Background suppression in time-resolved MR angiography without mask acquisition or operator intervention.

Purpose: To suppress static and background tissue in time-resolved MRA studies of the full thorax or abdomen without the need of a mask image or operator intervention.

Materials And Methods: The time course of each voxel is projected onto the orthogonal complement space of a matrix that spans static and linearly enhancing signal vectors. The norm of the solution, or the projection length, acts as a confidence measure for segmenting vascular and nonvascular tissue. Voxels whose confidence measures fall below an automatically detected threshold value are considered nonvascular. These voxels undergo an increasing level of suppression as the distance of the confidence measure from the threshold grows.

Results: MIPs of processed volunteer studies were compared to the original unaltered studies to assess the improvement in clarity of vascular structures. Qualitative and quantitative comparisons of full body MIPs verify excellent suppression of nonvascular tissue in time-resolved three-dimensional image volumes.

Conclusion: Contrast increased by an average factor of 13 in five volunteer studies, quantitatively emphasizing the improvement in MIP processing achieved by this method. Improvement in the clarity of vascular structures in subvolume MIPs is also demonstrated to emphasize the significant increase in ease with which regions of interest can be identified.