140,915 research outputs found
Motion Artifact Reduction in Breast Dynamic Infrared Imaging
Dynamic infrared imaging is a promising technique in breast oncology. In this study a QWIP infrared camera is used to acquire a sequence of consecutive thermal images of the patient's breast for 10 s. Information on the local blood perfusion is obtained from the spectral analysis of the time series at each image pixel. Due to respiratory and motion artifacts, the direct comparison of the temperature values that a pixel assumes along the sequence becomes difficult. In fact, the small temperature changes due to blood perfusion, of the order of 10-50 mK, which constitute the signal of interest in the time domain, are superimposed onto large temperature fluctuations due to the subject's motion, which represent noise. To improve the time series signal-to-noise ratio, and, as a consequence, enhance the specificity and sensitivity of the dynamic infrared examination, it is important to realign the thermal images of the acquisition sequence thus reducing motion artifacts. In a previous study we demonstrated that a registration algorithm based on fiducial points is suitable to both clinical applications and research, when associated with a proper set of skin markers. In this paper, we quantitatively evaluate the performance of different marker sets by means of a model that allows for estimating the signal-to-noise ratio increment due to registration, and we conclude that a 12-marker set is a good compromise between motion artifact reduction and the time required to prepare the patien
Incremental low rank noise reduction for robust infrared tracking of body temperature during medical imaging
Thermal imagery for monitoring of body temperature provides a powerful tool to decrease
health risks (e.g., burning) for patients during medical imaging (e.g., magnetic resonance imaging).
The presented approach discusses an experiment to simulate radiology conditions with infrared
imaging along with an automatic thermal monitoring/tracking system. The thermal tracking system
uses an incremental low-rank noise reduction applying incremental singular value decomposition
(SVD) and applies color based clustering for initialization of the region of interest (ROI) boundary.
Then a particle filter tracks the ROI(s) from the entire thermal stream (video sequence). The thermal
database contains 15 subjects in two positions (i.e., sitting, and lying) in front of thermal camera.
This dataset is created to verify the robustness of our method with respect to motion-artifacts and in
presence of additive noise (2–20%—salt and pepper noise). The proposed approach was tested for the
infrared images in the dataset and was able to successfully measure and track the ROI continuously
(100% detecting and tracking the temperature of participants), and provided considerable robustness
against noise (unchanged accuracy even in 20% additive noise), which shows promising performanc
A Framework for Temperature Imaging using the Change in Backscattered Ultrasonic Signals
Hyperthermia is a cancer treatment that elevates tissue temperature to 40 to 43oC. It would benefit from a non-invasive, safe, inexpensive and convenient thermometry to monitor heating patterns. Ultrasound is a modality that meets these requirements. In our initial work, using both prediction and experimental data, we showed that the change in the backscattered energy: CBE) is a potential parameter for TI. CBE, however, was computed in a straightforward yet ad hoc manner. In this work, we developed and exploited a mathematical representation for our approach to TI to optimize temperature accuracy. Non-thermal effects of noise and motion confound the use of CBE. Assuming additive white Gaussian noise, we applied signal averaging and thresholding to reduce noise effects. Our motion compensation algorithms were also applied to images with known motion to evaluate factors affecting the compensation performance. In the framework development, temperature imaging was modeled as a problem of estimating temperature from the random processes resulting from thermal changes in signals. CBE computation was formalized as a ratio between two random variables. Mutual information: MI) was studied as an example of possible parameters for temperature imaging based on the joint distributions. Furthermore, a maximum likelihood estimator: MLE) was developed. Both simulations and experimental results showed that noise effects were reduced by signal averaging. The motion compensation algorithms proved to be able to compensate for motion in images and were improved by choosing appropriate interpolation methods and sample rates. For images of uniformly distributed scatterers, CBE and MI can be computed independent of SNR to improve the temperature accuracy. The application of the MLE also showed improvements in temperature accuracy compared to the energy ratio from the signal mean in simulations. The application of the framework to experimental data requires more work to implement noise reduction approaches in 3D heating experiments. The framework identified ways in which we were able to reduce the effects of both noise and motion. The framework formalized our approaches to temperature imaging, improved temperature accuracy in simulations, and can be applied to experimental data if the noise reduction approaches can be implemented for 3D experiments
A PCA-based approach for subtracting thermal background emission in high-contrast imaging data
Ground-based observations at thermal infrared wavelengths suffer from large
background radiation due to the sky, telescope and warm surfaces in the
instrument. This significantly limits the sensitivity of ground-based
observations at wavelengths longer than 3 microns. We analyzed this background
emission in infrared high contrast imaging data, show how it can be modelled
and subtracted and demonstrate that it can improve the detection of faint
sources, such as exoplanets. We applied principal component analysis to model
and subtract the thermal background emission in three archival high contrast
angular differential imaging datasets in the M and L filter. We describe how
the algorithm works and explain how it can be applied. The results of the
background subtraction are compared to the results from a conventional mean
background subtraction scheme. Finally, both methods for background subtraction
are also compared by performing complete data reductions. We analyze the
results from the M dataset of HD100546 qualitatively. For the M band dataset of
beta Pic and the L band dataset of HD169142, which was obtained with an annular
groove phase mask vortex vector coronagraph, we also calculate and analyze the
achieved signal to noise (S/N). We show that applying PCA is an effective way
to remove spatially and temporarily varying thermal background emission down to
close to the background limit. The procedure also proves to be very successful
at reconstructing the background that is hidden behind the PSF. In the complete
data reductions, we find at least qualitative improvements for HD100546 and
HD169142, however, we fail to find a significant increase in S/N of beta Pic b.
We discuss these findings and argue that in particular datasets with strongly
varying observing conditions or infrequently sampled sky background will
benefit from the new approach.Comment: 12 pages, 17 figures, 1 table, Accepted for publication in A&
Optimized Herschel/PACS photometer observing and data reduction strategies for moving solar system targets
The "TNOs are Cool!: A survey of the trans-Neptunian region" is a Herschel
Open Time Key Program that aims to characterize planetary bodies at the
outskirts of the Solar System using PACS and SPIRE data, mostly taken as
scan-maps. In this paper we summarize our PACS data reduction scheme that uses
a modified version of the standard pipeline for basic data reduction, optimized
for faint, moving targets. Due to the low flux density of our targets the
observations are confusion noise limited or at least often affected by bright
nearby background sources at 100 and 160\,m. To overcome these problems we
developed techniques to characterize and eliminate the background at the
positions of our targets and a background matching technique to compensate for
pointing errors. We derive a variety of maps as science data products that are
used depending on the source flux and background levels and the scientific
purpose. Our techniques are also applicable to a wealth of other Herschel solar
system photometric observations, e.g. comets and near-Earth asteroids. The
principles of our observing strategies and reduction techniques for moving
targets will also be applicable for similar surveys of future infrared space
projects.Comment: Accepted for publication in Experimental Astronom
Detection of multimode spatial correlation in PDC and application to the absolute calibration of a CCD camera
We propose and demonstrate experimentally a new method based on the spatial
entanglement for the absolute calibration of analog detector. The idea consists
on measuring the sub-shot-noise intensity correlation between two branches of
parametric down conversion, containing many pairwise correlated spatial modes.
We calibrate a scientific CCD camera and a preliminary evaluation of the
statistical uncertainty indicates the metrological interest of the method
Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing
Amorphous tantala (a-Ta2O5) is an important technological material that has
wide ranging applications in electronics, optics and the biomedical industry.
It is used as the high refractive index layers in the multi-layer dielectric
mirror coatings in the latest generation of gravitational wave interferometers,
as well as other precision interferometers. One of the current limitations in
sensitivity of gravitational wave detectors is Brownian thermal noise that
arises from the tantala mirror coatings. Measurements have shown differences in
mechanical loss of the mirror coatings, which is directly related to Brownian
thermal noise, in response to thermal annealing. We utilise scanning electron
diffraction to perform Fluctuation Electron Microscopy (FEM) on Ion Beam
Sputtered (IBS) amorphous tantala coatings, definitively showing an increase in
the medium range order (MRO), as determined from the variance between the
diffraction patterns in the scan, due to thermal annealing at increasing
temperatures. Moreover, we employ Virtual Dark-Field Imaging (VDFi) to
spatially resolve the FEM signal, enabling investigation of the persistence of
the fragments responsible for the medium range order, as well as the extent of
the ordering over nm length scales, and show ordered patches larger than 5 nm
in the highest temperature annealed sample. These structural changes directly
correlate with the observed changes in mechanical loss.Comment: 22 pages, 5 figure
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