Photoacoustic imaging generates ultrasound waves by irradiating organic tissues with pulses or modulated steady lasers. Ultrasound sensors are used to seize ultrasound indicators in a distributed method. Then, the sunshine absorption distribution of organic tissues could be reconstructed with the assistance of picture reconstruction algorithms. In contrast with optical imaging, photoacoustic imaging gives larger spatial decision, larger penetration depth, and selective optical absorption distinction, thereby enabling detailed visualization of the distribution of hemoglobin, lipid, melanin, and different chromophores in organic tissues.
As the important thing component of the photoacoustic imaging system, ultrasound sensors immediately resolve the imaging efficiency. The mainstream ultrasound sensors are primarily based on the piezoelectric impact, which converts mechanical waves into electrical fees. The sensitivity of such sensors is said to the dimensions of piezoelectric components. To realize ample sensitivity, millimeter-scale piezoelectric components are required, which limits the miniaturization of the gadget. As a particular optical fiber with a dimension of a number of microns or a whole bunch of nanometers, microfiber has the traits of small dimension, giant evanescent subject, and excessive sensitivity to the setting. So, can or not it’s utilized to ultrasound sensing with excessive sensitivity?
The analysis group of Prof. Qizhen Solar from Huazhong College of Science and Know-how proposed a miniaturized microfiber ultrasound sensor. Extremely delicate ultrasound detection was demonstrated utilizing microfiber with a big evanescent subject and environmental sensitivity. Additional, the photoacoustic imaging system primarily based on the microfiber sensor was first realized, to the perfect of our data.
Researchers optimized the dimeter of microfiber to 7μm in view of the bigger evanescent subject. As proven in Fig.1b, the sensitivity of the sensor is additional enhanced through the use of the Polydimethylsiloxane (PDMS) materials with a excessive elastic-optical coefficient to encapsulate the microfiber. When the ultrasound wave is utilized to the sensor, the refractive index of PDMS will change correspondingly as a result of elastic-optical impact, ensuing within the modulation of the efficient refractive index of the microfiber. A Mach-Zehnder interferometer is constructed to demodulate the section modifications of the interrogation laser induced by the incident ultrasound waves. A suggestions stabilizer primarily based on the Proportion Integration Differentiation (PID) technique is used to compensate for the low-frequency fluctuation brought on by noise. The experimental outcomes present that the sensitivity of linear microfiber ultrasound sensors is improved by one order of magnitude in contrast with commonplace single-mode fiber sensors. The sensor displays a low noise equal stress of 153Pa and a broad response bandwidth as much as 14MHz (-10dB). As well as, the sensor can be utilized for the detection of weaker indicators, by optimizing the microfiber and detection system to enhance the sensitivity and bandwidth of the sensor.
The analysis group additionally demonstrated a photoacoustic imaging system primarily based on the microfiber sensor. The efficiency of the imaging system is evaluated by imaging three human hairs. The signal-to-noise ratio (SNR) of the system may attain 31dB even on the depth of 12mm. The axial and lateral resolutions are 65μm and 250μm at 5mm depth, respectively. This know-how is anticipated for top decision, giant imaging depth, and aspect photoacoustic/ultrasound imaging, which has essential significance and utility worth in human well being examination and organic science analysis.