Automated unwrapping of MR phase images applied to BOLD MR-venography at 3 tesla

Abstract

Purpose: To improve the diagnostic value of BOLD MR-Venography by removing artifacts related to phase wrapping, particularly in regions of large background susceptibilities at high magnetic field strengths. Materials and Methods: High resolution, T2*-weighted, single echo images were acquired on a 3 T system (Medspec 30/80 Avance, Bruker Medical, Ettlingen, Germany) with a three-dimensional, first order velocity compensated gradient echo sequence using a quadrature transmit/receive birdcage head coil. Data of nine healthy subjects and 19 patients were evaluated (age range: 27 to 76 years). To achieve improved MR-venograms, a fully automated region-growing phase unwrapping algorithm and subsequent high pass filtering were applied to phase images prior to the computation of minimum intensity projections. Results: Considerably improved visualization of venous structures in regions of large background susceptibility-induced field inhomogeneities is demonstrated in healthy subjects and patients with brain tumors. Conclusion: BOLD MR venograms are improved compared to previous post-processing algorithms. It is now feasible to obtain high-resolution images also in inhomogeneous regions, which increases the clinical potential of BOLD MR-Venography. © 2003 Wiley-Liss, Inc.