VESSEL ENHANCEMENT FILTERING IN 3-DIMENSIONAL MR-ANGIOGRAPHY

For a variety of reasons, small vessels have low signal intensity in m agnetic resonance angiography. When the vessel signal intensity is low er than the signal intensity of background tissues, these vessels tend not to be visible on maximum-intensity-projection images. The authors developed a nonlinear second-difference spatial filtering technique t hat enhances the details of small vessels while suppressing both noise and uniform background tissue. Two similar nonlinear second-differenc e filters are presented and compared with the linear Laplacian second- difference filter. To evaluate the performance of these filters, they were applied to intracranial three-dimensional time-of-flight MR angio graphic data and the results compared with the vessel enhancement obta ined with a simple second-difference Laplacian filter and with magneti zation transfer contrast (MTC) techniques. The comparisons demonstrate d that nonlinear filtering and MTC techniques result in similar improv ement in small-vessel visibility and apparent continuity. A quantitati ve comparison demonstrated that the improvement in the contrast-to-noi se ratio is much greater with the nonlinear filters than the Laplacian filter.