B Ohnesorge

Siemens, Princeton, New Jersey, United States

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Publications (105)286.44 Total impact

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    ABSTRACT: Fragestellung: Mit dem Mehrzeilendetektorspiral-CT (MSCT) sind effektive Aufnahmezeiten von 250ms möglich. Die Möglichkeiten und Grenzen dieser CT-Technologie zur nativen und kontrastverstärkten Untersuchung der Koronargefäße sollen in dieser Arbeit dargestellt werden. Methode: Die native Untersuchung der Koronargefäße zur Quantifizierung von Koronarkalk wurde bei einem Patienten mit Adipositas (140kg) mit dem Elektronenstrahl-CT (EBCT) und dem MSCT vorgenommen. Bei 56 Patienten wurde eine kontrastverstärkte MSCT-Angiographie der Koronargefäße vorgenommen und festgestellt, bei welcher Herzfrequenz eine diagnostisch ausreichende Bildqualität zu erreichen ist. Ergebnisse: Bei der Untersuchung des Patienten mit Adipositas konnte mit dem MSCT eine erheblich bessere Bildqualität erreicht werden, die eine Quantifizierung von Koronarkalk erheblich erleichterte. Mit der MSCT-Angiographie der Koronargefäße konnte bei einer Herzfrequenz von 59±8 Schlägen/min eine diagnostisch gute Bildqualität erreicht werden. Schlussfolgerung: Auch wenn mit einer effektiven Aufnahmezeit von 250ms Limitationen bei höheren Herzfrequenzen zu erwarten sind, können mit dem MSCT entscheidende Vorteile in der Bildqualität in der nativen und kontrastverstärkten Untersuchung der Koronargefäße erreicht werden. Purpose: Multirow-detector-spiral-CT (MSCT) allows for 250ms 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 (140kg) 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 250ms MSCT has clear advantage of image quality in the assessment of non enhanced and contrast enhanced coronary arteries.
    Der Radiologe 04/2012; 40(2):118-122. · 0.47 Impact Factor
  • 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)
    12/2008: pages 3-22;
  • 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).
    12/2008: pages 37-51;
  • 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.
    12/2008: pages 23-36;
  • 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).
    Archiv für Kreislaufforschung 04/2008; 103(2):161-73. · 5.90 Impact Factor
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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.
    Radiology 07/2007; 243(3):775-84. · 6.34 Impact Factor
  • 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.
    Journal of Thoracic Imaging 03/2007; 22(1):4-16. · 1.26 Impact Factor
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    ABSTRACT: In the last few years, multi-slice CT has become an alternative to catheter angiography. CTA is now the method of choice for detecting coronary arteries anomalies, fistulas, and aneurysms due to the 3D capability of this technique. Moreover, it is noninvasive, reproducible, and operator-independent. Especially in complex anomalies, if catheter angiography is not possible, multi-slice CT can accurately depict the anatomy of the heart and vessels. In contrast to catheter angiography, the thrombotic portion of aneurysms can be visualized with multislice CT. The new generation of CT scanners, with up to 64 slices, may improve image quality and resolution due to the smaller slice thickness and shorter breath-hold time. However, the ability of multi-slice CT to detect dissection and vasculitis of coronary arteries remains to be proven in future studies.
    12/2006: pages 245-257;
  • 12/2006: pages 239-244;
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    ABSTRACT: PURPOSE To investigate influence of heart rate on the presence of motion artefacts and image reconstruction interval providing optimal image quality using Dual Source CT (DSCT) Coronary Angiography. METHOD AND MATERIALS We studied 30 patients (24 men; mean age, 66±13.2) with atypical chest pain, stable or unstable angina pectoris, or non-ST-segment elevation myocardial infarction, scheduled for diagnostic conventional coronary angiography. All patients were scanned with a DSCT scanner (Somatom Definition, Siemens Medical Solutions Forcheim, Germany) equipped with an improved temporal resolution of 83 ms. Only patients in sinus rhythm were included. Patients with contra-indications to Iodinated contrast material were excluded. No ß-blockers were administered prior to the scan. A bolus of 70 ml of high Iodine contrast material was injected at 5 ml/s followed by a saline chaser of 50 ml at 5 ml/s. Mean scan time was 7.8±1.9s. Pitch varied between 0.2 and 0.5. Datasets were standard reconstructed during the mid-to-end diastolic and end-systolic phase using a single-segment ECG-gated reconstruction algorithm. Patients were classified in 3 groups: patients with low (group 1:80bpm) 30% (9 of 30). Image quality was classified by 2 independent observers as good, adequate or poor, based on the presence of motion artefacts, on a per-segment level. RESULTS A total of 347 segments were evaluated. Poor image quality was seen in 0% (2 of 347) of segments in group 1, in 3% (11 of 347) in group 2, and in 6% (21 of 347) in group 3. Optimal image quality was seen in the mid-to-end diastolic phase in 93% (323 of 347) of segments in group 1, in 65% (226 of 347) in group 2, and in 23% (80 of 347) in group 3. CONCLUSION Motion artefacts are reduced due to improved temporal resolution of 83 ms, thereby providing nearly motion-free image quality in patients with high heart rates. End-systolic reconstructions provide optimal image quality in patients with fast heart rates. CLINICAL RELEVANCE/APPLICATION The high temporal resolution of DSCT scanners results in an improved image quality in high heart rates when compared to previous scanner generations.
    Radiological Society of North America 2006 Scientific Assembly and Annual Meeting; 11/2006
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    ABSTRACT: PURPOSE To prospectively evaluate the diagnostic accuracy of Dual-Source Computed Tomography (DSCT) coronary angiography to detect significant stenoses (defined as ≥50% lumen diameter reduction) in patients referred for conventional coronary angiography without the use of pre-scan beta-blockers. METHOD AND MATERIALS We studied 30 patients (24 men; mean age 66±13.2) with atypical chest pain, stable or unstable angina pectoris, non-ST-segment elevation myocardial infarction, scheduled for diagnostic conventional coronary angiography. All patients were scanned with a DSCT scanner (Somatom Definition, Siemens Medical Solutions Forcheim, Germany) equipped with an improved temporal resolution of 83 ms as compared to previous CT scanner generations. Only patients able to breath hold for 10 s and in sinus rhythm were included. Patients with contra-indications to Iodinated contrast material were excluded. No ß-blockers were administered prior to the scan. A bolus of 70 ml of contrast material with a high iodine concentration was injected with a flow rate of 5 ml/s followed by a saline chaser of 50 ml at 5 ml/s. Mean scan time was 7.8±1.9 seconds. Pitch varied between 0.2 and 0.5. Mean heart rate was 73±16. The CT angiograms were analyzed by 2 observers blinded to the results of invasive coronary angiography, which was used as the standard of reference. RESULTS Conventional coronary angiography demonstrated the absence of significant disease in 20% (6 of 30), single vessel disease in 27% (8 of 30), and multi-vessel disease in 53% (16 of 30) of patients. Sensitivity of CT coronary angiography for detecting significant stenoses on a segment-based analysis was 92%, specificity was 96%, and positive and negative predictive values were 73% and 99% respectively. CONCLUSION Our preliminary results show that the diagnostic accuracy of DSCT coronary angiography for the detection of significant lesions in patients referred for conventional angiography is high, even in patients with fast heart rates. CLINICAL RELEVANCE/APPLICATION Improved diagnostic accuracy of CT coronary angiography in high heart rates reduces the need for pre-scan ß-blockers and makes CT a more robust technique to non-invasively detect significant stenoses.
    Radiological Society of North America 2006 Scientific Assembly and Annual Meeting; 11/2006
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    ABSTRACT: The objective of our study was to compare diagnostic accuracy of MDCT coronary angiography in a population of patients with mild heart rhythm irregularities before and after editing the ECG. Thirty-eight patients who underwent MDCT coronary angiography and conventional coronary angiography were enrolled in the study. The inclusion criterion was the presence of mild heart rhythm irregularities (i.e., premature beats; atrial fibrillation; mistriggering; or low heart rate, defined as 40 beats per minute or less) during the scan. All patients underwent MDCT with the following parameters: 16 detectors; collimation, 0.75 mm; gantry rotation time, 375 msec; 120 kV; and effective milliampere-second setting, 500-600. Images were reconstructed in two settings: before ECG editing and after ECG editing (i.e., arbitrary modification of temporal windows within the cardiac cycle at the site of mild heart rhythm irregularities). Data sets were scored for the presence of significant stenoses (> or = 50% lumen reduction) in coronary segments > or = 2 mm diameter. The results of the two groups were compared with a McNemar test, and a p value of less than 0.05 was considered significant. The sensitivity, specificity, and negative and positive predictive values of MDCT coronary angiography for the detection of significant stenoses before and after ECG editing were 63% (41/65) and 92% (78/85); 97% (251/260) and 96% (305/317); 87% (62/71) and 87% (81/93); 91% (251/275) and 97% (305/313), respectively (p < 0.05). The proportion of nonassessable segments was reduced from 17% (70/416) before ECG editing to 2% (10/416) after. ECG editing significantly improves diagnostic accuracy in a selected population of patients with mild heart rate irregularities.
    American Journal of Roentgenology 04/2006; 186(3):634-8. · 2.90 Impact Factor
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    ABSTRACT: Multi-detector computed tomography (CT) scanners, by virtue of their high temporal and spatial resolution, permit imaging of the coronary arteries. However, motion artifacts, especially in patients with higher heart rates, can impair image quality. We thus evaluated the performance of a new dual-source CT (DSCT) with a heart rate independent temporal resolution of 83 ms for the visualization of the coronary arteries in 14 consecutive patients. METHODS: Fourteen patients (mean age 61 years, mean heart rate 71 min(-1)) were studied by DSCT. The system combines two arrays of an X-ray tube plus detector (64 slices) mounted on a single gantry at an angle of 90 degrees With a rotation speed of 330 ms, a temporal resolution of 83 ms (one-quarter rotation) can be achieved independent of heart rate. For data acquisition, intraveous contrast agent was injected at a rate of 5 ml/s. Images were reconstructed with 0.75 slice thickness and 0.5 mm increment. The data sets were evaluated concerning visibility of the coronary arteries and occurrence of motion artifact. RESULTS: Visualization of the coronary arteries was successful in all patients. Most frequently, image reconstruction at 70% of the cardiac cycle provided for optimal image quality (50% of patients). Of a total of 226 coronary artery segments, 222 (98%) were visualized free of motion artifact. In summary, DSCT constitutes a promising new concept for cardiac CT. High and heart rate independent temporal resolution permits imaging of the coronary arteries without motion artifacts in a substantially increased number of patients as compared to earlier scanner generations. Larger and appropriately designed studies will need to determine the method's accuracy for detection of coronary artery stenoses.
    European Journal of Radiology 04/2006; 57(3):331-5. · 2.51 Impact Factor

Publication Stats

6k Citations
286.44 Total Impact Points

Institutions

  • 2000–2007
    • Siemens
      • • Siemens Medical Solutions
      • • Computed Tomography
      Princeton, New Jersey, United States
  • 2005–2006
    • Medical University of South Carolina
      Charleston, South Carolina, United States
  • 2002–2006
    • University Hospital München
      München, Bavaria, Germany
    • Universitätsklinikum Tübingen
      • Division of Diagnostic and Interventional Radiology
      Tübingen, Baden-Württemberg, Germany
  • 2001–2002
    • Technische Universität München
      • Institute of Radiology
      München, Bavaria, Germany
  • 2000–2002
    • Ludwig-Maximilian-University of Munich
      • Department of Clinical Radiology
      München, Bavaria, Germany
    • University of Tuebingen
      • Institute for Physiology
      Tübingen, Baden-Wuerttemberg, Germany