Determination of neutron flux parameters (f, α, φth and φe) of the irradiation sites of Isfahan MNSR reactor using empirical and MCNPX2.6 simulation approaches.

Miniature Neutron Source reactors (MNSRs) are ideal for applications such as nuclear research, neutron activation analysis, etc., provided that their neutron flux parameters (φth, φe, f and α) are known. This paper present the results of the neutron flux parameters at inner and outer irradiation sites of Isfahan MNSR reactor determined through simulation with MCNPX2.6 code and experimentally using bare and cadmium-covered gold foils irradiation and bare triple (AuZr) monitor methods. In empirical approach, the obtained φth, φe, f [fbare] and α-values were 5.02 × 1011 ncm-2s-1 (±4.5%), 3.13 × 1010 ncm-2s-1 (±2.3%), 16.0 (±6.7%) [17.3 (±9.9%)] and -0.121 (±0.2%), for inner site; and 2.93 × 1011 ncm-2s-1 (±2.3%), 6.48 × 109 ncm-2s-1 (±3.1%), 45.2 (±5.4%) [42.5 (±7.1%)] and -0.011 (±1.8%), respectively, for outer site. In simulation approach, while, they were found to be 4.76 × 1011 ncm-2s-1 (±0.9%), 2.00 × 1010 ncm-2s-1 (±2.2%), 23.8 (±3.1%) and -0.078 (±0.13%), for the inner site; and 2.67 × 1011 ncm-2s-1 (±1.1%), 3.79 × 109 ncm-2s-1 (±5.4%), 70.4 (±6.5%) and -0.017 (±0.4%) for the outer site, respectively. Comparison of empirical and simulation results clearly revealed that: the inner site's φth and f values correspond with those measured during the first startup of the reactor; the values of φth are more reliable than φe,-values, as are the inner site's f and α results in comparison with outer site's values; the inner site's φth and φe are ∼1.7 and 5 times, respectively, larger than those of outer site; and the inner site 's α and f-values are more than 4.8 and 2.4 times larger and less than the outer site's values, respectively.

Feasibility of 153Sm production using MNSR research reactor through a multi-stage approach.

The main objective of this study was to explore the feasibility of producing 153Sm radioisotope in miniature neutron source reactors (MNSRs) in Isfahan-Iran. As the first step of this study, the MNSR's geometry was created by using the MCNP6.2 simulation code and afterwards a validity check was performed by comparing the results with the experimental data. Then, by applying values obtained through simulation, the production process was followed up to 20 irradiation cycles using different irradiation and cooling periods (irradiation setups). The results showed that the proposed simulation technique has an acceptable agreement with the experiments (with a difference of nearly 6%). In spite of limitations, such as irradiation time and flux in such reactors, our results showed that by choosing the correct irradiation setup, it is possible to produces 153Sm up to 852.26 mCi g-1 in 20 successive irradiation cycles. However, after the 10th cycle, the production reached 90% of the maximum point. Nevertheless, the continuance of the irradiation process with a new target (by 10 plus 10 discrete irradiation) can double the total activity in comparison with 20 successive irradiation cycles, without any increase in the fuel consumption of the reactor. These findings increase the prospect of a large-scale production of the life-saving 153Sm radioisotope in MNSR reactors.

The feasibility study of 177Lu production in Miniature Neutron Source Reactors using a multi-stage approach in Isfahan, Iran.

Miniature neutron source reactors (MNSRs) are among the safest and economic research reactors with potentials to be used for neutron studies. This manuscript explores the feasibility of 177Lu production in Isfahan MNSR reactor using direct production route. In this study, to assess the specific activity of the produced radioisotope, a simulation was carried out through the MCNPX2.6 code. The simulation was validated by irradiating a lutetium disc-like (99.98 chemical purity) at the thermal neutron flux of 5 × 1011 ncm2s-1 and an irradiation time of 4min. After the spectrometry of the irradiated sample, the experimental results of 177Lu production were compared with the simulation results. In addition, factor from the simulation was extracted by replacing it in the related equations in order to calculate specific activity through a multi-stage approach, and by using different irradiation techniques. The results showed that the simulation technique designed in this study is in agreement with the experimental approach (with a difference of approximately 3%). It was also found that the maximum 177Lu production at the maximum flux and irradiation time allows access to 723.5mCi/g after 27 cycles. Furthermore, the comparison of irradiation techniques showed that increasing the irradiation time is more effective in 177Lu production efficiency than increasing the number of irradiation cycles. In a way that increasing the irradiation time would postpone the saturation of the productions. On the other hand, it was shown that the choice of an appropriate irradiation technique for 177Lu production can be economically important in term of the effective fuel consumption in the reactor.

Management of left ventricular distension during peripheral extracorporeal membrane oxygenation for cardiogenic shock.

The application of peripheral veno-arterial extracorporeal membrane oxygenation in the management of inotrope-refractory cardiogenic shock has proven controversial because of concerns about sub-optimal drainage of the left heart, resulting in left ventricular distension and pulmonary oedema. In this article, we will discuss the pathophysiological basis and clinical implications of left ventricular distension following institution of peripheral extracorporeal life support. We will also review the clinical strategies used to circumvent left ventricular distension and pulmonary oedema in these patients.

Uric acid: a risk factor for coronary atherosclerosis?

BACKGROUND AND OBJECTIVES: It is uncertain whether high serum uric acid levels are a true independent risk factor for coronary atherosclerosis or whether the association is due to other confounding variables. We therefore studied the relationship between elevated serum uric acid levels and coronary atherosclerosis after adjustment was made for confounding factors such as age, gender, body mass index, smoking, lipid profile, blood pressure and blood glucose levels. METHODS: A cross-sectional study was conducted on 240 patients referred for coronary angiography to heart centres in the Shahid-Chamran and Sina hospitals, Isfahan, Iran. Blood chemistry data as well as traditional risk factors and uric acid levels were measured at enrollment. We used vessel, stenosis and extent scores to indicate the degree of coronary artery involvement. RESULTS: This study was conducted on 240 patients with a mean age of 56 +/- 10.9 years (66% male; 37% female) who underwent coronary angiography. Student's t-test analyses revealed that there were significant differences in the mean uric acid levels between male and female patients (p = 0.001). We found no statistically significant correlation between serum uric acid levels and coronary atherosclerosis (p > 0.05). In addition, multivariate logistic regression analyses, using coronary atherosclerosis as dependent variable and traditional risk factors and uric acid levels as independent variables, did not show any significant difference. CONCLUSION: These findings indicated that uric acid is not associated with coronary atherosclerosis. Any correlation reported in other studies was probably due to the relationship between high serum uric acid levels and other cardiovascular risk factors.

Smooth muscle cell proliferation but not neointimal formation is dependent on alloantibody in a murine model of intimal hyperplasia.

Transplant coronary artery disease is the pre-eminent cause of late cardiac allograft failure. It is primarily characterized by a concentric intimal hyperplasia, which we designate transplant intimal hyperplasia (TIH). Although the pathogenesis of TIH is predominately immune driven, the specific role of alloantibodies in the disease process remains undefined. In this study we investigated the contribution of alloantibodies to the development of TIH in a murine model. Orthotopic, carotid artery transplantation was performed between B10A(2R) (H-2(h2)) donor mice and B-cell deficient muMT(-/-) knockout or wild-type C57BL/6 (H-2(b)) recipients in the absence of immunosuppression. Grafts were harvested at 35 days and subjected to planimetry and immunohistochemistry. Alloantibodies were detectable in wild-type recipients within 7 days of transplantation and recipients developed marked TIH at 35 days. Allografts harvested from B-cell deficient recipient mice also developed TIH, which was comparable in severity with wild-type recipients. However, whereas allografts from wild-type recipients showed marked intimal smooth muscle cell (SMC) proliferation, the neointima in B-cell deficient recipients lacked SMCs. Post-transplantation administration of anti-donor serum to muMT(-/-) recipients restored neointimal SMC population but did not influence the severity of TIH. Significant neointimal formation occurs in the absence of alloantibodies but lacks a SMC component. Therefore, SMC migration and proliferation is antibody dependent.

Role of alloantibodies in the pathogenesis of graft arteriosclerosis in cardiac transplantation.

Graft arteriosclerosis (GA) remains the leading obstacle to long-term survival of cardiac allografts. The pathogenesis of this chronic disease, though perceived to be multifactorial, is most likely immune-driven. Based on clinical and experimental observations, the humoral arm of the immune system has long been suspected to play a pivotal role in the disease process. In this article, we shall review the evidence generated from key clinical and experimental studies on the role of alloantibodies in GA. We will argue that although the strong correlation between the presence of anti-donor antibodies in clinical and experimental GA is highly suggestive of a pathogenic role for alloantibodies, a direct causal link between GA and the humoral arm of the alloresponse cannot yet be established based on the currently available evidence, and may in fact be one of a number of pathogenic processes that potentiate this vasculopathy. Finally, in this article, we shall discuss some of the potential mechanisms by which alloantibodies may exert their pathogenic effect in GA.

Association of IgM with IgG ANCA in patients presenting with pulmonary hemorrhage.

ANCA are markers for systemic vasculitis such as Wegener's granulomatosis (WG) and microscopic polyarteritis (MPA) and are usually of the IgG isotype. However, IgM ANCA may rarely occur in isolation, and in these circumstances, we have found that they are associated clinically with a syndrome of pulmonary hemorrhage and systemic vasculitis. How frequently IgM ANCA may occur in conjunction with IgG has not previously been investigated. We report here a study of 24 consecutive patients with IgG ANCA-positive systemic vasculitis (14 WG, 10 MPA) in whom we determined whether IgM ANCA occurred in association with IgG ANCA, and if so, whether this had clinical importance. Eight patients were found to have IgM ANCA as well as IgG ANCA, and of these, seven presented with severe pulmonary hemorrhage. None of the IgM ANCA-negative patients presented with pulmonary hemorrhage. Although the occurrence of pulmonary hemorrhage in ANCA positive vasculitis was closely correlated with the presence of IgM ANCA, the antigen specificity of these IgM autoantibodies was variable, since both myeloperoxidase (4 patients), PR3 (3 patients), and an unknown ANCA antigen (1 patient) were found to be targets. We conclude that knowledge of ANCA isotype may have important clinical and therapeutic implications for the management of patients with systemic vasculitis.