An endoscope capable of Coherent Anti-Stokes Raman scattering (CARS) imaging would be of significant clinical value
for improving early detection of endoluminal cancers. However, developing this technology is challenging for many
reasons. First, nonlinear imaging techniques such as CARS are single point measurements thus requiring fast scanning in
a small footprint if video rate is to be achieved. Moreover, the intrinsic nonlinearity of this modality imposes several
technical constraints and limitations, mainly related to pulse and beam distortions that occur within the optical fiber and
the focusing objective.
Here, we describe the design and report modeling results of a new CARS endoscope. The miniature microscope
objective design and its anticipated performance are presented, along with its compatibility with a new spiral scanningfiber
imaging technology developed at the University of Washington. This technology has ideal attributes for clinical
use, with its small footprint, adjustable field-of-view and high spatial-resolution. This compact hybrid fiber-based
endoscopic CARS imaging design is anticipated to have a wide clinical applicability.
As part of the Infrared Eye project, this article describes the design of large-deviation, achromatic Risley prisms scanning systems operating in the 0.5 - 0.92 and 8 - 9.5 μm spectral regions. Designing these systems is challenging due to the large deviation required (zero - 25 degrees), the large spectral bandwidth and the mechanical constraints imposed by the need to rotate the prisms to any position in 1/30 second. A design approach making extensive use of the versatility of optical design softwares is described. Designs consisting of different pairs of optical materials are shown in order to illustrate the trade-off between chromatic aberration, mass and vignetting. Control of chromatic aberration and reasonable prism shape is obtained over 8 - 9.5 μm with zinc sulfide and germanium. The design is more difficult for the 0.5 - 0.92 μm band. Trade-offs consist in using sapphire with Cleartran® over a reduced bandwidth (0.75 - 0.9 μm ) or acrylic singlets with the Infrared Eye in active mode (0.85 - 0.86 μm). Non-sequential ray-tracing is used to study the effects of fresnelizing one element of the achromat to reduce its mass, and to evaluate detector narcissus in the 8 - 9.5 μm region.
A prototype for laser mammography based on a time-domain technique has been developed. The system uses a streak camera and a Titanium:sapphire laser which provides ultrashort pulses at a repetition rate of 80 MHz. A multi-port scanning head which includes optical fibers scans the breast in a point-by-point scanning procedure. Time-resolved transmission is measured at 15000 locations in 7 minutes. The breast is slightly compressed in both the cranio-caudal and the mediolateral projections. Amplitude calibration of the streak camera has been performed allowing for absolute measurement of time- resolved transmission. In addition to the shape of the time-resolved transmission, the absolute amplitude is relevant in properly evaluating the absorption and scattering coefficients. Promising results on solid phantoms and in vivo have been obtained. Both breasts of 10 volunteers have been scanned to date and a larger pilot study is planned in the near future. In addition to the usual time-gating processing, images of the scattering and absorption contributions are also extracted using an original data processing technique.