The structural characteristics of biological tissues can provide essential information for diagnosing clinical diseases. Medical imaging methods, such as X-ray imaging, computed tomography, magnetic resonance imaging, positron emission tomography, and ultrasound imaging, can obtain the structure and function of the tissues; however, these methods cannot detect small lesions due to low imaging resolutions. A biopsy, the gold standard for tumor diagnosis, is painful and invasive, and some tissues cannot be sampled. Optical coherence tomography (OCT) is a label-free, noninvasive, three-dimensional optical imaging method with micrometer resolution and is used for optical biopsy. In the traditional benchtop OCT system, the large scanning probe fixed on a bench cannot reach into a narrow cavity, and the detection process requires a high degree of patient cooperation. Therefore, the use of benchtop OCT systems for clinical applications is limited to a certain extent. A handheld OCT system has a separated sample arm packaged into a miniaturized handheld probe, which is connected to the main OCT system via an optical fiber. The miniaturized probe can be held conveniently and inserted into the narrow cavity, increasing the applicability and flexibility. We propose a video-guided handheld high-speed OCT system with an A-line speed of 200 kHz. The compact handheld probe is easy to hold and can be inserted into narrow cavities. A camera integrated into the probe can capture real-time video for guiding OCT imaging. An image registration method is also developed to eliminate image misalignment due to hand tremors during OCT imaging.

A handheld OCT system based on a swept source was built for tissue imaging, as shown in Figure 1. The handheld probe was connected to the main system through an optical fiber. The handheld probe was made to have a smaller size and lower power consumption by employing a microelectromechanical system-based scanner for beam scanning. A visible imaging camera integrated inside the handheld probe allows for real-time imaging, facilitating rapid localization of the region of interest, and guiding OCT imaging. The system has a high scanning speed with an A-line rate of 200 kHz, a lateral resolution of 31.4 μm, and an axial resolution of 5.2 μm in tissue. To improve the image quality, an image registration method was developed to eliminate image dithering. The handheld OCT system was validated using ex-vivo porcine cornea and tooth. The images obtained by the handheld OCT system were also compared with those obtained by the benchtop OCT system.

The ex-vivo porcine cornea and tooth were imaged using the handheld OCT system, as shown in Figure 2. Figures 2(a) and 2(d) show the images of the cornea and tooth, respectively, captured by a cell phone. Real-time videos can be captured to guide the imaging location and determine the region of interest using the camera in the handheld OCT system. The images of the cornea and tooth captured by the video camera are shown in Figures 2(b) and 2(e), respectively. Single B-scan images of the cornea and tooth are captured by the handheld OCT system, as shown in Figures 2(c) and 2(f), respectively. The results show that the handheld OCT system can acquire high-resolution cross-sectional structural images for the cornea and tooth. During imaging using the handheld probe, the hand tremor causes OCT image misalignment, and image registration is required. Figure 3 shows the OCT images of the porcine cornea and tooth with/without image registration. After multiple rounds of B-scanning at the same location, the images were averaged, as shown in Figures 3(a) and 3(c). The averaged images are blurry, showing image misalignment. After image registration, the image misalignment is corrected, and the averaging B-scan images present a clear tissue structure, as shown in Figures 3(b) and 3(d). To evaluate the imaging performance, the images obtained from the handheld OCT system were compared with those from the benchtop OCT system, as shown in Figure 4. Figures 4(a) and 4(b) show the single B-scan images of the ex-vivo porcine tooth from the benchtop and handheld OCT systems, respectively. The results show that there are no significant differences between the images acquired by the two systems. The CNRs of the images from the handheld and benchtop OCT systems are 3.28±0.01 and 3.30±0.02, respectively. As there is no image misalignment during imaging using the benchtop OCT system, it can provide a reference for evaluating the image registration method. After image registration, the averaging B-scan images from the handheld OCT system show a structure similar to that of the images from the benchtop OCT system. Moreover, the registered images from the handheld OCT system have a quality similar to that of the images from the benchtop OCT system.

In this study, a video-guided high-speed handheld OCT system with an A-line scanning rate of 200 kHz is designed and constructed. Compared with the traditional benchtop OCT system, the handheld system has a compact and easy-to-hold handheld probe, which extends the applications and increases the flexibility of OCT imaging. A video camera inside the probe allows real-time imaging to quickly localize the region of interest and guide the OCT image. An image registration method can eliminate image misalignment during OCT imaging. The imaging performance of the system was verified by imaging ex-vivo porcine cornea and tooth. The results show that the handheld OCT system can provide a more convenient method for tissue imaging, thus exhibiting great potential for imaging the tissues in a narrow cavity and serving the needs of less-cooperative patients.