Structural changes in actin-containing filaments of muscle.
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Actins↗
Biomedical subjects
J C Haselgrove
Publications and source records attributed to J C Haselgrove.
Reproducibility of visual activation in functional magnetic resonance imaging at very high field strength (4 Tesla).
PURPOSE: The reproducibility of functional magnetic resonance imaging (fMRI) has been studied on 1.5 Tesla (T) (high field strength) scanners. We report the reproducibility of visual activation in fMRI at 4 T (very high field strength). METHODS: Five healthy subjects were scanned twice in the same session with a 4 T scanner during binocular flashing visual stimulation. The activated areas during the first and second acquisition were compared. RESULTS: Activation of the visual cortex was observed in all subjects and activation of lateral geniculate nucleus was also detected in four subjects. The ratio of overlapping activated voxels in the first and second acquisition was 0.81 +/- 0.05. CONCLUSIONS: Reproducibility of visual activation using fMRI at 4 T was found to be acceptable, and the results from 4T scanners show a reliability similar to those at 1.5 T.
Adult↗
Reproducibility of visual activation during checkerboard stimulation in functional magnetic resonance imaging at 4 Tesla.
PURPOSE: To investigate the reproducibility of visual activation by checkerboard stimulation, we used functional magnetic resonance imaging (fMRI) at 4 Tesla (T). METHODS: Four subjects were studied with fMRI at 4 T during checkerboard visual stimulation. The functional images were realigned and spatially normalized to the standard brain. For each subject, statistical parametric maps were made for each study, and the reproducibility was determined based on the number of supra-threshold voxels (Z > 3.5, 4.5, and 5.5). RESULTS: The mean ratio for the number of supra-threshold (Z > 4.5) voxels was 0.75, and the mean ratio for the overlapping voxels was 0.61. Restricting the region of interest within the posterior half of the brain improved reproducibility values at the low threshold (Z > 3.5), but did not improve the values at the higher thresholds. CONCLUSIONS: Despite the fact that more than half of the supra-threshold voxels were found to be active for the repeated scans, visual activation with checkerboard stimulation seems to be less reproducible than that by flash stimulation.
Adolescent↗
Investigation of the nonlinear aspects of imaging through a highly scattering medium.
The edge-spread function that is expected when imaging a sharp edge in a highly scattering medium using a time-of-flight imaging system has been investigated. Experimental results have been compared with computer simulations. The effect of scattering is to broaden the image of the edge, accompanied by an offset of the midpoint (50% transmission) of the edge. Small random errors in the measurement of the time of flight results in an increase in the offset of the edge position at very short times of flight. The offset in the midpoint of the edge is evidence of the nonlinear nature imaging process, in view of which we conclude that nonlinear algorithms will be necessary to maximize the image information available from measured intensities.
Algorithms↗
Effects of check size on visual cortex activation studied by functional magnetic resonance imaging.
We studied functional magnetic resonance imaging (fMRI) of visual cortex during checkerboard visual stimulation with three standard check sizes to examine whether activation in the visual cortex varied among these sizes. We acquired fMRI at 1.5 T in 8 normal subjects, each receiving the best refractive correction. Each subject underwent an experiment consisting of four conditions: black and white checkerboards with three check sizes (0.25-, 0.5-, and 1.0-degree) flickering at 8 Hz, and a black screen. SPM96 was used for a group data analysis with a random effects model after each of the subject's data was motion-corrected and spatially normalized to a standard brain. The activation in the visual cortex showed the greatest signal changes with the 0.5-degree check among the three check sizes. When standard check sizes are used to stimulate visual cortex in fMRI experiments, our results suggest that 0.5-degree checks flickering at 8 Hz produce the most vigorous activation in visual cortex.
Adult↗
Functional magnetic resonance imaging of eye dominance at 4 tesla.
We studied eye dominance in visual cortex and lateral geniculate nucleus (LGN) using functional magnetic resonance imaging (fMRI) at a very high magnetic field (4 tesla). Eight normal volunteers were studied with fMRI at 4 tesla during alternating monocular visual stimulation. The acquisition was repeated twice in 4 subjects to confirm reproducibility. In addition, magnetic resonance signal intensities during three conditions (right eye stimulation, left eye stimulation, and control condition) were compared to determine whether the observed area was truly or relatively monocular in 2 subjects. In both the individual and group analyses, the anterior striate cortex was consistently activated by the contralateral eye more than the ipsilateral eye. Additionally, we found evidence that there were areas in the bilateral LGN which were more active during the stimulation of the contralateral eye than during the stimulation of the ipsilateral eye. The activated areas were reproducible, and the mean ratio of the overlapping area was 0.71 for the repeated scans. The additional experiment revealed that the area in the anterior visual cortex could be divided into two parts, one truly monocular and the other relatively monocular. Our finding confirmed previous fMRI results at 1.5 tesla showing that eye dominance was observed in the contralateral anterior visual cortex. However, the eye dominance in the visual cortex was found not only in the most anterior area corresponding to the monocular temporal crescent but also in the more posterior area, presumably showing the greater sensitivity of the temporal visual field (nasal retina) as compared with the nasal visual field (temporal retina) in the peripheral visual field (peripheral retina). In addition, it is suggested that the nasotemporal asymmetry of the retina and the visual fields is represented in the LGN as well as in the visual cortex.
Adult↗