Bernd Ohnesorge

Siemens, Princeton, New Jersey, United States

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Publications (105)284.88 Total impact

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    ABSTRACT: Purpose: Multirow-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.
    No preview · Article · Apr 2012 · Der Radiologe
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    ABSTRACT: Coronary artery imaging is a demanding application for any non-invasive imaging modality. On the one hand, high temporal resolution is needed to virtually freeze the cardiac motion and to avoid motion artifacts in the images. On the other hand, sufficient spatial resolution — at best sub-millimeter — is required to adequately visualize small and complex anatomical structures such as the coronary arteries. The complete coronary artery tree has to be examined within one short breath-hold time to avoid breathing artifacts and to limit the amount of contrast agent if necessary. In 1984, electron beam computed tomography (EBCT) was introduced as a non-invasive imaging modality for the diagnosis of coronary artery disease (Boyd and Lipton 1982; Agatston et al. 1990; Achenbach et al. 1998, Becker et al. 2000a). The temporal resolution of 100 ms allowed for motion-free imaging of the cardiac anatomy in the diastolic heart phase even at higher heart rates.
    No preview · Article · Jan 2009
  • Thomas Flohr · Bernd Ohnesorge
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    ABSTRACT: Cardio-thoracic imaging with CT requires short exposure time for the acquisition of the axial slices and the corresponding dedicated scan and image reconstruction techniques to virtually freeze the cardiac motion and to avoid motion artifacts in the images. Scan and image reconstruction needs to be synchronized with the heart motion, e.g., by using information from the patient’s electro-cardiogram (ECG) that is recorded in parallel to the CT scan data acquisition.
    No preview · Chapter · Dec 2008
  • Thomas Flohr · Bernd Ohnesorge
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    ABSTRACT: The broad introduction of multi-detector row computed tomography (MDCT) into clinical practice in 1998 constituted a fundamental evolutionary step in the development and ongoing refinement of CT-imaging techniques. The first generation of MDCT systems offered simultaneous acquisition of four slices at a shortest gantry rotation time of 0.5 s and provided considerable improvement of scan speed and longitudinal (z-axis) resolution and better utilization of the available X-ray power compared with previous generations of single-slice CT systems (Klingenbeck et al. 1999; Mc Collough and Zink 1999; Hu et al. 2000). As a consequence, high-resolution imaging of larger anatomical volumes, such as the entire thorax, with a single scan acquisition and a single contrast medium injection became feasible, see Figure 1.1. Fig. 1.1a–c.Case study (coronal MPRs) of a thorax examination in a patient with pulmonary embolism, illustrating the increased clinical performance from (a) single-slice CT (8-mm slices) to (b) 4-slice CT (1.25-mm slices), and (c) 64-slice CT (0.75-mm slices). Compared with single-slice CT scanners, four-slice CT systems brought about considerably improved longitudinal resolution in equivalent examination times (30 s to cover the thorax). Sixty-four-slice CT scanners provide significantly reduced examination times (5 s to cover the thorax) in combination with isotropic sub-millimeter resolution. The single-slice and 4-slice images were synthesized from the 64-slice CT data (courtesy of Profs. J. Remy and M. Remy-Jardin, Hopital Calmette, Lille, France)
    No preview · Chapter · Dec 2008
  • Thomas Flohr · Bernd Ohnesorge
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    ABSTRACT: Image postprocessing is the use of imaging techniques either to derive additional information from the original axial images of a CT scan or to hide unwanted information that distracts from the clinical findings. The basis for image postprocessing is a three-dimensional image volume, which in most cases consists of a stack of individual axial images. The fundamental three-dimensional unit in this volume is called a “voxel.” Ideally, the spatial resolution of volume image data is high and isotropic, i.e., each voxel is of equal dimensions in all three spatial axes. Isotropic sub-millimeter resolution is the basis for image display in arbitrarily oriented imaging planes and advanced image postprocessing techniques. With the advent of multi-detector row CT (MDCT) and its ongoing refinement, isotropic sub-millimeter voxels can be obtained for the majority of clinical examinations, improving the diagnostic quality of image postprocessing and turning it into a vital component of medical imaging today, in particular for CT angiography (Prokop et al. 1997; Rankin 1999; Addis et al. 2001; Lawler et al. 2002).
    No preview · Chapter · Dec 2008
  • Thomas G Flohr · Bernd M Ohnesorge
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    ABSTRACT: Imaging of the heart with computed tomography (CT) was already introduced in the 1980Is and has meanwhile entered clinical routine as a consequence of the rapid evolution of CT technology during the last decade. In this review article, we give an overview on the technology and clinical performance of different CT-scanner generations used for cardiac imaging, such as Electron Beam CT (EBCT), single-slice CT und multi-detector row CT (MDCT) with 4, 16 and 64 simultaneously acquired slices. We identify the limitations of current CT-scanners, indicate potential of improvement and discuss alternative system concepts such as CT with area detectors and dual source CT (DSCT).
    No preview · Article · Apr 2008 · Archiv für Kreislaufforschung
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    ABSTRACT: To prospectively compare the dose performance of a 64-channel multi-detector row computed tomographic (CT) scanner and a 64-channel dual-source CT scanner from the same manufacturer. To minimize dose in the cardiac (dual-source) mode, the evaluated dual-source CT system uses a cardiac beam-shaping filter, three-dimensional adaptive noise reduction, heart rate-dependent pitch, and electrocardiographically based modulation of the tube current. Weighted CT dose index per 100 mAs was measured for the head, body, and cardiac beam-shaping filters. Kerma-length product was measured in the spiral cardiac mode at four pitch values and three electrocardiographic modulation temporal windows. Noise was measured in an anthropomorphic phantom. Data were compared with data from a 64-channel multi-detector row CT scanner. For the multi-detector row and dual-source CT systems, respectively, weighted CT dose index per 100 mAs was 14.2 and 12.2 mGy (head CT), 6.8 and 6.4 mGy (body CT), and 6.8 and 5.3 mGy (cardiac CT). In the spiral cardiac mode (no electrocardiographically based tube current modulation, 0.2 pitch), equivalent noise occurred at volume CT dose index values of 23.7 and 35.0 mGy (coronary artery calcium CT) and 58.9 and 61.2 mGy (coronary CT angiography) for multi-detector row CT and dual-source CT, respectively. The use of heart rate-dependent pitch values reduced volume CT dose index to 46.2 mGy (0.265 pitch), 34.0 mGy (0.36 pitch), and 26.6 mGy (0.46 pitch) compared with 61.2 mGy for 0.2 pitch. The use of electrocardiographically based tube current-modulation and temporal windows of 110, 210, and 310 msec further reduced volume CT dose index to 9.1-25.1 mGy, dependent on the heart rate. For electrocardiographically gated coronary CT angiography, image noise equivalent to that of multi-detector row CT can be achieved with dual-source CT at doses comparable to or up to a factor of two lower than the doses at multi-detector row CT, depending on heart rate of the patient.
    No preview · Article · Jul 2007 · Radiology
  • Thomas Flohr · Bernd Ohnesorge

    No preview · Chapter · May 2007
  • Thomas G Flohr · U Joseph Schoepf · Bernd M Ohnesorge
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    ABSTRACT: With the latest generations of multidetector row computed tomography (CT) scanners, CT of the heart is about to fulfill its promise to become the premier noninvasive imaging modality for the cardiac assessment. The performance of this modality has been continuously improved to a point where CT, beyond mere feasibility studies, is firmly establishing its role in the diagnostic work-up of patients with suspected cardiac disease. This has been enabled by ongoing technical refinements, which are the topic of this contribution. This review traces the evolution of CT for cardiac applications, describes the current status of scanner technology with special emphasis on dual-source CT, and provides insights into potential future developments for further refinement of this technique.
    No preview · Article · Mar 2007 · Journal of Thoracic Imaging
  • B.M. Ohnesorge · T.G. Flohr · C.R. Becker · A. Knez · M.F. Reiser

    No preview · Article · Jan 2007
  • Thomas Flohr · Bernd Ohnesorge
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    ABSTRACT: The application of imaging techniques to original axial images of a CT scan in order to derive additional information or hide unwanted information that distracts from the clinical findings is called image post-processing. Image post-processing requires modification of a 3D image volume, which in most cases consists of a stack of individual axial images. The fundamental 3D unit in this volume is called a «voxel». Ideally, volume image data are of high spatial resolution and isotropic in nature, i.e., each voxel is of equal dimensions in all three spatial axes, and forms the basis for image display in arbitrarily oriented imaging planes and advanced image postprocessing techniques. With the advent of multi-slice CT and its on-going refinement, isotropic sub-millimeter voxels can be obtained for the majority of clinical examinations. This has improved the diagnostic quality of image post-processing such that it has become a vital component of medical imaging today, in particular for CT angiography (Prokop 1997, Rankin 1999, Addis 2001). The axial source images contain the basic information of a CT scan. They can be supplemented by basic 3D post-process ing tools and advanced methods for the analysis of complex anatomy, automated quantification, and functional evaluation (Vogl 2002, van Ooijen 2003, de Feyter 2005).
    No preview · Article · Jan 2007
  • Bernd Ohnesorge
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    ABSTRACT: This chapter gives an overview of the scan protocols for the main cardiac imaging applications and for the various multi-slice CT technology levels that are in regular clinical use today. More protocols that are used in specific patient populations or under research conditions can be also found in Chap. 7. The first multi-slice cardiac CT imaging protocols were already developed in 1999 (Ohnesorge 2000) for a broad range of clinical applications based on the first available 4-slice CT scanners. These represent the minimum technology level that is required for basic cardiac applications, such as coronary calcium scoring and display of the larger cardiac anatomy. More advanced applications, such as coronary artery diagnosis and assessment of cardiac function, have become feasible with the more recent introduction of 16- to 64-slice CT scanners with increased spatial and temporal resolution and shorter breath-hold times (Lawler 2004, Schoepf 2004, Schoenhagen 2004, Ohnesorge 2005, Flohr 2005, Gaspar 2005, Schoepf 2006, Lardo 2006). The protocols presented in this chapter are designed to provide a suitable balance of best possible clinical outcome, on the one hand, and minimum possible radiation exposure, on the other. The given parameters apply for a wide range of CT scanners from all major manufacturers and also indicate the minimum technology level needed for a certain clinical application. Where feasible, different protocol options using prospective ECG triggering or retrospective ECG gating are introduced, and the advantages and disadvantages discussed. For contrast- enhanced applications, we provide suggestions for contrast-agent protocols with optimized timing of vascular and anatomical enhancement. The discussion of clinical indications and evaluation techniques is not the subject of this chapter but of other chapters in this book.
    No preview · Article · Jan 2007

  • No preview · Chapter · Dec 2006

  • No preview · Chapter · Dec 2006
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    Full-text · Chapter · Dec 2006

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    ABSTRACT: The use of percutaneous intervention (PCI) for the treatment of ischemic coronary artery disease has expanded dramatically over the last two decades. Initially, balloon angioplasty offered an alternative to bypass surgery in focal lesions, but it involved a considerable risk of acute dissection, thrombosis, or late coronary re-stenosis. Continuous technical innovation has expanded the indications for PCI and reduced both the procedural risk and the occurrence of post-procedural re-stenosis. Nowadays, most interventions involve intra-coronary expansion of stents. Still, until the introduction of coated stents, neointimal hyperplasia caused clinically significant re-stenosis in at least 20% of patients (Kiemeneij 2001). Although the occurrence of re-stenosis may be less in the future with increasing use of drugeluting stents, the progression of atherosclerotic degeneration in the remaining coronary arteries is not affected (Morice 2002). Multi-slice spiral CT allows minimally invasive angiographic imaging of the coronary arteries. The diagnostic accuracy to detect coronary stenoses is good (Nieman 2001, Achenbach 2001), particularly in the absence of extensive vascular calcification and in patients with low heart rates: The introduction of 16-slice and 64-slice CT scanners with sub-millimeter resolution have resulted in further improvements (Nieman 2002, Ropers 2003, Leschka 2005). Patients who previously underwent PCI often developed recurrent symptoms due either to re-stenosis at the location of the previous obstruction or to progression of atherosclerosis at other sites. Post-PCI patients are more likely to require repeated angiographic coronary evaluation, so that a non-invasive technique would therefore be desired. Possible clinical indications for multi-slice coronary CTA could include suspected early occlusion of stents after the procedure, late in-stent restenosis, or progression of coronary artery disease in non-stented vessel segments.
    No preview · Chapter · Dec 2006
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    Full-text · Chapter · Dec 2006

Publication Stats

9k Citations
284.88 Total Impact Points

Institutions

  • 2000-2007
    • Siemens
      • Siemens Medical Solutions
      Princeton, New Jersey, United States
    • Ludwig-Maximilian-University of Munich
      • Department of Clinical Radiology
      München, Bavaria, Germany
  • 2006
    • University Hospital München
      München, Bavaria, Germany
  • 2005-2006
    • Medical University of South Carolina
      Charleston, South Carolina, United States
  • 2002
    • MeVis Medical Solutions AG
      Bremen, Bremen, Germany
    • Universitätsklinikum Tübingen
      • Division of Diagnostic and Interventional Radiology
      Tübingen, Baden-Württemberg, Germany
  • 2001-2002
    • University of Tuebingen
      • Department of Internal Medicine
      Tübingen, Baden-Württemberg, Germany