Multiple studies in the literature have proposed diagnostic thresholds based on Multi-Energy Computed Tomography (MECT) iodine maps. However, it is critical to determine the minimum detectable iodine concentration for MECT systems to assure the clinical accuracy for various measured concentrations for these image types. In this study, seven serial dilutions of iohexol were made with concentrations from 0.03 to 2.0 mg Iodine/mL in 50 mL centrifuge tubes. The dilutions and one blank vial were scanned five times each in two scatter conditions: within a 20.0 cm diameter (Head) phantom, and a 30.0 cm x 40.0 cm elliptical (Body) phantom. This was repeated on a total of six scanners from three vendors: fast-kVp switching, dual-source dual-energy CT, dual-layer detector CT, and split-filter CT. Scan parameters and dose were matched as closely as possible across systems, and iodine maps were reconstructed. Regions-of-Interest (ROIs) were placed on 5 consecutive images within each vial, for a total of 25 measurements per sample. The mean and standard deviation were calculated for each sample. The Limit of Detection (LOD) was defined as the concentration that had a 95% chance of having a signal above the 95% confidence interval of the measured blank samples. The range of LODs was 0.021 – 0.484 mg I/mL in the head phantom and 0.125 – 0.547 mg I/mL in the body phantom. The LOD for iodinated contrast using MECT systems changed with scatter and attenuation conditions. The limit of detection for all conditions was under 0.5 mg Iodine/mL.
Pregnant women with shortness of breath are increasingly referred for CT Angiography to rule out Pulmonary Embolism (PE). While this exam is typically focused on the lungs, extending scan boundaries and overscan can add to the irradiated volume and have implications on fetal dose. The purpose of this work was to estimate radiation dose to the fetus when various levels of overscan were encountered.
Two voxelized models of pregnant patients derived from actual patient anatomy were created based on image data. The models represent an early (< 7 weeks) and late term pregnancy (36 weeks). A previously validated Monte Carlo model of an MDCT scanner was used that takes into account physical details of the scanner. Simulated helical scans used 120 kVp, 4x5 mm beam collimation, pitch 1, and varying beam-off locations (edge of the irradiated volume) were used to represent different protocols plus overscan. Normalized dose (mGy/100mAs) was calculated for each fetus.
For the early term and the late term pregnancy models, fetal dose estimates for a standard thoracic PE exam were estimated to be 0.05 and 0.3 mGy/100mAs, respectively, increasing to 9 mGy/100mAs when the beam-off location was extended to encompass the fetus.
When performing PE exams to rule out PE in pregnant patients, the beam-off location may have a large effect on fetal dose, especially for late term pregnancies. Careful consideration of ending location of the x-ray beam - and not the end of image data - could result in significant reduction in radiation dose to the fetus.
We analyze localized textural consistencies in high-resolution Micro CT scans of coronary arteries to identify the appearance of diagnostically relevant changes in tissue. For the efficient and accurate processing of CT volume data, we use fast algorithms associated with three-dimensional so-called isotropic multiresolution wavelets that implement a redundant, frame-based image encoding without directional preference. Our algorithm identifies textural consistencies by correlating coefficients in the wavelet representation.
Multidetector CT (MDCT) systems offer larger coverage and wider z-axis beams, resulting in larger cone angles. One impact on radiation dose is that while radiation profiles at isocenter are constant when contiguous axial scans are performed, the increased beam divergence from the larger cone angle results in significant surface dose variation. The purpose of this work was to measure the magnitude of this effect. Contiguous axial scans were acquired using an MDCT for two sizes of cylindrical phantoms and an anthropomorphic phantom. Film dosimetry and/or radiation detector measurements were performed on the surface of each phantom. Detailed mathematical models were developed for the MDCT scanner and all phantoms. Monte Carlo simulations of contiguous axial scans were performed for each phantom model. From cylindrical phantoms, film dosimetry at the surface showed differences between peak and valley that reached 50%. From the anthropomorphic phantom, measured values ranged from 7.9 to 16.2 mGy at the phantom surface. Monte Carlo simulations demonstrated these variations in both cylindrical and anthropomorphic phantoms. The magnitude of variation was also related to object size. Even when contiguous axial scans are performed on MDCT, surface radiation profiles show considerable variation. This variation will increase as MDCT cone angles increase and when non-contiguous scans (e.g. pitch > 1) are acquired. The variation is also a function of object size. While average surface doses may remain constant, peak doses may increase, which may be significant for radiation sensitive organs at or near the surface (e.g. breast, thyroid).
In this study we developed a new reconstruction kernel specifically for chest CT imaging. An experimental flat-panel CT scanner was used on large dogs to produce 'ground-truth’ reference chest CT images. These dogs were also examined using a clinical 16-slice CT scanner. We concluded from the dog images acquired on the clinical scanner that the loss of subtle lung structures was due mostly to the presence of the background noise texture when using currently available reconstruction kernels. This qualitative evaluation of the dog CT images prompted the design of a new recon kernel. This new kernel consisted of the combination of a low-pass and a high-pass kernel to produce a new reconstruction kernel, called the 'Hybrid’ kernel. The performance of this Hybrid kernel fell between the two kernels on which it was based, as expected. This Hybrid kernel was also applied to a set of 50 patient data sets; the analysis of these clinical images is underway. We are hopeful that this Hybrid kernel will produce clinical images with an acceptable tradeoff of lung detail, reliable HU, and image noise.
We have been acquiring respiratory-gated micro-CT images of live mice and rats for over a year with our General Electric (formerly Enhanced Vision Systems) hybrid scanner. This technique is especially well suited for the lung due to the inherent high tissue contrast. Our current studies focus on the assessment of lung tumors and their response to experimental agents, and the assessment of lung damage due to chemotherapy agents. We have recently installed a custom-built dual flat-panel cone-beam CT scanner with the ability to scan laboratory animals that vary in size from mice to large dogs. A breath-hold technique is used in place of respiratory gating on this scanner. The objective of this pilot study was to converge on scan acquisition parameters and optimize the visualization of lung damage in a mouse model of fibrosis. Example images from both the micro-CT scanner and the flat-panel CT scanner will be presented, as well as preliminary data describing spatial resolution, low contrast resolution, and radiation dose parameters.
One aspect of image quality that should be considered when migrating scan protocols from single-slice helical CT (SSCT) to multi-slice CT (MSCT) is z-axis high-contrast resolution. The aim of this study was to compare z-axis high-contrast resolution of MSCT with that of a similarly designed SSCT for various combinations of slice thickness and pitch. A point response phantom was used to acquire slice sensitivity profiles (SSPs) and calculate z-axis resolution (10% of MTF). Additionally, a resolution pattern phantom was used to subjectively evaluate limiting z-axis resolution. Both analytical and subjective results revealed that the SSCT had higher z-axis resolution than the MSCT for nominal 5 mm slice thickness (at comparable pitches). However, for nominal 10 mm slice thickness the MSCT demonstrated z-axis resolution that was comparable or superior to SSCT. Additionally, notable differences in the shape of the SSP for axial scans were observed on the MSCT unit due to the presence of detector septa. Several conclusions can be drawn from these results including: (1) z-axis resolution is not necessarily 'better' for MSCT and should be evaluated prior to transferring scan protocols from single- to multi-slice CT, and (2) a simple acrylic plate resolution phantom may be used to quickly and effectively evaluate z-axis resolution.
Three-dimensional tomographic data sets are routinely produced in CT and MRI studies. Particularly good quality sagittal and coronal views can be obtained when the z-slice thickness is similar to the x and y pixel size within the original transverse views. When image data has been acquired on the same subject at two separate occasions, it may be useful or necessary to rotate and translate the data from the second study so that it is spacially aligned with the first study. We have developed interactive graphic software to interpolate image files in three orthogonal planes which can be arbitrarily oriented and to align the data from two studies using subtraction views as an indicator of alignment and differential value. The design elements for this software are described in this paper. Two thin slice x-ray CT studies from the same subject are used to illustrate the software.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.