MR imaging of cerebral blood flow

Paramagnetic contrast agents produce local magnetic field inhomogeneity when they pass through the cerebrovascular system. This effect can be monitored with T2*-weighted gradient echo images, which show transient signal loss, while a bolus of GdDTPA is passing through the brain tissue. This signal loss is correlated to the local cerebral tissue perfusion and the local cerebral blood volume. In a prospective study 10 volunteers and 14 patients with cerebral infarcts and brain tumours were examined. After bolus application of GdDTPA a dynamic series of rapid T2*-weighted gradient echo images were recorded, and the local dynamics of contrast flow in brain tissue was examined. From the series of images, local changes in signal intensity were calculated pixel by pixel and presented as parameter images. By this method, infarcted areas and brain tumours can be distinguished from normal tissue by their contrast flow dynamics. The abnormal contrast dynamics depend on changes in local tissue perfusion and alterations in local blood volume. The separation of the influence of both parameters however is still an unsolved problem. (orig.)