Dual-Echo Arteriovenography Imaging with 7T MRI

Abstract

Purpose: To implement a dual-echo sequence MRI technique at 7T for simultaneous acquisition of time-of-flight (TOF) MR angiogram (MRA) and blood oxygenation level-dependent (BOLD) MR venogram (MRV) in a single MR acquisition and to compare the image qualities with those acquired at 3T. Materials and Methods: We implemented a dual-echo sequence with an echo-specific k-space reordering scheme to uncouple the scan parameter requirements for MRA and MRV at 7T. The MRA and MRV vascular contrast was enhanced by maximally separating the k-space center regions acquired for the MRA and MRV and by adjusting and applying scan parameters compatible between the MRA and MRV. The same imaging sequence was implemented at 3T. Four normal Subjects were imaged at both 3T and 7T. MRA and MRV at 7T were reconstructed both with and without phase-mask filtering and were compared quantitatively and qualitatively with those at 3T with phase-mask filtering. Results: The depiction of small cortical arteries and veins on MRA and MRV at 7T was substantially better than that at 3T, due to about twice higher contrast-to-noise ratio (CNR) for both arteries (164 +/- 57 vs. 77 +/- 26) and veins (72 +/- 8 vs. 36 +/- 6). Even without use of the phase-masking filtering, the venous contrast at 7T (65 +/- 7) was higher than that with the filtering at 3T (36 +/- 6). Conclusion: The dual-echo arteriovenography technique we implemented at 7T allows the improved visualization of small vessels in both the MRA and MRV because of the greatly increased signal-to-noise ratio (SNR) and susceptibility contrast, compared to 3T.