Photoacoustic imaging (PAI) has traditionally relied on slow, fragile and expensive lasers as excitation sources. Advances in solid-state device technology have recently resulted in the development of a new class of high power light emitting diodes (LEDs) that can be used as fast, robust and cheap excitation sources for PAI.
Here, we report the characterization and technical validation of a dual-mode multi-wavelength LED-based PAI/ultrasound imaging system (AcousticX) that has the potential to perform real-time in vivo imaging. LEDs operating with a pulse length of 70 ns and a repetition rate of up to 4 KHz at wavelengths of 690, 750, 810, 850 and 980 nm were tested. Ultrasound detection was made using a linear-array transducer with a center frequency of 10.05 MHz and a fractional bandwidth of 77%. We performed several systematic studies to evaluate the precision, penetration depth, spatial resolution, and sensitivity of the system. Measurements were made in tissue-mimicking phantoms to independently assess the impact of system variables on precision, including sample positioning and frame averaging. Temporal variation was assessed by repeated measurements over minutes, hours and days in the phantoms. Sensitivity to spectral differences was established by imaging the phantoms using all available multi-wavelength LEDs. The LED-based PAI system was able to detect small molecule dyes at 500 nM concentration at depth and to differentiate oxy- and deoxy-hemoglobin in mouse blood. Our studies indicate that LED-based PAI would be capable of providing real-time structural, functional and molecular imaging information up to depths of 2.5 cm in tissue.
James Joseph, Mithun Kuniyil Ajith Singh, Joanna Brunker, Naoto Sato, Toshitaka Agano, Yusuke Shigeta, and Sarah E. Bohndiek, "Characterization and technical validation of a multi-wavelength LED-based photoacoustic/ultrasound imaging system (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 1049410 (Presented at SPIE BiOS: January 29, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2290309.5752215455001.
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