65,861 research outputs found
Comparison of Magnetic Resonance Imaging-Compatible Optical Detectors for In-Magnet Tissue Spectroscopy: Photodiodes Versus Silicon Photomultipliers
Tissue spectroscopy inside the magnetic resonance imaging (MRI) system adds a significant value by measuring fast vascular hemoglobin responses or completing spectroscopic identification of diagnostically relevant molecules. Advances in this type of spectroscopy instrumentation have largely focused on fiber coupling into and out of the MRI; however, nonmagnetic detectors can now be placed inside the scanner with signal amplification performed remotely to the high field environment for optimized light detection. In this study, the two possible detector options, such as silicon photodiodes (PD) and silicon photomultipliers (SiPM), were systematically examined for dynamic range and wavelength performance. Results show that PDs offer 108 (160 dB) dynamic range with sensitivity down to 1 pW, whereas SiPMs have 107 (140 dB) dynamic range and sensitivity down to 10 pW. A second major difference is the spectral sensitivity of the two detectors. Here, wavelengths in the 940 nm range are efficiently captured by PDs (but not SiPMs), likely making them the superior choice for broadband spectroscopy guided by MRI
Beam halo and bunch purity monitoring
Beam halo measurements imply measurements of beam profiles with a very high
dynamic range; in transverse and also longitudinal planes. This lesson gives an
overview of high dynamic range instruments for beam halo measurements. In
addition halo definitions and quantifications in view of beam instrumentation
are discussed.Comment: 29 pages, contribution to the CAS - CERN Accelerator School: Beam
Instrumentation, 2-15 June 2018, Tuusula, Finland. arXiv admin note: text
overlap with arXiv:1303.676
Volumetric high dynamic range windowing for better data representation
Volume data is usually generated by measuring devices (eg. CT scanners, MRI
scanners), mathematical functions (eg., Marschner/Lobb function), or by
simulations. While all these sources typically generate 12bit integer or
floating point representations, commonly used displays are only capable of
handling 8bit gray or color levels. In a typical medical scenario, a 3D
scanner will generate a 12bit dataset, which will be downsampled to an 8bit
per-voxel accuracy. This downsampling is usually achieved by a linear
windowing operation, which maps the active full accuracy data range of 0 up to
4095 into the interval between 0 and 255.
In this paper, we propose a novel windowing operation that is based on methods
from high dynamic range image mapping. With this method, the contrast of
mapped 8bit volume datasets is significantly enhanced, in particular if the
imaging modality allows for a high tissue differentiation (eg.,
MRI). Henceforth, it also allows better and easier segmentation and
classification. We demonstrate the improved contrast with different error
metrics and a perception-driven image difference to indicate differences
between three different high dynamic range operators
Image-Based Motion Compensation for Structured Light Scanning of Dynamic Surfaces
Structured light scanning systems based on temporal pattern codification produce dense and robust results on static scenes but behave very poorly when applied to dynamic scenes in which objects are allowed to move or to deform during the acquisition process. The main reason for this lies in the wrong combination of encoded correspondence information because the same point in the projector pattern sequence can map to different points within the camera images due to depth changes over time.
We present a novel approach suitable for measuring and compensating such kind of pattern motion.
The described technique can be combined with existing active range scanning systems designed for static surface reconstruction making them applicable for the dynamic case. We demonstrate the benefits of our method by integrating it into a gray code based structured light scanner, which runs at thirty 3d scans per second
Astrometry with "Carte du Ciel" plates, San Fernando zone. I. Digitization and measurement using a flatbed scanner
We present an original method of digitizing and astrometrically reducing
"Carte du Ciel" plate material using an inexpensive flatbed scanner, to
demonstrate that for this material there is an alternative to more specialized
measuring machines that are very few in number and thus not readily available.
The sample of plates chosen to develop this method are original "Carte du Ciel"
plates of the San Fernando zone, photographic material with a mean epoch
1903.6, and a limiting photographic magnitude ~14.5, covering the declination
range of -10 < dec < -2. Digitization has been made using a commercial flatbed
scanner, demonstrating the internal precision that can be attained with such a
device. A variety of post-scan corrections are shown to be necessary. In
particular, the large distortion introduced by the non-uniform action of the
scanner is modelled using multiple scans of each plate. We also tackle the
specific problems associated with the triple-exposure images on some plates and
the grid lines present on all. The final measures are reduced to celestial
coordinates using the Tycho-2 Catalogue. The internal precision obtained over a
single plate, 3microns ~ 0.18" in each axis, is comparable to what is realized
with similar plate material using slower, less affordable, and less widely
available conventional measuring machines, such as a PDS microdensitometer. The
accuracy attained over large multi-plate areas, employing an overlapping plate
technique, is estimated at 0.2".Comment: 16 pages, 19 figures and 3 tables. Accepted for publication in A&
Three-dimensional measurements with a novel technique combination of confocal and focus variation with a simultaneous scan
The most common optical measurement technologies used today for the three dimensional measurement of technical surfaces are Coherence Scanning Interferometry (CSI), Imaging Confocal Microscopy (IC), and Focus Variation (FV). Each one has its benefits and its drawbacks. FV will be the ideal technology for the measurement of those regions where the slopes are high and where the surface is very rough, while CSI and IC will provide better results for smoother and flatter surface regions. In this work we investigated the benefits and drawbacks of combining Interferometry, Confocal and focus variation to get better measurement of technical surfaces. We investigated a way of using Microdisplay Scanning type of Confocal Microscope to acquire on a simultaneous scan confocal and focus Variation information to reconstruct a three dimensional measurement. Several methods are presented to fuse the optical sectioning properties of both techniques as well as the topographical information. This work shows the benefit of this combination technique on several industrial samples where neither confocal nor focus variation is able to provide optimal results.Postprint (author's final draft
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