Shuguang Guo

3D In Vivo optical coherence tomography based on a low-voltage, large-scan-range 2D MEMS mirror

3D in vivo optical imaging on a mouse has been obtained using a 2D MEMS mirror for lateral scanning in a time-domain optical coherence tomography (OCT) system. The MEMS mirror aperture size is 1 x 1 mm(2), and the device footprint is 2 x 2 mm(2). The MEMS mirror scans +/- 30 degrees optical angles about both x and y-axis at only 5.5V DC voltage. An endoscopic probe with an outer diameter of 5.8 mm has been designed, manufactured and packaged. The probe scans an average transverse area of 2 mm x 2 mm. The imaging speed of the probe is about 2.5 frames per second, limited by the speed of the employed optical delay line.

Optically based-indentation technique for acute rat brain tissue slices and thin biomaterials.

Currently, micro-indentation testing of soft biological materials is limited in its capability to test over long time scales due to accumulated instrumental drift errors. As a result, there is a paucity of measures for mechanical properties such as the equilibrium modulus. In this study, indentation combined with optical coherence tomography (OCT) was used for mechanical testing of thin tissue slices. OCT was used to measure the surface deformation profiles after placing spherical beads onto submerged test samples. Agarose-based hydrogels at low-concentrations (w/v, 0.3-0.6%) and acute rat brain tissue slices were tested using this technique over a 30-min time window. To establish that tissue slices maintained cell viability, allowable testing times were determined by measuring neuronal death or degeneration as a function of incubation time with Fluor-Jade C (FJC) staining. Since large deformations at equilibrium were measured, displacements of surface beads were compared with finite element elastic contact simulations to predict the equilibrium modulus, μ(∞) . Values of μ(∞) for the low-concentration hydrogels ranged from 0.07 to 1.8 kPa, and μ(∞) for acute rat brain tissue slices was 0.13 ± 0.04 kPa for the cortex and 0.09 ± 0.015 kPa for the hippocampus (for Poisson ratio = 0.35). This indentation technique offers a localized, real-time, and high resolution method for long-time scale mechanical testing of very soft materials. This test method may also be adapted for viscoelasticity, for testing of different tissues and biomaterials, and for analyzing changes in internal structures with loading.

A Miniature Fourier Transform Spectrometer by a Large-Vertical-Displacement Microelectromechanical Mirror

A microelectromechanichal system (MEMS) mirror based miniature Fourier transform spectrometer is reported. A spectral resolution of 19.2 cm-1has been achieved with a 261 ?m physical scan range generated by the large-vertical-displacement MEMS mirror.

A mirror-tilt-insensitive Fourier transform spectrometer based on a large vertical displacement micromirror with dual reflective surface

We report a miniature mirror-tilt-insensitive (MTI) Fourier transform spectrometer. A large-vertical-displacement (LVD) MEMS mirror is used to generate large scan range for high spectral resolution. The LVD MEMS mirror is also reflective on both surfaces. The maximum tilting angle of the MEMS mirror is 1.7° for its entire 1-mm scan range. The combination of a corner-cube retroreflector and dual-reflective MEMS mirror has been used to compensate the mirror tilting successfully and resulted in high spectral resolution of 8.1 cm−1.

The potential of optical coherence tomography in meniscal tear characterization

Meniscal tear is one of the most common knee injuries leading to pain and discomfort. Partial and total meniscectomies have been widely used to treat the avascular meniscal injuries in which tears do not heal spontaneously. However, the meniscectomies would cause an alteration of the tibiofemoral contact mechanics resulting in progressive osteoarthritis (OA). To mitigate the progression of OA, maximal preservation of meniscal tissue is recommended. The clinical challenge is deciding which meniscal tears are amenable to repair and which part of damaged tissues should be removed. Current diagnosis techniques such as arthroscopy and magnetic resonance imaging can provide macrostructural information of menisci, but the microstructural changes that occur prior to the observable meniscal tears cannot be identified by these techniques. Serving as a nondestructive optical biopsy, optical coherence tomography (OCT), a newly developed imaging modality, can provide high resolution, cross-sectional images of tissues and has been shown its capabilty in arthroscopic evaulation of articular cartilage. Our research was to demonstrate the potential of using OCT for nondestructive characterization of the histopathology of different types of meniscal tears from clinical cases in dogs, providing a fundamental understanding of the failure mechanism of meniscal tears. First, cross-sectional images of torn canine menisci obtained from the OCT and scanning electronic microscopy (SEM) were be compared. By studying the organization of collegan fibrils in torn menisci from the SEM images, the feasibility of using OCT to characterize the organization of collegan fibrils was elucidated. Moreover, the crack size of meniscal tears was quantatitively measured from the OCT images. Changes in the crack size of the tear may be useful for understanding the failure mechanism of meniscal tears.

The potential of optical coherence tomography for diagnosing meniscal pathology

Meniscal tears are often associated with anterior cruciate ligament (ACL) injury and may lead to pain and discomfort in humans. Maximal preservation of meniscal tissue is highly desirable to mitigate the progression of osteoarthritis. Guidelines of which meniscal tears are amenable to repair and what part of damaged tissues should be removed are elusive and lacking consensus. Images of microstructural changes in meniscus would potentially guide the surgeons to manage the meniscal tears better, but the resolution of current diagnostic techniques is limited for this application. In this study, we demonstrated the feasibility of using optical coherence tomography (OCT) for the diagnosis of meniscal pathology. Torn medial menisci were collected from dogs with ACL insufficiency. The torn meniscus was divided into three tissue samples and scanned by OCT and scanning electron microscopy (SEM). OCT and SEM images of torn menisci were compared. Each sample was evaluated for gross and microstructural abnormalities and reduction or loss of birefringence from the OCT images. The abnormalities detected with OCT were described for each type of tear. OCT holds promise in non-destructive and fast assessment of microstructural changes and tissue birefringence of meniscal tears. Future development of intraoperative OCT may help surgeons in the decision making of meniscal treatment.

In Vivo 3D and Doppler OCT Imaging Using Electrothermal MEMS Scanning Mirrors

Most cancers occur inside human body, so endoscopic high-resolution imaging modalities are required for early cancer detection and surgical removal. This paper reports in vivo endoscopic 3D imaging based on optical coherence tomography (OCT). Endoscopic imaging is enabled by integrating rapid-scanning MEMS mirror into a miniature imaging probe. The MEMS mirror has an aperture size of 1 mm by 1 mm and a chip size of 2 mm by 2 mm. The optical scan angle exceeds ±25 V at 6 Vdc, and thus large, constant-velocity, linear scan can be realized. The outer diameter of the probe is only 5 mm. The axial resolution is about 10 μm and the imaging speed is 2.5 frames per second. Doppler OCT imaging has also been demonstrated.

3D polarization-sensitive optical coherence tomography of canine meniscus based on a 2D high-fill-factor microelectromechanical Mirror

A miniature optical imaging probe based on a high-fill-factor MEMS mirror has been developed for nondestructive diagnosis of articular joint diseases and injuries. The MEMS mirror scans ±30° at less than 6 V in both x- and y-axis. The outer diameter of the probe is 5.8 mm. Three-dimensional polarization-sensitive optical coherence tomography of canine meniscus has been successfully demonstrated.

3D endoscopic optical coherence tomography based on rapid-scanning MEMS mirrors

The paper reports 3D in vivo endoscopic imaging enabled by integrating rapid-scanning MEMS mirrors into an optical coherence tomography (OCT) imaging probe. OCT provides high-resolution cross-sectional information suitable for in vivo noninvasive early cancer diagnosis. However, conventional OCT systems are bulky and slow, and thus are difficult to apply to internal organs where most cancers are originated. Microelectromechanical systems (MEMS) technology offers the advantages of small size and fast speed and can be used to miniaturize optical imaging probes. The MEMS mirrors have large aperture size (1 mm × 1 mm), large scan range (≫ ±25°) and low drive voltage (≪ 10 V). A 5.8mm-diameter FEB-protected MEMS-OCT has been built and 3D OCT images of live mice have been successfully acquired with a resolution of ∼10µm and a frame rate of 2.5 frames per second.