Research Article Evaluation of the X-Ray Absorption by Gold Nanoparticles Solutions

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1 ISRN Nanotechnology Volume 3, Article ID , 5 pages Research Article Evaluation of the X-Ray Absorption by Gold Nanoparticles Solutions R. Künzel, E. Okuno, R. S. Levenhagen, 2 and N. K. Umisedo Universidade de São Paulo, Instituto de Física, Departamento de Física Nuclear, Cidade Universitária, São Paulo, SP, Brazil 2 Universidade Federal de São Paulo, Departamento de Ciências Exatas e da Terra, Rua Prof. Artur Riedel 275, Diadema, SP, Brazil Correspondence should be addressed to R. Künzel; roselikunzel@gmail.com Received 4 January 3; Accepted 4 February 3 Academic Editors: D. R. Chen, C.-L. Hsu, and D. K. Sarker Copyright 3 R. Künzel et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The increase in the X-ray absorption due to gold nanoparticles was investigated by using aqueous solutions containing gold (Au) nanoparticles. A sample with 5 nm in size nanoparticles and.5 mg/ml gold concentration and a distilled water sample were used. Transmitted X-ray beams through the samples were registered with a CdTe detector and with an ionization chamber. Results show an enhancement in the X-ray absorption in the range % 6% for beams generated from kv to kv tube voltages, respectively. Results show that the use of gold nanoparticles, even at low concentrations, should result in a significant contrast enhancement for low-energy X-ray beams.. Introduction X-ray radiography procedures are one of the most useful tools adoptedintheearlydiagnosisofcancerinbothtimeandcost related to the process of image acquisition []. The efficacy of these techniques relies on the image quality which depends on the X-ray absorption by the tissues that are being exposed []. In some of these radiological procedures, such as X-ray computed tomography, a contrast agent is injected directly into the blood stream followed by immediate imaging. The contrast agent leads to increased X-ray attenuation by the targeted tissue resulting in an enhanced image contrast [, 2]. Currently, contrast agents used in clinical routine procedures are mainly based on iodine-containing molecules. However, such iodine-based compounds present a shortimaging time which results from its rapid renal clearance [3, 4]. In this way, biocompatible nanostructured materials are being investigated in order to improve the image contrast and to enhance the image acquisition time [3 7]. Gold nanoparticles (GNPs) have been the subject of numerous theoretical and experimental studies related to its applications as contrast agents in the X-ray imaging field [3, 5, 8]. The use of these particles in computed tomography has attractive properties such as high atomic number (Z =79)and density (ρ =9.3g/cm 3 ), high X-ray attenuation coefficients, and enhanced time of blood circulation providing imaging contrast for longer time periods [5, 9]. As the radiographic image contrast depends on the radiation absorption by the target materials, the effect of gold nanoparticles in the X-ray image could be evaluated by means of X-ray spectroscopy. In this work we report the spectral changes on X-ray beams transmitted through a gold nanoparticle aqueous solution registered with a X- ray spectrometer. We chose this detector due to its good performance in the diagnostic energy range [ 2]. Results presented here account for the effect of gold nanoparticles at a low concentration on the X-ray attenuation compared to distilled water for broad beam spectra. The effects on the airkerma and subject contrast by the gold nanoparticle solution relative to water are also evaluated. 2. Materials and Methods 2.. Nanoparticles Samples. In this work we used aqueous solutions of highly monodispersed gold nanoparticles with

2 2 ISRN Nanotechnology Pb collimator Sample Focal spot W collimator cm 5 m Detector Figure : Experimental setup used in the measurements of the transmitted spectra of X-ray through the materials. X-ray tube was a Philips MG nm diameter (Nanoprobes). The sample was composed of.5 mg/ml gold concentration (.5% wt) in distilled water. A pure sample of distilled water was also used for comparison. Both samples were placed into a plastic container with rectangular base shape and internal thickness of 2 cm X-Ray Spectroscopy. The knowledge of the X-ray spectra is an important tool for investigations of the dose delivered tothepatientandtheimagequality[]. In this work, the X-ray spectra were generated by a Philips equipment MG 45model,equippedwithatungstenanodetubewithaBe window with 2.2 mm thickness. The anode angle is of 22.A XR-T-CdTe detector (Amptek Inc., Bedford, MA, USA) with 9 mm 2 nominal active area and mm nominal thickness was used to detect the radiation beam. The detector has a μm Be window and is cooled by Peltier cells. Output pulses were processed by a Digital Pulse Processor (DPP) PX4. Transmitted spectra through the above-mentioned solutions have been recorded with the detector positioned in the center of the radiation field at 5 cm from the focal spot as illustrated in Figure. A lead collimator with aperture of 8 mm was positioned at the window of the X-ray tube and before the sample. An EXVC tungsten collimator housing and a collimator with μm aperture and 2 mm thickness was used in front of the detector. Alignment between the focal spot and CdTe detector was performed with a laser device. Rise Time Discriminator (RTD) was switched off in the DPP system. Pile-up was maintained less than 2% in all the acquisitions. The transmitted X-ray spectra were registered for beams generated in the voltage range between and kv. Energy calibration of the X-ray spectra was performed with the gamma and X-rays emitted by 24 Am, 33 Ba, and 52 Eu radioactive sources. The air kerma produced by the spectra transmitted through the samples was also measured with an ionization chamber. The experimental setup used in the measurements of the air kerma was the same as showed in Figure. In this case, the CdTe detector with its tungsten collimator was replaced by the ionization chamber. The ionization chamber used in this work was a Radcal 6cc (model 95) Spectrum Correction. The raw photon distribution measured with the CdTe detector were corrected in this work in order to obtain the true X-ray spectra. The raw X-ray spectra were corrected for the energy dependence of the detection peak efficiency and escape of fluorescent X-rays by means of the analysis of the X and gamma rays emitted from 24 Am, 33 Ba, and 52 Eu radioactive sources [3]. Photon mass attenuation coefficients were obtained from data provided by NIST [4]. ThecorrectedX-rayspectrawereusedtocalculate the air kerma and the mean energy for each X-ray spectra [5]. The relative air kerma was calculated as follows: RK = Kerma Au, () Kerma W where Kerma Au istheairkermaproducedbythebeams transmitted through the gold nanoparticle solution and Kerma W to those produced by the beams transmitted through the water sample. Total signal due to the beams transmitted through the samples was calculated by integrating the photon fluence spectra over all the energy range as follows: E max Φ= Φ (E) de. (2) E min The subject contrast (Cs) was evaluated according to the following relation: Cs = (Φ W Φ Au ), (3) Φ W where Φ W isthephotonfluence(photons/cm 2 )transmitted through the water sample and Φ Au is the photon fluence calculated from the spectra transmitted through the gold nanoparticle solution sample. The value of Cs is a number between. and. [2]. We attempt to constrain the firstorder behavior of the data performing a nonlinear least squares fitting of an exponential function of the type Cs = Ae Bx +Cwith a Levenberg-Marquardt algorithm [6]. Grayscale intensity images were generated by considering the photon fluence spectra transmitted through water and through the gold nanoparticle solution for kv and 25 kv tube voltage X-ray beams. The images were built up with the aidofacomputationalcodebasedonthegnuplotgraphing utility. 3. Results and Discussion Measured transmitted X-ray spectra through a sample of distilled water and a gold solution containing nanoparticles with 5 nm are illustrated in Figure 2. The X-ray beams transmitted through pure distilled water were normalized to the unity at the maximum of the

3 ISRN Nanotechnology kv 25 kv (a) (b).5 8 kv.5 kv Water.5% gold Water.5% gold (c) (d) Figure 2: Comparison of the experimental X-ray spectra transmitted through a solution of gold nanoparticles with.5% wt Au concentration and a pure water sample. The data were registered for gold nanoparticles with 5 nm in size and X-ray beams generated at, 25, 8, and kv tube voltages. spectra. As stated in Section 2., bothsampleshavemm thickness, and the gold concentration in the solution was.5 mg/ml (.5% wt). According to Figure 2, itispossible to observe that the X-ray absorption is clearly higher for the gold nanoparticles solution mainly for the kv and 25 kv X-ray beams. The air kerma values calculated from these beams transmitted through the pure water sample are about 7% higher than those calculated for the beams transmitted through the.5% gold nanoparticle solution for kv. For the 25 kv X-ray beams, this difference was 3%. In the case of beams measured at 8 and kv tube voltages, the difference in the X-ray absorption is about 7% and 6%, respectively. Figure 3 shows the air kerma values produced by the beams transmitted through the sample of 5 nm nanoparticles with.5% Au concentration and through the water sample. In this figure, the air kerma values are presented as a ratio of the values measured for the beams transmitted through the gold nanoparticle solution and those measured for the beams transmitted through the water sample. The values presented in this figure are due to measurements performed with an ionization chamber and calculated from the corrected X- ray beams. In both cases the beams were generated in the range from kv to kv tube voltages. A good agreement among the air kerma values measured with the ionization chamber and calculated from the corrected X-ray spectra is observed over all the energy range. Results based on the ionization chamber measurements show that for the kv beam the X-ray absorption is about % higher than for the beam transmitted through the gold nanoparticle solution when compared to that transmitted through the pure distilled water sample. For the 25 kv beam the absorption by the nanoparticle solution was about 3% higher than that relative to distilled water. In the case of the 3 and 35 kv X-ray beams, this difference was % and 9%, respectively. For beams generated with tube voltages from 5 kv to kv, this difference varies from % to 4%. Figure 4 brings the grayscale images produced with the beams transmitted through the distilled water sample and the gold nanoparticles solution presented in Figure 3, for

4 4 ISRN Nanotechnology Normalized intensity (a.u.) Relative air kerma Mean energy (kev) (a) Ionization chamber Spectra calculated 4. Conclusion X-ray absorptions by samples of gold nanoparticles solutions and distilled water were investigated in this work. A solution with.5 mg/ml gold nanoparticle concentration and a water sample were used in order to evaluate the X-ray absorption and its effect on the air kerma values and subject contrast. We conclude, based on the experimental results, that the Xray absorption for a solution with.5% gold nanoparticle concentration increases from % to 6% for beams generated between kv and kv, respectively. Also, a significative subject contrast enhancement was observed for low-energy beams. Effectively, targeted tissues with these electron-dense nanoparticles, even at a very low concentration, are able to (b) Figure 4: Grayscaled images generated for the kv and 25 kv Xray beams. 25 Subject contrast (%) kv and 25 kv tube voltages. The image contrast in this figure is presented as a function of the X-ray beam energy. The upper and the bottom parts of Figure 4 concern in the beam transmitted through the water sample while the middle part refers to the beams transmitted through the gold nanoparticles solution. The ticks on the intensity axis in Figure 4 indicate the boundary between the gray intensity produced by the beams transmitted through water and those transmitted through the gold nanoparticles solution. These figures show that the maximum contrast occurs in the ranges of 6 to 8 kev for the kv beams and 8 to 22 kev for the 25 kv X-ray beams. Figure 5 brings the subject contrast calculated from the photon fluence of the beams transmitted through the solution containing nanoparticles and the water sample. Results show that the subject contrast enhancement due to the gold nanoparticles varies from about 7% to 2% for beams with a mean energy ranging from 7 kev to 63 kev. Normalized intensity (a.u.) Figure 3: Comparison of the relative air kerma values measured with an ionization chamber and calculated from the corrected x-ray spectra. The data were registered for beams generated in the voltage range from to kv Mean energy (kev) Calculated Data fitting Figure 5: Subject contrast calculated for beams transmitted through the water sample and through the gold nanoparticle solution for beams generated in the kv to kv tube voltage range.

5 ISRN Nanotechnology 5 display significant enhanced X-ray absorption resulting in a higher image contrast or absorbed dose. Acknowledgments This paper has been partially supported by FAPESP (Fundação de Amparo àpesquisadoestadodesão Paulo) through Process /686-4 and CNPq. scattered x-ray spectra in mammography for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, Physics in Medicine and Biology,vol.5,no.8,pp.77 9,6. [6] D. Marquardt, An Algorithm for Least-Squares estimation of nolinear parameters, SIAM Journal on Applied Mathematics, vol., no. 2, pp , 963. References [] A. B. Wolbarst, Physics of Radiology, Medical Physics Publishing, Madison, Wis, USA, 5. [2] J. T. Bushberg, J. A. Seibert, E. M. Leidholdt, and J. M. Boone, The Essential Physics of Medical Imaging, Lippincott Williams & Wilkins, 2nd edition, 2. [3] J. F. Hainfeld, D. N. Slatkin, T. M. Focella, and H. M. Smilowitz, Gold nanoparticles: a new X-ray contrast agent, British Journal of Radiology,vol.79,no.939,pp ,6. [4] D.Kim,S.Park,H.L.Jae,Y.J.Yong,andS.Jon, Antibiofouling polymer-coated gold nanoparticles as a contrast agent for in vivo X-ray computed tomography imaging, the American Chemical Society,vol.29,no.24,pp ,7. [5]D.P.Cormode,T.Skajaa,Z.A.Fayad,andW.J.M.Mulder, Nanotechnology in medical imaging: probe design and applications, Arteriosclerosis, Thrombosis, and Vascular Biology,vol. 29, no. 7, pp. 992, 9. [6] A.L.Dias,R.Künzel, R. S. Levenhagen, and E. Okuno, Application of computed tomography images in the evaluation of magnetic nanoparticles biodistribution, Magnetism and Magnetic Materials,vol.322,no.6,pp ,. [7] J.L.Ducote,Y.Alivov,andS.Molloi, Imagingofnanoparticles with dual-energy computed tomography, Physics in Medicine and Biology,vol.56,no.7,pp.3 44,. [8] C. Xu, G. A. Tung, and S. Shouheng, Size and concentration effect of gold nanoparticles on X-ray attenuation as measured on computed tomography, Chemistry of Materials, vol.,no. 3, pp , 8. [9] R. Guo, H. Wang, C. Peng et al., X-ray attenuation property of dendrimer-entrapped gold nanoparticles, Physical Chemistry C,vol.4,no.,pp.5 56,. [] L.Abbene,G.Gerardi,S.DelSordo,andG.Raso, Performance of a digital CdTe X-ray spectrometer in low and high counting rate environment, Nuclear Instruments and Methods in Physics Research A,vol.62,no. 3,pp ,. [] S. Miyajima, Thin CdTe detector in diagnostic x-ray spectroscopy, Medical Physics, vol. 3, no. 5, pp , 3. [2] E. Di Castro, R. Pani, R. Pellegrini, and C. Bacci, The use of cadmium telluride detectors for the qualitative analysis of diagnostic x-ray spectra, Physics in Medicine and Biology, vol. 29, no. 9, pp. 7 3, 984. [3] K. Aoki and M. Koyama, Measurement of diagnostic x-ray spectra using a silicon photodiode, Medical Physics,vol.6,no. 4, pp , 989. [4] M. J. Berger, J. H. Hubbell, S. Seltzer et al., XCOM: Photon Cross Section Database (Version 3.), NationalInstitute of Standards and Technology, Gaithersburg, Md, USA,, [5] R. Künzel,S.B.Herdade,P.R.Costa,R.A.Terini,andR.S. Levenhagen, Ambient dose equivalent and effective dose from

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