Aaron Axford

University of Oxford

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Evaluation of an integrated variable flip angle protocol to estimate coil B₁ for hyperpolarized MRI

Magnetic Resonance in Medicine (2024)

Kylie Yeung Kher Lik Ng Jordan McGing Aaron Axford Sarah Birkhoelzer

The purpose of this work is to validate a simple and versatile integrated variable flip angle (VFA) method for mapping B1 in hyperpolarized MRI, which can be used to correct signal variations due to coil inhomogeneity. Simulations were run to assess performance of the VFA B1 mapping method compared to the currently used constant flip angle (CFA) approach. Simulation results were used to inform the design of VFA sequences, validated in four volunteers for hyperpolarized xenon-129 imaging of the lungs and another four volunteers for hyperpolarized carbon-13 imaging of the human brain. B1 maps obtained were used to correct transmit and receive inhomogeneity in the images. Simulations showed improved performance of the VFA approach over the CFA approach with reduced sensitivity to T1. For xenon-129, the B1 maps accurately reflected the variation of signal depolarization, but in some cases could not be used to correct for coil receive inhomogeneity due to a lack of transmit-receive reciprocity resulting from suboptimal coil positioning. For carbon-13, the B1 maps showed good agreement with a separately acquired B1 map of a phantom and were effectively used to correct coil-induced signal inhomogeneity. A simple, versatile, and effective VFA B1 mapping method was implemented and evaluated. Inclusion of the B1 mapping method in hyperpolarized imaging studies can enable more robust signal quantification.

Flip angle

Flip

10.1002/mrm.30378

Cite

Citations (0)

Lung function of office workers exposed to humidifier fever antigen.

Occupational and Environmental Medicine (1981)

I Ashton Aaron Axford C Bevan J. E. Cotes

Office workers who became sensitised to antigens derived from humidifier sludge developed episodes of fever, malaise, and other symptoms, including polyuria and mild chest tightness. The episodes usually occurred on a Monday evening and were to some extent dose-related. Lung function was assessed over a day shift on two occasions, including one after which almost all the susceptible subjects developed symptoms. The symptoms were preceded by a 6% reduction in forced expiratory volume and vital capacity, a corresponding increase in residual volume, and a reduction in flow rate after 75% vital capacity had been expired. There were no changes in peak expiratory flow, forced expiratory flow at 50% of vital capacity, or transfer factor. In some subjects the transfer factor was apparently reduced 36 hours later, but for this there may have been another explanation. The physiological features were considered to reflect narrowing of small airways in the lung. The changes, however, were minimal and not the main cause of the symptoms. A feature of the episode was the severity of the constitutional symptoms despite the low airborne dust levels.

Vital capacity

Malaise

Residual volume

Anorexia

10.1136/oem.38.1.34

Cite

Citations (14)

Mapping transmit and receive B1 using variable flip angle acquisition on a person-by-person basis for hyperpolarized Carbon-13 and Xenon-129 MRI

Proceedings on CD-ROM - International Society for Magnetic Resonance in Medicine. Scientific Meeting and Exhibition/Proceedings of the International Society for Magnetic Resonance in Medicine, Scientific Meeting and Exhibition (2024)

Kylie Yeung Zack Ravetz Kher Lik Ng Gabriele Abueid W. Hickes

Hyperpolarized MRI allows the imaging of processes such as gas exchange and metabolism. Calibration of transmit and receive (Tx/Rx) B1 is required to account for coil inhomogeneities in reconstruction. A variable flip angle (VFA) method, which is fast and readily implemented, allows for a simultaneous B1/T1 measurement. In this study, a mathematical model of VFA calibration was developed, tested, validated in a hyperpolarized Carbon-13 (13C) phantom and in vivo with hyperpolarized Xenon-129 imaging of human lungs.

Flip angle

10.58530/2023/4498

Cite

Citations (0)

Neurological complications after a single severe exposure to toluene di-isocyanate.

Occupational and Environmental Medicine (1976)

Pamela M. Le Quesne Aaron Axford C. B. McKerrow Amy P. Jones

A total of 23 men complained of neurological symptoms after a single severe exposure to toluene di-isocyanate. Effects of exposure were immediate in five men and consisted of euphoria, ataxia, and loss of consciousness. These men and nine others complained of headache, difficulty in concentration, poor memory, and confusion during the next three weeks. Four years later it was found that nine further men had experienced symptoms that they had not been aware of at three weeks. In all, 13 men still complained of poor memory, personality change, irritability, or depression after four years. Psychometric testing showed a selective defect for relatively long-term recall in those with persistent symptoms at four years.

Irritability

Euphoriant

Depression

Confusion

Personality changes

Memory Impairment

10.1136/oem.33.2.72

Cite

Citations (32)

Integrated B0 and B1 mapping and image correction for hyperpolarized Carbon-13 metabolic imaging in the human brain

Kylie Yeung Jordan McGing Aaron Axford Sarah Birkhoelzer Ayaka Shinozaki

Motivation: B0 and B1 inhomogeneities affect signal quantification and kinetic modelling but are challenging to map and correct for in hyperpolarized MRI due to the signal being exogenous and non-renewable. Goal(s): Develop a fully-integrated B0 and B1 mapping method that does not require specialized pulse sequence programming, additional hardware, nor any additional carbon-13 dose. Approach: Varying echo times and flip angles in the imaging sequence. Results: The in-vivo field maps agreed well with independently acquired maps and could correct for B0 off-resonance blurring and B1 inhomogeneity. Impact: A fully-integrated B0 and B1 mapping and correction method for hyperpolarized carbon-13 MRI is presented and validated in vivo. This method is readily implemented and can improve image quality, helping 13C metabolic imaging become more robust for clinical studies.

Human brain

10.58530/2024/3034

Cite

Citations (0)

Increased Cerebral Lactate-to-Pyruvate Ratio in Primary Progressive Multiple Sclerosis using Hyperpolarized Pyruvate MRI.

Jordan McGing Marco Pisa Andrew Lockhart Kylie Yeung Aaron Axford

Motivation: There remains an absence of imaging modalities capable of probing the neuroinflammatory processes that precede the well-defined brain structural changes in Primary Progressive Multiple Sclerosis (PPMS). Goal(s): We investigated whether hyperpolarized [1-13C]pyruvate MRI can delineate alterations in cerebral glycolytic and oxidative metabolism between treatment naïve PPMS and healthy volunteers. Approach: Two treatment naïve PPMS patients and two sex matched healthy volunteers underwent [1-13C]pyruvate MRI to characterise cerebral glycolytic and oxidative metabolism. Results: A global increase in [1-13C]lactate: [1-13C]pyruvate was found in both PPMS patients relative to sex-matched healthy controls (0.23 ± 0.12 vs 0.16 ± 0.08). The 13C bicarbonate:[1-13C]pyruvate ratio was no different. Impact: These preliminary findings demonstrate a global increase in cerebral glycolytic metabolism in treatment naïve PPMS relative to age and gender matched healthy controls. This may reflect diffuse neuroinflammatory processes and suggests [1-13C]pyruvate MRI could be used to monitor disease activity.

10.58530/2024/2945

Cite

Citations (0)

An end-to-end assessment on the accuracy of adaptive radiotherapy in an MR-linac

Physics in Medicine and Biology (2021)

Aaron Axford Νικόλαος Δικαίος David A. Roberts Catharine H. Clark Philip Evans

To develop and demonstrate an end-to-end assessment procedure for adaptive radiotherapy (ART) within an MR-guided system.A 3D printed pelvic phantom was designed and constructed for use in this study. The phantom was put through the complete radiotherapy treatment chain, with planned internal changes made to model prostate translations and shape changes, allowing an investigation into three ART techniques commonly used. Absolute dosimetry measurements were made within the phantom using both gafchromic film and alanine. Comparisons between treatment planning system (TPS) calculations and measured dose values were made using the gamma evaluation with criteria of 3 mm/3% and 2 mm/2%.Gamma analysis evaluations for each type of treatment plan adaptation investigated showed a very high agreement with pass rates for each experiment ranging from 98.10% to 99.70% and 92.60% to 97.55%, for criteria of 3%/3 mm and 2%/2 mm respectively. These pass rates were consistent for both shape and position changes. Alanine measurements further supported the results, showing an average difference of 1.98% from the TPS.The end-to-end assessment procedure provided demanding challenges for treatment plan adaptations to demonstrate the capabilities and achieved high consistency in all findings.

10.1088/1361-6560/abe053

Cite

Citations (14)

Clinical improvement of patients with emphysema after radiotherapy.

Thorax (1977)

Aaron Axford J. E. Cotes T. J. Deeley Connor W. Smith

In advanced emphysema the reduced lung retractive force permits dynamic compression of the airways during expiration; this gives rise to breathlessness which is often refractory to conventional remedies. Radiotherapy causes shrinkage of lung tissue and has therefore been given as treatment to 10 patients with emphysema. They have been followed for two years, during which time three have died from various causes, but no adverse effect of radiotherapy has been observed. All the patients at some time experienced a reduction in breathlessness on exertion and an increase in the range of their daily activities; the distensibility of their lungs was on average reduced but the response to test exercise was not altered. The possibility that the clinical improvement may have been a placebo effect is now being investigated.

Expiration

Refractory (planetary science)

Pulmonary emphysema

Exertion

10.1136/thx.32.1.35

Cite

Citations (22)

Lung volumes, ventilatory capacity, and transfer factor in healthy British boy and girl twins

Thorax (1973)

J. E. Cotes James M. Dabbs A. Hall Aaron Axford K. M. Laurence

Cotes, J. E., Dabbs, J. M., Hall, A. M., Axford, A. T., and Laurence, K. M. (1973). Thorax, 28, 709-715. Lung volumes, ventilatory capacity, and transfer factor in healthy British boy and girl twins. Normal values are reported for the lung volumes, ventilatory capacity, and transfer factor of 212 healthy British twin children aged 8 to 16 years. The boys and the girls share a common relationship to height for the residual volume, peak expiratory flow rate, and Kco (transfer factor per litre of lung volume). For the inspiratory capacity and the transfer factor, also its membrane component (Dm), the values for the boys exceed those for the girls by, on average, 10%. This difference may be due, at least in part, to the boys taking more exercise.

Residual volume

Girl

Thorax (insect anatomy)

Transfer factor

10.1136/thx.28.6.709

Cite

Citations (59)

Accidental exposure to isocyanate fumes in a group of firemen.

Occupational and Environmental Medicine (1976)

Aaron Axford C. B. McKerrow Amy P. Jones Pamela M. Le Quesne

British Journal of Industrial Medicine, 33

Accidental

Respiratory tract

10.1136/oem.33.2.65

Cite

Citations (56)