Premium
A study on understanding the physical mechanism of change in ultrasonic envelope statistical property during temperature elevation
Author(s) -
Omura Masaaki,
Takeuchi Michio,
Nagaoka Ryo,
Hasegawa Hideyuki
Publication year - 2021
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.14890
Subject(s) - thermal expansion , nakagami distribution , ultrasonic sensor , envelope (radar) , thermal conductivity , materials science , thermal , transducer , computational physics , optics , mechanics , physics , acoustics , thermodynamics , mathematics , statistics , telecommunications , radar , decoding methods , fading , computer science
Purpose Our previous studies demonstrate that the variation in ultrasonic envelope statistics is correlated with the temperature change inside scattering media. This variation is identified as the change in the scatterer structure during thermal expansion or contraction. However, no specific evidence has been verified to date. This study numerically reproduces the change in the scatterer distribution during thermal expansion or contraction using finite element simulations and also investigates how the situation is altered by different material properties. Methods The material properties of a linear elastic solid depend on the thermal expansion coefficient, thermal conductivity, specific heat, and initial scatterer number density. Three‐dimensional displacements, calculated in the simulation, were sequentially used to update the positions of the randomly distributed scatterers. Ultrasound signals from the scatterer distribution were generated by simulating a 7.5‐MHz linear array transducer whose specifications were the same as those in the experimental measurements of several phantoms and excised porcine livers. To represent the change in the envelope statistical feature, the absolute value of the ratio change in the logarithmic Nakagami (NA) parameter, Δ m , at each time was calculated as a value normalized with the initial NA parameter. Results The change in the scatterer number density relates to the volume change during temperature elevation. The magnitude of the Δ m shift against the temperature change increases depending on the higher thermal expansion coefficient. In contrast, the relationship between Δ m and the scatterer number density is similar with any material property. Additionally, the changes in Δ m obtained by several experimental phantoms with low to high scatterer number densities are comparable with the numerical simulation results. Conclusions The change in Δ m is indirectly related to the change in the scatterer number density owing to the volume change during thermal expansion or contraction.