Absolute measurement of ultrasonic backscatter from single microbubbles

Area of Science:

• Acoustical physics
• Biomedical engineering
• Ultrasound imaging

Background:

• Accurate measurement of microbubble behavior in ultrasound fields is crucial but challenging.
• Characterizing the received ultrasound beam is not well-described in existing literature.
• Existing methods lack precise calibration for received ultrasound signals.

Purpose of the Study:

• To develop and validate a novel system for characterizing received ultrasound beams.
• To enable precise measurement of echoes from single microbubbles at specific locations.
• To calibrate phased array transducers for improved ultrasound imaging.

Main Methods:

• Utilized a hydrodynamically focused flow system for precise microbubble positioning.
• Employed a commercial ultrasound scanner (Philips Sonos 5500) for data acquisition.
• Measured scatter from solid spheres (30-60 microm radii) as a baseline.
• Quantified receiver spectral sensitivity across a 1.2 to 4.5 MHz frequency range.

Main Results:

• Successfully measured echoes from single microbubbles at well-defined positions.
• Validated theoretical predictions for the behavior of solid sphere scatterers.
• Developed software to simulate experimental conditions accurately.
• Achieved calibration of a phased array transducer by quantifying spectral sensitivity.

Conclusions:

• The new system provides a reliable method for received ultrasound beam characterization.
• This technique enhances the accuracy of microbubble-based ultrasound measurements.
• The calibration method is demonstrated using the microbubble agent Definity.
• Improved ultrasound calibration is essential for advanced diagnostic applications.