Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

We developed an ultrahigh speed, handheld swept source optical coherence tomography (SS-OCT) ophthalmic instrument using a 2D MEMS mirror. A vertical cavity surface-emitting laser (VCSEL) operating at 1060 nm center wavelength yielded a 350 kHz axial scan rate and 10 µm axial resolution in tissue. The long coherence length of the VCSEL enabled a 3.08 mm imaging range with minimal sensitivity roll-off in tissue. Two different designs with identical optical components were tested to evaluate handheld OCT ergonomics. An iris camera aided in alignment of the OCT beam through the pupil and a manual fixation light selected the imaging region on the retina. Volumetric and high definition scans were obtained from 5 undilated normal subjects. Volumetric OCT data was acquired by scanning the 2.4 mm diameter 2D MEMS mirror sinusoidally in the fast direction and linearly in the orthogonal slow direction. A second volumetric sinusoidal scan was obtained in the orthogonal direction and the two volumes were processed with a software algorithm to generate a merged motion-corrected volume. Motion-corrected standard 6 x 6 mm2 and wide field 10 x 10 mm2 volumetric OCT data were generated using two volumetric scans, each obtained in 1.4 seconds. High definition 10 mm and 6 mm B-scans were obtained by averaging and registering 25 B-scans obtained over the same position in 0.57 seconds. One of the advantages of volumetric OCT data is the generation of en face OCT images with arbitrary cross sectional B-scans registered to fundus features. This technology should enable screening applications to identify early retinal disease, before irreversible vision impairment or loss occurs. Handheld OCT technology also promises to enable applications in a wide range of settings outside of the traditional ophthalmology or optometry clinics including pediatrics, intraoperative, primary care, developing countries, and military medicine.

Handheld ultrahigh speed swept source optical coherence tomography instrument using a MEMS scanning mirror

Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration.

Resonant Magnetic Field Sensors Based On MEMS Technology.

This paper presents the design, optimization, fabrication, and test results of an electrothermally actuated tip-tilt-piston micromirror with a large optical aperture of 1 mm. The fabrication of the device is a combination of thin-film surface micromachining and bulk silicon micromachining based on silicon-on-insulator wafers. The device has 3-DOF of actuations, including rotations around two axes in the mirror plane, and out-of-plane piston actuation. The micromirror shows an optical scan range of plusmn30deg about both x- and y-axes and displaces 480 mum in the z-axis, all at dc voltages that are less than 8 V. Dynamic testing of the micromirror shows that the thermal response time of each actuator is about 10 ms. Resonant frequencies of the piston and rotation motion are 336 and 488 Hz, respectively. The unique structural design of the device ensures that there is no lateral shift for the piston motion and no rotation-axis shift for the rotation scanning. With the large tip-tilt-piston scan ranges and low driving voltage, this type of device is very suitable for biomedical imaging and laser beam steering applications.

An Electrothermal Tip–Tilt–Piston Micromirror Based on Folded Dual S-Shaped Bimorphs

This paper discusses a systematic optimization process for the fabrication of better surface plasmon resonance (SPR)-based optical fibre sensors in order to enhance their performance when used for refractive index measurement. A set of key optimization parameters has been investigated, including the size of the gold-nanoparticles (AuNPs), the pH of the gold-nanoparticle solutions prior to the coating, the coating time of the gold-nanoparticles on the fibre substrate and the coating temperature used. A series of tests undertaken has confirmed that the increase of the gold nanoparticles size (within the limits of the experiment carried out) makes the device more sensitive. The variation of the pH of the gold solutions within the range investigated appears not significantly to affect the sensitivities of the devices created. Under the circumstances considered, the longer coating time results in a higher surface density which therefore allows a stronger SPR effect, creating a higher level of sensitivity of the device. In addition, the coating temperature has been investigated in this paper for 60 nm AuNP solutions and it has been concluded that the sensor fabricated at a temperature of 25 °C has demonstrated a better performance compared to others, evaluated when the surrounding refractive index of the sensors was varied over the range from 1.333 to 1.424.

Optimization of gold-nanoparticle-based optical fibre surface plasmon resonance (SPR)-based sensors

A novel silicon on insulator (SOI) MEMS process has been designed and developed to realize a two axes thermally actuated single crystal silicon micromirror device, which consists of a mirror plate, four flexural springs and four thermal actuators The mirror plate has the same thickness as a SOI device layer ie 4 µm The SOI layer is selectively thinned down to 2 µm for fabricating flexural springs and thermal actuators The thinning of the SOI layer is essential to lower (control) the flexural rigidity of the springs and the actuators and thus to achieve a higher tilt angle at low thermal power The developed single wafer process is based on dry reactive ion etching CMOS compatible chemistries The minimum chip size design of 1 mm × 1 mm has a 400 µm diameter mirror plate Other chip designs include the mirror diameters in the range from 200 to 500 µm This paper also presents a study on the mirror plate curvature, thermal actuation mechanism and the experimental results The measured maximum angular deflection achieved was 17° at an operating applied voltage of less than 2 V, and the radius of curvature of the mirror plate was in the range from 20 to 50 mm The micromirror was developed for a miniature catheter optical probe for optical coherence tomography in vivo imaging A low cross-sectional size of the probe and higher resolution are essential for investigating inaccessible pathologies in vivo This required a compact micromirror chip and yet sufficiently large mirror plate (typically ~500 µm or more), this trade-off was the key motivation for the research presented in this paper

http://iopscience.iop.org/article/10.1088/0960-1317/18/2/025001/pdf

A two axes scanning SOI MEMS micromirror for endoscopic bioimaging

A miniaturized optical bioprobe package is developed using a 3D micro mirror and is tested for bio-imaging application. A silicon optical bench is designed and micro machined to assemble the fiber, lens and the 3D micro mirror device. A 45 degree angle trench is used to place the micro mirror to achieve larger scanning range. Trace lines are formed on the optical bench and are connected to silicon micro mirror using solder. A GRIN lens with lower numerical aperture has been used to focus the optical beam onto the micro mirror. The bio probe is packaged and is tested in a Time domain OCT (optical coherence tomography) setup and optical image is obtained for plant tissue.

Design, Fabrication and Assembly of an Optical Biosensor Probe Package for OCT (Optical Coherence Tomography) Application

A miniaturized optical bioprobe package is developed using a 3-D micromirror and is tested for bio-imaging application. A silicon optical bench is designed and micromachined to assemble the fiber, lens, and the 3-D micromirror device. A 45deg angle trench is used to place the micromirror to achieve larger scanning range. Trace lines are formed on the optical bench and are connected to silicon micromirror using solder. A GRIN lens with lower numerical aperture has been used to focus the optical beam onto the micromirror. The bioprobe is packaged and is tested in a time domain optical coherence tomography (OCT) setup and optical image is obtained for plant tissue.

J. Teo

Papers

A two axes scanning SOI MEMS micromirror for endoscopic bioimaging

Design, Fabrication and Assembly of an Optical Biosensor Probe Package for OCT (Optical Coherence Tomography) Application

Design, Fabrication, and Assembly of an Optical Biosensor Probe Package for OCT (Optical Coherence Tomography) Application