Introduction: Myocardial perfusion SPECT by 99mTc-Sestamibi and 99mTc-Tetrofosmin radiopharmaceuticals usually presents a false significant increase in the radiotracer uptake in the inferior myocardium due to the uptake in organs such as liver, bowel, stomach and biliary system. The present study evaluated a suitable SLIT angle for differentiating extra-cardiac activities by SLIT SLAT collimation.Methods: The Siemens E.CAM gamma camera equipped with a Low Energy High Resolution (LEHR) COLLIMATOR was simulated with the Simulating Medical Imaging Nuclear Detectors (SIMIND) Monte Carlo program. Following the verification of the simulation, a SLIT SLAT COLLIMATOR was simulated for SPECT imaging of a NURBS-based Cardiac Torso (NCAT) phantom with different SLIT angels ranged from 0 to 30 degrees. The reconstructed images were qualitatively assessed with blinded observer method by three nuclear medicine specialists.Results: The improved differentiation of the bowel activity from the cardiac was obtained by a SLIT-SLAT COLLIMATOR with the SLIT angle of 7 degree. While for gastric activity differentiation an angle of 15 degree for the SLIT was useful.Conclusion: The results showed that SLIT SLAT collimation with 7 and 15 SLIT angle provide a suitable differentiation of the bowel and gastric activities from the cardia, respectively.

Introduction: The COLLIMATOR design and optimization are essential in small animal molecular imaging for preclinical studies. In this study, a mathematical model was derived and used to optimize the SLIT COLLIMATOR for small animal imaging applications.  Materials and Methods: The geometric efficiency was formulated as a source-to-detector distance for a certain amount of the COLLIMATOR resolution (). The first-order derivative of the derived formula gives the optimized parameters. The detector performance was modeled in terms of intrinsic resolution . Furthermore, the edge penetration effect was considered using the validated model. Results: Optimum source-to-detector distance  was found as . For an ideal detector, optimal, geometric efficiency  and SLIT aperture width  were found as ,  and , respectively. Where   and  are the source-to-COLLIMATOR distance and detector length, respectively. For the fixed resolution of 1.0 mm, the sensitivity for different source-to-COLLIMATOR distances of 50.0, 100.0, and 150.0 mm was calculated as, , and , respectively. In addition, for a sub-millimeter resolution of 0.5 mm at 15.0, 30.0, and 50.0 mm, the geometric efficiency was calculated as, , , and . For a typical source-to-COLLIMATOR distance (15.0 mm), the optimal geometric efficiencies are, , , , and   for the resolutions of 0.25, 0.50, 1.0, 1.5, and 2.0 mm, respectively. Conclusion: Based on the analytic model predictions, the performance characteristics of the SLIT COLLIMATOR in terms of geometric efficiency and resolution were extracted. The importance of the proposed model lies both in its speed and ease of application.

Purpose: Gamma cameras are one of the most promising technologies for in-vivo range monitoring in proton therapy. Monte Carlo (MC) simulation is a common calculation-based technique to design and optimize gamma cameras. However, it is prohibitively time-consuming. Analytical modeling speeds up the process of finding the optimal design. Materials and Methods: We proposed an analytical method using the efficiency-resolution trade-off for optimizing a knife-edge COLLIMATOR based on the range retrieval precision of protons. Monte Carlo simulation was used for validation of obtained COLLIMATOR efficiencies. Results: The model predicts that for the optimal range retrieval precision, the ratio of the source-to-detector distance (𝑟,𝑑,) to the source-to-COLLIMATOR distance (𝑟,𝑐,) should be ranging from 1. 7 𝑡, 𝑜,1. 9. For a special case, it was found that assuming an ideal detector (𝑅,𝑖,= 0), the falloff retrieval precision is optimal at 𝑟,𝑑,= 2𝑟,𝑐,independent of the COLLIMATOR resolution. Moreover, using the optimized camera, the difference between the MC calculated range and the absolute range was 0. 5 cm (the relative error is about 3%). Conclusion: It was found that the COLLIMATOR parameters are in good agreement in comparison with that of the MC results reported in the literature. The analytical method studied in this work can be used to design and optimize imaging systems based on KE COLLIMATORs in combination with new detectors in a fast and reliable way.

In Single Photon Emission Computed Tomography (SPECT), COLLIMATOR selection, optimization, and also geometric calibration have a major impact on the acquired image quality and also on an accurate detectability and diagnosis. The COLLIMATOR optimization phenomena consider some parameters such as field of view, resolution, sensitivity, resolution at depth, septal thickness and penetration for a specific application task. While the parallel hole COLLIMATOR is usually used in SPECT and planar imaging but due to the limited solid angle covered by the COLLIMATOR, the system sensitivity and resolution were highly reduced. Meanwhile, other types of COLLIMATORs such as pin-hole, multi-pin-hole, slant and SLIT-SLAT COLLIMATORs were introduced with a trade-off between sensitivity and resolution. This article reviews improvements on COLLIMATORs also by considering the geometry and geometric calibration methods for improving the image quality in single photon emission computed tomography.

Controlling systems are modern systems of designing structures that have become widely used in the building industry today. One of these control systems is the use of a damper. These systems can be generally categorized into active, inactive, semi-active, and hybrid systems. Among the mentioned systems, the inactive dampers do not require the use of an external power source. Contrary to conventional methods of designing earthquake resistant structures in which major earthquake energy is absorbed by the yielding of specific points of the structure (typically, the ends of the beams and columns in the moment frame systems), in inactive control systems, the major part of this energy is absorbed by certain devices which are called seismic dampers. One of these types of dampers, which can be replaced after damage from large earthquakes, is the Steel SLIT Damper (SSD). Steel SLIT damper is a kind of inactive energy depreciator with behavior dependent on displacement. Steel SLIT dampers are mainly made of metal or special alloys that are easily yielded and have an acceptable performance to dissipate energy under severe seismic loads. In these dampers, the blades between the SLITs dissipate seismic energy by absorbing non-elastic deformations and prevent it from being transferred to the main structural members. In this study an investigation on experimental behavior of steel SLIT dampers was performed. One specimen was considered as a reference without any SLIT, 4 specimens had SLIT with constant width and cross section but different height and 3 specimens had elliptical SLIT with constant cross section and different height. Cyclic loading was applied to all the specimens in the form of displacement control and the results of experiments such as load capacity, absorbed energy, stiffness, ductility and damping were presented and compared. In addition a numerical study was performed by finite element software (ABAQUS) and the results showed a good correlation in comparison to experimental results. The experimental study showed that elliptical split dampers had better performance in terms of bearing capacity, ductility and energy absorption, with a mean increase of 73. 76%, 15. 91% and 129. 49%, compared to SLIT steel dampers with constant width, respectively. A noticeable point about the steel dampers with elliptical SLIT was that in addition to increasing the bearing capacity, the displacement capacity as well as ductility increased, while in the dampers that have been investigated, the simultaneous increase in load capacity and ductility has not been found. Also in dampers with elliptical SLIT the more length of SLITs was participated in energy dissipation, strength and stress tolerance compared to the dampers with constant width. According to the experimental and numerical results obtained from this study, it can be concluded that the use of elliptical SLIT dampers with respect to the performance in terms of bearing capacity, energy absorption, ductility and displacement capacity, has a significant effect on seismic performance improvement in comparison to dampers with constant SLIT width. In these dampers (with elliptical SLIT), the ratio of height to SLIT width (h/b) equal to 4. 85, has shown the best performance compared to other h/b ratios.

Introduction: Gamma cameras are proposed for online range verification and treatment monitoring in proton therapy. An Analytical formula was derived and validated for sensitivity of a SLIT COLLIMATOR based on the photon fluence concept. Methods: Fluence formulation was generalized for photons distribution function and solved for high-energy point sources. The effect of the COLLIMATOR SLIT size and source off-axis position on the sensitivity of the COLLIMATOR were included in the formula. Results: The analytically calculated sensitivities of the SLIT COLLIMATOR were in good agreement with Monte Carlo results according to the Bland-Altman agreement test and Pearson correlation (r =0. 998) statistical analysis with 𝑝 < 0. 05. The mean relative error between calculated sensitivities with the derived formula and Monte Carlo was up to 0. 8%. Moreover, we found that under certain conditions, the established formula is converted to the Anger equation for the pinhole COLLIMATOR. Conclusion: The analytical formula developed in this research can estimate the SLIT COLLIMATOR sensitivity with an acceptable accuracy. The derived closed-form sensitivity formula can be applied in KE COLLIMATOR design and optimization studies.

Introduction: Studies carried out with synchrotron radiation have shown that micro-beam radiation therapy (MRT) has unique advantages in the treatment of cancerous tumors. In this method, the determination of dose distribution and calculation of peak to valley dose ratio (PVDR) are considered as the most important steps in treatment planning. The PVDR is a criterion to evaluate the destruction of cancer cells and protection of normal cells in the tissues surrounding a tumor. Materials and Methods: Using a multi-SLIT COLLIMATOR, planar sliced beams were generated in an X-ray generator in order to determine dose distribution in a multilayer phantom made of plexiglass. An ionization chamber was used to measure absorbed dose. Given the large size of the sensitive area of the chamber in comparison with the narrow beams, a mono-SLIT COLLIMATOR made of tungsten with a SLIT of 0. 3×7. 5 mm2 in its center was placed in front of the ionization chamber. Furthermore, by using Geant4 computer code, a model, including X-ray source, multi-SLIT COLLIMATOR, phantom, mono-SLIT COLLIMATOR, and detector, was designed to compare experimental and simulation results. Findings: The investigation of dose distribution in the phantom with both methods indicated the presence of peaks and valleys. Given the low intensity of Xray beam generated by the X-ray generator, and limited exposure time, the experimental errors were considerable. When using 1 mm (Air)+0. 5 mm (W) COLLIMATOR, PVDRs were obtained as 8. 7 and 10. 5 for ionization chamber and simulation, respectively, in the depth of 8 mm of the phantom. On the other hand, with a 1 mm (Air)+1 mm (W) COLLIMATOR, the values obtained for this parameter were 11. 1 and 13. 3 for ionization chamber and simulation, respectively. Conclusions: Based on the results, a multiSLIT COLLIMATOR made of tungsten could produce multi-slice X-ray. The estimated dose distribution using the Geant4 code was more accurate than the one obtained through ionization chamber, which can be due to the possibility of using a detector in much smaller dimensions in the Geant4 code.

The X-ray backscatter imaging systems have unique inspection capabilities and practical features due to their high sensitivity to organic materials, low radiation dose, and ability to scan from one side of the object. The scan is performed by an X-ray pencil beam. The shape, size, and intensity of the beam play a significant role in the image quality and the radiation dose received by the person. To create a pencil-shaped beam, the cone-shaped beam of the X-ray tube passes through a fan beam COLLIMATOR and a chopper wheel. Different designs were simulated to optimize the fan beam COLLIMATOR and chopper wheel, considering factors such as length and gap of the COLLIMATOR, as well as the SLIT width of the disc using the MCNPX2.6 code. To minimize leakage dose, a 4-mm tungsten/copper alloy disc was determined to be the most suitable in terms of thickness and material. Based on the simulation results from image quality tests, it was found that a COLLIMATOR with a length of 20 cm, a 1 mm gap, and a 1 mm SLIT width of the disc produced the most optimal X-ray beam for backscatter whole-body imaging systems. The best image quality was achieved at a disc rotational speed of 1500 rpm and a relative speed of vertical movement at 40 cm/s.