Journal of X-Ray Science and Technology - Volume 22, issue 6

Authors: Tan, Wenli | Zhan, Songhua | Yang, Shuohui | Zhuang, Yuan | Cheng, Ruixin | Zhan, Hongsheng

Article Type: Research Article

Abstract: OBJECTIVE: The aim of this study was to investigate the significance of the combined use of BMI and AEC in reducing the radiation dose of CT volume scans of the lumbar spine. METHODS: A prospective study was performed to continuously collect data from 50 patients (age range from 19 to 60 years, male versus female 20/30) whose BMIs were less than 25 kg/m^{2} (group A) and 50 patients (age range from 21 to 82 years, male …versus female 24/26) whose BMIs were equal to or more than 25 kg/m^{2} (group B). The 50 patients in each group were randomly divided into 5 subgroups with each subgroup having lower radiation dose from subgroup 1 to 5. All the patients were performed lumbar spiral CT scans (GE LightSpeed VCT 64-slice scanner) and the scan parameters were different in different subgroups. Volume CT dose index (CTDIvol) was recorded. The qualities of the images were graded. The one-way ANOVA and Kruskal-Wallis test were done. RESULTS: Both in group A and B, there were significant differences in CTDIvol among the 5 subgroups (P< 0.001). The quality of the images in the 5 subgroups of group A didn't show statistical difference. The standard deviation (SD) and signal to noise ratio (SNR) values of the L4-5 psoas major muscles in subgroup 5 of group B was statistical different from the other 4 subgroups (P< 0.01). CONCLUSION: Use of BMI combined with AEC reduces radiation dosage, without compromising the image quality. For patients in group A and group B, parameters of subgroup 5 and subgroup 4 may respectively be applied for lower dose CT scanning. Show more

Keywords: Body mass index (BMI), automatic exposure control (AEC), spiral CT, radiation dosage, lumbar vertebrae

DOI: 10.3233/XST-140455

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 697-706, 2014

Authors: Chen, Yi | Xi, Yan | Zhao, Jun

Article Type: Research Article

Abstract: BACKGROUND: The temporal resolution of current computed tomography (CT) systems is limited by the rotation speed of their gantries. OBJECTIVE: A helical interlaced source detector array (HISDA) CT, which is a stationary CT system with distributed X-ray sources and detectors, is presented in this paper to overcome the aforementioned limitation and achieve high temporal resolution. METHODS: Projection data can be obtained from different angles in a short time and do not require source, detector, …or object motion. Axial coverage speed is increased further by employing a parallel scan scheme. Interpolation is employed to approximate the missing data in the gaps, and then a Katsevich-type reconstruction algorithm is applied to enable an approximate reconstruction. RESULTS: The proposed algorithm suppressed the cone beam and gap-induced artifacts in HISDA CT. The results also suggest that gap-induced artifacts can be reduced by employing a large helical pitch for a fixed gap height. CONCLUSIONS: HISDA CT is a promising 3D dynamic imaging architecture given its good temporal resolution and stationary advantage. Show more

Keywords: Stationary CT, distributed X-ray sources, temporal resolution, Katsevich-type algorithm, dynamic imaging

DOI: 10.3233/XST-140456

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 707-725, 2014

Authors: Luo, Yanji | Cui, Min-Yi | Liao, Bing | Pui, Margaret H. | Dong, Zhi | Li, Xue-Hua | Sun, Can-Hui | Peng, Zhen-Peng | Li, Zi-Ping | Feng, Shi-Ting

Article Type: Research Article

Abstract: Cryptococcus neoformans and Candida are common opportunistic pathogens of human. There is very limited literature on Cryptococcus neoformans cholangitis or Candida cholangitis in immunocompetent patient while mixed Cryptococcus neoformans and Candida cholangitis has not been reported in the literature ever before. We hereby report the imaging findings of a case of mixed Cryptococcus neoformans and Candida cholangitis in an immunocompetent boy. The CT features included nodules in the cystic duct and common bile duct, …dilatation of the intra- and extrahepatic bile ducts with mural thickening, irregular hypodense mass-like lesion extending along the bile ducts from the liver hilum to the periphery which was confirmed by the presence of enlarged and confluent lymph nodes. CT characteristics can contribute to timely diagnosis and treatment of this disease. Show more

Keywords: Bile duct, cryptococcus, candida, computed tomography, fungal infection

DOI: 10.3233/XST-140457

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 727-733 , 2014

Authors: Liu, Xin | Lee, Hyoung Koo

Article Type: Research Article

Abstract: BACKGROUND: While spectral CT using single photon counting detector has shown a number of advantages in diagnostic imaging, knowledge of the detector response function of an energy-resolved detector is needed to correct the signal bias and reconstruct the image more accurately. OBJECTIVE: The objective of this paper is to study the photo counting detector response function using laboratory sources, and investigate the signal bias correction method. METHODS: Our approach is to model the detector response function …over the entire diagnostic energy range (20 keV <E< 140 keV) using a semi-analytical method with 12 parameters. The model includes a primary photo peak, an exponential tail, and four escape peaks. Four radioactive isotopes including Cdmium-109, Barium-133, Americium-241 and Cobalt-57 are used to generate the detector response function at six photon energies. The 12 parameters are obtained by non-linear least-square fitting with the measured detector response functions at the six energies. The correlations of the 12 parameters with energy are also investigated with the measured data. RESULTS: The analytical model generally describes the detector response function and is in good agreement with the measured data. The trend lines of the 12 parameters indicate higher energies tend to cause grater spectrum distortion. The spectrum distortion caused by the detector response function on spectral CT reconstruction is analyzed theoretically, and a solution to correct this spectrum distortion is also proposed. CONCLUSION: In spectral and fluorescence CT, the spectrum distortion caused by detector response function poses a problem and cannot be ignored in any quantitative analysis. The detector response function of a CdTe detector can be obtained by a semi-analytical method. Show more

Keywords: Photon counting, detector response function, spectrum distortion

DOI: 10.3233/XST-140458

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 735-744, 2014

Authors: Zhao, Xing | Hu, Jing-Jing | Zhao, Yun-Song | Zhang, Hui-Tao | Zhang, Peng

Article Type: Research Article

Abstract: Today's clinical dual energy computed tomography (DECT) scanners generally measure different rays for different energy spectra and acquire spatial mismatched raw data sets. The deficits in clinical DECT technologies suggest that mainly image based material decomposition methods are in use nowadays. However, the image based material decomposition is an approximate technique, and beam hardening artifacts remain in decomposition results. A recently developed image based iterative method for material decomposition from inconsistent rays …(MDIR) can achieve much better image quality than the conventional image based methods. Inspired by the MDIR method, this paper proposes an iterative method to indirectly perform raw data based DECT even with completely mismatched raw data sets. The iterative process is initialized by density images that were obtained from an image based material decomposition. Then the density images are iteratively corrected by comparing the estimated polychromatic projections and the measured polychromatic projections. Only three iterations of the method are sufficient to greatly improve the qualitative and quantitative information in material density images. Compared with the MDIR method, the proposed method needs not to perform additional water precorrection. The advantages of the method are verified with numerical experiments from inconsistent noise free and noisy raw data. Show more

Keywords: Dual energy computed tomography, iterative algorithm, basis material decomposition, calibration

DOI: 10.3233/XST-140459

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 745-762, 2014

Authors: Liu, Xin

Article Type: Research Article

Abstract: This study describes a deterministic method for simulating the first-order scattering in a medical computed tomography scanner. The method was developed based on a physics model of x-ray photon interactions with matter and a ray tracing technique. The results from simulated scattering were compared to the ones from an actual scattering measurement. Two phantoms with homogeneous and heterogeneous material distributions were used in the scattering simulation and measurement. It was found that the simulated scatter profile …was in agreement with the measurement result, with an average difference of 25% or less. Finally, tomographic images with artifacts caused by scatter were corrected based on the simulated scatter profiles. The image quality improved significantly. Show more

Keywords: x-ray computed tomography, scattering, deterministic simulation, ray tracing

DOI: 10.3233/XST-140460

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 763-772, 2014

Authors: Li, Xiaozhong | Liu, Taiyun | Wang, Lin

Article Type: Research Article

Abstract: Developmental malformations of lumbar transverse processes commonly include hypertrophy of the transverse process, overgrowth of the transverse process, and persistence of the transverse process epiphysis. To date, the intertransverse pseudarthrosis malformation has not been reported. In this case report, we identified a case of intertransverse pseudarthrosis through X-ray imaging, which was confirmed by CT scanning. And intertransverse pseudarthrosis of spine was proved by Surgery.

Keywords: Lumbar, malformation, transverse process, pseudarthrosis

DOI: 10.3233/XST-140461

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 773-776, 2014

Authors: Ghanbari, K. | Ghoranneviss, M. | Elahi, A. Salar | Saviz, S.

Article Type: Research Article

Abstract: Hard x-ray emission from the Runaway electrons is an important issue in tokamaks. Suggesting methods to reduce the Runaway electrons and therefore the emitted hard x-ray is important for tokamak plasma operation. In this manuscript, we have investigated the effects of external fields on hard x-ray intensity and Magneto-Hydro-Dynamic (MHD) activity. In other words, we have presented the effects of positive biased limiter and Resonant Helical Field (RHF) on the MHD fluctuations and hard x-ray emission …from the Runaway electrons. MHD activity and hard x-ray intensity were analyzed using Wavelet transform in the presence of external fields and without them. The results show that the MHD activity and therefore the hard x-ray intensity can be controlled by the external electric and magnetic fields. Show more

Keywords: Tokamak, runaway electrons, x-ray, MHD activity, Wavelet transform

DOI: 10.3233/XST-140462

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 777-783, 2014

Authors: Ren, Liqiang | Wu, Di | Fajardo, Laurie L. | Li, Yuhua | Zheng, Bin | Liu, Hong

Article Type: Research Article

Abstract: BACKGROUND: Accurately depicting breast tumors located posteriorly, close to the chest wall musculature, with conventional mammography is a technical challenge. OBJECTIVE: This study demonstrates the proof of concept of an x-ray fluorescence mapping (XFM) technique to address this issue. METHODS: A tissue-equivalent gel phantom is designed to mimic structures in the central part of a compressed breast. The posterior aspect of the breast and adjacent pectoralis major muscle are represented by another 10-mm-thickness breast …tissue simulation phantom (BR12) that is attached to the back of the gel phantom as a region of interest (ROI). Two gold nanoparticle (GNP) solutions are embedded into the ROI to simulate varying GNP uptake within breast lesions. The ROI is imaged through performing the XFM technique with an x-ray pencil-beam and a single spectrometer. RESULTS: A 2D mapping of the middle plane in the ROI demonstrates feasibility and matches well the known spatial distribution and different GNP concentrations. 3D reconstruction of the ROI is easily rendered by repeating the 2D mapping process. CONCLUSION: XFM system geometry and its insensitivity to attenuation coefficients of breast tissue components are unique characteristics that may complement conventional mammography and improve the detection of breast cancers located posteriorly, adjacent to or overlying the chest wall musculature. Show more

Keywords: Breast cancer detection, posteriorly located breast tumors, chest wall musculature, breast-mimicking phantom, x-ray fluorescence mapping (XFM), gold nanoparticles (GNPs)

DOI: 10.3233/XST-140463

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 785-796, 2014

Authors: Zhao, Zhanqi | Frerichs, Inéz | Pulletz, Sven | Müller-Lisse, Ullrich | Möller, Knut

Article Type: Research Article

Abstract: BACKGROUND: Due to the ill-posed problem, the electrical impedance within the thorax cannot be exactly reconstructed. OBJECTIVE: The aim of our study was to prove that reconstruction with individual thorax geometry improved the quality of EIT (electrical impedance tomography) images. METHODS: Seven mechanically ventilated patients with acute respiratory distress syndrome were examined by EIT. The thorax contours were determined from routine computed tomography (CT) images based on automatic threshold filtering. EIT raw data was …reconstructed offline with (1) back-projection with circular forward model; (2) GREIT reconstruction method with circular forward model and (3) GREIT with individual thorax geometry. The resulting EIT images were compared to rescaled CT images. The distance between the lung contour and the thorax contour was calculated for each method and the differences to that in CT were denoted as position differences. Shape differences was defined as the ratio of thorax (or lungs) size in EIT and that in rescaled CT. RESULTS: Method (3) has the smallest position differences (6.6 ± 2.8, 5.3 ± 3.3, 2.3 ± 1.4 in pixel, for each reconstruction method respectively; mean ± SD). The thorax and lungs sizes in the transformed CT images were 514 ± 73 and 177 ± 39. Shape differences of thorax were 1.81 ± 0.26, 1.81 ± 0.26, 1.10 ± 0.12 and that of lungs were 1.69 ± 0.45, 1.52 ± 0.45, 1.34 ± 0.35 for each method respectively. CONCLUSION: The reconstructed images using the GREIT method with individual thorax geometry were more realistic. Improvement of EIT image quality may foster the acceptance of EIT in routine clinical use. Show more

Keywords: Computed tomography, electrical impedance tomography, image reconstruction, individual thorax geometry

DOI: 10.3233/XST-140464

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 6, pp. 797-807, 2014