Biomedical subjects

Uwe Pietrzyk

Publications and source records attributed to Uwe Pietrzyk.

5 recordsLinked to original sources

PubMed2006

Processing the spatial configuration of complex actions involves right posterior parietal cortex: An fMRI study with clinical implications.

The left hemispheric dominance for complex motor behavior is undisputed. Clinical observations of complex motor deficits in patients with right hemispheric lesions, however, suggest an additional contribution of the right hemisphere to higher motor control. We assessed, using functional MRI (fMRI), which brain regions are implicated in processing the spatial aspects of complex, object-related actions. Using a blocked, factorial design, 17 healthy volunteers were asked to detect either spatial or sequential errors (factor ERROR) in complex activities of daily living, presented as video sequences with the appropriate object(s) or as pantomimes (factor STIMULUS). Observing complex actions (irrespective of stimulus type) activated a bilateral frontoparietal network. Observing actions with objects (relative to pantomimes) differentially increased neural activity in the fusiform gyrus and inferior occipital cortex bilaterally. Observing pantomimes, i.e., the same actions but without any object, differentially activated right prefrontal cortex, anterior cingulate cortex, the precuneus, and left cerebellum. The left cingulate cortex was differentially activated when subjects assessed the sequencing of actions. By contrast, assessing the spatial configuration of complex actions differentially increased neural activity in right posterior parietal cortex. A significant interaction of ERROR and STIMULUS was revealed for the right inferior parietal cortex only. These findings suggest a specific role of the right hemisphere, especially of right posterior parietal cortex, in processing spatial aspects of complex actions and thus provide a physiological basis for the observed apraxic motor deficits in patients with right hemispheric damage.

Activities of Daily Living↗

PubMed2006

Concepts of registration and correction of head motion in positron emission tomography.

The long acquisition times (up to hours) in PET brain imaging bear a high risk of head motion, which results in artefacts like blurred images and may even lead to misinterpretation and useless data. With the increased resolution of high performance PET scanners, the influence of head movements becomes more and more relevant. Especially in the analysis of small brain structures, e.g. during ROI-analysis, head motion results in inaccuracies of quantified data. This may also influence the kinetic analysis and generate artifacts in parametric images calculated from a motion-affected image sequence. This work presents the feasibility of head motion registration using an external motion tracking system. The implementation of the multi acquisition frame method and an event-by-event method to correct PET data for motion are described. The effects of motion correction are demonstrated on the basis of phantom measurements and patient data. The influence of motion correction on parametric imaging is described in a receptor study.

Artifacts↗

PubMed2005

On the use of positioning aids to reduce misregistration in the head and neck in whole-body PET/CT studies.

UNLABELLED: Involuntary patient motion from insufficient patient preparation may lead to local misregistration of PET/CT images and, thus, can invalidate the attempt to fuse the resulting images. We estimate the efficacy of selected patient support structures in reducing the likelihood of patient motion in the area of the head and neck during whole-body PET/CT studies. METHODS: Motion of the head and neck was estimated in 51 healthy volunteers during simulated whole-body PET/CT studies using an infrared camera-based tracking system. Four patient positioning schemes (arms down) were studied, with the neck placed on a standard PET head holder with no support at the sides (setup A), on a special head holder fitted with a subject-specific mold from construction foam (setup B), on a vacuum-lock bag (setup C), and on a special head holder fitted with a vacuum-lock bag (setup D). We report the average motion of the head and neck as the difference in the position of a set of target points between the simulated CT image and PET image of the head and neck. To estimate the efficacy of additional patient support measures in clinical practice, we reviewed the misregistration of the head and neck in whole-body PET/CT studies of 10 patients each who were imaged using setups A and C by comparing the mean translational and rotational alignment parameters from a semiautomatic linear registration approach needed to realign the CT and PET images. RESULTS: Average translational and rotational misalignment of the head and neck was highest for setup A, at 7 mm and 1 degrees , respectively. Misalignment was reduced to a minimum of 1.4 mm and 0.3 degrees for setup D. Setup B resulted in a similar reduction in patient motion of the head and neck: 2.4 mm and 0.4 degrees , whereas setup C provided only somewhat improved support, with a resulting average misalignment of 4.5 mm and 0.7 degrees. In clinical PET/CT, we found setup C to reduce translational misalignment of the CT and PET images of the head and neck to 2 mm, compared with 6 mm for setup A, whereas no significant reduction of rotational misalignment was observed. CONCLUSION: Average motion of the head and neck in unrestrained subjects during whole-body PET/CT examinations can be reduced by use of rigid positioning aids, such as foam molds, or vacuum-lock bags. Vacuum-lock bags are reusable, quickly adaptable, and olfactory neutral and can be used routinely, either alone or in combination with a head holder, in whole-body PET/CT for high-quality examinations.

Equipment Failure Analysis↗

PubMed2005

Motion artifact reduction on parametric PET images of neuroreceptor binding.

UNLABELLED: PET studies of cerebral neuroreceptors are often recorded over periods ranging from 1 to 2 h, and head movements during the studies not only lead to blurred images but also may seriously disturb the kinetic analysis. We report the effect of motion on parametric images of the distribution volume ratio (DVR), as well as possible improvements if the dynamic PET data are corrected for head movements. METHODS: The study was performed with the 5-hydroxytryptamine 2A receptor ligand (18)F-altanserin. During PET scanning, which was performed in list mode for 1 h, the position of the head was monitored by an infrared motion-tracking system. The list mode data were sorted into time frames of between 10 s and 2 min. Motion was corrected using the multiple-acquisition-frame (MAF) approach, which calculates individual attenuation files for each emission frame and its corresponding head position to avoid misalignment of transmission and emission data. After reconstruction of attenuation-corrected emission frames, each image frame was realigned to match the head position of the first frame of the emission scan. The resulting motion-corrected dynamic images were evaluated using the noninvasive Logan plot to obtain parametric images of DVR. RESULTS: DVR images of motion-affected (18)F-altanserin scans showed artifacts whose extent depended on the amount of movement. The artifacts were mainly at the border between gray matter and white matter and at the outer border of gray matter. They were seen as discontinuities and small spots whose values exceeded the expected DVR values or were even negative and that disappeared when motion correction was applied. These effects in human data were also seen on simulated (18)F-altanserin images that contained no statistical noise. CONCLUSION: Whereas the native PET images looked just blurred if the patient moved during the PET scan, parametric images of the Logan DVR, which are calculated by pixelwise linear regression, contained severe discontinuities primarily at the cortical edge. MAF-based motion correction was able to avoid these errors.

Artifacts↗

PubMed2003

Postictal psychosis in temporal lobe epilepsy.

PURPOSE: Postictal psychosis is a well-known complication, occurring especially in patients with temporal lobe epilepsy. It usually runs a benign course. The literature on this topic is sparse, and the underlying pathogenic mechanisms are not known. METHODS: We report five patients with temporal lobe epilepsy in whom postictal psychosis developed during the course of video-EEG monitoring; they were studied with hexamethyl-propyleneamine-oxime single-photon emission computed tomography (HMPAO-SPECT) during and after the psychotic event. RESULTS: In comparison to the interictal state, all SPECT scans obtained during postictal psychosis were remarkable for bifrontal and bitemporal hyperperfusion patterns. Some studies also demonstrated unilateral left lateral frontal hyperperfusion. These cortical blood-flow patterns appeared to be distinct from those obtained during complex partial seizures. CONCLUSIONS: Our data suggest that postictal psychoses in patients with temporal lobe epilepsy are associated with hyperactivation of both temporal and frontal lobe structures. This hyperperfusion may reflect ongoing (subcortical) discharges, active inhibitory mechanisms that terminate the seizure, or simply a dysregulation of cerebral blood flow.

Adult↗