M Fenchel

University of Tuebingen, Tübingen, Baden-Württemberg, Germany

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Publications (208)456.49 Total impact

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    ABSTRACT: With further increase of CT numbers and their dominant contribution to medical exposure, there is a recent quest for more effective dose control. While re-introduction of iterative reconstruction (IR) has proved its potential in many applications, a novel focus is placed on more noise efficient detectors. Our purpose was to assess the potential of IR in combination with an integrated circuit detector (ICD) for aggressive dose reduction in head CT. Non-contrast low-dose head CT (190 mAs, CTDIvol 33.2 mGy) was performed in fifty consecutive patients, using a new noise efficient detector and IR. Images were assessed in terms of quantitative and qualitative image quality and compared with standard dose acquisitions (320 mAs, CTDIvol 59.7 mGy), using a conventional detector and filtered-back-projection. By combining IC detector and IR in low-dose exams, signal-to-noise was improved by about 13% above baseline level in the standard-dose control group. Both, contrast-to-noise ratio (2.02±0.6 vs. 1.88±0.4; p=0.18) and objective measurements of image sharpness (695± 84 vs.705± 151 Change in HU/Pixel; p=0.79) were fully preserved in the low-dose group. Likewise, there was no significant difference in the grading of several subjective image quality parameters when both noise reducing strategies were used in the low-dose exams. Combination of noise efficient detector with IR allows for meaningful dose reduction in head CT without compromise of standard image quality. Advances in knowledge: Our study demonstrates the feasibility of almost 50% dose reduction in head CT (1.1 mSv per scan) through combination of novel dose reducing strategies.
    The British journal of radiology 04/2015; 88(1050):20140404. DOI:10.1259/bjr.20140404 · 2.03 Impact Factor
  • M. Horger · C. Claussen · U. Kramer · M. Fenchel · M. Lichy · S. Kaufmann ·
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    ABSTRACT: Objective: To assess feasibility of whole-body diffusion-weighted MRI (wbDWI) for very early evaluation of response to therapy in different lymphoma subtypes. Materials and methods: 20 patients (10 male, 10 female; mean age 50.7±16.1±17.2 years) underwent wbDWI (calculation of apparent diffusion coefficient [ADC] with b=0, 800s/mm(2)) at baseline and within a median of 7 days after therapy onset. Lymphoma manifestations were evaluated with respect to changes in ADC and size at follow-up with up to six of the largest lesions per patient undergoing quantification. An increase in ADC as well as a decrease in size at follow-up was classified as responder, whereas neither change in ADC nor in size (or progression) was considered non-responder. Results were confirmed at interim measurements (after 3-4 chemotherapy cycles) and 6 months after treatment. Results: 90 lymphoma lesions were analyzed. 18 patients were classified as responders and 2 as non-responder at FU (mean, 1 week). DWI results accurately (100%) correlated with the subsequent interim course of all lesions. mean baseline ADC was 0.79±0.28×10(-3)s/mm(2). For responders mean follow-upADC increased by 64.6±56.5% (p<0.001) whereas lesions size decreased by mean 14.4±13.3% (p<0.001). In the non-responder, both values did not significantly change. In patients classified as responders six months after treatment, meanADC increase at FU was 70.3±57.8% (p<0.001) whereas mean size decrease vs. baseline was 15.8±13.6% as compared to non-responders (22.4±39.9%) and 5.4±0.9%, respectively. Conclusion: wbDWI with ADC analysis represents a feasible diagnostic tool for very early response assessment in lymphoma patients enabling also prediction of long-term response.
    European Journal of Radiology 09/2014; 83(9). DOI:10.1016/j.ejrad.2014.05.027 · 2.37 Impact Factor
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    ABSTRACT: Purpose: Iterative reconstruction has recently been revisited as a promising concept for substantial CT dose reduction. The purpose of this study was to assess the potential benefit of sinogram affirmed iterative reconstruction (SAFIRE) in head CT by comparing objective and subjective image quality at reduced tube current with standard dose filtered back projection (FBP). Materials and methods: Non-contrast reduced dose head CT (255 mAs, CTDIvol 47.8 mGy) was performed in thirty consecutive patients and reconstructed with SAFIRE and FBP. Images were assessed in terms of quantitative and qualitative image quality and compared with FBP of standard dose acquisitions (320 mAs, CTDI vol 59.7 mGy). Results: In reduced dose CT examinations, use of SAFIRE versus FBP resulted in 47% increase in contrast-to-noise ratio (CNR) (2.49 vs. 1.69; p<0.0001). While reduction of tube current was associated with 13% decrease in CNR, quantitative degradation of image quality at lower dose was more than compensated through SAFIRE (2.49 vs. 1.96; p=0.0004). Objective measurements of image sharpness were comparable between FBP and SAFIRE reconstructions (575.9 ± 74.1 vs. 583.4 ± 74.7 change in HU/Pixel; p=0.28). Compared to standard dose FBP, subjective grading of noise as well as overall image quality scores were significantly improved when SAFIRE was used in reduced dose exams (1.3 vs. 1.6, p=0.006; 1.3 vs. 1.7, p=0.026). Conclusion: At 20% dose reduction, reconstruction of head CT by SAFIRE provides above standard objective and subjective image quality, suggesting potential for more vigorous dose savings in neuroradiology CT applications.
    European journal of radiology 04/2013; 82(9). DOI:10.1016/j.ejrad.2013.03.011 · 2.37 Impact Factor
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    ABSTRACT: Introduction: High-pitch CT angiography (CTA) is a recent innovation that allows significant shortening of scan time with volume coverage of 43 mm per second. The aim of our study was to assess this technique in CTA of the head and neck. Methods: CTA of supra-aortic arteries was performed in 50 patients using two acquisition protocols: conventional single-source 64-slice (pitch 1.2) and high-pitch dual-source 128-slice CT (pitch 3.2). Subjective and objective image quality of supra-aortic vessel ostia as well as intra- and extra-cranial segments was retrospectively assessed by blinded readers and radiation dose compared between the two protocols. Results: Conventional and high-pitch CTA achieved comparable signal-to-noise ratios in arterial (54.3 ± 16.5 versus 57.3 ± 14.8; p = 0.50) and venous segments (15.8 ± 6.7 versus 18.9 ± 8.9; p = 0.21). High-pitch scanning was, however, associated with sharper delineation of vessel contours and image quality significantly improved at the level of supra-aortic vessel ostia (p < 0.0001) as well as along the brachiocephalic trunk (p < 0.0001), the subclavian arteries (p < 0.0001), proximal common carotid arteries (p = 0.01), and vertebral V1 segments (p < 0.0001). Using the high-pitch mode, the dose-length product was reduced by about 35% (218.2 ± 30 versus 141.8 ± 20 mGy × cm). Conclusions: Due to elimination of transmitted cardiac motion, high-pitch CTA of the neck improves image quality in the proximity of the aortic arch while significantly lowering radiation dose. The technique thus qualifies as a promising alternative to conventional spiral CTA and may be particularly useful for identification of ostial stenosis.
    Neuroradiology 12/2012; 55(4). DOI:10.1007/s00234-012-1120-y · 2.49 Impact Factor
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    ABSTRACT: Rationale and objectives: Computed tomographic angiography is the standard in routine follow-up after endovascular aneurysm repair, causing radiation exposure; thus, dose-saving strategies should be applied. The aim of this study was to evaluate the novel sinogram-affirmed iterative reconstruction (SAFIRE) algorithm in terms of clinical usability and potential reduction of radiation exposure. Materials and methods: Forty-six patients underwent computed tomographic angiographic follow-up after endovascular aneurysm repair. Data were acquired using a dual-source computed tomographic scanner running both x-ray tubes at the same voltage (120 kV). Raw data were reconstructed using projections of both tubes with filtered back projection (FBP) and of only one tube with FBP and SAFIRE, corresponding to synthetic acquisition with half the radiation dose of the clinical routine radiation dose. Image sets were objectively compared regarding signal-to-noise ratio and edge sharpness. Two radiologists independently assessed a set of subjective criteria, including diagnostic usability, depiction of contrasted vessels, and image noise. Results: Half-dose (HD) SAFIRE images showed significantly higher signal-to-noise ratios compared to full-dose FBP images (P < .001), while having equal edge sharpness (P = .56). Most of the subjectively assessed parameters, such as diagnostic usability and depiction of contrasted vessels, were rated similar for HD SAFIRE and full-dose FBP images. Full-dose FBP images depicted fine anatomic structures more clearly (P < .05), while HD SAFIRE data sets showed less noise (P < .01). HD FBP images performed worse on all criteria (P < .001). Interrater agreement was good (κ = 0.74-0.80). Conclusions: Using the SAFIRE algorithm, the radiation dose of high-contrast abdominal computed tomographic angiography is reducible from routine clinical levels by up to 50% while maintaining good image quality and diagnostic accuracy.
    Academic radiology 10/2012; 20(2). DOI:10.1016/j.acra.2012.08.015 · 1.75 Impact Factor
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    ABSTRACT: Purpose. The aim of the present work was to test the feasibility of the time-resolved MR-angiography (TWIST-MRA) of cervical arteries using double bolus injection. Material and Methods. TWIST-MRA with a temporal resolution of 8.4 seconds for each frame and a spatial resolution with a voxel size of 0.61 × 0.58 × 0.8 mm3 was performed in 24 patients. A biphasic bolus injection protocol was used with the second injection being started 21 seconds after the first contrast dye bolus. Diagnostic image quality was rated according to a 4-point scale. Results. In 12 patients (50%) no clear separation between the cervical venous and arterial vessels was evident after the first bolus injection. Using TWIST-MRA data acquired after the second bolus a sufficient diagnostic image quality (rating ≥3, mean 3.5) could be obtained in 22 of 24 patients (92%). Discussion. The double bolus injection protocol using TWIST-MRA allows for very good separation of the cervical arteries.
    10/2012; 2012:203538. DOI:10.1155/2012/203538
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    ABSTRACT: Objective: The purpose of this article is to provide a practical review of the spectrum of imaging findings in patients with tick-borne encephalitis (TBE) and to address possible differential diagnoses. Conclusion: Imaging findings in TBE resemble those of other infections, such as meningoencephalitis. However, a predilection for the thalami, basal ganglia, cerebellum, and anterior horns of the spinal cord suggests the possibility of TBE.
    American Journal of Roentgenology 08/2012; 199(2):420-7. DOI:10.2214/AJR.11.7911 · 2.73 Impact Factor
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    ABSTRACT: To quantify and compare T2 signal and apparent diffusion coefficient (ADC) in pilocytic and pilomyxoid astrocytoma (PA and PMA) and correlate results with myxoid content. Echo-planar diffusion weighted images (DWI) and standard magnetic resonance imaging (MRI) findings were reviewed retrospectively in patients with PA (n=34) and PMA (n=8). Regions of interest (ROIs) were drawn on ADC maps within tumor parts with lowest ADC values. Apparent diffusion coefficient values in tumor were normalized to those in cerebrospinal fluid (ADC/CSF). The ratio of T2 signal intensity in solid tumor parts to CSF (T2/CSF) was registered. Myxoid matrix was histologically quantified retrospectively in 8 PMAs and 17 PAs and correlated with imaging findings. Mean ADC/CSF for PA and PMA was 0.53±0.10 and 0.69±0.10 (p<0.01). Mean T2/CSF for PA and PMA was 0.78±0.19 and 0.93±0.09 (p<0.01). Mean proportion of myxoid tumor matrix in PA was 50% (range, 10-100%) and 93% (range, 90-100%) in PMA (p=0.004). Eight patients (32%; all PA) had less than 50% myxoid content and 17 (68%; 8 PA; 9 PMA) had more. There was positive correlation of ADC/CSF, T2/CSF and ADC (r2=0.61, 0.65 and 0.60 respectively) and significant difference between the groups with more and less than 50% myxoid content (p=0.01 for ADC/CSF and T2/CSF and p=0.02 for ADC). General imaging features of PA and PMA are non-specific, ADC values and T2 signal intensity are generally higher in the latter, reflecting the proportion of myxoid matrix in these tumors.
    The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 07/2012; 39(4):491-8. DOI:10.1017/S0317167100014013 · 1.53 Impact Factor
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    ABSTRACT: Purpose. To estimate effective dose and organ equivalent doses of prospective ECG-triggered high-pitch CTCA. Materials and Methods. For dose measurements, an Alderson-Rando phantom equipped with thermoluminescent dosimeters was used. The effective dose was calculated according to ICRP 103. Exposure was performed on a second-generation dual-source scanner (SOMATOM Definition Flash, Siemens Medical Solutions, Germany). The following scan parameters were used: 320 mAs per rotation, 100 and 120 kV, pitch 3.4 for prospectively ECG-triggered high-pitch CTCA, scan range of 13.5 cm, collimation 64 × 2 × 0.6 mm with z-flying focal spot, gantry rotation time 280 ms, and simulated heart rate of 60 beats per minute. Results. Depending on the applied tube potential, the effective whole-body dose of the cardiac scan ranged from 1.1 mSv to 1.6 mSv and from 1.2 to 1.8 mSv for males and females, respectively. The radiosensitive breast tissue in the range of the primary beam caused an increased female-specific effective dose of 8.6%±0.3% compared to males. Decreasing the tube potential, a significant reduction of the effective dose of 35.8% and 36.0% can be achieved for males and females, respectively (P < 0.001). Conclusion. The radiologist and the CT technician should be aware of this new dose-saving strategy to keep the radiation exposure as low as reasonablly achievable.
    05/2012; 2012:724129. DOI:10.1155/2012/724129
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    ABSTRACT: To retrospectively determine which features of urinary calculi are associated with their detection after virtual elimination of contrast medium at dual-energy computed tomographic (CT) urography by using a novel tin filter. The institutional ethics committee approved this retrospective study, with waiver of informed consent. A total of 152 patients were examined with single-energy nonenhanced CT and dual-energy CT urography in the excretory phase (either 140 and 80 kV [n=44] or 140 and 100 kV [n=108], with tin filtration at 140 kV). The contrast medium in the renal pelvis and ureters was virtually removed from excretory phase images by using postprocessing software, resulting in virtual nonenhanced (VNE) images. The sensitivity regarding the detection of calculi on VNE images compared with true nonenhanced (TNE) images was determined, and interrater agreement was evaluated by using the Cohen k test. By using logistic regression, the influences of image noise, attenuation, and stone size, as well as attenuation of the contrast medium, on the stone detection rate were assessed. Threshold values with maximal sensitivity and specificity were calculated by means of receiver operating characteristic analyses. Eighty-seven stones were detected on TNE images; 46 calculi were identified on VNE images (sensitivity, 52.9%). Interrater agreement revealed a κ value of 0.95 with TNE images and 0.91 with VNE data. Size (long-axis diameter, P=.005; short-axis diameter, P=.041) and attenuation (P=.0005) of the calculi and image noise (P=.0031) were significantly associated with the detection rate on VNE images. As threshold values, size larger than 2.9 mm, maximum attenuation of the calculi greater than 387 HU, and image noise less than 20 HU were found. After virtual elimination of contrast medium, large (>2.9 mm) and high-attenuation (>387 HU) calculi can be detected with good reliability; smaller and lower attenuation calculi might be erased from images, especially with increased image noise.
    Radiology 05/2012; 264(1):119-25. DOI:10.1148/radiol.12110851 · 6.87 Impact Factor
  • A Korn · C Braun · M Fenchel · U Ernemann · M Horger ·

    RöFo - Fortschritte auf dem Gebiet der R 05/2012; 184(5):397-401. DOI:10.1055/s-0031-1274843 · 1.40 Impact Factor
  • M Horger · M Fenchel · D Spira · T Nägele · CD Claussen · S Heckl · U Ernemann ·

    RöFo - Fortschritte auf dem Gebiet der R 05/2012; 184(S 01). DOI:10.1055/s-0032-1311496 · 1.40 Impact Factor
  • M Horger · M Fenchel · D Spira · T Nägele · U Ernemann · S Heckl ·

    RöFo - Fortschritte auf dem Gebiet der R 05/2012; 184(S 01). DOI:10.1055/s-0032-1311495 · 1.40 Impact Factor
  • M Horger · CD Claussen · D Spira · M Fenchel · M Lichy · S Kaufmann ·

    RöFo - Fortschritte auf dem Gebiet der R 05/2012; 184(S 01). DOI:10.1055/s-0032-1311427 · 1.40 Impact Factor

  • RöFo - Fortschritte auf dem Gebiet der R 05/2012; 184(S 01). DOI:10.1055/s-0032-1311052 · 1.40 Impact Factor
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    M Fenchel · F Roser · T Nägele · U Ernemann · M Horger ·

    RöFo - Fortschritte auf dem Gebiet der R 03/2012; 184(3):191-5. DOI:10.1055/s-0031-1274771 · 1.40 Impact Factor

  • RöFo - Fortschritte auf dem Gebiet der R 02/2012; 184(02). DOI:10.1055/s-0031-1300874 · 1.40 Impact Factor
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    ABSTRACT: IR has recently demonstrated its capacity to reduce noise and permit dose reduction in abdominal and thoracic CT applications. The purpose of our study was to assess the potential benefit of IR in head CT by comparing objective and subjective image quality with standard FBP at various dose levels. Ninety consecutive patients were randomly assigned to undergo nonenhanced and contrast-enhanced head CT at a standard dose (320 mAs; CTDI, 60.1) or 15% (275 mAs; CTDI, 51.8) and 30% (225 mAs; CTDI, 42.3) dose reduction. All acquisitions were reconstructed with IR in image space, and FBP and images were assessed in terms of quantitative and qualitative IQ. Compared with FBP, IR resulted in lower image noise (P ≤ .02), higher CNR (P ≤ .03), and improved subjective image quality (P ≤ .002) at all dose levels. While degradation of objective and subjective IQ at 15% dose reduction was fully compensated by IR (CNR, 1.98 ± 0.4 at 320 mAs with FBP versus 2.05 ± 0.4 at 275 mAs with IR; IQ, 1.8 versus 1.7), IQ was considerably poorer at 70% standard dose despite using the iterative approach (CNR, 1.98 ± 0.3 at 320 mAs with FBP versus 1.85 ± 0.4 at 225 mAs with IR, P = .18; IQ, 1.8 versus 2.2, P = .03). Linear regression analysis of CNR against tube current suggests that standard CNR may be obtained until approximately 20.4% dose reduction when IR is used. Compared with conventional FBP, IR of head CT is associated with significant improvement of objective and subjective IQ and may allow dose reductions in the range of 20% without compromising standard image quality.
    American Journal of Neuroradiology 02/2012; 33(2):218-24. DOI:10.3174/ajnr.A2749 · 3.59 Impact Factor
  • M Fenchel · A Korn · T Nägele · U Ernemann · M Horger ·

    RöFo - Fortschritte auf dem Gebiet der R 12/2011; 183(12):1093-6. · 1.40 Impact Factor
  • M. Fenchel · A. Korn · T. Nägele · U. Ernemann · M. Horger ·

    RöFo - Fortschritte auf dem Gebiet der R 12/2011; 183(12):1093-1096. DOI:10.1055/s-0031-1295619 · 1.40 Impact Factor

Publication Stats

2k Citations
456.49 Total Impact Points


  • 2004-2014
    • University of Tuebingen
      • Department of Internal Medicine
      Tübingen, Baden-Württemberg, Germany
  • 2003-2010
    • Universitätsklinikum Tübingen
      • Division of Diagnostic and Interventional Radiology
      Tübingen, Baden-Württemberg, Germany
  • 2008
    • Universitätsklinikum Erlangen
      Erlangen, Bavaria, Germany
  • 2007
    • University of California, Los Angeles
      • Department of Radiology
      Los Ángeles, California, United States