Imperial College London

DrJamesAvery

Faculty of MedicineDepartment of Surgery & Cancer

Honorary Lecturer
 
 
 
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Contact

 

james.avery Website

 
 
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Location

 

036Paterson WingSt Mary's Campus

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Summary

 

Publications

Publication Type
Year
to

46 results found

Monfort Sanchez E, Avery J, Wei J, Qian J, Mandal N, Agarwal A, Mwiinga M, Banda R, Darzi A, Kelly P, Thompson Aet al., 2024, Transcutaneous fluorescence spectroscopy: development and characterization of a compact, portable, fiber-optic sensor, Journal of Biomedical Optics, ISSN: 1083-3668

Journal article

Runciman M, Franco E, Avery J, Rodriguez y Baena F, Mylonas Get al., 2023, Model based position control of soft hydraulic actuators, IEEE International Conference on Robotics and Automation, Publisher: IEEE, Pages: 1-7

In this article, we investigate the model based position control of soft hydraulic actuators arranged in an an-tagonistic pair. A dynamical model of the system is constructed by employing the port-Hamiltonian formulation. A control algorithm is designed with an energy shaping approach, which accounts for the pressure dynamics of the fluid. A nonlinear observer is included to compensate the effect of unknown external forces. Simulations demonstrate the effectiveness of the proposed approach, and experiments achieve positioning accuracy of 0.043 mm with a standard deviation of 0.033 mm in the presence of constant external forces up to 1 N.

Conference paper

Alian A, Mylonas G, Avery J, 2023, Soft continuum actuator tip position and contact force prediction, using electrical impedance tomography and recurrent neural networks, IEEE International Conference on Soft Robotics (RoboSoft), Publisher: IEEE, Pages: 1-6, ISSN: 2769-4534

Enabling dexterous manipulation and safe human-robot interaction, soft robotsare widely used in numerous surgical applications. One of the complicationsassociated with using soft robots in surgical applications is reconstructingtheir shape and the external force exerted on them. Several sensor-based andmodel-based approaches have been proposed to address the issue. In this paper,a shape sensing technique based on Electrical Impedance Tomography (EIT) isproposed. The performance of this sensing technique in predicting the tipposition and contact force of a soft bending actuator is highlighted byconducting a series of empirical tests. The predictions were performed based ona data-driven approach using a Long Short-Term Memory (LSTM) recurrent neuralnetwork. The tip position predictions indicate the importance of using EIT dataalong with pressure inputs. Changing the number of EIT channels, we evaluatedthe effect of the number of EIT inputs on the accuracy of the predictions. Theleast RMSE values for the tip position are 3.6 and 4.6 mm in Y and Zcoordinates, respectively, which are 7.36% and 6.07% of the actuator's totalrange of motion. Contact force predictions were conducted in three differentbending angles and by varying the number of EIT channels. The results of thepredictions illustrated that increasing the number of channels contributes tohigher accuracy of the force estimation. The mean errors of using 8 channelsare 7.69%, 2.13%, and 2.96% of the total force range in three different bendingangles.

Conference paper

Monfort Sánchez E, Avery J, Gan J, Qian J, Mwiinga M, Banda R, Hoare J, Ashranfian H, Darzi A, Kelly P, Thompson AJet al., 2023, A compact fluorescence sensor for low-cost non-invasive monitoring of gut permeability in undernutrition, Optics and Biophotonics in Low-Resource Settings IX, Publisher: SPIE, Pages: 1-7, ISSN: 1605-7422

Undernutrition is associated with approximately 45% of deaths among children under the age of 5. Furthermore, in 2020, around 149 million children suffered impaired physical/cognitive development due to lack of adequate nutrition. Environmental enteropathy (EE) is associated with undernutrition and is characterized by a multifaceted breakdown in gut function, including an increase in intestinal permeability that can lead to inflammatory responses. However, the role and mechanisms associated with EE (particularly gut permeability) are not well understood. This is partly because current techniques to assess changes in gut permeability, such as endoscopic biopsies, histopathology and chemical tests such as Lactulose:Mannitol assays, are either highly invasive, unreliable or difficult to perform on specific groups of patients (such as infants and patients with urine retention problems). Therefore, low-cost, non-invasive and reliable diagnostic tools are urgently needed for better evaluation of intestinal permeability. Here, we present a compact transcutaneous fluorescence spectroscopy sensor for non-invasive evaluation of gut permeability and report the first in vivo data collected from volunteers in an undernutrition trial. Using this technique and device, fluorescence signals are detected transcutaneously after oral ingestion of a fluorescent solution. Preliminary results demonstrate the potential use of the presented sensor for clinical assessment of gut permeability in low-income settings.

Conference paper

Alian A, Zari E, Wang Z, Franco E, Avery JP, Runciman M, Lo B, Rodriguez y Baena F, Mylonas Get al., 2023, Current engineering developments for robotic systems in flexible endoscopy, Techniques and Innovations in Gastrointestinal Endoscopy, Vol: 25, Pages: 67-81, ISSN: 2590-0307

The past four decades have seen an increase in the incidence of early-onset gastrointestinal cancer. Because early-stage cancer detection is vital to reduce mortality rate, mass screening colonoscopy provides the most effective prevention strategy. However, conventional endoscopy is a painful and technically challenging procedure that requires sedation and experienced endoscopists to be performed. To overcome the current limitations, technological innovation is needed in colonoscopy. In recent years, researchers worldwide have worked to enhance the diagnostic and therapeutic capabilities of endoscopes. The new frontier of endoscopic interventions is represented by robotic flexible endoscopy. Among all options, self-propelling soft endoscopes are particularly promising thanks to their dexterity and adaptability to the curvilinear gastrointestinal anatomy. For these devices to replace the standard endoscopes, integration with embedded sensors and advanced surgical navigation technologies must be investigated. In this review, the progress in robotic endoscopy was divided into the fundamental areas of design, sensing, and imaging. The article offers an overview of the most promising advancements on these three topics since 2018. Continuum endoscopes, capsule endoscopes, and add-on endoscopic devices were included, with a focus on fluid-driven, tendon-driven, and magnetic actuation. Sensing methods employed for the shape and force estimation of flexible endoscopes were classified into model- and sensor-based approaches. Finally, some key contributions in molecular imaging technologies, artificial neural networks, and software algorithms are described. Open challenges are discussed to outline a path toward clinical practice for the next generation of endoscopic devices.

Journal article

Alian A, Mylonas G, Avery J, 2023, Soft Continuum Actuator Tip Position and Contact Force Prediction, Using Electrical Impedance Tomography and Recurrent Neural Networks

Enabling dexterous manipulation and safe human-robot interaction, soft robots are widely used in numerous surgical applications. One of the complications associated with using soft robots in surgical applications is reconstructing their shape and the external force exerted on them. Several sensor-based and model-based approaches have been proposed to address the issue. In this paper, a shape sensing technique based on Electrical Impedance Tomography (EIT) is proposed. The performance of this sensing technique in predicting the tip position and contact force of a soft bending actuator is highlighted by conducting a series of empirical tests. The predictions were performed based on a data-driven approach using a Long Short-Term Memory (LSTM) recurrent neural network. The tip position predictions indicate the importance of using EIT data along with pressure inputs. Changing the number of EIT channels, we evaluated the effect of the number of EIT inputs on the accuracy of the predictions. The least RMSE values for the tip position are 3.6 and 4.6 mm in Y and Z coordinates, respectively, which are 7.36% and 6.07% of the actuator's total range of motion. Contact force predictions were conducted in three different bending angles and by varying the number of EIT channels. The results of the predictions illustrated that increasing the number of channels contributes to higher accuracy of the force estimation. The mean errors of using 8 channels are 7.69%, 2.13%, and 2.96% of the total force range in three different bending angles.

Conference paper

Avery J, Runciman M, Fiani C, Monfort Sanchez E, Akhond S, Liu Z, Aristovich K, Mylonas Get al., 2022, Lumen shape reconstruction using a soft robotic balloon catheter andelectrical impedance tomography, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Publisher: IEEE, ISSN: 2153-0866

Incorrectly sized balloon catheters can lead to increased post-surgical complications, yet even with preoperative imaging, correct selection remains a challenge. With limited feedback during surgery, it is difficult to verify correct deployment. We propose the use of integrated impedance measurements and Electrical Impedance Tomography (EIT) imaging to assess the deformation of the balloon and determine the size and shape of the surrounding lumen. Previous work using single impedance measurements, or pressure data and analytical models, whilst demonstrating high sizing accuracy, have assumed a circular cross section. Here we extend these methods by adding a multitude of electrodes to detect elliptical and occluded lumen and obtain EIT images to localise deformations. Using a 14 Fr (5.3 mm) catheter as an example, numerical simulations were performed to find the optimal electrode configuration of two rings of 8 electrodes spaced 10 mm apart. The simulations predicted that the maximum detectable aspect ratio decreased from 0.9 for a 14mm balloon to 0.5 at 30mm. The sizing and ellipticity detection results were verified experimentally. A prototype robotic balloon catheter was constructed to automatically inflate a compliant balloon while simultaneously recording EIT and pressure data. Data were collected in experiments replicating stenotic vessels with an elliptical and asymmetrical profile, and the widening of a lumen during angioplasty. After calibration, the system was able to correctly localise the occlusion and detect aspect ratios of 0.75. EIT images further localised the occlusion and visualised the dilation of the lumen during balloon inflation.

Conference paper

Wei J, Monfort Sanchez E, Avery J, Barbouti O, Hoare J, Ashrafian H, Darzi A, Thompson Aet al., 2022, Non-invasive assessment of intestinal permeability in healthy volunteers using transcutaneous fluorescence spectroscopy, Methods and Applications in Fluorescence, Vol: 10, Pages: 1-9, ISSN: 2050-6120

The permeability of the intestinal barrier is altered in a multitude of gastrointestinal conditions such as Crohn's and coeliac disease. However, the clinical utility of gut permeability is currently limited due to a lack of reliable diagnostic tests. To address this issue, we report a novel technique for rapid, non-invasive measurement of gut permeability based on transcutaneous ('through-the-skin') fluorescence spectroscopy. In this approach, participants drink an oral dose of a fluorescent dye (fluorescein) and a fibre-optic fluorescence spectrometer is attached to the finger to detect permeation of the dye from the gut into the blood stream in a non-invasive manner. To validate this technique, clinical trial measurements were performed in 11 healthy participants. First, after 6 h of fasting, participants ingested 500 mg of fluorescein dissolved in 100 ml of water and fluorescence measurements were recorded at the fingertip over the following 3 h. All participants were invited back for a repeat study, this time ingesting the same solution but with 60 g of sugar added (known to transiently increase intestinal permeability). Results from the two study datasets (without and with sugar respectively) were analysed and compared using a number of analysis procedures. This included both manual and automated calculation of a series of parameters designed for assessment of gut permeability. Calculated values were compared using Student's T-tests, which demonstrated significant differences between the two datasets. Thus, transcutaneous fluorescence spectroscopy shows promise in non-invasively discriminating between two differing states of gut permeability, demonstrating potential for future clinical use.

Journal article

DeLorey C, Davids JD, Cartucho J, Xu C, Roddan A, Nimer A, Ashrafian H, Darzi A, Thompson AJ, Akhond S, Runciman M, Mylonas G, Giannarou S, Avery Jet al., 2022, A cable‐driven soft robotic end‐effector actuator for probe‐based confocal laser endomicroscopy: Development and preclinical validation, Translational Biophotonics, ISSN: 2627-1850

Journal article

Monfort Sanchez E, Avery J, Darzi A, Thompson Aet al., 2022, Development of a compact fluorescence spectroscopy sensor for non-invasive monitoring gut function, Optica Biophotonics Congress: Biomedical Optics 2022, Publisher: Optica Publishing Group

Monitoring gut permeability is currently either invasive, inaccurate or difficult to perform in infants. We present a compact fluorescence sensor that overcomes some of these limitations, paving the way for non-invasive gut permeability monitoring.

Conference paper

Avery J, Runciman M, Fiani C, Sanchez EM, Akhond S, Liu Z, Aristovich K, Mylonas Get al., 2022, Lumen Shape Reconstruction using a Soft Robotic Balloon Catheter and Electrical Impedance Tomography, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Publisher: IEEE, Pages: 3414-3421, ISSN: 2153-0858

Conference paper

Runciman M, Avery J, Darzi A, Mylonas Get al., 2021, Open loop position control of soft hydraulic actuators for minimally invasive surgery, Applied Sciences-Basel, Vol: 11, Pages: 1-16, ISSN: 2076-3417

Minimally invasive surgery (MIS) presents many constraints on the design of robotic devices that can assist medical staff with a procedure. The limitations of conventional, rigid robotic devices have sparked interest in soft robotic devices for medical applications. However, problems still remain with the force exertion and positioning capabilities of soft robotic actuators, in conjunction with size restrictions necessary for MIS. In this article we present hydraulically actuated soft actuators that demonstrate highly repeatable open loop positioning and the ability to exert significant forces in the context of MIS. Open loop position control is achieved by changing the actuator volume, which causes contraction. In one degree of freedom (DOF) configurations, root mean square error (RMSE) values of 0.471 mm, 1.506 mm, and 0.350 mm were recorded for a single actuator against gravity, a single actuator with a pulley, and a horizontal antagonistic configuration, respectively. Hysteresis values of 0.711 mm, 0.958 mm, and 0.515 mm were reported in these experiments. In addition, different numbers of soft actuators were used in configurations two and three DOFs to demonstrate position control. When deactivated, the soft actuators are low-profile and flexible as they are constructed from thin films. As such, a robot with a deployable structure and three soft actuators was constructed. The robot is therefore able to reversibly transition from low to high volume and stiffness, which has potential applications in MIS. A user successfully controlled the deployable robot in a circle tracing task.

Journal article

Avery J, Aristovich K, 2021, The impact of 2D assumptions in 3D brain imaging, 21st International Conference on Biomedical Applications of Electrical Impedance Tomography (EIT2021)

Conference paper

McDermott B, Elahi A, Santorelli A, O Halloran M, Avery J, Porter Eet al., 2021, 21st International Conference on Biomedical Applications of Electrical Impedance Tomography (EIT2021), 21st International Conference on Biomedical Applications of Electrical Impedance Tomography (EIT2021)

Conference paper

Fiani C, Aristovich K, Avery J, 2021, Improving Aortic Stent Sizing Through Integrated ImpedanceMeasurements, 21st International Conference on Biomedical Applications of Electrical Impedance Tomography

Conference paper

Hannan S, Aristovich K, Faulkner M, Avery J, Walker MC, Holder DSet al., 2021, Imaging slow brain activity during neocortical and hippocampal epileptiform events with electrical impedance tomography, Physiological Measurement, Vol: 42, Pages: 1-19, ISSN: 0967-3334

Objective. Electrical impedance tomography (EIT) is an imaging technique that produces tomographic images of internal impedance changes within an object using surface electrodes. It can be used to image the slow increase in cerebral tissue impedance that occurs over seconds during epileptic seizures, which is attributed to cell swelling due to disturbances in ion homeostasis following hypersynchronous neuronal firing and its associated metabolic demands. In this study, we characterised and imaged this slow impedance response during neocortical and hippocampal epileptiform events in the rat brain and evaluated its relationship to the underlying neural activity. Approach. Neocortical or hippocampal seizures, comprising repeatable series of high-amplitude ictal spikes, were induced by electrically stimulating the sensorimotor cortex or perforant path of rats anaesthetised with fentanyl-isoflurane. Transfer impedances were measured during ≥30 consecutive seizures, by applying a sinusoidal current through independent electrode pairs on an epicortical array, and combined to generate an EIT image of slow activity. Main results. The slow impedance responses were consistently time-matched to the end of seizures and EIT images of this activity were reconstructed reproducibly in all animals (p < 0.03125, N = 5). These displayed foci of activity that were spatially confined to the facial somatosensory cortex and dentate gyrus for neocortical and hippocampal seizures, respectively, and encompassed a larger volume as the seizure progressed. Centre-of-mass analysis of reconstructions revealed that this activity corresponded to the true location of the epileptogenic zone, as determined by EEG recordings and fast neural EIT measurements which were obtained simultaneously. Significance. These findings suggest that the slow impedance response presents a reliable marker of hypersynchronous neuronal activity during epileptic seizures and can thus be utilised for investigating the

Journal article

Avery J, Packham B, Koo H, Hanson B, Holder Det al., 2020, Self-abrading servo electrode helmet for electrical impedance tomography, Sensors, Vol: 20, ISSN: 1424-8220

Electrical Impedance Tomography (EIT) is a medical imaging technique which has the potential to reduce time to treatment in acute stroke by rapidly differentiating between ischaemic and haemorrhagic stroke. The potential of these methods has been demonstrated in simulation and phantoms, it has not yet successfully translated to clinical studies, due to high sensitivity to errors in scalp electrode mislocation and poor electrode-skin contact. To overcome these limitations, a novel electrode helmet was designed, bearing 32 independently controlled self-abrading electrodes. The contact impedance was reduced through rotation on an abrasive electrode on the scalp using a combined impedance, rotation and position feedback loop. Potentiometers within each unit measure the electrode tip displacement within 0.1 mm from the rigid helmet body. Characterisation experiments on a large-scale test rig demonstrated that approximately 20 kPa applied pressure and 5 rotations was necessary to achieve the target 5 kΩ contact impedance at 20 Hz. This performance was then replicated in a simplified self-contained unit where spring loaded electrodes are rotated by servo motors. Finally, a 32-channel helmet and controller which sequentially minimised contact impedance and simultaneously located each electrode was built which reduced the electrode application and localisation time to less than five minutes. The results demonstrated the potential of this approach to rapidly apply electrodes in an acute setting, removing a significant barrier for imaging acute stroke with EIT.

Journal article

Hannan S, Faulkner M, Aristovich K, Avery J, Walker MC, Holder DSet al., 2020, Optimised induction of on-demand focal hippocampal and neocortical seizures by electrical stimulation, Journal of Neuroscience Methods, Vol: 346, Pages: 108911-108911, ISSN: 0165-0270

BACKGROUND: Epilepsy is a common neurological disorder affecting over 60 million people globally, approximately a third of whom are refractory to pharmacotherapy. Surgical resection of the epileptogenic zone is frequently unsuitable or ineffective, particularly for individuals with focal neocortical or mesial temporal lobe epilepsy. Therefore, there is a need to develop animal models for elucidating the mechanisms of focal epilepsies and evaluating novel treatment strategies. NEW METHOD: We present two adapted in vivo seizure models, the neocortical and hippocampal epileptic afterdischarge models, that enable stereotyped seizures to be induced on demand by electrical stimulation in anaesthetised, neurologically intact rats. The stimulation parameters and anaesthetic were optimised to generate electrographically reproducible, self-sustaining seizures with a well-defined focal origin. RESULTS: Neocortical or hippocampal seizures were consistently generated under fentanyl-isoflurane anaesthesia by stimulating the sensorimotor cortex or perforant path, respectively, with 100 Hz trains of biphasic square-wave pulses. The induced seizures were suppressed by propofol, an established antiseizure anaesthetic, thus validating the clinical responsiveness of the developed models. COMPARISON WITH EXISTING METHODS: The high degree of reproducibility in seizure presentation, predictable seizure induction and ability to operate in anaesthetised animals renders these models overall less laborious and more cost-effective than most conventionally used seizure models. CONCLUSIONS: The proposed models provide an efficient method for the high-throughput screening of novel antiseizure therapies, including closed-loop stimulation paradigms, and are well-suited to in vivo investigations that require tight regulation of seizure timing under anaesthetised conditions, particularly neuroimaging studies aimed at understanding the development of epileptogenic networks.

Journal article

Avery J, Shulakova D, Runciman M, Mylonas GP, Darzi Aet al., 2020, Tactile sensor for minimally invasive surgery using Electrical Impedance Tomography, IEEE Transactions on Medical Robotics and Bionics, Vol: 2, Pages: 561-564, ISSN: 2576-3202

Whilst offering numerous benefits to patients, minimally invasive surgery (MIS) has a disadvantage in the loss of tactile feedback to the surgeon, traditionally offering valuable qualitative tissue assessment, such as tumour identification and localisation. Tactile sensors aim to overcome this loss of sensation by detecting tissue characteristics such as stiffness, composition and temperature. Tactile sensors have previously been incorporated into MIS robotic end effectors, which require lengthy scanning procedures due to localised sensitivity. Distributed tactile sensors, or “artificial skin” offer a map of tissue properties in a single instance but are often not suitable for MIS applications due to limited biocompatibility or large collapsed volumes. We propose a deployable, soft, tactile sensor with a deformable saline chamber and integrated Electrical Impedance Tomography (EIT) electrodes. During contact with tissue, the saline is displaced from the chamber and the lesion size and stiffness can be inferred from the resultant impedance changes. Through optimisation of the EIT measurement protocol and hardware the sensor was capable of localising the centre of mass of palpation targets within 1.5 mm in simulation and 2.3–4.6mm in phantom experiments. Reconstructed image metrics differentiated target objects from 8–30 mm.

Journal article

Dowrick T, Avery J, Faulkner M, Holder D, Aristovich Ket al., 2020, EIT-MESHER – Segmented FEM mesh generation and refinement, Journal of Open Research Software, Vol: 8, Pages: 1-4, ISSN: 2049-9647

EIT-MESHER (https://github.com/EIT-team/Mesher) is C++ software, based on the CGAL library, which generates high quality Finite Element Model tetrahedral meshes from binary masks of 3D volume segmentations. Originally developed for biomedical applications in Electrical Impedance Tomography (EIT) to address the need for custom, non-linear refinement in certain areas (e.g. around electrodes), EIT-MESHER can also be used in other fields where custom FEM refinement is required, such as Diffuse Optical Tomography (DOT).

Journal article

Avery J, Tom D, Aristovich K, Faulkner Met al., 2020, EIT Mesher

EIT-MESHER is C++ software, based on the CGAL library, which generates high quality Finite Element Model tetrahedral meshes from binary masks of 3D volume segmentations. Originally developed for biomedical applications in Electrical Impedance Tomography (EIT) to address the need for custom, non-linear refinement in certain areas (e.g. around electrodes), EIT-MESHER can also be used in other fields where custom FEM refinement is required, such as Diffuse Optical Tomography (DOT).

Software

McDermott BJ, Elahi A, Santorelli A, O'Halloran M, Avery J, Porter Eet al., 2020, Multi-frequency symmetry difference electrical impedance tomography with machine learning for human stroke diagnosis, Physiological Measurement, Vol: 41, Pages: 1-17, ISSN: 0967-3334

Objective: Multi-Frequency Symmetry Difference Electrical Impedance Tomography (MFSD-EIT) can robustly detect and identify unilateral perturbations in symmetric scenes. Here, an investigation is performed to assess if the algorithm can be successfully applied to identify the aetiology of stroke with the aid of machine learning. Methods: Anatomically realistic four-layer Finite Element Method models of the head based on stroke patient images are developed and used to generate EIT data over a 5 Hz – 100 Hz frequency range with and without bleed and clot lesions present. Reconstruction generates conductivity maps of each head at each frequency. Application of a quantitative metric assessing changes in symmetry across the sagittal plane of the reconstructed image and over the frequency range allows lesion detection and identification. The algorithm is applied to both simulated and human (n=34 subjects) data. A classification algorithm is applied to the metric value in order to differentiate between normal, haemorrhage and clot values. Results: An average accuracy of 85% is achieved when MFSD-EIT with Support Vector Machines (SVM) classification is used to identify and differentiate bleed from clot in human data, with 77% accuracy when differentiating normal from stroke in human data. Conclusion: Applying a classification algorithm to metrics derived from MFSD-EIT images is a novel and promising technique for detection and identification of perturbations in static scenes. Significance: The MFSD-EIT algorithm used with machine learning gives promising results of lesion detection and identification in challenging conditions like stroke. The results imply feasible translation to human patients.

Journal article

McDermott BJ, Ohalloran M, Avery J, Porter Eet al., 2020, Bi-frequency symmetry difference EIT - feasibility and limitations of application to stroke diagnosis, IEEE Journal of Biomedical and Health Informatics, Vol: 24, Pages: 2407-2419, ISSN: 2168-2194

OBJECTIVE: Bi-Frequency Symmetry Difference (BFSD)-EIT can detect, localize and identify unilateral perturbations in symmetric scenes. Here, we test the viability and robustness of BFSD-EIT in stroke diagnosis. METHODS: A realistic 4-layer Finite Element Method (FEM) head model with and without bleed and clot lesions is developed. Performance is assessed with test parameters including: measurement noise, electrode placement errors, contact impedance errors, deviations in assumed tissue conductivity, deviations in assumed anatomy, and a frequency-dependent background. A final test is performed using ischemic patient data. Results are assessed using images and quantitative metrics. RESULTS: BFSD-EIT may be feasible for stroke diagnosis if a signal-to-noise ratio (SNR) of ≥60dB is achievable. Sensitivity to errors in electrode positioning is seen with a tolerance of only ±5mm, but a tolerance of up to ±30mm is possible if symmetry is maintained between symmetrically opposite partner electrodes. The technique is robust to errors in contact impedance and assumed tissue conductivity up to at least ±50%. Asymmetric internal anatomy affects performance but may be tolerable for tissues with frequency-dependent conductivity. Errors in assumed external geometry marginally affect performance. A frequency-dependent background does not affect performance with carefully chosen frequency points or use of multiple frequency points across a band. The Global Left-Hand Side (LHS) & Right-Hand Side (RHS) Mean Intensity metric is particularly robust to errors. CONCLUSION: BFSD-EIT is a promising technique for stroke diagnosis, provided parameters are within the tolerated ranges. SIGNIFICANCE: BFSD-EIT may prove an important step forward in imaging of static scenes such as stroke.

Journal article

Hannan S, Faulkner M, Aristovich K, Avery J, Walker MC, Holder DSet al., 2020, In vivo imaging of deep neural activity from the cortical surface during hippocampal epileptiform events in the rat brain using electrical impedance tomography, NeuroImage, Vol: 209, Pages: 1-13, ISSN: 1053-8119

Electrical impedance tomography (EIT) is a medical imaging technique which reconstructs images of the internal impedance changes within an object using non-penetrating surface electrodes. To date, EIT has been used to image fast neural impedance changes during somatosensory evoked potentials and epileptiform discharges through the rat cerebral cortex with a resolution of 2 ​ms and <300 ​μm. However, imaging of neural activity in subcortical structures has never been achieved with this technique. Here, we evaluated the feasibility of using EIT to image epileptiform activity in the rat hippocampus using non-penetrating electrodes implanted on the cortical surface. Hippocampal epileptiform events, comprising repetitive 30–50 ​Hz ictal spikes, were induced by electrically stimulating the perforant path of rats anaesthetised with fentanyl-isoflurane. For each of ≥30 seizures, impedance measurements were obtained by applying 100 ​μA current at 1.4 ​kHz through an independent pair of electrodes on a 54-electrode planar epicortical array and recording boundary voltages on all remaining electrodes. EIT images of averaged ictal spikes were reconstructed using impedance recordings from all seizures in each animal. These revealed a focus of neural activity localised to the dentate gyrus which was spatially and temporally aligned to local field potential (LFP) recordings and could be reconstructed reproducibly in all animals with a localisation accuracy of ≤400 ​μm (p ​< ​0.03125, N ​= ​5). These findings represent the first experimental evidence of the ability of EIT to image neural activity in subcortical structures from the surface of the cortex with high spatiotemporal resolution and suggest that this method may be used for improving understanding of functional connectivity between cortico-hippocampal networks in both physiological and pathophysiological states.

Journal article

Runciman M, Avery J, Zhao M, Darzi A, Mylonas GPet al., 2020, Deployable, variable stiffness, cable driven robot for minimally invasive surgery, Frontiers in Robotics and AI, Vol: 6, Pages: 1-16, ISSN: 2296-9144

Minimally Invasive Surgery (MIS) imposes a trade-off between non-invasive access and surgical capability. Treatment of early gastric cancers over 20 mm in diameter can be achieved by performing Endoscopic Submucosal Dissection (ESD) with a flexible endoscope; however, this procedure is technically challenging, suffers from extended operation times and requires extensive training. To facilitate the ESD procedure, we have created a deployable cable driven robot that increases the surgical capabilities of the flexible endoscope while attempting to minimize the impact on the access that they offer. Using a low-profile inflatable support structure in the shape of a hollow hexagonal prism, our robot can fold around the flexible endoscope and, when the target site has been reached, achieve a 73.16% increase in volume and increase its radial stiffness. A sheath around the variable stiffness structure delivers a series of force transmission cables that connect to two independent tubular end-effectors through which standard flexible endoscopic instruments can pass and be anchored. Using a simple control scheme based on the length of each cable, the pose of the two instruments can be controlled by haptic controllers in each hand of the user. The forces exerted by a single instrument were measured, and a maximum magnitude of 8.29 N observed along a single axis. The working channels and tip control of the flexible endoscope remain in use in conjunction with our robot and were used during a procedure imitating the demands of ESD was successfully carried out by a novice user. Not only does this robot facilitate difficult surgical techniques, but it can be easily customized and rapidly produced at low cost due to a programmatic design approach.

Journal article

Chapman CAR, Smith TM, Kelly M, Avery J, Rouanet T, Aristovich K, Chew DJ, Holder DSet al., 2019, Optimisation of bioimpedance measurements of neuronal activity with an <i>ex vivo</i> preparation of <i>Cancer pagurus</i> peripheral nerves, JOURNAL OF NEUROSCIENCE METHODS, Vol: 327, ISSN: 0165-0270

Journal article

Avery J, Runciman M, Darzi A, Mylonas GPet al., 2019, Shape sensing of variable stiffness soft robots using electrical impedance tomography, International Conference on Robotics and Automation (ICRA), Publisher: IEEE, Pages: 9066-9072, ISSN: 1050-4729

Soft robotic systems offer benefits over traditional rigid systems through reduced contact trauma with soft tissues and by enabling access through tortuous paths in minimally invasive surgery. However, the inherent deformability of soft robots places both a greater onus on accurate modelling of their shape, and greater challenges in realising intraoperative shape sensing. Herein we present a proprioceptive (self-sensing) soft actuator, with an electrically conductive working fluid. Electrical impedance measurements from up to six electrodes enabled tomographic reconstructions using Electrical Impedance Tomography (EIT). A new Frequency Division Multiplexed (FDM) EIT system was developed capable of measurements of 66 dB SNR with 20 ms temporal resolution. The concept was examined in two two-degree-of-freedom designs: a hydraulic hinged actuator and a pneumatic finger actuator with hydraulic beams. Both cases demonstrated that impedance measurements could be used to infer shape changes, and EIT images reconstructed during actuation showed distinct patterns with respect to each degree of freedom (DOF). Whilst there was some mechanical hysteresis observed, the repeatability of the measurements and resultant images was high. The results show the potential of FDM-EIT as a low-cost, low profile shape sensor in soft robots.

Conference paper

McDermott BJ, Avery J, O'Halloran M, Aristovich KY, Porter Eet al., 2019, Bi-frequency symmetry difference electrical impedance tomography—a novel technique for perturbation detection in static scenes, Physiological Measurement, Vol: 40, ISSN: 0967-3334

OBJECTIVE: A novel method for the imaging of static scenes using Electrical Impedance Tomography (EIT) is reported with implementation and validation using numerical and phantom models. The technique is applicable to regions featuring symmetry in the normal case, asymmetry in the presence of a perturbation, and where there is a known, frequency-dependent change in the electrical conductivity of the materials in the region. METHODS: The stroke diagnostic problem is used as a motivating sample application. The head is largely symmetrical across the sagittal plane. A haemorrhagic or ischaemic lesion located away from the sagittal plane will alter this natural symmetry, resulting in a symmetrical imbalance that can be detected using EIT. Specifically, application of EIT stimulation and measurement protocols at two distinct frequencies detects deviations in symmetry if an asymmetrically positioned lesion is present, with subsequent identification and localisation of the perturbation based on known frequency-dependent conductivity changes. Anatomically accurate computational models are used to demonstrate the feasibility of the proposed technique using different types, sizes, and locations of lesions with frequency-dependent (or independent) conductivity. Further, a realistic experimental head phantom is used to validate the technique using frequency-dependent perturbations emulating the key numerical simulations. RESULTS: Lesion presence, type, and location are detectable using this novel technique. Results are presented in the form of images and corresponding robust quantitative metrics. Better detection is achieved for larger lesions, those further from the sagittal plane, and when measurements have a higher signal-to-noise ratio. CONCLUSION: Bi-Frequency Symmetry Difference EIT is an exciting new modality of EIT with the ability to detect deviations in the symmetry of a region that occur due to the presence of a lesion. Notably, this modality does not require a time c

Journal article

Hannan S, Faulkner M, Aristovich KY, Avery J, Holder DSet al., 2019, Investigating the safety of fast neural electrical impedance tomography in the rat brain, Physiological Measurement, Vol: 40, ISSN: 0967-3334

OBJECTIVE: Electrical Impedance Tomography (EIT) can be used to image impedance changes which arise due to fast electrical activity during neuronal depolarisation and so holds therapeutic potential for improving the localisation of epileptic seizure foci in patients with treatment-resistant epilepsy to aid surgical resection of epileptogenic tissue. Prolonged cortical stimulation may, however, induce neural injury through excitotoxicity and electrochemical reactions at the tissue-electrode interface. The purpose of this work was to assess whether current levels used in fast neural EIT studies induce histologically detectable tissue damage when applied continuously to the rat cerebral cortex. APPROACH: A 57-electrode epicortical array was placed on one or both hemispheres of adult Sprague-Dawley rats anaesthetised with isoflurane. In an initial series of experiments, current was injected simultaneously at 10, 25, 50, 75 and 100 µA for 1 hour at 1.725 kHz through five electrodes across two epicortical arrays to provide a preliminary indication of the safety of these current levels. Since no obvious cortical damage was observed in these rats, the current level chosen for further investigation was 100 µA, the upper-bound of the range of interest. In a separate series of experiments, 100 µA was applied through a single electrode for 1 hour at 1.725 kHz to verify its safety. Following termination of stimulation, brain samples were fixed in formalin and histologically processed with Haematoxylin and Eosin (H&E) and Nissl stains. MAIN RESULTS: Histological analysis revealed that continuous injection of 100 µA current, equating to a current density of 354 Am-2, into the rat cortex at 1.725 kHz does not cause cortical tissue damage or any alterations to neuronal morphology. SIGNIFICANCE: The safety of current injections during typical EIT protocols for imaging fast neural activity have been validated. The current density established to be safe for

Journal article

Avery J, Dowrick T, Witkowska-Wrobel A, Faulkner M, Aristovich KY, Holder DSet al., 2019, Simultaneous EIT and EEG using frequency division multiplexing, Physiological Measurement, Vol: 40, ISSN: 0967-3334

OBJECTIVE: Methods have previously been reported for simultaneous EIT and EEG recording, but these have relied on post-hoc signal processing to remove switching artefacts from the EEG signal and require dedicated hardware filters and the use of separate EEG and EIT electrodes. This work aims to demonstrate that an uncorrupted EEG signal can be collected simultaneously with EIT data by using frequency division multiplexing (FDM), and to show that the EIT data provides useful information when compared to EEG source localisation.&#13; &#13; Approach: A custom FDM EIT current source was created and evaluated in resistor phantom and neonatal head tank experiments, where a static and dynamic perturbation was imaged. EEG and EIT source localisation were compared when an EEG dipole was placed in the tank. EEG and EIT data were collected simultaneously in a human volunteer, using both a standard EEG and a Visual Evoked Potential (VEP) paradigms.&#13; &#13; Main Results: Differences in EEG and VEP collected with and without simultaneous EIT stimulation showed no significant differences in amplitude, latency or PSD (p-values \textgreater{} 0.3 in all cases). Compared with EEG source localisation, EIT reconstructions were more accurately able to reconstruct both the centre of mass and volume of a perturbation.&#13; &#13; Significance: The reported method is suitable for collecting EIT in a clinical setting, without disrupting the clinical EEG or requiring additional measurement electrodes, which lowers the barrier to entry for data collection. EIT collection can be integrated with existing clinical workflows in EEG/ECoG, with minimal disruption to the patient or clinical team.

Journal article

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