LED-based photoacoustic imaging system - why it achieves the same signal to noise ratio as solid-state-laser-based system; A review

摘要

Photoacoustic imaging is expected to be a next-generation diagnostic modality. However, systems using a solid statelaser (SSL) are expensive, large in size and poor in operability of probes. In addition, protective goggles are requiredbecause of laser light. Therefore, we have adopted the LED technology and improved the signal-to-noise-ratio (SNR) ofthe LED-based system, which had been 1 / 2.3 million of the SSL, to the same level with four innovative technologies.These innovative technologies include a) High power and high density LED array technology: Use of high power LEDchips with luminous efficiency comparable to laser diode, high density mounting of LED chips on Aluminum base andcompact design, b) Giant and ultra-short-pulse drive circuit technology: High speed on-and-off by low-resistance MetalOxide Semiconductor Field Effect Transistor (MOSFET), and position separation of high-voltage drive circuit fromultrasonic probe (USP) by series connection of LEDs, c) Optical pulse generation technology optimum for frequencyresponse characteristic of USP, d) Noise reduction technology for faint signals using ultra-amplification: Minimizationof quantization noise of Analog-digital-converter (ADC) by wide band ultra-amplification of 86 dB, and noise reductionby averaging of >100 times. Using these technologies, we have developed an LED-based photoacoustic imaging system.To use the system, we have discovered the mechanism of the absorption of pulsed light converted into photoacousticsignal detection is a "linear system" by frequency response characteristic analysis using an ideal point source phantom,and clarified the ultra-amplification over 80 dB and the SNR over 4 are required for real-time imaging using a biologicalphantom. Furthermore human in-vivo real-time functional imaging using dual-wavelength of both 820nm and 940nm hasshowed that the LED-based system can be used clinically.