Quantification of breast tissue density: correlation between single-sided portable NMR and micro-CT measurements

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 samples 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 samples. 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) and the relative tissue water content obtained from portable-NMR diffusion measurements (R = 0.92, p

Translational and rotational dynamics of water molecules in aligned collagenous tissues: Implications for assessing collagen organisation with magnetic resonance imaging

This thesis investigates the restricted rotational and translational dynamics of water molecules as they interact with collagen fibre networks. Knowledge of the relationship between these motions and the magnetic resonance proton signal can be used to determine collagen fibre organisation in anisotropic, collagen-rich tissues. Both experimental magnetic resonance techniques and theoretical computer simulations were used to probe water-collagen interactions. The results of this work allow for a more comprehensive analysis of collagen organisation, and changes to this organisation as a result of biomechanical load, in collagen-rich tissues using magnetic resonance imaging

Molecular dynamics of a hydrated collagen peptide: Insights into rotational motion and residence times of single-water bridges in collagen

Magnetic resonance transverse spin relaxation\ud time constants (T₂) of water protons in ordered collagenous tissues are dependent on the orientation of the tissue relative to the static magnetic field. This dependence is commonly referred to as the magic angle (MA) effect and has been attributed to the restricted rotational motion of icelike water bridges in the hydrated triple-helix collagen molecule. Understanding of the molecular mechanism of the MA effect is important for clinical and research applications of magnetic resonance spectroscopy and imaging to tissues, such as articular cartilage, tendons, and ligaments. In this work, we have used molecular dynamics simulations to investigate the subnanosecond time scale dynamics of single-water bridges in a model collagen peptide. We ascertain the residence times and the patterns of restricted rotational motion of water molecules. The key findings are strongly anisotropic rotation patterns of water molecules at bridge sites and a dynamic, rather than icelike, nature of the single-water bridges within the individual triple-helix collagen molecule

Corrigendum: Diffusion tensor of water in partially aligned fibre networks (2013 J. Phys. D: Appl. Phys. 46 455401)

This is a corrigendum for the article 2013 J. Phys. D: Appl. Phys. 46 455401 ePrints 6390

Chapter 7: Quantification of articular cartilage microstructure by the analysis of the diffusion tensor

In this Chapter, we present approaches to 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 MRI data into quantitative microstructural and compositional characteristics of articular cartilage. The chapter begins with a brief introduction to diffusion NMR and diffusion imaging, focussing 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

Assessment of collagen fiber orientation dispersion in articular cartilage by small-angle X-ray scattering and diffusion tensor imaging: preliminary results

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 samples. Thirteen pairs of samples were excised from bovine knee joints; each pair was taken from neighboring locations in the same bone. One sample 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 individual 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.</p

Correlative Visualization of Root Mucilage Degradation Using X-ray CT and MRI

Root exudates are a crucial component of the rhizosphere. Often, they take a form of a gel exuded by the plant roots and are thought to influence the soil aggregation, root penetration into soil, soil nutrient availability, immobilization of toxic cations, and microbial activity amongst other things. In addition, the capacity of exudates to store water makes the plants potentially less susceptive to drought. Major components of root exudates are high molecular weight organic compounds consisting of predominantly polysaccharides and proteins, which makes it challenging to visualize using current rhizosphere visualization techniques, such as X-ray computed tomography (CT). In this contribution, we use correlative X-ray CT (resolution ~20 μm) in combination with Magnetic Resonance Imaging (MRI, resolution ~120 μm) to set up groundwork to enable in situ visualization of mucilage in soil. This multimodal approach is necessary because mucilage density closely matches that of water. We use chia seeds as mucilage analog, because it has been found to have a similar consistency to root mucilage. Moreover, to understand mucilage development in time, a series of samples made by chia seeds placed in different porous media were prepared. Structurally and chemically, mucilage breaks down toward a water-like substance over a course of 2 weeks. Depending on its relative concentration, these changes were found to be less dominant when seeds were mixed in porous media. Having set up the groundwork for correlative imaging of chia seeds in water and an artificial soil (Nafion and sand/beads) this enables us to expand this imaging to deal with plant root exudates under natural conditions

Changes in tissue diffusion and anisotropy following mechanical loading of ovine annulus fibrosus: A pilot study using magnetic resonance imaging

The current pilot study sought to explore the functional micro-mechanics of the anulus fibrosus using both imaging and experimental methods, in order to better understand the underlying mechanisms which govern the interplay between disc mechanical function and microstructure. A comparison of DTI of anulus fibrosus samples before and after mechanical testing showed clear changes in diffusivity, indicating the tissue becomes more anisotropic following mechanical testing. This increase in anisotropy is possibly due to the collagen fibres becoming more aligned

Correlative visualization of root mucilage degradation using X-ray CT and NMRI

Root exudates are a crucial component of the rhizosphere. Often, they take a form of a gel exuded by the plant roots and are thought to influence the soil aggregation, root penetration into soil, soil nutrient availability, immobilization of toxic cations, and microbial activity amongst other things. In addition, the capacity of exudates to store water makes the plants potentially less susceptive to drought. Major components of root exudates are high molecular weight organic compounds consisting of predominantly polysaccharides and proteins, which makes it challenging to visualize using current rhizosphere visualization techniques, such as X-ray computed tomography (CT). In this contribution, we use correlative X-ray CT (resolution ~20 μm) in combination with Magnetic Resonance Imaging (MRI, resolution ~120 μm) to set up groundwork to enable in situ visualization of mucilage in soil. This multimodal approach is necessary because mucilage density closely matches that of water. We use chia seeds as mucilage analog, because it has been found to have a similar consistency to root mucilage. Moreover, to understand mucilage development in time, a series of samples made by chia seeds placed in different porous media were prepared. Structurally and chemically, mucilage breaks down toward a water-like substance over a course of 2 weeks. Depending on its relative concentration, these changes were found to be less dominant when seeds were mixed in porous media. Having set up the groundwork for correlative imaging of chia seeds in water and an artificial soil (Nafion and sand/beads) this enables us to expand this imaging to deal with plant root exudates under natural conditions