Silvia Obenauer
University of Göttingen
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Featured researches published by Silvia Obenauer.
European Radiology | 2002
Uwe Fischer; Friedemann Baum; Silvia Obenauer; Susanne Luftner-Nagel; D. von Heyden; R. Vosshenrich; E. Grabbe
Abstract. The goal of this prospective study was to compare a full-field digital mammography system (FFDM) to a conventional screen-film mammography system (SFM) for the detection and characterization of microcalcifications. Fifty-five patients with 57 isolated microcalcification clusters were examined using a FFDM system (Senographe 2000D, GE Medical Systems, Milwaukee, Wis.) and a SFM system (Senographe DMR, GE Medical Systems, Milwaukee, Wis.). A conventional screen-film mammogram and a digital contact mammogram were obtained of each cluster. The image quality and the number of calcification particles were evaluated, and a characterization (BI-RADS 1–5) of microcalcifications was given by four experienced readers. Histopathology revealed 16 benign lesions (sclerosing adenosis, dysplasia, hamartoma, radial scar) in 15 patients and 21 malignant tumors (in situ carcinoma, invasive carcinoma) in 20 patients. Twenty patients had benign changes verified by long-term follow-up. Image quality of FFDM was assessed as superior to SFM in more than 50% of the cases. The FFDM showed more calcifications in 41% of all cases. Sensitivity and specificity for FFDM vs SFM were 95.2 vs 91.9% and 41.4 vs 39.3%, respectively. Moreover, FFDM demonstrated a higher diagnostic accuracy (deviation: 0.86 BI-RADS steps) compared with FSM (deviation 0.93 BI-RADS steps). The FFDM system with a 100-µm pixel size provides better image quality than SFM in patients with mammographic microcalcifications. The FFDM has a higher sensitivity and a higher reliability in characterizing microcalcifications.
European Radiology | 2005
Silvia Obenauer; K.-P. Hermann; E. Grabbe
The Breast Imaging Reporting and Data System (BI-RADS) of the American College of Radiology (ACR) is a tool created to reduce variability in the terminology used in mammographic reports. An illustration of mammographic examples from our institution interpreted according to the BI-RADS lexicon of the American College of Radiology (ACR) is presented. A literature review concerning the usefulness and limitations of the BI-RADS lexicon is given.
Clinical Imaging | 2003
Katharina Marten; R. Vosshenrich; M. Funke; Silvia Obenauer; Friedemann Baum; E. Grabbe
OBJECTIVE Müllerian duct anomalies (MDAs) result from nondevelopment or nonfusion of the müllerian ducts and occur in 1-5% of women. Accurate diagnosis of the various subtypes is of great importance as MDAs are frequently associated with a broad variety of clinical symptoms. Recently, evidence arose that MRI might play a major role in diagnosis of MDAs. We present four cases of diverse subtypes of MDAs and the corresponding MRI findings. MATERIALS AND METHODS Patients (n = 4) with clinical suspicion of MDAs were examined with MRI. Coronal and transaxial T1- and T2-weighted images were acquired. Diagnosis was made and patients were grouped according to the American Fertility Societys classification. Patients underwent laparoscopy or laparotomy in order to confirm the diagnosis. RESULTS MRI revealed MDAs in all patients. In detail, one patient was diagnosed with hypoplastic uterus, one with unicornuate uterus with a noncommunicating rudimentary horn, one with bicornuate uterus bicollis with a double vagina and one with septate uterus. MRI diagnosis was correct in all cases, as confirmed by subsequent surgical intervention. CONCLUSION MRI is a valuable tool in diagnosis of MDA subtypes. Its use will help to spare patients mutilating surgery and to prevent pregnancy-associated complications.
European Radiology | 2004
Katharina Marten; Tobias Seyfarth; Florian Auer; Edzard Wiener; Andreas Grillhösl; Silvia Obenauer; Ernst J. Rummeny; Christoph Engelke
To evaluate the performance of experienced versus inexperienced radiologists in comparison and in consensus with an interactive computer-aided detection (CAD) system for detection of pulmonary nodules. Eighteen consecutive patients (mean age: 62.2 years; range 29–83 years) prospectively underwent routine 16-row multislice computed tomography (MSCT). Four blinded radiologists (experienced: readers 1, 2; inexperienced: readers 3, 4) assessed image data against CAD for pulmonary nodules. Thereafter, consensus readings of readers 1+3, reader 1+CAD and reader 3+CAD were performed. Data were compared against an independent gold standard. Statistical tests used to calculate interobserver agreement, reader performance and nodule size were Kappa, ROC and Mann–Whitney U. CAD and experienced readers outperformed inexperienced readers (Az=0.72, 0.71, 0.73, 0.49 and 0.50 for CAD, readers 1–4, respectively; P<0.05). Performance of reader 1+CAD was superior to single reader and reader 1+3 performances (Az=0.93, 0.72 for reader 1+CAD and reader 1+3 consensus, respectively, P<0.05). Reader 3+CAD did not perform superiorly to experienced readers or CAD (Az=0.79 for reader 3+CAD; P>0.05). Consensus of reader 1+CAD significantly outperformed all other readings, demonstrating a benefit in using CAD as an inexperienced reader replacement. It is questionable whether inexperienced readers can be regarded as adequate for interpretation of pulmonary nodules in consensus with CAD, replacing an experienced radiologist.
European Radiology | 2002
K.-P. Hermann; Silvia Obenauer; M. Funke; E. Grabbe
Abstract. The objective of this study was a comparison of a full-field digital mammography (FFDM) system and a conventional screen-film mammography (SFM) system with respect to the detectability of simulated small masses and microcalcifications in the magnification mode. All images were obtained using 1.8 times magnification. The FFDM images were obtained at radiation dose levels of 1.39, 1.0, 0.7, 0.49 and 0.24 times that of the SFM images. A contrast-detail phantom was used to compare the detection of simulated lesions using a four alternative forced-choice reader study with three readers. The correct observation ratio (COR) was calculated as the fraction of correctly identified lesions to the total number of simulated lesions. Soft-copy reading was performed for all digital images. Direct magnification images acquired with the digital system showed a lower object contrast threshold than those acquired with the conventional system. For equal radiation dose, the digital system provided a significantly increased COR (0.95) compared with the screen-film system (0.82). For simulated microcalcifications, the corresponding difference was 0.90 to 0.72. The digital system allowed equal detection to screen-film at 40% of the radiation dose used for screen film. Digital magnification images are superior to screen-film magnification images for the detection of simulated small masses and microcalcifications even at a lower radiation dose.
The Journal of Pathology | 2006
Michal Grzmil; Silke Kaulfuss; Paul Thelen; Bernhard Hemmerlein; Stefan Schweyer; Silvia Obenauer; Tae Won Kang; Peter Burfeind
Recently, deregulated expression of the anti‐apoptotic protein Bax inhibitor‐1 (BI‐1) has been shown in several human cancers. In this report, we show that BI‐1 is expressed at various levels in six different human breast cancer cell lines. In order to investigate the function of BI‐1 in oestrogen‐dependent MCF‐7, T‐47D and oestrogen‐independent MDA‐MB‐231 breast cancer cells, the RNA interference technique was used to knock down BI‐1 expression specifically. Suppression of BI‐1 expression caused a significant increase in spontaneous apoptosis in MDA‐MB‐231 cells, whereas MCF‐7 and T‐47D cells remained almost unaffected. Furthermore, BI‐1 expression analysis using a cancer profiling array showed up‐regulation of BI‐1 expression in cancer samples of breast, uterus and ovary, whereas down‐regulated BI‐1 expression was identified in stomach, colon, kidney, lung and rectal cancer. In addition, immunohistochemical studies using a BI‐1‐specific antibody on human breast cancer specimens also revealed that BI‐1 is expressed in the majority of cases. Moreover, to analyse whether BI‐1 expression is oestrogen receptor‐dependent, tumour cells were treated with oestradiol, ICI and tamoxifen: this showed no significant changes in BI‐1 expression. Taken together, our results demonstrate that BI‐1 expression is differentially deregulated in different cancers and that BI‐1 plays an important role in preventing certain breast cancer cells from undergoing apoptosis. Thus, the development of novel therapeutic strategies based on targeting BI‐1 gene expression in breast cancer could be restricted to selected individual cancer types. Copyright
European Radiology | 2002
Friedemann Baum; Uwe Fischer; Silvia Obenauer; E. Grabbe
Abstract. For the first time, full-field digital mammography (FFDM) allows computer-aided detection (CAD) analysis of directly acquired digital image data. The purpose of this study was to evaluate a CAD system in patients with histologically correlated breast cancer depicted with FFDM. Sixty-three cases of histologically proven breast cancer detected with FFDM (Senographe 2000D, GE Medical Systems, Buc, France) were analyzed using a CAD system (Image Checker V2.3, R2 Technology, Los Altos, Calif.). Fourteen of these malignancies were characterized as microcalcifications, 37 as masses, and 12 as both. The mammographic findings were categorized as BI-RADS 3 (n=5), BI-RADS 4 (n=17) and BI-RADS 5 (n=40). The sensitivity for malignant lesions and the rate of false-positive marks per image were calculated. The sensitivity and its 95% confidence interval (CI) were estimated. The sensitivity of the CAD R2 system in breast cancer seen on FFDM was 89% for microcalcifications [CI95%=(70%; 98%)] and 81% for masses [CI95%=(67%; 91%)]. As expected, the detection rate was higher in lesions categorized as BI-RADS 5 (37 of 40) compared with lesions categorized as BI-RADS 4 (11 of 17). In the group categorized as BI-RADS 3 the detection rate was 4 of 5 lesions; however, this group was very small. The rate of false-positive marks was 0.35 microcalcification marks/image and 0.26 mass marks/image. The overall rate of false-positive marks was 0.61 per image. CAD based on FFDM provides an optimized work flow. Results are equivalent to the results reported for CAD analysis of secondarily digitized image data. Sensitivity for microcalcifications is acceptable and for masses is low. The number of false-positive marks per image should be reduced.
Clinical Radiology | 2003
Katharina Marten; Christoph Engelke; M. Funke; Silvia Obenauer; Friedemann Baum; E. Grabbe
AIM The purpose of this study was to determine the feasibility of echocardiogram (ECG)-gated multi-slice CT angiography (MCTA) in patients with clinical suspicion of acute venous thromboembolism (VTE), to investigate the effect of ECG-gating on cardiac motion artefacts, and to determine the diagnostic reader agreement of ECG-gated MCTA in comparison with conventional MCTA. MATERIALS AND METHODS Forty-eight consecutive patients were prospectively enrolled and randomly underwent ECG-gated (n=25, group 1) or non-ECG-gated (n=23, group 2) eight-slice pulmonary MCTA. Image data were evaluated by three independent chest radiologists with respect to the presence or absence of emboli at different arterial levels (main, lobar, segmental, and subsegmental arteries), and with regard to cardiac motion artefacts. Statistical tests used to calculate inter-observer agreement were weighted kappa statistics, extended kappa statistics and confidence indices indicating three-reader agreement accuracy. RESULTS Twenty-seven patients (56.3%) were diagnosed to have pulmonary embolism (13 from group 1, 14 from group 2). Cardiac motion artefacts were significantly more frequent in group 2 (70% in group 2 versus 13% in group 1, p=0.0001). The overall diagnostic agreement was excellent with both MCTA techniques (three-reader confidence index for all vascular territories: 0.76 and 0.84 for groups 1 and 2, respectively (extended kappa=0.69 and 0.78, respectively); three-reader confidence index for diagnosis of VTE: 0.94 and 0.85 for groups 1 and 2, respectively (extended kappa=0.91 and 0.73, respectively), weighted kappa=0.81-0.83 and 0.92-0.95 for groups 1 and 2, respectively, and did not differ significantly between the two groups. In addition there was no significant difference of inter-observer agreement in either group at any assessed pulmonary arterial level. CONCLUSION ECG-gated pulmonary MCTA is feasible in patients with clinical suspicion of VTE. However, ECG-gated image acquisition did not influence the diagnostic reader agreement accuracy and inter-observer agreement of MCTA. Hence, it does not appear to be advantageous for the MCTA diagnosis of pulmonary embolism.
Molecular Carcinogenesis | 2008
Ines Ecke; Albert Rosenberger; Silvia Obenauer; Christian Dullin; Fritz Aberger; Sarah Kimmina; Stefan Schweyer; Heidi Hahn
Mutations in the Hedgehog (Hh) receptor Patched (Ptch) are responsible for a variety of tumors, which show ligand‐independent stimulation of the Hh/Ptch signaling cascade. Cyclopamine is an alkaloid of the corn lily Veratrum californicum, which blocks activity of the pathway by inhibition of Smoothened (Smo), the signal transduction partner of Ptch. This results in growth inhibition of Hh/Ptch‐dependent tumor cells in vitro, of subcutaneous xenografts as well as of precancerous lesions in Ptch+/− mice. However, the evidence that treatment with cyclopamine is an effective anti‐cancer therapy against full‐blown tumors is sparse. Here, we have investigated the responsiveness of full‐blown Hh/Ptch‐associated rhabdomyosarcoma (RMS) to this drug. Hh pathway activity and proliferation of cultured primary RMS cells was inhibited by cyclopamine. Hh signaling was also partially suppressed by the drug in RMS in vivo, but cyclopamine treatment did not result in stable disease or tumor regression. It also did not affect proliferation, apoptosis or the differentiation status of RMS. This was in contrast to anti‐proliferative effects on tumor growth caused by doxorubicin, an anthracycline routinely used in therapy of human RMS. In summary, our data indicate that there must be additional factors that render full‐blown Hh/Ptch‐associated RMS insensitive against anti‐proliferative effects of cyclopamine in vivo.
Journal of Digital Imaging | 2006
Silvia Obenauer; Christian Sohns; Carola Werner; E. Grabbe
The goal of this study was to evaluate the performance of a computer-aided detection (CAD) system in full-field digital mammography (Senographe 2000D, General Electric, Buc, France) in finding out carcinomas depending on the parenchymal density. A total of 226 mediolateral oblique (MLO) and 186 craniocaudal (CC) mammographic views of histologically proven cancers were retrospectively evaluated with a digital CAD system (ImageChecker V2.3 R2 Technology, Los Altos, CA, USA). Malignant tumors were detected correctly by CAD in MLO view in 84.85% in breasts with parenchymal tissue density of the American College of Radiology (ACR) type 1, in 70.33% of the ACR type 2, in 68.12% of the ACR type 3, and in 69.70% of the ACR type 4. For the CC view, similar results were found according to the ACR types. Using the chi-square and McNemar tests, there was no statistical significance. However, a trend of better detection could be seen with decreasing ACR type. In conclusion, there seems to be a tendency for breast tissue density to affect the detection rate of breast cancer when using the CAD system.