Correlation of Functional MR Imaging with Perimetric Examination in Patients with Visual Field Defects Due to Lesions Involving the Afferent Visual System

Abstract

We assessed fMRI in the objective evaluation of visual function during treatment planning and postoperative follow-up in patients with occipital lobe and/or the afferent visual system lesions. Ten normal volunteers and eleven patients harbouring brain lesions with MR evidence of calcarine cortex and/or visual pathway damage underwent ophthalmoscopy, Goldmann perimetry and fMRI examination. Blood oxygenation sensitive series (gradient-echo, T2*-weighted, single-shot EPI: TR = 2 sec, TE = 40 ms, FA = 40 degrees voxel volume 3.1 mm x 3.1 mm x 5 mm) were obtained using a 1.5-Tesla clinical imager with six contiguous slices, covering the occipital lobe parallel to the calcarine fissure. A repetitive, phasic experiment for visual stimulation was achieved using a binocular, stroboscopic, white light flashing at 10 HZ and was repeated twice to test reproducibility. Functional maps, generated using a cross correlation technique, were overlaid onto concurrent high resolution anatomic MR images and compared to Goldmann perimetry results. All volunteers demonstrated symmetric, bilateral, regional signal intensity changes (2%-5%) between photic stimulation and darkness in the primary visual cortex and dorsolateral and ventrolateral al extrastriate areas. Cortical activation maps in ten patients clearly localised asymmetric response within specific regions in the primary visual cortex and correlated with Goldmann perimetry results. Displacement of the eloquent calcarine cortex was demonstrated in a patient with normal perimetry results. Primary visual area activation increased in two patients following surgery. fMRI performed on a conventional MR system can objectively evaluate visual function in neurosurgical patients with occipital lobe and/or afferent visual system lesions as part of treatment planning and postoperative follow-up.