COMMUTATOR FILTER - A NOVEL TECHNIQUE FOR THE IDENTIFICATION OF STRUCTURES PRODUCING SIGNIFICANT SUSCEPTIBILITY INHOMOGENEITIES AND ITS APPLICATION TO FUNCTIONAL MRI

A robust postprocessing method to detect regions of magnetic field cha nge is presented. High resolution gradient echo data is acquired to cr eate a complex baseline image. From this image, two low resolution ima ges are obtained by applying a low pass filter on the magnitude image and the complex image, respectively. Subtraction of the magnitude of t he filtered complex image from the filtered magnitude image gives a ne w image called a commutator image in which regions of susceptibility-i nduced field variation are greatly enhanced, Results on phantoms and a pplications to visualize paramagnetic venous blood vessels in the huma n brain are presented. The use of this technique on a 3D gradient echo data set represents a new approach to obtain an MR venogram. The appl ication of this method to blood oxygenation level dependent (BOLD) fun ctional brain MR imaging is demonstrated and the important role suscep tibility plays in this model is verified.