Hemispheric control of motor function: a whole brain echo planar fMRI study.

The aim of this study was to explore whether recruitment of the ipsilateral motor cortex during non-dominant motor movement reflects left hemispheric control of motor function or simply the greater complexity or unfamiliarity of the motor task. BOLD fMRI was performed in normal right-handers during two motor tasks: (1) sequential finger movements (SM task) with the right or left hand; and (2) random finger movements (RM task) with the right hand. In all subjects, activation was predominantly in the contralateral motor areas (primary sensorimotor, lateral premotor, parietal and supplementary motor regions) and ipsilateral cerebellum. While the ipsilateral motor areas were also activated, single subject analysis revealed these areas to be more extensive and to be seen in more subjects during the non-dominant hand SM task and dominant hand RM task than during the more familiar dominant hand SM task. Similarly, group analysis also revealed ipsilateral activation in the primary sensorimotor and lateral premotor areas, but only during the non-dominant SM task and the dominant hand RM task. Non-dominant hand movements, perhaps because they are less 'automatic', appear to require more cortical activity similar to complex tasks with the dominant hand, and result in greater recruitment of ipsilateral cortical motor areas and striatum. The study also illustrates how potentially meaningful subtleties seen on individual maps may be obscured with group averaging approaches.

Abnormal functional lateralization of the sensorimotor cortex in patients with schizophrenia.

Previous neuroimaging studies have suggested that patients with schizophrenia fail to recruit appropriate focal patterns of cortical responses to cognitive tasks. We investigated whether patients with schizophrenia show a normal focal response to a simple motor task. Seven strongly right-handed patients with schizophrenia and seven strongly right-handed normal subjects performed motor tasks of increasing complexity. Patients were unable to recruit as focal a response even to a simple, automatic sequential finger movement task. They showed greater ipsilateral activation in the primary sensorimotor and lateral premotor regions and had a significantly lower laterality quotient than normal subjects. These phenomena increased with the complexity of the task. These results demonstrate a functional disturbance in the cortical motor circuitry of patients with schizophrenia.

Analysis of interpolation effects in the reslicing of functional MR images.

PURPOSE: Typically, the final step in volume registration is the reslicing of the volume of interest. The purpose of this work is to examine the effects of this reslicing on functional MRI (fMRI) data using different interpolation methods. METHOD: Functional whole-brain echo planar imaging (EPI) volumes were resliced using six different interpolation methods: trilinear, tricubic splines, and a 3D sinc function using a rectangular and a Hanning window, both with half-window lengths of 3 and 4 voxels. RESULTS: Interpolation by tricubic spline and 3D sinc using a Hanning window had comparable errors, although tricubic spline interpolation was computationally the fastest. Interpolation by trilinear and 3D sinc using a rectangular window had relatively large errors, although the speed of trilinear makes it desirable for some applications. CONCLUSION: Interpolations using all of the tested methods adversely affected the fMRI data, although these effects differed for each method.

Effect of magnetization transfer on the measurement of cerebral blood flow using steady-state arterial spin tagging approaches: a theoretical investigation.

A simple four-compartment model for magnetization transfer was used to obtain theoretical expressions for the relationship between regional cerebral blood flow and delta M, the change in longitudinal magnetization of brain water spins when arterial water spins are perturbed. The theoretical relationship can be written in two forms, depending on the approach used to normalize delta M. Using the first approach, the calculation of cerebral blood flow requires a knowledge of R1(omega 1, delta omega), the longitudinal relaxation rate observed in the presence of continuous off-resonance RF irradiation. Using the second approach, the calculation of cerebral blood flow requires a knowledge of R1(omega 1, delta omega), where R1(omega 1, delta omega) is given by the product of R1(omega 1, delta omega) and the fractional steady-state longitudinal water magnetization in the presence of off-resonance RF irradiation. If the off-resonance RF irradiation used for arterial tagging does not produce appreciable magnetization transfer effects, R1(omega 1, delta omega) can be approximated by the longitudinal relaxation rate measured in the absence of off-resonance RF irradiation, R1obs. Theoretical expressions obtained by using the four-component model for magnetization transfer are compared with equivalent expressions obtained by using two-compartment models.

Whole-brain functional mapping with isotropic MR imaging.

PURPOSE: To assess the reliability and sensitivity of gradient-echo, isotropic multisection echo-planar magnetic resonance (MR) imaging for within-subject whole-brain mapping. MATERIALS AND METHODS: Eight right-handed healthy volunteers underwent gradient-echo, echo-planar MR imaging while they performed a motor task on three occasions over 2-3 months. Ninety-six whole-brain volumes were acquired in 8 minutes 48 seconds. A rigorous statistical threshold for determining activation was set at P < .05 and was Bonferroni corrected for approximately 15,000 cortical voxels. RESULTS: In all subjects, reproducible activation was demonstrated in multiple cortical areas and in the cerebellum specific to the motor system. Of the activated voxels, 75%-78% were confined to the motor areas during all sessions. No statistically significant difference was found in the proportion of activated voxels in any motor region (relative to the total number of activated voxels in the whole brain) across the three sessions. The centers of mass of the activated areas were within 2.5 resolution elements of the image across the three sessions. CONCLUSION: Isotropic multisection echo-planar MR imaging, has the potential for noninvasive, reliable within-subject mapping of whole-brain functional anatomy.

Fast 3D functional magnetic resonance imaging at 1.5 T with spiral acquisition.

A new method to perform rapid 3D fMRI in human brain is introduced and evaluated in normal subjects, on a standard clinical scanner at 1.5 Tesla. The method combines a highly stable gradient echo technique with a spiral scan method, to detect brain activation related changes in blood oxygenation with high sensitivity. A motor activation paradigm with a duration of less than 5 min, performed on 10 subjects, consistently showed significant changes in signal intensity in the area of the motor cortex. In all subjects, these changes survived high statistical thresholds.