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  • Author: Jiri Vasina x
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Approximate methods for the optical characterization of inhomogeneous thin films: Applications to silicon nitride films

Abstract

In this paper the overview of the most important approximate methods for the optical characterization of inhomogeneous thin films is presented. The following approximate methods are introduced: Wentzel–Kramers–Brillouin–Jeffreys approximation, method based on substituting inhomogeneous thin films by multilayer systems, method based on modifying recursive approach and method utilizing multiple-beam interference model. Principles and mathematical formulations of these methods are described. A comparison of these methods is carried out from the practical point of view, ie advantages and disadvantages of individual methods are discussed. Examples of the optical characterization of three inhomogeneous thin films consisting of non-stoichiometric silicon nitride are introduced in order to illustrate efficiency and practical meaning of the presented approximate methods.

Open access
PET/CT imaging in polymyalgia rheumatica: praepubic 18F-FDG uptake correlates with pectineus and adductor longus muscles enthesitis and with tenosynovitis

Abstract

Background

The role of 18F-fluorodeoxyglucose positron emission computed tomography (18F-FDG PET/CT) is increasing in the diagnosis of polymyalgia rheumatica (PMR), one of the most common inflammatory rheumatic diseases. In addition to other locations, increased 18F-FDG accumulation has been detected in the praepubic region in some patients. However, a deeper description and pathophysiological explanation of this increased praepubic accumulation has been lacking. The aim of the presented study is to confirm a decrease in praepubic 18F-FDG accumulation in response to therapy and to describe potential correlations to other 18F-FDG PET/CT scan characteristics during the course of disease. As a secondary objective, we describe the pathological aspects of the observed praepubic 18F-FDG uptake.

Patients and methods

A retrospective review of patients with newly suspected PMR undergoing baseline and follow up 18F-FDG PET/CT between February 2010 and March 2016 is given. Those with a visually detected presence of praepubic 18F-FDG accumulation were further analysed. The uptake was assessed visually and also semi-quantitatively in the defined region of interest by calculation of target-to-liver ratios. Other regions typical for PMR were systematically described as well (shoulders, hips, sternoclavicular joints, ischiogluteal bursae, spinous interspaces).

Results

Twenty-three out of 89 screened patients (26%) presented with initial praepubic 18F-FDG PET/CT positivity, 15 of whom also underwent follow up 18F-FDG PET/CT examination. Five out of 15 patients presented with increased 18F-FDG accumulation in large arteries as a sign of giant cell arteritis. During follow up examination, decrease in 18F-FDG accumulation caused by therapeutic intervention was observed in all evaluated locations in all analysed patients and no new positivity was indicated, including periarticular, extraarticular tissues or target large vessels. Praepubical accumulation of 18F-FDG was diminished in all patients (15/15, 100%) after treatment with steroids.

Conclusions

Increased praepubic 18F-FDG uptake in patients with PMR is relatively common and this region should be systematically evaluated during differential diagnosis of rheumatic and malignant disease. Praepubic inflammation is probably related to enthesitis and tenosynovitis at the origin of pectineus and adductor longus muscles ventrally from the pubis.

Open access