13,784 research outputs found
Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery
One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-opera- tive morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeon’s navigation capabilites by observ- ing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted in- struments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D opti- cal imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions
Calibrating evanescent-wave penetration depths for biological TIRF microscopy
Roughly half of a cells proteins are located at or near the plasma membrane.
In this restricted space the cell senses its environment, signals to its
neighbors and ex-changes cargo through exo- and endocytotic mechanisms. Ligands
bind to receptors, ions flow across channel pores, and transmitters and
metabolites are transported against con-centration gradients. Receptors, ion
channels, pumps and transporters are the molecular substrates of these
biological processes and they constitute important targets for drug discovery.
Total internal reflection fluorescence microscopy suppresses background from
cell deeper layers and provides contrast for selectively imaging dynamic
processes near the basal membrane of live-cells. The optical sectioning of
total internal reflection fluorescence is based on the excitation confinement
of the evanescent wave generated at the glass-cell interface. How deep the
excitation light actually penetrates the sample is difficult to know, making
the quantitative interpretation of total internal reflection fluorescence data
problematic. Nevertheless, many applications like super-resolution microscopy,
colocalization, fluorescence recovery after photobleaching, near-membrane
fluorescence recovery after photobleaching, uncaging or
photo-activation-switching, as well as single-particle tracking require the
quantitative interpretation of evanescent-wave excited images. Here, we review
existing techniques for characterizing evanescent fields and we provide a
roadmap for comparing total internal reflection fluorescence data across
images, experiments, and laboratories.Comment: 18 text pages, 7 figures and one supplemental figur
Calibrating Array Detectors
The development of sensitive large format imaging arrays for the infrared
promises to provide revolutionary capabilities for space astronomy. For
example, the Infrared Array Camera (IRAC) on SIRTF will use four 256 x 256
arrays to provide background limited high spatial resolution images of the sky
in the 3 to 8 micron spectral region. In order to reach the performance limits
possible with this generation of sensitive detectors, calibration procedures
must be developed so that uncertainties in detector calibration will always be
dominated by photon statistics from the dark sky as a major system noise
source. In the near infrared, where the faint extragalactic sky is observed
through the scattered and reemitted zodiacal light from our solar system,
calibration is particularly important. Faint sources must be detected on this
brighter local foreground.
We present a procedure for calibrating imaging systems and analyzing such
data. In our approach, by proper choice of observing strategy, information
about detector parameters is encoded in the sky measurements. Proper analysis
allows us to simultaneously solve for sky brightness and detector parameters,
and provides accurate formal error estimates.
This approach allows us to extract the calibration from the observations
themselves; little or no additional information is necessary to allow full
interpretation of the data. Further, this approach allows refinement and
verification of detector parameters during the mission, and thus does not
depend on a priori knowledge of the system or ground calibration for
interpretation of images.Comment: Scheduled for ApJS, June 2000 (16 pages, 3 JPEG figures
Polarimetric Calibration of Large-Aperture Telescopes II: The sub-aperture method
A new method for absolute polarimetric calibration of large telescopes is
presented. The proposed method is highly accurate and is based on the
calibration of a small sub-aperture, which is then extended to the full system
by means of actual observations of an astronomical source. The calibration
procedure is described in detail along with numerical simulations that explore
its robustness and accuracy. The advantages and disadvantages of this technique
with respect to other possible alternatives are discussed.Comment: Journal of the Optical Society of America-A, submitte
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