Photoacoustics: filling a gap

Photoacoustic or optoacoustic imaging is a hybrid imaging modality where laser pulses of high intensity and short duration are used to generate wideband ultrasonic waves from a sample due to fast thermoelastic expansion and contraction. These ultrasound waves can be captured by transducers similar to the ones used for conventional ultrasound imaging systems with a coupling medium in between the sample and the transducers.

Photoacoustic scan and tomography

Photoacoustic line scan or A-scan is 1 dimensional amplitude is a measurement in one direction and this is performed in multiple angles to produce a tomographic scan.

Multispectral photoacoustic tomography

Photoacoustic imaging can be performed in wide range of scales such as:

  • Microscopy: Single very high frequency transducer (50-200MHz) with lowest imaging depth, typically used to image cells.
  • Mesoscopy: High frequency transducer(s) operating in the range of (15-50 MHz) with shallow imaging depth, typically used to image superficial thin blood vessels.
  • Tomography: Low frequency transducer array (2-8MHz) with few centimeters of imaging depth, typically used to image thick blood vessels (arteries and veins) and muscles.

Special requirements for photoacoustic imaging:

  • High energy laser source capable of fast switching to a range of wavelengths
  • Sensitive transducer elements or arrays with reflective (non-absorbing) coatings
  • Low noise pre-amplifier
  • Coupling medium transparent to the excitation wavelengths
  • High speed data acquisition cards
  • High computational power for heavy matrix operations depending on reconstruction methods
  • Characterization of ultrasound transducers, illumination profiles and translation stages