A brief overview of the current state of the art is given, along with a description of the main opportunities, possibilities and challenges that the future will bring to this exciting and promising field.

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.

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.

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 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.