Peter Erhard - Academia.edu (original) (raw)

Papers by Peter Erhard

Bei traumatologischen und orthopadischen Eingriffen gehort die Blutsperre zur taglichen Routine. ... more Bei traumatologischen und orthopadischen Eingriffen gehort die Blutsperre zur taglichen Routine. Obwohl die obere Zeitgrenze der Tourniquet-Ischamie von 2 h rein empirisch festgelegt ist, wird diese in der Regel akzeptiert. Gerade aber bei komplexeren Eingriffen ware es wunschenswert, diese Zeitspanne verlangern zu konnen. Es ist daher erstaunlich, das die pharmakologische Beeinflusbarkeit des ischamie- und reperfusionsbedingten Schadens am Skelettmuskel bis jetzt wenig untersucht worden ist.

NeuroImage, 2019

The sensitivity to subject motion is one of the major challenges in functional MRI (fMRI) studies... more The sensitivity to subject motion is one of the major challenges in functional MRI (fMRI) studies in which a precise alignment of images from different time points is required to allow reliable quantification of brain activation throughout the scan. Especially the long measurement times and laborious fMRI tasks add to the amount of subject motion found in typical fMRI measurements, even when head restraints are used. In case of moving subjects, prospective motion correction can maintain the relationship between spatial image information and subject anatomy by constantly adapting the image slice positioning to follow the subject in real time. Image-based prospective motion correction is well-established in fMRI studies and typically computes the motion estimates based on a volume-to-volume image registration, resulting in low temporal resolution. This study combines fMRI using simultaneous multislice imaging with multislice-to-volume-based image registration to allow sub-TR motion detection with subsequent real-time adaption of the imaging system. Simultaneous multislice imaging is widely used in fMRI studies and, together with multislice-to-volume-based image registration algorithms, enables computing suitable motion states after only a single readout by registering the simultaneously excited slices to a reference volume acquired at the start of the measurement. The technique is evaluated in three human BOLD fMRI studies (n = 1, 5, and 1) to explore different aspects of the method. It is compared to conventional, volume-to-volume-based prospective motion correction as well as retrospective motion correction methods. Results show a strong reduction in retrospectively computed residual motion parameters of up to 50% when comparing the two prospective motion correction techniques. An analysis of temporal signal-to-noise ratio as well as brain activation results shows high consistency between the results before and after additional retrospective motion correction when using the proposed technique, indicating successful prospective motion correction. The comparison of absolute tSNR values does not show an improvement compared to using retrospective motion correction alone. However, the improved temporal resolution may provide improved tSNR in the presence of more exaggerated intra-volume motion.

Neuropsychologia, 2005

The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exis... more The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exist between clinical studies in apraxic patients and neuroimaging findings on imitation. We therefore aimed to investigate: (1) which areas are recruited during imitation under conditions similar to clinical tests for apraxic deficits; (2) whether there are common lateralized areas subserving imitation irrespective of the acting limb side; and also (3) whether there are differences between hand and finger gestures. We used fMRI in 12 healthy, right handed subjects to investigate the imitation of four types of variable gestures that were presented by video clips (16 different finger and 16 different hand gestures with either the right or the left arm). The respective control conditions consisted of stereotyped gestures (only two gestures presented in pseudorandom order). Subtraction analysis of each type of gesture imitation (variable>stereotyped) revealed a bilateral activation pattern including the inferior parietal cortex Brodmann Area (BA 40), the superior parietal cortex, the inferior frontal cortex (opercular region), the prefrontal motor cortex, the lateral occipito-temporal junction, and the cerebellum. These results were supported by statistical conjunction of all four subtraction analyses and by the common analysis of all four types of gesture imitation. The direct comparison of the right and left hemispheric activation revealed a lateralization to the left only of the inferior parietal cortex. Comparisons between different types of gesture imitation yielded no significant results. In conclusion, gesture imitation recruits bilateral fronto-parietal regions, with significant lateralization of only one area, namely the left inferior parietal cortex. These in vivo data indicate left inferior parietal dominance for gesture imitation in right handers, confirming lesion-based theories of apraxia.

Alcoholism: Clinical and Experimental Research, 2012

Background-Heavy prenatal alcohol exposure leads to widespread cognitive deficits, including prob... more Background-Heavy prenatal alcohol exposure leads to widespread cognitive deficits, including problems with spatial working memory (SWM). Neuroimaging studies report structural and functional abnormalities in FASD, but interpretations may be complicated by the co-occurrence of a family history of alcoholism. Since, this history is also linked to cognitive deficits and brain abnormalities, it is difficult to determine the extent to which deficits are unique to prenatal alcohol exposure. Methods-Age-matched subjects selected from two neuroimaging studies, underwent functional imaging while engaging in a task assessing memory for spatial locations relative to a vigilance condition assessing attention. Pairwise comparisons were made for the following three groups: children with histories of heavy prenatal alcohol exposure (ALC, n=18); those with no prenatal alcohol exposure, but a confirmed family history of alcoholism (FHP, n=18); and non-exposed, family history negative controls (CON, n=17). Results-Relative to CON and FHP, the ALC group showed increased BOLD response in the left middle and superior frontal gyri for the spatial working memory condition relative to the vigilance condition (SWM contrast). Additionally, the ALC group showed unique BOLD response increases in the left lingual gyrus and right middle frontal gyrus relative to CON, and left cuneus and precuneus relative to FHP. Both ALC and FHP showed greater activation compared to CON in the lentiform nucleus and insular region. Conclusions-These results confirm previous studies suggesting SWM deficits in FASD. Differences between the ALC group and the CON and FHP groups suggest the left middle and superior frontal region may be specifically affected in alcohol-exposed children. Conversely, differences from the CON group in the lentiform nucleus and insular region for the ALC and FHP groups may indicate this region is associated with family history of alcoholism rather than specifically with prenatal alcohol exposure.

Aktuelle Neurologie, 2004

& Audiovisual perception and imitation are essential for musical learning and skill acquisition. ... more & Audiovisual perception and imitation are essential for musical learning and skill acquisition. We compared professional pianists to musically naive controls with fMRI while observing piano playing finger-hand movements and serial finger-thumb opposition movements both with and without synchronous piano sound. Pianists showed stronger activations within a fronto-parieto-temporal network while observing piano playing compared to controls and contrasted to perception of serial finger-thumb opposition movements. Observation of silent piano playing additionally recruited auditory areas in pianists. Perception of piano sounds coupled with serial finger-thumb opposition movements evoked increased activation within the sensorimotor network. This indicates specialization of multimodal auditorysensorimotor systems within a fronto-parieto-temporal network by professional musical training. Musical ''language,'' which is acquired by observation and imitation, seems to be tightly coupled to this network in accord with an observationexecution system linking visual and auditory perception to motor performance. &

NeuroImage

Childhood obesity is a rising problem caused in part by unhealthy food choices. Food choices are ... more Childhood obesity is a rising problem caused in part by unhealthy food choices. Food choices are based on a neural value signal encoded in the ventromedial prefrontal cortex, and self-control involves modulation of this signal by the dorsolateral prefrontal cortex (dlPFC). We determined the effects of development, body mass (BMI Cole score) and body mass history on the neural correlates of healthy food choice in children. 141 children (aged 10-17y) from Germany, Hungary and Sweden were scanned with fMRI while performing a food choice task. Afterwards health and taste ratings of the foods were collected. In the food choice task children were asked to consider the healthiness or tastiness of the food or to choose naturally. Overall, children made healthier choices when asked to consider healthiness. However, children who had a higher weight gain per year chose less healthy foods when considering healthiness but not when choosing naturally. Pubertal development stage correlated positively while current body mass correlated negatively with dlPFC activation when accepting foods. Pubertal development negatively and current body mass positively influenced the effect of considering healthiness on activation of brain areas involved in salience and motivation. In conclusion, children in earlier stages of pubertal development and children with a higher body weight exhibited less activation in the dlPFC, which has been implicated in self-control during food choice. Furthermore, pubertal development and body mass influenced neural responses to a health cue in areas involved in salience and motivation. Thus, these findings suggest that children in earlier stages of pubertal development, children with a higher body mass gain and children with overweight may possibly be less susceptible to healthy eating interventions that rely on self-control or that highlight health aspects of food.

BMC Neuroscience

Background: Memory performance of an individual (within the age range: 50-55 years old) showing s... more Background: Memory performance of an individual (within the age range: 50-55 years old) showing superior memory abilities (protagonist PR) was compared to an age-and education-matched reference group in a historical facts ("famous events") retrieval task. Results: Contrasting task versus baseline performance both PR and the reference group showed fMRI activation patterns in parietal and occipital brain regions. The reference group additionally demonstrated activation patterns in cingulate gyrus, whereas PR showed additional widespread activation patterns comprising frontal and cerebellar brain regions. The direct comparison between PR and the reference group revealed larger fMRI contrasts for PR in right frontal, superior temporal and cerebellar brain regions. Conclusions: It was concluded that PR generally recruits brain regions as normal memory performers do, but in a more elaborate way, and furthermore, that he applied a memory-strategy that potentially includes executively driven multi-modal transcoding of information and recruitment of implicit memory resources.

PloS one, 2017

When two tasks are performed simultaneously, performance often declines in one or both tasks. The... more When two tasks are performed simultaneously, performance often declines in one or both tasks. These so-called dual-task costs are more pronounced in old than in young adults. One proposed neurological mechanism of the dual-task costs is that old compared with young adults tend to execute single-tasks with higher brain activation. In the brain regions that are needed for both tasks, the reduced residual capacity may interfere with performance of the dual-task. This competition for shared brain regions has been called structural interference. The purpose of the study was to determine whether structural interference indeed plays a role in the age-related decrease in dual-task performance. Functional magnetic resonance imaging (fMRI) was used to investigate 23 young adults (20-29 years) and 32 old adults (66-89 years) performing a calculation (serial subtraction by seven) and balance-simulation (plantar flexion force control) task separately or simultaneously. Behavioral performance dec...

Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, Jan 24, 2017

Learning new motor skills is important for everyday life and independent living in older age. Whi... more Learning new motor skills is important for everyday life and independent living in older age. While studies on motor sequence learning and motor adaptation revealed age differences that are mostly related to frontal decline with increasing age, data for fine finger force modulation are missing. Twelve young (YA, 18-28 years) and twelve middle-aged older (OA, 55-65 years) adults practiced a force modulation task in precision grip while lying in a 3T MR scanner. Participants followed a sine wave between 5 and 25% of their maximum voluntary contraction (MVC) at a frequency of 0.3 Hz. Ten trials of 30 s were performed to examine learning curves and related changes in Blood Oxygen Level Dependent (BOLD) responses were assessed with functional magnetic resonance imaging (fMRI). Training slopes were similar for YA and OA, with only a trend for differences in performance level. Both age groups revealed decreasing activations with practice in frontal and parietal regions as well as in the ce...

Http Dx Doi Org 10 1080 13554794 2010 532135, May 3, 2011

Savants and prodigies are individuals with exceptional skills in particular mental domains. In th... more Savants and prodigies are individuals with exceptional skills in particular mental domains. In the present study we used functional magnetic resonance imaging to examine neural correlates of calendar calculation in two individuals, a savant with Asperger's disorder and a self-taught mathematical prodigy. If there is a modular neural organization of exceptional performance in a specific mental domain, calendar calculation should be reflected in a considerable overlap in the recruitment of brain circuits across expert individuals. However, considerable individual differences in activation patterns during calendar calculation were noted. The present results indicate that activation patterns produced by complex mental processing, such as calendar calculation, seem to be influenced strongly by learning history and idiosyncratic strategy usage rather than a modular neural organization. Thus, well-known individual differences in complex cognition play a major role even in experts with exceptional abilities in a particular mental domain and should in particular be considered when examining the neural architecture of complex mental processes and skills.

Visualizing and measuring the uncertainty of DTI-based techniques is an important new challenge i... more Visualizing and measuring the uncertainty of DTI-based techniques is an important new challenge in the area of neuroimaging. In this paper, we demonstrate how fiber tracking and quantification of DTI parameters depend on the resolution of the underlying DTI data. For measuring the resulting differences, we propose a novel algorithm that allows for an automatic quantification of MR DTI parameters along arbitrarily oriented fiber bundles as well as an approach for quickly measuring the volume of the sheath enclosing a bundle. Our measurements show that the degree of uncertainty does not depend only on the chosen image resolution but also on the kind of fiber bundle. Introduction: Over the last few years, diffusion tensor imaging (DTI) received raising attention within the neurosurgical and neurological community. Fiber tracking [1] as well as quantification algorithms [2] have been proposed with the motivation to identify major white matter tracts afflicted by an individual pathology ...

Bei traumatologischen und orthopadischen Eingriffen gehort die Blutsperre zur taglichen Routine. ... more Bei traumatologischen und orthopadischen Eingriffen gehort die Blutsperre zur taglichen Routine. Obwohl die obere Zeitgrenze der Tourniquet-Ischamie von 2 h rein empirisch festgelegt ist, wird diese in der Regel akzeptiert. Gerade aber bei komplexeren Eingriffen ware es wunschenswert, diese Zeitspanne verlangern zu konnen. Es ist daher erstaunlich, das die pharmakologische Beeinflusbarkeit des ischamie- und reperfusionsbedingten Schadens am Skelettmuskel bis jetzt wenig untersucht worden ist.

NeuroImage, 2019

The sensitivity to subject motion is one of the major challenges in functional MRI (fMRI) studies... more The sensitivity to subject motion is one of the major challenges in functional MRI (fMRI) studies in which a precise alignment of images from different time points is required to allow reliable quantification of brain activation throughout the scan. Especially the long measurement times and laborious fMRI tasks add to the amount of subject motion found in typical fMRI measurements, even when head restraints are used. In case of moving subjects, prospective motion correction can maintain the relationship between spatial image information and subject anatomy by constantly adapting the image slice positioning to follow the subject in real time. Image-based prospective motion correction is well-established in fMRI studies and typically computes the motion estimates based on a volume-to-volume image registration, resulting in low temporal resolution. This study combines fMRI using simultaneous multislice imaging with multislice-to-volume-based image registration to allow sub-TR motion detection with subsequent real-time adaption of the imaging system. Simultaneous multislice imaging is widely used in fMRI studies and, together with multislice-to-volume-based image registration algorithms, enables computing suitable motion states after only a single readout by registering the simultaneously excited slices to a reference volume acquired at the start of the measurement. The technique is evaluated in three human BOLD fMRI studies (n = 1, 5, and 1) to explore different aspects of the method. It is compared to conventional, volume-to-volume-based prospective motion correction as well as retrospective motion correction methods. Results show a strong reduction in retrospectively computed residual motion parameters of up to 50% when comparing the two prospective motion correction techniques. An analysis of temporal signal-to-noise ratio as well as brain activation results shows high consistency between the results before and after additional retrospective motion correction when using the proposed technique, indicating successful prospective motion correction. The comparison of absolute tSNR values does not show an improvement compared to using retrospective motion correction alone. However, the improved temporal resolution may provide improved tSNR in the presence of more exaggerated intra-volume motion.

Neuropsychologia, 2005

The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exis... more The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exist between clinical studies in apraxic patients and neuroimaging findings on imitation. We therefore aimed to investigate: (1) which areas are recruited during imitation under conditions similar to clinical tests for apraxic deficits; (2) whether there are common lateralized areas subserving imitation irrespective of the acting limb side; and also (3) whether there are differences between hand and finger gestures. We used fMRI in 12 healthy, right handed subjects to investigate the imitation of four types of variable gestures that were presented by video clips (16 different finger and 16 different hand gestures with either the right or the left arm). The respective control conditions consisted of stereotyped gestures (only two gestures presented in pseudorandom order). Subtraction analysis of each type of gesture imitation (variable>stereotyped) revealed a bilateral activation pattern including the inferior parietal cortex Brodmann Area (BA 40), the superior parietal cortex, the inferior frontal cortex (opercular region), the prefrontal motor cortex, the lateral occipito-temporal junction, and the cerebellum. These results were supported by statistical conjunction of all four subtraction analyses and by the common analysis of all four types of gesture imitation. The direct comparison of the right and left hemispheric activation revealed a lateralization to the left only of the inferior parietal cortex. Comparisons between different types of gesture imitation yielded no significant results. In conclusion, gesture imitation recruits bilateral fronto-parietal regions, with significant lateralization of only one area, namely the left inferior parietal cortex. These in vivo data indicate left inferior parietal dominance for gesture imitation in right handers, confirming lesion-based theories of apraxia.

Alcoholism: Clinical and Experimental Research, 2012

Background-Heavy prenatal alcohol exposure leads to widespread cognitive deficits, including prob... more Background-Heavy prenatal alcohol exposure leads to widespread cognitive deficits, including problems with spatial working memory (SWM). Neuroimaging studies report structural and functional abnormalities in FASD, but interpretations may be complicated by the co-occurrence of a family history of alcoholism. Since, this history is also linked to cognitive deficits and brain abnormalities, it is difficult to determine the extent to which deficits are unique to prenatal alcohol exposure. Methods-Age-matched subjects selected from two neuroimaging studies, underwent functional imaging while engaging in a task assessing memory for spatial locations relative to a vigilance condition assessing attention. Pairwise comparisons were made for the following three groups: children with histories of heavy prenatal alcohol exposure (ALC, n=18); those with no prenatal alcohol exposure, but a confirmed family history of alcoholism (FHP, n=18); and non-exposed, family history negative controls (CON, n=17). Results-Relative to CON and FHP, the ALC group showed increased BOLD response in the left middle and superior frontal gyri for the spatial working memory condition relative to the vigilance condition (SWM contrast). Additionally, the ALC group showed unique BOLD response increases in the left lingual gyrus and right middle frontal gyrus relative to CON, and left cuneus and precuneus relative to FHP. Both ALC and FHP showed greater activation compared to CON in the lentiform nucleus and insular region. Conclusions-These results confirm previous studies suggesting SWM deficits in FASD. Differences between the ALC group and the CON and FHP groups suggest the left middle and superior frontal region may be specifically affected in alcohol-exposed children. Conversely, differences from the CON group in the lentiform nucleus and insular region for the ALC and FHP groups may indicate this region is associated with family history of alcoholism rather than specifically with prenatal alcohol exposure.

Aktuelle Neurologie, 2004

& Audiovisual perception and imitation are essential for musical learning and skill acquisition. ... more & Audiovisual perception and imitation are essential for musical learning and skill acquisition. We compared professional pianists to musically naive controls with fMRI while observing piano playing finger-hand movements and serial finger-thumb opposition movements both with and without synchronous piano sound. Pianists showed stronger activations within a fronto-parieto-temporal network while observing piano playing compared to controls and contrasted to perception of serial finger-thumb opposition movements. Observation of silent piano playing additionally recruited auditory areas in pianists. Perception of piano sounds coupled with serial finger-thumb opposition movements evoked increased activation within the sensorimotor network. This indicates specialization of multimodal auditorysensorimotor systems within a fronto-parieto-temporal network by professional musical training. Musical ''language,'' which is acquired by observation and imitation, seems to be tightly coupled to this network in accord with an observationexecution system linking visual and auditory perception to motor performance. &

NeuroImage

Childhood obesity is a rising problem caused in part by unhealthy food choices. Food choices are ... more Childhood obesity is a rising problem caused in part by unhealthy food choices. Food choices are based on a neural value signal encoded in the ventromedial prefrontal cortex, and self-control involves modulation of this signal by the dorsolateral prefrontal cortex (dlPFC). We determined the effects of development, body mass (BMI Cole score) and body mass history on the neural correlates of healthy food choice in children. 141 children (aged 10-17y) from Germany, Hungary and Sweden were scanned with fMRI while performing a food choice task. Afterwards health and taste ratings of the foods were collected. In the food choice task children were asked to consider the healthiness or tastiness of the food or to choose naturally. Overall, children made healthier choices when asked to consider healthiness. However, children who had a higher weight gain per year chose less healthy foods when considering healthiness but not when choosing naturally. Pubertal development stage correlated positively while current body mass correlated negatively with dlPFC activation when accepting foods. Pubertal development negatively and current body mass positively influenced the effect of considering healthiness on activation of brain areas involved in salience and motivation. In conclusion, children in earlier stages of pubertal development and children with a higher body weight exhibited less activation in the dlPFC, which has been implicated in self-control during food choice. Furthermore, pubertal development and body mass influenced neural responses to a health cue in areas involved in salience and motivation. Thus, these findings suggest that children in earlier stages of pubertal development, children with a higher body mass gain and children with overweight may possibly be less susceptible to healthy eating interventions that rely on self-control or that highlight health aspects of food.

BMC Neuroscience

Background: Memory performance of an individual (within the age range: 50-55 years old) showing s... more Background: Memory performance of an individual (within the age range: 50-55 years old) showing superior memory abilities (protagonist PR) was compared to an age-and education-matched reference group in a historical facts ("famous events") retrieval task. Results: Contrasting task versus baseline performance both PR and the reference group showed fMRI activation patterns in parietal and occipital brain regions. The reference group additionally demonstrated activation patterns in cingulate gyrus, whereas PR showed additional widespread activation patterns comprising frontal and cerebellar brain regions. The direct comparison between PR and the reference group revealed larger fMRI contrasts for PR in right frontal, superior temporal and cerebellar brain regions. Conclusions: It was concluded that PR generally recruits brain regions as normal memory performers do, but in a more elaborate way, and furthermore, that he applied a memory-strategy that potentially includes executively driven multi-modal transcoding of information and recruitment of implicit memory resources.

PloS one, 2017

When two tasks are performed simultaneously, performance often declines in one or both tasks. The... more When two tasks are performed simultaneously, performance often declines in one or both tasks. These so-called dual-task costs are more pronounced in old than in young adults. One proposed neurological mechanism of the dual-task costs is that old compared with young adults tend to execute single-tasks with higher brain activation. In the brain regions that are needed for both tasks, the reduced residual capacity may interfere with performance of the dual-task. This competition for shared brain regions has been called structural interference. The purpose of the study was to determine whether structural interference indeed plays a role in the age-related decrease in dual-task performance. Functional magnetic resonance imaging (fMRI) was used to investigate 23 young adults (20-29 years) and 32 old adults (66-89 years) performing a calculation (serial subtraction by seven) and balance-simulation (plantar flexion force control) task separately or simultaneously. Behavioral performance dec...

Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, Jan 24, 2017

Learning new motor skills is important for everyday life and independent living in older age. Whi... more Learning new motor skills is important for everyday life and independent living in older age. While studies on motor sequence learning and motor adaptation revealed age differences that are mostly related to frontal decline with increasing age, data for fine finger force modulation are missing. Twelve young (YA, 18-28 years) and twelve middle-aged older (OA, 55-65 years) adults practiced a force modulation task in precision grip while lying in a 3T MR scanner. Participants followed a sine wave between 5 and 25% of their maximum voluntary contraction (MVC) at a frequency of 0.3 Hz. Ten trials of 30 s were performed to examine learning curves and related changes in Blood Oxygen Level Dependent (BOLD) responses were assessed with functional magnetic resonance imaging (fMRI). Training slopes were similar for YA and OA, with only a trend for differences in performance level. Both age groups revealed decreasing activations with practice in frontal and parietal regions as well as in the ce...

Http Dx Doi Org 10 1080 13554794 2010 532135, May 3, 2011

Savants and prodigies are individuals with exceptional skills in particular mental domains. In th... more Savants and prodigies are individuals with exceptional skills in particular mental domains. In the present study we used functional magnetic resonance imaging to examine neural correlates of calendar calculation in two individuals, a savant with Asperger's disorder and a self-taught mathematical prodigy. If there is a modular neural organization of exceptional performance in a specific mental domain, calendar calculation should be reflected in a considerable overlap in the recruitment of brain circuits across expert individuals. However, considerable individual differences in activation patterns during calendar calculation were noted. The present results indicate that activation patterns produced by complex mental processing, such as calendar calculation, seem to be influenced strongly by learning history and idiosyncratic strategy usage rather than a modular neural organization. Thus, well-known individual differences in complex cognition play a major role even in experts with exceptional abilities in a particular mental domain and should in particular be considered when examining the neural architecture of complex mental processes and skills.

Visualizing and measuring the uncertainty of DTI-based techniques is an important new challenge i... more Visualizing and measuring the uncertainty of DTI-based techniques is an important new challenge in the area of neuroimaging. In this paper, we demonstrate how fiber tracking and quantification of DTI parameters depend on the resolution of the underlying DTI data. For measuring the resulting differences, we propose a novel algorithm that allows for an automatic quantification of MR DTI parameters along arbitrarily oriented fiber bundles as well as an approach for quickly measuring the volume of the sheath enclosing a bundle. Our measurements show that the degree of uncertainty does not depend only on the chosen image resolution but also on the kind of fiber bundle. Introduction: Over the last few years, diffusion tensor imaging (DTI) received raising attention within the neurosurgical and neurological community. Fiber tracking [1] as well as quantification algorithms [2] have been proposed with the motivation to identify major white matter tracts afflicted by an individual pathology ...