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Publications (70)
Objectives:
The importance of monitoring cerebrospinal fluid for the development of edema in ischemic stroke has been emphasized; however, studies on the relationship between intraventricular cerebrospinal fluid behavior and edema through longitudinal observations and analysis are rare. This study aimed to investigate the correlation between the d...
The most widely used gradient-echo (GE) blood oxygenation level-dependent (BOLD) contrast has high sensitivity, but low specificity due to draining vein contributions, while spin-echo (SE) BOLD approach at ultra-high magnetic fields is highly specific to neural active sites but has lower sensitivity. To obtain high specificity and sensitivity, we p...
It is important to understand microvascular alterations in the brain of Alzheimer disease (AD) patients which usually has amyloid-beta plaques in an imaging voxel, causing a phase dispersion in an MRI signal. The objective of this study was to simulate the changes of transverse relaxation rates and microvascular indexes with and without the presenc...
Background
There is currently no study in the literature that has evaluated microvascular (MV) alterations with accumulation of amyloid‐beta plaque proteins or the presence of microbleeds in the AD brain. Therefore, in this study, we simulated MRI signal changes by assuming three different environmental conditions in the imaging voxel: only the nor...
Quantitative measurement of cerebrospinal fluid (CSF) flow and volume and longitudinal monitoring of CSF dynamics provide insights into the compensatory characteristics of post-stroke CSF. In this study, we compared the MRI pseudo-diffusion index ( D*) of live and sacrificed rat brains to confirm the effect of ventricular CSF flow on diffusion sign...
The spatial heterogeneity in the temporal occurrence of pseudo-normalization of MR apparent diffusion coefficient values for ischemic lesions may be related to morphological and functional vascular remodeling. As the area of accelerated pseudo-normalization tends to expand faster and more extensively into the chronic stage, detailed vascular charac...
Mapping mesoscopic cortical functional units such as columns or laminae is increasingly pursued by ultra-high field (UHF) functional magnetic resonance imaging (fMRI). The most popular approach for high-resolution fMRI is currently gradient-echo (GE) blood oxygenation level-dependent (BOLD) fMRI. However, its spatial accuracy is reduced due to its...
Magnetic resonance imaging (MRI) is a non-invasive in vivo imaging tool, providing high enough spatial resolution to obtain both the anatomical and the physiological information of patients. However, MRI generally suffers from relatively low sensitivity often requiring the aid of contrast agents (CA) to enhance the contrast of vessels and/or the ti...
Increasing evidence suggests that alterations in cerebral microvasculature play a critical role in the pathogenesis of Alzheimer's disease (AD). The objective of this study was to characterize and evaluate the cerebral microvascular architecture of AD transgenic (Tg) mice and compare it with that of non-Tg mice using brain microvascular indices obt...
Purpose Growing evidence suggests that alterations of the cerebral microvasculature play a critical role in the pathogenesis of Alzheimer’s disease (AD). The objective of this study was to characterize and evaluate the cerebral microvascular architecture in the AD transgenic (Tg) mice model compared with non-Tg mice using brain microvascular indice...
The cover image is based on the Research Article Pattern recognition analysis of directional intravoxel incoherent motion MRI in ischemic rodent brains by MinJung Jang et al., https://doi.org/10.1002/nbm.4268.
Using superparamagnetic iron oxide nanoparticles (SPION) as a single contrast agent, we investigated dual contrast cerebrovascular magnetic resonance imaging (MRI) for simultaneously monitoring macro- and microvasculature and their association with ischemic edema status (via apparent diffusion coefficient [ADC]) in transient middle cerebral artery...
This study aimed to demonstrate a reliable automatic segmentation method for independently separating reduced diffusion and decreased perfusion areas in ischemic stroke brains using constrained nonnegative matrix factorization (cNMF) pattern recognition in directional intravoxel incoherent motion MRI (IVIM-MRI). First, the feasibility of cNMF-based...
Background:
The manual segmentation of intact blood-brain barrier (BBB) regions in the stroke brain is cumbersome, due to the coexistence of infarction, large blood vessels, ventricles, and intact BBB regions, specifically in areas with weak signal enhancement following contrast agent injection.
Hypothesis:
That from dynamic susceptibility contr...
Purpose
Sensitivity and specificity of blood oxygenation level–dependent (BOLD) functional MRI (fMRI) is sensitive to magnetic field strength and acquisition methods. We have investigated gradient‐echo (GE)‐ and spin‐echo (SE)‐BOLD fMRI at ultrahigh fields of 9.4 and 15.2 Tesla.
Methods
BOLD fMRI experiments responding to forepaw stimulation were...
Tumor heterogeneity can be elucidated by mapping subregions of the lesion with differential imaging characteristics, called habitats. Dynamic Contrast Enhanced (DCE-)MRI can depict the tumor microenvironments by identifying areas with variable perfusion and vascular permeability, since individual tumor habitats vary in the rate and magnitude of the...
Purpose:
To automate dynamic contrast-enhanced MRI (DCE-MRI) data analysis by unsupervised pattern recognition (PR) to enable spatial mapping of intratumoral vascular heterogeneity.
Methods:
Three steps were automated. First, the arrival time of the contrast agent at the tumor was determined, including a calculation of the precontrast signal. Se...
Objective
To simulate the B1-inhomogeneity-induced variation of pharmacokinetic parameters on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).
Materials and Methods
B1-inhomogeneity-induced flip angle (FA) variation was estimated in a phantom study. Monte Carlo simulation was performed to assess the FA-deviation-induced measurement...
A variable repetition-delay (TR) spin echo sequence with repeated refocusing pulses, i.e., a variable TR turbo-spin echo (TSE), provides an attractive means of acquiring an accurate T1 map information that is free from gradient echo-based artifacts such as magnetic field inhomogeneities particularly for ultra-high field (at 7T and above) preclinica...
The cover image, by HyungJoon Cho et al., is based on the Research Article UTE–ΔR2–ΔR2* combined MR whole-brain angiogram using dual-contrast superparamagnetic iron oxide nanoparticles, DOI: 10.1002/nbm.3514.
The ability to visualize whole-brain vasculature is important for quantitative in vivo investigation of vascular malfunctions in cerebral small vessel diseases, including cancer, stroke and neurodegeneration. Transverse relaxation-based ΔR2 and ΔR2 * MR angiography (MRA) provides improved vessel-tissue contrast in animal deep brain with the aid of...
Purpose:
To enhance the temporal resolution of calibration-free dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) by implementing compressed sensing assisted turbo spin echo (CS-TSE) acquisition.
Materials and methods:
The dynamic sparse sampling variables including acceleration factor, randomized phase encoding distributions, and r...
With the applications of magnetic resonance imaging (MRI) at higher magnetic fields increasing, there is demand for MRI contrast agents with improved relaxivity at higher magnetic fields. Macromolecule-based contrast agents, such as protein-based ones, are known to yield significantly higher r1 relaxivity at low fields, but tend to lose this merit...
Exploiting ultrashort-TE (UTE) MRI, T1 -weighted positive contrast can be obtained from superparamagnetic iron oxide nanoparticles (SPIONs), which are widely used as a robust T2 -weighted, negative contrast agent on conventional MR images. Our study was designed (a) to optimize the dual-contrast MRI method using SPIONs and (b) to validate the feasi...
Intravascular superparamagnetic iron oxide nanoparticles (SPION) - enhanced MR transverse relaxation rates (∆R2(⁎) and ∆R2) are widely used to investigate in vivo vascular parameters, such as the cerebral blood volume (CBV), microvascular volume (MVV), and mean vessel size index (mVSI, ∆R2(⁎)/∆R2). Although highly efficient, regional comparison of...
Recent advances in MRI acquisition for microscopic flows enable unprecedented sensitivity and speed in a portable NMR/MRI microfluidic analysis platform. However, the application of MRI to microfluidics usually suffers from prolonged acquisition times owing to the combination of the required high resolution and wide field of view necessary to resol...
Exploiting the field response of magnetic tracers, magnetic particle imaging (MPI) allows direct, local quantification of the tracer concentration in bulk structures. Here, we investigated the use of characteristic field response functions to spatially resolve the absolute concentration of multiple nanoparticle species by simulation. In particular,...
In comparison to the well-documented significance of intravascular deoxyhemoglobin (deoxyHgb), the effects of dissolved oxygen on the blood-oxygen-level-dependent (BOLD) signal have not been widely reported. Based on the fact that the prolonged inspiration of high oxygen fraction gas can result in up to a sixfold increase of the baseline tissue oxy...
Long scan times of 3D volumetric MR acquisitions usually necessitate ultrafast in vivo gradient-echo acquisitions, which are intrinsically susceptible to magnetic field inhomogeneities. This is especially problematic for contrast-enhanced (CE)-MRI applications, where non-negligible T2* effect of contrast agent deteriorates the positive signal contr...
Unlabelled:
Contrast-enhancing magnetic resonance mechanism, employing either positive or negative signal changes, has contrast-specific signal characteristics. Although highly sensitive, negative contrast typically decreases the resolution and spatial specificity of MRI, whereas positive contrast lacks a high contrast-to-noise ratio but offers hi...
Structural and functional features of various cerebral cortices have been extensively explored in neuroscience research. We used manganese-enhanced MRI, a non-invasive method for examining stimulus-dependent activity in the whole brain, to investigate the activity in the layers of primary cortices and sensory, such as auditory and olfactory, pathwa...
This study was conducted to evaluate feasibility of sunitinib-CLIO conjugate as a vascular endothelial growth factor receptor/platelet-derived growth factor receptor (VEGFR/PDGFR)-specific magnetic resonance (MR) probe.
VEGFR/PDGFR-targeting MR probe was synthesized by conjugating cross-linked iron-oxide (CLIO) with tyrosine-kinase inhibitor (sunit...
A method of in vitro or in vivo nuclear magnetic resonance and/or magnetic resonance imaging, to determine bone properties by measuring the effects of molecular diffusion inside the bone specimen to derive parameters that are related to the structure of the trabecular bones. The method is a non-invasive probe that provides topological information o...
P22 viral capsids and ferritin protein cages are utilized as templating macromolecules to conjugate Gd (III)-chelating agent complexes, and we systematically investigates the effects of the macromolecules' size and the conjugation positions of Gd (III)-chelating agents on the MR relaxivities and the resulting image contrasts. The relaxivity values...
Tumor hypoxia develops heterogeneously, affects radiation sensitivity and the development of metastases. Prognostic information derived from the in vivo characterization of the spatial distribution of hypoxic areas in solid tumors can be of value for radiation therapy planning and for monitoring the early treatment response. Tumor hypoxia is caused...
Insufficient vascular reserve after an ischemic stroke may induce biochemical cascades that subsequently deteriorate the blood-brain barrier (BBB) function. However, the direct relationship between poor cerebral blood volume (CBV) restoration and BBB disruption has not been examined in acute stroke. To quantify BBB integrity at acute stages of tran...
In solid tumors, hypoxia contributes significantly to radiation and chemotherapy resistance and to poor outcomes. The "gold standard" pO(2) electrode measurements of hypoxia in vivo are unsatisfactory because they are invasive and have limited spatial coverage. Here, we present an approach to identify areas of tumor hypoxia using the signal versus...
We report on experimental observations of trapped-mode resonances in double-layered symmetric electric ring resonators separated by dielectric inserts. The resulting metamaterial introduces trapped-mode resonances that were thought to be produced only by asymmetric metamaterial unit cells. Experimental verification of the newly observed trapped mod...
When a porous material is inserted into a uniform magnetic field, spatially varying fields typically arise inside the pore space due to susceptibility contrast between the solid matrix and the surrounding fluid. As a result, direct measurement of the field variation may provide a unique opportunity to characterize the pore geometry. The sensitivity...
Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) provides critical information regarding tumor perfusion and permeability by injecting a T(1) contrast agent, such as Gd-DTPA, and making a time-resolved measurement of signal increase. Both temporal and spatial resolutions are required to be high to achieve an accurate and reproducible...
Tumor hypoxia, which develops heterogeneously in locally advanced tumors is known to affect radiation sensitivity and development to metastases. In vivo knowledge of hypoxia distribution in solid tumors provides prognostic information and can be potentially used for input for dose escalation in radiation therapy. Tumor hypoxia results from a mismat...
NMR can probe the microstructures of anisotropic materials such as liquid crystals, stretched polymers and biological tissues through measurement of the diffusion propagator, where internal structures are indicated by restricted diffusion. Multi-dimensional measurements can probe the microscopic anisotropy, but full sampling can then quickly become...
Non-invasive measurements of structural orientation provide unique information regarding the connectivity and functionality of fiber materials. In the present study, we use a capillary model to demonstrate that the direction of fiber structure can be obtained from susceptibility-induced magnetic field anisotropy. The interference pattern between in...
We present experimental results on the multilayering effects of an electric ring resonator. The electromagnetic response of the electric ring resonator is measured via a scattering matrix using a vector network analyzer at the X-band frequency. Structures of the electric ring resonator with up to four layers were tested and analyzed using commercia...
The endothelin-1 antagonist, Atrasentan (ABT-627) was used to modify perfusion in the human tumor xenograft model, HT29, growing in nude mice. Atrasentan produced a significant increase in perfusion, as measured in vivo by Gd-DTPA DCE-MRI. Changes in tumor hypoxia were assessed by comparing the binding of two hypoxia tracers, pimonidazole and EF5 g...
The diffusion/relaxation behavior of polarized spins of pore filling fluid, as often probed by NMR relaxometry, is widely used to extract information on the pore-geometry. Such information is further interpreted as an indicator of the key transport property of the formation in the oil industry. As the importance of reservoirs with complex pore geom...
Trabecular bone structure is known to play a crucial role in the overall strength, and thus fracture risk, of such areas of the skeleton as the vertebrae, spine, femur, tibiae, or radius. Several MR methods devoted to probing this structure depend upon the susceptibility difference between the solid bone matrix and the intervening fluid/marrow/fat,...
In vivo knowledge of the spatial distribution of viable, necrotic, and hypoxic areas can provide prognostic information about the risk of developing metastases and regional radiation sensitivity and may be used potentially for localized dose escalation in radiation treatment. In this study, multimodality in vivo magnetic resonance imaging (MRI) and...
We visualized inhomogeneous local magnetic field (internal magnetic field) gradients arising from susceptibility contrast between an array of cylindrical glass tubes (solid matrix) and surrounding water (pore fluids) in a uniform applied magnetic field. MRI was performed to determine the spatially resolved decay rates due to diffusion in the intern...
IntroductionMMME TechniqueDiffusion MeasurementApplication: FlowSummary
When a porous material is inserted in a uniform magnetic field, spatially varying fields typically arise inside the pore space due to susceptibility contrasts between the solid matrix and the surrounding fluid.
Susceptibility contrast is present in many porous media of interest, such as fluid filled rocks, cements, granular media, colloids and tra...
Recent years have seen significant progress in the NMR study of porous media from natural and industrial sources and of cultural significance such as paintings. This paper provides a brief outline of the recent technical development of NMR in this area. These advances are relevant for broad NMR applications in material characterization.
The structure factor provides a fundamental characterization of porous and granular materials as it is the key for solid crystals via measurements of x-ray and neutron scattering. Here, we demonstrate that the structure factor of the granular and porous media can be approximated by the pair correlation function of the inhomogeneous internal magneti...
A new approach to MR trabecular bone characterization is presented. This method probes the diffusion of spins through internal magnetic field gradients due to the susceptibility contrast between the bone and water (or marrow) phases. The resulting spin magnetization decay encodes properties of the underlying structure. This method, termed decay due...
We describe several applications of a versatile pulse sequence family employing multiple spin echoes within one acquisition to accelerate multidimensional experiments. The core sequence, called multiple modulation multiple echo, measures the maximal set of spin echoes generated from a set of RF pulses with unequal time spacings. These echoes can be...
Here, we describe the design and performance characteristics of a low temperature probe for dynamic nuclear polarization (DNP) experiments, which is compatible with demanding multiple-pulse experiments. The competing goals of a high-Q microwave cavity to achieve large DNP enhancements and a high efficiency NMR circuit for multiple-pulse control lea...
In this article, we demonstrate a single-scan method to measure an average flow velocity vector along an arbitrary direction. This method is based on the MMME sequence and utilizes static and pulsed magnetic field gradients along multiple directions for the optimal determination of flow velocity components in three-dimensional space. Experimentally...
In this article, the authors demonstrate a rapid NMR method to measure a full three-dimensional diffusion tensor. This method is based on a multiple modulation multiple echo sequence and utilizes static and pulsed magnetic field gradients to measure diffusion along multiple directions simultaneously. The pulse sequence was optimized using a well-kn...
We have measured the decay of NMR multiple quantum coherence intensities both under the internal dipolar Hamiltonian as well as when this interaction is effectively averaged to zero, in the cubic calcium fluoride (CaF2) spin system and the pseudo-one-dimensional system of fluoroapatite. In calcium fluoride the decay rates depend both on the number...
Solid state Nuclear Magnetic Resonance (NMR) allows us to explore a large coherent spin system and provides an ideal test-bed for studying strongly interacting multiple-spin system in a large Hilbert space. In this thesis, we experimentally investigate the spin dynamics in a rigid lattice of dipolarly coupled nuclear spins using multiple quantum NM...
The multiple-modulation-multiple-echo sequence, previously used for rapid measurement of diffusion, is extended to a method for single shot imaging. Removing the gradient switching requirement during the application of RF pulses by a constant frequency encoding gradient can shorten experiment time for ultrafast imaging. However, having the gradient...
We present a new experimental investigation of the NMR free induction decay (FID) in a lattice of spin-1∕2 nuclei in a strong Zeeman field. Following a π∕2 pulse, evolution under the secular dipolar Hamiltonian preserves the coherence number in the Zeeman eigenbasis, but changes the number of correlated spins in the state. The observed signal is se...
Multiple quantum coherences are typically characterised by their coherence number and the number of spins that make up the state, though only the coherence number is normally measured. We present a simple set of measurements that extend our knowledge of the multiple quantum state by recording the coherences in both the $x$ basis and the usual $z$ b...
Reciprocal space measurements of spin diffusion in a single crystal of calcium fluoride (CaF2) have been extended to dipolar ordered states. The experimental results for the component of the spin diffusion rate parallel to the external field are D(parallel)(D)=29+/-3x10(-12) cm(2)/s for the [001] direction and D(parallel)(D)=33+/-4x10(-12) cm(2)/s...
We present improved line-narrowing sequences for dipolar coupled spin systems, based on a train of magic-echoes which are compensated for the effects of finite pulse widths and utilize symmetry properties of supercycles. Sequences are introduced for spectroscopy and imaging by proper choice of a phase alternating scheme. Using a 16 pulse time-suspe...
The dipolar-ordered state (ρ∝Hd) can be prepared from a state of Zeeman equilibrium at high field by adiabatically removing the Zeeman field. It is also possible to produce dipolar-ordered states in the rotating frame using two well-known methods—adiabatic demagnetization in the rotating frame and the Jeener–Broekaert (JB) pulse pair. Using multipl...
In this paper, we demonstrate a rapid simultaneous measurement of diffusion constant D, T 1 and T 2 relaxation times in just two scans. Theoretical standard deviations of D, T 1 T 2 for a wide range of T 1 and T 2 were predicted for given sequences with a random experimental error of 3%. By carefully selecting of sequence parameters for samples wit...
