Antony Hodgson


Relevant Degree Programs


Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Nov 2020)
Automatic characterization of developmental dysplasia of the hip in infants using ultrasound imaging (2018)

Developmental dysplasia of the hip (DDH) is the most common pediatric hip condition, representing a spectrum of hip abnormalities ranging from mild dysplasia to irreducible hip dislocation. Thirty-three years ago, the introduction of the Graf method revolutionized the use of ultrasound (US) and replaced radiography for DDH diagnoses. However, it has been shown that current US-based assessments suffer from large inter-rater and intra-rater variabilities which can lead to misdiagnosis and inappropriate treatment for DDH. In this thesis, we propose an automatic dysplasia metric estimator based on US and hypothesize that it significantly reduces the subjective variability inherent in the manual measurement of dysplasia metrics. To this end, we have developed an intensity invariant feature to accurately extract bone boundaries in US images, and have further developed an image processing pipeline to automatically discard US images which are inadequate for measuring dysplasia metrics, as defined by expert radiologists. If found adequate, our method automatically measures clinical dysplasia metrics from the US image. We validated our method on US images of 165 hips acquired through clinical examinations, and found that automatic extraction of dysplasia metrics improved the repeatability of diagnoses by 20%. We extended our automatic metric extraction method to three-dimensional (3D) US to increase robustness against operator dependent transducer placement and to better capture the 3D morphology of an infant hip. We present a new random forests-based method for segmenting the femoral head from a 3D US volume, and a method for automatically estimating a 3D femoral head coverage measurement from the segmented head. We propose an additional 3D hip morphology-derived dysplasia metric for identifying an unstable acetabulum. On 40 clinical hip examinations, we found our methods significantly improved the reproducibility of diagnosing femoral head coverage by 65% and acetabular abnormalities by 75% when compared to current standard methods.

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Towards a novel minimally invasive three dimensional ultrasound imaging based computer assisted orthopaedic surgery system for bone fracture reduction (2010)

Current practice in orthopaedic surgery relies on intra-operative two dimensional (2D) fluoroscopy as the main imaging modality for localization and visualization of bone tissue, fractures, implants, and surgical tool positions. However, with such projection imaging, surgeons typically face considerable difficulties in accurately localizing bone fragments in three dimensional (3D) space and assessing the adequacy and accuracy of reduced fractures. Furthermore, fluoroscopy involves significant radiation exposure. Ultrasound (US) has recently emerged as a potential non-ionizing imaging alternative that promises safer operation while remaining relatively cheap and widely available. US image data, however, is typically characterized by high levels of speckle noise, reverberation, anisotropy and signal dropout which introduce significant difficulties in interpretation of captured data, automatic detection and segmentation of image features and accurate localization of imaged bone surfaces.In this thesis we propose a novel technique for automatic bone surface and surgical tool localization in US that employs local phase image information to derive symmetry-based features corresponding to tissue/bone or tissue/surgical tool interfaces through the use of 2D Log-Gabor filters. We extend the proposed method to 3D in order to take advantage of correlations between adjacent images. We validate the performance of the proposed approach quantitatively using realistic phantom and in-vitro experiments as well as qualitatively on in-vivo and ex-vivo data. Furthermore, we evaluate the ability of the proposed method in detecting gaps between fractured bone fragments. The current study is therefore the first to show that bone surfaces, surgical tools and fractures can be accurately localized using local phase features computed directly from 3D ultrasound image volumes. Log-Gabor filters have a strong dependence on the chosen filter parameters, the values of which significantly affect the outcome of the features being extracted. We present a novel method for contextual parameter selection that is autonomously adaptive to image content. Finally, we investigate the hypothesis that 3D US can be used to detect fractures reliably in the emergency room with three clinical studies. We believe that the results presented in this work will be invaluable for all future imaging studies with US in orthopaedics.

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Quantitative modelling and assessment of surgical motor actions in minimally invasive surgery (2009)

The goal of this research was to establish a methodology for quantifying performance ofsurgeons and distinguishing skill levels during live surgeries. We integrated threephysical measures (kinematics, time and movement transitions) into a modelingtechnique for quantifying performance of surgical trainees. We first defined a newhierarchical representation called Motor and Cognitive Modeling Diagram forlaparoscopic procedures, which: (1) decomposes ‘tasks’ into ‘subtasks’ and at the very detailed level into individual movements ‘actions’; and (2) includes an explicit cognitive/motor diagrammatic representation that enables to take account of the operative variability as most intraoperative assessments are conducted at the ‘whole procedure’ level and do not distinguish between performance of trivial and complicated aspects of the procedure. Then, at each level of surgical complexity, we implemented specific mathematical techniques for providing a quantitative sense of how far a performance is located from a reference level:(1) The Kolgomorov-Smirnov statistic to describe the similarity between twoempirical cumulative distribution functions (e.g., speed profiles)(2) The symmetric normalized Jensen-Shannon Divergence to compare transitionprobability matrices(3) The Principal Component Analysis to identify the directions of greatest variability in a multidimensional space and to reduce the dimensionality of the data using a weight space.Two experimental studies were completed in order to show feasibility of our proposedassessment methodology by monitoring movements of surgical tools while: (1) dissecting mandarin oranges, and (2) performing laparoscopic cholecystectomy procedures at the operating room to compare residents and expert surgeons when executing two surgical tasks: exposing Calot’s Triangle and dissecting the cystic duct and artery.Results demonstrated the ability of our methodology to represent selected tasks using the Motor and Cognitive Modeling Diagram and to differentiate skill levels. We aim to use our approach in future studies to establish correspondences between specific surgical tasks and the corresponding simulations of these tasks, which may ultimately enable us to do validated assessments in a simulated setting, and to test its reliability in differentiating skill levels at the operating room as the number of subjects and procedures increase.

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Master's Student Supervision (2010 - 2018)
Monitoring stroke rehabilitation of arm movement outside of the clinical setting (2018)

Stroke is the leading cause of disability in North America. Fifty-four percent of stroke survivors suffer from upper body hemiparesis, a weakness that limits the client’s ability to perform functional tasks with the affected side of the body. Stroke rehabilitation aims to recover limb mobility through thousands of repeated functional movements that lead to neural regeneration. However, time constraints in clinical rehabilitation lead to an average of 32 arm repetitions per session, which is insufficient for optimal recovery. Accurate monitoring of client activity outside of the clinical setting could enable therapists to track what they do, improving recovery. To address this problem, we have designed the Arm Rehabilitation Monitor (ARM), a wrist-worn device that collects movement data in unconstrained environments, and processes it offline to identify reach actions. Reach actions were identified as functionally meaningful tasks that lead to better rehabilitation. We enrolled 15 participants with mild to moderate hemiparesis due to stroke to perform two activities: (1) a functional assessment of the arm, and (2) an activity of daily living (ADL) task that consisted of making a pizza. The data recorded by the IMU on both activities was used to train three different machine learning algorithms (Random Forest, Convolutional Neural Networks and Shapelets) to detect reaching gestures.We found that the ARM obtained the best results with the Random Forest and CNN algorithms. The CNN algorithm had the best F1-score (0.523) for the Clinic-Home inter-subject tests, while the RF algorithm obtained the best score (0.486) in the Clinic-Home intra-subject configuration. We used the ARM to estimate the time spent reaching and the number of reach counts. The CNN algorithm predicted the reach time for the Clinic-Home inter-subject tests to be 1.07x ( 0.55x) the true reach time and the reach counts to be 1.28x ( 0.40x) the true number of reach gestures. In turn, the RF algorithm predicted the reach time for the Clinic-Home intra-subject configuration to be 1.16x ( 0.84x) and the reach counts to be 1.26x (0.40x). Both results have a smaller standard deviation when estimating reach counts than a comparable commercial accelerometer worn on the wrist.

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A clinical C-arm base-tracking system using computer vision for intraoperative guidance (2017)

Mobile C-arm X-ray machines are commonly used for imaging during orthopaedic surgeries to visualize internal anatomy during procedures. However, there is evidence indicating that excess operating time and radiation exposure result from the use of scouting images to aid C-arm positioning during surgery. Additionally, C-arms are currently used primarily as a qualitative tool. Several techniques have been proposed to improve positioning, reduce radiation exposure, and increase quantitative utility, but they require accurate C-arm position tracking. There have been attempts by other research groups to develop C-arm tracking systems, but there are currently no solutions suitable for use in an operating room. The objective of this thesis is therefore to present the development and verification of a real-time C-arm base-tracking system called OPTIX (On-board Position Tracking for Intraoperative X-rays).The proposed tracking system uses a single floor-facing camera mounted to the base of a C-arm. A computer vision algorithm was developed that tracks motion relative to the operating room floor. This system is capable of relative motion tracking as well as absolute position recovery for previous positions.The accuracy of the system was evaluated on a real C-arm in a simulated operating room. The experimental results demonstrated that the relative tracking algorithm can measure C-arm translation with errors of less than 0.75% of the total distance travelled, and orientation with errors better than 5% of the cumulative rotation. With the incorporated loop closure step, OPTIX can be used to achieve C-arm repositioning with translation errors of less than 1.10±0.07 mm and rotation errors of less than 0.17 ±0.02°. These results are well within the desired system requirements of 5 mm and 3.1°.The system has shown promising results for use as a C-arm base-tracking system. The system has clinically acceptable accuracies and should lead to a reduced need for scouting images when re-obtaining a previous position. The base-tracking system can be integrated with a C-arm joint tracking system, or implemented on its own for steering guidance. When implemented in an operating room, OPTIX has the potential to lead to a reduction in operating time and harmful radiation exposure to surgical staff.

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Artificial X-ray imaging system (AXIS) design and evaluation on C-arm performance in operating room and educational settings (2017)

Fluoroscopic C-arms are operated by medical radiography technologists (MRTs) in Canadian operating rooms (ORs). Newly trained MRTs often experience most of their practical learning curve with C-arms in the OR, where achieving the radiographic views requested by surgeons can be challenging. New MRTs often require several scout X-rays during C-arm positioning, resulting in unnecessary radiation exposure and added OR time. To address this problem we have designed an Artificial X-ray Imaging System (AXIS) in order to assess the utility of artificial X-rays in improving the C-arm positioning performance by inexperienced users. AXIS is designed to generate Digitally Reconstructed Radiographs (DRRs), or artificial X-ray images, based on the relative position of a C-arm and manikin. We enrolled 30 participants into our user study, each of whom performed four activities: an introduction session, an AXIS-guided evaluation, a non-AXIS-guided evaluation, and a questionnaire. The main goal of the study was to compare C-arm positioning performance with and without AXIS guidance. For each evaluation, the participants had to replicate a set of target X-ray images by taking real radiographs of the manikin with the C-arm. During the AXIS evaluation, artificial X-rays were generated at 2 Hz for guidance, while in the non-AXIS evaluation, the participants had to acquire real X-rays to guide them toward the correct view. We recorded the number of real X-rays and time required per task, as well as tracked the C-arm’s pose and compared it to the target pose to determine positioning accuracy. We found that users required 53% fewer scout X-rays and achieved 10% better C-arm displacement accuracies when guided by AXIS, without requiring more time to complete the imaging tasks. From the questionnaires we found that, on average, participants felt significantly more confident in their ability to capture correct anatomical views when they were guided by AXIS. Moreover, the participants found the usefulness of AXIS in guiding them to the desired view to be ‘very good’. Overall, we are encouraged by these findings and plan to further develop this system with the goal of deploying it both for training and intraoperative uses.

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LaserGauge: development of a device for automatic measurement of bore depth in bone during surgery (2017)

Purpose: This thesis comprised two main phases. Initial work focused on clarifying the need and use case for a novel device to measure drilled bore depth in bone during osteosynthesis surgery. Next, I demonstrated the feasibility and reliability of an optical sensing device for automatic measurement of drilled bore depth in bone during surgery compared with conventional methods.Methods: I completed a structured Needs Assessment followed by an Engineering Design process to develop a series of prototypes using laser displacement sensors mounted on a surgical drill to determine drilled bore depth in bone. In all versions of the prototypes bore depth was computed based on a characteristic pattern of drilling velocity in bicortical bone. Prototypes consisted of one or more laser displacement sensors sending displacement and time data to a microprocessor and then a personal computer. After data filtering with a second order Butterworth filter velocity and acceleration were calculated using differentiation and double differentiation. Characteristic spikes in velocity and acceleration indicated cortical breach and allowed identification of bore depth. Exploratory experiments were done with multiple sensor arrangement concepts in porcine long bones, and more rigorous final evaluation experiments were done with the lead designs in pig hind limbs with comparison to CT scan as ‘gold standard’.Results: In exploratory experiments a design involving two laser displacement sensors angled towards the drilling axis measuring distance from a mock drill guide performed better than alternative designs. This design in final evaluation experiments showed superior performance to the conventional depth gauge under three clinically relevant drilling conditions (standard deviation 0.70 mm vs. 1.38 mm, 0.86 mm vs. 3.79 mm, 0.80 mm vs. 3.19 mm). A positive bias was present in all drilling conditions.Conclusions: An optical sensing device can be used to measure bore depth in bone during surgery.

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Leveraging the Use of Existing C-Arms for Roentgen Stereophotogrammetric Analysis (2016)

“You can’t improve it unless you can measure it” is a common sentiment in engineering. For total knee replacement patients, failed implants requiring revision surgery is a significant risk. Our long-term goal, therefore, is to develop and evaluate a protocol that will allow us to accurately measure the full 3D position of an implant in the early post-surgical period in order to detect signs of relative motion occurring between implant and bone. By doing this, we will be able to gain insights into the failure mechanisms behind total knee replacement implants. The 'gold standard' method for measuring relative motion is known as Roentgen Stereophotogrammetric Analysis (RSA) – a technique which extracts 3D information about the implant and bone positions from two roughly orthogonal radiographs. This information can be used to quantify the migration of an implant over time to submillimeter accuracy, a metric that has been shown to reliably predict implant longevity in patients (Pijls 2012). Unfortunately, commercial RSA systems are expensive, which has limited their use in clinical settings. Our goal in this project was to develop an RSA protocol based on C-arm fluoroscopy machines, many of which already exist in most hospitals. We successfully developed such a protocol and evaluated its accuracies and precisions through a series of phantom-based verifications. Results were highly promising: accuracies ranged between -39 to 11 μm for translations and -0.025 to 0.029° for rotations, while system precisions ranged between 16 to 27 μm and 0.041 to 0.059°. This performance was comparable to RSA systems in the literature, where traditional and more expensive radiographic equipment was typically employed. In addition, inter-rater reliability tests also showed a high degree of correlation (ICC > 0.999) between two raters who were trained to use the protocol. We conclude that we have developed an RSA protocol appropriate for measuring relative motion of knee replacement implants in phantoms and cadaveric specimens by leveraging the use of existing C-arm technology. This research places us in position to further develop the protocol for use in extensive prospective clinical assessments – research that can potentially drive future improvements in surgical technique and implant design.

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Implementation and Verification of a Flexible Optical Tracker (2015)

Despite being demonstrably better than conventional surgical techniques with regards to implant alignment and outlier reduction, computer navigation systems have not faced widespread adoption in surgical operating rooms. We believe that one of the reasons for the low uptake stems from the bulky design of the optical tracker assemblies. These trackers must be rigidly fixed to a patient’s bone and they occupy a significant portion of the surgical workspace, which makes them difficult to use. In this thesis we introduce the design for a new optical tracker system, and subsequently we evaluate the tracker’s performance.The novel tracker consists of a set of low-profile flexible pins that can be placed into a rigid body and individually deflect without greatly affecting the pose estimation. By relying on a pin’s stiff axial direction while neglecting lateral deviations, we gain sufficient constraint over the underlying body. We used an unscented Kalman filter based algorithm as a recursive body pose estimator that can account for relative marker displacements.We assessed our tracker’s performance through a series of simulations and experiments inspired by a total knee arthroplasty. We found that the flexible tracker performs comparably to conventional trackers with regards to accuracy and precision, with tracking errors under 0.3mm for typical operating conditions. The tracking error remained below 0.5mm during pin deflections of up to 40mm. Our algorithm ran at computation speeds greater than real-time at 30Hz which means that it would be suitable for use in real-time applications.We conclude that this flexible pin concept provides sufficient accuracy to be used as a replacement for rigid trackers in applications where its lower profile, its reduced invasiveness and its robustness to deflection are desirable characteristics.

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Effecto fo bracing and navigation display design on targeting accuracy and plunge depth during surgical drilling (2014)

The success of many orthopaedic procedures relies on the accurate and timely machining of bone, which can be difficult to achieve. Errors during machining can negatively affect implant placement or cause neurovascular injury. Bracing can improve the performance of both humans and machines during a variety of interactive tasks such as writing and grinding. The purpose of this thesis was to assess the feasibility of braced computer assisted orthopaedic surgery by testing the influence of bracing on theperformance of a surgically relevant task.We developed a computer assisted orthopaedic surgery research system and experimental bracing devices for two surgical drilling tasks: navigated targeting and cortical drilling. The performance of each device was tested in a user study with 25 (13 male, 12 female) non-expert subjects.In the navigated targeting task, subjects aligned a drill bit with a randomly generated trajectory while using a rigid brace to support the forearm and two different versions of guidance displays to provide visual feedback: a 2D axial display and a 3D-perspective display. Bracing reduced variation within- and between-trials, but did not affect final accuracy or targeting speed. There was a significant increase in final radial (170 %, 95% CI: 140–210 %) and angular error (350 %, 95% CI: 300–400 %) with the 3D-perspective display.In the cortical drilling task, subjects attempted to minimize plunge of the drill bit after breakthrough. An experimental damper-based bracing device was designed by developing a numerical model to predict drill plunge, extending the model to predict the behaviour with bracing, and estimating an optimal brace damping range. Subjects drilled through oak workpieces using a standard high speed steel drill bit and a brad point drill bit at 4 damping levels. At a level of 10Ns/mm, there was a significant decrease in plunge depth of 74% (95% CI: 71–76 %) and no significant difference in drilling duration.This thesis provides experimental evidence that a simple bracing strategy can improve the performance of a clinically relevant task; Applying bracing to computer assisted orthopaedic surgery may be an effective way to improve performance and warrants further investigation.

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Tool bracing for performance improvement in simulated femoral head-neck osteochondroplasty (2013)

Bracing is defined as a parallel mechanical link between a tool user, the environment, and/or the workpiece that alters the mechanical impedance between the tool and workpiece with the goal of improving task performance. Bracing is used in a variety of settings including robotics/automation and more recently in medicine/dentistry, however it remains relatively understudied in formal ways. This thesis explored whether bracing could be beneficial in a current orthopaedic problem. We selected a candidate orthopaedic procedure based on selection criteria that included three degrees of freedom, and the ability to abstract/simulate the surgical task using phantom tests.Femoral head-neck osteochondroplasty is used to treat a deformity of the anterosuperior femoral head-neck region called cam-type femoroacetabular impingement. During this procedure a surgeon uses a spherical burr to remove the cam lesion and restore the normal contour of the femoral head-neck. The goal of this thesis was to evaluate whether a proposed bracing technique could enable a user to perform a cam resection more accurately and quickly than a currently employed arthroscopic technique.We first performed a pilot study with 4 subjects to examine the impact of bracing on simulated bone milling and found that bracing could reduce errors on the order of 7-14% and procedure length on the order of 30-50% but these findings were limited by a small sample and effect size. Workspace issues with the brace indicated the need for a redesign, which we combined with the creation of a higher fidelity surgical simulation. We showed that the most effective brace design projected a remote center of motion combined with a spring for axial stiffness.This improved brace design was tested using 20 non-surgeons and 5 surgeons. While bracing had no detectable effect on the surgeon population, bracing reduced procedure length and error by 37% and 27% respectively in the non-surgeon population when compared to the unbraced condition. Unfortunately, when compared to the surgical simulation condition, there was no detectable effect of bracing. This finding suggests that an optimal level of bracing may exist but how to experimentally determine this level remains a topic for future study.

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A biologically-inspired eye model for testing oculomotor control theories (2012)

This research presents a new biologically motivated robotic model of the human eye. The model incorporates aspects of the anatomy that are functionally important for understanding biological oculomotor systems. The 3DOF robotic eye is driven by 6 DC motors through low friction dyneema cables. The DC motors represent muscle actuation while dyneema cables represent the 6 extraocular muscles (EOM). The globe’s natural orbital support is emulated by a low-friction gimbal structure that supports the eye on the anteroposterior axis at the back of the globe, where there is no tendon interference. Moreover, we have used the Buckingham Π theorem dimensionless analysis to scale the geometric and dynamic properties of the biological eye according to the model’s specified dimensions and inertia. Lastly, to confirm the functionality of the eye and to verify that the initial design requirements have been satisfied, we have implemented a controller design to drive this redundant (6 actuators, 3 DOF) system.The presented robotic eye model is to be employed as a test bed for testing theories about oculomotor control. Furthermore, this system could also be used to assess proposed surgical corrections for various oculomotor diseases.

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