Noninvasive detection of coronary artery stenosis by multislice helical computed tomography.
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Aged↗
Biomedical subjects
B Ohnesorge
Publications and source records attributed to B Ohnesorge.
[Cardiac imaging with rapid, retrospective ECG synchronized multilevel spiral CT].
PURPOSE: In this paper a method for cardiac imaging with fast multi-slice CT and retrospectively ECG-gated spiral acquisition is presented. METHODS: A fast multi-slice CT system with 4 simultaneously acquired slices and 0.5 s rotation time is used (Siemens Somatom VolumeZoom). Continuous spiral data of the entire heart volume is acquired together with the patient's ECG and reconstructed with dedicated spiral algorithms providing 250 ms temporal resolution. Three-dimensional image data sets are built up from overlapping slices that are reconstructed in an arbitrary, user-defined phase of the heart cycle (e.g. diastolic phase). To evaluate the capability of the method for functional imaging complete three-dimensional image volumes are reconstructed from the same spiral data set in different phases of the heart cycle. RESULTS: A spiral data set of the entire heart volume may be acquired within a single breath-hold. Typical scan times for standard examinations with 3 mm slice width are 10-15 s, and for high-resolution CT angiographies of the coronary arteries with 1.25 mm slice width about 30-35 s. Motion-free reconstruction of the heart and coronary arteries with high spatial resolution is possible in the diastolic phase of the heart cycle. Multi-phase reconstructions from the same spiral scan data set are possible, however, motion artifacts in heart phases with fast cardiac motion may not be completely avoided. CONCLUSION: Fast multi-slice spiral CT with retrospectively ECG-gated spiral reconstruction is well suited for three-dimensional and functional imaging of the heart, especially for high-resolution imaging of calcified coronary plaques and CT-angiography of the coronary arteries.
Algorithms↗
[Initial experiences with multi-slice detector spiral CT in diagnosis of arteriosclerosis of coronary vessels].
PURPOSE: Multi-row-detector-spiral-CT (MSCT) allows for 250 ms effective exposure time. The purpose of this study was to demonstrate the possibilities and limitations of this CT technology for non enhanced and contrast enhanced investigation of the coronary arteries. METHODS: Investigation of the coronary arteries without contrast medium for quantification of coronary calcifications was performed in an obese patient (140 kg) with MSCT and electron beam CT (EBCT). In 56 patients contrast enhanced CT angiography of the coronary arteries was performed to determine image quality depending on the heart rate. RESULTS: In the obese patient superior image quality could be achieved with MSCT allowing for reliable quantification of coronary calcifications. With MSCT angiography of the coronary arteries good image quality was achieved in patients with a heart rate of 59 +/- 8 beats per minute. CONCLUSION: Even if there are limitations in patients with higher heart rates with an effective exposure time of 250 ms MSCT has clear advantage of image quality in the assessment of non enhanced and contrast enhanced coronary arteries.
Adult↗
Visualization and quantification of coronary calcifications with electron beam and spiral computed tomography.
This contribution reviews the pathology and morphology of coronary calcifications. It summarizes the indications for investigation of the coronary arteries. The standard protocols for scan acquisition using electron beam and conventional computed tomography are described as well as various methods for evaluation such as the traditional Agatston scoring method and the newer three-dimensional scoring algorithms. Guidelines for interpreting scores are also reviewed. Major limitations of the reproducibility of the calcium score measurement are summarized. Future aspects of multirow-detector spiral computed tomography with retrospective electrocardiographic triggering for quantifying coronary calcium are discussed.
Calcinosis↗
[Cardiac multidetector-row CT: first clinical results of retrospectively ECG-gated spiral with optimized temporal and spatial resolution].
PURPOSE: The significantly improved temporal and spatial resolution of Multidetector-Row CT opens up new possibilities for cardiac imaging. A method with retrospectively ECG-gated spiral acquisition is presented. MATERIALS AND METHODS: A total of 10 patients underwent cardiac CT on a fast multi-slice CT system with 4 simultaneously acquired slices and 0.5 s rotation time (Siemens Somatom Volume Zoom). Continuous spiral data of the entire heart volume (5 studies precontrast for calcium scoring, 5 studies with contrast) were acquired together with the patient's ECG and reconstructed with dedicated spiral algorithms providing 250 ms temporal resolution. Three-dimensional image data sets were built up from overlapping slices that were reconstructed in an arbitrary, user-defined phase of the heart cycle (e.g., diastolic phase). To evaluate the capability of the method for functional imaging, complete image volumes were reconstructed from the same spiral data set in different phases of the heart cycle. RESULTS: Within a single breath-hold, a spiral data set of the entire heart volume could be acquired. Typical scan times for standard examinations with 3-mm slice width were 12-17 s, and for high-resolution CT angiographies of the coronary arteries with 1.25-mm slice width about 25-35 s. Motion-free reconstruction of the heart and coronary arteries with high spatial resolution were possible in the diastolic phase of the heart cycle. Multiphase reconstructions from the same spiral scan data set were possible. CONCLUSIONS: Fast multi-slice spiral CT with retrospectively ECG-gated spiral reconstruction is well suited for three-dimensional and functional imaging of the heart, especially for high-resolution imaging of calcified coronary plaques and CT-angiography of the coronary arteries.
Coronary Angiography↗
Efficient correction for CT image artifacts caused by objects extending outside the scan field of view.
The purpose of this paper is to develop a method of eliminating CT image artifacts generated by objects extending outside the scan field of view, such as obese or inadequately positioned patients. CT projection data are measured only within the scan field of view and thus are abruptly discontinuous at the projection boundaries if the scanned object extends outside the scan field of view. This data discontinuity causes an artifact that consists of a bright peripheral band that obscures objects near the boundary of the scan field of view. An adaptive mathematical extrapolation scheme with low computational expense was applied to reduce the data discontinuity prior to convolution in a filtered backprojection reconstruction. Despite extended projection length, the convolution length was not increased and thus the reconstruction time was not affected. Raw projection data from ten patients whose bodies extended beyond the scan field of view were reconstructed using a conventional method and our extended reconstruction method. Limitations of the algorithm are investigated and extensions for further improvement are discussed. The images reconstructed by conventional filtered backprojection demonstrated peripheral bright-band artifacts near the boundary of the scan field of view. Images reconstructed with our technique were free of such artifacts and clearly showed the anatomy at the periphery of the scan field of view with correct attenuation values. We conclude that bright-band artifacts generated by obese patients whose bodies extend beyond the scan field of view were eliminated with our reconstruction method, which reduces boundary data discontinuity. The algorithm can be generalized to objects with inhomogeneous peripheral density and to true "Region of Interest Reconstruction" from truncated projections.
Algorithms↗
Cardiac imaging by means of electrocardiographically gated multisection spiral CT: initial experience.
The authors introduce a method for cardiac investigations by using electrocardiographically gated spiral scanning with a four-section computed tomographic system. Three-dimensional images were reconstructed by means of a 250-msec temporal resolution and continuous volume coverage by using a dedicated multisection cardiac volume reconstruction algorithm. Motion-free thin-section volume images were acquired with thin sections and overlapping image increments within a single breath hold. Data segment shifts in time allowed for multiphase imaging.
Calcinosis↗
Imaging of noncalcified coronary plaques using helical CT with retrospective ECG gating.
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Adult↗
[The technical bases and uses of multi-slice CT].
In this review the technical principles and applications of multi-slice CT are discussed. Multi-slice CT systems allow simultaneous acquisition of up to 4 slices by using multi-row detector systems. Intuitive geometrical arguments are used to establish the limitation to a maximum of 4 slices which is kept by all currently existing multi-slice CT systems. Two different construction principles of the detector are discussed, the "Fixed Array" detector and the "Adaptive Array" detector. The extension of conventional 360 LI and 180 LI spiral interpolation techniques to multi-slice spiral CT is explained as well as a new generalized multi-slice spiral weighting concept, the so-called "Adaptive Axial Interpolation". Several techniques to improve multi-slice spiral image quality are discussed. Finally, some examples for clinical applications are given, and the principle of ECG triggered and ECG gated cardiac examinations with optimized temporal resolution is presented. Multi-slice CT systems are a milestone with respect to increased volume coverage, shorter scan times, improved axial (longitudinal) resolution and better use of the X-ray tube output. Additionally, new clinical applications are possible such as Cardiac CT.
Electrocardiography↗
Efficient object scatter correction algorithm for third and fourth generation CT scanners.
X-ray photons which are scattered inside the object slice and reach the detector array increase the detected signal and produce image artifacts as "cupping" effects in large objects and dark bands between regions of high attenuation. The artifact amplitudes increase with scanned volume or slice width. Object scatter can be reduced in third generation computed tomography (CT) geometry by collimating the detector elements. However, a correction can still improve image quality. For fourth generation CT geometry, only poor anti-scatter collimation is possible and a numeric correction is necessary. This paper presents a correction algorithm which can be parameterized for third and fourth generation CT geometry. The method requires low computational effort and allows flexible application to different body regions by simple parameter adjustments. The object scatter intensity which is subtracted from the measured signal is calculated with convolution of the weighted and windowed projection data with a spatially invariant "scatter convolution function". The scatter convolution function is approximated for the desired scanner geometry from pencil beam simulations and measurements using coherent and incoherent differential scatter cross section data. Several examples of phantom and medical objects scanned with third and fourth generation CT systems are discussed. In third generation scanners, scatter artifacts are effectively corrected. For fourth generation geometry with poor anti-scatter collimation, object scatter artifacts are strongly reduced.
Algorithms↗
Subsecond multi-slice computed tomography: basics and applications.
The recent advent of multislice-scanning is the first real quantum leap in computed tomography since the introduction of spiral CT in the early 90s. We discuss basic theoretical considerations important for the design of multislice scanners. Then, specific issues, like the design of the detector and spiral interpolation schemes are addressed briefly for the SOMATOM PLUS 4 Volume Zoom. The theoretical concepts are validated with phantom measurements. We finally show the large potential of the new technology for clinical applications. The concurrent acquisition of multiple slices results in a dramatic reduction of scan time for a given scan technique. This allows scanning volumes previously inaccessible. Similarly, given volumes can be scanned at narrower collimation, i.e. higher axial resolution in a given time. From data acquired at narrow collimation, both high-resolution studies and standard images can be reconstructed in the so-called Combi-Mode. This on the one hand reduces dose exposure to the patient because repeated scanning of a patient is no longer required. On the other hand, standard reconstructions benefit from narrow collimation as Partial Volume Artifacts are drastically suppressed. The rotational speed of 0.5 s of the SOMATOM PLUS 4 Volume Zoom furthermore opens up a whole range of new applications in cardiac CT. For the first time, virtually motion-free images can be acquired even for large volumes in a single breathhold by the combination of fast rotation and ECG triggering, respectively gating. We explain the underlying concepts and present initial results. The paper concludes with a brief discussion of the impact of the new technique on image display and postprocessing.
Artifacts↗
[Transendoscopic laser surgery of exercise-induced dorsal displacement of the soft palate in horses].
From 1995 to 1997 11 racehorses, one Hanoverian and one Pony were presented to the clinic with a sudden appearing, very loudly gurgling expiratory respiratory noise. Considering the preliminary report and the clinical and endoscopical findings, as exercise induced dorsal displacement of the soft palate (DDSP) was found to be the cause of the respiratory noise. The 13 horses were treated in general anaesthesia by transendoscopic coagulation of the caudal margin of the soft palate with a Neodym-YAG-Laser. This surgical intervention had to be repeated on four horses with unchanged signs. Eight of 13 horses (62%) did not show any respiratory noises after the operation. These horses were again successfully raced and ridden. Only an improvement was observed in two horses (15%), while in three patients (23%) the respiratory noise was unchanged after surgery. The laser chirurgic approach to the exercise induced DDSP offers, compared to previous therapies important advantages, like shorter recoveries, combined with similar success rates.
Animals↗
Rapid carrier relaxation in self-assembled InxGa1-xAs/GaAs quantum dots.
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Journal Article↗
Magnetic tailoring of the nature of the fundamental optical transition in a ZnSe/(Zn,Mn)Se heterostructure.
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Journal Article↗
[Laryngeal hemiplegia in warmblood horses--a study of stallions, mares and their offspring].
Laryngoscopic examination during sedation was performed on 24 stallions and on their offspring (240 foals and 474 adult horses). Additionally the dams (n = 308) of 35 foals and 216 horses were examined. With the bilateral comparison of the arytaenoid movements the function of the abductory and adductory laryngeal muscles were evaluated and the left abductory dysfunction (idiopathic laryngeal hemiplegia, ILH) was divided into six degrees. The incidence and degree of ILH depended on age and the occurrence of the same dysfunction in the parents. Foals suffered in significantly lower number (24.7 per cent) than adult horses (49.7 per cent). The progeny of unaffected parents suffered significantly less from ILH (8.9 per cent of the foals, 39.6 per cent of the adult offspring) than did comparable progeny of affected parents (41 per cent of the foals, 60.9 per cent of the adult offspring). There was no correlation between the occurrence of ILH and sex. 120 horses were examined laryngoscopically and during work to get an information about the correlation between a visible ILH and the appearance of a typical inspiratory noise. 54.3 per cent of the horses with ILH had a typical inspiratory noise. 80.9 per cent of the horse with a typical inspiratory noise showed ILH.
Age Factors↗