Transverse NMR relaxation as a probe of mesoscopic structure

Transverse NMR relaxation in a macroscopic sample is shown to be extremely sensitive to the structure of mesoscopic magnetic susceptibility variations. Such a sensitivity is proposed as a novel kind of contrast in the NMR measurements. For suspensions of arbitrary shaped paramagnetic objects, the transverse relaxation is found in the case of a small dephasing effect of an individual object. Strong relaxation rate dependence on the objects' shape agrees with experiments on whole blood. Demonstrated structure sensitivity is a generic effect that arises in NMR relaxation in porous media, biological systems, as well as in kinetics of diffusion limited reactions.Comment: 4 pages, 3 figure

Modeling the R2* relaxivity of blood at 1.5 Tesla

BOLD (Blood Oxygenation Level Dependent) imaging is used in fMRI to show differences in activation of the brain based on the relative changes of the T2* (= 1/R2*) signal of the blood. However, quantification of blood oxygenation level based on the T2* signal has been hindered by the lack of a predictive model which accurately correlates the T2* signal to the oxygenation level of blood. The T2* signal decay in BOLD imaging is generated due to blood containing paramagnetic deoxyhemoglobin (in comparison to diamagnetic oxyhemoglobin). This generates local field inhomogeneities, which cause protons to experience different phase shifts, leading to dephasing and the MR signal decay. The blood T2* signal has been shown to decay with a complex behavior1, termed Non-Lorenztian, and thus is not adequately described by the traditional model of simplemono-exponential decay. Theoretical calculations show that diffusion narrowing substantially affects signal loss in our data. Over the past decade, several theoretical models have been proposed to describe this Non-Lorenztian behavior in the blood T2* signal in BOLD fMRI imaging. The goal of this project was to investigate different models which have been proposed over the years and determine a semi-phenomenological model for the T2* behaviorusing actual MR blood data

Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu

We measure the magnetic susceptibility of ultrathin Co films with an in-plane uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie temperature the influence of the magnetic anisotropy can be investigated by means of the parallel and transverse susceptibilities along the easy and hard axes. By comparison with a theoretical analysis of the susceptibilities we determine the isotropic exchange interaction and the magnetic anisotropy. These calculations are performed in the framework of a Heisenberg model by means of a many-body Green's function method, since collective magnetic excitations are very important in two-dimensional magnets.Comment: 7 pages, 3 figure

Magnetic properties of quantum Heisenberg ferromagnets with long-range interactions

Quantum Heisenberg ferromagnets with long-range interactions decayin as $1/r^p$ in one and two dimensions are investigated by means of the Green's function method. It is shown that there exists a finite-temperature phase transition in the region $d<p<2 d$ for the $d$-dimensional case and that no transitions at any finite temperature exist for $p\ge 2 d$; the critical temperature is also estimated. We study the magnetic properties of this model. We calculate the critical exponents' dependence on $p$; these exponents also satisfy a scaling relation. Some of the results were also found using the modified spin-wave theory and are in remarkable agreement with each other.Comment: 13 pages(LaTeX REVTeX), 2 figures not included (postscript files available on request), submitted to Phys.Rev.

'Theory for the enhanced induced magnetization in coupled magnetic trilayers in the presence of spin fluctuations'

Motivated by recent experiments, the effect of the interlayer exchange interaction $J_{inter}$ on the magnetic properties of coupled Co/Cu/Ni trilayers is studied theoretically. Here the Ni film has a lower Curie temperature $T_{C,\rm Ni}$ than the Co film in case of decoupled layers. We show that by taking into account magnetic fluctuations the interlayer coupling induces a strong magnetization for T\gtsim T_{C,\rm Ni} in the Ni film. For an increasing $J_{inter}$ the resonance-like peak of the longitudinal Ni susceptibility is shifted to larger temperatures, whereas its maximum value decreases strongly. A decreasing Ni film thickness enhances the induced Ni magnetization for T\gtsim T_{C,\rm Ni}. The measurements cannot be explained properly by a mean field estimate, which yields a ten times smaller effect. Thus, the observed magnetic properties indicate the strong effect of 2D magnetic fluctuations in these layered magnetic systems. The calculations are performed with the help of a Heisenberg Hamiltonian and a Green's function approach.Comment: 4 pages, 3 figure

Probe-based confocal laser endomicroscopy in diagnosis of diffuse cystic lung disease in Sjögren’s syndrome

Sjögren’s syndrome is systemic autoimmune disease characterized by lymphocytic infiltration of various organs with wide frequency of pulmonary involvement. Diffuse cystic lung disease in Sjögren’s syndrome is a rare condition and requires differential diagnosis with other cystic pathologies such as lymphangioleyomiomatosis or Langerhans cell histiocytosis. Probe-based confocal laser endomicroscopy (pCLE) is a method of in vivo investigation of airways and lung tissue on microscopic level during bronchoscopy. We used this method in diffuse cystic lung disease caused by Sjögren’s syndrome. The pCLE image showed a large number of fluorescent cells presumably lymphocytes in bronchioles, dilated alveolar spaces with fluid and thin alveolar walls. We think that the presence of the bronchiolar cells pattern can be used to differentiate between the pulmonary manifestations of Sjögren's disease and other cystic lung diseases

Field strength dependence of grey matter R2* on venous oxygenation

The relationship between venous blood oxygenation and change in transverse relaxation rate (ΔR2 *) plays a key role in calibrated BOLD fMRI. This relationship, defined by the parameter β, has previously been determined using theoretical simulations and experimental measures. However, these earlier studies have been confounded by the change in venous cerebral blood volume (CBV) in response to functional tasks. This study used a double-echo gradient echo EPI scheme in conjunction with a graded isocapnic hyperoxic sequence to assess quantitatively the relationship between the fractional venous blood oxygenation (1-Yv) and transverse relaxation rate of grey matter (ΔR2 * GM), without inducing a change in vCBV. The results demonstrate that the relationship between ΔR2 * and fractional venous oxygenation at all magnet field strengths studied was adequately described by a linear relationship. The gradient of this relationship did not increase monotonically with field strength, which may be attributed to the relative contributions of intravascular and extravascular signals which will vary with both field strength and blood oxygenation

Туберкулез у взрослых и детей в Северо-Западном федеральном округе: динамика эпидемиологических показателей и критерии их оценки

The epidemic situation is monitored by numerous rates that may not reflect it objectively which will subsequently lead to higher incidence rates and severe forms of tuberculosis in both adults and children in the regions with the most unfavorable situation.The objective: to evaluate epidemiological rates for tuberculosis in the Northwestern Federal District to identify the most significant, and assess the epidemic situation in the region using these most significant rates.Subjects and Methods. We analyzed the main epidemiological rates of pediatric tuberculosis according to federal statistics (Forms 8 and 33) in 11 districts of the Northwestern District in 2019-2021. Annual figures were obtained from open demographic data of the state statistics (https://www.fedstat.ru). Statistical analysis was pe`rformed using the free software R (v.3.5.1) and the commercial Statistical Package for the Social Sciences (SPSS Statistics for Windows, Version 24.0, IBM Corp., 2016). Hierarchical cluster analysis and k-means clustering were used with the selection of the lowest and highest values of rates. A formula is proposed for calculating the coefficient of full coverage with preventive screening (COP) for tuberculosis of the population which allows adjusting the analyzed epidemic rates taking into account the maximum coverage of the population with preventive screening and determining the accuracy of previous analysis.Results. According to the data obtained, in 2017 and 2018, Vologda Oblast and Nenets Autonomous Okrug were epidemically favorable regions, while in 2020 and 2021 Kaliningrad, Leningrad and Novgorod Oblasts were regarded as favorable regions that were steadily improving their performance. Regions with unfavorable tuberculosis situation include Pskov Oblast, St. Petersburg and the Komi Republic. At the same time, the first two regions occupy this position stably from 2017 to 2021. The use of the coefficient of low coverage with screening for tuberculosis made it possible to determine that Murmansk Oblast, St. Petersburg, Leningrad and Pskov Oblasts in 2020 and 2021 are prognostically unfavorable regions despite a decline in official tuberculosis rates. The data obtained correlate with a high percentage of positive tests with the tuberculosis recombinant tuberculosis allergen (TRA) in children in the regions mentioned above.Conclusions. The analysis of the data clearly demonstrates the possibility of determining the epidemically most favorable or unfavorable regions using four rates: coverage with preventive screening, incidence in the adult population, incidence in children aged 0 to 17 years, and tuberculosis mortality. Cluster analysis using these rates, calculation of rates using the developed coefficient of low coverage with screening for tuberculosis, and analysis of positive results of TRA test in children allows identifying the most epidemically unfavorable regions, despite the decrease in some rates that can be regarded as favorable.Мониторинг эпидемической ситуации проводится с учетом большого числа показателей, которые могут не совсем объективно отражать ее, что в последующем приведет к повышению уровня заболеваемости и появлению тяжелых форм туберкулеза как у взрослого населения, так и у детей в наиболее неблагоприятных регионах.Цель исследования: оценка эпидемиологических показателей по туберкулезу в Северо-Западном федеральном округе для выявления наиболее значимых, а также эпидемической ситуации в регионе с применением наиболее значимых показателей.Материалы и методы. Был проведен анализ основных эпидемиологических показателей по туберкулезу у детей по данным федеральной статистики (формы № 8 и № 33) в 11 округах Северо-Западного региона за период с 2019 по 2021 г. Ежегодные показатели получены из открытых демографических данных государственной статистики (https://www.fedstat.ru). Статистический анализ проводился с использованием свободной программной среды вычислений R (v.3.5.1) и коммерческого пакета программного обеспечения Statistical Package for the Social Sciences (SPSS Statisticsfor Windows, версия 24.0, IBM Corp., 2016). Применялись иерархический кластерный анализ и кластеризация методом k-средних с выбором наиболее низких и высоких значений показателей. Предложена формула расчета коэффициента полного охвата профилактическим обследованием (ПОН) на туберкулез населения, который позволяет скорректировать анализируемые эпидемические показатели с учетом максимально полного охвата населения ПОН и определить правильность проведенного ранее анализа.Результаты исследования. Согласно полученным данным, в 2017 и 2018 г. эпидемически благоприятными регионами были Вологодская область и Ненецкий автономный округ, тогда как в 2020 и 2021 г. Калининградская, Ленинградская и Новгородские области расценены как благоприятные регионы, которые стабильно улучшают свои показатели. К неблагоприятным регионам относятся Псковская область, г. Санкт-Петербург и Республика Коми. При этом первые два региона занимают данную позицию стабильно с 2017 по 2021 г. Применение коэффициента низкого охвата ПОН на туберкулез позволило определить, что Мурманская область, г. Санкт-Петербург, Ленинградская и Псковская области в 2020 и 2021 г. являются прогностически неблагоприятными регионами, несмотря на снижение официальных показателей по туберкулезу. Полученные данные коррелируют с высоким процентом положительных проб с аллергеном туберкулезным рекомбинантным (АТР) у детей в обозначенных выше регионах.Выводы. Проведенный анализ данных наглядно демонстрирует возможность определения эпидемически наиболее благоприятных или неблагоприятных регионов, используя четыре показателя: охват ПОН, показатель заболеваемости взрослого населения, показатель заболеваемости детского населения в возрасте от 0 до 17 лет и смертность от туберкулеза. Кластерный анализ с применением данных показателей, расчет показателей с применением разработанного коэффициента низкого охвата ПОН на туберкулез и анализ положительных результатов по пробе с АТР у детей позволяет выявить наиболее эпидемически неблагоприятные регионы, несмотря снижение отдельных показателей, которые могут быть расценены как благоприятные