Backward-mode multiwavelength photoacoustic scanner using a planar Fabry-Perot polymer film ultrasound sensor for high-resolution three-dimensional imaging of biological tissues

Abstract

A multiwavelength backward-mode planar photoacoustic scanner for 3D imaging of soft tissues to depths of several millimeters with a spatial resolution in the tens to hundreds of micrometers range is described. The system comprises a tunable optical parametric oscillator laser system that provides nanosecond laser pulses between 600 and 1200 nm for generating the photoacoustic signals and an optical ultrasound mapping system based upon a Fabry-Perot polymer film sensor for detecting them. The system enables photoacoustic signals to be mapped in 2D over a 50 mm diameter aperture in steps of 10 microm with an optically defined element size of 64 microm. Two sensors were used, one with a 22 microm thick polymer film spacer and the other with a 38 mum thick spacer providing -3 dB acoustic bandwidths of 39 and 22 MHz, respectively. The measured noise equivalent pressure of the 38 microm sensor was 0.21 kPa over a 20 MHz measurement bandwidth. The instrument line-spread function (LSF) was measured as a function of position and the minimum lateral and vertical LSFs found to be 38 and 15 microm, respectively. To demonstrate the ability of the system to provide high-resolution 3D images, a range of absorbing objects were imaged. Among these was a blood vessel phantom that comprised a network of blood filled tubes of diameters ranging from 62 to 300 microm immersed in an optically scattering liquid. In addition, to demonstrate the applicability of the system to spectroscopic imaging, a phantom comprising tubes filled with dyes of different spectral characteristics was imaged at a range of wavelengths. It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.

Photoacoustic technique to measure beam profile of pulsed laser systems

“…Optical detection of the photoacoustic transients could also be used for laser beam profile measurements. 15 Further investigation regarding detection films with high laser damage threshold needs to be performed. In conclusion, we have demonstrated the utility of the photoacoustic technique to provide quantitative, 2D spatially resolved beam profile measurement of pulsed lasers.…”

Hybrid photoacoustic and ultrasound section imaging with optical ultrasound detection

“…Furthermore, conventional transducers are not optically transparent, which hinders illumination of the object and gives rise to artifacts if scattered light absorbed at the transducer surface generates pyroelectric signals. Therefore, there have been efforts to develop specialized detectors for PA imaging, involving piezoelectric films or optical detection of ultrasound [8][9][10][11][12]. The latter includes various techniques employing optical interferometers or optical reflection sensors [9][10][11][12], which have in common that the bandwidth is broad, often starting nearly from DC and ranging up to several tens of Megahertz.…”

“…Therefore, there have been efforts to develop specialized detectors for PA imaging, involving piezoelectric films or optical detection of ultrasound [8][9][10][11][12]. The latter includes various techniques employing optical interferometers or optical reflection sensors [9][10][11][12], which have in common that the bandwidth is broad, often starting nearly from DC and ranging up to several tens of Megahertz. Moreover, optical detectors have the property of being optically transparent, making it easy to combine sound detection with optical excitation using pulsed light sources.…”

“…Apart from implementations with a camera [20,21] data are usually measured with a single scanning detector [10,22]. Depending on the laser pulse repetition rate, the data acquisition time required for one full 3D image can range from several minutes [23] to about half hour [22].…”

Generating arbitrary ultrasound fields with tailored optoacoustic surface profiles

“…Measurements of the acoustic field were made using a previously described optical scanner. 17 This uses a planar Fabry-Perot thin film interferometer for acoustic detection over a 2-D plane.…”