23Cerebrovascular reactivity mapping (CVR), using magnetic resonance imaging (MRI) 24 and carbon dioxide as a stimulus, provides useful information on how cerebral blood 25 vessels react under stress. This information has proven to be useful in the study of 26 vascular disorders, dementia and healthy ageing. However, clinical adoption of this 27 form of CVR mapping has been hindered by relatively long scan durations of 7 to 12 28 minutes. By replacing the conventional block presentation of carbon dioxide enriched 29 air with a sinusoidally modulated stimulus, the aim of this study was to investigate 30 whether more clinically acceptable scan durations are possible. Firstly, the conventional 31 block protocol was compared with a sinusoidal protocol of the same duration of 7 32 minutes. Estimates of the magnitude of the CVR signal (CVR magnitude) and the 33 relative timing of the CVR response (CVR phase) were found to be in good agreement 34 between the stimulus protocols. Secondly, data from the sinusoidal protocol was 35 reanalysed using decreasing amounts of data in the range 1 to 6 minutes. The CVR 36 magnitude was found to tolerate this reduction in scan duration better than CVR phase. 37However, these analyses indicate that scan durations in the range of 3 to 5 minutes 38 produce robust data. 39 40 3
Oxygen loaded microbubbles are being investigated as a means of reducing tumour hypoxia in order to improve response to cancer therapy. To optimise this approach, it is desirable to be able to measure changes in tissue oxygenation in real-time during treatment. In this study, the feasibility of using magnetic resonance imaging (MRI) for this purpose was investigated. Longitudinal relaxation time (T1) measurements were made in simple hydrogel phantoms containing two different concentrations of oxygen microbubbles. T1 was found to be unaffected by the presence of oxygen microbubbles at either concentration. Upon application of ultrasound to destroy the microbubbles, however, a statistically significant reduction in T1 was seen for the higher microbubble concentration. Further work is needed to assess the influence of physiological conditions upon the measurements, but these preliminary results suggest that MRI could provide a method for quantifying the changes in tissue oxygenation produced by microbubbles during therapy.
Clinical pain is difficult to study using standard blood oxygenation level dependent (BOLD) imaging. Arterial spin labelling (ASL) offers an attractive alternative as it can measure perfusion during a state or a prolonged stimulation. We propose a paradigm which uses arm repositioning to evoke clinically-relevant musculoskeletal pain in patients with shoulder impingement syndrome. We also present an analysis pipeline using tools from the FMRIB Software Library (FSL) optimised for analysis of perfusion images of middle-aged and elderly patients. Patients with shoulder pain and healthy controls were scanned using multi post-labelling delay pseudocontinuous ASL (pCASL), initially in the supine position and then with one arm raised to evoke clinical pain. The proposed paradigm resulted in increased perfusion in the patient group in cortical and subcortical regions known to be involved in sensory processing and movement integration, such as the ipsilateral primary somatosensory cortex, ipsilateral operculum/insular cortex, ipsilateral putamen and bilaterally in the thalamus, midbrain, and the cerebellum. Perfusion changes were not present in the control group, which suggests that they were related to pain rather than just arm repositioning. The optimised analysis improved registration of perfusion images in comparison to standard approaches.
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