PubMed Health⌕ Search

Biomedical subjects

D Sakellariou

Publications and source records attributed to D Sakellariou.

11 recordsLinked to original sources
PubMed2006

Theory of MRI in the presence of zero to low magnetic fields and tensor imaging field gradients.

Today, all commonly practiced magnetic resonance imaging (MRI) reconstruction methods assume that the magnetic field created by the gradient coils is everywhere truncated by a dominant static uniform magnetic field. However, with the advent of SQUID detected MRI at microtesla fields, the opposite limit attracts attention, i.e., image formation in the unperturbed tensor field of the gradient coils. Here, we show by numerical simulations that, in principle, it is possible to reconstruct the image of an object in the absence of a uniform static field, working with the same gradient field setup as used in conventional MRI. Our calculations show that this approach could increase the image resolution limit attainable at low fields with a minimal incorporation of additional hardware and pulse sequences.

Journal Article↗
PubMed2001

Approach to high-resolution ex situ NMR spectroscopy.

Nuclear magnetic resonance (NMR) experiments are typically performed with samples immersed in a magnet shimmed to high homogeneity. However, there are many circumstances in which it is impractical or undesirable to insert objects or subjects into the bore of a high-field magnet. Here we present a methodology based on an adaptation of nutation echoes that provides resolved spectra in the presence of matched inhomogeneous static and radiofrequency fields, thereby opening the way to high-resolution ex situ NMR. The observation of chemical shifts is regained through the use of multiple-pulse sequences of correlated, composite z-rotation pulses, producing resolved NMR spectra of liquid samples.

Magnetic Resonance Spectroscopy↗
PubMed2001

Improved resolution in proton NMR spectroscopy of powdered solids.

We present a new solid-state nuclear magnetic resonance experiment that yields, under CRAMPS decoupling conditions, a significant reduction in proton line widths for powdered organic solids. This experiment which relies on a constant-time acquisition of the proton transverse magnetization, removes the contribution of nonrefocusable broadening from the proton line widths. Although this new technique suffers from relatively low sensitivity, we demonstrate in this paper its feasibility on two model samples, L-alanine and the dipeptide Ala-Asp. In both cases a factor of between 2 and 3 in line width reduction is obtained for most of the proton resonances.

Alanine↗
PubMed2001

Spectral editing in solid-state NMR using scalar multiple quantum filters.

In this paper we describe the use of heteronuclear scalar couplings in solid-state NMR in order to generate multiple-quantum filtering (MQF) pulse sequences. These sequences can be used to edit CP/MAS spectra according to carbon multiplicity. Analytic expressions for the intensity of the MQF signals are obtained using the standard product operator formalism. Experiments that demonstrate the technique are shown in powder samples of camphor and a tripeptide.

Journal Article↗
PubMed2001

Early recovery of oxygen kinetics after submaximal exercise test predicts functional capacity in patients with chronic heart failure.

BACKGROUND: Oxygen (O2) uptake at peak exercise (VO2 peak) is an objective measurement of functional capacity in patients with chronic heart failure (CHF). The significance of recovery O2 kinetics parameters in predicting exercise capacity, and the parameters of submaximal exercise testing have not been thoroughly examined. METHODS AND RESULTS: Thirty-six patients (mean age = 48+/-14 years) with CHF and New York Heart Association functional class I, II, or III, and eight healthy volunteers (mean age = 39+/-13 years) were studied with maximal and submaximal cardiopulmonary exercise testing (CPET). The first degree slope of O2 uptake decay during early recovery from maximal (VO2/t-slope), and submaximal exercise (VO2/t-slope)(sub), were calculated, along with VO2 half-time (T(1/2)VO2). Patients with CHF had a longer recovery of O2 uptake after exercise than healthy volunteers, expressed by a lower VO2/t-slope (0.616+/-0.317 vs. 0.956+/-0.347 l min(-1) min(-1), P=0.029) and greater T(1/2)VO2 (1.28+/-0.30 vs. 1.05+/-0.15 min, P = 0.005). VO2/t-slope correlated with the VO2 peak (r = 0.84, P<0.001), anaerobic threshold (r = 0.79, P<0.001), and T(1/2)VO2, a previously established estimate of recovery O2 kinetics (r = -0.59, P<0.001). (VO2/t-slope)(sub) was highly correlated with VO2/t-slope after maximal exercise (r=0.87, P<0.001), with the VO2 peak (r=0.87, P<0.001) and with T(1/2)VO2 after maximal exercise (r=-0.62, P<0.001). VO2/t-slope after maximal and submaximal exercise was reduced in patients with severe exercise intolerance (F=9.3, P<0.001 and F=12.8, P<0.001, respectively). CONCLUSIONS: Early recovery O2 kinetics parameters after maximal and submaximal exercise correlate closely with established indices of exercise capacity in patients with CHF and in healthy volunteers. These findings support the use of early recovery O2 kinetics after submaximal exercise testing as an index of functional capacity in patients with CHF.

Adult↗
PubMed1997

Flow-cytometric analysis of peripheral blood lymphocytes in patients with chronic idiopathic neutropenia of adults.

Flow-cytometric analysis of peripheral blood lymphocytes was performed in 96 patients with chronic idiopathic neutropenia of adults (CINA) and in 36 age- and sex-matched healthy volunteers (controls) using a panel of monoclonal antibodies. Patients were classified arbitrarily into group A (68 patients with 2500-1500 neutrophils/microliter) and group B (28 patients with neutrophil counts below 1500/microliter). We found that CINA patients displayed low numbers of peripheral blood lymphocytes compared with the controls, which correlated with the numbers of circulating neutrophils. This decrease was due mainly to the reduction of T lymphocytes and, to lesser degree, to the decline of NK cells. Both CD4+ and CD8+ T cells decreased, so that the CD4+/CD8+ cell ratio remained within normal range. Moreover, decrease of T lymphocytes was due essentially to the diminution of CD45RO+ T-cell subsets (CD4+/CD45RO+ and CD8+/CD45RO+), while CD45RA+ T cells did not change. A highly significant positive correlation was found between the numbers of CD45RO+ T cells and the numbers of circulating neutrophils. All these alterations were more pronounced in the patients of group B than in those of group A. NK cells were found to be significantly reduced in the patients of group B, but not in those of group A. The numbers of both CD16+ and CD56+ cells correlated with the numbers of circulating neutrophils. Patients of group B had also low numbers of CD57+ cells, probably due to the reduction of T cells and NK cells. B cells did not change significantly. No significant changes were found also in the numbers of lymphocytes carrying activation-related cell surface markers. We concluded that lymphocyte reduction in CINA patients is due mainly to the diminution of CD45RO+ cells, and we postulated that the most probable explanation for this abnormality is an increased extravasation of these cells, which pass into the tissues following an accelerated adhesion to endothelial cells. This hypothesis and its relationship with the underlying neutropenia in CINA patients remain to be clarified.

Adolescent↗
PubMed1996

Primary thyroid non-Hodgkin's lymphomas: clinicopathological observations on patients living in the island of Crete.

Fifteen patients with primary thyroid non-Hodgkin's lymphomas (PT-NHLs) living in the island of Crete were studied. Patients' median age was 69 years, male/female ratio 1.5/1 and stage I/stage II ratio 2/1 (stages III and IV were excluded). According to the Working Formulation Classification, 2 cases were with low, 10 with intermediate and 3 with high grade of malignancy. Remission rate was 80%, median overall survival 61 months and median disease free survival 59 months. No significant difference in survival were found between stage I and II, as well as between males and females. Conclusing, PT-NHLs in the island of Crete are more frequent in males than in females, and are predominantly (67%) of the intermediate grade of malignancy.

Adult↗
PubMed1995

Evidence for involvement of activated CD8+/HLA-DR+ cells in the pathogenesis of neutropenia in patients with B-cell chronic lymphocytic leukaemia.

B-cell chronic lymphocytic leukaemia (B-CLL) is often associated with peripheral blood cytopenias resulting, in most cases, from bone marrow infiltration, hypersplenism, or circulating autoantibodies. The present study was undertaken to investigate the possible involvement of a cell-mediated suppression of granulopoiesis in these patients. We studied two groups of patients, 8 neutropenic and 26 non-neutropenic, defined by the arbitrarily taken cutoff count of 2000 neutrophils/microliters. We found that neutropenic patients had higher numbers of peripheral blood CD3+, CD8+ and CD57+ cells, and higher numbers of activated CD8+/HLA-DR+ cells than the non-neutropenic ones. A negative correlation between CD8+ cells and circulating neutrophils, and a suggested negative correlation between CD8+/HLA-DR+ cells and circulating neutrophils were noted in the patients studied. Furthermore, we investigated the capacity of immunomagnetically isolated CD8+ cells to inhibit in vitro colony formation by normal granulocyte/macrophage colony-forming units (CFU-GM) and we found that inhibition was more pronounced when CD8+ cells, added in the culture, were derived from neutropenic than from non-neutropenic patients. The degree of colony inhibition correlated with the number of circulating neutrophils and the numbers of CD8+ and CD8+/HLA-DR+ cells in the patients studied. Since tumour necrosis factor-alpha (TNF-alpha) has been reported to be involved in myelosuppression, we also investigated the capacity of isolated CD8+ cells to release this cytokine into the culture supernatant fluids, and we found that comparable amounts of TNF-alpha were produced after stimulation in both neutropenic and non-neutropenic patients. Elevated serum TNF-alpha concentrations were noted only in a number of neutropenic and non-neutropenic patients. All these data taken together provide strong evidence that a T-cell subpopulation of activated CD8+/HLA-DR+ cells may be involved in the pathogenesis of neutropenia, at least in a subset of B-CLL patients, suppressing myelopoiesis by a TNF-alpha-unrelated mechanism. Efforts to isolate this cell subpopulation by flow cytometry for further analysis and a better understanding of its effect on myelopoiesis in patients with B-CLL are in progress in our laboratory.

Adult↗