Objective In microplastic surgery, hyaluronic acid is injected into the dermis layer under the wrinkle depression to achieve the wrinkle removal effect. However, the percutaneous needle can puncture facial arteries, causing the penetration of hyaluronic acid into the blood vessels to form emboli and induce vascular embolism, resulting in local tissue ischaemia, blindness, and even stroke. The visualisation of human facial blood vessels can solve this problem. Photoacoustic imaging is a mesoscopic imaging method with high specificity and contrast based on optical absorption differences and ultrasound information carriers. This method combines the advantages of high resolution of optical imaging and large penetration depth of ultrasonic imaging. It has been widely studied in the biomedical imaging field. As an important branch of photoacoustic imaging, photoacoustic microscopy can obtain high-resolution and high-contrast images of blood vessels in the dermis layer of the human skin in a noninvasive and label-free manner. Therefore, a photoacoustic microscopy was proposed to navigate injection-based microplastic surgeries.
Methods The needle inserted at a fixed angle was imaged using a photoacoustic microscopic probe to obtain the injection point of the needle. Then, the three-dimensional (3D) vascular imaging of the target area was performed. Based on the image fusion and quantitative evaluation, it can be assessed whether the needle will puncture the facial arteries, thereby reducing the risk of surgery. In this study, the feasibility of this method is confirmed using leaf vein imaging and in vivo mouse-ear imaging. Image reconstructions were performed using a user-defined programme, LABVIEW (2019, National Instruments, USA). The three-dimensional images and image fusion were obtained using functions provided by ImageJ (National Institutes of Health, USA). The user-defined algorithm implemented in MATLAB (R2019b, MathWorks, USA) was used to calculate the number of pixels in the intersection area of the image fusion.
Results and Discussions Leaf veins were used to simulate the blood vessels of the dermis layer. The diameter of the leaf vein trunk was approximately 300--500 μm (for simulating facial arteries) and that of leaf vein branches was <100 μm (for simulating capillary networks). The experimental results are consistent with the prediction results of fusion images (Fig. 3). Move the sample matrix to simulate the movement of the sample. The 3D images of the blood vessels in different positions and the needle were fused, and the number of pixels in the intersection area was calculated. After image fusion, the number of pixels intersecting the vessels (positions 1 and 4) with a diameter of >100 μm is 35 and 31, respectively. The number of pixels intersecting the capillaries (positions 2 and 5) is 8 and 5, respectively. The number of pixels in positions 3 and 6 without the blood vessels is 0 (Fig. 4).
Conclusions The experimental results of leaf veins show that photoacoustic microscopy can predict the relative position of the needle, simulate the blood vessels, and navigate the needle into a safe area. Results of the in vivo mouse-ear experiment show that photoacoustic microscopy can quantitatively determine the type of blood vessel punctured by the needle based on the number of pixels in the intersection area. Therefore, this study is expected to realize the preoperative navigation of injection-based microplastic surgeries and shows good application prospects for improving the safety of injection-based microplastic surgeries. However, some aspects still require improvement. The wavelength of the laser employed herein is 532 nm. Naturally, blood vessels show high absorption at this wavelength; however, the imaging depth is limited owing to the strong scattering of light by biological tissues. Furthermore, high wavelengths of the laser will be used in the future, e.g., 1064 nm, to achieve high imaging depth. Currently, only the upper surface information of the needle can be extracted owing to the limitation by the optical excitation mode of the system; moreover, post-processing algorithms are needed to determine whether the needle touches the blood vessel. In the next step, a complete needle can be simulated using the real size of the needle to improve the accuracy of the experiment. Additionally, there is a certain degree of blindness in the selection of the injection position and the probe must be moved repeatedly. The large imaging view and high imaging speed will considerably improve the detection efficiency. Moreover, owing to the limitation of the imaging speed, the proposed system can only realize preoperative navigation, not intraoperative navigation. Further, this system cannot monitor the process of needle entering the sample in real time. Subsequent work will focus on the aforementioned issues to improve the system.
