Temperature elevations computed for three-layer and four-layer obstetrical tissue models in nonlinear and linear...

Area of Science:

• Biomedical Engineering
• Acoustics
• Medical Imaging

Background:

• Obstetrical ultrasound is a crucial diagnostic tool.
• Understanding thermal effects of ultrasound on fetal tissues is vital for safety.
• Nonlinear acoustic propagation effects may influence temperature elevation.

Purpose of the Study:

• To compute and compare temperature elevations in fetal tissues using linear and nonlinear ultrasound propagation models.
• To investigate the impact of abdominal wall attenuation on thermal distribution.
• To evaluate thermal effects in different tissue models representing various stages of gestation.

Main Methods:

• Numerical computation of temperature elevations in three-layer and four-layer tissue models.
• Application of a new theory for nonlinear absorption increase.
• Simulation of ultrasound pulses (3 MHz, 1.33 µs duration, 3.3 kHz PRF) with varying intensities (5-10 W/cm²).

Main Results:

• Nonlinear propagation resulted in ~50% higher maximum temperature elevation in a three-layer model (2.36°C vs 1.84°C).
• Increased abdominal wall attenuation shifted heat production, reducing the difference between nonlinear and linear propagation effects on fetal temperature.
• Temperature elevations were significantly lower (~3.6x) in a four-layer model (including uterus) with negligible nonlinear effects.

Conclusions:

• Nonlinear propagation can significantly increase fetal temperature elevations, particularly in simpler tissue models.
• Abdominal wall attenuation plays a critical role in heat distribution and the significance of nonlinear effects.
• Fetal temperature elevations are directly proportional to pulse repetition frequency and can be mitigated by lowering it.