Temperature-Dependent Thermal Expansion of Tissue Under Pulsed Microwave Heating
Abstract
(Approved for Public Release)Thermal expansion coefficient is a measure of how a material s dimensions change in response to temperature variations. The accurate knowledge of a material s thermal expansion coefficient is crucial in understanding its behavior whensubject to thermal stress cause by different heating sources, such as direct heating, electromagnetic energy absorption, acoustic energy absorption, or absorption of other energy formats. Understanding the thermal expansion properties of tissue in response to electromagnetic wave absorption is critical in investigating the potential brain injury risks due to high radio frequency and microwaveoperational exposures, as well as in developing real-time thermoacoustic monitoring techniques during pulsed microwave ablation of tissue. Existing literature lacks the documentation of temperature-dependent thermal expansion coefficient, especially under pulsed heating. Impact of pulsed electromagnetic waves causes the tissue to heat up rapidly, which in turn leads to complicated thermal expansion behavior. The commonly adopted slow-heating method (such as water bath heating) for thermal expansion coefficient measurementconsiders neither the contradicting coagulation-induced shrinkage and thermal expansion, nor the nonlinearity in thermal expansion under rapid absorption of electromagnetic energy. To gain insights into those missing pieces, we propose to conduct experimental andmodeling study of tissue thermal expansion under heating in both slow and fast timescalesIn aim 1, we will build an experimental system to quantitatively measure the tissue thermal expansion dynamics under both slow and fast heating. Slow heating will be generated by putting tissue slices in a water immersion medium with controlled temperature. The temperature range of 25-70 degree Celsius will be considered. Heating with different temperature rising speeds, corresponding to different thermal doses, will be conducted. Fast heating will begenerated by a microwave antenna emitting microwave pulses with center frequency in the range of 1-10 GHz and pulsewidth of 0.5-1.5 microseconds. The tissue thermal expansion motion will be recorded by a high-speed camera. Under pulsed heating, the tissue will also generate thermoacoustic waves that will be captured by ultrasound transducers attached to the peripheral of the tissue slice. Those camera recordings and thermoacoustic signals will be used in aim 2 for understanding the complex thermal expansion under simultaneous fast and slow heating and for extracting the thermal expansion coefficient as a function of temperature.In aim2, we will develop a multi-physics simulation platform for extracting the thermal expansion coefficient under slow and fast heating. We will develop a multi-physics model for simulating the thermal stress caused by different heating schemes, the tissue volume expansion dynamics, and the generation/propagation of thermoacoustic signals during pulsed microwave impact under different macroscopicenvironmental temperatures, taking into consideration the tissue shrinkage caused by coagulation after certain thermal dose. For the model to accurately reproduce the physical process of thermal expansion, we will obtain and incorporate a complete set of dielectric, thermal, and acoustic properties of bovine liver and porcine brain tissue as functions of temperature. We will extract thermal expansion coefficient as a function of temperature by comparing the simulated and the camera-measured tissue thermal dynamics under the same conditions. We will also extract thermal expansion coefficient by comparing the simulated and the measured thermoacoustic signals, which will provide an alternative route for capturing the fast-heating thermal expansion coefficient other than the conventional method using a high-speed camera with constrains in the sampling rate and resolution.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 11, 2023
- Source ID
- N000142312776
Entities
People
- Chu Ma
Organizations
- Office of Naval Research
- United States Navy
- University of Wisconsin System