Scatter is a significant source of image artifacts in wide-cone CT. Scatter management includes both scatter rejection and
scatter correction. The common scatter rejection approach is to use an anti-scatter grid (ASG). Conventional CT
scanners (with detector coverage not exceeding 40mm along the patient axis) typically employ one-dimensional (1D)
ASGs. Such grids are quite effective for small cone angles. For larger cone angles, however, simply increasing the
aspect ratio of a 1D ASG is not sufficient. In addition, a 1D ASG offers no scatter rejection along the patient axis. To
ensure adequate image quality in wide-cone CT, a two-dimensional (2D) ASG is needed.
In this work, we measured the amount of scatter and the degree of image artifacts typically attributable to scatter for four
prototype 2D ASG designs, and we compared those to a 1D ASG. The scatter was measured in terms of the scatter-toprimary
ratio (SPR). The cupping and ghosting artifacts were assessed through quantitative metrics.
For the 2D ASGs, when compared to the 1D ASG, the SPR decreased by up to 66% and 75% for 35cm water and 48cm
polyethylene, respectively, phantoms, at 80-160mm apertures (referenced to isocenter), as measured by the pinhole
method. As measured by the two-aperture method, the SPR reduction was 59%-68% at isocenter for the 35cm water
phantom at 160mm aperture. The cupping artifact was decreased by up to ~80%. The ghosting artifact was reduced as
well. The results of the evaluation clearly demonstrate the advantage of using a 2D ASG for wide-cone CT.
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.
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.
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.
Increasing the spatial resolution of current multislice clinical CT system is always desirable. However, further
resolution improvement by reducing the pixel pitch or the aperture of the detector elements is difficult
because of the tradeoff between the pixel size and dose level. In this paper, we demonstrate a methodology
for improving spatial resolution of a clinical multislice CT without reducing the detector element size. The
flying focal spot (i.e. electron beam wobbling) technique is used to increase the data sampling rate for in-plane (x-y) and z-axis scan acquisitions. In order to reduce the number of focal spot positions to achieve a certain spatial resolution, a super resolution technique using projections onto convex sets (POCS) is applied
here to improve projection raw data sampling with reduced number of focal spot positions. The results indicate that it is possible to significantly increase spatial resolution on current multislice clinical CT systems
without reducing the detector element size. In absence of noise, super resolution algorithms employing iterative regularization, such as POCS, can reduce the required number of focal spot positions. Thus, technical requirements on the multislice CT systems, such as rotation time and number of projections per rotation, can be much relaxed. However, noise reduction methods and methods of reducing projections per rotation, such as compressed sensing, are needed to work with super resolution technique to keep the radiation exposure from exceeding the current limit of clinical multislice CT.
Dual energy computed tomography (CT) has been previously shown to be capable of quantifying iron concentration in a
phantom model. In this work, a commercial three material decomposition algorithm was investigated with the aim of
quantifying iron concentration in vivo with dual energy CT. Iron (III) nitrate solutions of five/seven different
concentrations were placed in syringes of two different cross-sectional areas within anthropomorphic phantoms of three
different sizes and scanned using various x-ray tube potentials and beam filtration levels. A commercial three material
decomposition software package was used to measure iron concentration values in specified regions of interest. These
data were used to assess the effects of tube potential, beam filtration, phantom size, and object size on the ability of dual
energy CT to accurately quantify iron concentration. The object's cross sectional area (diameter of syringe containing
the iron solution) affected the accuracy of the iron quantification, with measurements averaged over a larger region of
interest having improved accuracy. In most cases, the greater spectral separation afforded by the tin filtration improved
the accuracy of the iron quantification. Using the larger syringes (approximately 100 mm2 cross sectional area) and
small phantom size, dual energy CT measurements of the three highest iron concentrations (approximately 10 - 18
mg/ml) had a maximum percent difference from the known value of 21%.
It is of clinical interest to quantify the concentration of materials in a three-component mixture with known chemical
compositions, such as bone-mineral density (BMD) in a trabecular bone composed of calcium hydroxyappitite (CaHA),
yellow- and red-marrow, and iron content in the liver composed of soft tissue, fat, and iron. Both pre- and postreconstruction
dual-energy CT methods have been used to achieve this goal. The
pre-reconstruction method is more
accurate due to the elimination of beam-hardening artifacts. After obtaining the equivalent densities of the two basis
materials, however, it is unclear how to accurately estimate the concentration of each material in the presence of the third
material in the mixture. In this work, we present a pre-reconstruction three-material decomposition method in dualenergy
CT to quantify the concentration of each material in a
three-component mixture with known chemical
compositions. This method employs a specific physical constraint on the equivalent densities of the two basis materials
obtained from the conventional basis-material decomposition. We evaluated this method using simulation studies on two
types of three-component mixtures: bone-water-fat and
Iron-water-CaHA. The results demonstrated that an accurate
estimation of the concentration for each material can be achieved with the proposed method.
In this paper, we demonstrate a methodology for quantitative evaluation of noise reduction algorithms for very low-dose
(1/10th typical dose) renal CT perfusion imaging. Three types of noise reduction algorithms are evaluated, including the
commonly used low pass filtering, edge-preserving algorithms, and spatial-temporal filtering algorithms, such as
recently introduced local highly constrained back projection (HYPR-LR) technique and multi-band filtering (MBF). The
performance of these noise reduction methods was evaluated in terms of background signal-to-noise ratio (SNR), spatial
resolution, fidelity of the time-attenuation curves of renal cortex, and computational speed. The spatial resolution was
quantified by an on-scene modulation transfer function (MTF) measurement method. The fidelity of time-attenuation
curves was quantified by statistical analysis using a Chi-square test. The results indicate that algorithms employing
spatial-temporal correlations of images, such as HYPR and MBF, can achieve spatial resolution similar to the images
acquired using routine dose levels. Edge-preserving algorithms, such as anisotropic diffusion and bilateral filtering, also
show good performance in terms of background SNR and spatial resolution, but they are rather slow compared to HYPR
and MBF. However, edge-preserving algorithms can be applied in the situations where images do not have strong
spatial-temporal correlation. Finally, all the noise reduction algorithms show a high fidelity of the time-attenuation
curves, which can be explained by a strong iodine attenuation signal in the highly perfused kidney.
KEYWORDS: Iron, X-ray computed tomography, Chemical elements, Liver, X-rays, Signal attenuation, Mass attenuation coefficient, Tissues, Magnesium, In vivo imaging
Dual-energy x-ray material decomposition has been proposed as a noninvasive quantitative imaging technique for more
than 20 years. In this paper, we summarize previously developed dual-energy material decomposition methods and
propose a simple yet accurate method for quantitatively measuring chemical composition in vivo. In order to take
advantage of the newly developed dual-source CT, the proposed method is based upon post reconstruction (image space)
data. Different from other post reconstruction methods, this method is designed to directly measure element composition
(mass fraction) in a tissue by a simple table lookup procedure. The method has been tested in phantom studies and also
applied to a clinical case. The results showed that this method is capable of accurately measuring elemental
concentrations, such as iron in tissue, under low noise imaging conditions. The advantage of this method lies in its
simplicity and fast processing times. We believe that this method can be applied clinically to measure the mass fraction
of any chemical element in a two-material object, such as to quantify the iron overload in the liver (hemochromatosis).
Further investigations on de-noising techniques, as well as clinical validation, are merited.
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