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Osteoarthritis (OA) is reported to be one of the most prevalent diseases in aging horses and it significantly affects high motion joints of the equine distal limb with the distal interphalangeal joint (DIPJ) frequently affected. OA is characterised by cartilage degeneration, in addition to deterioration of other joint tissues including synovium, subchondral bone and ligaments. Joint degeneration causes pain, lameness, poor performance and can lead to premature euthanasia. Chondrocytes are the primary cell type of cartilage and they have limited ability for repair and replication. Early detection of cartilage damage is therefore essential to help prevent irreversible cartilage degeneration and progression of OA. There are no diagnostic tools available to diagnose early onset of disease in either human or veterinary medicine which has led to exploration of quantitative magnetic resonance imaging (MRI) techniques such as T2 mapping. During cartilage deterioration the collagen and proteoglycan content decreases and it is replaced by free water which increases cartilage T2 relaxation time. A small number of T2 mapping studies have been performed in equine joints using high field systems (3.0 T) however, there have not been any T2 mapping studies using low field (0.27 T) MRI, which is the most widely available system in UK equine practice. The first objective of this study was to validate a T2 mapping sequence on a low field MR system and investigate whether T2 relaxation time increases in cartilage with higher OARSI (Osteoarthritis Research Society International) histology scores. Furthermore, the study then aimed to verify low field T2 measurements with the gold standard measurement at high field. Another approach to detect early OA is analysis of microRNAs in biofluids. MicroRNAs are small noncoding RNAs that regulate gene expression at the post-transcriptional level by inhibiting translation or degrading target messenger RNA. During cellular damage microRNA profiles change, which can be associated with specific diseases. The second objective of this research was to identify differentially expressed microRNAs in the plasma and synovial fluid of horses with mild and severe DIPJ OA through small RNA-sequencing; diagnosis of OA was based on macroscopic and histological evaluation. This was followed by microRNA mimic and inhibitor transfection experiments to determine the effects of selected OA related microRNAs on equine chondrocytes in monolayer culture. To investigate the first objective eight phantoms with known T2 values underwent low field MRI to validate the T2 mapping sequence on the low field MR system and then 38 ex vivo DIPJs were imaged. A further 9 ex vivo DIPJs were imaged on both the low and high field MR system. After imaging, the DIPJs were disarticulated and samples collected for histology. Sections were graded using the OARSI scoring system. The T2 relaxation time corresponding to the section of cartilage tissue sampled was then calculated. The study successfully validated a T2 mapping sequence on a low field MR system and there was a positive correlation between low and high field T2 measurements. Results found a higher mean T2 (83-104 ms) in pathological cartilage tissue examined in this study compared to normal equine cartilage tissue, which is reported to be 40-61 ms. However, the T2 relaxation time did not increase with increasing OARSI grades in the samples analysed in this study. Small RNA-sequencing demonstrated three microRNAs (miR-16, miR-25 and miR-92a) were significantly downregulated in equine synovial fluid from horses with severe OA (P In conclusion, this thesis presents the first study to investigate quantitative T2 mapping of cartilage on a low field MR system. T2 relaxation time did not increase with increasing OARSI grades however, additional developments enhancing spatial resolution may enable T2 mapping to become a useful diagnostic tool in the future. The thesis also presents novel data on the role of miR-92a in the equine chondrocyte and further research developing in vitro 3D culture systems to allow retention of the chondrogenic phenotype will permit more studies to investigate miR-92a in the future.

The extension from Quantitative Magnetic Resonance Imaging to synthetic imaging has the clear advantage of being able to continually image the patient after the exam. MR techniques such as DWI are commonly used but have some clear disadvantages resulting from the use of echoplanar imaging. It should then be asked whether one imaging technique is objectively better. If one technique is better, the incorporation in clinical settings could produce better diagnostic rates, and save valuable time. In order to quantitatively assess the quality of these techniques, the SNR and CNR values of similar tissues were compared. The pre-analysis discussion concentrating on the spatial resolution and artifacts, supports that synthetic images have an advantage over DWI due to higher resolution and absence of artifacts. The SNR and CNR values were calculated for each patient and image type for the comparison, initially assuming that the synthetic images would have a higher mean SNR and CNR. In most cases the differences between scan types was found to not be statistically significant. In conclusion, this analysis could not support the initial theory that the synthetic images had a higher SNR or CNR. The research shows that they are more likely to be comparable. An investigation of the diagnostic power of the synthetic in comparison to standard DWI would give clinical relevance to these results.

Magnetic Resonance (MR) is an exceptionally powerful and versatile measurement technique. The basic structure of an MR experiment has remained nearly constant for almost 50 years. Here we introduce a novel paradigm, Magnetic Resonance Fingerprinting (MRF) that permits the non-invasive quantification of multiple important properties of a material or tissue simultaneously through a new approach to data acquisition and post-processing. MRF provides a new mechanism to quantitatively detect and analyze complex changes that can represent physical alterations of a substance or early indicators of disease. MRF can also be used to specifically identify the presence of a target material or tissue, which will increase the sensitivity, specificity, and speed of an MR study, and potentially lead to new diagnostic testing methodologies. Because of its basis in pattern recognition, MRF inherently suppresses measurement errors and thus can improve accuracy and efficiency compared to previous approaches. By taking the advantage of the extra degrees of freedom of the MRF concept, the MRF-Music sequence is presented as a special form of the MRF to improve the patients’ comfort level during the MR scans while still maintaining a high image quality and scan efficiency.