Clinical X‐ray computed tomography has grown in importance for all of its applications, but most importantly for evaluation of the head, chest, abdomen, pelvis, and cardiovascular system. CT delivers ...an increasing fraction of the overall population radiation dose. Many limitations are present due to sensitivity to motion, metal artifacts, patient size, and limited functional information with a relatively high radiation dose. There are technical developments which promise to reduce these constraints, but at a significant cost. Most important are large area detectors with 64 to 256 rows of detectors, multiple energy channels, algorithmic improvements, and multimodality systems (especially PET/CT). CT is now the essential (and often the only) radiologic imaging procedure needed to manage many patients with acute or chronic diseases. Its speed and versatility, as well as reliability and simplicity of operation ensure that its role will continue for the foreseeable future. CT is used extensively for emergencies, cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, orthopedic and other applications. Further technology development is aimed at common applications where reimbursement for CT scanning services is available or will likely become available. Multicenter clinical trials are underway that compare cardiac CT with other modalities, especially SPECT and cardiac catheterization. The most demanding CT applications are cardiovascular, where complex motion and small morphologic features coexist. Clinical cardiac CT consists of bolus intravenous contrast material injection with EKG gating and simultaneous x‐ray scanning. Larger area detectors and higher frame acquisition rates partly address but don't solve all of the problems encountered due to respiratory, random body, and cardiac motion, in a spectrum of patients from infant to massively obese adult sizes (< 1 kg to 250 kg or more). The challenges and pitfalls in CT will be delineated and evaluated relative to current and future technology.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The most common 3D visualization applications in clinical diagnostic radiology now are cardiac and colon, but the technology is often used in vascular, orthopedics, craniofacial deformities, ...thoracic, and many other areas. In the past, dedicated workstations and highly skilled operators were required to produce CT or MR angiograms, body region or organ surface views, and analysis products. Many centers have dedicated technologists who work in a “3D lab” to extract vessel trees, disarticulate limbs, synthesize transparencies and cine sequences. These services are now reimbursed by 3rd party payors, and almost all CT & MRI scanners today have integrated post‐processing tools. Since generation of advanced visualizations is not a good use of scanner console time if the process cannot be accomplished unattended in a short time, new enterprise systems has been introduced that allow thin clients located anywhere to employ software tools and generate custom views interactively. In the surgeon's office, at the oncology clinic, or even in the operating room, it is now feasible to manipulate 3D image data sets. Very specialized tools for white matter tractography, MR spectroscopic imaging, functional MRI, and myocardial perfusion are examples of new software agents tailored to subspecialty requirements. Several vendors provide post‐processing services for prosthesis or implant custom sizing and design, based on 3D image data sets, where the advanced visualization images are quantified and synthesized in their facilities.
4D imaging and higher dimensions are increasingly common, since almost all cardiac CT and MRI examinations require them. Whole organ and body region perfusion, in the brain and elsewhere employ 4D methods. Multimodality and multitemporal data sets, as well as multispectral (e.g., dual energy 3D data, for example) are acquired and analyzed with software tools that focus on specific clinical issues in neuroradiology and cardiothoracic practice.
So, the most important current trends involve routinely collecting 3D and 4D data sets which are intended for more than simple subjective image review, but are destined to be post‐processed and analyzed with enterprise software tools on thin clients, so immediate results can be obtained that are tailored to subspecialty needs.
Educational Objectives:
1. To understand the sources of 3D and 4D images in clinical diagnostic radiology, including the data acquisition systems and protocols.
2. To learn how advanced visualization and image analysis are evolving from dedicated workstations to enterprise software applications.
3. To see how subspecialized software tools for highly specific imaging applications are used in clinical radiology.
4. To explain 4D datasets are used for cardiac and neuroimaging, where the image analysis results are often quantitative rather than morphologic.
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Context. In optical interferometry, the visibility squared moduli are generally assumed to follow a Gaussian distribution and to be independent of each other. A quantitative analysis of the relevance ...of such assumptions is important to help improving the exploitation of existing and upcoming multi-wavelength interferometric instruments. Aims. The aims of this study are to analyse the statistical behaviour of both the absolute and the colour-differential squared visibilities: distribution laws, correlations and cross-correlations between different baselines. Methods. We use observations of stellar calibrators obtained with the AMBER instrument on the Very Large Telescope Interferometer (VLTI) in different instrumental and observing configurations, from which we extract the frame-by-frame transfer function. Statistical hypotheses tests and diagnostics are then systematically applied. We also compute the same analysis after correcting the instantaneous squared visibilities from the piston and jitter chromatic effects, using a low-order fit subtraction. Results. For both absolute and differential squared visibilities and under all instrumental and observing conditions, we find a better fit for the Student distribution than for the Gaussian, log-normal, and Cauchy distributions. We find and analyse clear correlation effects caused by atmospheric perturbations. The differential squared visibilities allow us to keep a larger fraction of data with respect to selected absolute squared visibilities and thus benefit from reduced temporal dispersion, while their distribution is more clearly characterised. Conclusions. The frame selection based on the criterion of a fixed signal-to-noise value might result in either a biased sample of frames or one with severe selection. Instead, we suggest an adaptive frame selection procedure based on the stability of the modes of the observed squared visibility distributions. In addition, taking into account the correlations effects between measured squared visibilities should help improve the models used in inverse problems and, thus, the accuracy of model fits and image reconstruction results. Finally, our results indicate that re-scaled differential squared visibilities usually constitute a valuable alternative estimator of squared visibility.
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Iterative deblurring methods using the expectation maximization (EM) formulation and the algebraic reconstruction technique (ART), respectively, are adapted for metal artifact reduction in medical ...computed tomography (CT). In experiments with synthetic noise-free and additive noisy projection data of dental phantoms, it is found that both simultaneous iterative algorithms produce superior image quality as compared to filtered backprojection after linearly fitting projection gaps. Furthermore, the EM-type algorithm converges faster than the ART-type algorithm in terms of either the I-divergence or Euclidean distance between ideal and reprojected data in the authors' simulation. Also, for a given iteration number, the EM-type deblurring method produces better image clarity but stronger noise than the ART-type reconstruction. The computational complexity of EM- and ART-based iterative deblurring is essentially the same, dominated by reprojection and backprojection. Relevant practical and theoretical issues are discussed.
Computed tomography is not the most frequent radiologic imaging procedure, but is arguably the most important in terms of clinical impact. CT is used extensively for emergencies, cardiovascular, ...pulmonary, gastrointestinal, endocrine, neurological, orthopedic and other applications ‐ often as the first and only imaging procedure needed for diagnosis. The chances are very high that a patient will have a CT scan in the emergency department, as an outpatient or as an inpatient for a multitude of indications ‐ pain, trauma, suspected infection or malignancy, and frequently to clarify or resolve a question raised by another abnormal test, such as an EKG abnormality or ultrasound finding. Despite the universality of CT in hospitals and clinics as well as free‐standing imaging centers, the technology continues to evolve with greater coverage, faster acquisition and multienergy sources or detectors. The most demanding imaging applications are cardiovascular, where complex motion and small morphologic features coexist, so imaging methods that are very satisfactory elsewhere in the body may not be successful. Clinical cardiac CT consists of administering toxic materials, e.g., contrast media, while monitoring the EKG and illuminating the body with high brightness x‐rays. Larger area detectors and higher frame acquisition rates are welcome improvements, but don't solve all of the problems encountered with variability due to respiratory, random body, and cardiac motion, especially in a spectrum of patients from infant to massively obese adult sizes (< 1 kg to 250 kg or more). The challenges and pitfalls in CT will be delineated and evaluated relative to current and future technology.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Aims. We investigate the structure of the circumstellar disk of the T Tauri star S CrA N and test whether the observations agree with the standard picture proposed for Herbig Ae stars. Methods. Our ...observations were carried out with the VLTI/AMBER instrument in the H and K bands with the low spectral resolution mode. For the interpretation of our near-infrared AMBER and archival mid-infrared MIDI visibilities, we employed both geometric and temperature-gradient models. Results. To characterize the disk size, we first fitted geometric models consisting of a stellar point source, a ring-shaped disk, and a halo structure to the visibilities. In the H and K bands, we measured ring-fit radii of 0.73 ± 0.03 mas (corresponding to 0.095 ± 0.018 AU for a distance of 130 pc) and 0.85 ± 0.07 mas (0.111 ± 0.026 AU), respectively. This K-band radius is approximately two times larger than the dust sublimation radius of ≈0.05 AU expected for a dust sublimation temperature of 1500 K and gray dust opacities, but approximately agrees with the prediction of models including backwarming (namely a radius of ≈0.12 AU). The derived temperature-gradient models suggest that the disk is approximately face-on consisting of two disk components with a gap between star and disk. The inner disk component has a temperature close to the dust sublimation temperature and a quite narrow intensity distribution with a radial extension from 0.11 AU to 0.14 AU. Conclusions. Both our geometric and temperature-gradient models suggest that the T Tauri star S CrA N is surrounded by a circumstellar disk that is truncated at an inner radius of ≈ 0.11 AU. The narrow extension of the inner temperature-gradient disk component implies that there is a hot inner rim.
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Population-based prospective surveillance of invasive pneumococcal disease was done in Southern California from 31 March 1992 to 1 April 1995; 814 cases were identified, for an incidence of ...12.5/100,000 persons/year. The incidence among persons ≤2, ≤5, and ≥65 years of age was 145, 72, and 32/100,000, respectively. More than 95% of cases included bacteremia; incidence of meningitis was 0.8/100,000. Among children ≤2 years of age, 79% of isolates were obtained in the outpatient setting, compared with 16% of isolates among persons ≥15 years of age. Eighty percent of isolates were serotypes included in heptavalent pneumococcal conjugate vaccines currently being evaluated. Children ≤2 years of age were at highest risk of having an isolate resistant to penicillin. Among resistant isolates, high-level resistance increased from 4% to 21% over a 3-year period. Prospective epidemiologic data are needed to perform a protective efficacy trial of pneumococcal conjugate vaccines in infants, among whom most invasive pneumococcal disease is vaccine-preventable.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Computed tomography is the most important modality for many patients, since CT is the first and only examination they have before therapy or for followup. As the technology evolves, we observe ...changes the range of CT applications and its clinical utilization. We are in the midst of rapid expansion of clinical CT imaging use, due to increased speed and coverage, necessitating an evaluation of its current and potential future contributions. The needs of clinical medicine not yet met by CT, but potentially achievable in screening, diagnosis, therapy and followup are valid goals for technology developers. Despite intrinsic limitations due to use of ionizing radiation and substantial fixed costs, CT has room for growth and its technological evolution is not near the end.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star. Stellar light reflected by the planet was tentatively identified in the 34-day CoRoT run acquired in ...October − November 2008. Aims. We constrain the properties of the magnetic field of HD 46375 based on spectropolarimetric observations with the NARVAL spectrograph at the Pic du Midi observatory. In addition, we use a high-resolution NARVAL flux spectrum to contrain the atmospheric parameters. With these constraints, we perform an asteroseismic analysis and modelling of HD 46375 using the frequencies extracted from the CoRoT light curve. Methods. We used Zeeman Doppler imaging to reconstruct the magnetic map of the stellar surface. In the spectroscopic analysis we fitted isolated lines using 1D LTE atmosphere models. This analysis was used to constrain the effective temperature, surface gravity, and chemical composition of the star. To extract information about the p-mode oscillations, we used a technique based on the envelope autocorrelation function (EACF). Results. From the Zeeman Doppler imaging observations, we observe a magnetic field of ≈5 Gauss. From the spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with high metallicity Fe/H = +0.39. Owing to the relative faintness of the star (mhip = 8.05), the signal-to-noise ratio is too low to identify individual modes. However, we measure the p-mode excess power and large separation Δν0 = 153.0 ± 0.7μHz. Conclusions. We are able do constrain the fundamental parameters of the star thanks to spectrometric and seismic analyses. We conclude that HD 46375 is similar to a young version of α Cen B. This work is of special interest because of its combination of exoplanetary science and asteroseismology, which are the subjects of the current Kepler mission and the proposed Plato mission.
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