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Abstract

Physiological aging of the brain is accompanied by ubiquitous degeneration of neurons and oligodendrocytes. An alteration of the cellular matrix of an organ impacts its macroscopic viscoelastic properties which can be detected by magnetic resonance elastography (MRE) – to date the only method for measuring brain mechanical parameters without intervention. However, the wave patterns detected by MRE are affected by atrophic changes in brain geometry occurring in an individual's life span. Moreover, regional variability in MRE-detected age effects is expected corresponding to the regional variation in atrophy. Therefore, the sensitivity of brain MRE to brain volume and aging was investigated in 66 healthy volunteers aged 18–72. A linear decline in whole-brain elasticity was observed (−0.75%/year, R-square = 0.59, p<0.001); the rate is three times that determined by volume measurements (−0.23%/year, R-square = 0.4, p<0.001). The highest decline in elasticity (−0.92%/year, R-square = 0.43, p<0.001) was observed in a region of interest placed in the frontal lobe with minimal age-related shrinkage (−0.1%, R-square = 0.06, p = 0.043). Our results suggest that cerebral MRE can measure geometry-independent viscoelastic parameters related to intrinsic tissue structure and altered by age.

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Normal brain development and aging: quantitative analysis at in vivo MR imaging in healthy volunteers.

E Courchesne, H Chisum, J. Townsend … (2000)

To quantitate neuroanatomic parameters in healthy volunteers and to compare the values with normative values from postmortem studies. Magnetic resonance (MR) images of 116 volunteers aged 19 months to 80 years were analyzed with semiautomated procedures validated by means of comparison with manual tracings. Volumes measured included intracranial space, whole brain, gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF). Results were compared with values from previous postmortem studies. Whole brain and intracranial space grew by 25%-27% between early childhood (mean age, 26 months; age range, 19-33 months) and adolescence (mean age, 14 years; age range, 12-15 years); thereafter, whole-brain volume decreased such that volunteers (age range, 71-80 years) had volumes similar to those of young children. GM increased 13% from early to later (6-9 years) childhood. Thereafter, GM increased more slowly and reached a plateau in the 4th decade; it decreased by 13% in the oldest volunteers. The GM-WM ratio decreased exponentially from early childhood through the 4th decade; thereafter, it gradually declined. In vivo patterns of change in the intracranial space, whole brain, and GM-WM ratio agreed with published postmortem data. MR images accurately depict normal patterns of age-related change in intracranial space, whole brain, GM, WM, and CSF. These quantitative MR imaging data can be used in research studies and clinical settings for the detection of abnormalities in fundamental neuroanatomic parameters.

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Viscoelastic properties of individual glial cells and neurons in the CNS.

Yun-Bi Lu, Kristian Franze, Gerald Seifert … (2006)

One hundred fifty years ago glial cells were discovered as a second, non-neuronal, cell type in the central nervous system. To ascribe a function to these new, enigmatic cells, it was suggested that they either glue the neurons together (the Greek word "gammalambdaiotaalpha" means "glue") or provide a robust scaffold for them ("support cells"). Although both speculations are still widely accepted, they would actually require quite different mechanical cell properties, and neither one has ever been confirmed experimentally. We investigated the biomechanics of CNS tissue and acutely isolated individual neurons and glial cells from mammalian brain (hippocampus) and retina. Scanning force microscopy, bulk rheology, and optically induced deformation were used to determine their viscoelastic characteristics. We found that (i) in all CNS cells the elastic behavior dominates over the viscous behavior, (ii) in distinct cell compartments, such as soma and cell processes, the mechanical properties differ, most likely because of the unequal local distribution of cell organelles, (iii) in comparison to most other eukaryotic cells, both neurons and glial cells are very soft ("rubber elastic"), and (iv) intriguingly, glial cells are even softer than their neighboring neurons. Our results indicate that glial cells can neither serve as structural support cells (as they are too soft) nor as glue (because restoring forces are dominant) for neurons. Nevertheless, from a structural perspective they might act as soft, compliant embedding for neurons, protecting them in case of mechanical trauma, and also as a soft substrate required for neurite growth and facilitating neuronal plasticity.

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The impact of aging and gender on brain viscoelasticity.

Ingolf Sack, Bernd Beierbach, Jens Wuerfel … (2009)

Viscoelasticity is a sensitive measure of the microstructural constitution of soft biological tissue and is increasingly used as a diagnostic marker, e.g. in staging liver fibrosis or characterizing breast tumors. In this study, multifrequency magnetic resonance elastography was used to investigate the in vivo viscoelasticity of healthy human brain in 55 volunteers (23 females) ranging in age from 18 to 88 years. The application of four vibration frequencies in an acoustic range from 25 to 62.5 Hz revealed for the first time how physiological aging changes the global viscosity and elasticity of the brain. Using the rheological springpot model, viscosity and elasticity are combined in a parameter mu that describes the solid-fluid behavior of the tissue and a parameter alpha related to the tissue's microstructure. It is shown that the healthy adult brain undergoes steady parenchymal 'liquefaction' characterized by a continuous decline in mu of 0.8% per year (P<0.001), whereas alpha remains unchanged. Furthermore, significant sex differences were found with female brains being on average 9% more solid-like than their male counterparts rendering women more than a decade 'younger' than men with respect to brain mechanics (P=0.016). These results set the background for using cerebral multifrequency elastography in diagnosing subtle neurodegenerative processes not detectable by other diagnostic methods.

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Author and article information

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: Role: Editor

Journal

Journal ID (nlm-ta): PLoS One

Journal ID (publisher-id): plos

Journal ID (pmc): plosone

Title: PLoS ONE

Publisher: Public Library of Science (San Francisco, USA )

ISSN (Electronic): 1932-6203

Publication date Collection: 2011

Publication date (Electronic): 12 September 2011

Volume: 6

Issue: 9

Electronic Location Identifier: e23451

Affiliations

[1 ]Department of Radiology, Charité-Universitätsmedizin Berlin, Campus Mitte, Berlin, Germany

[2 ]Institute of Medical Informatics, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany

[3 ]NeuroCure Clinical Research Center, Charité-Universitätsmedizin Berlin, Campus Mitte, Berlin, Germany

[4 ]Experimental and Clinical Research Center, Charité-Universitätsmedizin Berlin and Max Delbrück Center for Molecular Medicine, Berlin, Germany

University of California, San Francisco, United States of America

Author notes

* E-mail: ingolf.sack@ 123456charite.de

Conceived and designed the experiments: IS JB FP. Performed the experiments: IS K-JS. Analyzed the data: IS K-JS DK. Contributed reagents/materials/analysis tools: IS JB DK. Wrote the paper: IS FP JB.

Article

Publisher ID: PONE-D-11-05652

DOI: 10.1371/journal.pone.0023451

PMC ID: 3171401

PubMed ID: 21931599

SO-VID: 1b20f521-681c-49f0-aeb9-92cc60539daa

Copyright © Sack et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Date received : 28 March 2011

Date accepted : 17 July 2011

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Pages: 7

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The Influence of Physiological Aging and Atrophy on Brain Viscoelastic Properties in Humans

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Most cited references 31

Normal brain development and aging: quantitative analysis at in vivo MR imaging in healthy volunteers.

Viscoelastic properties of individual glial cells and neurons in the CNS.

The impact of aging and gender on brain viscoelasticity.

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