were quantified byMRI. Results:After adjusting for age and cardiovascular risk factors, there was a significant negative association between Ab burden and FMD (p<0.01), such that for each 0.1 increase in Ab burden, FMD decreased by 0.8%. Decreased brachial artery FMD response was found in individuals with elevated Ab compared with the non-elevated group (p<0.01). The optimal cut point of FMD predicting Ab elevation was 5% (AUC1⁄40.836, p<0.01, 95%CI: 0.742 0.930), with 81.8% sensitivity and 75.4% specificity. Higher PI was demonstrated in elevated Ab individuals (p1⁄40.04), but was not correlated with Ab burden. WML were not associated with Ab. Conclusions:Among cognitively normal older adults, poor central and peripheral vascular health is predictive of Ab burden. FMD, specifically, has potential value as a vascular biomarker for neuropathologic changes associated with Alzheimer’s disease.

DETECTION OF INCREASED MAGNETIC SUSCEPTIBILITIES IN THE CEREBRAL CORTEX IN PATIENTS WITH ALZHEIMER’S DISEASE: COMPARISON OF QUANTITATIVE SUSCEPTIBILITY MAPPING BETWEEN CONVENTIONAL AND BRAIN SURFACE CORRECTION METHOD

acoustic radiation, ATR: anterior thalamic radiation, CGC: cingulate gyrus part of cingulum, CGH: parahippocampal part of cingulum, CST: corticospinal tract, FMA: forceps major, FMI: forceps minor, IFO: inferior fronto-occipital fasciculus, ILF: inferior longitudinal fasciculus, SLF: superior longitudinal fasciculus, PTR: posterior thalamic radiation, STR: superior thalamic radiation, UNC: uncinate fasciculus. Poster Presentations: Monday, July 23, 2018 P848