Arvin Arani

Measuring the effects of aging and sex on regional brain stiffness with MR elastography in healthy older adults.

Changes in tissue composition and cellular architecture have been associated with neurological disease, and these in turn can affect biomechanical properties. Natural biological factors such as aging and an individuals sex also affect underlying tissue biomechanics in different brain regions. Understanding the normal changes is necessary before determining the efficacy of stiffness imaging for neurological disease diagnosis and therapy monitoring. The objective of this study was to evaluate global and regional changes in brain stiffness as a function of age and sex, using improved MRE acquisition and processing that have been shown to provide median stiffness values that are typically reproducible to within 1% in global measurements and within 2% for regional measurements. Furthermore, this is the first study to report the effects of age and sex over the entire cerebrum volume and over the full frontal, occipital, parietal, temporal, deep gray matter/white matter (insula, deep gray nuclei and white matter tracts), and cerebellum volumes. In 45 volunteers, we observed a significant linear correlation between age and brain stiffness in the cerebrum (P<.0001), frontal lobes (P<.0001), occipital lobes (P=.0005), parietal lobes (P=.0002), and the temporal lobes (P<.0001) of the brain. No significant linear correlation between brain stiffness and age was observed in the cerebellum (P=.74), and the sensory-motor regions (P=.32) of the brain, and a weak linear trend was observed in the deep gray matter/white matter (P=.075). A multiple linear regression model predicted an annual decline of 0.011 ± 0.002 kPa in cerebrum stiffness with a theoretical median age value (76 years old) of 2.56 ± 0.08 kPa. Sexual dimorphism was observed in the temporal (P=.03) and occipital (P=.001) lobes of the brain, but no significant difference was observed in any of the other brain regions (P>.20 for all other regions). The model predicted female occipital and temporal lobes to be 0.23 kPa and 0.09 kPa stiffer than males of the same age, respectively. This study confirms that as the brain ages, there is softening; however, the changes are dependent on region. In addition, stiffness effects due to sex exist in the occipital and temporal lobes.

Magnetic resonance elastography of frontotemporal dementia

To investigate the feasibility of utilizing brain stiffness as a potential biomarker for behavioral variant frontotemporal dementia (bvFTD) patients. Magnetic resonance elastography (MRE) is a noninvasive technique for evaluating the mechanical properties of brain tissue in vivo. MRE has demonstrated decreased brain stiffness in patients with Alzheimers disease.

MR Elastography Demonstrates Increased Brain Stiffness in Normal Pressure Hydrocephalus.

The authors performed MR elastography on 10 patients with normal pressure hydrocephalus and 21 age- and sex-matched volunteers. Shear waves with 60-Hz vibration frequency were transmitted to the brain by a pillow-like passive driver. Significant increase in stiffness was observed in the cerebrum, occipital lobe, parietal lobe, and temporal lobe in the NPH group compared with controls. BACKGROUND AND PURPOSE: Normal pressure hydrocephalus is a reversible neurologic disorder characterized by a triad of cognitive impairment, gait abnormality, and urinary incontinence that is commonly treated with ventriculoperitoneal shunt placement. However, multiple overlapping symptoms often make it difficult to differentiate normal pressure hydrocephalus from other types of dementia, and improved diagnostic techniques would help patient management. MR elastography is a novel diagnostic tool that could potentially identify patients with normal pressure hydrocephalus. The purpose of this study was to assess brain stiffness changes in patients with normal pressure hydrocephalus compared with age- and sex-matched cognitively healthy individuals. MATERIALS AND METHODS: MR elastography was performed on 10 patients with normal pressure hydrocephalus and 21 age- and sex-matched volunteers with no known neurologic disorders. Image acquisition was conducted on a 3T MR imaging scanner. Shear waves with 60-Hz vibration frequency were transmitted into the brain by a pillowlike passive driver. A novel postprocessing technique resistant to noise and edge artifacts was implemented to determine regional brain stiffness. The Wilcoxon rank sum test and linear regression were used for statistical analysis. RESULTS: A significant increase in stiffness was observed in the cerebrum (P = .001), occipital lobe (P < .001), parietal lobe (P = .001), and the temporal lobe (P = .02) in the normal pressure hydrocephalus group compared with healthy controls. However, no significant difference was noted in other regions of the brain, including the frontal lobe (P = .07), deep gray and white matter (P = .43), or cerebellum (P = .20). CONCLUSIONS: This study demonstrates increased brain stiffness in patients with normal pressure hydrocephalus compared with age- and sex-matched healthy controls; these findings should motivate future studies investigating the use of MR elastography for this condition and the efficacy of shunt therapy.

Higher-Resolution Magnetic Resonance Elastography in Meningiomas to Determine Intratumoral Consistency

BACKGROUND Magnetic resonance elastography (MRE) analyzes shear wave movement through tissue to determine stiffness. In a prior study, measurements with first-generation brain MRE techniques correlated with intraoperative observations of overall meningioma stiffness. OBJECTIVE To evaluate the diagnostic accuracy of a higher-resolution MRE technique to preoperatively detect intratumoral variations compared with surgeon assessment. METHODS Fifteen meningiomas in 14 patients underwent MRE. Tumors with regions of distinctly different stiffness were considered heterogeneous. Intratumoral portions were considered hard if there was a significant area ≥6 kPa. A 5-point scale graded intraoperative consistency. A durometer semiquantitatively measured surgical specimen hardness. Statistics included χ, sensitivity, specificity, positive and negative predicative values, and Spearman rank correlation coefficient. RESULTS For MRE and surgery, 9 (60%) and 7 (47%) tumors were homogeneous, 6 (40%) and 8 (53%) tumors were heterogeneous, 6 (40%) and 10 (67%) tumors had hard portions, and 14 (93%) and 12 (80%) tumors had soft portions, respectively. MRE sensitivity, specificity, and positive and negative predictive values were as follows: for heterogeneity, 75%, 100%, 100%, and 87%; for hardness, 60%, 100%, 100%, and 56%; and for softness, 100%, 33%, 86%, and 100%. Overall, 10 tumors (67%) matched well with MRE and intraoperative consistency and correlated between intraoperative observations (P = .02) and durometer readings (P = .03). Tumor size ≤3.5 cm or vascular tumors were more likely to be inconsistent (P < .05). CONCLUSION MRE was excellent at ruling in heterogeneity with hard portions but less effective in ruling out heterogeneity and hard portions, particularly in tumors more vascular or <3.5 cm. MRE is the first technology capable of prospectively evaluating intratumoral stiffness and, with further refinement, will likely prove useful in preoperative planning.

Quantitative 3D magnetic resonance elastography: Comparison with dynamic mechanical analysis

Magnetic resonance elastography (MRE) is a rapidly growing noninvasive imaging technique for measuring tissue mechanical properties in vivo. Previous studies have compared two‐dimensional MRE measurements with material properties from dynamic mechanical analysis (DMA) devices that were limited in frequency range. Advanced DMA technology now allows broad frequency range testing, and three‐dimensional (3D) MRE is increasingly common. The purpose of this study was to compare 3D MRE stiffness measurements with those of DMA over a wide range of frequencies and shear stiffnesses.

MR Elastography Demonstrates Unique Regional Brain Stiffness Patterns in Dementias

OBJECTIVE The purpose of this study was to investigate age-corrected brain MR elastography (MRE) findings in four dementia cohorts (Alzheimer disease, dementia with Lewy bodies, frontotemporal dementia, and normal pressure hydrocephalus) and determine the potential use as a differentiating biomarker in dementia subtypes. SUBJECTS AND METHODS Institutional review board approval and written informed consent were obtained to perform MRE on 84 subjects: 20 patients with normal pressure hydrocephalus, eight with Alzheimer disease, five with dementia with Lewy bodies, five with frontotemporal dementia, and 46 cognitively normal control subjects. Shear waves of 60-Hz vibration frequency were transmitted into the brain using a pillowlike passive driver, and brain stiffness was determined in eight different regions (cerebrum, frontal, occipital, parietal, temporal, deep gray matter-white matter, sensorimotor cortex, and cerebellum). All stiffness values were age-corrected and compared with control subjects. The Wilcoxon rank sum test and linear regression were used for statistical analysis. RESULTS Regional stiffness patterns unique to each dementing disorder were observed. Patients with Alzheimer disease and frontotemporal dementia showed decreased cerebral stiffness (p = 0.001 and p = 0.002, respectively) with regional softening of the frontal and temporal lobes. Patients with Alzheimer disease additionally showed parietal lobe and sensorimotor region softening (p = 0.039 and p = 0.018, respectively). Patients with normal pressure hydrocephalus showed stiffening of the parietal, occipital, and sensorimotor regions (p = 0.007, p < 0.001, and p < 0.0001, respectively). Patients with dementia with Lewy bodies did not show significant stiffness changes in any of the regions. CONCLUSION Quantitative MRE of changes in brain viscoelastic structure shows unique regional brain stiffness patterns between common dementia subtypes.

Cardiac MR elastography for quantitative assessment of elevated myocardial stiffness in cardiac amyloidosis

To evaluate if cardiac magnetic resonance elastography (MRE) can measure increased stiffness in patients with cardiac amyloidosis. Myocardial tissue stiffness plays an important role in cardiac function. A noninvasive quantitative imaging technique capable of measuring myocardial stiffness could aid in disease diagnosis, therapy monitoring, and disease prognostic strategies. We recently developed a high‐frequency cardiac MRE technique capable of making noninvasive stiffness measurements.

Acute pressure changes in the brain are correlated with MR elastography stiffness measurements: initial feasibility in an in vivo large animal model

The homeostasis of intracranial pressure (ICP) is of paramount importance for maintaining normal brain function. A noninvasive technique capable of making direct measurements of ICP currently does not exist. MR elastography (MRE) is capable of noninvasively measuring brain tissue stiffness in vivo, and may act as a surrogate to measure ICP. The objective of this study was to investigate the impact of changing ICP on brain stiffness using MRE in a swine model.

Regional assessment of in vivo myocardial stiffness using 3D magnetic resonance elastography in a porcine model of myocardial infarction

The stiffness of a myocardial infarct affects the left ventricular pump function and remodeling. Magnetic resonance elastography (MRE) is a noninvasive imaging technique for measuring soft‐tissue stiffness in vivo. The purpose of this study was to investigate the feasibility of assessing in vivo regional myocardial stiffness with high‐frequency 3D cardiac MRE in a porcine model of myocardial infarction, and compare the results with ex vivo uniaxial tensile testing.

In vivo, high-frequency three-dimensional cardiac MR elastography: Feasibility in normal volunteers

Noninvasive stiffness imaging techniques (elastography) can image myocardial tissue biomechanics in vivo. For cardiac MR elastography (MRE) techniques, the optimal vibration frequency for in vivo experiments is unknown. Furthermore, the accuracy of cardiac MRE has never been evaluated in a geometrically accurate phantom. Therefore, the purpose of this study was to determine the necessary driving frequency to obtain accurate three‐dimensional (3D) cardiac MRE stiffness estimates in a geometrically accurate diastolic cardiac phantom and to determine the optimal vibration frequency that can be introduced in healthy volunteers.