The determination of accurate material composition of a kidney stone is crucial for understanding the formation of
the kidney stone as well as for preventive therapeutic strategies. Radiations probing instrumental activation analysis
techniques are excellent tools for identification of involved materials present in the kidney stone. In particular, x-ray
fluorescence (XRF) can be very useful for the determination of minor and trace materials in the kidney stone. The
X-ray fluorescence measurements were performed at the Radiation Measurements and Spectroscopy Laboratory
(RMSL) of department of nuclear engineering of Missouri University of Science and Technology and different kidney
stones were acquired from the Mayo Clinic, Rochester, Minnesota. Presently, experimental studies in conjunction
with analytical techniques were used to determine the exact composition of the kidney stone. A new type of
experimental set-up was developed and utilized for XRF analysis of the kidney stone. The correlation of applied
radiation source intensity, emission of X-ray spectrum from involving elements and absorption coefficient
characteristics were analyzed. To verify the experimental results with analytical calculation, several sets of kidney
stones were analyzed using XRF technique. The elements which were identified from this techniques are Silver
(Ag), Arsenic (As), Bromine (Br), Chromium (Cr), Copper (Cu), Gallium (Ga), Germanium (Ge), Molybdenum
(Mo), Niobium (Nb), Rubidium (Rb), Selenium (Se), Strontium (Sr), Yttrium (Y), Zirconium (Zr). This paper
presents a new approach for exact detection of accurate material composition of kidney stone materials using XRF
instrumental activation analysis technique.
A novel cold cathode field emission array (FEA) X-ray source based on ultra-nanocrystalline diamond (UNCD) field emitters is being constructed as an alternative for detection of obscured objects and material. Depending on the geometry of the given situation the flat-panel X-ray source could be used in tomography, radiography, or tomosynthesis. Furthermore, the unit could be used as a portable X-ray scanner or an integral part of an existing detection system. UNCD field emitters show great field emission output and can be deposited over large areas as the case with carbon nanotube “forest” (CNT) cathodes. Furthermore, UNCDs have better mechanical and thermal properties as compared to CNT tips which further extend the lifetime of UNCD based FEA. This work includes the first generation of the UNCD based FEA prototype which is being manufactured at the Center for Nanoscale Materials within Argonne National Laboratory with standard microfabrication techniques. The prototype is a 3x3 pixel FEA, with a pixel pitch of 500 μm, where each pixel is individually controllable.
The successful creation and operation of a neutron and X-ray combined computed tomography (NXCT) system has been demonstrated by researchers at the Missouri University of Science and Technology. The NXCT system has numerous applications in the field of material characterization and object identification in materials with a mixture of atomic numbers represented. Presently, the feasibility studies have been performed for explosive detection and homeland security applications, particularly in concealed material detection and determination of the light atomic number materials. These materials cannot be detected using traditional X-ray imaging. The new system has the capability to provide complete structural and compositional information due to the complementary nature of X-ray and neutron interactions with materials. The design of the NXCT system facilitates simultaneous and instantaneous imaging operation, promising enhanced detection capabilities of explosive materials, low atomic number materials and illicit materials for homeland security applications. In addition, a sample positioning system allowing the user to remotely and automatically manipulate the sample makes the system viable for commercial applications. Several explosives and weapon simulants have been imaged and the results are provided. The fusion algorithms which combine the data from the neutron and X-ray imaging produce superior images. This paper is a compete overview of the NXCT system for feasibility studies of explosive detection and homeland security applications. The design of the system, operation, algorithm development, and detection schemes are provided.
This is the first combined neutron and X-ray computed tomography system in operation. Furthermore, the method of fusing neutron and X-ray images together is a new approach which provides high contrast images of the desired object. The system could serve as a standardized tool in nondestructive testing of many applications, especially in explosives detection and homeland security research.
A neutron and X-ray combined computed tomography system (NXCT) has been developed1 at the Missouri University of Science & Technology. It is believed that it will provide a superior method for non-destructive testing and evaluation. The system is housed within the Missouri University of Science & Technology Reactor (MSTR) and is the first such imaging platform and synthesis method to be developed. The system utilizes neutrons obtained directly from the reactor core and X-rays an X-ray generator. Characterization of the newly developed digital imaging system is imperative to the performance evaluation, as well as for describing the associated parameters. The preliminary evaluation of the NXCT system was performed in terms of image uniformity, linearity and spatial resolution. Additionally, the correlation between the applied beam intensity, the resulting image quality, and the system sensitivity was investigated. The combined neutron/X-ray digital imaging system was evaluated in terms of performance parameters and results are detailed. The MTF of the X-ray imaging module was calculated using the Edge method. The spatial frequency at 10% of the MTF was found to be 8 lp/mm, which is in agreement with the value of 8.5 lp/mm determined from the square wave response method. The highest detective quantum efficiency of the X-ray imaging module was found to be 0.13. Furthermore, the NPS spectrum for the neutron imaging module was also evaluated in a similar way as the X-ray imaging module. In order to improve the image quality of the neutron imaging module, a pin-hole mask phantom was used to correct the geometrical non-linearity of the delay line anode readout. The non-linearity correction of the delay line anode readout has been shown through the corrected images of perforated cadmium strip and electroformed phantom.
Knowledge of scatter generated by bowtie filter is crucial for providing artifact free images on the wide-cone low-dose
CT scanners. We investigate and determine the scatter level and artifact generated by the widely used bowtie filter in a
wide-cone low-dose CT system. Our approach is to use Monte Carlo simulation to estimate the scatter level generated by
a bowtie filter made of a material with low atomic number. First, major components of CT systems, such as source, prepatient
collimator, flat filter, bowtie filter, body phantom, and an optional post patient collimator (anti-scatter grid), are
built into a 3D model. The scattered photon fluence and the primary transmitted photon fluence are simulated by
MCNP5 - a Monte Carlo simulation toolkit. With the increased interests in the low dose and wide coverage CT
technology, a tube potential of 80 kVp with more than 10 degree of cone angle is selected. The biased sinogram is
created by superimposing scatter signal generated by the bowtie filter onto the primary x-ray beam signal. Finally,
images with artifacts are reconstructed with the biased signal. Methods to reduce bowtie filter scatter are also discussed
and demonstrated.
A contrast enhancement algorithm is developed for enhancing the contrast of x-ray images. The algorithm is based on
Laplacian pyramid image processing technique. The image is decomposed into three frequency sub-bands- low, medium, and high. Each sub-band contains different frequency information of the image. The detail structure of the image lies on the high frequency sub-band and the overall structure lies on the low frequency sub-band. Apparently it is difficult to extract detail structure from the high frequency sub-bands. Enhancement of the detail structures is necessary in order to find out the calcifications on the mammograms, cracks on any object such as fuel plate, etc. In our proposed method contrast enhancement is achieved from high and medium frequency sub-band images by decomposing the image based on multi-scale Laplacian pyramid and enhancing contrast by suitable image processing. Standard Deviation-based Modified Adaptive contrast enhancement (SDMACE) technique is applied to enhance the low-contrast information on the sub-bands without overshooting noise. An alpha-trimmed mean filter is used in SDMACE for sharpness enhancement. After modifying all sub-band images, the final image is derived from reconstruction of the sub-band images from lower resolution level to upper resolution level including the residual image. To demonstrate the effectiveness of the algorithm an x-ray of a fuel plate and two mammograms are analyzed. Subjective evaluation is performed to evaluate the effectiveness of the algorithm. The proposed algorithm is compared with the well-known contrast limited adaptive histogram equalization (CLAHE) algorithm. Experimental results prove that the proposed algorithm offers improved contrast of the x-ray images.
A novel x-ray source based on carbon nanotubes (CNTs) field emitters is being developed as an alternative for medical
imaging diagnostic technologies. The design is based on an array of millions of micro sized x-ray sources similar to the
way pixels are arranged in flat panel displays. The trajectory and focusing characteristics of the field emitted electrons,
as well as the x-ray generation characteristics of each one of the proposed micro-sized x-ray tubes are simulated. The
electron field emission is simulated using the OOPIC PRO particle-in-cell code. The x-ray generation is analyzed with
the MCNPX Monte Carlo code. MCNPX is used to optimize both the bremsstrahlung radiation energy spectra and to
verify the angular distribution for 0.25-12 μm thick molybdenum, rhodium and tungsten targets. Also, different
extracting, accelerating and focusing voltages, as well as different focusing structures and geometries of the micro cells
are simulated using the OOPIC Pro particle-in-cell code. The electron trajectories, beam spot sizes, I-V curves,
bremsstrahlung radiation energy spectra, and angular distribution are all analyzed for a given cell. The simulation results
show that micro x-ray cells can be used to generate suitable electron currents using CNT field emitters and strike a thin
tungsten target to produce an adequate bremsstrahlung spectrum. The shape and trajectory of the electron beam was
modified using focusing structures in the microcell. Further modifications to the electron beam are possible and can help
design a better x-ray transmission source.
We fabricated an X-ray beam filter housing which can acquire large-area 2-dimensional images with a designated narrow band X-ray energy which was generated from the wide energy spectrum of the X-ray beam. The filter housing consists of an array of reflectors and each reflector filters the input X-ray energy from an ordinary X-ray tube and passes an X-ray beam of quasi-monochromatic energy. With a precise alignment of the whole reflectors in the filter housing device it is possible to make the total quasi-monochromatic X-ray beams cover a large area for imaging. The substrate of the
reflector itself absorbs some of X-ray photons, which generates shadow of the layers on the image. In order to solve this problem the system was made to rotate around the focal spot of the X-ray tube during the X-ray image acquisition, which resembles the motion of a searchlight, hence there is no blind spot to the X-ray beam. At a preliminary stage we obtained images for a short exposure time of less than 1 second. Representative spectra and full field CDMAM
phantom image of 197 mm × 238 mm acquired from the filter housing rotation method are presented. And the advantage of the monochromatic X-ray against the conventional polychromatic X-ray in terms of contrast is investigated.
For non-uniformity correction a flat field x-ray image is needed, and to obtain it the center of detector is usually aligned with the focal spot of the x-ray tube, which is conserved when examining patients to preserve the flat field. In some of radiographic techniques, however, it is necessary to move the x-ray tube off the center position of detector or tilt the detector. We investigated the effect of X-ray tube positions with respect to detector on the non-uniformity correction, and propose a method to reduce the effect using a new algorithm with computer simulation. Gain images were taken in two SIDs. Pixel values at second SID was calculated using the pixel values at first SID, gain coefficient that represents pixels own unique radiation sensitivity characteristics and the formula based on the solid angle of each detector pixel facing to the x-ray source. Gain coefficient was adjusted using the difference between calculated and real pixel values. Calculation was repeated with new gain coefficient until the gain coefficient was converged into prescribed range. Non-uniformity of blank x-ray images taken with the detector tilted by 0 to 45 degrees was corrected and five ROIs across the image were defined and analyzed. When the proposed algorithm was used for the flat field correction standard deviations of pixel values in the ROIs were reduce to 10% of the cases of usual flat field correction.
KEYWORDS: Cameras, Point spread functions, Device simulation, Medical imaging, Image restoration, Monte Carlo methods, Scattering, Photodetectors, Collimators, Photodiodes
A new gamma camera using a-Si:H photodetectors has been designed for the imaging of heart and other small organs. In this new design the photomultiplier tubes and the position sensing circuitry are replaced by 2D array of a-Si:H p-i-n pixel photodetectors and readout circuitry which are built on a substrate. Without the photomultiplier tubes this camera is light weight, hence can be made portable. To predict the characteristics and the performance of this new gamma camera we did Monte Carlo simulations. In the simulations 128 X 128 imaging array of various pixel sizes were used. 99mTc (140 keV) and 201Tl (70 keV) were used as radiation sources. From the simulations we could obtain the resolution of the camera and the overall system, and the blurring effects due to scattering in the phantom. Using the Wiener filter for image processing, restoration of the blurred image could be achieved. Simulation results of a-Si:H based gamma camera were compared with those of a conventional gamma camera.
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