Abstract
The purpose of the study was to evaluate the effect of the number of applied diffusion-sensitizing gradients on the measurement of the fractional anisotropy (FA) and the fiber number of three-dimensional fiber tractography of the corpus callosum in the normal adult brain by using diffusion tensor image (DTI). We performed DTI in 11 normal adult volunteers with the use of different numbers of diffusion-sensitizing gradient directions (6, 15, and 32) while maintaining all other parameters constant. A single-shot spin-echo planner imaging technique was used at 1.5 Tesla with the following parameters: TR/TE/FA 7228 ms/70 ms/90 degrees, averaging number 3, b value 600 s/mm(2), SENSE factor 2.5, measured voxel size 2 x 2 x 2 mm(3). The acquisition time was 2 min 54 sec for 6 directions, 6 min 9 sec for 15 directions, and 12 min 18 sec for 32 directions. The imaging field ranged from 1 cm below the pons to 2 - 3 cm above the lateral ventricle. The FA and the number of tracked fibers were measured in the genii, body, narrowing portion, and splenium of the corpus callosum by using the region of interest method. Anatomical measurements of the lengths of the genu, body, narrowing portion and splenium of the corpus callosum were performed. The lengths, with the FA and the number of tracked fibers, were compared between 6, 15, and 32 directions by using a statistical analysis. Although the FA values and the anatomical length of the genu, body, narrowing portion and splenium were not significantly different when using 6 (P = 0.669) 15 (P = 0.146), and 32 (P = 0.089) diffusion-sensitizing gradient directions for the cross-sectional area of the corpus callosum, the number of tracked fibers and the anatomical length were significantly different when using among 6 (P = 0.001), 15 (P = 0.001), and 32 (P = 0.001) directions. The present study has demonstrated that the number of tracked fibers can be more useful than the FA values for measuring the corpus callosum by using DTI. Especially, the scan time can be reduced by direct calculation from diffusion-sensitizing gradients using 15 directions.