Current Computed Tomography Scanners Research Articles

Non-destructive exploration of late Gothic panel painting using X-ray tomography and flattening of the reconstructed data

The use of computed tomography (CT) for studying artwork has a long tradition in the restoration and care of collections in memory institutions. The result of the related tomographic reconstruction is a virtual spatial model in which we can examine the production technology, the internal structure, various damaged areas, and previous restoration interventions. The extension of standard CT to dual energy CT provides additional information to help distinguish materials with similar densities but different chemical compositions. As will be shown, pigment differences that appear very similar in optical light can be identified in this way. The differences found were confirmed by X-ray fluorescence and Raman spectroscopy analytical techniques. Current laboratory CT scanners make it possible to examine the layered structures of paintings and polychrome sculptures. In the case of wood panel paintings, however, we are faced with the common deformation of the panels. So, when examining the CT data, we can only see a small section of the paint layer, and it is difficult to examine the whole artwork in its entire context. This disadvantage can be solved by a virtual straightening of the panel, as will be demonstrated.

Comparative analysis of patient scatter to phantom scatter for computed tomography systems.

Current computed tomography (CT) shielding practices are largely based on calculations of scattered radiation emitted from an acrylic head or body phantom, such as the Computed Tomography Dose Index (CTDI) phantom, or anthropomorphic phantoms of these two anatomical categories. This report considers the difference in scattered air kerma or dose from phantom models, to actual patient scatter under a variety of clinical scan conditions. Empirical patient scatter measurements recorded at different positions around the gantry, for 3 different CT scanners, resulted in average patient scatter fractions per unit Dose Length Product (DLP: mGycm) at 1m from the isocentre of 0.09 ± 0.03 and 0.17 ± 0.04 µGy (mGycm)-1 for head and body scans respectively. For the purposes of shielding design and scattered dose estimates to staff it is recommended that a single standard deviation be applied to these averages in the continued interest of conservatism. These values are reasonably comparative to the widely published scatter fractions by the National Council of Radiological Protection using the CTDI phantom, and the British Institute of Radiology using head and body anthropomorphic phantoms.

Role of Computed Tomography in Pre- and Postoperative Evaluation of a Double-Outlet Right Ventricle.

Double-outlet right ventricle (DORV) is a type of ventriculoarterial connection in which both great arteries arise entirely or predominantly from the right ventricle. The morphology of DORV is characterized by a ventricular septal defect (location and relationship with the semilunar valve); bilateral coni and aortomitral continuity; the presence or absence of outflow tract obstruction; tricuspid-pulmonary annular distance; and associated cardiac anomalies. The surgical approach varies with the type of DORV and is based on multiple variables. Computed tomography (CT) is a robust diagnostic tool for the preoperative and postoperative assessment of DORV. Unlike echocardiography and magnetic resonance imaging (MRI), CT imaging is not limited by small acoustic window, need for anaesthesia and can be used in patients with metallic implants. Current generations CT scanners with high spatial and temporal resolution, wide detectors, high-pitch scanning mode, dose-reduction algorithms, and advanced three-dimensional post-processing tools provide a low-risk, high-quality alternative to diagnostic cardiac catheterization or MRI, and have been increasingly utilized in nearly every type of congenital heart defect, including DORV.

Optimal Imaging at the Primary Stroke Center.

Optimal Imaging at the Primary Stroke Center.

An additional tilted-scan-based CT metal-artifact-reduction method for radiation therapy planning.

PurposeAs computed tomography (CT) imaging is the most commonly used modality for treatment planning in radiation therapy, metal artifacts in the planning CT images may complicate the target delineation and reduce the dose calculation accuracy. Although current CT scanners do provide certain correction steps, it is a common understanding that there is not a universal solution yet to the metal artifact reduction (MAR) in general. Particularly noting the importance of MAR for radiation treatment planning, we propose a novel MAR method in this work that recruits an additional tilted CT scan and synthesizes nearly metal‐artifact‐free CT images.MethodsThe proposed method is based on the facts that the most pronounced metal artifacts in CT images show up along the x‐ray beam direction traversing multiple metallic objects and that a tilted CT scan can provide complementary information free of such metal artifacts in the earlier scan. Although the tilted CT scan would contain its own metal artifacts in the images, the artifacts may manifest in a different fashion leaving a chance to concatenate the two CT images with the metal artifacts much suppressed. We developed an image processing technique that uses the structural similarity (SSIM) for suppressing the metal artifacts. On top of the additional scan, we proposed to use an existing MAR method for each scan if necessary to further suppress the metal artifacts.ResultsThe proposed method was validated by a simulation study using the pelvic region of an XCAT numerical phantom and also by an experimental study using the head part of the Rando phantom. The proposed method was found to effectively reduce the metal artifacts. Quantitative analyses revealed that the proposed method reduced the mean absolute percentages of the error by up to 86% and 89% in the simulation and experimental studies, respectively.ConclusionsIt was confirmed that the proposed method, using complementary information acquired from an additional tilted CT scan, can provide nearly metal‐artifact‐free images for the treatment planning.

Evaluation of the BreastSimulator software platform for breast tomography

The aim of this work was the evaluation of the software BreastSimulator, a breast x-ray imaging simulation software, as a tool for the creation of 3D uncompressed breast digital models and for the simulation and the optimization of computed tomography (CT) scanners dedicated to the breast. Eight 3D digital breast phantoms were created with glandular fractions in the range 10%–35%. The models are characterised by different sizes and modelled realistic anatomical features. X-ray CT projections were simulated for a dedicated cone-beam CT scanner and reconstructed with the FDK algorithm. X-ray projection images were simulated for 5 mono-energetic (27, 32, 35, 43 and 51 keV) and 3 poly-energetic x-ray spectra typically employed in current CT scanners dedicated to the breast (49, 60, or 80 kVp). Clinical CT images acquired from two different clinical breast CT scanners were used for comparison purposes. The quantitative evaluation included calculation of the power-law exponent, β, from simulated and real breast tomograms, based on the power spectrum fitted with a function of the spatial frequency, f, of the form S(f) = α/f β. The breast models were validated by comparison against clinical breast CT and published data. We found that the calculated β coefficients were close to that of clinical CT data from a dedicated breast CT scanner and reported data in the literature. In evaluating the software package BreastSimulator to generate breast models suitable for use with breast CT imaging, we found that the breast phantoms produced with the software tool can reproduce the anatomical structure of real breasts, as evaluated by calculating the β exponent from the power spectral analysis of simulated images. As such, this research tool might contribute considerably to the further development, testing and optimisation of breast CT imaging techniques.

X-ray-computed tomography contrast agents.

X-ray-computed tomography contrast agents.

Quantification of Vasa Vasorum Density in Multi-Slice Computed Tomographic Coronary Angiograms

This study is motivated by the possibility of using computed tomography (CT) to detect early coronary atherosclerosis by the increased CT values within the arterial wall resulting from vasa vasorum proliferation. Coronary arteries (n = 5) with early atherosclerotic changes were injected with Microfil and scanned (micro-CT). Noise was added to the CT projection data sets (to represent the radiation exposure of current clinical CT scanners) and then reconstructed to generate 3-dimensional images at different voxel sizes. Higher CT values were detected because of contrast agent in vasa vasorum if voxel size was less than (150 microm)(3). Contrast in the main lumen increased the CT values dramatically at voxels greater than (100 microm)(3), whereas CT values of the same specimen without contrast in the main lumen remained constant. Voxel sizes less than (200 microm)(3) are needed to quantitate arterial wall opacification due to vasa vasorum proliferation.

Radiation Dose Issues in Longitudinal Studies Involving Computed Tomography

Computed tomography (CT) examinations are increasingly used for clinical diagnostic and research purposes, as they provide in vivo anatomic information similar to that provided by gross anatomy. In conjunction with physiologic maneuvers or contrast media, CT may also provide in vivo physiologic information. Using calibrated acquisition protocols, accurate noninvasive measurements of tissue density, air volume, blood volume, and capillary perfusion can be performed. Serial CT scans can provide longitudinal measurements indicative of disease progression or regression, allowing noninvasive assessment of treatment effects. However, the X-ray radiation associated with CT has been associated with a small but significant increased risk of malignancy, which may be fatal. Large studies have detected this small risk, which appears to be related to the cumulative radiation dose of all previous exposures in a linear fashion. It has been shown that the risk from a given radiation exposure is greater in young people and females compared with older males. The combination of these two risk-enhancing factors, found in pregnant females, provides the greatest risk. Radiation risk decreases with increasing age for both men and women, asymptotically approaching zero. Radiation risk can be calculated using dose metrics provided on current CT scanners as outlined in this article. Ethically, given that radiation is associated with measurable risk, clinically indicated and research CT examinations must provide an increase in knowledge that has substantial benefit to the subject. This benefit should be related to the potential of saving of life or to the prevention or mitigation of serious disease.

Investigations on an isolated skull with gunshot wounds using flat-panel CT

The use of computed tomography (CT) scanners is rapidly becoming established in forensic medicine. Current multislice CT (MSCT) scanners attain a resolution of 0.42 mm. An isolated skull with gunshot injuries was examined with a high-resolution eXplore Locus Ultra flat-panel CT (eLU-CT) and MSCT. Structures and minute fissures in the bone interior, which were neither visible macroscopically nor with the MSCT data, could be imaged with the eLU-CT data. In addition, a tiny interior impact defect from a retained missile could be detected by eLU-CT, which clearly aided the reconstruction of the gunshots in this case.

Multidetector CT for Visualization of Coronary Stents

Whereas the clinical diagnosis of in-stent thrombosis is straightforward, that of in-stent restenosis remains a problem, because although many patients experience chest pain after coronary stent placement, that symptom is secondary to ischemia in only a few. The use of a noninvasive technique to identify such patients for early invasive intervention versus more conservative management is thus highly desirable. Multidetector computed tomography (CT) performed with 16-section scanners recently emerged as such a technique and has overtaken modalities such as electron-beam CT and magnetic resonance imaging as an alternative to conventional angiography for the assessment of in-stent restenosis. The improved hardware design of the current 64-section CT scanners allows even better delineation of stent struts and lumen. The more reliable criterion of direct lumen visualization thus may be substituted for the presence of distal runoff, which lacks specificity for a determination of in-stent patency because of the possibility of collateral pathways. However, the capability to accurately visualize the in-stent lumen depends partly on knowledge of the causes of artifacts and how they can be compensated for with postprocessing and proper image display settings. In addition, an understanding of the major stent placement techniques used in the treatment of lesions at arterial bifurcations is helpful.

Organ and effective dose evaluation in diagnostic radiology based on in-phantom dose measurements with novel photodiode-dosemeters

Organ and the effective doses of patients undergoing clinical X ray examinations of chest and abdomen were evaluated with an anthropomorphic phantom and a new dosimetry system. The system was comprised of 34 pin photodiode dosemeters placed in/on particular tissues or organs of the anthropomorphic phantom, where the tissues and organs are defined by the International Commission on Radiological Protection (ICRP) to estimate the effective doses. Dosemeter signals were acquired on a personal computer directly, and converted into absorbed doses, from which the organ and the effective doses were evaluated on the computer. Our study showed that organ doses ranged from <0.01 to 0.72 mGy in routine X-ray radiography of chest and of abdomen and from 0.07 to 55.91 mGy in routine computed tomography (CT) examinations with current multi-slice CT scanners. The effective dose observed in the chest CT examination was approximately 300 times higher than that in chest radiography.

Performance evaluation of an 85-cm-bore X-ray computed tomography scanner designed for radiation oncology and comparison with current diagnostic CT scanners

Introduction: The demand for computed tomography (CT) virtual simulation is constantly increasing with the wider adoption of three-dimensional conformal and intensity-modulated radiation therapy. Virtual simulation CT studies are typically acquired on conventional diagnostic scanners equipped with an external patient positioning laser system and specialized planning and visualization software. Virtual simulation technology has matured to a point where conventional simulators may be replaced with CT scanners. However, diagnostic CT scanner gantry bores (typically 65–70 cm) can present an obstacle to the CT simulation process by limiting patient positions, compared to those that can be attained in a conventional simulator. For example, breast cancer patients cannot always be scanned in the treatment position without compromising reproducibility and appropriateness of setup. Extremely large patients or patients requiring special immobilization or large setup devices are often unable to enter the limited-bore gantry. A dedicated 85-cm-bore radiation oncology CT scanner has the potential to eliminate these problems. The scanner should provide diagnostic-quality images at diagnostic-comparable dose levels. The purpose of this study was to independently evaluate the performance of a novel 85-cm-bore CT X-ray scanner designed specifically for radiation oncology and compare it against diagnostic-type, 70-cm-bore scanners that may be used in the same setting.Methods and Materials: We performed image quality and dosimetric measurements on an 85-cm-bore CT scanner (AcQSim CT, Marconi Medical Systems, Inc., Cleveland, OH) and a 70-cm-bore, diagnostic-type scanner (UltraZ CT, Marconi Medical Systems, Inc.). Image quality measurements were performed using a manufacturer-supplied phantom (Performance Phantom, Marconi Medical Systems, Inc.), following the manufacturer’s suggested testing procedures, and an independent image quality phantom (CATPHAN 500, The Phantom Laboratory, New York, NY). The standard image quality parameters evaluated for the purpose of comparison were as follows: slice thickness accuracy, high-contrast resolution (limiting spatial resolution), low-contrast resolution, uniformity and noise, and CT number accuracy and linearity. Standard head and body protocols were employed throughout most of our measurements and were kept equal between the two scanners. The computed tomography dose index was measured for standard head and body imaging protocols using accepted methods and procedures. For comparison purposes, data for a diagnostic-type, 70-cm-bore scanner (GE HighSpeed CT/i) were extracted from the literature. The results obtained for the 85-cm-bore scanner are compared with the following: (1) manufacturer-provided autoperformance phantom test results (validating its use for routine quality assurance), (2) a similar set of measurements performed on a conventional 70-cm-bore, diagnostic-type CT scanner (UltraZ CT, Marconi Medical Systems, Inc.), and (3) current available data on other diagnostic-type CT scanners (GE HighSpeed CT/i).Results: Head and body doses seem on average to be slightly (1–2 cGy) higher for the 85-cm-bore unit than for conventional 70-cm units. Measured slice thickness was within acceptable criteria, ±0.5 mm. There does not seem to be any significant difference in high-contrast resolution. Both units render a limiting value of ∼7–8 lp/cm for slice thickness 8–10 mm. Both units exhibit comparable CT number uniformity, accuracy, and linearity. Noise levels seem to be slightly increased (by ∼0.05–0.2%) for the large-bore geometry. Low-contrast resolution for both units was comparable (4.5–5.5 mm @ 0.35%). All image quality parameters are well within diagnostic acceptable levels.Conclusion: The overall imaging performance and mechanical integrity of the 85-cm-bore scanner are comparable to those of conventional diagnostic scanners that may be employed in a radiation oncology setting.

ORBITAL IMAGING: A Comparison of Computed Tomography and Magnetic Resonance Imaging

Advances in radiologic imaging over the past 20 to 30 years have revolutionized the diagnosis of orbital pathology. The plain film used to be the main radiologic tool; it now has limited use. Computed tomography (CT) and magnetic resonance (MR) imaging both offer excellent resolution of orbital tissues. The current CT scanners have better spatial resolution with lower noise, shorter scanning times with reduced radiation exposure, better reconstruction algorithms, and the capability of generating thinner sections. 26,31 MR imaging technology has also improved, allowing for better resolution from the use of surface and head coils. Ultrasonography offers a readily available, inexpensive alternative. The advent of color Doppler imaging gives a dynamic view of blood flow through the orbit. The dilemma now is which study to order and exactly how to order it. This article focuses on CT and MR imaging of orbital pathology.

Prospective evaluation of computed tomography and mediastinoscopy in mediastinal lymph node staging.

Precise mediastinal lymph node (LN) staging is imperative in otherwise operable non-small cell lung cancer (NSCLC), as it determines subsequent treatment and possible inclusion in a neoadjuvant trial. The roles of mediastinoscopy and computed tomography (CT) remain controversial. To determine the accuracy of current CT scanners, a prospective study was performed. From April 1993 until September 1995, 100 consecutive patients with NSCLC without distant metastases underwent staging by CT and cervical mediastinoscopy. Naruke's map was used for classification, and LNs larger than 1 cm were considered CT positive. There were 91 males and 9 females, with a mean age of 64 (range 45-82) yrs. Fifty nine tumours were central and 41 peripheral, 64 right-sided and 36 left-sided. Thoracotomy with mediastinal LN sampling was performed in 74 patients, nonoperated patients having multilevel stage IIIA or stage IIIB disease. Twenty five (25%) mediastinoscopies were positive and three were false-negative (3%). There were 29 false-positive CT scans and 12 false-negative. Overall sensitivity and specificity of CT were 63 and 57%, respectively, and of mediastinoscopy 89 and 100%, respectively. Positive and negative predictive values of CT were 41 and 77%, respectively, and of mediastinoscopy 100 and 96%, respectively. Accuracy of CT was 59% and of mediastinoscopy 97%. Accuracy of CT was lowest for left-sided and centrally located tumours, and for LN station 7. Even with current computed tomography scanners, sensitivity and specificity remain low. Although overall cost may increase, routine cervical mediastinoscopy is necessary for precise staging of non-small cell lung cancer, and subcarinal lymph nodes should be routinely sampled.

Monolithically Integrated X-Ray Detector Arrays for Computed Tomography

AbstractThe design and performance of a high sensitivity monolithic X-ray detector array fabricated by depositing CdTe photodiodes on CdWO4 scintillators for computed tomography (CT) are presented. CdTe photodiodes offer improved sensitivity due to the better match to the CdWO4 scintillator emission spectrum than the Si photodiodes used in current CT scanners. A CdTe photodiode fabricated on glass mechanically stacked to a CdWO4 scintillator showed 30% improvement in signal strength over Si photodiodes stacked to CdWO4-. Monolithic X-ray detector arrays were fabricated by depositing a CdTe photodiode structure on CdWO4 using close-spaced sublimation technique. Preliminary results on the detector's X-ray response, signalto- noise ratio and the X-ray temporal response show that monolithic CdTe X-ray detectors are suitable for practical CT scanner applications.

Normal intrahepatic bile ducts: CT depiction.

Visualization of intrahepatic bile ducts (IHBDs) at computed tomography (CT) has previously been considered evidence of biliary obstruction. The authors have found that hepatic CT enhanced with contrast material and with the use of ceramic scintillation detectors allows frequent visualization of normal IHBDs. One hundred patients without imaging, laboratory, or clinical evidence of hepatobiliary or pancreatic disease were prospectively examined to assess the frequency of visualization, location, and size of IHBDs. IHBDs were visualized in 40% of the patients and had an average size of 2.0 mm in the central part of the liver and 1.8 mm in the peripheral part of the liver. Ducts were seen in the right lobe more often than in the left lobe. There was no statistically significant relationship between visualization of IHBDs and patient age. Demonstration of IHBDs on current CT scanners is a normal finding and does not indicate biliary obstruction.

Cochlear patency problems in cochlear implantation

Sensory deafness may be associated with partial or total obliteration of the cochlear scalae. Before undertaking cochlear implant surgery, a preoperative assessment of cochlear patency with high-resolution computed tomography (CT) is indicated. To determine the accuracy of pre-implant CT, a review of the radiographic and surgical findings in 36 implanted ears was performed. An abnormal CT scan was found to be a reliable predictor of compromised cochlear patency at operation. These findings help the surgeon to select the side most favorable for implantation and to anticipate problems that may be encountered during device insertion. A normal pre-implant CT scan, however, does not exclude the possibility of compromised cochlear patency. A 46% false negative rate was encountered, presumably because subtle degrees of osseous or fibrous obliteration of the cochlea are beyond the resolution by current generation CT scanners. In our opinion, the radiographic finding of cochlear ossification is not a contraindication to an attempt at cochlear implantation. The only assured way of determining the extent of cochlear patency is by performing an "exploratory cochleostomy" with fenestration of the basal cochlear turn. Drilling anteriorly through an ossified basal scala tympani will often expose an adequate lumen and permit insertion of even a long multichannel electrode into a partially ossified cochlea. Nevertheless, it is essential that the implant team be prepared with devices appropriate for whatever existing or surgically created lumen may be available.