Magnetic resonance elastography (MRE) of brain relies on inducing and measuring shear waves in the brain. However, studies have shown vibration could induce changes in cerebral blood flow (CBF), which has a modulation effect and may affect the biomechanical properties measured. This study aims to propose and validate an indirect excitation method, which can generate shear waves in the brain with minimal changes in CBF.
We devised an electromagnetic actuation system to generate stable vibrations beneath the neck. This system circumvents direct skull stimulation, instead transmitting shear waves to the brain indirectly via the spine and brainstem. To ensure the electromagnetic compatibility and actuation efficiency, we conducted tests using two phantoms. One served to evaluate the system’s electromagnetic compatibility, while the other assessed its actuation performance. The repeatability, reliability, octahedral shear strain (OSS), and CBF outcomes of our indirect excitation method were rigorously examined.
Phantom results showed that the proposed actuator did not interfere with the routine imaging sequence and successfully generated multifrequency shear waves. When compared with the conventional direct head stimulation method, brain MRE results from the proposed actuator showed no significant differences in terms of intraclass correlation coefficients and coefficients of variation. Moreover, the OSS generated by the indirect excitation in the frontal and parietal lobes decreased by 25.96% and 16.73% respectively. Evaluation of CBF in healthy volunteers revealed no significant changes for the indirect excitation method, whereas significant decreases in CBF were observed in four subregions when employing direct excitation. This work presents the first demonstration of an indirect excitation brain MRE system that minimizes CBF changes, thus holding potential for more precise and comfortable brain MRE.