Photoacoustics is the imaging of ultrasound backscatter originating from a laser's flash into tissue where chromophores (usually haemaglobin, melanin or customized nano-particles) absorb the light energy and rise in temperature during a laser pulse (~5 nanoseconds, <0.1 degree centigrade), and expand. This creates an acoustic wave from the near wall of the vessel, containing the chromophores, moving towards the transducer i.e. creating a compression, and the far wall moving away from the transducer i.e. creating a rarefaction which can be detected by a standard piezoelectric transducer. The frequency of the photoacoustic wave is determined by the transit time of sound across the vessel. Thus the bandwidth of the transducer determines what size vessels can be imaged so a wide bandwidth single crystal transducer is optimal.
Tissue is relatively transparent in the infra red (700 to 969 nanometers) so the laser's light can disperse sufficient energy over several centimeters to create detectable acoustic waves. A 10 to 30 millijoule laser pulse is optimal for imaging and this can be generated by a NdYag laser with an OPO wavelength converter. This type of laser can usually only fire 10 to 20 times a second leaving time for the UltraVision to generate several regular ultrasound images of the same tissue and fuse the ultrasound and photo acoustic images for identification of the morphology.
Nano-particals, usually gold rods, can be conjugated to antibodies and once injected they can be concentrated at the specific disease location and then their property of very efficiently converting specific wavelengths of light into heat can be used to image the site by photoacoustic methods.
Our system uses the location of the elements in the transducer to estimate the origin of the waves and thus forms a two dimensional map or image of the chromophores from the flash.
As a Photoacoustic Platform, the UltraVision is supplied with a photo sensor trigger which when coupled to the system uses a small fraction of a laser flash to trigger the scanner into acquiring the image data into the Flash Buffer (40-100 micro-seconds) where all 64-channels are accumulated. The data in the Flash Buffer is then beamformed into 64 or128 acoustic lines which are sent to the PC in the form of an image frame. Algorithms are available to the researcher which move the aperture across the transducer to acquire data from subsequent laser flashes, which are added to the Flash Buffer the contents of which are subsequently added in the Synthetic Receive Memory to form higher resolution images of wider fields of view.
This beamforming method of back-projection forms an image of 128 acoustic lines of 2048 sample points in 7 milliseconds. As the typical laser requires 100 milliseconds to recharge, the remaining time before the next laser flash may be used to form several conventional ultrasound images and then the photoacoustic and ultrasound images are presented in the display.
As well as implementing the WinProbe algorithms for photoacoustics, the researcher has access to the "Raw RF data" from the analog to digital converters to apply his or her own algorithms of data interpretation. The researcher is usually limited to work in a C or Mat Lab environment which is many orders of magnitude slower than the FPGA. WinProbe can offer consulting on placing the researcher's tested algorithms into the FPGA.
The photo sensor trigger supplied with the system and it allows the researcher to be operating the system within minutes of unpacking the UltraVision system with an operational laser.
UltraVision Corporation: 11770 US Highway 1, Suite 302E, Palm Beach Gardens, Florida, 33408-3054 Tel: (561) 626-4055 Info@winprobe.com
UltraVision Corporation is an accredited ISO13485:2016 / ISO 9001: 2015 manufacturer of medical ultrasound systems