Subwavelength metal apertures significantly enhance single molecule fluorescence signaling systems, but require
efficient illumination and collection optics. On-chip micromirror structures offer a way to markedly improve the
coupling efficiency between such subwavelength metal apertures and the external fluorescence illumination and
collection optics, which in turn greatly simplifies several aspects of instrument design including optics,
optomechanics, and thermal control. Modeling and experimental verification of the gains in illumination and
collection efficiency for subwavelength metal apertures leads to a micromirror design that is both highly efficient
yet also manufacturable. A combination of ray-based and finite-difference-time-domain models is used to optimize
conical micromirrors colocated with subwavelength metal apertures for the case where the illumination light
interacts strongly with the micromirror and the collection optics have modest numerical aperture (NA~0.5).
Experimental methods employing either freely diffusing or immobilized dye molecules are used to measure the
illumination and collection efficiencies of fabricated micromirror prototypes. An overall fluorescence gain of
~100x, comprising a 20x improvement with flood illumination efficiency together with a 5x improvement in
collection efficiency, are both predicted and experimentally verified.
Here we describe a simple optical design for a MEMS-based dual-axes fiber optic confocal scanning microscope that has
been miniaturized for handheld imaging of tissues, and which is capable of being further scaled to smaller dimensions
for endoscope compatibility while preserving its field-of-view (FOV), working distance, and resolution. Based on the
principle of parallel beams that are focused by a single parabolic mirror to a common point, the design allows the use of
replicated optical components mounted and aligned within a rugged cylindrical housing that is designed for use as a
handheld tissue microscope. A MEMS scanner is used for high speed scanning in the X-Y plane below the tissue
surface. An additional design feature is a mechanism for controlling a variable working distance, thus producing a scan
in the Z direction and allowing capture of 3-D volumetric images of tissue. The design parameters that affect the
resolution, FOV, and working distance are analyzed using ASAPTM optical modeling software and verified by
experimental results. Other features of this design include use of a solid immersion lens (SIL), which enhances both
resolution and FOV, and also provides index matching between the optics and the tissue.
Ultrahigh resolution optical coherence tomography (OCT) is an emerging imaging modality that enables noninvasive imaging of tissue with 1- to 3-µm resolutions. Initial OCT studies have typically been performed using harvested tissue specimens (ex vivo). No reports have investigated postexcision tissue degradation on OCT image quality. We investigate the effects of formalin fixation and commonly used cell culture media on tissue optical scattering characteristics in OCT images at different times postexcision compared to in vivo conditions. OCT imaging at 800-nm wavelength with 1.5-µm axial resolution is used to image the hamster cheek pouch in vivo, followed by excision and imaging during preservation in phosphate-buffered saline (PBS), Dulbecco's Modified Eagle's Media (DMEM), and 10% neutral-buffered formalin. Imaging is performed in vivo and at sequential time points postexcision from 15 min to 10 to 18 h. Formalin fixation results in increases in scattering intensity from the muscle layers, as well as shrinkage of the epithelium, muscle, and connective tissue of ~50%. PBS preservation shows loss of optical contrast within two hours, occurring predominantly in deep muscle and connective tissue. DMEM maintains tissue structure and optical scattering characteristics close to in vivo conditions up to 4 to 6 h after excision and best preserved tissue optical properties when compared to in vivo imaging.
High performance, short coherence length light sources with broad bandwidths and high output powers are critical for high speed, ultrahigh resolution OCT imaging. We demonstrate an all-fiber continuous-wave Raman light source based on a photonic crystal fiber, pumped by a continuous-wave Yb-fiber laser, which generates 330 mW output power and 140 nm bandwidths. The light source is compact, robust, turnkey and requires no optical alignment. In vivo high speed, ultrahigh resolution OCT imaging of tissues with < 5 μm axial resolution at 1.3 μm center wavelength is demonstrated.
Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10-15 um for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher axial resolution (<5 um), using a portable, broadband, Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus and colon on animal model display tissue microstructures and architectural details at ultrahigh resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using the standard endoscope. OCT images of normal esophagus and Barrett's esophagus are demonstrated with distinct features.
Early detection of gastrointestinal cancer is essential for the patient treatment and medical care. Endoscopically guided biopsy is currently the gold standard for the diagnosis of early esophageal cancer, but can suffer from high false negative rates due to sampling errors. Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10 - 15 m for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher resolution (< 5 m), using a portable, broadband, Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus, gastro-esophageal junction and colon on animal model display tissue microstructures and architectural details at high resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using standard endoscope. OCT images of normal esophagus, Barrett's esophagus, and esophageal cancers are demonstrated with distinct features. The ability of high resolution endoscopic OCT to image tissue morphology at an unprecedented resolution in vivo would facilitate the development of OCT as a potential imaging modality for early detection of neoplastic changes.
We demonstrate compact ultrahigh resolution OCT systems for in vivo studies, with broadband light sources based on a commercially available Nd:Glass femtosecond laser and nonlinear fiber continuum generation. In vivo OCT images of hamster cheek pouch and human skin acquired at 4 frames per second and with 5.5 μm axial resolution are presented. These systems are robust, compact and portable.
We demonstrate methods for achieving high resolution imaging using alternate scanning techniques in optical coherence tomography and optical coherence microscopy. These techniques enable high transverse resolutions and overcome depth of field limitations. Cellular level resolutions in human tissue may be achieved.
Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr4+:Forsterite laser, ultrahigh image resolutions of 5um are achieved. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.
We demonstrate real time, ultrahigh resolution OCT imaging using a portable mode-locked Cr:forsterite laser. OCT imaging at 5.5 um axial resolution was performed of normal and cancerous human prostate tissue and correlated with histology.
Ultrahigh resolution OCT imaging is demonstrated using compact broadband light sources based on a commercially available Nd:Glass femtosecond laser with nonlinear fiber continuum generation. A tapered single mode fiber is used to generate broadband light centered at 1300 nm. Broadband light near 1064 nm can also be generated using a high numerical aperture single mode germanium doped fiber. These light sources enable ultrahigh resolution OCT imaging with 5-6 μm axial resolution at both 1064 nm and 1300 nm.
We demonstrate in vivo optical coherence tomography imaging of neoplasia in patients using an integrated OCT colposcope. OCT images of epithelial structure were correlated with histological findings in patients with cervical intraepithelial neoplasia and cancer.
We demonstrate a low cost, high-speed scanning delay line using a Herriott cell cavity and electromagnetic actuation. Path length scanning at 2 kHz repetition rate is demonstrated for real time OCT imaging.