Quantifying image distortion in MRI for Radiotherapy treatment planning

MRI is a key medical imaging modality. It provides high quality 3D images with unique soft tissue contrast which are useful across a huge range of clinical applications including imaging tumours and for surgical planning. One key application is in radiotherapy, where MRI is increasingly used to plan the delivery of radiation to the site of a tumour while minimising the dose to neighbouring, healthy tissue. Compared to more traditional approaches using CT, MRI provides improved tissue contrast and quantitative imaging biomarker definition (making the tumour easier to delineate) for targeting and treatment monitoring, and also removes the need to expose the patient to Ionising radiation during imaging.

One very important consideration, however, is spatial distortion in the MR images. The presence of a patient in the scanner distorts the applied magnetic field and means that images contain small errors in the size, shape, and position of tissue features. This means that the errors and uncertainties in radiation delivery cannot be fully quantified, meaning that very conservative estimates must be used instead of the careful approaches applied elsewhere in the treatment planning pipeline.

This PhD aims to develop a detailed understanding of MR image distortion to fully quantify its effects and incorporate them into the treatment planning pipeline. The project is partly based on carefully building and imaging test objects (also known as phantoms) which distort the field in a controlled way, building from simple, easily understood objects to more complex objects which are more representative of the geometry and biomarker characteristics of organs such as the brain, and partly on modelling the physics behind image distortion. The aim is to quantitatively characterise the distortion field and to incorporate this into Radiotherapy audits. There is scope to include physics-based modelling, statistics, and other advanced approaches such as AI to inform treatment planning and monitoring with the most complete and accurate description of image distortion possible.

The supervision team comprises experts in MRI, modelling, and measurement science. It is in partnership with a leading MRI phantom manufacturer who bring knowledge of advanced materials and manufacturing capabilities. We also work closely with teams who provide radiotherapy audits nationally across the UK. The successful applicant would gain experience across practical imaging, advanced modelling, image analysis, and measurement science and would have the opportunity to emphasize their own strengths and interests in completing the work.

The project will cover:

1. Development of susceptibility-matched materials, including evaluation of manufacturability and associated uncertainties in manufacturing

2. Design and characterization of 3D printed distortion phantoms of a range of complexities Including mimics of key physical properties

3. MRI scanning of test objects and volunteers

4. Simulation of phantoms and applied field and pulse sequences

5. Assessing the performance of image distortion correction algorithms, quantifying errors in reconstruction

6. Quantification of image-based uncertainties due to field distortion effects and processing