The link between tissue elasticity and thermal dose in vivo

Area of Science:

• Biomedical Engineering
• Ultrasound Physics
• Thermal Therapy

Background:

• Accurate monitoring of thermal dose is crucial for effective thermal therapy.
• Tissue stiffness changes in response to thermal insult, but in vivo relationships are not well-established.
• Shear wave elastography (SWE) offers a non-invasive method to measure tissue stiffness in real-time.

Purpose of the Study:

• To investigate the in vivo relationship between tissue stiffness and thermal dose.
• To establish a thermal dose threshold for tissue necrosis using stiffness measurements.
• To evaluate the potential of SWE for guiding thermal therapy.

Main Methods:

• Experiments were conducted on anesthetized rats with controlled leg heating (38°C–48.5°C) for 15 min to 3 h.
• Shear wave elastography (ultrafast ultrasound, 10,000 fps) was used to measure muscle stiffness in real-time.
• In situ temperature was measured using optical fiber sensors.
• Stiffness was derived from shear wave speed, and thermal dose was calculated.

Main Results:

• Tissue stiffness increased significantly with heating duration and temperature.
• A consistent relationship between stiffness and thermal dose was observed across all experiments.
• A thermal dose threshold of 202 minutes was identified for an eightfold increase in stiffness.
• The time-temperature relationship derived from stiffness matched established cell death data.

Conclusions:

• Increased tissue stiffness is a reliable indicator of thermal necrosis in vivo.
• Shear wave elastography can be utilized to determine necrosis thresholds in thermal therapy.
• SWE provides a valuable tool for real-time monitoring and control of thermal therapies.