Monte Carlo X-ray transport simulation of small-angle X-ray scattering instruments using measured sample cross sections

2016 ◽  
Vol 49 (1) ◽  
pp. 188-194 ◽  
Author(s):  
Mina Choi ◽  
Bahaa Ghammraoui ◽  
Andreu Badal ◽  
Aldo Badano

Small-angle X-ray scattering (SAXS) has recently been proposed as a novel noninvasivein vivomolecular imaging technique to characterize molecular interactions deep within the body using high-contrast probes. This article describes a detailed Monte Carlo X-ray transport simulation technique that utilizes user-provided cross sections to describe X-ray interaction in virtual samples and explore SAXS instrument design choices. The accuracy of the simulation code is validated with sample material cross sections derived from analytical models and empirical measurements of a homogeneous spherical gold nanoparticle (GNP) monomer, a dimer and heterogeneous mixtures of the two in aqueous solution. Analytical and measured scattering profiles from these samples were converted to cross sections using an absolute water standard. Our Monte Carlo estimates of the fraction of dimers from analytically derived and empirically derived cross sections are strongly correlated, with less than 1.5 and 16% error, respectively, to the expected concentration of monomer and dimer species. In addition, a variety of monoenergetic X-ray beams were simulated to investigate coherent scatteringversusradiation dose for a range of sample sizes. For GNP spheres in aqueous solution, the energy range that produces the most coherent scattering at the detector per deposited energy was between 31 and 49 keV for a sample thickness of 1 mm to 10 cm. The method described here for the detailed simulation of SAXS using measured and modeled cross sections will enable instrumentation optimization forin vivomolecular imaging applications.

1985 ◽  
Vol 40 (5-6) ◽  
pp. 364-372 ◽  
Author(s):  
P. Zipper ◽  
R. Wilfing ◽  
M. Kriechbaum ◽  
H. Durchschlag

Abstract The sulfhydryl enzyme malate synthase from baker’s yeast was X-irradiated with 6 kGy in air-saturated aqueous solution (enzyme concentration: ≃ 10 mg/ml; volume: 120 μl), in the absence or presence of the specific scavengers formate, superoxide dismutase, and catalase. After X-irradiation, a small aliquot of the irradiated solutions was tested for enzymic activity while the main portion was investigated by means of small-angle X-ray scattering. Additionally, an unir­radiated sample without additives was investigated as a reference. Experiments yielded the fol­lowing results: 1. X-irradiation in the absence of the mentioned scavengers caused considerable aggregation, fragmentation, and inactivation of the enzyme. The dose Dt37 for total (= repairable + non­-repayable) inactivation resulted as 4.4 kGy. The mean radius of gyration was found to be about 13 nm. The mean degree of aggregation was obtained as 5.7, without correction for fragmenta­tion. An estimation based on the thickness factor revealed that about 19% of material might be strongly fragmented. When this amount of fragments was accordingly taken into account, a value of 7.1 was obtained as an upper limit for the mean degree of aggregation. The observed retention of the thickness factor and the finding of two different cross-section factors are in full accord with the two-dimensional aggregation model established previously (Zipper and Durchschlag, Radiat. Environ. Biophys. 18, 99 - 121 (1980)). 2. The presence of catalytic amounts of superoxide dismutase and/or catalase, in the absence of formate, during X-irradiation reduced both aggregation and inactivation significantly. 3. The presence of formate (10 or 100 mᴍ) during X-irradiation led to a strong decrease of aggregation and inactivation. This effect was more pronounced with the higher formate concen­tration or when superoxide dismutase and/or catalase were simultaneously present during X-irradiation. The presence of formate also reduced the amount of fragments significantly. 4. The results clearly show that the aggregation and inactivation of malate synthase upon X-irradiation in aqueous solution are mainly caused by OH·; to a minor extent O·̄2 and H2O2 are additionally involved in the damaging processes.


2010 ◽  
Vol 58 (9) ◽  
pp. 5286-5291 ◽  
Author(s):  
Melissa M. Basil-Jones ◽  
Richard L. Edmonds ◽  
Timothy F. Allsop ◽  
Sue M. Cooper ◽  
Geoff Holmes ◽  
...  

2019 ◽  
Vol 92 (4) ◽  
pp. 152-157
Author(s):  
Tomotaka NAKATANI ◽  
Shinji KOHARA ◽  
Taiki HOSHINO ◽  
So FUJINAMI ◽  
Masaki TAKATA

2005 ◽  
Vol 109 (15) ◽  
pp. 7073-7083 ◽  
Author(s):  
Jörgen Jansson ◽  
Karin Schillén ◽  
Markus Nilsson ◽  
Olle Söderman ◽  
Gerhard Fritz ◽  
...  

1996 ◽  
Vol 248 (1) ◽  
pp. 121-127 ◽  
Author(s):  
T. Laitalainen ◽  
R. Serimaa ◽  
S. Vahvaselkä ◽  
Anne Reunanen

2021 ◽  
Author(s):  
A. Czajka ◽  
G. Liao ◽  
O. O. Mykhaylyk ◽  
S. P. Armes

SAXS is used to study the formation of polymer/silica nanocomposite particles prepared by surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate in the presence of silica nanoparticles using a azo initiator at 60 °C.


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