Recently, various type of photoacoustic imaging (PAI) that can visualize properties and distribution of light absorber have been researched. We developed PAI system using LED light source and evaluated characteristics of photoacoustic signal intensity versus Indocyanine Green (ICG) concentration. In this experiment, a linear type PZT array transducer (128-elements, 10.0MHz center frequency) was used to be able to transmit and receive ultrasound and also detect photoacoustic signal from the target object. The transducer was connected to the PAI system, and two sets of LED light source that had 850nm wavelength chip array were set to the both side of the transducer. The transducer head was placed at a distance of 20 mm from the target in the water bath. The target object was a tube filled with ICG in it. The tubes containing ICG at concentrations from 300nanomolar to 3millimolar were made by diluting original ICG solution. We measured the photoacoustic signal strength from RF signal generated from the ICG in the tube, and the results showed that the intensity of the signal was almost linear response to the concentration in log-log scale.
We have achieved penetration depth of 30mm by photoacoustic imaging system using LED light source integrated transducer to image a clinical metal needle inserted into a tissue mimicking phantom. We developed the transducer that integrated near-infrared LED array light source, which was connected to a photoacoustic imaging system which drove LED array light source and controlled photoacoustic data acquisition process. Conventionally solid-state laser has been used as the light source for photoacoustic imaging system. Because LED is diffused light source, laser safety glasses is not necessary, also inflexible fibers are not used to guide light close to a transducer, and we integrated LED light source inside the transducer, which became compact and practical size for conventional ultrasound equipment users. We made LED light source unit as detachable to the transducer easily, so wave-length of light can be selectable by changing the LED light source unit.
We have successfully imaged photoacoustic differences of light absorbance between two images acquired by different wave-length LED array light source. Compared to photoacoustic imaging system using conventional solid-state laser light source, LED light source can be driven at higher frequency pulses, so we were able to get the subtraction image at higher frame rate that calculated from two images which were captured at each wave-length LED light pulse timing. We developed LED array light source which is composed to have two different wave-length chips, so each wave-length light pulse can be controlled and emitted freely. Thus LED array light source can be composed as multiple selectable wavelength more than two, and a various combination of subtraction image may become available at high frame rate.
When we consider the needle visualization in the field of point of care by utilizing the photoacoustic imaging system, and using the conventional solid state laser light source, the issue arises such as device size and not a green system due to the high power consumption. Therefore, we aimed at an environmentally friendly and compact system with low power consumption by using a NIR-LED array light source. The intensity of NIR-LED light is weak, but, by averaging photoacoustic signals with multiple pulse, we have improved S/N of the photoacoustic signal. As a result, we’ve achieved penetration depth of 30mm.
We’ve successfully measured photoacoustic signal by NIR-LED array that has very small power, approx. 1/1500 of light amount compared with Nd:YAG OPO light. In order to achieve high output power, we drove NIR-LED array with unusual amount of electric current. The experiment results showed that the photoacoustic signal strength was about 1/40 of the laser, which suggests NIR-LED array has good photoacoustic reception efficiency versus the ultrasound transducer bandwidth. NIR-LED array photoacoustic system may be able to achieve high-speed imaging which cannot be obtained by the solid-state laser. NIR-LED system can be a game changer for photoacoustic imaging.
We’ve developed NIR-LED array light source module for photoacoustic imaging system, which is ultra-small and consumes extremely low power. Conventional photoacoustic imaging system uses solid state laser light source, which consumes large amount of electricity. Instead, we’ve developed high intensity NIR-LED chips on a 1cm x 6cm board, which produces approx. 1.0kW output power and obtained photoacoustic signal by driving NIR-LED light source module with about 100 ns pulse. Comparing to the laser light source, our module is much smaller than 1/15000 the volume and less than 1/1000 the power consumption approximately. We’ve achieved penetration depth of 30mm.
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