Analysis Of Difference Images Research Articles

TOF MLEM Adaptation for the Total-Body J-PET With a Realistic Analytical System Response Matrix

We report a study of the original image reconstruction algorithm based on the time-of-flight maximum likelihood expectation maximisation (TOF MLEM), developed for the total-body (TB) Jagiellonian PET (J-PET) scanners. The method is applicable to generic cylindrical or modular multi-layer layouts and is extendable to multi-photon imaging. The system response matrix (SRM) is represented as a set of analytical functions, uniquely defined for each pair of plastic scintillator strips used for the detection. A realistic resolution model (RM) in detector space is derived from fitting the Monte Carlo simulated emissions and detections of annihilation photons on oblique transverse planes. Additional kernels embedded in SRM account for TOF, parallax effect and axial smearing. The algorithm was tested on datasets, simulated in GATE for the NEMA IEC and static XCAT phantoms inside a 24-module 2-layer TB J-PET. Compared to the reference TOF MLEM with none or a shift-invariant RM, an improvement was observed, as evaluated by the analysis of image quality, difference images and ground truth metrics. We also reconstructed the data with additive contributions, pre-filtered geometrically and with non-TOF scatter correction applied. Despite some deterioration, the obtained results still capitalise on the realistic RM with better edge preservation and superior ground truth metrics. The envisioned prospects of the TOF MLEM with analytical SRM include its application in multi-photon imaging and further upgrade to account for the non-collinearity, positron range and other factors.

Identifying and characterizing dust point sources in the southwestern United States using remote sensing and GIS

Documenting geomorphology and land use/land cover associated with the aeolian dust sources is needed to build more robust models simulating wind erosion and dust emission. It is also important to set the base for future studies aiming to quantify the effect of anthropogenic land-use change on dust emission. In this research, dust point sources were detected in the Southern Great Plains and Chihuahuan Desert regions of the United States (U.S.) for 2001–2016, encompassing a period of extreme drought. Dust points were detected using overlay analysis of brightness temperature difference images of MODIS and MODIS true color images for the days where dust plumes were visible. This study aims to identify low emission surfaces as well as high emission surfaces in terms of geomorphology and land cover. A total of 1508 dust points were detected, where 1258 points are located in the Southern Great Plains, and 187 points are located in the Chihuahuan Desert. Point pattern analysis showed a significant cluster of these points in West Texas (Nearest Neighbor Ratio = 0.33, р < 0.001) where cultivated lands and grasslands are the dominant land cover and aeolian sand sheet is the dominant geomorphic class. Ephemeral lakes (i.e., playas) produce the most dust sources per unit area. Cultivated croplands enclose 43% of the dust points, while shrublands and grasslands, combined, enclose 45% of the points. Results from this study confirms the importance of playas as a dynamic source of dust in southwestern U.S. Moreover, this study suggests that anthropogenic factors play a major role in dust emission within southwestern U.S, although bare lands in particular that are not subjected to anthropogenic factors (e.g., the White Sands dune field) are also emitting dust. Future research is needed to statistically analyze the contribution of different land-cover types on dust emission in the region.

Quantitative phase contrast MRI of penetrating arteries in centrum semiovale at 7T

Pathological changes of penetrating arteries (PA) within the centrum semiovale is an important contributing factor of cerebral small vessel disease (SVD). However, quantitative characterization of the PAs remains challenging due to their sub-voxel sizes. Here, we proposed a Model-based Analysis of Complex Difference images (MACD) of phase contrast MRI capable of measuring the mean velocities (vmean), diameters (D), and volume flow rates (VFR) of PAs without contamination from neighboring static tissues at 7 T.Simulation, phantom and in vivo studies were performed to evaluate the reproducibility and errors of the proposed method. For comparison, a Model-based Analysis of Phase difference images (MAP) was also carried out in the simulation. The proposed MACD analysis approach was applied in vivo to study the age dependence of PA properties in healthy subjects between 21 and 55 years old.Simulation showed that our proposed MACD approach yielded smaller errors than MAP, with errors increasing at lower velocities and diameters for both methods. In the phantom study, errors of the MACD-derived vmean, D, and VFR were ≤20% of their true values when vmean≥1cm/s and similar at different spatial resolutions. On the other hand, errors of the uncorrected apparent velocities were 24–60% and depended strongly on voxel size. The MACD errors linearly increased with the angle (α) between the vessel and slice normal direction at α ≤ 2° but remained almost constant at larger α. Results of the in vivo studies showed that the coefficients of repeatability for vmean, D, and VFR for PAs with α = 0° were 0.67 cm/s, 0.060 mm, and 0.067 mm3/s, respectively. No significant age dependence was found for the number, vmean, D, and VFR of PAs. The mean vmean, D, and VFR over all PAs with α = 0° were 1.79 ± 0.62 cm/s, 0.17 ± 0.05 mm, and 0.36 ± 0.18 mm3/s, respectively.Quantitative measurements of PAs with the MACD method may serve as a useful tool for illuminating the vascular pathology in cerebral SVD.

Sparkle measurement revisited: A closer look at the details

Four years after introduction of the first instrument for measurement of sparkle, the foundations have been reconsidered, and the pool of practical experience has been analyzed to provide a more detailed and complete picture of the subject matter. The following aspects are introduced and discussed: observation conditions and resulting requirements for imaging (sampling) and filtering, analysis of spatial periods and frequencies as a basis for filtering, spatial filtering concepts, sparkle in the frequency domain, sparkle evaluation based on analysis of single images and difference images, origins of unwanted sparkle components, scaling and offset in sparkle evaluation, and verification of the method.

42.4: Sparkle Measurement Revisited: A Closer Look at the Details

AbstractThree years after introduction of the first instrument for measurement of sparkle the foundations have been reconsidered and the pool of practical experience has been analyzed to provide a more detailed and complete picture of the subject matter. The following aspects are introduced and discussed: observation conditions and resulting requirements for the imaging optics, imaging of the display under test (2‐dimensional sampling), analysis of spatial periods and frequencies as basis for separation of periodic and statistic intensity modulations, sparkle evaluation based on analysis of single images and difference images, spatial filtering concepts, sparkle in the frequency domain, pseudo‐sparkle, scaling and bias in sparkle evaluation, verification of the method.

Critical behavior of phase interfaces in porous media: Analysis of scaling properties with the use of noncoherent and coherent light

Image sequences of the surface of disordered layers of porous medium (paper) obtained under noncoherent and coherent illumination during capillary rise of a liquid are analyzed. As a result, principles that govern the critical behavior of the interface between liquid and gaseous phases during its pinning are established. By a cumulant analysis of speckle-modulated images of the surface and by the statistical analysis of binarized difference images of the surface under noncoherent illumination, it is shown that the macroscopic dynamics of the interface at the stage of pinning is mainly controlled by the power law dependence of the appearance rate of local instabilities (avalanches) of the interface on the critical parameter, whereas the growth dynamics of the local instabilities is controlled by the diffusion of a liquid in a layer and weakly depends on the critical parameter. A phenomenological model is proposed for the macroscopic dynamics of the phase interface for interpreting experimental data. The values of critical indices are determined that characterize the samples under test within this model. These values are compared with the results of numerical simulation for discrete models of directed percolation corresponding to the Kardar-Parisi-Zhang equation.

Land cover assessment with MODIS imagery in southern African Miombo ecosystems

Global land use and land cover products in highly dynamic tropical ecosystems lack the detail needed for natural resource management and monitoring at the national and provincial level. The MODIS sensor provides improved opportunities to combine multispectral and multitemporal data for land use and land cover mapping. In this paper we compare the MODIS Global Land Cover Classification Product with recent land use and land cover maps at the national level over a characteristic location of Miombo woodlands in the province of Zambezia, Mozambique. The performances of three land cover-mapping approaches were assessed: single-date supervised classification, principal component analysis of band-pair difference images, and multitemporal NDVI analysis. Extensive recent field data were used for the definition of the test sites and accuracy assessment. Encouraging results were achieved with the three approaches. The classification results were refined with the help of a digital elevation model. The most consistent results were achieved using principal component analysis of band-pair difference images. This method provided the most accurate classifications for agriculture, wetlands, grasslands, thicket and open forest. The overall classification accuracy reached 90%. The multitemporal NDVI provided a more accurate classification for the dense forest cover class. The selection of the right image dates proved to be critical for all the cases evaluated. The flexibility of these alternatives makes them promising options for rapid and inexpensive land cover mapping in regions of high environmental variability such as tropical developing countries.

Robust real-time ground plane motion compensation from a moving vehicle

One method to detect obstacles from a vehicle moving on a planar road surface is the analysis of motion-compensated difference images. In this contribution, a motion compensation algorithm is presented, which computes the required image-warping parameters from an estimate of the relative motion between camera and ground plane. The proposed algorithm estimates the warping parameters from displacements at image corners and image edges. It exploits the estimated confidence of the displacements to cope robustly with outliers. Knowledge about camera calibration, measuremts from odometry, and the previous estimate are used for motion prediction and to stabilize the estimation process when there is not enough information available in the measured image displacements. The motion compensation algorithm has been integrated with modules for obstacle detection and lane tracking. This system has been integrated in experimental vehicles and runs in real time with an overall cycle of 12.5 Hz on low-cost standard hardware.

Characterization and correction of pulse pile-up in simultaneous emission-transmission computed tomography.

We have developed an emission-transmission CT (ETCT) system capable of both single-photon emission computed tomography (SPECT) imaging and x-ray transmission CT imaging using a common photon counting detector. In principle, SPECT and x-ray CT projection data can be acquired simultaneously with the ETCT system; however, doing so results in contamination of the SPECT projection data due to pulse pile-up caused by the relatively high x-ray fluence rate. In this study, we characterize the effects of pulse pile-up for simultaneous ETCT imaging through computer simulation and experimental studies. We demonstrate that pulse pile-up in the SPECT energy window can be well approximated by a simple quadratic relationship between the pile-up rate and the x-ray fluence rate for sufficiently small x-ray fluence rates. Using this quadratic relationship, we developed a simple pile-up correction scheme that subtracts the pile-up counts from the emission data and also truncates the exterior regions of the emission projection data. Analysis of difference images and profiles indicate that this method permits us to reconstruct SPECT images with no apparent noise or resolution degradation in comparison to those obtained via sequential emission and transmission scans.