Journal of X-Ray Science and Technology - Volume 21, issue 4

Authors: Alivov, Yahya | Feng, Jun | Molloi, Sabee

Article Type: Research Article

Abstract: We studied in details the effect of various X-ray tube parameters (cathode size, anode size, anode – lens distance, etc.) on TiO_{2} nanotube field emission electron-beam focal spot size (FSS) and lens voltages for a single electrode lens system. The simulations were performed using commercially available SIMION 8.1 software. A wide range of parameters was simulated to determine conditions when FSS and lens focusing voltage had minimum values. In particular, the dependence of FSS …and lens voltages on cathode size (d_{S} ) was studied for different size lens apertures (d_{L} ) and different anode voltages. The cathode size d_{S} was varied in the range from 0.1 mm to d_{L} ; the d_{L} was changed from 4 to 24 mm in 4 mm increments. The simulations were performed for two different V_{A} values 60 kV and 120 kV. It was found that for 20 mm and 24 mm diameter lens apertures the maximum cathode size when the resulting FSS was not greater than 1600 μm (the focal spot size in clinical X-ray CT) were 17.5 mm and 16.2 mm, respectively. The lens voltages V_{f} corresponding to 17.5 mm and 16.2 mm cathode size in 20 mm and 24 mm aperture diameter x-ray tubes are 1850 V and −1550 V, respectively. Show more

Keywords: Nanotubes, field emitters, X-ray source, electron beam, electrostatic electron lens, focal spot size

DOI: 10.3233/XST-130387

Citation: Journal of X-Ray Science and Technology, vol. 21, no. 4, pp. 567-577, 2013

Authors: Liu, Fenglin | Wang, Ge | Cong, Wenxiang | Hsieh, Scott S. | Pelc, Norbert J.

Article Type: Research Article

Abstract: A bowtie is a filter used to shape an x-ray beam and equalize its flux reaching different detector channels. For development of spectral CT with energy discriminating photon-counting (EDPC) detectors, here we propose and evaluate a dynamic bowtie for performance optimization based on a patient model or a scout scan. With a mechanical rotation of a dynamic bowtie and an adaptive adjustment of an x-ray source flux, an x-ray beam intensity profile can be modulated. First, …a mathematical model for dynamic bowtie filtering is established for an elliptical section in fan-beam geometry, and the contour of the optimal bowtie is derived. Then, numerical simulation is performed to compare the performance of the dynamic bowtie in the cases of an ideal phantom and a realistic cross-section relative to the counterparts without any bowtie and with a fixed bowtie respectively. Our dynamic bowtie can equalize the expected numbers of photons in the case of an ideal phantom. In practical cases, our dynamic bowtie can effectively reduce the dynamic range of detected signals inside the field of view. Although our design is optimized for an elliptical phantom, the resultant dynamic bowtie can be applied to a real fan-beam scan if the underlying cross-section can be approximated as an ellipse. Furthermore, our design methodology can be applied to specify an optimized dynamic bowtie for any cross-section of a patient, preferably using rapid prototyping technology. Show more

Keywords: Dynamic bowtie, tube current modulation, elliptical phantom, computed tomography (CT)

DOI: 10.3233/XST-130386

Citation: Journal of X-Ray Science and Technology, vol. 21, no. 4, pp. 579-590, 2013

Article Type: Other

Citation: Journal of X-Ray Science and Technology, vol. 21, no. 4, pp. 591-599, 2013