Sci-Fri PM: Planning-11: Selection and optimization of angiographic roadmap images for magnetic resonance guided...

As endovascular magnetic resonance (MR) techniques for device tracking and guidance move closer to demonstrating clinical feasibility, more investigation in the generation and optimization of vascular roadmap images is need to achieve the full benefit of MR-guided procedure. MR angiographic roadmap imaging requires high signal-to-noise (SNR), good vascular-to-background contrast and short acquisition time. These requirements not only qualify the appropriate roadmaps for therapy, but also guide in the optimization of their acquisition parameters. We hypothesize that among the well established MR angiographic techniques, low-resolution phase-contrast (PC) images would prove satisfactory for vascular roadmap imaging. To verify this, four potential MR angiography techniques, specifically, time-of-flight, contrast-enhanced, phase-contrast and black-blood angiography, were explored for roadmap imaging using a canine model on a 3 T MR scanner. PC angiography was specifically performed to evaluate impact of key parameters on the SNR efficiency and vascular-to-background contrast efficiency in order to optimize the sequence for therapeutic use. Data were collected from five canines. Phase-contrast angiography was found to be most suitable for generating vascular roadmap for MR-guided endovascular therapy. It was also found that small acquisition matrix and large FOV produced satisfactory roadmap images provided that the size of the vessel of interest was more than a few times the in-plane pixel dimension. Also, reducing the phase encoding steps had minimal effect on vessel oriented parallel to the phase encode direction.