EPI at 7T : functional imaging and off-resonance correction techniques

The work presented in this thesis describes the development and implementation of a number of ideas and methods that allow fMRI to be carried out using echo-planar imaging at ultra high field strength, despite the significant problems associated with this. In the first study, EPI is used to probe how the gradient echo (GE) and spin echo (SE) BOLD responses relate to the underlying neurological processes, whilst the brain is in both its active and resting states. These finding show that SE BOLD contrast is harder to detect but less localised to areas around large draining veins than GE BOLD contrast and thus potentially more localised to sites that represent true functional areas of activation. The second study describes how dynamic delta B0 mapping can be performed during fMRI experiments with a hyperoxic challenge in order to assess the magnitude and extent of delta B0 effects that arise due to susceptibility differences between air and tissue. Developing on this, this work describes the steps involved in the design and implementation of a dual echo GE/SE EPI sequence and how it can be used to enable off-resonance effects, such as image distortion and signal concentration/dilution, to be corrected on a dynamic basis for, simultaneously acquired, GE and SE data. The final study demonstrates how such a sequence can be used to detect resting state networks. Showing that the correspondingly low temporal separation of the GE and SE data allows GE and SE BOLD contrast mechanisms to be compared in a number of novels ways in different resting state networks

EPI at 7T : functional imaging and off-resonance correction techniques

The work presented in this thesis describes the development and implementation of a number of ideas and methods that allow fMRI to be carried out using echo-planar imaging at ultra high field strength, despite the significant problems associated with this. In the first study, EPI is used to probe how the gradient echo (GE) and spin echo (SE) BOLD responses relate to the underlying neurological processes, whilst the brain is in both its active and resting states. These finding show that SE BOLD contrast is harder to detect but less localised to areas around large draining veins than GE BOLD contrast and thus potentially more localised to sites that represent true functional areas of activation. The second study describes how dynamic delta B0 mapping can be performed during fMRI experiments with a hyperoxic challenge in order to assess the magnitude and extent of delta B0 effects that arise due to susceptibility differences between air and tissue. Developing on this, this work describes the steps involved in the design and implementation of a dual echo GE/SE EPI sequence and how it can be used to enable off-resonance effects, such as image distortion and signal concentration/dilution, to be corrected on a dynamic basis for, simultaneously acquired, GE and SE data. The final study demonstrates how such a sequence can be used to detect resting state networks. Showing that the correspondingly low temporal separation of the GE and SE data allows GE and SE BOLD contrast mechanisms to be compared in a number of novels ways in different resting state networks

Dual-Phase Cardiac Diffusion Tensor Imaging with Strain Correction

Purpose In this work we present a dual-phase diffusion tensor imaging (DTI) technique that incorporates a correction scheme for the cardiac material strain, based on 3D myocardial tagging. Methods: In vivo dual-phase cardiac DTI with a stimulated echo approach and 3D tagging was performed in 10 healthy volunteers. The time course of material strain was estimated from the tagging data and used to correct for strain effects in the diffusion weighted acquisition. Mean diffusivity, fractional anisotropy, helix, transverse and sheet angles were calculated and compared between systole and diastole, with and without strain correction. Data acquired at the systolic sweet spot, where the effects of strain are eliminated, served as a reference. Results: The impact of strain correction on helix angle was small. However, large differences were observed in the transverse and sheet angle values, with and without strain correction. The standard deviation of systolic transverse angles was significantly reduced from 35.9±3.9° to 27.8°±3.5° (p<0.001) upon strain-correction indicating more coherent fiber tracks after correction. Myocyte aggregate structure was aligned more longitudinally in systole compared to diastole as reflected by an increased transmural range of helix angles (71.8°±3.9° systole vs. 55.6°±5.6°, p<0.001 diastole). While diastolic sheet angle histograms had dominant counts at high sheet angle values, systolic histograms showed lower sheet angle values indicating a reorientation of myocyte sheets during contraction. Conclusion: An approach for dual-phase cardiac DTI with correction for material strain has been successfully implemented. This technique allows assessing dynamic changes in myofiber architecture between systole and diastole, and emphasizes the need for strain correction when sheet architecture in the heart is imaged with a stimulated echo approach

Creating and curating an archive: Bury St Edmunds and its Anglo-Saxon past

This contribution explores the mechanisms by which the Benedictine foundation of Bury St Edmunds sought to legitimise and preserve their spurious pre-Conquest privileges and holdings throughout the Middle Ages. The archive is extraordinary in terms of the large number of surviving registers and cartularies which contain copies of Anglo-Saxon charters, many of which are wholly or partly in Old English. The essay charts the changing use to which these ancient documents were put in response to threats to the foundation's continued enjoyment of its liberties. The focus throughout the essay is to demonstrate how pragmatic considerations at every stage affects the development of the archive and the ways in which these linguistically challenging texts were presented, re-presented, and represented during the Abbey’s history

Six minute walk distance or stair negotiation? Choice of activity assessment following total knee replacement

Background and Purpose. Physiotherapists evaluating changing functional performance in patients who have undergone total knee replacement (TKR) will often measure a number of gait-related activities, including six-minute walk distance (6MWD) and the capacity to ascend and descend stairs. In this report, we investigated the correlations between the 6MWD and stair ascent and descent power in a group of patients who had participated in a clinical trial at 2, 8 and 26 weeks post-TKR to establish whether there is redundancy in conducting all three tests. Methods. Retrospective analysis of data from a clinical trial was used. One hundred patients (57 female, 43 male) were tested on their 6MWD and power generated and absorbed during stair ascent and descent, respectively. Linear regression modelling was used to determine correlations between pairs of variables at the three measurement intervals. Results. There were consistent relationships between each pair of variables at each measurement interval (r > 0.70; p < 0.001) and also a consistency in the regressions between measurements. Conclusion. The findings indicate that there is no particular benefit to the therapist in measuring more than one of the three variables if the purpose of the measurement is to serve as an indicator of ambulatory functional status for routine clinical assessment

Predictors of functional ambulation and patient perception following total knee replacement and short-term rehabilitation

Purpose. To investigate whether measured and patient-perceived function 6 months after total knee replacement (TKR) can be predicted from factors measured during post-operative rehabilitation. Method.Retrospective analysis of data from a randomised clinical trial involving 100 patients after TKR. High- and low-performing subjects for pain, WOMAC score and 6-min walk test (6MWT) at 2, 8 and 26 weeks post-TKR were partitioned and analysed. Multiple stepwise regression analysis was applied to the contributing factors to determine associations with outcome. Results.Prediction of outcome was unconvincing based upon variables recorded at 2 weeks; however, status at 8 weeks was a better indicator of functional performance and perception at 26 weeks. 6MWT at 26 weeks could be predicted from VAS pain scores and 6MWT at 8 weeks (r0.789; p<0.001). Prediction of pain and patient perceived function at 26 weeks was also dependent on performance in 6MWT at 8 weeks (r 0.51; p<0.05). Males and those with lower body mass index values demonstrated better functional outcomes. Conclusion.Functional status at 2 weeks post-surgery gives few indicators of ultimate status, possibly because of pain, joint swelling and other immediate post-operative factors. However, measurements taken at 8 weeks, following an outpatient-based exercise programme, provides a reasonable estimate of performance and response 26 weeks after surgery. Patient and clinician expectations for longer-term recovery could be informed by these findings

Land-based versus water-based rehabilitation following total knee replacement : a randomized, single-blind trial

Objective. To compare outcomes between land-based and water-based exercise programs delivered in the early subacute phase up to 6 months after total knee replacement (TKR). Methods. Two weeks after surgery (baseline), 102 patients were randomized to participate in either land-based (n = 49) or water-based (n = 53) exercise classes. Treatment parameters were guided by current clinical practice protocols. Therefore, each study arm involved 1-hour sessions twice a week for 6 weeks, with patient-determined exercise intensity. Session attendance was recorded. Outcomes were measured at baseline and at 8 and 26 weeks postsurgery. Outcomes included distance on the 6-Minute Walk test, stair climbing power (SCP), the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index (n = 85 English-proficient patients), visual analog scale for joint pain, passive knee range of motion, and knee edema (circumference). Planned orthogonal contrasts, with an intent-to-treat approach, were used to analyze the effects of time and time-group interactions. Results. Compliance in both groups was excellent with 81% attending 8 or more sessions. Loss to followup was 5%. Significant improvements were observed across time in all outcomes at 8 weeks, with further improvements evident in all variables (except WOMAC pain) at 26 weeks. Minor between-group differences were evident for 4 outcomes (SCP, WOMAC stiffness, WOMAC function, and edema) but these appear clinically insignificant. Conclusion. A short-term, clinically pragmatic program of either land-based or water-based rehabilitation delivered in the early phase after TKR was associated with comparable outcomes at the end of the program and up to 26 weeks postsurgery

Status of physiotherapy rehabilitation after total knee replacement in Australia

BACKGROUND AND PURPOSE: Owing to a scarcity of clinical research, evidence-based clinical guidelines are not available to guide physiotherapy rehabilitation after total knee replacement surgery. This is despite the fact that, annually, over 20000 patients in Australia, over 300 000 patients in North America and 36 000 patients in the UK potentially require rehabilitation at this time to regain functional independence and to resume recreational and work-related physical activities. This survey of clinicians aimed to describe standard (usual) care after total knee replacement in Australia and to provide possible explanations for practice variance, if such variation exists. METHOD: A nationwide postal survey involving public and privately funded hospital physiotherapy departments was conducted. Purposive sampling was used to randomly select hospitals from the National Joint Replacement Registry. A series of closed and open-ended protocol-based questions were asked. RESULTS: A response rate of 65% (65/100) was obtained. Elements of consistency and diversity across the acute and post-acute phases were evident. Consistent findings included the provision of gait retraining and exercise prescription in the acute period, the requirement for independent ambulation as a criterion for discharge from acute care and the routine referral to ongoing outpatient or community-based physiotherapy. Less consistency was reported for the use of continuous passive motion and cryotherapy in the acute phase, the modes of ongoing rehabilitation, discharge from rehabilitation criteria and the tools for measuring outcomes. Both institutional and non-institutional factors appeared to explain the demonstrated practice variation. CONCLUSIONS: In order to propagate evidence-based practice guidelines and uniformity in care, well-designed clinical trials are required to identify cost-effective rehabilitation programmes after total knee replacement