Journal of X-Ray Science and Technology - Volume 18, issue 1

Authors: Hu, Yingkang | Zhu, Jiehua

Article Type: Research Article

Abstract: Analytic simulation in computed tomography(CT) generates projection data for evaluating and improving CT image reconstruction algorithms and has played an important role in the research and development of x-ray CT. The simulation is desired to be as realistic as possible while the computation needs to be efficient and accurate. Early primitive equation-based phantoms such as Shepp-Logan and FORBILD use only boxes, cylinders, and quadrics to simulate body parts. The superquadrics have been used in Computer Graphics …since 1980's, and in CT since 1990's. While their more complex shapes make them more realistic in simulation, the difficulties in solving their equations increase dramatically, which restricts their use, especially in ray-tracing and x-ray transform. Zhu et al. developed an algorithm for ray-intersecting the superellipsoid and used it to build a thorax phantom. No algorithms for ray-intersecting the supertoroid, however, are known up to now to the best of our knowledge. In this paper we propose such an algorithm and use it in computation of x-ray transform. The algorithm was tested by a phantom consisting of the top portion of vertebrae and a few ribs. Cone-beam data were produced from the phantom, and then used to reconstruct the phantom. Show more

Keywords: Computed tomography, computer graphics, x-ray transform, supertoroids, ray-intersecting

DOI: 10.3233/XST-2010-0229

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 1-13, 2010

Authors: Cai, Zhijun | Bai, Er-Wei | Wang, Ge | Sharafuddin, Melhem J. | Abada, Hicham T.

Article Type: Research Article

Abstract: Computed Tomography (CT) has become an effective diagnosis and evaluating tool in clinical; however, its radiation exposure has drawn great attention as more and more CT scans are performed every year. How to reduce the radiation dose and meanwhile keep the resultant CT images diagnosable becomes an important research topic. In this paper, we propose a dose reduction approach along with the adaptive bolus chasing CT Angiography (CTA) techniques, which are capable of tracking the contrast …bolus peak over all the blood vessel segments during the CTA scan. By modulating the tube current (and collimator width) online, we can reduce the total radiation dose and maintain the contrast to noise ratio (CNR) of the blood vessel. Numerical experiments on reference DSA data sets show that by using the proposed dose reduction method, the effective radiation dose can be saved about 39%. Show more

Keywords: Radiation exposure, dose reduction, computed tomography, computed tomography angiography (CTA), contrast to noise ratio (CNR), adaptive bolus chasing

DOI: 10.3233/XST-2010-0236

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 15-25, 2010

Authors: Ji, Changguo | Cui, Yidong | Cao, Wentian | Bao, Shanglian

Article Type: Research Article

Abstract: Purpose: The finite Hilbert transform (FHT) or inverse finite Hilbert transform (IFHT) is recently found to have some important applications in computerized tomography (CT) arena [1-6], where they are used to filter the derivatives of back-projected data in the chord-line based CT reconstruction algorithms. In this paper, we implemented, improved and validated a fast numerical solution to the FHT via a double exponential (DE) integration scheme. A same strategy can be used to compute IFHT. …Methods: To overcome the underflow of floating-point numbers, we first determined the range of variable transformation from the minimum positive value of single or double precision floating point number, the integration step can be further determined by the range of variable transformation and the integration level. Two functions with their known analytical FHTs are used to validate the implementation of the FHT via DE scheme. The surface map and 2D contour of the FHT transformation error with respect to integration level and the range of the variable transformation are used to numerically determine the optimal numbers for a fast FHT. Results: Given a specific precision, the lowest integration level and the optimal range of variable transformation, which are used to transform a signal with a certain degree of fluctuation, can be numerically determined by the surface map and 2D contour of the standard deviation of transformation error. These two numbers can then be taken to efficiently compute the FHT for other signals with the same or less degree of fluctuation. Conclusions: The FHT via DE scheme and the numerical method to determine the integration level and the range of transformation can be used for fast FHT in certain applications, such as data filtering in chord-line based CT reconstruction algorithms. Show more

Keywords: Finite Hilbert transform, CT reconstruction, double exponential integration

DOI: 10.3233/XST-2010-0237

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 27-38, 2010

Authors: Han, I. | Demir, L.

Article Type: Research Article

Abstract: The total mass attenuation coefficients (μ/ρ) for pure {Au} and Au_{99} {Be}_{1}, Au_{88} {Ge}_{12}, {Au}_{95} Zn_{5} alloys were measured at 59.5 and 88.0 keV photon energies. The samples were irradiated with ^{241} Am and ^{109} Cd radioactive point source using transmission arrangement. The γ- rays were counted by a Si(Li) detector with resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections …(σ _t and σ _e ), effective atomic and electron densities (Z_{eff} and N_{el} ) were determined using the obtained mass attenuation coefficients for investigated Au alloys. The theoretical mass attenuation coefficients of each alloy were estimated using mixture rule. Show more

Keywords: Mass attenuation coefficients, effective atomic number, effective electron density, alloy, Au

DOI: 10.3233/XST-2010-0238

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 39-46, 2010

Authors: Li, Xiaosong | Cheng, Gang | Huang, Naiyan | Wang, Lei | Liu, Fanguang | Gu, Ying

Article Type: Research Article

Abstract: Intravascular low level laser therapy (ILLLT) has been applied in the treatment of many diseases for about twenty years. However, much fundamental work has not been done on its dosimetry. The study was designed to compare the difference of light distribution during ILLLT between using flat end fiber and optical fiber coupled with cylindrical light diffuser. Light distribution of He-Ne laser was processed by Monte Carlo model. The laser output was 5 mW. The diameter of …both optical fibers was 400 μ. Four tissue optical parameters were chosen for simulation. The results showed that optical parameters of blood are important to determine the distribution of laser energy. The highest power density could increase to over 5000 mW/cm^{2} using flat end fiber. And the laser energy was absorbed by the blood cells in very small area before the tip of flat end fiber. But when using optical fiber coupled with cylindrical light diffuser, the highest power density was about 100 mW/cm^{2} . More volume of blood cells could be irradiated by laser light. In summary, optical fiber coupled with cylindrical light diffuser is superior to flat end fiber at the aspect of increasing the volume of irradiated blood and decreasing unwanted damage to blood cells during intravascular low level laser therapy. Show more

Keywords: Intravascular low level laser therapy, mathematical simulation, light distribution, optical fiber

DOI: 10.3233/XST-2010-0239

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 47-55, 2010

Authors: Pu, Lina | Liu, Zhipeng | Yin, Tao | An, Hao | Li, Song

Article Type: Research Article

Abstract: Repetitive Transcranial magnetic stimulation (TMS) is a relatively new technique, which is non-invasive and painless used to stimulate the central and peripheral neural tissues. The principle is generating time-varying magnetic fields to stimulate the cerebral cortex neuron and inducing eddy current inside the tissues. Many researches study on the distributing of magnetic field and electric field induced inside the human brain, whereas the static electric field was neglected roughly in many studies. In this paper, a …five-sphere model is established to simulate the human head used in rTMS. According to the different dielectric properties of the head tissues, the Laplace equation of static electric field is deduced by both of Gauss theorem and current's continuity principle. Boundary conditions used in different interface between two adjacent layers in the five-sphere model is proposed in this paper. Simulating study is conducted to calculate the distribution of the electric field in the model. Simulating results suggest that the model is useful to get the parameters of the most focus coil. Therefore this study could be potential to promote the development of rTMS stimulator. Show more

Keywords: rTMS, laplace's equation, boundary condition, finite element method, five-sphere model

DOI: 10.3233/XST-2010-0241

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 57-67, 2010

Authors: Tsai, Ming-Dar | Hsieh, Ming-Shium

Article Type: Research Article

Abstract: Burring surgery is mainly implemented for fine or critical structures and widely used in orthopedic, oral and maxillofacial, ENT and neurosurgery departments to delicately cut or polish bones, joints or other tissues. This paper describes a volume manipulation method that extends a voxel with multiple values to represent accurate burred changes on tissue surfaces. Tissue surface reconstruction is implemented for the local burred surface to provide a real-time visual response. A burring force vector for a …haptic response is calculated by detecting which parts of a bur contact tissue and summated from tissue removal loads on the contacted parts. A spine surgery example showed that rough surface features by gross cutting or smooth features by fine cutting can be clearly demonstrated and high haptic reality can be achieved by our simulations. The burring surgery simulator with the accurate visual and haptic responses can be an effective rehearsing and training tool. Show more

Keywords: Burring surgery, surgical simulation, haptic interaction, 3D reconstruction

DOI: 10.3233/XST-2010-0242

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 69-85, 2010

Authors: Etemadinezhad, Siavash | Rahimi, Seyed Ali

Article Type: Research Article

Abstract: Background and purpose: Radiographic techniques are essential methods of diagnosis, and their use has been increased, especially with the development of the new technologies. Inappropriate administration of these techniques may put both the patients and personnel at unnecessary risks. The objective of this research was to measure the skin dose of chest and skull radiographies used in Mazandaran hospitals and to compare these doses with national and international standards. Materials and methods: In this …cross-sectional study, six X-ray generators at six hospitals affiliated to Mazandaran University of Medical Sciences were included. One hundred and twenty patients referred to the radiology wards for radiographic examinations of chest and skull with normal body mass index (BMI) were selected (20 patients for each radiography unit). The generators were matched for mAs, kvp, type of amplifier sheets, and technical conditions as much as possible. Calibrated thermo luminescence dosimeters (TLD-USA, Lif-100) were used to measure the skin dose by placing them on the patients' back and the absorbed doses by TLDs were read by a TLD reader (model: Harshuu, TLD3500, Japan). Results: The mean values of the skin dose were 0.51 mGray for posteroanterior (PA), chest X-ray (CXR), 3.36 mGray for lateral CXR, 7.25 mGray for anterroposterior (AP) or PA skull X-rays, and 7.59 mGray for lateral skull X-rays. The measured values were higher than the national and international standards. Conclusion: The results of this research revealed that the conditions of the X-ray generators should be monitored and modified periodically. Modifying the X-ray generators plus improving technicians' skills would, to some extent, reduce the radiation exposure of the patients. Show more

Keywords: Exposure dose standard, dosimetry, radiography, TLD

DOI: 10.3233/XST-2010-0244

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 87-91, 2010

Authors: Zhou, Huaibei | Zhu, Li

Article Type: Research Article

DOI: 10.3233/XST-2010-0240

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 1, pp. 93-97, 2010