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Miniature Probe for Photoacoustic Imaging

5 Mar | By Biophotonics.World
Miniature Probe for Photoacoustic Imaging
Zhendong Guo (left) and Sung-Liang Chen in the lab at Shanghai Jiao Tong University

A research team at Shanghai Jiao Tong University, China has developed a miniature probe for photoacoustic microscopy (PAM). The probe, as an embodiment of PAM, is small and light, which may facilitate various potential clinical applications in future. Imaging of mouse ear in vivo using the probe has been demonstrated in the article published in Journal of Biophotonics in 2018.


Photoacoustic imaging is an emerging biomedical imaging modality. It combines the advantages of light and sound, specifically, optical contrast and ultrasound penetration in tissue. Besides, it is non-invasive and can visualize a variety of endogenous (label-free) and exogenous absorbers in biological systems in vivo. Different implementations of photoacoustic imaging allow the desired resolution and imaging depth. PAM that provides high resolution at the micrometer and even submicrometer scale by focused optical excitation is termed as optical-resolution PAM (OR-PAM). The high resolution renders OR-PAM fit for imaging of single red blood cells, DNA/RNA, and organelles.


Typically, sophisticated implementation of the OR-PAM imaging head as well as optical and sound alignment is required to realize high resolution and desired characteristics such as high sensitivity, sufficient working distance, and reflection-mode imaging. Further, the OR-PAM imaging head is usually bulky with a certain weight, which may restrict the clinical and widespread use of OR-PAM.


“We demonstrated a miniature OR-PAM probe for facilitating its implementation and pre-clinical/clinical applications,” said Sung-Liang Chen, an associate professor at UM-STJU Joint Institute, Shanghai Jiao Tong University, China. “We can achieve high resolution of 3.7 μm at long working distance of 5.5 mm using the probe with 2.7 mm in diameter, and since it is basically a fiber-based probe, it is with low cost and light weight,” explains Chen.


Chen’s research group used a single-mode optical fiber (SMF) and double gradient-index (GRIN) lenses for light focusing. The first GRIN lens (0.5 mm in diameter) was to effectively enhance the numerical aperture (NA) of the SMF, while the second GRIN lens (2 mm in diameter) served as an objective. Since effectively a high-NA SMF was used, high resolution with long working distance can be enabled. “Besides, the assembly and alignment of the components are relatively easy, and the resolution may be further enhanced by sacrificing working distance,” said Zhendong Guo, a PhD candidate working in Dr. Chen’s research group.


As for ultrasonic detection, a novel fiber-tip Fabry-Perot (FP) ultrasound sensor was used. The diameter of the FP sensor was ~250 μm, which is desired for making a miniature probe. “The fiber-tip sensor has several advantages such as high sensitivity and wide-angle detection, facilitating the alignment,” said Guangyao Li, a PhD candidate working in Dr. Chen’s research group. 


In vivo imaging of mouse ear was shown using the miniature OR-PAM probe. Single capillaries at superficial depth and deeper lying vessels were clearly visualized.


A miniature OR-PAM probe with high resolution was achieved. Employing miniature components including GRIN lenses and the FP sensor is the key of miniaturization. The probe can be further developed to facilitate clinical applications, such as furnishing with fast scanning capability. It also has potential in medical endoscopic applications. “More importantly, the low-cost probe has potential to become disposable consumables in future to expedite photoacoustic imaging being routinely used in clinics,” said Chen.


Author: Sung-Liang Chen


Related journal article: https://doi.org/10.1002/jbio.201800147

Methods and Techniques: Photoacoustic imaging (PAI, MSOT)

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