PET/CT and SPECT/CT imaging of 90Y hepatic radioembolization at therapeutic and diagnostic activity levels: Anthropomorphic phantom study.

Purpose: Prior to 90Y radioembolization procedure, a pretherapy simulation using 99mTc-MAA is performed. Alternatively, a small dosage of 90Y microspheres could be used. We aimed to assess the accuracy of lung shunt fraction (LSF) estimation in both high activity 90Y posttreatment and pretreatment scans with isotope activity of ~100 MBq, using different imaging techniques.

Evaluation of qualitative and quantitative data of Y-90 imaging in SPECT/CT and PET/CT phantom studies.

Introduction: We aimed to assess the feasibility of SPECT and PET Y-90 imaging, and to compare these modalities by visualizing hot and cold foci in phantoms for varying isotope concentrations.

Materials And Methods: The data was acquired from the Jaszczak and NEMA phantoms. In the Jaszczak phantom Y-90 concentrations of 0.

NVIDIA OptiX ray-tracing engine as a new tool for modelling medical imaging systems.

The most accurate technique to model the X- and gamma radiation path through a numerically defined object is the Monte Carlo simulation which follows single photons according to their interaction probabilities. A simplified and much faster approach, which just integrates total interaction probabilities along selected paths, is known as ray tracing. Both techniques are used in medical imaging for simulating real imaging systems and as projectors required in iterative tomographic reconstruction algorithms.

Persistent colonization of 2 hospital water supplies by L. pneumophila strains through 7 years--sequence-based typing and serotyping as useful tools for a complex risk analysis.

Contamination with Legionella spp. of hot water system (HWS) in hospitals is a considerable problem and elimination of bacteria poses difficulties. Obligatory control of Legionella spp.

Fast and accurate rotator for rotation-based iterative reconstruction algorithms.

We present an image rotation algorithm in which the values of pixels of the rotated image are computed as weighted averages of the original grid pixels, with the weights proportional to the overlapping areas of each corresponding pixel pair. The method preserves virtually perfectly the image uniformity and single pixel pulse value in the rotated image. These properties are particularly important to accurately model projections in iterative reconstruction algorithms.

Optical scanner for 3D radiotherapy polymer gel dosimetry.

Sophisticated techniques employed in radiotherapy for irradiation of tumours require comprehensive dosimetry allowing for precise, high resolution measurements of radiation dose distribution in three dimensions and verification of treatment planning systems. Polymer gel dosimetry has been shown to be a unique technique for three-dimensional high resolution measurements of absorbed radiation dose distributions. If exposed to ionizing radiation, radical polymerisation and crosslinking of monomeric components take place in a 3D polymer gel dosimeter, leading to the formation of large polymeric structures that scatter visible light.

Breast phantom for comparison X-ray and polarimetric optical tomography imaging.

Breast phantom made as combination of paraffin and INTRALIPID™ was tested by use of X-ray classical computed tomography and polarimetric optical tomography. The INTRALIPID™ is a liquid commonly used for simulation breast tissues optical properties but it is useless as X-ray phantom. During our tests we have observed that X-ray tomography allows to recognize a proper placement of INTRALIPID™ inclusions inside paraffin medium but we cannot distinguish density of INTRALIPID™ within each inclusions.

Iterative deconvolution of simultaneous 99mTc and 201Tl projection data measured on a CdZnTe-based cardiac SPECT scanner.

We present a method of correcting self-scatter and crosstalk effects in simultaneous technetium-99m/thallium-201 stress/rest myocardial perfusion (single photon emission computed tomography) SPECT scans. The method, which is in essence a hybrid between the triple energy window method and scatter modelling, is based on a model of spatial and spectral distribution of projection counts in several selected energy windows. The parameters of the model are determined from measurements of thin rod sources in air when no in-object scatter or attenuation effects are present.

Attenuation correction in SPECT without attenuation map.

A method of attenuation correction in Single Photon Emission Computed Tomography (SPECT), based on emission data only is presented. The algorithm uses the well known Helgason-Ludwig consistency conditions. However, it does not attempt to find the attenuation map, but rather the correction factors for the projection data, which makes the problem simpler and does not need to assume any particular template of the attenuation map.

Simultaneous dual-radionuclide myocardial perfusion imaging with a solid-state dedicated cardiac camera.

Purpose: We compared simultaneous dual-radionuclide (DR) stress and rest myocardial perfusion imaging (MPI) with a novel solid-state cardiac camera and a conventional SPECT camera with separate stress and rest acquisitions.

Methods: Of 27 consecutive patients recruited, 24 (64.5+/-11.

Performance evaluation of D-SPECT: a novel SPECT system for nuclear cardiology.

D-SPECT (Spectrum Dynamics, Israel) is a novel SPECT system for cardiac perfusion studies. Based on CZT detectors, region-centric scanning, high-sensitivity collimators and resolution recovery, it offers potential advantages over conventional systems. A series of measurements were made on a beta-version D-SPECT system in order to evaluate its performance in terms of energy resolution, scatter fraction, sensitivity, count rate capability and resolution.

Performance of three-photon PET imaging: Monte Carlo simulations.

We have recently introduced the idea of making use of three-photon positron annihilations in positron emission tomography. In this paper, the basic characteristics of the three-gamma imaging in PET are studied by means of Monte Carlo simulations and analytical computations. Two typical configurations of human and small animal scanners are considered.

Three-gamma annihilation imaging in positron emission tomography.

It is argued that positron annihilation into three photons, although quite rare, could still be used as a new imaging modality of positron emission tomography. The information gained when the three decay photons are detected is significantly higher than in the case of 511 keV two-gamma annihilation. The performance of three-gamma imaging in terms of the required detector properties, spatial resolution and counting rates is discussed.

Theory of oscillations in average crisis-induced transient lifetimes.

Analytical and numerical study of the roughly periodic oscillations emerging on the background of the well-known power law governing the scaling of the average lifetimes of crisis induced chaotic transients is presented. The explicit formula giving the amplitude of "normal" oscillations in terms of the eigenvalues of unstable orbits involved in the crisis is obtained using a simple geometrical model. We also discuss the commonly encountered situation when normal oscillations appear together with "anomalous" ones caused by the fractal structure of basins of attraction.

Noisefree stochastic multiresonance near chaotic crises.

We report on the phenomenon of noisefree stochastic multiresonance that appears in a natural way in systems where the threshold crossing probability has a nonmonotonous derivative with respect to the control parameter. In particular, we consider periodically driven chaotic dynamical systems above crisis threshold where the nonmonotonicity is caused by the fractal structure of precritical attractors and, possibly, their basins of attraction. The spectral power amplification as a function of the control parameter can be easily obtained from the postcritical average transient times, and the heights of its multiple maxima can be estimated on the basis of simple geometric models.

Stochastic multiresonance in a chaotic map with fractal basins of attraction.

Noise-free stochastic resonance in a chaotic kicked spin model at the edge of the attractor merging crisis is considered. The output signal reflects the occurrence of crisis-induced jumps between the two parts of the attractor. As the control parameter-the amplitude of the magnetic field pulses-is varied, the signal-to-noise ratio shows plateaus and multiple maxima, thus stochastic multiresonance is observed.

Influence of stable Floquet exponents on time-delayed feedback control.

The performance of time-delayed feedback control is studied by linear stability analysis. Analytical approximations for the resulting eigenvalue spectrum are proposed. Our investigations demonstrate that eigenbranches that develop from the stable Lyapunov exponents of the free system also have a strong influence on the control properties, either by hybridization or by a crossing of branches which interchanges the role of the leading eigenvalue.