Nonlinearity in a Medical Ultrasound Probe Under High Excitation Voltage

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Acoustics

Background:

• Tissue harmonic imaging is preferred for reducing reverberations.
• Controlling transmitted ultrasound pulses is crucial for optimal image quality.
• Harmonics in transmitted pulses can degrade image quality by interfering with tissue-generated harmonics.

Purpose of the Study:

• To experimentally characterize transmitted second-harmonic distortion in a medical ultrasound probe.
• To identify and compare sources of nonlinear distortion within the ultrasound probe and its transmit electronics.
• To investigate the phenomenon under conditions exceeding conventional operation.

Main Methods:

• Experimental characterization of a medical ultrasound probe used in tissue harmonic imaging.
• Quantification of second-harmonic distortion levels in transmitted ultrasound pulses.
• Separation and measurement of contributions from different components of the ultrasound transmit chain (electronics, cable, acoustic stack).

Main Results:

• Second-harmonic levels up to -20 dB relative to the fundamental frequency were observed under high-amplitude testing.
• Nonlinearities within the acoustic transducer stack were identified as the primary source of second-harmonic distortion.
• Contributions from transmit electronics, cable, and tuning circuitry were found to be negligible compared to the acoustic stack.

Conclusions:

• The acoustic transducer stack is the dominant source of second-harmonic distortion in transmitted ultrasound pulses.
• The nonlinear electrical impedance of the acoustic stack, varying with excitation voltage, explains the second-harmonic peak.
• Minimizing nonlinearities in the acoustic stack is essential for improving tissue harmonic imaging quality.