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.

Ultrasound Elastography and MR Elastography for Assessing Liver Fibrosis: Part 1, Principles and Techniques

“…Several driver systems have been designed to produce shear waves for MR elastography [40], including pneumatic, electromagnetic, piezoelectric, and focused ultrasound systems. The current commercial system is an acoustic driver with two components, an active and a passive driver: the active driver in the equipment room generates compression waves, which are transmitted through a flexible tube to the passive driver positioned against the right anterior chest wall of the subject in the scan room and secured using an elastic band.…”

Magnetic Resonance Elastography

“…Numerous driving mechanisms have been devised for MRE, each well-suited for particular uses, and each with its own limitations [34]. One of the oldest designs is an electromagnetic actuator [11,35] that generates vibrations with a small voice coil placed within the polarizing magnetic field of the MRI scanner.…”

Intraoperative magnetic resonance imaging–conditional robotic devices for therapy and diagnosis

“…Since the year 2000, the number of MR-conditional systems reported in literature has grown tremendously. 7,8 The scope for MRIconditional systems has since been extended to include the following: tools for functional MRI (fMRI) for neuroscience research, [9][10][11] assistive devices such as tool positioners, 12 minimally invasive robotic systems, 13 mechanical vibrators for implementation of MRI elastography, 14 and magnetic field steered drug delivery 15 and catheter manipulation. [16][17][18][19] MRI imposes severe restrictions on the design of mechatronic devices.…”