High-resolution three-dimensional (3-D) imaging (stereo imaging) by endoscopes in minimally invasive surgery, especially in space-constrained applications such as brain surgery, is one of the most desired capabilities. Such capability exists at larger than 4-mm overall diameters. We report the development of a stereo imaging endoscope of 4-mm maximum diameter, called Multiangle, Rear-Viewing Endoscopic Tool (MARVEL) that uses a single-lens system with complementary multibandpass filter (CMBF) technology to achieve 3-D imaging. In addition, the system is endowed with the capability to pan from side-to-side over an angle of ±25 deg, which is another unique aspect of MARVEL for such a class of endoscopes. The design and construction of a single-lens, CMBF aperture camera with integrated illumination to generate 3-D images, and the actuation mechanism built into it is summarized.
Studies have shown that stereo images improve surgeons' visuomotor tasks and therefore constructively affect the outcome of a minimally invasive surgery. Stereo images are captured by a stereo endoscope, which consists commonly of duplicate lens systems. However, stereo images can also be captured by a single lens system following a dual aperture scheme (DAS). DAS creates two spatially separated optical channels by placing a dual aperture plate in the limiting aperture of a single lens system. This paper describes efforts to miniaturize the DAS-based imaging system for use in minimally invasive surgery. To demonstrate feasibility, a prototype was fabricated using lens elements 3 mm in diameter and was tested for its stereo depth effect (SDE). The SDE of the prototype was then compared to a duplicate lens system that was constructed theoretically in the same diameter as the 3-mm prototype. The results show that the prototype yields 4/7 of the SDE of the theoretical model. However, the SDE of the prototype provides sufficient SDE, in a viewing range of 1 to 2.5 cm from the lens, for minimally invasive surgery.
We present a technique for imaging full-color 3-D images with a single camera in this paper. Unlike a typical 3-D-imaging system comprising two independent cameras each contributing one viewpoint, the technique presented here creates two viewpoints using a single-lens camera with a bipartite filter whose bandpass characteristics are complementary to each other. The bipartite filter divides the camera's limiting aperture into two spatially separated apertures or viewpoints that alternately image an object field using filter-passband matched, time-sequenced illumination. This technique was applied to construct a 3-D camera to image scenes at a working distance of 10 mm. We evaluated the effectiveness of the 3-D camera in generating stereo images using statistical comparison of the depth resolutions achieved by the 3-D camera and a similar 2D camera arrangement. The comparison showed that the complementary filters produce effective stereopsis at prescribed working distances.
In an effort to miniaturize a 3D imaging system, we created two viewpoints in a single objective lens camera. This was
accomplished by placing a pair of Complementary Multi-band Bandpass Filters (CMBFs) in the aperture area. Two key
characteristics about the CMBFs are that the passbands are staggered so only one viewpoint is opened at a time when
a light band matched to that passband is illuminated, and the passbands are positioned throughout the visible
spectrum, so each viewpoint can render color by taking RGB spectral images. However, each viewpoint takes a
different spectral image from the other viewpoint hence yielding a different color image relative to the other. This
color mismatch in the two viewpoints could lead to color rivalry, where the human vision system fails to resolve two
different colors. The difference will be closer if the number of passbands in a CMBF increases. (However, the number
of passbands is constrained by cost and fabrication technique.) In this paper, simulation predicting the color mismatch
is reported.
There are many advantages to minimally invasive surgery (MIS). An endoscope is the optical system of choice by the
surgeon for MIS. The smaller the incision or opening made to perform the surgery, the smaller the optical system needed.
For minimally invasive neurological and skull base surgeries the openings are typically 10-mm in diameter (dime sized)
or less. The largest outside diameter (OD) endoscope used is 4mm. A significant drawback to endoscopic MIS is that it
only provides a monocular view of the surgical site thereby lacking depth information for the surgeon. A stereo view
would provide the surgeon instantaneous depth information of the surroundings within the field of view, a significant
advantage especially during brain surgery.
Providing 3D imaging in an endoscopic objective lens system presents significant challenges because of the tight
packaging constraints. This paper presents a promising new technique for endoscopic 3D imaging that uses a single lens
system with complementary multi-bandpass filters (CMBFs), and describes the proof-of-concept demonstrations
performed to date validating the technique. These demonstrations of the technique have utilized many commercial off-the-
shelf (COTS) components including the ones used in the endoscope objective.
This paper reports on JPL's on-going research into MEMS gyroscopes. [1-4] This paper will describe the gyroscope's fabrication- methods, a new 8-electrode layout developed to improve performance and performance statistics of a batch of six gyroscopes (of the 8- electrode design) recently rate tested. Previously in our group, T. Tang and R. Gutierrez presented the results of their extensive use of ethylene diamine pyrocatechol (EDP) to deep-etch the inertial- sensitive r4esonators and post-supporting structures in a 4- electrode gyroscope design. Today, JPL is utilizing an in-house STS DRIE, replacing the old wet-etching steps. This has demonstrated superior precision in machining symmetry of the resonators, thus significantly reducing native rocking mode frequency splits. A performance test of six gyros has shown an average, un-tuned, frequency split of 0.4% (11Hz split for rocking modes at 2.7KHz). The new JPL MEMS gyroscope has a unique 8-electrode layout, whose large electrodes can provide significant electrostatic softening of the resonator's springs. This allows matching of the Coriolis sensitive rocking modal frequencies to be improved from the native 0.4% to an average tuned frequency split of 0.02%. In separate tests, electrostatic tuning in the 8-electrode design has demonstrated the ability to match frequency-splits to within 10mHz, thus ensuring full degeneracy in even a very high Q device. In addition, a newly selected ceramic package-substrate has improved the device's dampening loses such that a mean Q of 28,000 was achieved in the six gyroscope tested. These Q's ere measured via the ring-down time method. The improved fabrication development and other modifications described have led to the JPL's MEMS gyroscope achieving an average bias instability (Allan variance 1/f floor estimate) of 11degree/hr with best in the group being 2degree/hr. In an independent test, Honeywell Inc. reported one of our MEMS gyroscopes as achieving 1degree/hr bias instability flicker floor estimate measured at constant temperature.
Thomas George, Sam Bae, Indrani Chakraborty, Hillary Cherry, Christopher Evans, Beverley Eyre, Amanda Green, Allan Hui, Kevin King, H. Lynn Kim, Russell Lawton, Gisela Lin, Colleen Marrese, Juergen Mueller, Judith Podosek, Kirill Shcheglov, Tony Tang, Thomas VanZandt, Stephen Vargo, Joanne Wellman, Victor White, Dean Wiberg, Eui-Hyeok Yang
The MEMS Technology Group is part of the Microdevices Laboratory (MDL) at the Jet Propulsion Laboratory (JPL). The group pursues the development of a wide range of advanced MEMS technologies that are primarily applicable to NASA's robotic as well as manned exploration missions. Thus these technologies are ideally suited for the demanding requirements of space missions namely, low mass, low power consumption and high reliability, without significant loss of capability. End-to-end development of these technologies is conducted at the MDL, a 38,000 sq. ft. facility with approximately 5500 sq. ft. each of cleanroom (class 10 - 100,000) and characterization laboratory space. MDL facilities include computer design and simulation tools, optical and electron-beam lithography, thin film deposition equipment, dry and wet etching facilities including Deep Reactive Ion Etching, device assembly and testing facilities. Following the fabrication of the device prototypes, reliability testing of these devices is conducted at the state-of-the-art Failure Analysis Laboratory at JPL.
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