Volker Aurich

Non-Linear Gaussian Filters Performing Edge Preserving Diffusion

This paper presents a new diffusion method for edge preserving smoothing of images. In contrast to other methods it is not based on an anisotropic modification of the heat conductance equation, rather on a modification of the way the solution of the heat conductance equation is obtained by convolving the initial data with a Gaussian kernel. Hence the method uses simple non-linear modifications of Gaussian filters, thus avoiding iteration steps and convergence problems. A chain of three to five filters with suitable parameters provides excellent smoothing of fine image details without destroying the coarser structures. The size and contrast of the eliminated details can be selected. The choice of the parameters is not critical and the edges are not displaced when changing the scale. The filter stages can be implemented efficiently on almost any parallel hardware architecture.

Probabilistic 3D MRI atlas of the human cerebellar dentate/interposed nuclei.

In a previous study, a three-dimensional (3D) MRI atlas of the human cerebellar nuclei was introduced based on findings in one healthy human subject [Dimitrova, A., Weber, J., Redies, C., Kindsvater, K., Maschke, M., Kolb, F.P., Forsting, M., Diener, H.C., Timmann, D., 2002. MRI atlas of the human cerebellar nuclei. NeuroImage 17, 240-255]. The present MRI investigation was designed to study variability of the anatomy of the dentate/interposed nuclei in a larger group of healthy subjects. Similar to our previous study, iron-induced susceptibility artifacts were used to visualize the cerebellar nuclei as hypointensities on MR images. Data of 63 healthy subjects (27 female, 36 male; mean age 45.3+/-13.4 years, age range 22--71 years) were included. A 3D axial volume of the cerebellum was acquired using a T2*-weighted FLASH sequence on a Siemens Sonata 1.5 T MR scanner. Each volume was registered, re-sampled to 1.00 x 1.00 x 1.00 mm(3) voxel size and spatially normalized into a standard proportional stereotaxic space using SPM99. Dentate/interposed nuclei were traced on axial images and saved as regions of interest using MRIcro-software by two independent examiners. A probabilistic 3D MRI atlas of the cerebellar dentate/interposed nuclei is presented based on findings in all subjects.

Impairments of prehension kinematics and grasping forces in patients with cerebellar degeneration and the relationship to cerebellar atrophy

OBJECTIVE This study established the relationship between kinematic and grip force parameters in prehension tasks, disease severity and cerebellar atrophy in patients with cerebellar degeneration. METHODS Prehension was tested in a condition during which the hand reached out, grasped, and lifted an object. Task complexity was modified by limiting the transport component to a single-joint movement, and introducing a bimanual condition. RESULTS Compared to controls the cerebellar patients showed disturbances in hand transport, in hand shaping and the most pronounced in time to peak grip force and the grip/load force coupling. Task-dependent changes did not differ between groups. Ataxia scores revealed significant correlations with hand transport and shaping measures only. Ataxia subscores correlated with volume reduction of appropriate longitudinal cerebellar zones. Volume reduction of the intermediate zone was associated with grip force coordination deficits. CONCLUSIONS Results indicate that the cerebellum may have a more general role in motor control of grasping independent of task complexity. Temporal and coordinative measures of grip force appear to be most useful to assess the severity of grasping deficits in patients with cerebellar degeneration not detectable by clinical ataxia scales. SIGNIFICANCE To assess the severity and course of cerebellar disease grip force control in a standard prehension task is a sensitive quantitative measure.

Detection of colorectal polyps by multislice CT colonography with ultra-low-dose technique: comparison with high-resolution videocolonoscopy

BACKGROUND This prospective study compared multislice CT colonography with ultra-low-dose technique to high-resolution videocolonoscopy as the standard for detection of colorectal cancer and polyps. METHODS After standard bowel preparation, 115 patients underwent multislice CT colonography with an ultra-low-dose multislice CT colonography protocol immediately before videocolonoscopy. After noise reduction by using a mathematical algorithm, ultra-low-dose multislice CT colonographic images were analyzed in blinded fashion, and the results were compared with the results of high-resolution videocolonoscopy. RESULTS A total of 150 lesions were detected by high-resolution videocolonoscopy in 115 patients. For ultra-low-dose multislice CT colonography, sensitivities for detection of polyps less than 5 mm in size, 5 to 10 mm, and greater than 10 mm in diameter were 76%, 91%, and 100%, respectively. Although the sensitivity for detection of flat lesions was only 50%, the sensitivity and the specificity for detection of polyps 5 mm or greater in size were 94% and 84%, respectively. For adenomatous lesions greater than 5 mm in size, sensitivity was 94% and specificity was 92%. The overall specificity was 79%. The calculated effective radiation dose ranged between 0.75 and 1.25 mSv. CONCLUSIONS Compared with high-resolution videocolonoscopy, ultra-low-dose multislice CT colonography has excellent sensitivity and specificity for detection of colorectal lesions 5 mm or greater in size, and the radiation exposure is relatively low. However, before this technique can be generally recommended for colorectal screening, further improvement in the detection of flat and extremely small lesions must be achieved.

Preserved verb generation in patients with cerebellar atrophy.

A role of the right cerebellar hemisphere has been suggested in linguistic functions. Nevertheless, studies of verb generation in cerebellar patients provide inconsistent results. The aim of the present study was to examine verb generation in a larger group of cerebellar patients with well-defined lesions. Ten subjects with degenerative cerebellar disorders and ten healthy matched controls participated. Subjects had to generate verbs to the blocked presentation of photographs of objects (i.e. four blocks of sixteen objects). As control condition, the objects had to be named. Furthermore, dysarthria was quantified by means of a sentence production and syllable repetition task. Volumetric analysis of individual 3D-MR scans was performed to quantify cerebellar atrophy. Cerebellar patients were slower in the sentence production and syllable repetition tasks, and cerebellar volume was decreased compared to controls. Despite cerebellar atrophy and dysarthria, the answers produced did not differ between patients and controls. In addition, both groups revealed the same amount of decrease in verbal reaction time over blocks (i.e. learning). The results suggest that the role of the cerebellum in verb generation is less pronounced than previously suggested.

Degree of Cerebellar Ataxia Correlates with Three-Dimensional MRI-Based Cerebellar Volume in Pure Cerebellar Degeneration

The aim of the present study was to compare the severity of cerebellar ataxia as measured by the International Cooperative Ataxia Rating Scale (ICARS) by Trouillas et al. [ J Neurol Sci 1997;145:205–211] with the cerebellar volume in chronic cerebellar disease. Fifteen patients with pure cerebellar degeneration were investigated. Seven patients suffered from spinocerebellar ataxia type 6, 5 from idiopathic late-onset cerebellar ataxia, 2 from autosomal dominant cerebellar ataxia type III and 1 from episodic ataxia type 2. Volumetric analysis was based on individual three-dimensional MR images. Total ICARS score significantly inversely correlated with the cerebellar volume (r = –0.805, p < 0.0001), correlations between ICARS subscores and cerebellar volume were significant for upper and lower limb ataxia, ataxia of posture and gait, and dysarthria, but not for the oculomotor subscore. The results suggest that the degree of cerebellar atrophy in pure cerebellar degenerative disorders is accompanied by comparable functional impairment (i.e. degree of cerebellar ataxia).

Evaluation of multiple-session delay eyeblink conditioning comparing patients with focal cerebellar lesions and cerebellar degeneration.

The acquisition and timing of delay-conditioned eyeblink responses (CRs) have been shown to be significantly impaired in patients with disorders restricted to the cortex of the superior cerebellum. We were interested if patients improve incidences and timing of CRs across three sessions on three consecutive days. A standard delay paradigm was used in 9 patients with diffuse cerebellar degeneration, 13 patients with ischemic cortical cerebellar lesions and in 13 controls. High-resolution magnetic resonance imaging (MR imaging) was used to ensure that hemispheral lobules VI and/ or Crus I were lesioned in all stroke patients with the interposed nuclei being preserved. On day 1 patients with stroke but not with degenerative disorders showed significant CR acquisition, although total CR incidences remained significantly lower than in controls. No further improvement was visible on days 2 and 3 neither in patients with focal lesions nor in patients with cerebellar degeneration. CRs occurred earlier in cerebellar patients, most pronounced in patients with degenerative disorders. In patients with stroke but not in the degenerative group timing had improved on the third day close to values of the control subjects. Findings show that lesions of the cerebellar cortex produce permanent deficits in the acquisition of delay-conditioned eyeblink responses. Overall, mean CR incidence was higher in focal compared to degenerative disorders, most likely because the critical lobules (VI and Crus I) were lesioned only in part. Intact anterior lobe, which it thought to contribute to CR timing, may explain recovery of disordered timing in focal cerebellar patients.

Correlation of cerebellar volume with eyeblink conditioning in healthy subjects and in patients with cerebellar cortical degeneration

In the present study, acquisition and timing of conditioned eyeblink responses (CRs) were correlated with magnetic resonance imaging (MRI)-based cerebellar volume both in healthy human subjects and patients with cerebellar disease. Thirty-three healthy subjects and 25 patients with pure cortical cerebellar degeneration participated. Cerebellar volumes were measured for the cortex of the anterior lobe, the cortex of the posterior lobe, the white matter of the cerebellum and the cerebrum based on 3D MR images. CR parameters were assessed in a standard delay paradigm. In healthy subjects CR acquisition was significantly related to the volume of the grey matter of the posterior lobe, but neither to the volume of the grey matter of the anterior lobe, nor to the cerebellar white matter and nor to the cerebral volume. As expected, CR acquisition and volume of the cortex of the posterior lobe showed age-related decline in the controls. Furthermore, CR acquisition was significantly reduced in patients with cerebellar degeneration compared to controls. In the cerebellar group, however, no significant correlations between CR acquisition and any of the cerebellar volumes were observed. Floor effects are most likely responsible for this observation. Although CRs occurred significantly earlier in cerebellar patients compared to controls, no significant correlations between CR timing parameters and any of the cerebellar volumes were observed. Extending previous findings in healthy human subjects, age-related decline of the cerebellar cortex of the posterior lobe was related with a reduction of CR acquisition. Findings provide further evidence that the cerebellar cortex plays an important role in the acquisition of eyeblink conditioning in humans.

Dynamic changes in murine vessel geometry assessed by high‐resolution magnetic resonance angiography: A 9.4T study

To establish high‐resolution magnetic resonance angiography (MRA) protocols to monitor and quantify dynamic changes of vascular remodeling in pathologic mouse models.

Noise/dose reduction and image improvements in screening virtual colonoscopy with tube currents of 20 mAs with nonlinear Gaussian filter chains

Purpose: To evaluate a filter method to extract noise from 20mAs Computed Tomography (CT) data for virtual colonoscopy screening. Method: Nonlinear Gaussian filter chains (NLGF) applied to CT datasets were used to extract noise. To test the efficiency of NLGF a simulation of different ellipsoidal shells with different levels of noise were used. Phantom studies were performed using a multidetector CT (tube currents 10 to 140mAs). 15 patients at high risk for colon cancer underwent a virtual colonoscopy examination (140mAs) and conventional colonoscopy. Different noise levels were added to each CT raw dataset (analog to 40 and 20mAs scans). Virtual endoscopic fly-throughs were performed and rated by two radiologists (image quality). Results: NLGF were able to extract image noise while preserving image structures down to signal--to--noise ratio levels of 0.5. The phantom studies (perspex bars, simulated polyps) were reconstructed without relevant changes between 20 and 140mAs. There were no significant differences between the endoscopic fly-throughs of 140 and 20mAs examinations (2 readers). Conclusion: NLGF is a promising preprocessing method for effective noise reduction in CT datasets. Edges are preserved as well as accentuated in high contrast images.