Distortion-free diffusion tensor imaging of cranial nerves and of inferior temporal and orbitofrontal white matter.
The main impact of functional neuroimaging has been its ability to locate neuronal activity either directly (EEG, MEG) or through the hemodynamic response caused by neuronal activity (PET, fMRI). In the past decade functional neuroimaging has been extended to investigate how brain regions interact, using the concepts of functional and effective connectivity. These concepts are further strengthened by estimates of anatomical connectivity of the same subject. A tool to determine anatomical connectivity in vivo may be provided by diffusion tensor imaging (DTI) methods. These can be used to determine the orientation of fiber bundles in white matter on the basis of the diffusion characteristics of water. Commonly, DTI data are acquired using echo planar imaging which suffers from susceptibility artifacts in orbitofrontal and inferior temporal cortex. Here we demonstrate the use of an alternative pulse sequence, diffusion-weighted single-shot STEAM, for assessing fiber orientation in orbitofrontal cortex and the cranial nerves. The scope of DTI needs to be extended to these structures to investigate psychiatric disorders in which orbitofrontal pathology or temporo-frontal disconnection have been postulated.