RESUMEN
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.
Asunto(s)
Predominio Ocular/fisiología , Cuerpos Geniculados/fisiología , Corteza Visual/fisiología , Adulto , Femenino , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Reproducibilidad de los Resultados , Campos Visuales/fisiología , Percepción Visual/fisiologíaRESUMEN
OBJECTIVES: Functional magnetic resonance imaging (fMRI) at very high field strengths provides functional brain mapping with the enhanced signal to noise ratio and the larger blood oxygenation level-dependent (BOLD) effect. We report activated areas in the standard space detected by fMRI at 4 Tesla (T) during simple visual stimulation. MATERIALS AND METHODS: Twelve healthy young subjects were scanned using a 4 T scanner during binocular flashing visual stimulation. Functional images were realigned to the first scan and then spatially normalized. Individual and group data analyses were performed to identify areas of visual activation. RESULTS: Activation of the bilateral primary visual cortex (V1/V2) was observed along the entire calcarine fissure in all subjects. The activated area extended to the extrastriate cortex in all subjects. Activation of the bilateral lateral geniculate nucleus (LGN) was detected in all subjects. The group data showed activation of the bilateral primary visual cortex and the bilateral lateral geniculate nucleus. CONCLUSIONS: Robust activation of the vision-related areas was successfully obtained in all subjects using a 4 T magnetic resonance scanner. These results suggest that fMRI at very high field strengths may be effective in showing visual system physiology, and that it can be a promising method to assess visual function of human subjects.
Asunto(s)
Mapeo Encefálico , Cuerpos Geniculados/fisiología , Imagen por Resonancia Magnética/métodos , Corteza Visual/fisiología , Adulto , Femenino , Humanos , Masculino , Estimulación Luminosa , Visión Binocular/fisiologíaRESUMEN
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.
Asunto(s)
Corteza Visual/fisiología , Percepción Visual/fisiología , Adolescente , Adulto , Femenino , Humanos , Imagen por Resonancia Magnética , Masculino , Estimulación Luminosa , Reproducibilidad de los ResultadosRESUMEN
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.
Asunto(s)
Imagen por Resonancia Magnética , Visión Binocular/fisiología , Corteza Visual/fisiología , Vías Visuales/fisiología , Adulto , Femenino , Humanos , Masculino , Persona de Mediana Edad , Reproducibilidad de los ResultadosRESUMEN
It is shown that diffusion-weighted imaging is possible in the human breast. Diffusion constants were measured in the breast parenchyma of four volunteers with no known breast lesions. The apparent diffusion constant of water measured in regions of interest chosen in normal human breast fibroglandular tissue was 1.64 +/- 0.19 x 10(-5) cm2/S and that measured in the area of fatty breast tissue was 0.32 +/- 0.18 x 10(-5) cm2/S. The resulting images indicate that fibroglandular tissue and fat can be clearly distinguished in diffusion-weighted as well as in absolute diffusion images of the breast. Potential future applications of this technology for the study of breast pathologies are suggested.