Photoacoustic Imaging System Based On Fiber Bragg Gratings

Photoacoustic imaging(PAI) is a novel non-invasive and non-ionizing biomedical imaging technology. PAI works by receiving the ultrasonic signal generated by biological organizations, which is absorbing the optical energy, and utilizing the differences of the radiation intensity, to reconstruct the characteristics of the organizations. Traditional photoacoustic imaging systems are based on the piezoelectric ceramic ultrasonic detector. The accuracy of the imaging system depends on the characteristics of piezoelectric ceramic ultrasonic detector and image reconstruction algorithms. However, the miniaturization of the traditional photoacoustic imaging system is difficult to achieve, as the detection sensitivity of the ultrasonic detector is decreased with the reduction of surface area. Moreover, piezoelectric ceramic ultrasonic detector has certain frequency response and is susceptible to circuit thermal noise.Fiber grating sensor becomes a hot spot in the field of sensor with its unique advantage. Optical fiber Bragg grating sensor that we used is small in size and light in weight and less susceptible to electromagnetic interference. It is easy to be embedded in various kinds of composite structure. Based on these advantages, we introduced fiber Bragg grating sensor into biological tissue as an ultrasound detector. This fiber Bragg grating sensing technique combined with magnetic resonance imaging could promote the development of medical imaging technology. The sensing properties of the fiber Bragg grating sensor with receiving and transmitting ultrasound signal have been studied. We designed a demodulation system based on fiber Bragg grating sensor, which replaces the ultrasonic transducer as a photoacoustic imaging detection unit. This work laid a theoretical and experimental foundation for signal collection of photoacoustic imaging systems. The main contents are as following.1. We designed a sensing and demodulation system based on raster detector, which utilize the characteristics of the transmission and reflection, and expounded the measuring principle. Based on the sensing and demodulation system, a photoacoustic imaging system was built up. In this thesis, we introduce the selection of equipment, works of the imaging system, imaging algorithm and so on. The experimental results show that the photoacoustic images, which are formed by photoacoustic imaging system scanning 3mm*1.5mm pencil lead, are clear and have high resolution.2. We also researched the fiber Bragg grating sensing characteristics of ultrasonic frequency, sound pressure amplitude and sound pressure angle. The experimental results show that fiber Bragg grating sensor can respond to a continuous changing frequency, when operating frequency is below 3 MHz. The signal to noise ratio of imaging result is high by arranging the fiber optic sensor with slop. Photoacoustic images of independent multi-point sound sources and irregular sound sources are respectively formed through photoacoustic imaging system based on fiber Bragg grating. The resolution of images and the factors influencing the imaging quality are analyzed. The experimental results indicate that the locations of independent multi-point sound sources are clearly displayed, while the profiles of irregular sound sources are fuzzy. Thus, the sensitivity of fiber Bragg grating need to be further improved.The photoacoustic imaging system based on fiber Bragg grating detection that we designed forms images by utilizing the differences of sound pressure. The imaging results of independent multi-point sound sources are satisfactory. The research has certain theoretical and practical significance in the fields of systems miniaturization and photoacoustic endoscopic imaging. Moreover, It has the potential for further study that combines with other medical imaging systems.