Abstract
A 3D photoacoustic computed tomography (3D-PACT) system based on full-view illumination and ultrasound detection was developed and applied to 3D photoacoustic imaging of several phantoms. The system utilized an optics cage design to achieve full-view uniform laser illumination and completed 3D scanning with the rotation of a dual-element transducer (5 MHz) and the vertical motion of imaging target, which obtains the best solution in the mutual restriction relation between cost and performance. The 3D-PACT system exhibits a spatial resolution on the order of 300 μm, and the imaging area can be up to 52 mm in diameter. The transducers used in the system provides tomography imaging with large fields of view. In addition, the coplanar uniform illumination and acoustic detection configuration based on a quartz bowl greatly enhances the efficiency of laser illumination and signal detection, making it available for use on samples with irregular surfaces. Performance testing and 3D photoacoustic experiments on various phantoms verify that the system can perform 3D photoacoustic imaging on targets with complex surfaces or large sizes. In future, efforts will be made to achieve full-body 3D tomography of small animals and a multimodal 3D imaging system.
Highlights
Photoacoustic imaging (PAI) is a non-invasive and non-ionized multimodal biomedical imaging method based on transient thermoelastic effects of the biological tissue
The principle is that the energy of pulsed laser light deposited in biological tissue during the process of laser absorption is converted into an ultrasonic signal which is called the photoacoustic signal through instantaneous thermoelastic expansion, and the ultrasonic transducer can receive the signal that carries information about the properties of laser absorption in biological tissue [1,2,3,4,5,6,7]
Photoacoustic imaging effectively overcomes the limitations of existing pure optical imaging and pure ultrasound imaging, the contrast is based on the absorption of laser light during the photoacoustic excitation period, while the resolution is derived from the ultrasonic detection during the photoacoustic emission period
Summary
It is worth mentioning that this system was the first photoacoustic tomography system for innovatively using the structure of quartz bowl with the characteristics of light transmission and ultrasonic reflection for maintaining the photoacoustic coplanarity of the system while collecting photoacoustic signals. This means that the circular spot was in the same layer as the detection plane of ultrasonic transducer. The signal generated by the sample was reflected by the quartz bowl and detected by the dual-foci virtual point ultrasonic transducer (Olympus, Tokyo, Japan) placed vertically above the bowl with a 5 MHz central frequency and an 18 mm diameter of the detection a long focal zone (≈52 mm) that determined its applicability for large imaging targets. After amplification (Ultrasonic Transceiver, 5073PR, Olympus, Tokyo, Japan) and digitization (Data Acquisition card, ATS330, AlazarTech, Canada), the raw photoacoustic data was be sent and stored in a personal computer (PC) to reconstruct the
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