Optimization of a Multifrequency Magnetic Resonance Elastography Protocol for the Human Brain

Abstract

BACKGROUND AND PURPOSE: The brain's stiffness measurements from magnetic resonance elastography (MRE) strongly depend on actuation frequencies, which makes cross-study comparisons challenging. We performed a preliminary study to acquire optimal sets of actuation frequencies to accurately obtain rheological parameters for the whole brain (WB), white matter (WM), and gray matter (GM). METHODS: Six healthy volunteers aged between 26 and 72 years old went through MRE with a modified single-shot spin-echo echo planar imaging pulse sequence embedded with motion encoding gradients on a 3T scanner. Frequency-independent brain material properties and best-fit material model were determined from the frequency-dependent brain tissue response data (20 -80 Hz), by comparing four different linear viscoelastic material models (Maxwell, Kelvin-Voigt, Springpot, and Zener). During the material fitting, spatial averaging of complex shear moduli (G*) obtained under single actuation frequency was performed, and then rheological parameters were acquired. Since clinical scan time is limited, a combination of three actuation frequencies that would provide the most accurate approximation and lowest fitting error was determined for WB, WM, and GM by optimizing for the lowest Bayesian information criterion (BIC). RESULTS: BIC scores for the Zener and Springpot models showed these models approximate the multifrequency response of the tissue best. The best-fit frequency combinations for the reference Zener and Springpot models were identified to be 30-60-70 and 30-40-80 Hz, respectively, for the WB. CONCLUSIONS: Optimal sets of actuation frequencies to accurately obtain rheological parameters for WB, WM, and GM were determined from shear moduli measurements obtained via 3-dimensional direct inversion. We believe that our study is a first-step in developing a region-specific multifrequency MRE protocol for the human brain.

Nonlinear Dynamical Behavior of the Deep White Matter during Head Impact

“…Recently, Okamoto et al, induced external harmonic vibrations to the human skull to obtain the dynamics of the brain in vivo. In this study, they used magnetic resonance elastography (MRE) [58], a technique based on the imaging of shear-wave propagation in tissue as a result of external actuation [59,60]. They analyzed 15 human subjects and observed shear-wave reflection and/or redirection near the falx and the tentorium.…”

<p>Nanomechanics and Histopathology as Diagnostic Tools to Characterize Freshly Removed Human Brain Tumors</p>

“…For this reason, the direct comparison of MRE to AFM data is not possible. Moreover, even comparison between different studies using MRE is challenging, because the frequencies used during each MRE scan greatly impact the results and usually vary from 1 Hz up to two kHz, 23,58,59 while frequency modulation of the AFM technique does not allow the reaching of these limits. Additionally, the magnitude difference might be explained by exclusion of intracranial pressure and additional pressure gradients applied by the tumors, which is not observed in ex vivo AFM measurements.…”

Slit-like hypertensive hydrocephalus: Report of a late, complex, and multifactorial complication in an oncologic patient

“…However, MRE is an experimental technology, and there are conflicting data about the brain areas to evaluate and obtain pathognomonic results of brain stiffness. [ 4 , 10 , 12 , 21 ] Moreover, the patient was treated 29 years before our observation, and it was impossible to have MRE data to compare with the brain consistency before the radiochemotherapy treatments. Finally, we do not have the possibility to perform MRE in our region, but we are planning to provide it and to follow-up the patient with MRE to study eventual further brain stiffness modification.…”