Speed of Sound and Attenuation Temperature Dependence of Bovine Brain: Ex Vivo Study

Abstract

Objectives-Brain treatments using focused ultrasound (FUS) offer a new range of noninvasive transcranial therapies. The acoustic energy deposition during these procedures may induce a temperature elevation in the tissue; therefore, noninvasive thermal monitoring is essential. Magnetic resonance imaging is the current adopted monitoring modality, but its high operational costs and limited availability may hinder the accessibility to FUS treatments. Aiming at the development of a thermometric ultrasound (US) method for the brain, the specific objective of this investigation was to study the acoustic thermal response of the speed of sound (SOS) and attenuation coefficient (AC) of different brain tissues: namely white matter (WM) and cortical matter.Methods-Sixteen ex vivo bovine brain samples were investigated. These included 7 WM and 9 cortical matter samples. The samples were gradually heated to about 45 C and then repeatedly scanned while cooling using a computerized US system in the through-transmission mode. The temperature was simultaneously registered with thermocouples. From the scans, the normalized SOS and AC for both tissues were calculated.Results-The results demonstrated a characteristic cooldown temporal behavior for the normalized AC and SOS curves, which were related to the temperature. The SOS curves enabled clear differentiation between the tissue types but depicted more scattered trajectories for the WM tissue. As for the AC curves, the WM depicted a linear behavior in relation to the temperature. However, both tissue types had rather similar temperature patterns.Conclusions-These findings may contribute to the development of a US temperature-monitoring method during FUS procedures.

Ultrasound Mediated Polymerization for Cell Delivery, Drug Delivery, and 3D Printing

“…Brain tissue has been reported to exhibit attenuation coefficient of ≈0.75-1.45 dB cm −1 in the 1 MHz frequency. [34,35] Muscle tissues have been reported to exhibit a slightly higher attenuation coefficient, of 1 .3 to 3.3 dB cm −1 . [36][37][38] This means that acoustic waves passing through both tissues with a fixed thickness will be affected differently, with higher attenuation for waves passing through the muscle tissue, in comparison to the brain, leading to different Young's modulus values.…”

Tissue specific considerations in implementing high intensity focussed ultrasound under magnetic resonance imaging guidance

“…This is echoed by data from a registry study in radio-recurrent prostate cancer, where the extracellular volume fraction in a multivariate analysis was shown to be the only independent predictor of poor progression-free survival ( 13 ). In brain tissue, where extracellular volume fraction differs between grey and white matter, thermal responses between them have been shown to differ in ex vivo data: the attenuation coefficient curves of white matter show a definite linear behavior in relation to temperature ( 14 ).…”