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Biomedical subjects

B Ohnesorge

Publications and source records attributed to B Ohnesorge.

At least 19 recordsLinked to original sources
PubMed2001

[The NEN (Nicolet Electronic Naviation System) ENT navigation system. Initial clinical application].

BACKGROUND: Intraoperative computer navigation will soon play an important role in procedures performed on the anterior and lateral skull base. Electromagnetic systems compared to optical systems offer some advantages such as small hardware dimension and free unimpaired mobility of the surgeon. PATIENTS AND METHODS: The NEN navigational system (Nicolet Electromagnetic Navigation System) was used in 22 patients who underwent microscopic/endoscopic surgery for polypoid rhinosinusitis. It is the prototype of a new system, which localizes the surgical probe via the measurement of pulsed electromagnetic DC fields. This system was modified for the needs of head and neck surgery. Preoperative imaging data consisted of an axially oriented spiral computed tomography (CT) resulting in a slice thickness of 1 mm with a radiation dose slightly higher than a routine coronary CT scan of the paranasal sinuses. RESULTS: The data acquired during clinical application was used to optimize navigation accuracy. The number and positions of the markers were gradually modified and improved. Six markers including the volume of the paranasal sinus system (three non-coplanar frontal markers, one on each of the mastoid processes and one median marker on parietooccipital junction) offered the best navigation precision. Additionally, all surgical instruments measured as ferromagnetic, i.e., nasal specula, were replaced by titanium instruments. An adapter affixed to the maxilla-designed to hold a second sensor used to track the patient's head was developed. With these modifications, it was possible to improve navigation accuracy to 1.5 mm in the plane of the sphenoid bone while retaining free head movement of the patient. CONCLUSION: For routine procedures such as microscopic/endoscopic endonasal sinus surgery, the systems have to be cost effective and easy to operate.

Endoscopy↗
PubMed2001

Non-invasive characterisation of coronary lesion morphology and composition by multislice CT: first results in comparison with intracoronary ultrasound.

The reliable non-invasive detection of coronary artery disease (CAD) is a prime goal for future developments in clinical cardiology. In addition to the documentation of high-grade stenoses, the detection of vulnerable plaques is of major importance for risk stratification and early treatment to prevent plaque rupture. Recently, a new generation of fast spiral CT has been introduced using a multi-slice technique (MSCT), which is the first real quantum leap in CT since the introduction of spiral CT in the early 1990s. We report on non-invasive differentiation of coronary plaque morphology by MSCT in patients with lesions in the proximal left anterior descending artery (LAD). The results were compared with the findings of intracoronary ultrasound (ICUS). The ICUS and MSCT scans were analysed in 6 patients scheduled for ICUS-guided PTCA. One target lesion was selected in each patient. On ICUS, two lesions were classified as soft, two as intermediate and two as calcified according to established criteria based on echogenicity. By multislice CT, density measurements (expressed in Hounsfield Units, HU) were performed at 16 randomly selected areas within the plaques. The two soft plaques showed a mean density of 6+/-28 and -5+/-25 HU, the two intermediate plaques of 83+/-17 and 51+/-19 HU, and the two calcified plaques of 489+/-372 and 423+/-111 HU. To our knowledge, this is the first report on non-invasive characterisation of coronary lesions by MSCT. Plaque composition could be clearly differentiated and classified according to the ICUS results by determining tissue density within the lesions. Thus, this new technology holds promise for non-invasive risk assessment in patients with known or suspected CAD since also rupture-prone soft coronary lesions can be detected by use of this new technique.

Aged↗
PubMed2001

Noninvasive detection and evaluation of atherosclerotic coronary plaques with multislice computed tomography.

OBJECTIVES: The aim of the present study was to evaluate the accuracy in determining coronary lesion configuration by multislice computed tomography (MSCT). The results were compared with the findings of intracoronary ultrasound (ICUS). BACKGROUND: The risk of acute coronary syndromes caused by plaque disruption and thrombosis depends on plaque composition rather than stenosis severity. Thus, the reliable noninvasive assessment of plaque configuration would constitute an important step forward for risk stratification in patients with known or suspected coronary artery disease. Just recently, MSCT scanners became available for general purpose scanning. Due to improved spatial and temporal resolution, this new technology holds promise to allow for differentiation of coronary lesion configuration. METHODS: The ICUS and MSCT scans (Somatom Volume Zoom, Siemens, Forchheim, Germany) were performed in 15 patients. Plaque composition was analyzed according to ICUS (plaque echogenity: soft, intermediate, calcified) and MSCT criteria (plaque density expressed by Hounsfield units [HU]). RESULTS: Thirty-four plaques were analyzed. With ICUS, the plaques were classified as soft (n = 12), intermediate (n = 5) and calcified (n = 17). Using MSCT, soft plaques had a density of 14 +/- 26 HU (range -42 to +47 HU), intermediate plaques of 91 +/- 21 HU (61 to 112 HU) and calcified plaques of 419 +/- 194 HU (126 to 736 HU). Nonparametric Kruskal-Wallis test revealed a significant difference of plaque density among the three groups (p < 0.0001). CONCLUSIONS: Our results indicate that coronary lesion configuration might be correctly differentiated by MSCT. Since also rupture-prone soft plaques can be detected by MSCT, this noninvasive method might become an important diagnostic tool for risk stratification in the near future.

Adult↗
PubMed2001

Accuracy and reliability of quantitative measurements in coronary arteries by multi-slice computed tomography: experimental and initial clinical results.

AIM: To evaluate the accuracy of non-invasive measurements within coronary arteries by multi-slice computed tomography (MSCT). We present experimental as well as clinical data. MATERIALS AND METHODS: Silicon tubes simulating coronary arteries (outer diameter 6 mm, lumen diameter within stenotic area 2 mm) were used for experimental studies. Clinical data were derived from 15 patients in whom vessel diameters were assessed by MSCT, intracoronary ultrasound (ICUS) and quantitative coronary angiography (QCA). MSCT were performed in a Somatom Volume Zoom(trade mark)CT system (Siemens, Forchheim, Germany) at 2 collimated slice widths (2.5 mm, 1.0 mm). RESULTS: Outer silicon tube diameters were overestimated by MSCT (6.56 mm +/- 0.32 mm). All measurements revealed significantly better results on 1.0 collimation compared to 2.5 mm collimation (outer diameter: 6.36 mm +/- 0.22 mm vs 6.76 mm +/- 0.27 mm, P < 0.0001; lumen diameters: 1.83 mm +/- 0.14 mm vs 1.51 mm +/- 0.19 mm, P < 0.0001). The comparison of vessel diameters within human coronary arteries revealed comparable results between ICUS and MSCT (4.89 mm +/- 0.67 mm vs 4.91 mm +/- 0.71 mm, P = 0.79, r = 0.79, P < 0.0001). QCA-measurements showed significantly lower results (3.67 +/- 0.71, P < 0.0001, r = 0.62, P < 0.001). CONCLUSIONS: Experimental as well as initial clinical results indicate acceptable reliability and accuracy of quantitative measurements by MSCT, when using thin collimated slice widths. Partial volume effects lead to a systematic overestimation of vessel size. MSCT has the potential to become an important non-invasive diagnostic tool in patients with coronary artery disease.

Coronary Angiography↗
PubMed2001

[Optimizing image reconstruction timing for the RR interval in imaging coronary arteries with multi-slice computerized tomography].

PURPOSE: Multislice spiral CT is a newly developed technology that allows the non-invasive detection of coronary stenoses and plaques. The acquired raw data are reconstructed at a given time point in the RR interval of the heart cycle. Thus, determination of this time point is a key factor for picture quality and for reliable diagnostic results. This study was performed to investigate the optimal time point for reconstruction within the RR interval. MATERIALS AND METHODS: The coronary arteries of 13 patients were examined with CT. Raw data were reconstructed 250, 350, 450 and 550 ms before the following R wave (absolute reverse retrospective ECG gating) for each patient. Data were then analyzed with a volume rendering mode on a SIEMENS 3 D-Virtuoso workstation. A total of 91 segments (segments 1 and 2 of the RCA, segments 5, 6, 7 and proximal and distal parts of segment 11) were assessed and image quality was classified. RESULTS: Visualization of the left main coronary artery was of a good quality at all time points, segments 6 and 7 of the LAD as well as the proximal and distal parts of segment 11 of the RCX had the best quality at 450 ms absolute reverse retrospective ECG gating. The segments 1 and 2 of the RCA were of best quality 550% ms absolute reverse to the R peak. CONCLUSIONS: Classification of image quality of coronary artery CT scans after retrospectively ECG gated reconstruction is highly determined by the time point of reconstruction in the heart cycle. The optimization of this time point increases diagnostic accuracy and helps to avoid misinterpretation due to image artifacts.

Blood Flow Velocity↗
PubMed2001

ECG-gated reconstructed multi-detector row CT coronary angiography: effect of varying trigger delay on image quality.

PURPOSE: To evaluate the effectiveness of electrocardiographically (ECG)-gated retrospective image reconstruction for multi-detector row computed tomographic (CT) coronary angiography in reducing cardiac motion artifacts and to evaluate the influence of heart rate on cardiac image quality. MATERIALS AND METHODS: Sixty-five patients with different heart rates underwent coronary CT angiography. Raw helical CT data and ECG tracings were combined to retrospectively reconstruct at the defined consecutive z position with a temporal resolution of 250 msec per section. The starting points of the reconstruction were chosen between 30% and 80% of the R-R intervals. The relationships between heart rate, trigger delay, and image quality were analyzed. RESULTS: Optimal image quality was achieved with a 50% trigger delay for the right coronary artery and 60% for the left circumflex coronary artery. Optimal image quality for the left anterior descending coronary artery was equally obtained at 50% and 60% triggering. A significant negative correlation was observed between heart rate and image quality (P <.05). The best image quality was achieved when the heart rate was less than 74.5 beats per minute. CONCLUSION: To achieve high image quality, the heart rate should be sufficiently slow. Selection of appropriate trigger delays and a decreasing heart rate are effective to reduce cardiac motion artifacts.

Adult↗
PubMed2000

[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↗
PubMed2000

[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↗
PubMed2000

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↗
PubMed2000

[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↗
PubMed2000

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↗
PubMed2000

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↗
PubMed1999

[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↗
PubMed1999

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↗
PubMed1999

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↗