Cerebral Ultrasound Time-Harmonic Elastography Reveals Softening of the Human Brain Due to Dehydration

Abstract

Hydration influences blood volume, blood viscosity, and water content in soft tissues – variables that determine the biophysical properties of biological tissues including their stiffness. In the brain, the relationship between hydration and stiffness is largely unknown despite the increasing importance of stiffness as a quantitative imaging marker. In this study, we investigated cerebral stiffness (CS) in 12 healthy volunteers using ultrasound time-harmonic elastography (THE) in different hydration states: (i) during normal hydration, (ii) after overnight fasting, and (iii) within 1 h of drinking 12 ml of water per kg body weight. In addition, we correlated shear wave speed (SWS) with urine osmolality and hematocrit. SWS at normal hydration was 1.64 ± 0.02 m/s and decreased to 1.57 ± 0.04 m/s (p < 0.001) after overnight fasting. SWS increased again to 1.63 ± 0.01 m/s within 30 min of water drinking, returning to values measured during normal hydration (p = 0.85). Urine osmolality at normal hydration (324 ± 148 mOsm/kg) increased to 784 ± 107 mOsm/kg (p < 0.001) after fasting and returned to normal (288 ± 128 mOsm/kg, p = 0.83) after water drinking. SWS and urine osmolality correlated linearly (r = −0.68, p < 0.001), while SWS and hematocrit did not correlate (p = 0.31). Our results suggest that mild dehydration in the range of diurnal fluctuations is associated with significant softening of brain tissue, possibly due to reduced cerebral perfusion. To ensure consistency of results, it is important that cerebral elastography with a standardized protocol is performed during normal hydration.

Feasibility of assessing non-invasive intracranial compliance using FSI simulation-based and MR elastography-based brain stiffness

“…There is a substantial body of literature in the fields of non-linear viscoelastic dynamics and poroelasticity indicating that MRE-based brain stiffness is sensitive to changes in ICP 32 , 41 – 45 . Figure 7 demonstrates the variation and sensitivity of brain stiffness, as measured by MRE and ultrasound elastography, to blood and CSF dynamic parameters such as CPP, CBF, and ICP in subjects with various conditions, including hypothermia (as observed in a mouse study) 46 , hypercapnia 47 , hydration 48 , and intracranial hypertension 49 , as well as in healthy subjects 50 and healthy subjects undergoing the Valsalva maneuver 51 . It is essential to acknowledge that variations in brain stiffness in response to changes in CPP, CBF, and ICP do not consistently exhibit a direct relationship.…”

A Survey of Combat Athletes' Rapid Weight Loss Practices and Evaluation of the Relationship With Concussion Symptom Recall

“…15 The combination of hyperglycolysis, alongside additional physiological stressors (in a bout) and hypohydration, may induce a competing substrate demand, which could be further exacerbated by reduced overall blood volume. In addition, it is possible that damage to neurons (eg, diffuse axonal or shear injuries) is enhanced secondary to hypohydration because of altered membrane stability, 31 tissue elasticity, 34 and cerebrospinal fluid production, 35 leaving the brain more vulnerable to cortical damage from trauma. This could, subsequently, lead to prolonged recovery or further exposure to head trauma, which in chronic cases has been associated with later development of neurodegenerative diseases, for example, dementia pugilistica, chronic traumatic encephalopathy, and Alzheimer disease.…”

Noninvasive Detection of Intracranial Hypertension by Novel Ultrasound Time-Harmonic Elastography

“…A custom-designed patient bed modified with an amplifier and bass shaker unit was used to produce audible soundwaves underneath the participant's head (GAMPT, Merseburg, Germany). The waveform fed into the amplifier consisted of 6 superimposed frequencies of 27, 33, 39, 44, 50, and 56 Hz with identical amplitudes as proposed in Tzschätzsch et al 14 Vibration amplitudes within the brain were adjusted to be larger than 2 μm to ensure that SNR was sufficiently high 24 . Mean vibration amplitudes for all study participants are shown in Supplemental Figure 1, http://links.lww.com/RLI/A643.…”

“…The waveform fed into the amplifier consisted of 6 superimposed frequencies of 27, 33, 39, 44, 50, and 56 Hz with identical amplitudes as proposed in Tzschätzsch et al 14 Vibration amplitudes within the brain were adjusted to be larger than 2 μm to ensure that SNR was sufficiently high. 24 Mean vibration amplitudes for all study participants are shown in Supplemental Figure 1, http://links.lww.com/RLI/A643. A clinical ultrasound scanner (SonixMDP; UltraSonix, Scottsdale, AZ) equipped with a convex-array transducer (C5-2/60, 2 MHz) was used for data acquisition.…”

“…[34][35][36][37] Recent studies of MRE have revealed sensitivity of CS to pressure-related diseases such as normal-pressure hydrocephalus, however, with complex patterns of regional-, age-, and parameter-specific differences. 4,29,38 Previous work in MRE and cerebral THE has demonstrated sensitivity of CS to ICP 28 and cerebral perfusion pressure 39 influenced by hypercapnia, 25,40 body temperature, 41 hypoxia, 42 hydration, 24 and arterial pulsation. 43 The underlying coupling of CS and pressure is investigated by current research with a focus on biphasic fluid-solid tissue properties 29,44,45 or multiscale viscous interactions.…”