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The portable neutron energy spectrometer is designed to identify an unknown neutron source. The spectrometer is cylindrical in shape with a diameter of 12 cm and a length of 33 cm. This allows for a large surface area for incident neutrons to interact with and sufficient moderating material to thermalize neutrons up to 14.1 MeV in energy. The spectrometer utilizes eleven 2 cm × 2 cm high-efficiency...
This work focuses on the evaluation of spectroscopic background radiation measurements performed at an outdoor facility on the Schauinsland mountain in Germany. The detector system that was used consisted of two temperature stabilized Coplanar Grid (Cd,Zn)Te detectors together with a custom digital Multi Channel Analyzer. The research presented includes the evaluation of the spectroscopic outdoor...
We report on the recharging of the deep-donor that can drastically decrease the efficiency of charge collection in detector-grade CdZnTe:In crystals. We used several complementary experimental methods to characterize the material. Photoconductivity mapping was performed using measurements for both the contactless method and with evaporated Au contacts. Measurements of photoconductivity, photoconductivity...
High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55µm and 110µm) using a...
Myocardial blood flow quantification with PET and 13NH3 is a well established technique to evaluate the coronary flow reserve in patient with different cardiomyopathies. We performed an in depth evaluation of the variation in the results when modifying the reconstruction technique (OSEM algorithms, analytical algorithms, OSEM algorithms including time of flight and point spread function modelling),...
A novel regularization algorithm has been implemented in our previously described image registration program Ezys. The performance of the GPU enabled package is still very fast with typical 3D image registrations taking less than a minute. The method is based on a surface detection in images of interest. It allows more degrees of freedom near detected surfaces to obtain a good match of them, and enforces...
PET-guided radiation therapy treatment planning, clinical diagnosis, assessment of tumor growth and therapy response are dependent on the accurate delineation of the tumor volume. Several PET segmentation techniques have been proposed in the recent years. Most these techniques fail in the presence of heterogeneity in the lesion. In this work, an active contour model based on the work presented by...
The motion due to respiration is responsible for greatly reducing image quality of whole body positron emission tomography, PET. A simple method to produce a respiratory signal to enable gating of PET listmode data using the Microsoft Kinect, a consumer grade 3D scanner, is presented. Phantom data produced by a sinusoidally oscillating phantom being tracked by an existing commercially available respiratory...
Poisson noise is characteristic of count accumulation in positron emission tomography (PET) sinograms. We consider the denoising of low count PET sinograms by the following filters: block-matching and 3D (BM3D) filter, radial filter and stackgram filter. We also study the effect of first stabilizing the sinogram noise variance with Anscombe transformation, denoising the sinogram by the three methods...
In this work, a procedure to perform the normalization of the intensity values in FP-CIT SPECT images for the diagnosis of Parkinson's disease is presented. The proposed methodology is based on the fact that the shape of the distribution of intensity values is skewed and heavy-tailed, and therefore, it can be modelled in a parsimonious way using the alpha-stable distribution. We have proved that using...
Motivated by the need for a framework dedicated to multi modal images processing and analysis, as well as Wavelet and Contourlet transforms properties, we developed a WCHMT (Wavelet-Contourlet Hidden Markov Tree) as a quadtree-structured probabilistic graph that captures the statistical properties of the whole observed data. This combining strategy was applied to exploit advantages of both Wavelet...
Image registration tasks are often formulated in terms of minimization of a functional consisting of a data fidelity term penalizing the mismatch between the reference and the target image, and a term enforcing smoothness of shift between neighboring pairs of pixels (a min-sum problem). For registration of neighboring physical slices of microscopy specimens with discontinuities, Janáček [1] proposed...
Feature extraction and classification are two important parts in computer-aided detection (CAD) of abnormalities. For feature selection, typically we are interested in determining which, of a large number of potentially redundant or noisy features, are most discriminative for classification. Graph embedding is a relatively new category of feature selection methods. It uses a graph structure to model...
We developed SPECT imaging capability on a LabPET™ animal scanner. The add-on SPECT uses a multiple-pinhole collimator and a step-and-shoot helical scan scheme. The objective of this work was to determine 1) the effective imaging volume of a given scan protocol, and 2) the helical scan parameters, that is, the angular and axial step sizes, for achieving uniform high resolution images throughout the...
In image-guided radiation therapy (IGRT) an additional kV imaging system next to the linear particle accelerator provides information for an accurate patient positioning. However, due to the limited gantry rotation speed during treatment the typical acquisition time is much longer than the patient's breathing cycle resulting in low image quality. In particular, respiratory motion causes severe artifacts...
CT images are often affected by beam hardening artifacts due to the polyenergetic nature of the X-ray beam. Several correction methods have been proposed to be included in an FDK reconstruction scheme, which is still the prefered reconstruction algorithm in commercial X-ray CT scanners. In this work, we present a complete correction scheme for beam hardening artifact correction in an FDK-based reconstruction...
Parallax error in close-proximity applications of thick gamma-ray detectors, such as preclinical or organ-specific Positron Emission Tomography, motivates the need to accurately resolve interaction depth. In our lab, we routinely use a collimated gamma-ray source and apply an iterative maximum-likelihood clustering (MLC) algorithm to calibrate detector response statistics as a function of 3D interaction...
Motion-compensated PET of awake animals has the potential to greatly improve translational neurological investigations by enabling brain function to be studied during learning tasks and complex behaviors. Previously we have demonstrated the feasibility of performing motion-compensated brain PET on rodents, obtaining the necessary head motion data using marker-based techniques. However, markerless...
We have studied the impact of using rectangular-aperture pinholes in a multi-pinhole, stationary system for cardiac imaging of mice. The system will utilize the standard NaI(Tl) detectors on a clinical SPECT system. There are at least two advantages to using rectangular apertures: (1) the fields of view (FOV) in the axial and transverse directions become separable since they are determined by the...
The results show that energy spectra and flood maps for sub-millimeter crystals can be produced using the gated integrator PWM circuit (see Fig.6). To measure the goodness of crystal identification the silhouette statistic was used [8]. The silhouette for each point i is given by: equation where a(i) is the average distance from i to every other point in the crystal, and b(i) is the average distance...
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