جستجوی مقالات مرتبط با کلیدواژه « تصویربرداری » در نشریات گروه « فیزیک »

Albumin particles are used in nuclear medicine as carriers of diagnostic and therapeutic radionuclides. For this purpose, these particles were prepared using temperature. After size determination, the particles were labeled with gamma irradiated radionuclide 99mTc in the presence of stannous chloride as a reducing agent. Radiochemical purity was determined by chromatography methods. For labeled particles, stability in normal saline and biodistribution in normal and glioma tumorized rat were determined. The size of particles was determined in the range below 50 nm. Radiochemical purity of more than 98% was obtained. Evaluation of labeled particles stability showed a radiochemical purity of more than 90% during 6 hr in saline and human serum solutions. The results of biodistribution studies determined liver and tumor uptake followed by high kidneys washout. Gamma imaging scintigraphy in rat, showed tumor and kidneys. The results confirmed the ability of labeled particles as a tumor diagnostic radiopharmaceutical.

X-ray applications in imaging and beyond require efficient and optimal detectors. Energy separation, time loss, and manufacturing cost are among the features that led us to design a semiconductor detector. A low-gain avalanche diode (LGAD) with internal amplification allows, in a sufficient field, the internal propagation process by accelerating the carriers, the energy required for ionization, and the generation of secondary carriers to produce a better gain (higher signal-to-noise ratio) and also provide more time efficiency (in the range of nanoseconds). In this article, we simulate the LGAD silicon detector with Silvaco software by applying reverse bias voltage and radiation in the range of visible light to X-ray. Newton and Gummel's methods were used. In Newton's method, one of the mechanisms of radiation interaction with matter is considered variable and the rest are fixed. However, in Gummel's method, all mechanisms are solved simultaneously. In the X-ray wavelength range, the electron current in this detector is 10-4 amperes, and this current decreases with increasing energy. The dark current is 10-6 amperes. By applying visible light with 0.45-micrometer wavelength and 1 V/cm2 intensity, the detector current was obtained about 6.5×10-4 amperes. For 1.0×10-5 x-ray wavelength and 108 V/cm2 intensity, detector current was obtained about 3.5×10-4 amperes. Considering the quick response time of this detector and the current in the range of microamps, this detector is a suitable option for X-ray detection. Also, this detector shows superior performance in the visible light range.

Dual-energy X-ray radiography is an important inspection technology in imaging large cargos for finding illegal materials such as explosives, narcotics, weapons, etc. A useful aspect of dual-energy X-ray radiography is the possibility of discriminating and identifying materials with different atomic numbers which can be obtained by imaging large cargos at two different X-ray energies (normally above 3 MeV). In the present work, first a dual-energy X-ray radiography system including X-ray sources, collimator, and detector array was simulated using MCNPX code. Then, the obtained data from this radiography system for four step wedges of graphite, aluminum, steel, and lead materials were gathered and material discrimination curves were obtained using four algorithms including log-log, R-T, r-θ, and α2-α1. The results show that among the proposed algorithms for material discrimination, R-T, r-θ, and α2-α1 algorithms have better performance and due to the less overlap of material discrimination curves for low sample thicknesses, R-T algorithm can be a better choice for obtaining material discrimination curves in dual-energy radiography systems.

The aim of this study was to label quercetin as a natural flavonoid compound with technetium-99m and to study its biological distribution in different tissues of C57 mice bearing melanoma B16F10 cells for tumor diagnosis. Quercetin labeling was performed with technetium-99m at 1.5 mg quercetin and 40 μg SnCL2 at room temperature and pH about 5.  Labeling yield was evaluated using TLC in acetone and water / acetonitrile as solvents. Also, in animal study, the tissue activity of various organs including heart, lung, stomach, intestine, liver, kidney, blood, spleen, muscle, and tumor were measured through gamma counter. Radiochemical purity above 95% and radiochemical stability of 90% at one hour were observed. The results of biological distribution of the labeled compound showed the highest radioactivity uptake in liver, kidney, intestine and tumor (2.2 ± 0.17 at 2 h post injection) tissues. Quercetin labeled through direct method with high radiochemical purity can be used as a candidate for diagnostic radiotracer.

During radiotherapy by any radiation, it is always essential to stop absorbing the excess dose by a tissue. To better treat cancerous tissues and to make more precise irradiation for a cancerous tumor, there needs the accurate irradiation time to be estimated. First, the constituent materials of any of the existing organs in abdominal tissue are extracted and defined in the MCNPX code. Then, every organ in the abdominal tissue is voxelized by MATLAB software. Each of the voxels is defined based on Hounsfield unit of pixels in DICOM images. Then, the voxels are assigned to the related tissue which is comprised of its constituent materials, and they are filled up with them. Then, the liver tissue is segmented among the abdomen region from other tissues. Then, the geometry of the segmented liver tissue is generated as input data for MCNPX code, and the absorbed dose is computed. After obtaining the values of absorbed doses in liver tissue per each of incident fast neutron energies, the required irradiation time is obtained in second by making an appropriate proportion of absorbed dose and activity. This precise required irradiation time is obtained by an advanced software application (designed in this research using Delphi 7 programming language) through establishing a relationship between the absorbed dose and activity based upon the energy of clinical fast neutron source. The required irradiation time is calculated to reach the desired dose for each patient during fast neutron radiation therapy for similar liver tissues accordingly.

Qualitative analysis of petroleum reservoir rocks is still one of the most important topics of core laboratories and directly affects hydrocarbon-in-place، fluid flow، and prediction of field performance. Magnetic Resonance Imaging (MRI) as a non-invasive، millimeter resolution technique which only images fluids in porous media fits this purpose perfectly. Magnetic resonance is a radio frequency spectrometry، based on excitation of nucleus energy levels which can exploit a wide range of information on the saturation fluid، geometry of pores، and diffusion. Using magnetic gradients and signal encoding، this can be used as a tomography technique. Determining porosity regardless of rock lithology، reservoir rock quality، bound and free water (which presents production potential) and potential permeable tight beds are applications of this method، from among many others. Recent advances in imaging techniques along with new software and processing methods has resulted in exploiting the images containing valuable physical information. The main aims of this study are qualitative investigation of core sample، determining the number and distribution of vugs، presenting three-dimensional models and comparing this method with other conventional methods. We acquired images of cores adequate for revealing characteristics of matrix، vugs، and other different porosity types in carbonate rocks as well as their interaction. The images in the form of matrices of MR signal were analyzed using both image analysis and physics of MR signal. Studied samples are a selection from one of southern Iranian carbonate reservoirs، cleaned using Soxhlet extraction، dried in oven and saturated with synthetic reservoir brine. Rock type، pore-filling fluid، the MRI imaging hardware and software، pulse sequence، and image processing affect such study results. So، impacts of several items were considered and best available pulse sequence parameters were set. Presence of ferromagnetic minerals adversely affects image quality، so samples bearing these minerals are very difficult to image in high fields and have to be imaged with special pulse sequences and systems. Samples without ferromagnetic minerals، as in most carbonate rocks، can be imaged in high fields، so because of the superior quality of high field imaging، this method is used in our carbonate samples. Validity of MRI images was verified using histogram analysis of water، rock and air segments of the images subsequent to acquisition. Reference fluids، brine (the pore-filling fluid) and air، helped us in matching and comparing histograms and check the validity of signal from porous sample. In image analysis we utilized histogram، field of view، and segmentation techniques. Results of this analysis after using physical models of MRI signal in porous media led to numerical and visual models of rock samples. In addition to visual models of porosity، we prepared visual models of mean-T2 of invaluable to quantitative and qualitative study of porosity، ultimately resulting in determining fraction of vuggy، moldic، and inter-particle porosity. This model was constructed by superposition of image slices. Inter-particle porosity cannot be determined from sub-millimeter MRI image analysis، so it is calculated from the physics of MR signal. We determined the accuracy of the method in comparison with other conventional experiments such as helium porosimetry and petrographic image analysis which revealed reasonable accuracy of the method in determining porosity types and visualization. Effect of several items in the accuracy of this method is proposed. First، gravimetry porosity is always lower compared to the helium porosimetry، and porosity calculated from MRI imaging only is affected by water saturation of the sample، so MRI porosity should always be compared with gravimetry porosity. Second، MRI images are not only sensitive to water in porous samples، but also sensitive to pore size of the sample. Water in very fine pores is not shown in images unless echo time is set to 1-3ms، not possible in our study because of hardware limits. Third، magnetic field inhomogeneity can account for up to nine percent of signal intensity. This study obtained a new perspective in using MRI imaging for qualitative study of porosity and determining share of porosity types.