Measurement of broadband temperature-dependent ultrasonic attenuation and dispersion using photoacoustics.
The broadband ultrasonic characterization of biological fluids and tissues is important for the continued development and application of high-resolution ultrasound imaging modalities. Here, a photoacoustic technique for the transmission measurement of temperature-dependent ultrasonic attenuation and dispersion is described. The system uses a photoacoustic plane wave source constructed from a polymethylmethacrylate substrate with a thin optically absorbent layer. Broadband ultrasonic waves are generated by illuminating the absorbent layer with nanosecond pulses of laser light. The transmitted ultrasound waves are detected by a planar 7-microm high-finesse Fabry-Perot interferometer. Temperature-induced thickness changes in the Fabry-Perot interferometer are tracked to monitor the sample temperature and maintain the sensor sensitivity. The measured -6 dB bandwidth for the combined source and sensor is 1 to 35 MHz, with an attenuation corrected signal level at 100 MHz of -10 dB. The system is demonstrated through temperature-dependent ultrasound measurements in castor oil and olive oil. Power law attenuation parameters are extracted by fitting the experimental attenuation data to a frequency power law while simultaneously fitting the dispersion data to the corresponding Kramers-Krönig relation. The extracted parameters are compared with other calibration measurements previously reported in the literature.
Treeby
Bradley E
BE
Department of Medical Physics and Bioengineering, University College London, London, UK. btreeby@mpb.ucl.ac.uk
Cox
Benjamin T
BT
Zhang
Edward Z
EZ
Patch
Sarah K
SK
Beard
Paul C
PC
D000465:Algorithms; D002368:Castor Oil / Q000737:chemistry; D007368:Interferometry / Q000379:methods*; D007834:Lasers; D000069463:Olive Oil; D055095:Optics and Photonics / Q000379:methods*; D010938:Plant Oils / Q000737:chemistry; D012815:Signal Processing, Computer-Assisted; D013696:Temperature; D014463:Ultrasonography / Q000379:methods*
D000069463:Olive Oil; D010938:Plant Oils; D002368:Castor Oil