Journal of X-Ray Science and Technology - Volume 17, issue 1

Authors: Donovan, Molly | Zhang, Da | Liu, Hong

Article Type: Research Article

Abstract: Comprehensive research focus on the use of an edge test device for accurate determination of the modulation transfer function (MTF) in x-ray imaging has resulted in the development of numerous edge processing algorithms. While the overall results of the relative algorithms have been compared, the individual steps within the algorithms have not previously been evaluated for similarities and differences that could significantly affect the resultant MTF. Therefore a step by step investigation to evaluate the alternative …methods for each step separately holds the potential to provide insight into improving the overall algorithm by optimizing the method employed for each step. Thus this research study focused on comparing methods applicable for each step comprising the edge algorithm and providing a step by step guide for implementing the optimal algorithm based on given experimental conditions. In addition, new methods and combinations of methods were investigated in several of the algorithm steps, and were determined to provide comparable, if not superior, results to the existing methods. This included the use of different numbers of rows and columns in the region of interest (ROI) for determining the edge spread function (ESF), implementing a new three-step ESF filtering approach, and applying a median filter in both the ESF and line spread function (LSF) smoothing steps. Show more

Keywords: Modulation Transfer Function (MTF), X-ray imaging

DOI: 10.3233/XST-2009-0210

Citation: Journal of X-Ray Science and Technology, vol. 17, no. 1, pp. 1-15, 2009

Authors: Benítez, Ricardo Betancourt | Ning, Ruola | Conover, David | Liu, Shaohua

Article Type: Research Article

Abstract: The Noise Power Spectrum (NPS) is a function that yields information about the spatial frequency composition of noise in images obtained by a system. It is evaluated by calculating the absolute value squared of the noise image and normalizing it with respect to the voxel and matrix sizes. Consequently, the NPS has been one of the physical characteristics that is commonly used to quantitatively measure the physical performance of a system. In this article, we evaluated …the NPS of a Cone Beam CT Breast Imaging system by considering the following factors. First, we evaluated its symmetry around the x- and y-axis along with the influence of the cone angle and the matrix size on the NPS. Then, an analytical curve was suggested to best represent the NPS. Second, we analyzed the influence on the NPS of a set of seven parameters, namely the pixel size, exposure level, kVp value, number of projections acquired, voxel size, back projection filter, and the reconstruction algorithm employed. In addition, since the breast induced scattering in the image, we investigated the effect of the scattering-correction algorithm used in this system. Finally, we evaluated the uniformity of the NPS as a function of z with the matrix center located at {r = 0 mm}. The results demonstrate that the proposed curve is an ideal candidate that best represents the NPS. Hence, two parameters, the amplitude (A) and the width (σ), can be used to characterize the curve. The results also demonstrate that the voxel size and the cone angle are the only two parameters investigated in this study that do not affect the NPS. On the other hand, the matrix and pixel sizes, the back-projection filter and the reconstruction algorithm, the exposure level and the scattering correction, all influence the NPS. Finally, the results of the last part of this investigation suggest that this imaging system does not have a 3D isotropic noise distribution along the z-axis; yielding less noisy images at around z = 0.00 m and z = 80 mm. Show more

Keywords: Cone beam computer tomography, noise power spectrum, cone beam flat panel detector

DOI: 10.3233/XST-2009-0213

Citation: Journal of X-Ray Science and Technology, vol. 17, no. 1, pp. 17-40, 2009

Authors: Marinković, Predrag | Ilić, Radovan

Article Type: Research Article

Abstract: Three-dimensional point-kernel multiple scatter model for radiography simulation, based on dose X-ray buildup factors, is proposed and validated to Monte Carlo simulation. This model embraces nonuniform attenuation in object of imaging (patient body tissue). Photon multiple scattering is treated as in the point-kernel integration gamma ray shielding problems via scatter voxels. First order Compton scattering is described by means of Klein-Nishina formula. Photon multiple scattering is accounted by using dose buildup factors. …The proposed model is convenient in those situations where more exact techniques, like Monte Carlo, are not time consuming acceptable. Show more

Keywords: X-ray, radiography, dose buildup factor, scatter voxels

DOI: 10.3233/XST-2009-0215

Citation: Journal of X-Ray Science and Technology, vol. 17, no. 1, pp. 41-59, 2009

Authors: Ali, Imad | Ahmad, Salahuddin | Joel, Suresh | Williamson, Jeffrey F.

Article Type: Research Article

Abstract: It is well known that optical density (OD) of the radiochromic film (RCF) continues to grow after exposure at rates that have a complex dependence on dose, temperature, and densitometry wavelength. Dose rate and fractionation artifacts associated with variations in OD growth may limit the accuracy achievable by RCF dosimetry in brachytherapy and external beam applications, particularly at low doses (<5 Gy) and low dose rates (<10 cGy/h) where OD growth and sensitivity effects are …large. To identify densitometry wavelengths that minimize OD growth artifacts and enhance RCF sensitivity at low doses, we have investigated Model MD-55-2 RCF response as a function of densitometry wavelength, irradiation-to-densitometry time interval, dose and temperature. Using a Perkin Elmer spectrophotometer, the absorption spectrum in the 500–700 nm range was measured for doses ranging from 1–100 Gy, over post-irradiation times from 1 h to 60 days. An empirical model with time-independent, fast and slow growth components was used to fit single exposure data and the dependence of the resulting best-fit parameters on dose and densitometry wavelength was investigated. RCF OD variation with temperature in the range 22–40� was measured. Wavelengths in the 660–690 nm range were found to minimize the dose-dependence of OD post-exposure growth. Densitometry wavelengths in the range of 670–680 nm enhance RCF sensitivity and show small variations in OD with temperature in the range from 22–40�. Compared to 633 nm light, 675 nm densitometry reduces OD growth at 1 Gy from 70% to 10% over a period of nearly 1174.0 h relative to the initial OD measured at 1.7 h post-irradiation. In addition, RCF sensitivity is nearly doubled at this wavelength for all dose levels. Show more

DOI: 10.3233/XST-2009-0212

Citation: Journal of X-Ray Science and Technology, vol. 17, no. 1, pp. 61-73, 2009

Authors: Sharanabasappa, | Kaginelli, S.B. | Kerur, B.R. | Anilkumar, S. | Hanumaiah, B.

Article Type: Research Article

Abstract: The total mass attenuation coefficient for Potassium dichromate, Potassium chromate and Manganese acetate compounds are measured at different photon energies 5.895, 6.404, 6.490, 7.058, 8.041 and 14.390 keV using Fe-55, Co-57 and ^{241} Am source with Copper target, radioactive sources. The photon intensity is analyzed using a high resolution HPGe detector system coupled to MCA under good geometrical arrangement. The obtained values of mass attenuation coefficient values are compared with theoretical values. …This study suggests that measured mass attenuation coefficient values at and near absorption edges differ from the theoretical value by about 5–28%. Show more

Keywords: Mass attenuation coefficient, near absorption edge, cross section, resonance raman scattering, EXAFS

DOI: 10.3233/XST-2009-0211

Citation: Journal of X-Ray Science and Technology, vol. 17, no. 1, pp. 75-84, 2009

Authors: Manciu, Marian | Manciu, Felicia S. | Vulcan, Teodor | Nes, Elena | Waggener, Robert G.

Article Type: Research Article

Abstract: Megavoltage X-ray sources are commonly used for therapy planning, and knowledge of their spectral distribution is important for accurate dose calculations. There are many methods that could provide reasonable estimations of Megavoltage X-ray spectra, when very accurate attenuation data or at least very good set of initial guesses of the spectra are available. We present here a novel method, which can be used for accurate Megavoltage spectral reconstruction without any prior knowledge of spectral distribution; the …method performs well even when the available transmission data are affected by noise. The method is based on a search for a smooth function that minimizes the differences between measured and calculated attenuation data. The algorithm is compared with well-known existing algorithms, using computer simulated data, both error-free and containing added random Gaussian noise. The reconstructed spectra are subsequently used to calculate the transmission through 50 cm of bone, muscle or fat tissue. It is shown that the relative errors in dose calculations, using the spectra reconstructed via this method, are significantly smaller than those obtained via well-established reconstruction algorithms – Truncated Singular Value Decomposition (TSVD) and Expectation Maximization (EM). These results suggest that the novel algorithm might be practical for routine Megavoltage therapy X-ray source calibration. Show more

Keywords: Photon spectra, megavoltage photon beams, spectral reconstruction, bremsstrahlung, attenuation curves, inverse problem, linear accelerators

DOI: 10.3233/XST-2009-0214

Citation: Journal of X-Ray Science and Technology, vol. 17, no. 1, pp. 85-99, 2009