Functional activation using apparent diffusion coefficient-dependent contrast allows better spatial localization to the neuronal activity: evidence using diffusion tensor imaging and fiber tracking.

Recent studies suggested that functional activation using apparent diffusion coefficient (ADC) contrast can be used to detect synchronized functional MRI (fMRI) signal changes during brain activation. Such changes may reflect better spatial localization to the smaller vessels, which are closely coupled to the true neuronal activation. Since it is generally believed that there are neural pathways among neuronally relevant areas, methods that would allow clear delineation of such pathways could help validate the neuronal relevance of the activated functional areas. The development of diffusion tensor imaging (DTI) has shown promise in detailed nerve fiber tracking. In this report, DTI was adopted to track the fiber connections among the discrete areas determined using the ADC contrast, in an effort to confirm the neuronal origin of these activated areas. As a comparison, activated areas using blood oxygenation level-dependent (BOLD) contrast were also obtained. Our results showed that the areas determined by the ADC contrast consistently allowed better fiber tracking within, while the BOLD-activated areas were more spatially diffused due to the smearing effect of brain vasculature, rendering the task of fiber tracking more difficult. This observation provides converging evidence that the activated areas using ADC contrast are more closely coupled to the neuronal activity than those using BOLD contrast.