In-vivo digital volume correlation via magnetic resonance imaging : application to positional brain shift and deep tissue injury

• Main Author: Zappala, Stefano
• Format: Dissertation
• Language: English
• Published: Cardiff University 2022
• Subjects: QA75 Electronic computers. Computer science

This thesis aims to investigate the complexity of the physiological mechanical response of soft tissues, providing rich datasets for the verification of clinical systems limiting or preventing tissue injury. A thorough understanding of the sagging of the brain tissue under the effect of gravity (positional brain shift, PBS) is paramount for the design of an effective intra-operative correction of surgical trajectories; rich measurements of the response of the buttock to sitting loads can help the verification of computational models to couple with clinical measures for the prevention and control of pressure ulcers. Digital volume correlation (DVC) consists in measuring the local differences between scans depicting the deformed and undeformed stages of a sample under load, facilitating the characterisation of the mechanical response of the sample. The use of DVC in-vivo is limited, due to the limited quality of the scans constrained by the acquisition setting. Accuracy of three deformable registration methods was first assessed after optimisation against biomechanically plausible ground truths generated via finite element simulations. Against the simulation of PBS, the best accuracy achieved was of one order of magnitude smaller than the resolution of the images. For the simulation of deformations of the buttock due to sitting, optimal accuracy was around 10% of the average deformation fields applied. The best performing methods alongside their optimal parameter sets were then used to perform in-vivo measurements on real magnetic resonance scans of two separate datasets of healthy subjects. For PBS, the study revealed the need for intervention- and Abstract iv patient-specific correction of surgical trajectories given the effect of head geometry and orientation on the shift. For the deformation of the buttock due to sitting, the measure ments gave a three-dimensional depiction of the local and global pattern of deformation, which results were previously limited to thickness or surface measurements.