Biomedical subjects

Thorsten Schormann

Publications and source records attributed to Thorsten Schormann.

3 recordsLinked to original sources

PubMed2004

Delayed shrinkage of the brain after ischemic stroke: preliminary observations with voxel-guided morphometry.

BACKGROUND AND PURPOSE: The most important effect of cerebral ischemia is brain infarction. In this magnetic resonance imaging (MRI) study, the authors aimed at assessing postischemic brain atrophy. METHODS: Ten patients suffering from their first acute cerebral ischemia in the territory of the middle cerebral artery were studied retrospectively. Three-dimensional MRI volume scans were recorded in the acute and chronic stage after infarction and analyzed voxel by voxel intraindividually with the newly developed voxel-guided morphometry. RESULTS: Shrinkage of brain tissue was detected in all patients, not only in the perilesional cortical structures but also in contralateral homolog cortex areas and subcortically in the striatum and thalamus. This secondary shrinkage was not related to the size of the infarcts or to the clinical outcome of patients. CONCLUSIONS: Our study suggests that delayed brain atrophy after acute ischemic stroke involved areas anatomically connected with the ischemic brain lesion but nevertheless was accompanied by a simultaneous improvement of the neurological deficit.

Atrophy↗

PubMed2003

Voxel-guided morphometry ("VGM") and application to stroke.

Monitoring of cerebral diseases associated with a change of morphology (e.g., stroke) requires unprecedented accuracy for quantification of its morphological progression for each voxel. The purpose of this paper is to provide a technique [voxel-guided morphometry (VGM)] to quantify macroscopic anatomical differences. VGM consists of four steps: 1) coarse linear alignment by the extended principle axes theory (ePAT) generalized to affine movements; 2) a cross-correlation-based technique using a matrix-norm for fine linear alignment; 3) the applied high-dimensional multiresolution full multigrid method determines the nonlinear deformations, thereby achieving a complete exploitation of information and effective processing. The method measures a gray-value-guided movement of each voxel from source to target. The resulting high-dimensional deformation field is further processed by 4) determination of volume alterations for each voxel. Furthermore, the effect of linear registration errors on final morphometric measurements is discussed and the conditions for a bijective correspondence of voxels assuming small alterations are derived. To illustrate the technique the changing morphology of different subjects suffering from cerebral infarction is presented by using commonly available T1-weighted magnetic resonance volumes. VGM visualizes that ischemic as well as remote regions are affected by stroke.

Algorithms↗

PubMed2002

Comparison of spatial normalization procedures and their impact on functional maps.

The alignment accuracy and impact on functional maps of four spatial normalization procedures have been compared using a set of high resolution brain MRIs and functional PET volumes acquired in 20 subjects. Simple affine (AFF), fifth order polynomial warp (WRP), discrete cosine basis functions (SPM), and a movement model based on full multi grid (FMG) approaches were applied on the same dataset for warping individual volumes onto the Human Brain Atlas (HBA) template. Intersubject averaged structural volumes and tissue probability maps were compared across normalization methods and to the standard brain. Thanks to the large number of degrees of freedom of the technique, FMG was found to provide enhanced alignment accuracy as compared to the other three methods, both for the grey and white matter tissues; WRP and SPM exhibited very similar performances whereas AFF had the lowest registration accuracy. SPM, however, was found to perform better than the other methods for the intra-cerebral cerebrospinal fluid (mainly in the ventricular compartments). Limited differences in terms of activation morphology and detection sensitivity were found between low resolution functional maps (FWHM approximately 10 mm) spatially normalized with the four methods, which overlapped in 42.8% of the total activation volume. These findings suggest that the functional variability is much larger than the anatomical one and that precise alignment of anatomical features has low influence on the resulting intersubject functional maps. When increasing the spatial resolution to approximately 6 mm, however, differences in localization of activated areas appear as a consequence of the different spatial normalization procedure used, restricting the overlap of the normalized activated volumes to only 6.2%.

Adult↗