Michael Lamperth

The case for MR-compatible robotics: a review of the state of the art

The numerous imaging capabilities of magnetic resonance imaging (MRI) coupled with its lack of ionizing radiation has made it a desirable modality for real‐time guidance of interventional procedures. The combination of these abilities with the advantages granted by robotic systems to perform accurate and precise positioning of tools has driven the recent development of MR‐compatible interventional and assistive devices.

A review of magnetic resonance imaging compatible manipulators in surgery.

Abstract Developments in magnetic resonance imaging (MRI), coupled with parallel progress in the field of computer-assisted surgery, mean that an ideal environment has been created for the development of MRI-compatible robotic systems and manipulators, capable of enhancing many types of surgical procedure. However, MRI does impose severe restrictions on mechatronic devices to be used in or around the scanners. In this article a review of the developments in the field of MRI-compatible surgical manipulators over the last decade is presented. The manipulators developed make use of different methods of actuation, but they can be reduced to four main groups: actuation transmitted through hydraulics, pneumatic actuators, ultrasonic motors based on the piezoceramic principle and remote manual actuation. Progress has been made concerning material selection, position sensing, and different actuation techniques, and design strategies have been implemented to overcome the multiple restrictions imposed by the MRI environment. Most systems lack the clinical validation needed to continue on to commercial products.

Manufacturing and placing a bespoke support for the Marfan aortic root: description of the method and technical results and status at one year for the first ten patients

Fatal aortic dissection commonly occurs in Marfan syndrome. Prevention currently relies on elective replacement of the aortic root. We are evaluating the placement of a manufactured, bespoke external support derived from a computer aided design in a prospective study. In the first ten patients, measurements were made consistently of the ascending aorta at the level of closure of the aortic valve cusps from magnetic resonance imaging (MRI) studies taken preoperatively and at fixed intervals thereafter. Before and after images were presented for measurement amongst duplicate images of 37 unoperated Marfan patients to permit assessment of intra-observer measurement reproducibility. All images were presented in random sequence to a radiologist unaware of the research question. The largest difference between the preoperative measurement and that made at least one year after surgery was determined. All patients had surgery as planned without complications and were alive at one year. In eight of the ten patients, the largest observed change was a marked reduction in aortic root diameter. The primary objective of this surgery was achieved in each case, reinforcing the ascending aorta whilst leaving the native aortic valve intact and conserving the blood/endothelium interface.

The feasibility of MR-Image guided prostate biopsy using piezoceramic motors inside or near to the magnet isocentre

The excellent soft tissue contrast of Magnetic Resonance Imaging (MRI) has encouraged the development of MRI compatible systems capable of combining the advantages of robotic manipulators with high quality anatomical images. Continuing this development, a new five DOF prostate biopsy manipulator has been designed for use inside a closed 1.5T MRI scanner. Space constraints in the bore and the current trend to restrict field strength exposure for operators indicate that a master-slave configuration is ideal for controlling the robotic system from outside the bore. This system has been designed to work with piezoceramic motors and optical encoders placed inside or near the field of view of the scanner, using real time image guidance for targeting biopsies to specific lesions in the prostate. MRI tests have been performed to prove the feasibility of this concept and a one DOF proof-of-concept test rig implementing closed loop position control has been tested and is presented here. A first prototype of the slave manipulator has been designed and manufactured incorporating this new technology.

Magnetic resonance elastography hardware design: A survey:

Abstract Magnetic resonance elastography (MRE) is an emerging technique capable of measuring the shear modulus of tissue. A suspected tumour can be identified by comparing its properties with those of tissues surrounding it; this can be achieved even in deep-lying areas as long as mechanical excitation is possible. This would allow non-invasive methods for cancer-related diagnosis in areas not accessible with conventional palpation. An actuating mechanism is required to generate the necessary tissue displacements directly on the patient in the scanner and three different approaches, in terms of actuator action and position, exist to derive stiffness measurements. However, the magnetic resonance (MR) environment places considerable constraints on the design of such devices, such as the possibility of mutual interference between electrical components, the scanner field, and radio frequency pulses, and the physical space restrictions of the scanner bore. This paper presents a review of the current solutions that have been developed for MRE devices giving particular consideration to the design criteria including the required vibration frequency and amplitude in different applications, the issue of MR compatibility, actuation principles, design complexity, and scanner synchronization issues. The future challenges in this field are also described.

A Modular Approach to MRI-Compatible Robotics

The objective of the research described in this article is to create individual MR-compatible modules consisting of 1-DoF stages complete with actuators and position encoders for implementation of the closed-loop position control. These modules can connect together to form multi-DoF assemblies that can be located inside the scanner bore near to the patient anatomy that requires the intervention. This avoids the problems associated with remote actuation and transmission mechanisms, considerably reducing the size of the manipulator. As most robots consist of kinematic chains of 1-DoF stages, these modules would be suitable for a wide range of interventions, and their design can be optimized for the procedure for which they are applied to.

System for 3-D Real-Time Tracking of MRI-Compatible Devices by Image Processing

Real-time processing of MRIs is reported as a method of 3D tracking of mechanical devices within the field of view using passive microcoil fiducials. The specific implementation described makes use of two scan planes for full 3D tracking of a 5-DOF manipulator arm used for prostate biopsy under image guidance. Real-time tracking was observed with a maximum update rate of 0.42 frames per second for a maximum probe velocity of 10 mm/s. The localization of fiducials had a mean error of 0.36 (plusmn0.17) mm (p < 0.02), leading to a mean error in the needle tip position of 2.6 (plusmn0.3) mm (p < 0.05).

Robotic System for Transrectal Biopsy of the Prostate: Real-Time Guidance Under MRI

In this paper, to harness the possibility of real-time guidance of MRI, a robotic system has been developed to perform transrectal prostate biopsy inside a 1.5-T closed bore scanner. A specially developed MR pulse sequence is capable of tracking the needle location in real time while dynamically updating the scan planes to always include the needle and target.

Parameterised inventories for life cycle assessment

Background and ObjectiveLife cycle assessment (LCA) is a highly data intensive undertaking, where collecting the life cycle inventory (LCI) data is the most labour intensive part. The aim of this paper is to show a method for representing the LCI in a simplified manner which not only allows an estimative, quantitative LCA, but also the application of advanced analysis methods to LCA.Procedure and MethodThe method is based on two main components: Firstly the parameterisation of the life cycle inventory for complete product ranges, e.g. relative material composition (the parameterisation factor is product mass or product volume), relative manufacturing inputs and wastes (the parameterisation factor is production output, in number of items, mass or volume), inputs, wastes and emissions during use (the parameterisation factors are efficiency, emissions per unit energy converted, etc.). Secondly, the parameterisation factors are related to design parameters, e.g. the efficiency of three-phase induction motors increase as the torque output increases and decreases with the number of poles, while the mass of the same induction motor increases with torque. Determining these relationships is initially labour-intensive, but only has to be done once for a product type and it is just a matter of fitting appropriate models after the collection of the relevant data. Also, required data is not impossible to come by, and respective industries publish many of the relevant data for marketing and design purposes. Due to the wide variety of products-whereby here the term ‘product’ is used in the widest sense and can be a component, an assembly, a consumer product or service-the relationships are represented as ranges with upper and lower limits. One of the limits represents ‘the best practically possible’ and is a good indication of what the technologies’ capabilities are at the time. Top-down approaches allow the approximate determination of manufacturing inventories for product ranges. Bringing the two components together, the LCA analyst can use known design parameters and so quickly determine an estimate of the life cycle inventory, after which it is then a relatively simple step to carry out the full, approximate LCA. Furthermore, this method can be extended to include life cycle costing as an extension, to simultaneously assess economic aspects of the design.Case StudyThe method is further illustrated using a 3-phase asynchronous motor as an example and it is shown how the changing needs during the design process are utilised.Discussion and ConclusionThe paper introduces the concept of parameterised inventories for the use in LCA, describes the general procedure of determining the relationships of the parameterised inventories to design parameters and outlines future developments enabled by this method of inventory representation. The novel parts of the method are a simplified, but quantitative LCA method. For the first time this enables parametric studies and sensitivity analysis, not only for varying material compositions, but varying the underlying design parameters in complex interactions, and finding optimised sets of solutions for those design parameters to achieve one or more optimised criteri(on)a.PerspectiveThe full potential of the method as an analysis tool, especially in the early design phases, will be reached in an integrated engineering environment, where relevant LCA and cost data are automatically and systematically exchanged along the supply chain.

Haptic Needle Unit for MR-Guided Biopsy and Its Control

MRI provides high-resolution anatomical images and is ideal for certain image-guided interventions. Due to the physical separation between the patient region of interest and the workspace accessible by the clinician, direct force feedback from the target anatomy is missing during the interventions. This paper demonstrates the use of a master-slave haptic device for magnetic resonance-guided biopsy, using a novel haptic control scheme based upon a neural network speed model. Results have shown the feasibility of the proposed hardware design and control scheme.