Divided-pupil line-scanning confocal microscopy (DPLSCM) can provide a simple and low-cost approach for imaging of human tissues with pathology-like nuclear and cellular detail. Using results from a multidimensional numerical model of DPLSCM, we found optimal pupil configurations for improved axial sectioning, as well as control of speckle noise in the case of reflectance imaging. The modeling results guided the design and construction of a simple (10 component) microscope, packaged within the footprint of an iPhone, and capable of cellular resolution. We present the optical design with experimental video-images of in-vivo human tissues.
Coherent speckle influences the resulting image when narrow spectral line-width and single spatial mode illumination are used, though these are the same light-source properties that provide the best radiance-to-cost ratio. However, a suitable size of the detection pinhole can be chosen to maintain adequate optical sectioning while making the probability density of the speckle noise more normal and reducing its effect. The result is a qualitatively better image with improved contrast, which is easier to read. With theoretical statistics and experimental results, we show that the detection pinhole size is a fundamental parameter for designing imaging systems for use in turbid media.
Confocal point-scanning microscopy has been showing promise in the detection, diagnosing and mapping of skin lesions
in clinical settings. The noninvasive technique allows provides optical sectioning and cellular resolution for in vivo
diagnosis of melanoma and basal cell carcinoma and pre-operative and intra-operative mapping of margins. The imaging
has also enabled more accurate "guided" biopsies while minimizing the otherwise large number of "blind" biopsies.
Despite these translational advances, however, point-scanning technology remains relatively complex and expensive.
Line-scanning technology may offer an alternative approach to accelerate translation to the clinic. Line-scanning, using
fewer optical components, inexpensive linear-array detectors and custom electronics, may enable smaller, simpler and
lower-cost confocal microscopes. A line is formed using a cylindrical lens and scanned through the back focal plane of
the objective with a galvanometric scanner. A linear CCD is used for detection. Two pupil configurations were
compared for performance in imaging human tissue. In the full-pupil configuration, illumination and detection is made
through the full objective pupil. In the divided pupil approach, half the pupil is illuminated and the other half is used for
detection. The divided pupil configuration loses spatial and axial resolution due to a diminished NA, but the sectioning
capability and rejection of background is improved. Imaging in skin and oral mucosa illustrate the performance of the
two configurations.
The line-scanning confocal microscope is simpler than a point-scanning confocal microscope and allows for a smaller
and lower cost footprint, making it attractive for endoscopic clinical use. The optical configuration affects image fidelity.
Here, we present a benchtop version of an endoscopic line-scanning confocal microscope for intraoral imaging, with a
divided pupil and optimal detection configuration (magnification, pixel-to-resolution ratio) to enhance image fidelity.
Improved sectioning performance and reduction of "speckle" noise are demonstrated. A topology for use of a
deformable MEMs mirror-based optical axial focus control for imaging in depth is presented. Preliminary images of
human oral mucosa in vivo demonstrate feasibility for clinical application.
We present a design of a line-scanning confocal microscope for reduced speckle and improved sectioning performance
by the use of two pupil-modification techniques. The first is a divided-pupil configuration in which the illumination and
detection paths are separate in object space except in the focal (optical sectioning) plane. The second technique is a
novel implementation of a Nomarski prism and quarter-wave retarder, termed NRDIC, which has shown good results in
point-scanning confocal microscopy and we will present its translation to line-scanning confocal microscopy. A stable
turbid phantom that simulates the background-driven speckle was used for quantitative characterization. Compared to
standard full pupil line-scanning, we show improvements in signal to background of 1.8 and 9 for NRDIC and divided
pupil, respectively. Preliminary imaging in human skin in-vivo demonstrates the improvements in contrast and reduction
of speckle for both the NRDIC and divided pupil modes.
Scanning reflectance confocal microscopy (SRCM) is a flexible technology that provides cellular resolution images of
tissue morphology with tailored resolutions and fields of view. However, how accurately an object is represented, in
other words its fidelity, is critical in medical imaging and is not represented simply by optical resolution. In this work we
characterize the SRCMs fidelity of images derived within turbid media. We present theoretical and experimental results
showing the improved fidelity when using modal illumination. We investigated the use of TEM10 illumination and a
novel implementation of Nomarski differential-interference-contrast (DIC). Using a repeatable, stable turbid phantom
the system fidelity was characterized.
It is well known that use of laser illumination in microscopic imaging can lead to speckle in the resultant images. The
influence of speckle artifact is more pronounced particularly when investigating deep regions of biological samples.
Furthermore, the regions of turbid media above the focal plane of interest impart statistical modifications to the resulting
background and focal signal, which then coherently interfere at the pinhole plane. Through a coherent model of imaging
in a scanning reflectance confocal microscope (SRCM) and subsequent experimental evidence, we have shown that
engineering the electric field distribution in the system's pupils can be framed in the sense of two-beam-interference of
the focal signal and background light. With this model we have theoretically studied the effect of two spatially nonsymmetric
electric field distributions and their effect on resultant images for turbid media in a moderately high
numerical-aperture (NA = 0.9) SRCM system; these distributions are TEM10 and a novel Nomarski DIC. Signal and
background/speckle statistics were parameterized against these pupil distributions and compared to standard TEM00
pupil illumination.
Real-time medical imaging systems such as reflectance confocal microscopes and optical coherence microscopes are being tested in multiple-patient and multiple-center clinical trials. The modulation transfer function (MTF) of these systems at any given time influences the image information content and can affect the interpretation of the images. MTF is difficult to measure in real-time scanning systems when imaging at the Nyquist limit. We describe a measurement technique similar to the electronic imaging resolution standards ISO-12233 (electronic cameras) that can be applied to scanned spot imaging systems with asynchronous pixel clocks. This technique requires the acquisition of a single image of a reflective stripe object. An asynchronous pixel clock induces subpixel jitter in the edge location. The jitter is removed using a Fourier method, and an oversampled edge response function is calculated using algorithms developed in MATLAB. This technique provides fast, simple to use, and repeatable full-width at half maximum lateral resolution and MTF measurements based on only one test image. We present the results for reflectance confocal microscopes operating at 0.9 numerical aperature.
This paper discusses the optical design and tolerancing of an apochromatic, 0.9 NA immersion objective to be used in a coherence reflectance confocal microscope for in-vivo clinical imaging.
We consider the application of mid-infrared (MIR) wavelength quantum cascade lasers (QCL) as sources for free-space optical communications. QCL’s possess high modulation bandwidth and excellent optical performance in the atmospherically transparent MIR spectral range. In order to investigate this potential application area, we have performed a series of comparative evaluations on analog and digital free-space optical links operating in the near-infrared (NIR) (830nm, 1300nm and 1550nm) and mid-infrared (8μm). The measurements were made using well controlled atmospheric conditions in the 65ft long Pacific Northwest National Laboratory’s Aerosol Wind Tunnel Research Facility using water vapor, oil vapor and dust as the scattering media. We measured the transmitted intensity as a function of the density of scatterers in the tunnel. We also performed bit error rate analysis of signals transmitted at the DS-3 data rate. The QCL link consistently showed a higher performance level when compared to the NIR links for water fog, oil fog and dust scattering.
KEYWORDS: Modulation, Quantum cascade lasers, Semiconductor lasers, Analog electronics, Eye, Digital modulation, Telecommunications, Data communications, Temperature metrology, Laser damage threshold
In this paper we present measured modulation responses on quantum-cascade lasers (QCL) up to 10 GHz. The obtained modulation response shows a flat response over the whole frequency range, proving the broadband capabilities of these devices. Even more striking is the absence of a strong resonance peak, which demonstrates the absence of relaxation oscillations, a feature which often limits the high speed performance of standard diode lasers. This property is quite attractive for use of these devices as high-speed data sources, particularly in applications where linearity is important. To address this possible application, the digital modulation properties of these devices were tested in a standard bit-error-rate-measurement at 2.5 GBit/s for cryogenically cooled QCL, showing the suitability of QCLs in digital as well as analog telecommunication application. In addition we present recent data showing bit error measurements and eye diagrams obtained for the pulsed mode operation of QCL near room-temperature.
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