Publications
76 results found
Brujic D, Chappell KE, Ristic M, 2020, Accuracy of collagen fibre estimation under noise using directional MR imaging, Computerized Medical Imaging and Graphics, Vol: 86, Pages: 1-9, ISSN: 0895-6111
In tissues containing significant amounts of organised collagen, such as tendons, ligaments, menisci and articular cartilage, MR imaging exhibits a strong signal intensity variation caused by the angle between the collagen fibres and the magnetic field. By obtaining scans at different field orientations it is possible to determine the unknown fibre orientations and to deduce the underlying tissue microstructure. Our previous work demonstrated how this method can detect ligament injuries and maturity-related changes in collagen fibre structures. Practical application in human diagnostics will demand minimisation of scanning time and likely use of open low-field scanners that can allow re-orienting of the main field. This paper analyses the performance of collage fibre estimation for various image SNR values, and in relation to key parameters including number of scanning directions and parameters of the reconstruction algorithm. The analysis involved Monte Carlo simulation studies which provided benchmark performance measures, and studies using MR images of caprine knee samples with increasing levels of synthetic added noise. Tractography plots in the form of streamlines were performed, and an Alignment Index (AI) was employed as a measure of the detected orientation distribution. The results are highly encouraging, showing high accuracy and robustness even for low image SNR values.
Chappell K, Brujic D, Van Der Straeten C, et al., 2019, Detection of maturity and ligament injury using magic angle directional imaging, Magnetic Resonance in Medicine, Vol: 82, Pages: 1041-1054, ISSN: 0740-3194
Purpose: To investigate whether magnetic field–related anisotropies of collagen may be correlated with postmortem findings in animal models.Methods: Optimized scan planning and new MRI data‐processing methods were proposed and analyzed using Monte Carlo simulations. Six caprine and 10 canine knees were scanned at various orientations to the main magnetic field. Image intensities in segmented voxels were used to compute the orientation vectors of the collagen fibers. Vector field and tractography plots were computed. The Alignment Index was defined as a measure of orientation distribution. The knees were subsequently assessed by a specialist orthopedic veterinarian, who gave a pathological diagnosis after having dissected and photographed the joints.Results: Using 50% less scans than reported previously can lead to robust calculation of fiber orientations in the presence of noise, with much higher accuracy. The 6 caprine knees were found to range from very immature (< 3 months) to very mature (> 3 years). Mature specimens exhibited significantly more aligned collagen fibers in their patella tendons compared with the immature ones. In 2 of the 10 canine knees scanned, partial cranial caudal ligament tears were identified from MRI and subsequently confirmed with encouragingly high consistency of tractography, Alignment Index, and dissection results.Conclusion: This method can be used to detect injury such as partial ligament tears, and to visualize maturity‐related changes in the collagen structure of tendons. It can provide the basis for new, noninvasive diagnostic tools in combination with new scanner configurations that allow less‐restricted field orientations.
Zarrebini-Esfahani A, Aslaninejad M, Ristic M, et al., 2017, Experimental analysis of surface finish in normal conducting cavities, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 869, Pages: 76-83, ISSN: 0168-9002
A normal conducting 805 MHz test cavity with an in built button shaped sample is used to conduct a series of surface treatment experiments. The button enhances the local fields and influences the likelihood of an RF breakdown event. Because of their smaller sizes, compared to the whole cavity surface, they allow practical investigations of the effects of cavity surface preparation in relation to RF breakdown. Manufacturing techniques and steps for preparing the buttons to improve the surface quality are described in detail. It was observed that even after the final stage of the surface treatment, defects on the surface of the cavities still could be found.
Franco E, Rea M, Gedroyc W, et al., 2016, Control of a master-slave pneumatic system for teleoperated needle insertion in MRI, IEEE-ASME Transactions on Mechatronics, Vol: 21, Pages: 2595-2600, ISSN: 1083-4435
This paper presents the control of a pneumatically actuated master-slave system intended for teleoperated needle insertion in the liver under magnetic resonance imaging (MRI) guidance. It addresses the challenge of achieving accurate needle positioning and force feedback to the operator in the case of pneumatic actuation with significant friction. Using time-delay position control as the basis, we investigate force feedback via impedance control and admittance control. For impedance control, we propose a new adaptive friction compensation algorithm that only requires a single tuning parameter. Experiments on a 1-degree of freedom prototype system using silicone rubber phantoms with distinct densities highlight the differences between impedance control and admittance control, and demonstrate superior performance compared with a traditional impedance control scheme.
McGinley JVM, Ristic M, Young IR, 2016, A permanent MRI magnet for magic angle imaging having its field parallel to the poles, Journal of Magnetic Resonance, Vol: 271, Pages: 60-67, ISSN: 1090-7807
A novel design of open permanent magnet is presented, in which the magnetic field is oriented parallel to the planes of its poles. The paper describes the methods whereby such a magnet can be designed with a field homogeneity suitable for Magnetic Resonance Imaging (MRI). Its primary purpose is to take advantage of the Magic Angle effect in MRI of human extremities, particularly the knee joint, by being capable of rotating the direction of the main magnetic field B0 about two orthogonal axes around a stationary subject and achieve all possible angulations. The magnet comprises a parallel pair of identical profiled arrays of permanent magnets backed by a flat steel yoke such that access in lateral directions is practical. The paper describes the detailed optimization procedure from a target 150 mm DSV to the achievement of a measured uniform field over a 130 mm DSV. Actual performance data of the manufactured magnet, including shimming and a sample image, is presented. The overall magnet system mounting mechanism is presented, including two orthogonal axes of rotation of the magnet about its isocentre.
Franco E, Rea M, Gedroyc W, et al., 2016, Robot-Assistant for MRI-Guided Liver Ablation: a pilot study, Medical Physics, Vol: 43, ISSN: 0094-2405
Purpose:Percutaneous ablation under MRI-guidance allows treating otherwise inoperable liver tumors locally using a catheter probe. However, manually placing the probe is an error-prone and time consuming task that requires a considerable amount of training. The aim of this paper was to present a pneumatically actuated robotic instrument that can assist clinicians in MRI-guided percutaneous intervention of the liver and to assess its functionality in a clinical setting. The robot positions a needle-guide inside the MRI scanner bore and assists manual needle insertions outside the bore.Methods:The robot supports double oblique insertions that are particularly challenging for less experienced clinicians. Additionally, the system employs only standard imaging sequences and can therefore be used on different MRI scanners without requiring prior integration. The repeatability and the accuracy of the robot were evaluated with an optical tracking system. The functionality of the robot was assessed in an initial pilot study on two patients that underwent MRI-guided laser ablation of the liver.Results:The robot positioned the needle-guide in a repeatable manner with a mean error of 0.35 mm and a standard deviation of 0.32 mm. The mean position error corresponding to the needle tip, measured for an equivalent needle length of 195 mm over 25 fixed points, was 2.5 mm with a standard deviation of 1.2 mm. The pilot study confirmed that the robot does not interfere with the equipment used for MRI-guided laser ablation and does not visibly affect the MR images. The robot setup integrated seamlessly within the established clinical workflow. The robot-assisted procedure was successfully completed on two patients, one of which required a complex double oblique insertion. For both patients, the insertion depth and the tumor size were within the range reported for previous MRI-guided percutaneous interventions. A third patient initially enrolled in the pilot study and was considerably he
Franco E, Ristic M, 2016, Needle-guiding robot for laser ablation of liver tumors under MRI guidance, IEEE-ASME Transactions on Mechatronics, Vol: 21, Pages: 931-944, ISSN: 1083-4435
This paper presents the design, control and experimental evaluation of a needle-guiding robot intended for use in laser ablation (LA) of liver tumors under guidance by Magnetic Resonance Imaging (MRI). The robot provides alignment of a needle guide inside the MRI scanner bore and employs manual needle insertion. In order to minimize MR-image deterioration, the robot is actuated using plastic pneumatic cylinders and long pipes connecting to control valves located outside the MRI scanner room. A new Time Delay Control scheme (TDC) was employed to achieve high position accuracy without requiring pressure or force measurements in the MRI scanner. The control scheme was compared with experiments to a previously developed Sliding Mode Controller (SMC). A marker localization method based on the convolution theorem of Fourier transform was employed to register the robot in the MRI scanner coordinate system and to verify the position of the needle guide before the manual needle insertion. Experiments in a closed-bore MRI scanner showed a variation in SNR below 5%. A phantom study indicates that the targeting error in robot-assisted needle insertions is below 5 mm and suggest a potential time saving of 30 minutes compared to the manual MRI-guided LA procedure.
Franco E, Aurisicchio M, Ristic M, 2016, Design and control of 3-DOF needle positioner for MRI-guided laser ablation of liver tumours, International Journal of Biomechatronics and Biomedical Robotics, Vol: 3, ISSN: 1757-6792
This article presents the design and control of a pneumatic needle positioner for laser ablation of liver tumours under guidance by magnetic resonance imaging (MRI). The prototype was developed to provide accurate point-to-point remote positioning of a needle guide inside an MR scanner with the aim of evaluating the potential advantages over the manual procedure. In order to minimise alterations to the MR environment, the system employs plastic pneumatic actuators and 9 m long supply lines connecting with the control hardware located outside the magnet room. An improved sliding mode control (SMC) scheme was designed for the position control of the device. Wireless micro-coil fiducials are used for automatic registration in the reference frame of the MR scanner. The MRI-compatibility and the accuracy of the prototype are demonstrated with experiments in the MR scanner.
Franco E, Ristic M, 2015, Adaptive control of a master-slave system for teleoperated needle insertion under MRI-guidance, 23rd Mediterranean Conference on Control and Automation (MED), Publisher: IEEE, Pages: 61-67, ISSN: 2325-369X
This paper presents the control of a master-slave system for teleoperated needle insertion under guidance by Magnetic Resonance Imaging (MRI). The primary aim of our research is the robot-assisted laser ablation of liver tumors. The master-slave system consists of a master unit that sits next to the operator, outside the scanner room, and of a slave unit located inside the cylindrical MRI scanner. The needle insertion force is measured with a specially designed fiber optic force sensor mounted on the slave unit. Pneumatic actuation is employed in both master and slave in order to minimize the interference with the MRI environment. Accurate position control of the slave unit is achieved with a Time Delay Control scheme (TDC). Differently from previous designs, the force feedback on the master unit is provided by an adaptive controller that compensates the friction of the pneumatic actuator. The advantages over a baseline force controller are demonstrated with experiments on silicone rubber phantoms.
Perkonigg F, Brujic D, Ristic M, 2015, Platform for Multiagent Application Development Incorporating Accurate Communications Modeling, IEEE Transactions on Industrial Informatics, Vol: 11, Pages: 728-736, ISSN: 1941-0050
Multiagent systems are widely recognized as a method of choice for realization of distributed time-critical applications for the smart grid. However, no general solutions have been proposed for the difficult task of system development and validation, ready for deployment, which would fully account for the underlying communication network performance. We propose a novel platform designed for this purpose, which integrates a standard multiagent development framework [Java Agent Development (JADE)] and an industry standard communications network simulator (OPNET modeler). It was realized through generic extensions of the JADE framework to provide discrete event scheduling capabilities, while the OPNET modeler was extended to provide a generic method of associating the network nodes with agents running in JADE. The adopted method adheres to the high-level architecture standard. Importantly, applications developed using this platform may be deployed on the target system without manual modifications. A distributed protection application is presented and the performance is analyzed with respect to candidate agent behaviors and communication scenarios, demonstrating that the feasibility of the application critically depends on the choices made during its design and implementation.
Kardoulaki EM, Syms RRA, Young IR, et al., 2015, Thin-film micro-coil detectors: Application in MR-thermometry, Sensors and Actuators A: Physical, Vol: 226, Pages: 48-58, ISSN: 1873-3069
Galassi F, Brujic D, Rea M, et al., 2015, Fast and accurate localization of multiple RF markers for tracking in MRI-guided interventions, Magnetic Resonance Materials in Physics, Biology and Medicine, Vol: 28, Pages: 33-48, ISSN: 0968-5243
Object: A new method for 3D localization of N fiducial markers from 1D projections is presented and analysed. It applies to semi-active markers and active markers using a single receiver channel.Materials and methods: The novel algorithm computes candidate points using peaks in three optimally selected projections and removes fictitious points by verifying detected peaks in additional projections. Computational complexity was significantly reduced by avoiding cluster analysis, while higher accuracy was achieved by using optimal projections and by applying Gaussian interpolation in peak detection. Computational time, accuracy and robustness were analysed through Monte Carlo simulations and experiments. The method was employed in a prototype MRI guided prostate biopsy system and used in preclinical experiments.Results: The computational time for 6 markers was better than 2 ms, an improvement of up to 100 times, compared to the method by Flask et al. (J Magn Reson Imaging 14(5):617–627, 2001). Experimental maximum localization error was lower than 0.3 mm; standard deviation was 0.06 mm. Targeting error was about 1 mm. Tracking update rate was about 10 Hz.Conclusion: The proposed method is particularly suitable in systems requiring any of the following: high frame rate, tracking of three or more markers, data filtering or interleaving.
Franco E, Ristic M, 2014, Design and control of needle positioner for MRI-guided laser ablation of the liver, IEEE/ASME 10th International Conference on Mechatronic and Embedded Systems and Applications (MESA), Publisher: IEEE
This paper presents the design and control of a pneumatic needle positioner for laser ablation of liver tumors under guidance by Magnetic Resonance Imaging (MRI). The prototype was developed to provide accurate point-to-point remote positioning of a needle guide inside an MR scanner with the aim of evaluating the potential advantages over the manual procedure. In order to minimize alterations to the MR environment the system employs plastic pneumatic actuators and 9 m long supply lines connecting with the control hardware located outside the magnet room. An optimized Sliding Mode Control (SMC) scheme was designed for the position control of the device. Wireless micro-coil fiducials are used for automatic registration in the reference frame of the MR scanner. The MRI-compatibility and the accuracy of the prototype are demonstrated with experiments in the MR scanner.
Franco E, Ristic M, 2014, Time delay controller for the position control of a MRI-compatible pneumatic actuation with long supply lines, IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), Publisher: IEEE, Pages: 683-689, ISSN: 2159-6255
Pneumatic actuation with long supply lines is widely employed in robotic devices operating in the Magnetic Resonance Imaging (MRI) environment because it produces minimum alteration to the magnetic field. However the high friction of the cylinders and the delay introduced by the pipes make accurate position control challenging. This work presents design and control of an MRI-compatible pneumatic actuation that employs a commercially available, plastic cylinder and long supply lines connecting with the control hardware located outside the magnet room. The system has been designed to actuate a MRI-compatible needle-guiding robot intended for MRI-guided intervention of liver tumors. Accurate position control is achieved with a new Time Delay Control (TDC) scheme that includes a saturation function. The controller requires limited knowledge of the system's parameters and does not rely on pressure or force measurements. Simulation results and experiments demonstrate the advantages of the proposed controller over existing TDC schemes. The MRI-compatibility of the pneumatic actuation is verified in a 3T MRI scanner.
Ralphs SJL, North O, Ristic M, et al., 2014, THE USE OF KINEMATIC ANALYSIS OF BILE DUCT CANNULATION AS A MEANS OF OBJECTIVELY ASSESSING ENDOSCOPIC SKILL AT ERCP, GUT, Vol: 63, Pages: A43-A43, ISSN: 0017-5749
Ristic M, Gryska Y, McGinley JVM, et al., 2013, Supercapacitor Energy Storage for Magnetic Resonance Imaging Systems, IEEE Transactions on Industrial Electronics, Vol: PP, ISSN: 0278-0046
Magnetic Resonance Imaging (MRI) involves very short pulses of very high current. Substantial savings in the high cost of MRI installations may be realised by employing suitable electrical energy storage, for which supercapacitors are strong candidates in view of high specific power and long cycle life. A key question is whether the well-known capacitance degradation with increased frequency is compatible with the complex and highly variable duty cycles of various MRI sequences. Compatibility of the supercapacitor voltage range with the MRI system must also be considered. We present a detailed analysis of power duty profiles in MRI, using actual imaging sequences, that has not been reported previously. We also propose and validate a simplified supercapacitor model that can accurately simulate its performance in the MRI system, involving pulses several orders of magnitude shorter than those considered previously. Results of equivalent experiments involving Lithium-Ion Iron Phosphate (LiFePO4) batteries are also reported. Finally, we present a detailed analysis of the overall energy storage performance in a realistic neurological examination. The study is based on a specific system of our own design and we fully disclose its relevant parameters, so that the results would be of direct practical value to the wider community, including developers of MRI.
Syms RRA, Young IR, Ahmad MM, et al., 2013, Magneto-Inductive Catheter Receiver for Magnetic Resonance Imaging, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol: 60, Pages: 2421-2431, ISSN: 0018-9294
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- Citations: 16
Perkonigg F, Brujic D, Ristic M, 2013, MAC- Sim:A Multi-Agent and Communication Network Simulation Platform for Smart Grid Applications Based on Established Technologies, IEEE International Conference on Smart Grid Communications (SmartGridComm), Publisher: IEEE, Pages: 570-575, ISSN: 2373-6836
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- Citations: 7
North OJ, Ristic M, Wadsworth CA, et al., 2012, Design and Evaluation of Endoscope Remote Actuator for MRI-Guided Endoscopic Retrograde Cholangio-Pancreatography (ERCP), 4th IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob) / Symposium on Surgical Robotics, Publisher: IEEE, Pages: 787-792, ISSN: 2155-1782
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- Citations: 3
Ristic M, McGinley JVM, Lorenzoni F, 2011, Numerical Study of Quench Protection Schemes for a MgB<sub>2</sub> Superconducting Magnet, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, Vol: 21, Pages: 3501-3508, ISSN: 1051-8223
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- Citations: 10
Brujic D, Ainsworth I, Ristic M, 2011, Fast and accurate NURBS fitting for reverse engineering, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 54, Pages: 691-700, ISSN: 0268-3768
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- Citations: 48
Brujic D, Ristic M, Mattone M, et al., 2010, CAD based shape optimization for gas turbine component design, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, Vol: 41, Pages: 647-659, ISSN: 1615-147X
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- Citations: 25
Tse ZTH, Janssen H, Hamed A, et al., 2009, Magnetic resonance elastography hardware design: a survey, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 223, Pages: 497-514, ISSN: 0954-4119
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- Citations: 28
Ristic M, Brujic D, Thoma K, 2008, Economic dispatch of distributed combined heat and power systems participating in electricity spot markets, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, Vol: 222, Pages: 743-752, ISSN: 0957-6509
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- Citations: 9
Brujic D, Ristic M, Thoma K, 2007, Optimal operation of distributed CHP systems for participation in electricity spot markets, International Conference on Computer as a Tool (EUROCON 2007), Publisher: IEEE, Pages: 2389-2395
Xu HQ, Ristic M, Besant CB, et al., 2005, A Web-based system for manufacturing co-ordination in complex supply networks, INTERNATIONAL JOURNAL OF PRODUCTION RESEARCH, Vol: 43, Pages: 2049-2070, ISSN: 0020-7543
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- Citations: 9
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