Physics DPhil Projects

We are interested to supervise DPhil students in the following research projects, for entry in October 2016. We are also willing to consider other projects within our research areas. These projects do not imply funded positions - potential students would need to secure funding, either within Oxford or externally.

OPTIMAL STRATEGY FOR MEASURING CEREBROVASCULAR REACTIVITY

Supervisors: Dr Nic Blockley and Prof Peter Jezzard

Good cerebrovascular reactivity (CVR) is important to the healthy function of the brain. It represents the ability of blood vessels to dilate to increase blood flow and hence increase the delivery of oxygen and glucose to tissue. Impairment of CVR is common to many conditions from steno-occlusive disease to dementia to the ageing process. Until recently it appeared that MRI based approaches to mapping CVR had converged on a simple paradigm whereby blocks of breathing air with an elevated carbon dioxide (CO2) content are interleaved with breathing room air. However, the introduction of shaped CO2 challenges has blown the field open enabling information about the timing of CVR changes to be measured and measures of the entire vasodilatory range to be performed. In this project we will establish which of these methods offers the best balance of robust CVR information, patient comfort and examination duration.

REAL TIME CORRECTION OF HEAD MOTION

Supervisors: Prof Peter Jezzard

A problem affecting many MRI scan sequences is patient motion during the scan. There are several approaches to solving the problem. Probably the optimal solution is to monitor the patient motion in real time and then update the scan coordinate system as the scan is acquired so that the subject stays "fixed" in the scan acquisition coordinate frame. The route that we are trying in Oxford is to use a "navigator" MRI scan to track the position of the subject, and then continuously track the motion of the subject. This strategy can be applied to a number of different scan sequences, including functional and structural sequences, imaging and spectroscopy sequences, 3T and 7T sequences, and for both rigid body and deformable tissues. The project would involve a heavy element of coding in C++, as it would require use of the Siemens Image Calculation Environment (ICE). As such, someone with a good understanding of scientific programming would be required.

DIFFUSION IMAGING OF TISSUE MICROSTRUCTURE

Supervisors: Prof Karla Miller and Prof Saad Jbabdi

The microscopic structure of tissue is a key factor in proper tissue function. For example, the conduction of electrical signals is directly related to the size and insulation of axonal projections that carry information between brain regions. MRI has potential for detecting these properties by using water molecules as a probe for their molecular environment. We have been developing techniques for modeling these properties to enable extraction of biologically-meaningful microstructural properties. The next major step is to achieve measurements that can be obtained non-invasively in living subjects, a goal that remains elusive due to the limitations of clinical MRI scanners. We will explore the potential for our 7-tesla scanner to provide sufficient signal and gradient power to enable these measurements, with an aim to demonstrating their application in brain plasticity and/or neurodegeneration. This project will require skills in theoretical physics and software development, as well as a strong interest in biophysical modeling and neuroscience.

OXYGEN-BASED CONTRAST AS A SAFER ALTERNATIVE TO GADOLINIUM

Supervisors: Dr Nic Blockley and Prof Peter Jezzard

Gadolinium, in the form of Gd-DTPA, is frequently used as a contrast agent to measure several physiological properties of brain tissue, such as blood flow, blood volume and blood arrival time. However, several side effects of these contrast agents have been reported in recent years and this may limit their use in the future. Therefore it is desirable to develop alternative methods with a lower risk profile. Recently we have shown that respiratory challenges (administering gases with a different composition to room air) may enable us to acquire similar information. In this project we will investigate the use of oxygen as a contrast agent that is sensitive to blood volume and which may also be made sensitive to blood arrival time. This project will involve biophysical modelling of the interaction between brain physiology and the MR signal and acquisition of experimental data utilising multiple contrasts including oxygen and Gadolinium based contrast agents.