Hans-Christian Bauknecht

Differential activation of the dorsal striatum by high-calorie visual food stimuli in obese individuals

The neural systems regulating food intake in obese individuals remain poorly understood. Previous studies applied positron emission tomography and manipulated hunger and satiety to investigate differences in appetitive processing between obese and normal-weight individuals. However, it is not known whether manipulation of stimulus value may yield different neural activity in obese as compared to control subjects when intrinsic physiological states are kept constant. We used functional magnetic resonance imaging to investigate 13 obese and 13 normal-weight subjects and manipulated food motivation by presenting visual food stimuli differing in their caloric content and energy density. In contrast to controls, obese women selectively activated the dorsal striatum while viewing high-caloric foods. Moreover, in the high-calorie condition body mass index (BMI) predicted activation in the dorsal striatum, anterior insula, claustrum, posterior cingulate, postcentral and lateral orbitofrontal cortex. The results indicate that in obese individuals simple visual stimulation with food stimuli activates regions related to reward anticipation and habit learning (dorsal striatum). Additionally, high-calorie food images yielded BMI-dependent activations in regions associated with taste information processing (anterior insula and lateral orbitofrontal cortex), motivation (orbitofrontal cortex), emotion as well as memory functions (posterior cingulate). Collectively, the results suggest that the observed activation is independent of the physiological states of hunger and satiation, and thus may contribute to pathological overeating and obesity. Some of the observed activations (dorsal striatum, orbitofrontal cortex) are likely to be dopamine-mediated.

Advanced Segmentation Techniques for Lung Nodules, Liver Metastases, and Enlarged Lymph Nodes in CT Scans

This article presents advanced algorithms for segmenting lung nodules, liver metastases, and enlarged lymph nodes in CT scans. Segmentation and volumetry are essential tasks of a software assistant for oncological therapy monitoring. Our methods are based on a hybrid algorithm originally developed for lung nodules that combines a threshold-based approach with model-based morphological processing. We propose extensions that deal with particular challenges of each lesion type: lung nodules that are attached to non-convex parts of the pleura, rim-enhancing and peripheral liver metastases and lymph nodes with an extensive contact to structures of similar density. We evaluated our methods on several hundred lesions in clinical datasets and the quality of segmentations was rated by radiologists. The results were classified as acceptable or better in 81% to 92% of the cases for the different algorithms and readers.

4-D Imaging in Cerebrovascular Disorders by Using 320-Slice CT: Feasibility and Preliminary Clinical Experience

RATIONALE AND OBJECTIVES The authors report study protocols and initial clinical experience in assessing patients with acute and chronic cerebrovascular disorders using the recently introduced technique of volume computed tomography (VCT). MATERIALS AND METHODS Thirteen patients with presumptive cerebrovascular insufficiency underwent VCT using a 320-slice scanner (detector width, 160 mm), including time-resolved whole-brain perfusion and cerebral angiography (four-dimensional computed tomographic angiography [CTA] and computed tomographic perfusion [CTP]). Unenhanced cranial CT (cCT) and helical cervicocranial CT (three-dimensional CTA) were added according to clinical requirements. Study protocols are presented, and image quality, data management, and radiation exposure issues are discussed. RESULTS In 12 of 13 patients, the procedure was performed successfully on admission; in the other patient, the study was aborted for clinical reasons and repeated. Total scan time amounted to about 5 minutes, and data reconstruction times were up to 10 minutes. About 9000 primary images were generated, partially in the enhanced Digital Imaging and Communications in Medicine format, thus requiring new data postprocessing and management strategies. Image artifacts restricted the use of single-rotation cCT and incremental VCT (three-dimensional CTA). Overall exposure figures (computed tomographic dose index and dose-length product) were increased by 65% on average when three-dimensional CTA was added to volume cCT and four-dimensional CTA and CTP (5.0 mSv and 2178 mGy . cm, respectively). CONCLUSION Preliminary clinical experience indicates that whole-brain four-dimensional CTA and CTP is a robust technique that provides relevant clinical information with respect to whole-brain perfusion as well as cerebral hemodynamics. The exposure benefit of deriving time-resolved perfusion and vessel images from one source data set is compromised when adding three-dimensional CTA to the protocol. Other acquisition techniques specific to VCT, such as single-rotation cCT and incremental three-dimensional CTA, suffer from restrictions in terms of image quality at present.

OncoTREAT: a software assistant for cancer therapy monitoring

AbstractObjectCancer is one of the leading causes of death worldwide and therapy options are often associated with severe stress for the patient and high costs. Therefore, precise evaluation of therapy success is essential. Material and Methods In the framework of the VICORA research project (Virtual Institute for Computer Assistance in Clinical Radiology), a software application was developed to support the radiologist in evaluating the response to tumor therapy. The application provides follow-up support for oncological therapy monitoring by volumetric quantification of lung, liver and brain metastases as well as enlarged lymph nodes and assists the user by temporal registration of lesion positions. Results With close cooperation between computer scientists and radiologists the application was tested and optimized to achieve a high degree of usability. Several clinical studies were carried out to evaluate the robustness and reproducibility of the volumetry methods. Conclusion Automatic volumetry and segmentation allows reliable detection of tumor growth and has the potential to increase reliability and significance of monitoring tumor growth in follow-up examinations.

Intra- and Interobserver Variability of Linear and Volumetric Measurements of Brain Metastases Using Contrast-Enhanced Magnetic Resonance Imaging

Objectives:To compare the intra- and interobserver variability of diameter and semiautomated volume measurements of brain metastases on contrast-enhanced magnetic resonance imaging (CE-MRI) data. Materials and Methods:About 75 MRI staging examinations of patients with metastasized renal cell carcinoma, thyroid cancer, or malignant melanoma (mean age, 56 years; range, 40–75 years) were included. Patients had been examined with a routine MRI protocol, including a CE 3D T1-weighted MP-RAGE sequence (1-mm slice thickness). MRI data were retrospectively analyzed using the OncoTREAT segmentation system (MeVis, Bremen, Germany, version 1.6). Volume of 355 enhancing brain metastases included in the analysis as well as the largest diameter according to Response Evaluation Criteria for Solid Tumors were measured by 2 radiologists. Intra- and interobserver variability was calculated. Results:Metastases (n = 355) had a mean diameter of 12.2 mm (range, 3.4–44.3 mm) and a mean volume of 1.4 cm3 (range, 12–25.1 cm3). With respect to interobserver variability analysis revealed broader limits of agreement for response evaluation criteria for solid tumor measurements of all lesions (range, ±27.8%–±33.0%; unsigned mean: 0.2%–2.5%) than for volume measurements (range, ±21.4%–±23.3%; unsigned mean, 0.1%–0.3%) with statistically significant differences between diameter and volume measurements (P ≤ 0.001). Limits of agreement were similar for intra- and interobserver comparisons. Conclusion:Semiautomated segmentation of brain metastases on the basis of CE-MRI yielded reproducible volume measurements with a lower variability compared with linear measurements. Volumetry of contrast-enhancing brain metastases appears to be a suitable method for size determination in oncologic follow-up imaging.

Comparative evaluation of 2D time-of-flight and 3D elliptic centric contrast-enhanced MR venography in patients with presumptive cerebral venous and sinus thrombosis

We retrospectively evaluated an elliptic centric ordered 3D (ec 3D) magnetic resonance venography (MRV) technique in comparison to 2D time‐of‐flight (2D TOF) MRV in patients with presumptive cerebral venous sinus thrombosis (CVST). Twenty‐five patients (mean age 40.6 ± 16.5 years) with presumptive CVST underwent cerebral MRI including 2D TOF and ec 3D MRV. Radiologic findings and clinical outcome were correlated. MRV studies were evaluated by two neuroradiologists in a blinded manner for image quality, assessment of various sinus, internal cerebral veins (ICV), vein of Labbé and Galen (VL/VG) as well as for additional imaging procedures required. Sensitivity/specificity of ec 3D MRV amounted to 85.7%/97.2% as compared with 2D TOF 71.4%/55.6 %. Ec 3D MRV performed superior in terms of image quality as well as assessment of all sinus and veins except for the straight sinus. Additional imaging procedures were less often required in ec 3D MRV studies (28% vs. 66% for 2D TOF MRV; P < 0.001). Interobserver agreement was significantly increased by using ec 3D MRV (93.1% vs. 70.9% of readings). The results of our study provide additional evidence for the superiority of ec 3D compared with 2D TOF MR venography for the diagnosis or exclusion of acute CVST in daily clinical practice.

Comparative evaluation of 64-slice CT angiography and digital subtraction angiography in assessing the cervicocranial vasculature

Background: Noninvasive 64-slice computed tomography angiography (64-MSCTA) closely approximates conventional catheter angiography (DSA) in terms of detail resolution. Objective: Retrospective evaluation of cervicocranial (cc) 64-MSCTA in comparison with DSA in patients with presumptive cc vascular disorders. Material and methods: Twenty-four 64-MSCTA studies (32 mm detector width, slice thickness 0.5 mm, 120 kv, 150 mAs, pitch 0.75) of patients with presumptive cc vascular pathology (13 men, 11 women, mean age 38.3 ± 11.3 yrs, range 19–54 yrs) were assessed in comparison with DSA studies without abnormal findings in age matched patients (11 men, 13 women, mean age 39.7 ± 11.9 yrs, range 18–54 yrs). Study readings were performed in a blinded manner by two neuroradiologists with respect to image quality and assessibility of various cc vascular segments by using a five point scale. Radiation exposure was calculated for 64-MSCTA. Results: Each reader assessed 384/528 different vessel segments (64-MSCTA/DSA). Superior image quality was attributed to DSA with respect to the C1 ICA–C6 ICA, A3 ACA, and P3 PCA segments as well the AICA and SCA. 64-MSCTA was scored superior for C7 ICA and V4 VA segments. A significantly increased number of nonassessable V2- and V3 VA segments in DSA studies was noted. The effective dose for 64-MSCTA amounted to 2.2 mSv. Conclusions: 64-MSCTA provides near-equivalent diagnostic information of the cc vasculature as compared with DSA. According to our results, DSA should be considered primarily when peripheral vessels (A3/P3) or ICA segments close to the skull base (C2-5) are of interest, such as in primary angiitis or stenoocclusive ICA disease, respectively.

Virtual endoscopy of the tympanic cavity based on high-resolution multislice computed tomographic data.

Objective This study was designed to assess the value of high-resolution multislice computed tomography (MSCT) data of the petrous bone for the virtual endoscopic visualization of the tympanic cavity. Background The recently introduced MSCT technology has improved spatial resolution in the z axis as well as scan speed in computed tomography. Three-dimensional rendering of high-resolution MSCT data of the petrous bone may be expected to provide endoluminal views of superior image quality, thus competing with transtympanic endoscopy (otoendoscopy). Setting This study was conducted at a university teaching hospital. Materials and Methods Cadaveric phantom studies in a MSCT scanner were performed to define a data acquisition protocol, combining adequate detail resolution with low tube current. Subsequently, the cadaveric phantom underwent otoendoscopy. The postprocessing parameters of the three-dimensional rendering protocol were chosen to produce views closely resembling the corresponding otoendoscopic images. High-resolution data from 18 patients with pathologic conditions of the middle ear, as suggested by clinical findings and assessment of cross-sectional data, were postprocessed using the volume rendering technique to generate standardized virtual endoscopic views. A total of 36 virtual endoscopic scans of the tympanic cavity were generated. Results With regard to intermediate and high-density structures, virtual endoscopic images, based on MSCT data, yielded endoluminal views closely resembling corresponding otoendoscopic views. Virtual endoscopy seems useful for imaging ossicular pathologic conditions such as dysplasia and chain disruption as well as for assessing patient status before and after otosurgery. Conclusion MSCT data sets allow for generating virtual endoscopic views closely resembling otoendoscopic images. The technique is especially useful when ossicular pathologic changes are present as well as for preoperative and postoperative imaging of otologic procedures.

Effect of 7.0 Tesla Mri on Upper Eyelid Implants

To ensure the MRI compatibility of various eyelid implants in high-field MRI, 3 eyelid weights made of pure gold (99.99%), pure platinum (99.95%), and a platinum (97%)/iridium (3%) alloy were examined in vitro. Temperature changes, position changes, and imaging artifacts of the different implants were determined in a small-bore 7.0 Tesla MRI system. The 7.0 Tesla MRI system demonstrated that none of the eyelid implants carried a risk of heating or dislocation; therefore, these implants are MRI compatible up to a magnetic field strength of 7.0 Tesla.

3D contour based local manual correction of tumor segmentations in CT scans

Segmentation is an essential task in medical image analysis. For example measuring tumor growth in consecutive CT scans based on the volume of the tumor requires a good segmentation. Since manual segmentation takes too much time in clinical routine automatic segmentation algorithms are typically used. However there are always cases where an automatic segmentation fails to provide an acceptable segmentation for example due to low contrast, noise or structures of the same density lying close to the lesion. These erroneous segmentation masks need to be manually corrected. We present a novel method for fast three-dimensional local manual correction of segmentation masks. The user needs to draw only one partial contour which describes the lesions actual border. This two-dimensional interaction is then transferred into 3D using a live-wire based extrapolation of the contour that is given by the user in one slice. Seed points calculated from this contour are moved to adjacent slices by a block matching algorithm. The seed points are then connected by a live-wire algorithm which ensures a segmentation that passes along the border of the lesion. After this extrapolation a morphological postprocessing is performed to generate a coherent and smooth surface corresponding to the user drawn contour as well as to the initial segmentation. An evaluation on 108 lesions by six radiologists has shown that our method is both intuitive and fast. Using our method the radiologists were able to correct 96.3% of lesion segmentations rated as insufficient to acceptable ones in a median time of 44s.