Journal of X-Ray Science and Technology - Volume 20, issue 4
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Journal of X-Ray Science and Technology is an international journal designed for the diverse community (biomedical, industrial and academic) of users and developers of novel x-ray imaging techniques. The purpose of the journal is to provide clear and full coverage of new developments and applications in the field.
Areas such as x-ray microlithography, x-ray astronomy and medical x-ray imaging as well as new technologies arising from fields traditionally considered unrelated to x rays (semiconductor processing, accelerator technology, ionizing and non-ionizing medical diagnostic and therapeutic modalities, etc.) present opportunities for research that can meet new challenges as they arise.
Abstract: With increasing popularity and complexity of intensity-modulated radiation therapy (IMRT) delivery modalities including regular and arc therapies, there is a growing challenge for validating the accuracy of dose distributions. Gafchromic films have superior characteristics for dose verification over other conventional dosimeters. In order to optimize the use of Gafchromic films in clinical IMRT quality assurance procedures, the scanning parameters of EBT and EBT2 films with a flatbed scanner were investigated. The effects…of several parameters including scanning position, orientation, uniformity, film sensitivity and optical density (OD) growth after irradiation were quantified. The profiles of the EBT and EBT2 films had a noise level of 0.6% and 0.7%, respectively. Considerable orientation dependence was observed and the scanner value difference between landscape and portrait modes were about 12% and 10% for EBT and EBT2 films, respectively. The highest response sensitivity was observed using digitized red color images of the EBT2 film scanned with landscape mode. The total system non-uniformity composed of contributions from the film and the scanner was less than 1.7%. OD variations showed that EBT gray scale grew slower, however, reached higher growth values of 15% when compared with EBT2 gray scale which grew 12% after a long time (480 hours) post-irradiation. The EBT film using the red color channel showed the minimal growth where OD increased up to 3% within 3 days after irradiation, and took one week to stabilize.
Keywords: EBT Gafchromic film, film sensitivity, non-uniformity, orientation, optical density growth
Abstract: Future generations of CT systems would need a mean to cover an entire organ in a single rotation. A way to accomplish this is to physically increase detector size to provide, e.g., 120∼160 mm z (head-foot) coverage at iso-center. The x-ray cone angle of such a system is usually 3∼4 times of that of a 64-slice (40 mm) system, which leads to more severe cone beam artifacts in cardiac scans. In addition, the extreme x-ray take-off angles for…such a system cause severe heel effect, which would require an increase in anode target angle to compensate for it. One shortcoming of larger target angle is that tube output likely decreases because of shorter thermal length. This would result in an increase of image noise. Our goal is to understand from a physics and math point of view, what is the theoretical entitlement of artifacts, resolution, and noise impact of such a system. The image artifacts are assessed through computer simulation of a helical body phantom and visual comparison of reconstructed images between a 140 mm system and a 64-slice system. The IQ impact from target angle increase is studied analytically and experimentally by first finding the proper range of target angles that give the acceptable heel effect, then estimating the impact on peak power (flux) and z resolution using an empirical model of heel effect for given target angle and analytical models of z resolution and tube current loading factor for given target thermal length. The results show that, for a 140 mm system, 24.5% of imaging volume exhibits more severe cone beam artifacts than a 64-slice system, which also poses a patient dose concern. In addition, this system may suffer from a 36% peak power (flux) loss, which is equivalent to about 20% image noise increase. Therefore, a wide coverage CT system using a single x-ray source is likely to face some severe challenges in IQ and clinical accuracy.
Abstract: Purposes: Interior tomography problem can be solved using the so-called differentiated backprojection-projection onto convex sets (DBP-POCS) method, which requires a priori knowledge within a small area interior to the region of interest (ROI) to be imaged. In theory, the small area wherein the a priori knowledge is required can be in any shape, but most of the existing implementations carry out the Hilbert filtering either horizontally or vertically, leading to a vertical or horizontal strip that…may be across a large area in the object. In this work, we implement a practical DBP-POCS method with radial Hilbert filtering and thus the small area with the a priori knowledge can be roughly round (e.g., a sinus or ventricles among other anatomic cavities in human or animal body). We also conduct an experimental evaluation to verify the performance of this practical implementation. Methods: We specifically re-derive the reconstruction formula in the DBP-POCS fashion with radial Hilbert filtering to assure that only a small round area with the a priori knowledge be needed (namely radial DBP-POCS method henceforth). The performance of the practical DBP-POCS method with radial Hilbert filtering and a priori knowledge in a small round area is evaluated with projection data of the standard and modified Shepp-Logan phantoms simulated by computer, followed by a verification using real projection data acquired by a computed tomography (CT) scanner. Results: The preliminary performance study shows that, if a priori knowledge in a small round area is available, the radial DBP-POCS method can solve the interior tomography problem in a more practical way at high accuracy. Conclusions: In comparison to the implementations of DBP-POCS method demanding the a priori knowledge in horizontal or vertical strip, the radial DBP-POCS method requires the a priori knowledge within a small round area only. Such a relaxed requirement on the availability of a priori knowledge can be readily met in practice, because a variety of small round areas (e.g., air-filled sinuses or fluid-filled ventricles among other anatomic cavities) exist in human or animal body. Therefore, the radial DBP-POCS method with a priori knowledge in a small round area is more feasible in clinical and preclinical practice.
Abstract: In this paper, we study a new type of high order interior problems characterized by high order differential phase shift measurement. This problem is encountered in local x-ray phase-contrast tomography. Here we extend our previous theoretical framework from interior CT to interior differential phase-contrast tomography, and establish the solution uniqueness in this context. We employ the analytic continuation method and high order total variation minimization which we developed in our previous work for interior CT,…and prove that an image in a region of interest (ROI) can be uniquely reconstructed from truncated high order differential projection data if the image is known a priori in a sub-region of the ROI or the image is piecewise polynomial in the ROI. Preliminary numerical experiments support the theoretical finding.
Keywords: High order interior problem, ambiguity image, analytic function, high order total variation
Abstract: In order to evaluate the capacity of T1ρ-MRI(Magnetic Resonance Imaging) technique in distinguishing a four-layered zonal structure of articular cartilage for detecting the early-onset osteoarthritis (OA), eight 3-month-old female Danish landrace pigs, weighing 45.3 ± 5.5 kg, were used in this study. Two hind knees were randomly divided into two groups. IL-1β was injected into articular cavities in one group while physiological saline into another as a control one. Six hours later, the patellae were obtained…for T1ρ-MRI and histological examination to distinguish the four-layered zonal structure of articular cartilages. The thickness of each layer and their percentages in the entire cartilage were measured on both T1ρ-MR images and the histological slices. T1ρ values of every layer were calculated from T1ρ-mapping images. In the result, the four-layered zonal structure of articular cartilage was displayed on both T1ρ-MR images and the histological slices. The ICC between these two methods was 0.981 for single measures (P=0.001), and 0.990 for average measures (P = 0.001). Compared with control patellae, T1ρ values significantly increased on the superficial and calcified layers in the IL-1β treated patellae (P=0.037). Therefore, this study demonstrates that the four-layered zonal structure of the articular cartilage is visibly displayed on the T1ρ-MR images. T1ρ-MRI technique can detect the earliest event of cartilage degeneration while these measurable changes are not shown in the histological slices. It is possible to use this technique for observing the effects of early interventions on the early-onset OA.
Abstract: The power and flexibility of polynomial surfaces are unleashed when their degrees are no longer restricted to four or lower, as they are used in early CT phantoms. They have proved useful and appropriate for geometric simulation of human and animal anatomy. In this paper a general algorithm is presented for the x-ray transform of any polynomial surface, as long as its ray-surface intersection equation is implemented on the computer. A versatile and powerful polynomial…utility C++ class is created to simplify the implementation. Three groups of surfaces are implemented and applied to build a heart phantom closely simulating the Visible Man's heart. The x-ray transform algorithm is tested and verified by the successful reconstruction of the heart phantom.
Abstract: The combined system of micro-CT and fluorescence molecular tomography (FMT) offers a new tool to provide anatomical and functional information of small animals in a single study. To take advantages of the combined system, a data preprocessing method is proposed to extract the valid data for FMT reconstruction algorithms using a priori information provided by CT. The boundary information of the animal and animal holder is extracted from reconstructed CT volume data. A ray tracing method…is used to trace the path of the excitation beam, calculate the locations and directions of the optional sources and determine whether the optional sources are valid. To accurately calculate the projections of the detectors on optical images and judge their validity, a combination of perspective projection and inverse ray tracing method are adopted to offer optimal performance. The imaging performance of the combined system with the presented method is validated through experimental rat imaging.
Keywords: Micro-CT, fluorescence molecular tomography, multi-modal imaging, data preprocessing
Abstract: Background and purpose: Computational fluid dynamics method (CFDM) and optical flow method (OFM) effectively provide the hemodynamic information based on the digital subtraction angiogram (DSA). However, the quantitative analysis in comparison of CFDM and OFM is still absent. The goal of this study is to apply CFDM and OFM in quantitative analysis of stenting treatment. Material and method: A left carotid stenosis patient underwent stenting of percutaneous transluminal angioplasty was analyzed as an example.…CFDM and OFM for hemodynamic analysis on digital subtraction angiography before and after stenting treatment were presented. Results: Improvement gains of blood flow velocities on left internal carotid artery after stenting treament for different initial conditions on the common carotid artery were 1.91 ∼ 2.13, 1.62 ∼ 2.09, and 0.69 by CFDM with Newtonian and non-Newtonian fluids and OFM, respectively. With the CFDM analysis, the flow mapping by OFM using time resolved DSA data on the fly to estimate hemodynamic significance of a cervical carotid stenosis was explained. Conclusion: Quantificative blood flow estimations by CFDM and OFM to evaluate the treatment outcomes to patient with carotid stenosis are practical. Both methods are able to provide quantitative information of blood flow for stenting treatment. It is advantagious to use both methods in treatment evaluation.
Abstract: Purpose: The purpose of this study was to investigate the value of spectral CT monoenergetic imaging for detecting hemoglobin levels. Material and methods: Sixty-five hospitalized patients received chest non-contrast CT scan in gemstone spectral imaging (GSI) mode on a GE Discovery CT750 HD. This study was approved by the hospital ethics committee and informed consent was signed by every patient. Raw data were reconstructed at 1.25 mm and then transferred to a AW4.4 workstation. The CT value of the…ascending aorta at 40 keV∼140 keV was measured under GSI viewer of AW4.4. Hemoglobin contents were measured biochemically within 24 hrs after CT scan. The SPSS 16.0 software package was used to analyze the correlation between the obtained CT value and hemoglobin level. Results: At 40 keV ∼ 100 keV, the CT value decreased followed by the increase of keV and gradually stabilized at 100 keV ∼ 140 keV with an amplitude variation of 10 HU. The CT values measured at 40 keV ∼ 140 keV were well correlated with hemoglobin levels. The optimal correlation was observed at the monoenergetic level of 70 keV (r=0.633, p=0.000). The relationship between CT value and hemoglobin content could be expressed as CT value=13.015+0.245 × hemoglobin content. At 40 keV ∼ 140 keV, there is strong linear correlation between the CT value of the ascending aorta and hemoglobin content. The optimal linear relationship was observed at 70 keV. Conclusion: Spectral CT monoenergetic imaging can be applied for quantitative determination of hemoglobin content within a specified area of the circulatory system.
Keywords: Poly-energetic imaging, monoenergetic imaging, energy spectrum scan, hemoglobin
Abstract: The qualitative and quantitative analyses of crystalluria have clinical significance in the diagnosis and prognosis of urolithiasis. The aim of this paper is to provide a new accurate methodology to get qualitative and quantitative data on urine particulate in patients with renal stone disease. The procedure involves a urine collection, the separation of the solid residual by centrifugation, and its analysis by X-ray diffraction, utilizing a micro-diffractometer in order to analyze very low amounts of residual. The…spectrum obtained was converted into 2 � –I profiles and quantitatively refined by Rietveld method. The proposed methodology has the advantage to accurately quantify all crystalline phases and the amorphous component of the urine; anyway urine samples have to be centrifuged and analysed as soon as possible, because the quantitative results obtained by the X-ray microdiffraction showed that after some days and at room temperature urine increased significantly both amorphous and crystalline phases.