An electromagnetic actuator for brain magnetic resonance elastography with high frequency accuracy

Abstract

Our goal is to design, test and verify an electromagnetic actuator for brain magnetic resonance elastography (MRE). We proposed a grappler-shaped design that can transmit stable vibrations into the brain. To validate its performance, simulations were carried out to ensure the electromagnetic field generated by the actuator did not interfere with the B 0 field. The actuation vibration spectrum was analyzed to verify the actuation accuracy. Phantom and volunteer experiments were carried out to evaluate the performance of the actuator. Simulation of the magnetic field showed that the proposed actuator has a fringe field of less than 3 G in the imaging region.The phantom experiments showed that the proposed actuator did not interfere with the routine imaging sequences. The measured vibration spectra demonstrated that the frequency offset was about one third that of a pneumatic device and the transmission efficiency was three times higher. The shear moduli estimated from brain MRE were consistent with those from the literature. The actuation frequency of the proposed actuator has less frequency offset and off-center frequency components compared with the pneumatic counterpart. The whole actuator weighted only 980 g.The actuator can carry out multifrequency MRE on the brain with high accuracy. It is easy to use, comfortable for the patient and portable.

Mechanical vibration modulates regional cerebral blood flow and biomechanical co-variance network in a frequency-dependent manner

“…The order of frequency scanning between 20, 30, 40 Hz was randomized to minimize the potential influence of sequential measurement order. The actuator was used for both vibration actuation and MRE acquisition ( 38 ). A supine position was adopted for all imaging procedures.…”

“…MRE was performed during each vibration session ( 38 ). Single-shot echo-planar imaging (EPI) based MRE sequence with a first-nulling motion encoding gradient (MEG) was used for brain displacement measurement.…”

“…The order of the measurement frequency for each module was carried out in a randomized, counterbalanced way. The vibration motion was induced using a high-frequency accuracy electromagnetic actuator ( 38 ).…”

“…where the brain-blood water partition coefficient 𝜆 = 0.9 𝑚𝐿/𝑔 , 𝑆𝐼 𝑐𝑜𝑛𝑡𝑟𝑜𝑙 , 𝑆𝐼 𝑙𝑎𝑏𝑒𝑙 and 𝑆𝐼 𝑃𝐷 are the control, label, and proton density-weighted images, respectively, 𝑇 1,𝑏𝑙𝑜𝑜𝑑 = 1650 𝑚𝑠 is the longitudinal relaxation time of the blood at 3T, 𝛼 = 0.85 is the labeling efficiency for pCASL, 𝜏 is the label duration. MRE was performed during each vibration session (38). Single-shot echo-planar imaging (EPI) based MRE sequence with a first-nulling motion encoding gradient (MEG) was used for brain displacement measurement.…”

A Minireview on Brain Models Simulating Geometrical, Physical, and Biochemical Properties of the Human Brain

“…Recent MRI approaches, non-invasive, in-vivo and ex-vivo , yield more and more information, notably about the WM component such as the myelin density ( Sepehrband et al, 2015 ), and about the WM anisotropy such as direction-dependent moduli ( Smith et al, 2020 ). More specifically magnetic resonance elastography (MRE) enables the access to a large variety of physical parameters of the brain ( Yin et al, 2018 ), notably the comparison of ex vivo and in vivo measurements of brain tissue ( Chen et al, 2021 ) that enables to access to frequency-dependent behavior ( Lv et al, 2020 ; Qiu et al, 2021 ) . Interestingly, MRE fast analysis of regional variations of biomechanics could measure variations of neuronal activity as shown in rodent model ( Patz et al, 2019 ).…”