Influence of acquisition time on MR image quality estimated with nonparametric measures based on texture features

Correlation of parametrized image texture features (ITF) analyses conducted in different regions of interest (ROIs) overcomes limitations and reliably reflects image quality. +e aim of this study is to propose a nonparametrical method and classify the quality of a magnetic resonance (MR) image that has undergone controlled degradation by using textural features in the image. Images of 41 patients, 17 women and 24 men, aged between 23 and 56 years were analyzed. T2-weighted sagittal sequences of the lumbar spine, cervical spine, and knee and T2-weighted coronal sequences of the shoulder and wrist were generated. The implementation of parallel imaging with the use of GRAPPA2, GRAPPA3, and GRAPPA4 led to a substantial reduction in the scanning time but also degraded image quality. The number of degraded image textural features was correlated with the scanning time. Longer scan times correlated with markedly higher ITF image persistence in comparison with images computed with reduced scan times. Higher ITF preservation was observed in images of bones in the spine and femur as compared to images of soft tissues, i.e., tendons and muscles. Finally, a nonparametrized image quality assessment based on an analysis of the ITF, computed for different tissues, correlating with the changes in acquisition time of the MRimages, was successfully developed. The correlation between acquisition time and the number of reproducible features present in an MR image was found to yield the necessary assumptions to calculate the quality index

On the potential for a bottom active layer below coastal permafrost: the impact of seawater on permafrost degradation imaged by electrical resistivity tomography (Hornsund, SW Spitsbergen)

This paper presents the results of two-dimensional electrical resistivity tomography (ERT) of permafrost developed in coastal zone of Hornsund, SW Spitsbergen. The measurements were made using the Wenner-Schlumberger electrode array with an electrode spacing 5 m for overview and 1.5 or 1 m spacing for detailed imaging. Using the ERT inversion results, we studied the ‘sea influence’ on deeper parts of the frozen ground. During the investigations we tested hypotheses that the operation of seawater on shoreface may cause changes in the shape of the coastal permafrost base, and that the impact of seawater on more inland permafrost depends on the shape of the shoreline (differently in the embayment, and differently in a headland exposed to the open sea). Our study was inspired by previous ground temperature measurements conducted in several boreholes located in study area which captured the propagation of ground heat waves from the base of permafrost. Our resistivity models indicate a major differentiation in terms of resistivity of permafrost in the coastal zone. The resistivity measures obtained in deeper layers of ground were so low (< 100 Ω·m) that in the ‘warm permafrost’ conditions they exclude a possibility of freezing the coastal sediments and bedrock from the side of the sea. Low values continue further inland, going down under the surface layer of permafrost with higher resistivity. We interpret this situation as an influence of seawater's temperature and salinity on deeper parts of permafrost. Based on the measurements conducted within two years, we stated a change in the distribution of resistivity, both in the active layer, and in coastal front of permafrost in deeper parts of the ground. As observed in the inverse models, the geometric arrangement between the fields of extreme resistivity indicates the existence of a bottom active layer by the permafrost base, depending on thermal and chemical characteristics of seawater. The measurements conducted in the embayment, as well as on the headland exposed to the operation of storm waves, proved strong differences in the scale of the impact of seawater on permafrost

Kaliningrad Oblast 2016. The society, economy and army. OSW Report 12/2016

Moscow has been developing a new model of governance for Kaliningrad Oblast in 2016. The changes in the regional government (the governance of the oblast was entrusted to people sent from Moscow and had no links with the region) were part of it. These are a result of Russia’s depleting financial resources and austerity policy, the increasing militarisation of the Russian Federation and the important role the oblast plays in this policy, and the need to ensure a satisfactory result in the upcoming presidential election. Although there are at present no visible symptoms suggesting an intensification of protest sentiments, Moscow is taking preventive action to try to tighten its grip on local elites and residents. Kaliningrad Oblast remains an essential element of the Russian military strategy in the Baltic region. This is borne out by the deployment in the region of S-400 air defence systems, ships equipped with Kalibr missiles, and Bastion missile defence systems (which are nominally anti-ship weapons but are also adjusted to attacking ground targets). Furthermore, the deployment of Iskander missile systems has been launched which enables the creation of a so-called ‘Anti-Access/Area Denial’ (A2/AD) zone, extending the range of Russian weapons to the territories and airspace of the neighbouring NATO member states

3D PET image reconstruction based on Maximum Likelihood Estimation Method (MLEM) algorithm

Positron emission tomographs (PET) do not measure an image directly. Instead, they measure at the boundary of the field-of-view (FOV) of PET tomograph a sinogram that consists of measurements of the sums of all the counts along the lines connecting two detectors. As there is a multitude of detectors build-in typical PET tomograph structure, there are many possible detector pairs that pertain to the measurement. The problem is how to turn this measurement into an image (this is called imaging). Decisive improvement in PET image quality was reached with the introduction of iterative reconstruction techniques. This stage was reached already twenty years ago (with the advent of new powerful computing processors). However, three dimensional (3D) imaging remains still a challenge. The purpose of the image reconstruction algorithm is to process this imperfect count data for a large number (many millions) of lines-of-responce (LOR) and millions of detected photons to produce an image showing the distribution of the labeled molecules in space.Comment: 10 pages, 7 figure

Multiple scattering and accidental coincidences in the J-PET detector simulated using GATE package

Novel Positron Emission Tomography system, based on plastic scintillators, is developed by the J-PET collaboration. In order to optimize geometrical configuration of built device, advanced computer simulations are performed. Detailed study is presented of background given by accidental coincidences and multiple scattering of gamma quanta

Application of the compress sensing theory for improvement of the TOF resolution in a novel J-PET instrument

Nowadays, in positron emission tomography (PET) systems, a time of fl ight (TOF) information is used to improve the image reconstruction process. In TOF-PET, fast detectors are able to measure the difference in the arrival time of the two gamma rays, with the precision enabling to shorten signifi cantly a range along the line-of-response (LOR) where the annihilation occurred. In the new concept, called J-PET scanner, gamma rays are detected in plastic scintillators. In a single strip of J-PET system, time values are obtained by probing signals in the amplitude domain. Owing to compressive sensing (CS) theory, information about the shape and amplitude of the signals is recovered. In this paper, we demonstrate that based on the acquired signals parameters, a better signal normalization may be provided in order to improve the TOF resolution. The procedure was tested using large sample of data registered by a dedicated detection setup enabling sampling of signals with 50-ps intervals. Experimental setup provided irradiation of a chosen position in the plastic scintillator strip with annihilation gamma quanta

Plastic scintillators for positron emission tomography obtained by the bulk polymerization method

This paper describes three methods regarding the production of plastic scintillators. One method appears to be suitable for the manufacturing of plastic scintillator, revealing properties which fulfill the requirements of novel positron emission tomography scanners based on plastic scintillators. The key parameters of the manufacturing process are determined and discussed.Comment: 7 pages, 4 figure