12,459 research outputs found
Bio-Inspired Multi-Spectral Imaging Sensors and Algorithms for Image Guided Surgery
Image guided surgery (IGS) utilizes emerging imaging technologies to provide additional structural and functional information to the physician in clinical settings. This additional visual information can help physicians delineate cancerous tissue during resection as well as avoid damage to near-by healthy tissue. Near-infrared (NIR) fluorescence imaging (700 nm to 900 nm wavelengths) is a promising imaging modality for IGS, namely for the following reasons: First, tissue absorption and scattering in the NIR window is very low, which allows for deeper imaging and localization of tumor tissue in the range of several millimeters to a centimeter depending on the tissue surrounding the tumor. Second, spontaneous tissue fluorescence emission is minimal in the NIR region, allowing for high signal-to-background ratio imaging compared to visible spectrum fluorescence imaging. Third, decoupling the fluorescence signal from the visible spectrum allows for optimization of NIR fluorescence while attaining high quality color images. Fourth, there are two FDA approved fluorescent dyes in the NIR regionânamely methylene blue (MB) and indocyanine greenâwhich can help to identify tumor tissue due to passive accumulation in human subjects.
The aforementioned advantages have led to the development of NIR fluorescence imaging systems for a variety of clinical applications, such as sentinel lymph node imaging, angiography, and tumor margin assessment. With these technological advances, secondary surgeries due to positive tumor margins or damage to healthy organs can be largely mitigated, reducing the emotional and financial toll on the patient.
Currently, several NIR fluorescence imaging systems (NFIS) are available commercially or are undergoing clinical trials, such as FLARE, SPY, PDE, Fluobeam, and others. These systems capture multi-spectral images using complex optical equipment and are combined with real-time image processing to present an augmented view to the surgeon. The information is presented on a standard monitor above the operating bed, which requires the physician to stop the surgical procedure and look up at the monitor. The break in the surgical flow sometimes outweighs the benefits of fluorescence based IGS, especially in time-critical surgical situations. Furthermore, these instruments tend to be very bulky and have a large foot print, which significantly complicates their adoption in an already crowded operating room.
In this document, I present the development of a compact and wearable goggle system capable of real-time sensing of both NIR fluorescence and color information. The imaging system is inspired by the ommatidia of the monarch butterfly, in which pixelated spectral filters are integrated with light sensitive elements. The pixelated spectral filters are fabricated via a carefully optimized nanofabrication procedure and integrated with a CMOS imaging array. The entire imaging system has been optimized for high signal-to-background fluorescence imaging using an analytical approach, and the efficacy of the system has been experimentally verified. The bio-inspired spectral imaging sensor is integrated with an FPGA for compact and real-time signal processing and a wearable goggle for easy integration in the operating room. The complete imaging system is undergoing clinical trials at Washington University in the St. Louis Medical School for imaging sentinel lymph nodes in both breast cancer patients and melanoma patients
Astrometric calibration and performance of the Dark Energy Camera
We characterize the ability of the Dark Energy Camera (DECam) to perform
relative astrometry across its 500~Mpix, 3 deg^2 science field of view, and
across 4 years of operation. This is done using internal comparisons of ~4x10^7
measurements of high-S/N stellar images obtained in repeat visits to fields of
moderate stellar density, with the telescope dithered to move the sources
around the array. An empirical astrometric model includes terms for: optical
distortions; stray electric fields in the CCD detectors; chromatic terms in the
instrumental and atmospheric optics; shifts in CCD relative positions of up to
~10 um when the DECam temperature cycles; and low-order distortions to each
exposure from changes in atmospheric refraction and telescope alignment. Errors
in this astrometric model are dominated by stochastic variations with typical
amplitudes of 10-30 mas (in a 30 s exposure) and 5-10 arcmin coherence length,
plausibly attributed to Kolmogorov-spectrum atmospheric turbulence. The size of
these atmospheric distortions is not closely related to the seeing. Given an
astrometric reference catalog at density ~0.7 arcmin^{-2}, e.g. from Gaia, the
typical atmospheric distortions can be interpolated to 7 mas RMS accuracy (for
30 s exposures) with 1 arcmin coherence length for residual errors. Remaining
detectable error contributors are 2-4 mas RMS from unmodelled stray electric
fields in the devices, and another 2-4 mas RMS from focal plane shifts between
camera thermal cycles. Thus the astrometric solution for a single DECam
exposure is accurate to 3-6 mas (0.02 pixels, or 300 nm) on the focal plane,
plus the stochastic atmospheric distortion.Comment: Submitted to PAS
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance
The Helioseismic and Magnetic Imager (HMI) began near-continuous full-disk
solar measurements on 1 May 2010 from the Solar Dynamics Observatory (SDO). An
automated processing pipeline keeps pace with observations to produce
observable quantities, including the photospheric vector magnetic field, from
sequences of filtergrams. The primary 720s observables were released in mid
2010, including Stokes polarization parameters measured at six wavelengths as
well as intensity, Doppler velocity, and the line-of-sight magnetic field. More
advanced products, including the full vector magnetic field, are now available.
Automatically identified HMI Active Region Patches (HARPs) track the location
and shape of magnetic regions throughout their lifetime.
The vector field is computed using the Very Fast Inversion of the Stokes
Vector (VFISV) code optimized for the HMI pipeline; the remaining 180 degree
azimuth ambiguity is resolved with the Minimum Energy (ME0) code. The
Milne-Eddington inversion is performed on all full-disk HMI observations. The
disambiguation, until recently run only on HARP regions, is now implemented for
the full disk. Vector and scalar quantities in the patches are used to derive
active region indices potentially useful for forecasting; the data maps and
indices are collected in the SHARP data series, hmi.sharp_720s. Patches are
provided in both CCD and heliographic coordinates.
HMI provides continuous coverage of the vector field, but has modest spatial,
spectral, and temporal resolution. Coupled with limitations of the analysis and
interpretation techniques, effects of the orbital velocity, and instrument
performance, the resulting measurements have a certain dynamic range and
sensitivity and are subject to systematic errors and uncertainties that are
characterized in this report.Comment: 42 pages, 19 figures, accepted to Solar Physic
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