Time-of-flight MR-angiography with a helical trajectory and slice-super-resolution reconstruction

Purpose: To improve 2D noncontrast-enhanced MRA by using a helical time-of-flight (TOF) acquisition technique and a slice-super-resolution reconstruction. Methods: The TOF technique is combined with a helical trajectory with golden-angle-based radial projection reordering. A continuous spatial shift in slice direction is realized by adjusting the frequency of the excitation pulse between the individual projections. The limited resolution along the shift direction is improved by a deconvolution with simulated slice profile. The helical TOF (hTOF) was compared in vivo with a conventional 2D and 3D TOF. Results: Results from in vivo experiments on the carotid show that the visual resolution in slice direction can be improved by using hTOF and the slice-super-resolution reconstruction. The vessels appear up to 1.5 times sharper and can be better separated from each other. Compared to 2D TOF images, the stair step artifacts are strongly reduced in reformatted hTOF images, whereas measurement time is decreased by at least 35%. Compared to 3D TOF, the hTOF offers a higher blood-to-background contrast, better visualization of smaller vessels, and reduced measurement time. Conclusion: The hTOF benefits from a 2D acquisition and a 3D reconstruction, which makes it a promising technique for the noncontrast-enhanced imaging of the carotid.