15,010 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
Non-linear Kalman filters for calibration in radio interferometry
We present a new calibration scheme based on a non-linear version of Kalman
filter that aims at estimating the physical terms appearing in the Radio
Interferometry Measurement Equation (RIME). We enrich the filter's structure
with a tunable data representation model, together with an augmented
measurement model for regularization. We show using simulations that it can
properly estimate the physical effects appearing in the RIME. We found that
this approach is particularly useful in the most extreme cases such as when
ionospheric and clock effects are simultaneously present. Combined with the
ability to provide prior knowledge on the expected structure of the physical
instrumental effects (expected physical state and dynamics), we obtain a fairly
cheap algorithm that we believe to be robust, especially in low signal-to-noise
regime. Potentially the use of filters and other similar methods can represent
an improvement for calibration in radio interferometry, under the condition
that the effects corrupting visibilities are understood and analytically
stable. Recursive algorithms are particularly well adapted for pre-calibration
and sky model estimate in a streaming way. This may be useful for the SKA-type
instruments that produce huge amounts of data that have to be calibrated before
being averaged
A simple method for estimating the latency of interactive, real-time graphics simulations
One of the critical determinants of the effectiveness and usability of interactive graphics simulations is the latency with which visual updates can be made based on input from interaction devices. High latency can diminish performance and can lead to simulator sickness. We demonstrate a new method for measuring latency using a standard video camera. The method is simple to configure, sensitive and rapid to use. This is in contrast to previous methods which required specialized equipment, were laborious or could only determine gross changes in latency. We attach a tracker to a pendulum and move a simulated image on the screen using the tracker positions. We video both the pendulum and simulated image together, and fit two sine curves, one to centre of motion of pendulum and one to the centre of motion of the simulated image. From the phase difference between these two sine curves we can determine latency changes significantly less than the frame rate of the camera. We demonstrate the method by comparing the latency of a two different systems for a CAVE™-like display
Efficient high-dimensional entanglement imaging with a compressive sensing, double-pixel camera
We implement a double-pixel, compressive sensing camera to efficiently
characterize, at high resolution, the spatially entangled fields produced by
spontaneous parametric downconversion. This technique leverages sparsity in
spatial correlations between entangled photons to improve acquisition times
over raster-scanning by a scaling factor up to n^2/log(n) for n-dimensional
images. We image at resolutions up to 1024 dimensions per detector and
demonstrate a channel capacity of 8.4 bits per photon. By comparing the
classical mutual information in conjugate bases, we violate an entropic
Einstein-Podolsky-Rosen separability criterion for all measured resolutions.
More broadly, our result indicates compressive sensing can be especially
effective for higher-order measurements on correlated systems.Comment: 10 pages, 7 figure
Challenges in video based object detection in maritime scenario using computer vision
This paper discusses the technical challenges in maritime image processing
and machine vision problems for video streams generated by cameras. Even well
documented problems of horizon detection and registration of frames in a video
are very challenging in maritime scenarios. More advanced problems of
background subtraction and object detection in video streams are very
challenging. Challenges arising from the dynamic nature of the background,
unavailability of static cues, presence of small objects at distant
backgrounds, illumination effects, all contribute to the challenges as
discussed here
Advanced cranial navigation
Neurosurgery is performed with extremely low margins of error. Surgical inaccuracy may
have disastrous consequences. The overall aim of this thesis was to improve accuracy in
cranial neurosurgical procedures by the application of new technical aids. Two technical
methods were evaluated: augmented reality (AR) for surgical navigation (Papers I-II) and the
optical technique of diffuse reflectance spectroscopy (DRS) for real-time tissue identification
(Papers III-V).
Minimally invasive skull-base endoscopy has several potential benefits compared to
traditional craniotomy, but approaching the skull base through this route implies that at-risk
organs and surgical targets are covered by bone and out of the surgeon’s direct line of sight.
In Paper I, a new application for AR-navigated endoscopic skull-base surgery, based on an
augmented-reality surgical navigation (ARSN) system, was developed. The accuracy of the
system, defined by mean target registration error (TRE), was evaluated and found to be
0.55±0.24 mm, the lowest value reported error in the literature.
As a first step toward the development of a cranial application for AR
navigation, in Paper II this ARSN system was used to enable insertions of biopsy needles
and external ventricular drainages (EVDs). The technical accuracy (i.e., deviation from the
target or intended path) and efficacy (i.e., insertion time) were assessed on a 3D-printed
realistic, anthropomorphic skull and brain phantom; Thirty cranial biopsies and 10 EVD
insertions were performed. Accuracy for biopsy was 0.8±0.43 mm with a median insertion
time of 149 (87-233) seconds, and for EVD accuracy was 2.9±0.8 mm at the tip with a median
angular deviation of 0.7±0.5° and a median insertion time of 188 (135-400) seconds.
Glial tumors grow diffusely in the brain, and patient survival is correlated with
the extent of tumor removal. Tumor borders are often invisible. Resection beyond borders as
defined by conventional methods may further improve a patient’s prognosis. In Paper III,
DRS was evaluated for discrimination between glioma and normal brain tissue ex vivo. DRS
spectra and histology were acquired from 22 tumor samples and 9 brain tissue samples
retrieved from 30 patients. Sensitivity and specificity for the detection of low-grade gliomas
were 82.0% and 82.7%, respectively, with an AUC of 0.91.
Acute ischemic stroke caused by large vessel occlusion is treated with
endovascular thrombectomy, but treatment failure can occur when clot composition and
thrombectomy technique are mismatched. Intra-procedural knowledge of clot composition
could guide the choice of treatment modality. In Paper IV, DRS, in vivo, was evaluated for
intravascular clot characterization. Three types of clot analogs, red blood cell (RBC)-rich,
fibrin-rich and mixed clots, were injected into the external carotids of a domestic pig. An
intravascular DRS probe was used for in-situ measurements of clots, blood, and vessel walls,
and the spectral data were analyzed. DRS could differentiate clot types, vessel walls, and
blood in vivo (p<0,001). The sensitivity and specificity for detection were 73.8% and 98.8%
for RBC clots, 100% and 100% for mixed clots, and 80.6% and 97.8% for fibrin clots,
respectively.
Paper V evaluated DRS for characterization of human clot composition ex
vivo: 45 clot units were retrieved from 29 stroke patients and examined with DRS and
histopathological evaluation. DRS parameters correlated with clot RBC fraction (R=81,
p<0.001) and could be used for the classification of clot type with sensitivity and specificity
rates for the detection of RBC-rich clots of 0.722 and 0.846, respectively. Applied in an
intravascular probe, DRS may provide intra-procedural information on clot composition to
improve endovascular thrombectomy efficiency
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