Impact of fMRI-guided advanced DTI fiber tracking techniques on their clinical applications in patients with brain tumors

Introduction: White matter tractography based on diffusion tensor imaging has become a well-accepted non-invasive tool for exploring the white matter architecture of the human brain in vivo. There exist two main key obstacles for reconstructing white matter fibers: firstly, the implementation and application of a suitable tracking algorithm, which is capable of reconstructing anatomically complex fascicular pathways correctly, as, e.g., areas of fiber crossing or branching; secondly, the definition of an appropriate tracking seed area for starting the reconstruction process. Large intersubject, anatomical variations make it difficult to define tracking seed areas based on reliable anatomical landmarks. An accurate definition of seed regions for the reconstruction of a specific neuronal pathway becomes even more challenging in patients suffering from space occupying pathological processes as, e.g., tumors due to the displacement of the tissue and the distortion of anatomical landmarks around the lesion. Methods: To resolve the first problem, an advanced tracking algorithm, called advanced fast marching, was applied in this study. The second challenge was overcome by combining functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) in order to perform fMRI-guided accurate definition of appropriate seed areas for the DTI fiber tracking. In addition, the performance of the tasks was controlled by a MR-compatible power device. Results: Application of this combined approach to eight healthy volunteers and exemplary to three tumor patients showed that it is feasible to accurately reconstruct relevant fiber tracts belonging to a specific functional system. Conclusion: fMRI-guided advanced DTI fiber tracking has the potential to provide accurate anatomical and functional information for a more informed therapeutic decision makin

Perceptual dissociation of bimanual coordination: A fMRI study

In bimanual coordination tasks, subjects normally show a conspicuous advantage of symmetric movement patterns. This reliably becomes apparent when antiphase movements change into symmetry with increased movement velocities resulting from the coactivation of homologous muscles (e.g., Kelso et al., 1984; Johnson et al., 1998; Meesen et al., 2006). While these findings suggest that bimanual coordination is based on motor control, recent evidence suggested that bimanual coordination is governed by perceptual cues (Mechsner, Kerzel, Knoblich, and Prinz, 2001). To explore this controversy, we performed a fMRI study in 11 healthy, right-handed subjects using bimanual index finger abductions and adductions in a congruous condition, i.e. both palms down, and incongruous conditions with either the left or the right palm up. Our fMRI data showed a widespread bihemispheric network mediating bimanual coordination with significant differences (FDR < 0.05) for a perceptual dissociation: In the incongruous conditions with the one palm up there was a BOLD signal increase in a bilateral fronto-parietal network involving the motor and the premotor cortical areas, particularly in the right palm-up condition. These results accord with the notion of perceptual control of bilateral hand movements

Perceptual influence on bimanual coordination: an fMRI study

In bimanual coordination subjects typically show a spontaneous preference for movement symmetry. While there is experimental evidence for the principle of muscle homology, recent evidence suggested that bimanual coordination may be mediated as perceptual goals (Mechsner et al., 2001). To explore this controversy we performed a fMRI study in 11 healthy, right-handed subjects using bimanual index finger abductions and adductions in a congruous condition, i.e. both palms down, and incongruous conditions with either the left or right palm up. Our fMRI data showed a widespread bihemispheric network mediating proprioceptive coordination of the two hands with significant differences mainly for a perceptual dissociation: in the incongruous conditions with the one palm up there was a BOLD signal increase in a bilateral frontoparietal network involving the motor and premotor cortical areas, particularly in the right palm-up condition. These results accord with the notion that perceptual cues play an important role in the control of bilateral hand movement

I know where you'll look: an fMRI study of oculomotor intention and a change of motor plan

<p>Abstract</p> <p>Background</p> <p>Electrophysiological studies in monkeys showed that the intention to perform a saccade and the covert change in motor plan are reflected in the neural activity of the posterior parietal cortex (PPC).</p> <p>Methods</p> <p>To investigate whether such covert intentional processes are demonstrable in humans as well we used event related functional MRI. Subjects were instructed to fixate a central target, which changed its color in order to indicate the direction of a subsequent saccade. Unexpectedly for the subjects, the color changed again in half of the trials to instruct a spatially opposite saccade.</p> <p>Results</p> <p>The double-cue induced synergistic and prolonged signals in early visual areas, the motion specific visual area V5, PPC, and the supplementary and frontal eye field. At the single subject level it became evident that the PPC split up in two separate subareas. In the posterior region, the signal change correlated with the change in motor plan: activation strongly decreased when the cue instructed an ipsiversive saccade while it strongly increased when it instructed a contraversive saccade. In the anterior region, the signal change was motor related irrespective of the spatial direction of the upcoming saccade.</p> <p>Conclusion</p> <p>Thus, the human PPC holds at least two different areas for planning and executing saccadic eye movements.</p

Impact of fMRI-guided advanced DTI fiber tracking techniques on their clinical applications in patients with brain tumors

Introduction: White matter tractography based on diffusion tensor imaging has become a well-accepted non-invasive tool for exploring the white matter architecture of the human brain in vivo. There exist two main key obstacles for reconstructing white matter fibers: firstly, the implementation and application of a suitable tracking algorithm, which is capable of reconstructing anatomically complex fascicular pathways correctly, as, e.g., areas of fiber crossing or branching; secondly, the definition of an appropriate tracking seed area for starting the reconstruction process. Large intersubject, anatomical variations make it difficult to define tracking seed areas based on reliable anatomical landmarks. An accurate definition of seed regions for the reconstruction of a specific neuronal pathway becomes even more challenging in patients suffering from space occupying pathological processes as, e.g., tumors due to the displacement of the tissue and the distortion of anatomical landmarks around the lesion. Methods: To resolve the first problem, an advanced tracking algorithm, called advanced fast marching, was applied in this study. The second challenge was overcome by combining functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) in order to perform fMRI-guided accurate definition of appropriate seed areas for the DTI fiber tracking. In addition, the performance of the tasks was controlled by a MR-compatible power device. Results Application of this combined approach to eight healthy volunteers and exemplary to three tumor patients showed that it is feasible to accurately reconstruct relevant fiber tracts belonging to a specific functional system. Conclusion: fMRI-guided advanced DTI fiber tracking has the potential to provide accurate anatomical and functional information for a more informed therapeutic decision making

A portable and low-cost fMRI compatible pneumatic system for the investigation of the somatosensensory system in clinical and research environments

There still is a need for devices that allow reproducible stimulation of skin areas of the human body. We constructed a stimulation system and tested it by using brief pneumatic stimulation to the right thumb of nine healthy volunteers. BOLD-signals in response to tactile stimulation with frequencies of 1, 3 and 5Hz were measured using a 3 T MRI scanner. The stimulation device consists of synthetic membranes connected to plastic tubes capable of carrying compressed air, and an electronic component, which controls the on- and off-switching of an electromagnetic valve. The valve near the MR-scanner did not lower the image quality. Primary somatosensory activation contralateral to the stimulation site was reliably detected in response to a stimulus magnitude of 3.5 bar in all volunteers. 1Hz stimulation resulted in higher maximal percentage BOLD-signal changes. Our device is an easy-to-construct, low-cost and portable tool suitable for research and clinical environments. It permits passive non-painful stimulation relevant for clinical assessments and is also compatible with magnetoencephalography (MEG) and electroencephalography (EEG). In basic and clinical research, this device therefore contributes to meaningful comparisons between results obtained with different techniques

Effect of repetitive arm cycling following botulinum toxin injection for poststroke spasticity: evidence from FMRI.

BACKGROUND AND OBJECTIVE: Investigations were performed to establish if repetitive arm cycling training enhances the antispastic effect of intramuscular botulinum toxin (BTX) injections in postischemic spastic hemiparesis. Effects on cerebral activation were evaluated by functional magnetic resonance imaging (fMRI). METHODS: Eight chronic spastic hemisyndrome patients (49 ± 10 years) after middle cerebral artery infarction (5.5 ± 2.7 years) were investigated. BTX was injected into the affected arm twice, 6 months apart. Spasticity was assessed using the Ashworth Scale and range of motion before and 3 months after BTX injections. Images were analyzed using Brain Voyager QX 1.8, and fMRI signal changes were corrected for multiple comparisons. RESULTS: During passive movements of affected and nonaffected hands, fMRI activity was increased bilaterally in the sensorimotor cortex (MISI), secondary somatosensory areas (SII), and supplementary motor area predominantly in the contralesional hemisphere, compared with the rest. Following repetitive arm cycling, fMRI activity increased further in MISI of the lesioned hemisphere and SII of the contralesional hemisphere. For patients with residual motor activity, treatment-related fMRI activity increases were associated with reduced spasticity; in completely plegic patients, there was no fMRI activity change in SII but increased spasticity after training. CONCLUSION: Increased activity in SII of the contralesional hemisphere and in MISI of the lesioned hemisphere reflect a treatment-induced effect in the paretic arm. It is hypothesized that the increased BOLD activity results from increased afferent information related to the antispastic BTX effect reinforced by training