John Owers-Bradley

John Owers-Bradley
University of Nottingham | Notts · School of Physics and Astronomy

DPhil

About

126
Publications
3,760
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1,950
Citations
Introduction
Additional affiliations
January 1983 - present
University of Nottingham
January 1981 - present
Universität Bayreuth
January 1978 - December 1981
Northwestern University
Position
  • Reseacher

Publications

Publications (126)
Preprint
Full-text available
In dynamic nuclear polarization, polarization is transferred from electron to nuclear spins at low temperatures. So far, it is not possible to predict the relaxation of hyperpolarized solids, and applications are developed largely by trial and error. Here, we study the low-field nuclear spin relaxation in pyruvic acid, doped with trityl. We find th...
Article
Full-text available
Introduction Chronic Obstructive Pulmonary Disease (COPD) affects the small airways and is associated with ventilation heterogeneity. There is little data on the Multiple Breath Washout (MBW) in patients with COPD particularly the variability over eight weeks, using a shortened sulphur hexafluoride (SF 6 ) washout. This work evaluated the repeatabi...
Article
Background Within asthma, the small airways (≤2 mm in diameter) play an important role in pathophysiology. Using a combined clinical-computational approach, we sought to more precisely evaluate the contribution of the small airways to deep-breath induced airway dilation (in the absence of bronchial challenge), which may be impaired in severe asthma...
Conference Paper
Introduction It is reported that 2.7–33% of patients with COPD report sputum retention. This disparity is due to variability in outcomes. Current measures of sputum retention are labour intensive and with large variance, therefore there is a need for an objective measure. This study aims to explore the use of the Lung Clearance Index (LCI) as a sur...
Article
Rationale: Asthma is characterized by disease within the small airways. Several studies have suggested that forced oscillation technique-derived resistance at 5 Hz (R5) - resistance at 20 Hz (R20) is a measure of small airway disease; however, there has been limited validation of this measurement to date.Objectives: To validate the use of forced os...
Article
Full-text available
The use of commercialised forced oscillation (FOT) devices to assess impedance in obstructive diseases such as asthma has gained popularity. However, it has yet to be fully established whether resistance and reactance measurements are comparable across different FOT devices, particularly in disease. We compared two commercially available FOT device...
Conference Paper
Full-text available
Introduction and objectives Chronic Obstructive Pulmonary Disease (COPD) is a small airway disease associated with ventilation heterogeneity. The Lung Clearance Index (LCI) is a potential early marker of lung damage and has been demonstrated to be repeatable within visit for patients with stable COPD. We sought to evaluate the feasibility and repea...
Chapter
This chapter introduces the physical principles underlying hyperpolarized (HP) gas magnetic resonance. The properties of such HP gases, including spin I ≥1/2 noble gas isotopes and low molecular-mass gases like propane, are introduced in the context of biomedical applications. Of particular interest are mechanisms of relaxation and contrast, and th...
Article
Full-text available
Correction for 'Low-field thermal mixing in [1-(13)C] pyruvic acid for brute-force hyperpolarization' by David T. Peat et al., Phys. Chem. Chem. Phys., 2016, 18, 19173-19182.
Article
Full-text available
At ultralow temperatures, longitudinal nuclear magnetic relaxation times become exceedingly long and spectral lines are very broad. These facts pose particular challenges for the measurement of NMR spectra and spin relaxation phenomena. Nuclear spin noise spectroscopy is used to monitor proton spin polarization buildup to thermal equilibrium of a m...
Article
Full-text available
We detail the process of low-field thermal mixing (LFTM) between (1)H and (13)C nuclei in neat [1-(13)C] pyruvic acid at cryogenic temperatures (4-15 K). Using fast-field-cycling NMR, (1)H nuclei in the molecule were polarized at modest high field (2 T) and then equilibrated with (13)C nuclei by fast cycling (∼300-400 ms) to a low field (0-300 G) t...
Article
Full-text available
Multiple breath wash-out (MBW) testing requires prior wash-in of inert tracer gas. Wash-in efficiency can be enhanced by a rebreathing tracer in a closed circuit. Previous attempts to deploy this did not account for the impact of CO2 accumulation on patients and were unsuccessful. We hypothesised that an effective rebreathe wash-in could be deliver...
Article
Background: Lung clearance index (LCI) is the most frequently reported marker of ventilation heterogeneity (VH) measured non-invasively through multiple breath gas washout (MBW). Aims and objectives: We sought to evaluate the role of two recently reported parameters differentiating increases in LCI due to specific ventilation inequality; LCIvent an...
Article
The multiple-breath inert gas washout parameter acinar ventilation heterogeneity (Sacin) is thought to be a marker of acinar airway involvement but has not been validated by using quantitative imaging techniques in asthmatic patients. We aimed to use hyperpolarized (3)He diffusion magnetic resonance at multiple diffusion timescales and quantitative...
Article
Full-text available
Previous studies found larger lung volumes at school-age in formerly breastfed children, with some studies suggesting an effect modification by maternal asthma. We wanted to explore this further in children who had undergone extensive lung function testing. The current study aimed to assess whether breastfeeding was associated with larger lung volu...
Article
Background Multiple breath inert gas washout (MBW) is a technique for detecting abnormal ventilation distribution in patients with asthma and other airway diseases. Scond and Sacin are measures of convective-dependent inhomogeneity (CDI) and diffusion-convection-dependent inhomogeneity (DCDI) respectively. Hyperpolarised 3He diffusion magnetic reso...
Article
Nuclear magnetic resonance (NMR) techniques are extensively used in many areas of basic and clinical research, as well as in diagnostic medicine. However, NMR signals are intrinsically weak, and this imposes substantial constraints on the amounts and concentrations of materials that can be detected. The signals are weak because of the low energies...
Article
Many approaches are now available for achieving high levels of nuclear spin polarization. One of these methods is based on the notion that as the temperature is reduced, the equilibrium nuclear polarization will increase, according to the Boltzmann distribution. The main problem with this approach is the length of time it may take to approach therm...
Article
Full-text available
THE RESPIRATORY SYSTEM COMPRISES SEVERAL SCALES OF BIOLOGICAL COMPLEXITY: the genes, cells and tissues that work in concert to generate resultant function. Malfunctions of the structure or function of components at any spatial scale can result in diseases, to the detriment of gas exchange, right heart function and patient quality of life. Vast amou...
Article
Full-text available
Rationale: Histologic data from fatal cases suggest that extreme prematurity results in persisting alveolar damage. However, there is new evidence that human alveolarization might continue throughout childhood and could contribute to alveolar repair. Objectives: To examine whether alveolar damage in extreme-preterm survivors persists into late c...
Article
Full-text available
We present results from a study of the nonlinear intermodal coupling between different flexural vibrational modes of a single high-stress, doubly-clamped silicon nitride nanomechanical beam. The measurements were carried out at 100 mK and the beam was actuated using the magnetomotive technique. We observed the nonlinear behavior of the modes indivi...
Article
Over the years, several strategies have been developed for generating highly polarized nuclear spin systems, including dynamic nuclear polarization, optical pumping, and methods exploiting parahydrogen. Here, we present an alternative strategy, using an enhanced 'brute-force' approach (i.e. exposure to low temperatures and high applied magnetic fie...
Article
Variability of peak flow measurements has been related to clinical outcomes in asthma. We hypothesized that the entropy, or information content, of airway impedance over short time scales may predict asthma exacerbation frequency.Sixty-six patients with severe asthma and thirty healthy control subjects underwent impulse oscillometry at baseline, fo...
Article
Introduction and objectives There is evidence that the small airways may have an important role in asthma, and a number of physiological techniques have been developed to assess small airway dysfunction. We aimed to determine the within-visit and between-visit repeatability of putative small airway biomarkers, and explore the inter-relationships be...
Article
Introduction and Objectives Moderate and severe asthma are often associated with a degree of fixed airflow obstruction. We aimed to comprehensively characterise a group of patients with moderate to severe asthma using a variety of standard and novel physiological techniques, including hyperpolarised helium-3 magnetic resonance imaging (He-3 MRI), i...
Article
Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique which can reflect the ventilation inhomogeneity of respiratory airways. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multi-breath-nitrogen (MBNW) washout tests. In this work, instead of using nitrogen, helium is used as the tracer ga...
Article
The current hypothesis that human pulmonary alveolarization is complete by 3 years is contradicted by new evidence of alveolarization throughout adolescence in mammals. We reexamined the current hypothesis using helium-3 ((3)He) magnetic resonance (MR) to assess alveolar size noninvasively between 7 and 21 years, during which lung volume nearly qua...
Article
Full-text available
We present measurements of the dissipation and frequency shift in nanomechanical gold resonators at temperatures down to 10 mK. The resonators were fabricated as doubly-clamped beams above a GaAs substrate and actuated magnetomotively. Measurements on beams with frequencies 7.95 MHz and 3.87 MHz revealed that from 30 mK to 500 mK the dissipation in...
Article
Full-text available
We present results from a study of the dissipation in nanomechanical gold resonators. We fabricated a nanomechanical resonator consisting of a gold wire of width 300 nm, thickness 80 nm and length 7.5μm by etching away the underlying GaAs substrate. At low temperatures the resonator had a fundamental frequency of about 7.95 MHz, in part due to tens...
Conference Paper
Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique for lung function studies which can reflect the ventilation inhomogeneity of our respiratory airways [7,8,9]. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multi-breath-nitrogen (MBNW) washout tests. In this work, instead of using nit...
Article
A magneto-motive detection scheme has often been employed to study dissipation in semiconducting nano-mechanical resonators at millikelvin temperatures. This scheme involves placing the beam in a large applied magnetic field and driving the mechanical resonance by sending rf currents through a thin metal electrode plated on the beam. The motion is...
Article
Full-text available
In this paper we report measurements of the nuclear magnetic resonance (NMR) spectrum of 129Xe adsorbed on silica gel and Grafoil® substrates in a 15 tesla magnetic field and temperatures in the range 10mK to 1K. Liquid 3He is used to shorten the spin lattice relaxation time of the 129Xe spins and obtain a high degree of spin polarization of over 4...
Article
Full-text available
We show that it is possible to induce a large nuclear spin polarization in 129Xe adsorbed on a silica gel substrate using 3He as a relaxant, in a reasonable time. We also describe the complete production cycle for the generation of large quantities of hyperpolarized xenon from xenon gas by a cryogenic method for use in MRI and material science.
Article
Full-text available
The apparent diffusion coefficient of hyperpolarized (3)He in the lungs has been shown to correlate directly in animal models with the peripheral airspace size and can detect changes in lung microstructure. To study in vivo the (3)He apparent diffusion coefficient and to demonstrate its sensitivity to changes in lung morphometry as a result of agin...
Article
To investigate changes in lung microstructure in healthy adult subjects with no smoking history using diffusion-weighted 3He MRI. Diffusion magnetic resonance imaging using hyperpolarized helium 3 (3He) was applied to healthy volunteers to explore the dependence of lung microstructural changes with age, reflected by changes in the apparent diffusio...
Article
Full-text available
Hyperpolarized 129Xe has numerous applications in Nuclear magnetic resonance (NMR) and magnetic resonance imaging(MRI). As an alternative to the laser optical pumping method of production of hyperpolarized 129Xe gas, we have investigated the brute force technique which uses a very high magnetic field and millikelvin temperatures. One obstacle to th...
Article
Concerted double proton transfer in the hydrogen bonds of a carboxylic acid dimer has been studied using 13C field-cycling NMR relaxometry. Heteronuclear 13C-1H dipolar interactions dominate the 13C spin-lattice relaxation which is significantly influenced by the polarisation state of the 1H Zeeman reservoir. The methodology of field-cycling experi...
Article
We present NMR spectra of liquid 3He, confined to a cylindrical cell, in the temperature range from 2.3 to 1000 mK for a static field of 11.33 tesla and range of applied field gradients. The spectra are generated by taking the Fourier transform of the free induction decay (FID) following NMR tipping pulses. For small tipping angles, the spectra exh...
Article
Mechanical resonators, in the form of vibrating wires or torsional oscillators, have long been employed as sensors in liquid 3He and 3He–4He mixtures. The damping of resonators is due to the viscosity of the surrounding liquid which is a strong, well-known function of temperature for bulk Fermi liquids. It is therefore possible to use the viscous d...
Article
Vibrating wire resonators have long been used as probes of the helium liquids. They have been employed as viscometers or thermometers over a wide temperature range and a corresponding range of mean free paths, from the hydrodynamic regime to the ballistic regime. The scattering of helium quasiparticles from the surface of the wire may be diffuse or...
Article
We have investigated the spin-motion of spin-polarised solutions of Fermi-liquid 3He in 4He below 100mK. The linearised version of the equation of motion is solved for a finite cylindrical geometry with fully spin-reflecting boundary conditions, and is used to model an actual NMR spin-echo experiment. We include non-linear gradients as well as the...
Article
To evaluate the use of spin-tagging in conjunction with hyperpolarized gas imaging for monitoring lung ventilation and gas diffusion. Images were taken at 0.15 T using single shot RARE, with hyperpolarized (3)He gas prepared by the metastability exchange technique. Sinusoidal modulation of the longitudinal magnetization (tag) was produced by two 90...
Article
There is currently a debate on whether or not the transverse relaxation time is finite at low temperature in spin-polarized Fermi liquids. The experimental results so far have been contradictory. In this paper, the first in a series of two articles, we present NMR measurements carried out in 6.2% 3He-4He mixture at 11.3 T down to 3.5 mK. A careful...
Article
This is the second article in a series of two dealing with anisotropic spin diffusion. We describe a model for calculating spin-wave modes and spin-echo signals in 3He-4He mixtures. The model takes into account finite-size effects for a cylindrical sample. Using this model, we analyze the data presented in the first article, and conclude that the s...
Article
The problem of restricted diffusion in the presence of the spin rotation effect is investigated theoretically. The concept of diffusion modes is applied to calculate the attenuation of the spin echo signal in a θ-180° NMR sequence. First we study the diffusion modes in a one-dimensional geometry and show that there are in general two types of modes...
Conference Paper
Full-text available
Hyperpolarized gas imaging offers the best method to image air spaces and study lung ventilation [1]. The aim of this work is to investigate the feasibility of lung imaging at low field (0.15T) using small quantities of hyperpolarized comparison of pulse sequences including RARE and FLASH. In addition we have explored the use of tagging as a method...
Article
We present nmr measurements in a 6.2% 3 He- 4 He mixture carried out at 11.3 T with temperatures down to 3.5 mK, yielding a very high B/T ratio. We have measured the transverse spin diffusion with the spin-echo technique. We observe a saturation of the spin diffusion coefficient at low temperature corresponding to an anisotropy temperature Ta13mK....
Article
Measurements of the AC susceptibility and Faraday balance susceptibility performed on CoxGa1-x slow-cooled samples are reported for compositions 0.48<or=x<or=0.58. Measurements were performed in the temperature range 0.5K<T<400K and for magnetic fields of below about 1 mT and 0.75T. Spin-glass behaviour is identified for the composition range 0.50<...
Article
The authors have investigated the weak-localisation corrections to the resistance of AuPd wires of rectangular cross section in which the effective width is shorter than the inelastic scattering length. The transverse magnetoresistance of the wires can be described equally well by an inelastic scattering rate tau 1 varies as T2/3 or T1/2. This conc...
Article
We present NMR measurements in 3He at 150 mK in a high magnetic field leading to non-linear effects caused by the dipolar demagnetisation field. We report the first observation of long-lived free induction decays and provide a theoretical interpretation.
Article
We report new experiments on the transverse and longitudinal spin dynamics of liquid 3 He polarized by an 11.3T field. At the lowest temperatures probed, the transverse spin diffusion coefficient saturates with an apparent anisotropy temperature of Ta=122 mK. This temperature dependence is in accord with the general idea of spin-diffusion anisotro...
Article
The authors have measured the magnetoresistance and Hall resistance of an open-cross structure formed in a two-dimensional electron gas by electrostatic depletion. They observe effects similar to those seen by other authors in more closed geometries. They interpret results using the classical model of Beenakker and van Houten (1989). By measuring t...
Article
Dilute liquid - liquids offer a model system for testing theories of weakly interacting fermions. The ability to spin polarize the nuclei adds an extra dimension to the field. In this review, the extraordinary way in which the polarization of the nuclear spins can modify the macroscopic behaviour of the liquid is explained. Frequent reference to re...