title: Objective measurement of the navicular bursa volume in horses from low field magnetic resonance imaging (MRI) images using 3D Slicer® software
Creators: name: Marcatili, Marco
Publisher: name: University of Glasgow
Year: 2020
Subjects: subject: Lameness, navicular bursa, volume measurement.

description: Background: Navicular bursa (NB) effusion is considered a reaction of the structure to traumatic or degenerative processes. However, NB effusion can also be present in sound horses undergoing intense and regular exercise. To the best of the author’s knowledge an objective non invasive method for measuring the NB volume has not been described to date. Accurate measurement of the NB volume using magnetic resonance imaging MRI would allow a more precise diagnosis and monitoring of response to treatment in horses with navicular bursitis. Objectives: The overall objective was to validate an MRI based method for measuring NB volume in horses using 3D Slicer® software. This was achieved by two separate methodologies, ex vivo and clinical. During the ex vivo part of this study (Chapter 2 and 3) a method for measurement of the NB using MRI datasets was developed. During the clinical study (Chapter 4 and 5) the accuracy and precision of the method were calculated using MRI datasets. The second objective of this study was to evaluate the performance of the current gold standard (subjective assessment by a board certified radiologist) against the newly developed method for cases with normal, mild, moderate and severe NB effusion (Chapter 5). Hypothesis: The accuracy and precision of measurement of NB volume from MRI images in the horse using 3D Slicer® is sufficient for this method to be valuable in the investigation and management of lameness in clinical cases. Material and methods: During the ex-vivo part of the study (Chapter 2) two forelimbs harvested from two adult thoroughbreds euthanised for reasons other than lameness were evaluated. The study design was approved by the Ethics and Welfare Committee of the School of Veterinary Medicine, University of Glasgow. An MRI-compatible needle was positioned in the NB and connected to a syringe. 33 Waterwasinjectedin1000mm incrementsuptoatotalof3000mm.Lowfield ® (0.31T, O-Scan equine , Esaote Veterinary) sagittal T2 FSE and STIR MRI images were acquired before and after each injection. In order to visualise the landmarks for the NB boundaries 5000 mm3 of contrast medium (2 mmol/L, Gadovist®) 2 mmol/L were injected into the bursa of an additional forelimb prior to acquisition of T1 weighted sagittal MRI sequence. Volume was measured ® using 3D Slicer . In Chapter 3 the forelimbs of two adult thoroughbred euthanised for reasons unrelated to lameness were collected. The NB were each injected with water in 500 mm3 increments until a total of 6000 mm3 were injected. Sagittal T2 FSE MR sequences were acquired before the first injection and then after every injection. NB volume was measured by a single observer (intra-observer measurements) from the images using 3D Slicer® as described in Chapter 2. Three additional observers (two diplomates of the European College of Veterinary Surgeons and one diplomate of the American College of Veterinary Surgeons) performed volume measurements on NB injected with 1000, 1500, 2000 and 2500 mm3 in total (inter- observer measurements). The volume injected and volume measured were ®® recorded in a spreadsheet (Excel , Microsoft UK). Excel was used to perform arithmetical calculations and statistical analyses, including plotting graphs, with the exception the Ryan-Joiner statistic for which Minitab® 19 was used (Minitab Ltd). Data were tested for normality using Ryan- Joiner statistic. 3D Slicer® was used to plan the treatment of a clinical case diagnosed with a deep digital flexor tendon (DDFT) core lesion (Chapter 4). The DDFT lesion was treated using intralesional injection of platelet rich plasma (PRP). In chapter 5 twenty adult horses’ front feet MRI studies acquired using a low field ® MRI scanner (0.31T, O-Scan equine , Esaote Veterinary) were evaluated by a board certified radiologist who classified NB effusion as normal, mild, moderate or severe. NB volume was measured from sagittal T2 sequences using 3D Slicer® software. The ability of subjective measurements (current gold standard) to discriminate between groups was analysed using receiver operating characteristic (ROC) curves. Results: The ex-vivo part of the study (Chapter 2) highlighted reduced underestimation of the NB measurements performed on T2 weighted images. However the variability of T2 weighted images was increased compared to STIR images. T2 weighted images were therefore used in the clinical parts of the study (Chapter 4 and 5). Intra-observer accuracy (difference between injected and measured volume) was -40% (i.e. injected volume 1000 mm3 measured volume 600 mm3) over the range 500-6000 mm3 (Chapter 3). The accuracy was improved (-27%) for lower volumes (500-3000 mm3) (i.e. injected volume 1000 mm3 measured volume 730 mm3). Precision was similar for both volume ranges (28% and 30% respectively). The inter-observer accuracy was 54% and precision 73%. One of the observers’ measurements largely overestimated the NB volume. After these measurements were excluded the accuracy and precision were 32% and 69% respectively. Measurement of the volume of the DDFT core lesion after PRP injection resulted in underestimation of the lesion volume by 30% compared to the volume injected (Chapter 4). The results of the clinical study (Chapter 5) showed a statistically significant difference in the NB volume measured between NBs classified as having a normal or mild and severe degree of effusion. There was no statistically significant difference between moderate and all the other groups. A NB volume of 1768 mm3 was able to distinguish between normal/mild navicular bursa volume and moderate/severe navicular bursa effusion with sensitivity and specificity of 90%. Conclusion: The work presented supports the use of 3D Slicer® to objectively measure NB volume from sagittal T2w MR images in the horse. It also suggests that this method is superior to subjective assessment of NB volume. Objective measurement of NB volume may be helpful in indicating the presence of specific pathology (e.g. DDFT tear or fibrocartilage lesions), which may prompt further investigation and inform on best treatment and prognosis. Furthermore, the use of sequential measurement of synovial structures volume could be used to assess the response to the treatment.