Akira Yamamoto

Institutional review board approval and written informed consent were obtained. The purpose of this study was to prospectively validate usefulness of diffusion-tensor (DT) fiber tractography of the corticospinal tract at 3-T magnetic resonance imaging, in combination with the subcortical motor-evoked potential (MEP) technique, as a tool for tractography-guided neurosurgery. DT imaging and corticospinal tractography were performed at 3 T in eight patients (four men, four women; mean age, 41 years; age range, 23-58 years) with intracranial space-occupying lesions. Tractography data were transferred to a neuronavigation system, and tractography-guided neurosurgery was performed. During lesion resection, subcortical MEPs were recorded. Positive MEP response was observed in four patients. No patients developed new motor weakness postoperatively. Complementary use of tractography and MEP may be useful for intraoperative depiction of corticospinal tracts.

BACKGROUND AND PURPOSE: Knowing the exact location of the optic radiation preoperatively is important for surgery of the temporal lobe. We hypothesized that a greater number of motion-probing gradients (MPGs) would provide better results of diffusion tensor (DT) fiber tractography of the optic radiation. To test this hypothesis, this study evaluated differences in DT fiber tractography of the optic radiation under different MPG settings. METHODS: DT images were obtained in 12 healthy volunteers (7 men, 5 women) with a mean age of 32 years (range, 22-45 years) by using a 3T MR imaging scanner with single-shot echo-planar imaging with parallel acquisition (reduction factor = 2). MPG was applied in 6, 12, 40, and 81 independent directions. The first region of interest (ROI) was placed in the occipital lobe, and the second ROI was placed in the lateral geniculate body. Fibers penetrating both ROIs were considered as the optic radiation. Anteroposterior distance between the tip of the Meyer loop and the lateral geniculate body on an axial section was defined as a loop index. Numbers of fibers and loop indices in both cerebral hemispheres were evaluated statistically. RESULTS: The optic radiation was well visualized in full length by DT fiber tractography in 20 of 24 hemispheres (83%). No significant differences were noted in number of fibers and loop indices among different MPG settings. CONCLUSION: DT fiber tractography can frequently depict almost the entire optic radiation. MPG number does not exert any significant effect on visualization of the optic radiation, and 6-directional MPG is thus sufficient for this purpose.