Robustness of MR Elastography in the Healthy Brain: Repeatability, Reliability, and Effect of Different Reconstruction Methods

Abstract

Background Changes in brain stiffness can be an important biomarker for neurological disease. Magnetic resonance elastography (MRE) quantifies tissue stiffness, but the results vary between acquisition and reconstruction methods. Purpose To measure MRE repeatability and estimate the effect of different reconstruction methods and varying data quality on estimated brain stiffness. Study Type Prospective. Subjects Fifteen healthy subjects. Field Strength/Sequence 3T MRI, gradient‐echo elastography sequence with a 50 Hz vibration frequency. Assessment Imaging was performed twice in each subject. Images were reconstructed using a curl‐based and a finite‐element‐model (FEM)‐based method. Stiffness was measured in the whole brain, in white matter, and in four cortical and four deep gray matter regions. Repeatability coefficients (RC), intraclass correlation coefficients (ICC), and coefficients of variation (CV) were calculated. MRE data quality was quantified by the ratio between shear waves and compressional waves. Statistical Tests Median values with range are presented. Reconstruction methods were compared using paired Wilcoxon signed‐rank tests, and Spearman's rank correlation was calculated between MRE data quality and stiffness. Holm–Bonferroni corrections were employed to adjust for multiple comparisons. Results In the whole brain, CV was 4.3% and 3.8% for the curl and the FEM reconstruction, respectively, with 4.0–12.8% for subregions. Whole‐brain ICC was 0.60–0.74, ranging from 0.20 to 0.89 in different regions. RC for the whole brain was 0.14 kPa and 0.17 kPa for the curl and FEM methods, respectively. FEM reconstruction resulted in 39% higher stiffness than the curl reconstruction (P < 0.05). MRE data quality, defined as shear‐compression wave ratio, was higher in peripheral regions than in central regions of the brain (P < 0.05). No significant correlations were observed between MRE data quality and stiffness estimates. Data Conclusion MRE of the human brain is a robust technique in terms of repeatability. Caution is warranted when comparing stiffness values obtained with different techniques. Level of Evidence 1 Technical Efficacy Stage 1

Magnetic Resonance Elastography in Intracranial Neoplasms: A Scoping Review

“…Brain MRE results are generally reproducible when the same method is applied, but caution is warranted when comparing results across studies. 35 Summarizing results across studies is difficult due to variations in acquisition parameters, post-processing, study design, cohorts, and units. For example, variations in driving frequencies display different regions of the non-linear stress/strain relationship in viscoelastic bodies.…”

Decreased tissue stiffness in glioblastoma by MR Elastography is associated with increased cerebral blood flow

“…In an earlier study using this MRE method in healthy subjects, MRE data quality, measured as the curl-divergence ratio, was found to be lower in the deep gray matter regions than in regions closer to the skull. The study found no significant correlation between this data quality and stiffness measurements (15). The existing studies differ with respect to both MRE hardware and reconstruction methods.…”

“…The repeatability, assessed as the coefficient of variation, has been measured to be 4 % for the employed MRE technique (15). This should be taken into account if comparing small stiffness differences between subjects or longitudinal tracking over time.…”

“…To avoid artefacts from MRE reconstruction at the edge of the brain, elastography maps were eroded by 2 pixels. MRE data quality was assessed by degree of temporal nonlinearity in the MRE data, which is a measure of noise in the original phase data (29), and the ratio between the amplitude of the curl and the amplitude of the divergence (15). This ratio quantifies the signal (curl) to noise (divergence) since the divergence of the displacement is approximately zero due to the incompressible nature of tissue.…”

Actuators for MRE: New Perspectives With Flexible Electroactive Materials

“…Regarding the piston, Figure 3 shows that most of them are rigid despite the poor sample coupling that results from it. To our knowledge few groups have design rigid form fitting piston which makes sense to access soft tissue like breast [49], but which is more questionable for the head [40,109]. Having a flexible formfitting piston could ensure better sample coupling, in particular when the piston is in contact with a soft surface.…”