Functional MRI of Visual Cortex in the Patients with Occipital Lobe Ischemia

ABSTRACT

PURPOSE: To evaluate the usefulness of functional MRI(fMRI) of visual cortex in patients with ischemic infarction in the occipital lobe. MATERIALS AND METHODS: Four patients with the symptoms and signs of visual cortical ischemia were included. Functional MRI was performed by 2D-FLASH technique with the parameter of 90/56msec TR/TE, 40degrees flip angle, 240x240 FOV, 64x128 matrix number, 8.32 seconds acquisition time, 8mm slice thickness. An axial slice including both visual cortices was selected and alternative activation and resting of the visual cortex was performed using red color photostimulator. All patients undertook visual field test, and vascular abnormality was examined by MRA (n=4) and DSA (n=2). fMRI results were compared with the results of a visual field test, conventional MRI and cerebral angiography. RESULTS: On fMRI, decreased activity of the visual cortex was found in the occipital lobe corresponding to stenosis of the posterior cerebral artery or its branch noted on angiogram. However, 2 of 4 patients showed no abnormal findings on conventional MRI. Visual field defect was noted in 3 patients, one of whom showed no abnormality on conventional MRI and diffusion-weighted image, but revealed decreased activity in the corresponding visual cortex on fMRI. CONCLUSION: fMRI may be a sensitive method for detection of the status of decreased blood flow or vascular reserve which other methods can not.