Design, Construction, and Implementation of a Magnetic Resonance Elastography Actuator for Research Purposes

Abstract

Magnetic resonance elastography (MRE) is a technique for determining the mechanical response of soft materials using applied harmonic deformation of the material and a motion‐sensitive magnetic resonance imaging sequence. This technique can elucidate significant information about the health and development of human tissue such as liver and brain, and has been used on phantom models (e.g., agar, silicone) to determine their suitability for use as a mechanical surrogate for human tissues in experimental models. The applied harmonic deformation used in MRE is generated by an actuator, transmitted in bursts of a specified duration, and synchronized with the magnetic resonance signal excitation. These actuators are most often a pneumatic design (common for human tissues or phantoms) or a piezoelectric design (common for small animal tissues or phantoms). Here, we describe how to design and assemble both a pneumatic and a piezoelectric MRE actuator for research purposes. For each of these actuator types, we discuss displacement requirements, end‐effector options and challenges, electronics and electronic‐driving requirements and considerations, and full MRE implementation. We also discuss how to choose the actuator type, size, and power based on the intended material and use. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Design, construction, and implementation of a convertible pneumatic MRE actuator for use with tissues and phantom models Basic Protocol 2: Design, construction, and implementation of a piezoelectric MRE actuator for localized excitation in phantom models

Cerebral tomoelastography based on multifrequency MR elastography in two and three dimensions

“…Our actuator setup is position-sensitive and therefore we ensured that the volunteer's head was placed in a similar position on the driver setup during all follow-up examinations. Nevertheless, any other actuation setup (Runge et al, 2019;Smith et al, 2020;Qiu et al, 2021;Triolo et al, 2022) that achieves good wave penetration of the brain with high test-retest reproducibility is suitable for tomoelastography and can even further improve the consistency of cerebral MRE. Moreover, the transverse slice blocks were automatically aligned by the scanner.…”

MR Elastography in Cancer

“…Shear waves can be induced by acoustic actuators placed on the body surface near the field of view. 28 Commercially available setups use loudspeakers and passive drums. 29 Other concepts include multiple compressed air drivers for deep tissue stimulation in multifrequency MRE 30 or eccentric mass drivers for harmonic tissue stimulation.…”

“…The smaller the tissue, the higher the excitation frequency to ensure that at least a full wavelength is detected. Shear waves can be induced by acoustic actuators placed on the body surface near the field of view 28 . Commercially available setups use loudspeakers and passive drums 29 .…”

Increased Hindbrain Motion in Chiari Malformation I Patients Measured Through 3D Amplified MRI (3D aMRI)

“…The main reason for this difficulty is that the intrinsic motion of the brain is extremely small (in the order of 100 µm [20]), and therefore, very difficult to measure with conventional imaging tools. The most prominent method to track the brain motion is through magnetic resonance elastography (MRE) [21][22][23][24][25] in which an external actuator [26] is used to cause shear wave propagation into the brain tissue and then the resultant tissue displacement field is captured by using Phase-contrast MRI (PC-MRI) [22][23][24]27]. To capture the intrinsic brain motion without an external actuator however, previous medical imaging studies used cine PC-MRI [28], or displacement encoded imaging with stimulated echoes (DENSE) MRI [20,29,30].…”