In vivo viscoelastic properties of the brain in normal pressure hydrocephalus

Abstract

Nearly half a century after the first report of normal pressure hydrocephalus (NPH), the pathophysiological cause of the disease still remains unclear. Several theories about the cause and development of NPH emphasize disease-related alterations of the mechanical properties of the brain. MR elastography (MRE) uniquely allows the measurement of viscoelastic constants of the living brain without intervention. In this study, 20 patients (mean age, 69.1 years; nine men, 11 women) with idiopathic (n = 15) and secondary (n = 5) NPH were examined by cerebral multifrequency MRE and compared with 25 healthy volunteers (mean age, 62.1 years; 10 men, 15 women). Viscoelastic constants related to the stiffness (µ) and micromechanical connectivity (α) of brain tissue were derived from the dynamics of storage and loss moduli within the experimentally achieved frequency range of 25-62.5 Hz. In patients with NPH, both storage and loss moduli decreased, corresponding to a softening of brain tissue of about 20% compared with healthy volunteers (p < 0.001). This loss of rigidity was accompanied by a decreasing α parameter (9%, p < 0.001), indicating an alteration in the microstructural connectivity of brain tissue during NPH. This disease-related decrease in viscoelastic constants was even more pronounced in the periventricular region of the brain. The results demonstrate distinct tissue degradation associated with NPH. Further studies are required to investigate the source of mechanical tissue damage as a potential cause of NPH-related ventricular expansions and clinical symptoms.

Multiresolution MR elastography using nonlinear inversion

“…A moderate reduction in estimated mechanical property resolution will reduce the visibility of small scale mechanical property variations; however, many of the clinical MRE results reported to date have used a spatial average of mechanical properties taken over large regions. 2,5,17,31 A moderate reduction in the property resolution will not have a large effect on these types of measurements.…”

“…Tissue shear modulus is relevant to diagnosing diseases including cancer, 1 liver fibrosis, 2 and multiple sclerosis. 3 Other mechanical properties such as the viscoelastic loss modulus [3][4][5] have also shown promise as diagnostic criteria.…”

Shear Stiffness of 4 Common Intracranial Tumors Measured Using MR Elastography: Comparison with Intraoperative Consistency Grading

“…10,11,14,24 The recent development of a 3D multislab, multishot acquisition for whole-brain MRE could achieve high signal-to-noise efficacy. [25][26][27][28][29] 3D analysis could improve the results if the wave propagation is complicated, especially if there is throughplane oblique wave propagation that a 2D analysis would not visualize correctly.…”

“…7 Although MRE is not common in a neurologic setting, a series of attempts have been made to measure the stiffness of the brain affected by Alzheimer disease, 8,9 multiple sclerosis, 10 and normal-pressure hydrocephalus. 11,12 As for intracranial tumors, only a few studies involving meningiomas and glioblastomas have been published. 13,14 In these studies, a correlation between histopathologic characteristics and MRE has not been described in detail.…”

Viscoelastic modulus of agarose gels by magnetic resonance elastography using Micro-MRI

“…In the literature, Green et al (2008), Sack et al (2009), Streitberger et al (2011), have measured the viscoelastic modulus of brains in vivo using MRE with clinical MRI, considering both magnitude and phase of the displacement in the tissue. Asbach et al (2008) Viscoelastic modulus of agarose gels by magnetic resonance elastography using Micro-MRI…”