ORCID Profile
0000-0002-5695-153X
Current Organisations
Queensland University of Technology (QUT)
,
Queensland University of Technology
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Physical Chemistry Not Elsewhere Classified | Orthopaedics | Medical Physics | Physical Chemistry (Incl. Structural)
Skeletal system and disorders (incl. arthritis) | Chemical sciences | Physical sciences |
Publisher: American Chemical Society (ACS)
Date: 06-1994
DOI: 10.1021/OM00018A060
Publisher: Elsevier BV
Date: 04-2022
Publisher: The Royal Society of Chemistry
Date: 09-11-2016
Abstract: This unique book describes the latest information in the fundamental understanding of the biophysics and biochemistry of articular cartilage using the state-of-the-art practices in NMR and MRI. This is the first book of its kind, written by physicists and chemists on this important tissue, whose degradation contributes to osteoarthritis and related joint diseases. Connecting the fundamental science with the clinical imaging applications, the experts Editors provide an authoritative addition to the literature. Ideal for practising physical scientists and radiologists with an interest in the fundamental science as well as instrument manufacturers and clinical researchers working with articular cartilage.
Publisher: Public Library of Science (PLoS)
Date: 29-12-2014
Publisher: Elsevier BV
Date: 07-2008
Publisher: American Chemical Society (ACS)
Date: 06-12-2022
Publisher: Springer Science and Business Media LLC
Date: 27-08-2021
DOI: 10.1007/S10911-021-09494-3
Abstract: Regions of high mammographic density (MD) in the breast are characterised by a proteoglycan (PG)-rich fibrous stroma, where PGs mediate aligned collagen fibrils to control tissue stiffness and hence the response to mechanical forces. Literature is accumulating to support the notion that mechanical stiffness may drive PG synthesis in the breast contributing to MD. We review emerging patterns in MD and other biological settings, of a positive feedback cycle of force promoting PG synthesis, such as in articular cartilage, due to increased pressure on weight bearing joints. Furthermore, we present evidence to suggest a pro-tumorigenic effect of increased mechanical force on epithelial cells in contexts where PG-mediated, aligned collagen fibrous tissue abounds, with implications for breast cancer development attributable to high MD. Finally, we summarise means through which this positive feedback mechanism of PG synthesis may be intercepted to reduce mechanical force within tissues and thus reduce disease burden.
Publisher: American Chemical Society (ACS)
Date: 12-1998
DOI: 10.1021/JP982892J
Publisher: The Royal Society of Chemistry
Date: 16-11-2016
DOI: 10.1039/9781782623663-00191
Abstract: In this chapter, we present approaches to the numerical simulation of the diffusion of water molecules in fibre networks that serve as models of articular cartilage. The simulations are intended as a tool for the translation of experimental diffusion magnetic resonance imaging (MRI) data into quantitative microstructural and compositional characteristics of articular cartilage. The chapter begins with a brief introduction to diffusion nuclear magnetic resonance and diffusion imaging, focusing on diffusion tensor imaging. It discusses the current limitations of diffusion MRI in quantifying articular cartilage microstructure beyond the predominant direction of collagen fibre alignment. We then detail the construction of aligned and partially aligned networks of fibres that can serve as models of articular cartilage. We discuss the methods for the simulation of the diffusion of tracer molecules through the model networks (especially Langevin dynamics and Monte Carlo techniques), and reconstruction of the diffusion tensor from the simulated molecular trajectories. The aim of these simulations is to quantitatively link the eigenvalues and the fractional anisotropy of cartilage diffusion tensor to collagen fibre volume fraction and the degree of collagen fibre alignment. The global aim of this work is to move diffusion tensor imaging of articular cartilage beyond determination of the predominant direction of fibre alignment, and towards quantification of the fibre orientation distribution.
Publisher: Wiley
Date: 2006
DOI: 10.1002/CMR.A.20056
Publisher: Elsevier BV
Date: 11-2017
DOI: 10.1016/J.MRI.2017.07.010
Abstract: Kangaroo knee cartilages are robust tissues that can support knee flexion and endure high levels of compressive stress. This study aimed to develop a detailed understanding of the collagen architecture in kangaroo knee cartilages and thus obtain insights into the biophysical basis of their function. Cylindrical/square plugs from femoral and tibial hyaline cartilage and tibial fibrocartilage were excised from the knees of three adult red kangaroos. Multi-slice, multi-echo MR images were acquired at the s le orientations 0° and 55° ("magic angle") with respect to the static magnetic field. Maps of the transverse relaxation rate constant (R The R Our observations suggest that the well-developed superficial zone of femoral hyaline cartilage is suitable for supporting knee flexion the thick and well-aligned radial zone of tibial hyaline cartilage is adapted to endure high compressive stress while the innermost part of the radial zone of tibial fibrocartilage may facilitate anchoring of the collagen fibres to withstand high shear deformation. These findings may inspire new designs for cartilage tissue engineering.
Publisher: Elsevier BV
Date: 03-2015
Publisher: Wiley
Date: 11-2016
DOI: 10.1111/AJCO.12635_4
Publisher: American Chemical Society (ACS)
Date: 06-02-2003
DOI: 10.1021/LA026722G
Publisher: CSIRO Publishing
Date: 2020
DOI: 10.1071/CH19537
Abstract: Rotational motion of molecules plays an important role in determining NMR spin relaxation properties of liquids. The textbook theory of NMR spin relaxation predominantly uses the assumption that the reorientational dynamics of molecules is described by a continuous time rotational diffusion random walk with a single rotational diffusion coefficient. Previously we and others have shown that reorientation of water molecules on the timescales of picoseconds is not consistent with the Debye rotational-diffusion model. In particular, multiple timescales of molecular reorientation were observed in liquid water. This was attributed to the hydrogen bonding network in water and the consequent presence of collective rearrangements of the molecular network. In order to better understand the origins of the complex reorientational behaviour of water molecules, we carried out molecular dynamics (MD) simulations of a liquid that has a similar molecular geometry to water but does not form hydrogen bonds: hydrogen sulfide. These simulations were carried out at T=208K and p=1 atm (~5K below the boiling point). Ensemble-averaged Legendre polynomial functions of hydrogen sulfide exhibited a Gaussian decay on the sub-picosecond timescale but, unlike water, did not exhibit oscillatory behaviour. We attribute these differences to hydrogen sulfide’s absence of hydrogen bonding.
Publisher: IOP Publishing
Date: 23-10-2013
Publisher: American Chemical Society (ACS)
Date: 06-01-2009
DOI: 10.1021/AM800059C
Abstract: Nuclear magnetic resonance was used to probe the distribution of water and ionic species in a microstructured poly(methyl methacrylate) (PMMA) polymer optical fiber (MPOF), with a plan to assess the suitability of these fibers for aqueous chemosensing. The NMR spectra and the measurements of proton spin relaxation in hydrated fibers demonstrated the presence of two distinct pools of water: water residing in the microstructure channels and the hydration water residing in the polymer matrix of the fiber. No facile chemical exchange between these two pools was present. The NMR peaks of the two pools of water were separated by 1.53 ppm. Relaxation measurements of the fiber s les doped with aqueous copper sulfate showed that charged ions freely entered the microstructure channels but were completely excluded from the polymer matrix of the fiber. Measurements of the apparent diffusion coefficient of water along the axial direction of the fiber showed that water molecules moved unimpeded along the channels. This is the first reported magnetic-resonance study of microstructured optical fibers. The findings suggest that microstructured PMMA fibers are compatible with ionic aqueous solutions and could provide a robust and durable platform for chemical-sensing applications.
Publisher: American Chemical Society (ACS)
Date: 22-05-2019
Abstract: Dynamics of water molecules in hydrated collagen plays an important role in determining the structural and functional properties of collagenous tissues. Experimental results suggest that collagen-bridging water molecules exhibit dynamic and thermodynamic properties of one-dimensional ice. However, molecular dynamics (MD) studies performed to date have failed to identify icelike water bridges. It has been hypothesized that this discrepancy is due to the experimental measurements and computational MD analysis having been performed on very different systems: complete tissues with large-scale collagen fiber assemblies and in idual tropocollagen fragments, respectively. In this work, we explore ways of emulating a tissuelike macromolecular environment in MD simulations of hydrated collagen without increasing the size of the system to computationally prohibitive levels. We have investigated the effects of temperature and pressure on the dynamics of a small hydrated tropocollagen fragment. The occupancy and bond energies of interchain hydrogen bonds were relatively insensitive to temperature, suggesting that they play a key role in the stability of the collagen triple helix. The lifetimes of water bridges lengthened with decreasing temperature, but even at 280 K, no bridging water molecules exhibited icelike dynamics. We discuss the implications of these findings for the ability to emulate tissuelike conditions in hydrated collagen.
Publisher: Frontiers Media SA
Date: 14-07-2020
Abstract: Mammographic density (MD) is a strong and independent factor for breast cancer (BC) risk and is increasingly associated with BC progression. We have previously shown in mice that high MD, which is characterized by the preponderance of a fibrous stroma, facilitates BC xenograft growth and metastasis. This stroma is rich in extracellular matrix (ECM) factors, including heparan sulfate proteoglycans (HSPGs), such as the BC-associated syndecan-1 (SDC1). These proteoglycans tether growth factors, which are released by heparanase (HPSE). MD is positively associated with estrogen exposure and, in cell models, estrogen has been implicated in the upregulation of HPSE, the activity of which promotes SDC expression. Herein we describe a novel measurement approach (single-sided NMR) using a patient-derived explant (PDE) model of normal human (female) mammary tissue cultured ex vivo to investigate the role(s) of HPSE and SDC1 on MD. Relative HSPG gene and protein analyses determined in patient-paired high vs. low MD tissues identified SDC1 and SDC4 as potential mediators of MD. Using the PDE model we demonstrate that HPSE promotes SDC1 rather than SDC4 expression and cleavage, leading to increased MD. In this model system, synstatin (SSTN), an SDC1 inhibitory peptide designed to decouple SDC1-ITGαvβ3 parallel collagen alignment, reduced the abundance of fibrillar collagen as assessed by picrosirius red viewed under polarized light, and reduced MD. Our results reveal a potential role for HPSE in maintaining MD via its direct regulation of SDC1, which in turn physically tethers collagen into aligned fibers characteristic of MD. We propose that inhibitors of HPSE and/or SDC1 may afford an opportunity to reduce MD in high BC risk in iduals and reduce MD-associated BC progression in conjunction with established BC therapies.
Publisher: Wiley
Date: 23-02-2016
DOI: 10.1002/MRC.4416
Abstract: The remarkable flexibility of human red blood cells (RBCs) allows them to assume a range of shapes in normal and disease states. Biochemical mechanisms and energetic requirements associated with changes in RBC geometry are not well understood because of a lack of experimental procedures to fix and study cells in different morphological forms. By incorporating RBCs into stretchable gelatin hydrogels, we created conditions for adjustable elongation of their normal discocytic shape in all orientations. As the RBC-containing gels were stretched or compressed, the changes in the cell morphology were studied by using
Publisher: Elsevier BV
Date: 04-2012
DOI: 10.1016/J.MEDENGPHY.2011.07.027
Abstract: Orthopaedic fracture fixation implants are increasingly being designed using accurate 3D models of long bones based on computer tomography (CT). Unlike CT, magnetic resonance imaging (MRI) does not involve ionising radiation and is therefore a desirable alternative to CT. This study aims to quantify the accuracy of MRI-based 3D models compared to CT-based 3D models of long bones. The femora of five intact cadaver ovine limbs were scanned using a 1.5 T MRI and a CT scanner. Image segmentation of CT and MRI data was performed using a multi-threshold segmentation method. Reference models were generated by digitising the bone surfaces free of soft tissue with a mechanical contact scanner. The MRI- and CT-derived models were validated against the reference models. The results demonstrated that the CT-based models contained an average error of 0.15 mm while the MRI-based models contained an average error of 0.23 mm. Statistical validation shows that there are no significant differences between 3D models based on CT and MRI data. These results indicate that the geometric accuracy of MRI based 3D models was comparable to that of CT-based models and therefore MRI is a potential alternative to CT for generation of 3D models with high geometric accuracy.
Publisher: Trans Tech Publications, Ltd.
Date: 05-2013
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.699.457
Abstract: We used Magnetic Resonance microimaging (MRI) to study the compressive behaviour of synthetic elastin. Compression-induced changes in the elastin s le were quantified using longitudinal and transverse spin relaxation rates (R1 and R2, respectively). Spatially-resolved maps of each spin relaxation rate were obtained, allowing the heterogeneous texture of the s le to be observed with and without compression. Compression resulted in an increase of both the mean R1 and the mean R2, but most of this increase was due to sub-locations that exhibited relatively low R1 and R2 in the uncompressed state. This behaviour can be described by differential compression, where local domains in the hydrogel with a relatively low biopolymer content compress more than those with a relatively high biopolymer content.
Publisher: The Royal Society of Chemistry
Date: 16-11-2016
DOI: 10.1039/9781782623663-00062
Abstract: This chapter presents an introduction to nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) in the context of the applications of these techniques to cartilage. The introduction (Section 3.1) contains a brief overview of the relationship between the two techniques, and the following sections discuss their physical basis. Section 3.2 presents the vector model of NMR, which provides a conceptually simple picture of magnetic resonance intended to be accessible to all readers. Section 3.3 introduces the quantum-mechanical apparatus of magnetic resonance. The emphasis is placed on the density-matrix description of NMR this section should be accessible to researchers and students with a working knowledge of linear algebra and basic quantum mechanics. The physical basis of MRI is discussed in Section 3.4.
Publisher: Wiley
Date: 2003
DOI: 10.1002/CMR.A.10092
Publisher: Mary Ann Liebert Inc
Date: 06-2014
Publisher: Elsevier BV
Date: 07-2004
Publisher: Springer Science and Business Media LLC
Date: 05-2018
DOI: 10.1038/S41598-018-25186-1
Abstract: Knee injury often triggers post-traumatic osteoarthritis (PTOA) that affects articular cartilage (AC), subchondral bone, meniscus and the synovial membrane. The available treatments for PTOA are largely ineffective due to late diagnosis past the “treatment window”. This study aimed to develop a detailed understanding of the time line of the progression of PTOA in murine models through longitudinal observation of the femorotibial joint from the onset of the disease to the advanced stage. Quantitative magnetic resonance microimaging (µMRI) and histology were used to evaluate PTOA-associated changes in the knee joints of rats subjected to knee meniscectomy. Systematic longitudinal changes in the articular cartilage thickness, cartilage T 2 and the T 2 of epiphysis within medial condyles of the tibia were all found to be associated with the development of PTOA in the animals. The following pathogenesis cascade was found to precede advanced PTOA: meniscal injury → AC swelling → subchondral bone remodelling → proteoglycan depletion → free water influx → cartilage erosion. Importantly, the imaging protocol used was entirely MRI-based. This protocol is potentially suitable for whole-knee longitudinal, non-invasive assessment of the development of OA. The results of this work will inform the improvement of the imaging methods for early diagnosis of PTOA.
Publisher: American Chemical Society (ACS)
Date: 04-1997
DOI: 10.1021/JP963235Z
Publisher: American Physical Society (APS)
Date: 17-09-2012
Publisher: Elsevier BV
Date: 02-2000
Publisher: Elsevier BV
Date: 06-2005
DOI: 10.1016/J.JMR.2005.02.003
Abstract: We present a design scheme for phase-sensitive, convection-compensating diffusion experiments with gradient-selected homonuclear double-quantum filtering. The scheme consists of three blocks: a 1/2J evolution period during which antiphase single-quantum coherences are created a period of double-quantum evolution and another 1/2J period, during which antiphase single-quantum coherences are converted back into an in-phase state. A single coherence transfer pathway is selected using an asymmetric set of gradient pulses, and both diffusion sensitization and convection compensation are built into the gradient coherence transfer pathway selection. Double-quantum filtering can be used either for solvent suppression or spectral editing, and we demonstrate ex les of both applications. The new experiment performs well in the absence of a field-frequency lock and does not require magnitude Fourier transformation. The proposed scheme may offer advantages in diffusion measurements of spectrally crowded systems, particularly small molecules solubilized in colloidal solutions or bound to macromolecules.
Publisher: Elsevier BV
Date: 02-2021
Publisher: American Chemical Society (ACS)
Date: 12-1997
DOI: 10.1021/JP972194J
Publisher: American Chemical Society (ACS)
Date: 03-2004
DOI: 10.1021/LA0362371
Abstract: Pulsed field gradient spin-echo NMR diffusion and relaxation measurements were used to investigate how the Na+ ionophore monensin affected the dynamics of sodium ions in a Myverol 18-99/saline bicontinuous Ia3d cubic phase (BCP). The monensin Na+ binding number was estimated from 23Na line widths to be between 3 and 6. The dependence of the apparent Na+ diffusion coefficient on the concentration of monensin revealed monensin-induced Na+ transport. At high monensin concentrations, the enhancement of D(Na+) was offset by Na+-monensin binding. The greatest enhancement was measured at short diffusion times (delta < or = 5 ms), which we explain in terms of the bicontinuous topology of the cubic phase and a combination of tortuosity and bilayer permeability effects. We also propose numerical simulations which would enable the separation of the two effects. To our knowledge, this is the first study of ionophore-mediated cation diffusion in a bicontinuous cubic phase. The approach could be used to study the dynamics of hydrophilic species in the aqueous channels of BCPs and similar structures, as well as to measure the ion-transporting efficiency of ionophores.
Publisher: Wiley
Date: 04-02-2018
DOI: 10.1002/MRM.27098
Publisher: Springer Science and Business Media LLC
Date: 21-02-2017
DOI: 10.1038/SREP42905
Abstract: Diffusion-weighted magnetic resonance imaging (DW-MRI) was used to evaluate the effects of single-agent and combination treatment regimens in a spheroid-based animal model of ovarian cancer. Ovarian tumour xenografts grown in non-obese diabetic/severe-combined-immunodeficiency (NOD/SCID) mice were treated with carboplatin or paclitaxel, or combination carboplatin aclitaxel chemotherapy regimens. After 4 weeks of treatment, tumours were extracted and underwent DW-MRI, mechanical testing, immunohistochemical and gene expression analyses. The distribution of the apparent diffusion coefficient (ADC) exhibited an upward shift as a result of each treatment regimen. The 99-th percentile of the ADC distribution (“maximum ADC”) exhibited a strong correlation with the tumour size (r 2 = 0.90) and with the inverse of the elastic modulus (r 2 = 0.96). Single-agent paclitaxel (n = 5) and combination carboplatin aclitaxel (n = 2) treatment regimens were more effective in inducing changes in regions of higher cell density than single-agent carboplatin (n = 3) or the no-treatment control (n = 5). The maximum ADC was a good indicator of treatment-induced cell death and changes in the extracellular matrix (ECM). Comparative analysis of the tumours’ ADC distribution, mechanical properties and ECM constituents provides insights into the molecular and cellular response of the ovarian tumour xenografts to chemotherapy. Increased s le sizes are recommended for future studies. We propose experimental approaches to evaluation of the timeline of the tumour’s response to treatment.
Publisher: Wiley
Date: 07-11-2017
DOI: 10.1002/JMRI.25531
Abstract: To assess the feasibility of diffusion tensor imaging (DTI) for evaluating changes in anulus fibrosus (AF) microstructure following uniaxial compression. Six axially aligned s les of AF were obtained from a merino sheep disc two each from the anterior, lateral, and posterior regions. The s les were mechanically loaded in axial compression during five cycles at a rate and maximum compressive strain that reflected physiological conditions. DTI was conducted at 7T for each s le before and after mechanical testing. The mechanical response of all s les in unconfined compression was nonlinear. A stiffer response during the first loading cycle, compared to the remaining cycles, was observed. Change in diffusion parameters appeared to be region-dependent. The mean fractional anisotropy increased following mechanical testing. This was smallest in the lateral (2% and 9%) and largest in the anterior and posterior s les (17-25%). The mean average diffusivity remained relatively constant (<2%) after mechanical testing in the lateral and posterior s les, but increased (by 5%) in the anterior s les. The mean angle made by the principal eigenvector with the spine axis in the lateral s les was 73° and remained relatively constant (<2%) following mechanical testing. This angle was smaller in the anterior (55°) and posterior (47°) regions and increased by 6-16° following mechanical testing. These preliminary results suggest that axial compression reorients the collagen fibers, such that they become more consistently aligned parallel to the plane of the endplates. 1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017 :1723-1735.
Publisher: Springer New York
Date: 2011
Publisher: AIP Publishing
Date: 09-2001
DOI: 10.1063/1.1386655
Abstract: A theory is presented for radiation d ing (RD) in the toroid cavity nuclear magnetic resonance detector, a cylindrically symmetric inhomogeneous-rf field detector in which the magnitude of B1 is inversely proportional to the distance from the cylindrical symmetry axis. The equations of motion of the magnetization components are obtained and discussed. Numerical simulations of conventional- and composite-pulse experiments are presented, along with a discussion of the effects of RD on the evolution of magnetization. Preliminary simulations of RD in the presence of inhomogeneous line broadening are also presented. The signature effect of radiation d ing in the TCD is the winding or unwinding of magnetization gratings that has recently been observed by other researchers. The observed magnitude of the effect is linked to the effective filling factor, which currently appears to be limited by the stray inductance of the detection circuit. The results are of interest in connection with recent findings regarding the interaction of RD with the dipolar demagnetizing field.
Publisher: Springer Science and Business Media LLC
Date: 23-10-2010
DOI: 10.1007/S00249-010-0629-4
Abstract: We used Monte Carlo simulations of Brownian dynamics of water to study anisotropic water diffusion in an idealised model of articular cartilage. The main aim was to use the simulations as a tool for translation of the fractional anisotropy of the water diffusion tensor in cartilage into quantitative characteristics of its collagen fibre network. The key finding was a linear empirical relationship between the collagen volume fraction and the fractional anisotropy of the diffusion tensor. Fractional anisotropy of the diffusion tensor is potentially a robust indicator of the microstructure of the tissue because, to a first approximation, it is invariant to inclusion of proteoglycans or chemical exchange between free and collagen-bound water in the model. We discuss potential applications of Monte Carlo diffusion-tensor simulations for quantitative biophysical interpretation of magnetic resonance diffusion-tensor images of cartilage. Extension of the model to include collagen fibre disorder is also discussed.
Publisher: Elsevier BV
Date: 10-2022
DOI: 10.1016/J.MRI.2022.07.004
Abstract: Mammographic Density (MD) is the degree of radio-opacity of the breast in an X-ray mammogram. It is determined by the Fibroglandular: Adipose tissue ratio. MD has major implications in breast cancer risk and breast cancer chemoprevention. This study aimed to investigate the feasibility of accurate, low-cost quantification of MD in vivo without ionising radiation. We used single-sided portable nuclear magnetic resonance ("Portable NMR") due to its low cost and the absence of radiation-related safety concerns. Fifteen (N = 15) healthy female volunteers were selected for the study and underwent an imaging routine consisting of 2D X-ray mammography, quantitative breast 3T MRI (Dixon and T
Publisher: Elsevier BV
Date: 10-2005
DOI: 10.1016/J.JMR.2005.06.001
Abstract: Oscillating-gradient spin echo (OGSE) diffusion experiments have long been used to measure the short-time apparent diffusion coefficient, D(app)(t), in the presence of restricted diffusion, as well as the spectrum of the slow-motion velocity autocorrelation function. In this work, we focus on two previously unexplored aspects of OGSE experiments: convection compensation and acquisition of pure-phase diffusion spectra in the presence of homonuclear scalar couplings. We demonstrate that convection compensation afforded by single-echo OGSE compares well with that in double-echo convection-compensated PGSE experiments. We also show that, in the presence of homonuclear scalar couplings, setting the OGSE echo time to 1/2J enables acquisition of pure-phase diffusion spectra and yields more reliable D estimates than mixed-phase PGSE or OGSE spectra. Pure-phase OGSE acquisition is also compatible with measurements of the apparent diffusion coefficient at an arbitrary diffusion time. These features of OGSE can be valuable in diffusion measurements of scalar-coupled small-molecule probes in cellular and other heterogeneous systems.
Publisher: Elsevier BV
Date: 05-2018
DOI: 10.1016/J.MRI.2017.12.032
Abstract: Measurements of the orientational dispersion of collagen fibers in articular cartilage were made using diffusion tensor imaging (DTI) and small-angle X-ray scattering (SAXS) on matched bovine articular cartilage s les. Thirteen pairs of s les were excised from bovine knee joints each pair was taken from neighboring locations in the same bone. One s le from each pair was used for DTI measurements and the other for SAXS measurements. Fractional anisotropy (FA) values were calculated from the DTI data both for the in idual imaging voxels and for whole regions of interest (ROI). The FA values were used as a measure of fiber dispersion and compared to the ellipticities of the fiber orientation distributions obtained from SAXS. Neither the spatially-resolved FA values nor whole-ROI FA values showed any correlation with SAXS ellipticities. We attribute the lack of DTI-SAXS correlation to two principal factors: (1) the significant difference in the imaging resolution of the two techniques and (2) the inherent limitations of both the SAXS data analysis methodology and the diffusion tensor model in the case of multi-modal fiber orientation distributions. We discuss how these factors could be overcome in future work.
Publisher: Wiley
Date: 22-03-2017
DOI: 10.1002/MRC.4432
Abstract: The apparent diffusion coefficients of
Publisher: American Chemical Society (ACS)
Date: 29-11-2017
Abstract: The rotational motion of water molecules plays the dominant role in determining NMR spin-relaxation properties of liquid water and many biological tissues. The traditional theory of NMR spin relaxation predominantly uses the assumption that the reorientational dynamics of water molecules is described by a continuous-time rotational-diffusion random walk with a single rotational-diffusion coefficient. However, recent experimental and theoretical studies have demonstrated that water reorientation occurs by large, discrete angular jumps superimposed on a continuous-time rotational-diffusion process. We have investigated the rotational-diffusion propagator of the proton-proton (H-H) vector of water molecules in liquid water at 298 K using molecular dynamics (MD) simulations. Analysis of the MD-simulated reorientational trajectories reveals that reorientation of the intramolecular H-H vector occurs through a combination of the two mechanisms: rotational diffusion proper and discrete large-angle jumps. We demonstrate that, empirically, the rotational-diffusion propagator of the intramolecular H-H vector in liquid water can be described in terms of multiple rotational-diffusion coefficients. A model with two rotational-diffusion coefficients was found to provide a reasonable (albeit imperfect) fit of the MD-simulated propagator on the time scales relevant to NMR spin relaxation near room or physiological temperature (picoseconds to nanoseconds). We report the apparent values of the two rotational-diffusion coefficients determined from the propagator analysis at 298 K and discuss their physical meaning.
Publisher: Elsevier BV
Date: 08-2012
DOI: 10.1016/J.JMR.2012.05.004
Abstract: We present a formalism for the analysis of sensitivity of nuclear magnetic resonance pulse sequences to variations of pulse sequence parameters, such as radiofrequency pulses, gradient pulses or evolution delays. The formalism enables the calculation of compact, analytic expressions for the derivatives of the density matrix and the observed signal with respect to the parameters varied. The analysis is based on two constructs computed in the course of modified density-matrix simulations: the error interrogation operators and error commutators. The approach presented is consequently named the Error Commutator Formalism (ECF). It is used to evaluate the sensitivity of the density matrix to parameter variation based on the simulations carried out for the ideal parameters, obviating the need for finite-difference calculations of signal errors. The ECF analysis therefore carries a computational cost comparable to a single density-matrix or product-operator simulation. Its application is illustrated using a number of ex les from basic NMR spectroscopy. We show that the strength of the ECF is its ability to provide analytic insights into the propagation of errors through pulse sequences and the behaviour of signal errors under phase cycling. Furthermore, the approach is algorithmic and easily amenable to implementation in the form of a programming code. It is envisaged that it could be incorporated into standard NMR product-operator simulation packages.
Publisher: Wiley
Date: 29-04-2019
DOI: 10.1002/MRM.27781
Abstract: Elevated mammographic density (MD) is an independent risk factor for breast cancer (BC) as well as a source of masking in X-ray mammography. High-frequency longitudinal monitoring of MD could also be beneficial in hormonal BC prevention, where early MD changes herald the treatment's success. We present a novel approach to quantification of MD in breast tissue using single-sided portable NMR. Its development was motivated by the low cost of portable-NMR instrumentation, the suitability for measurements in vivo, and the absence of ionizing radiation. Five breast slices were obtained from three patients undergoing prophylactic mastectomy or breast reduction surgery. Carr-Purcell-Meiboom-Gill (CPMG) relaxation curves were measured from (1) regions of high and low MD (HMD and LMD, respectively) in the full breast slices (2) the same regions excised from the full slices and (3) excised s les after H Two major peaks, identified as fat and water, were consistently observed in the T T
Publisher: American Chemical Society (ACS)
Date: 12-2016
Abstract: Magnetic resonance transverse spin relaxation time constants (T
Publisher: The Royal Society of Chemistry
Date: 16-11-2016
DOI: 10.1039/9781782623663-00001
Abstract: Cartilage is a supporting connective tissue that, together with the bone, forms the framework supporting the body as a whole. There are many distinct types of cartilage, which exhibit numerous similarities as well as differences. Among them, articular cartilage is the best known and the most studied type. Articular cartilage is the thin layer of connective tissue that covers the articulating ends of bones in synovial (diarthrodial) joints. It provides a smooth surface for joint movement and acts as a load-bearing medium that protects the bone and distributes stress. The intense interest in articular cartilage is motivated by the critical role its degradation plays in arthritis and related joint diseases, which are the number one cause of disability in humans. This chapter discusses the physical, chemical and cellular properties of cartilage that give the tissue its extraordinary load-bearing characteristics.
Publisher: Elsevier BV
Date: 10-2019
DOI: 10.1016/J.MRI.2019.06.006
Abstract: Mammographic density (MD) is a strong independent risk factor for breast cancer. Traditional screening for MD using X-ray mammography involves ionising radiation, which is not suitable for young women, those with previous radiation exposure, or those having undergone a partial mastectomy. Therefore, alternative approaches for MD screening that do not involve ionising radiation will be important as the clinical use of MD increases, and as more frequent MD testing becomes desirable for research purposes. We have previously demonstrated the potential utility of spin relaxation-based, single-sided portable-NMR measurements for the purpose of MD quantification. We present here a more refined analysis by quantifying breast tissue density in excised s les on a continuous scale (0% to 100% fibroglandular tissue content) using micro-CT (μCT), and comparing the results to spin-relaxation and diffusion portable-NMR measurements of the same s les. μCT analysis of mammary tissues containing high- and low-MD (HMD and LMD, respectively) regions had Hounsfield Unit (HU) histograms with a bimodal pattern, with HMD regions exhibiting significantly higher HU values than LMD regions. Quantitative MD (%HMD) values obtained using μCT exhibited an excellent correlation with portable-NMR results, namely longitudinal spin-relaxation time constants (T
Publisher: American Chemical Society (ACS)
Date: 06-05-2008
DOI: 10.1021/JP8006415
Abstract: NMR line shapes of the lipid and aqueous species in bicontinuous cubic phase (BCP) s les prepared by centrifugation are inhomogeneously broadened. The broadening of the lipid peaks is removed by magic-angle spinning (MAS). In this work, we studied the mechanism of this broadening using (1)H and (13)C NMR spectroscopy of a myverol/water BCP. It is demonstrated that the inhomogeneity possesses an intrinsic contribution that is independent of instrumental or setup factors and can be attributed to the microscopic organization of the BCP bilayer. A mechanism of the inhomogeneous broadening is proposed, which involves a spatially nonuniform diamagnetically induced magnetic field determined by the mesoscopic structure and the diamagnetic susceptibilities of the two BCP domains. The proposed mechanism does not require that molecular reorientation of the lipid be slow for the inhomogeneous broadening to survive. We discuss how this inhomogeneous broadening can be employed as a probe of compositional uniformity and microscopic organization of BCP s les.
Publisher: MDPI AG
Date: 29-06-2021
Abstract: High mammographic density (MD) increases breast cancer (BC) risk and creates a stiff tissue environment. BC risk is also increased in BRCA1/2 gene mutation carriers, which may be in part due to genetic disruption of the tumour suppressor gene Ras association domain family member 1 (RASSF1A), a gene that is also directly regulated by tissue stiffness. High MD combined with BRCA1/2 mutations further increase breast cancer risk, yet BRCA1/2 mutations alone or in combination do not increase MD. The molecular basis for this additive effect therefore remains unclear. We studied the interplay between MD, stiffness, and BRCA1/2 mutation status in human mammary tissue obtained after prophylactic mastectomy from women at risk of developing BC. Our results demonstrate that RASSF1A expression increased in MCF10DCIS.com cell cultures with matrix stiffness up until ranges corresponding with BiRADs 4 stiffnesses (~16 kPa), but decreased in higher stiffnesses approaching malignancy levels ( kPa). Similarly, higher RASSF1A protein was seen in these cells when co-cultivated with high MD tissue in murine biochambers. Conversely, local stiffness, as measured by collagen I versus III abundance, repressed RASSF1A protein expression in BRCA1, but not BRCA2 gene mutated tissues regional density as measured radiographically repressed RASSF1A in both BRCA1/2 mutated tissues. The combinatory effect of high MD and BRCA mutations on breast cancer risk may be due to RASSF1A gene repression in regions of increased tissue stiffness.
Start Date: 2008
End Date: 12-2011
Amount: $140,000.00
Funder: Australian Research Council
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