Purpose Non-contrast-enhanced magnetic resonance angiography (MRA) is a widely accepted diagnostic imaging method. However, neurovascular diseases that present with slow or complex flow (eg, aneurysms) may not be fully appreciated due to flow artifacts1. In this report, the feasibility of using Chemical Exchange Transfer Saturation (CEST)2 for angiography is investigated (angioCEST). Since contrast in CEST imaging is generated by the exchangeable protons in solute and not by blood flow, it is hypothesised that angioCEST will be less sensitive to slow/complex flow.
Materials and Methods To evaluate generated CEST contrast from blood, experiments were performed using cylindrical tubes filled with porcine blood in acid citrate dextrose (ACD) that were emerged in saline. Imaging was performed on a 3.0T whole-body scanner using a custom-made solenoid T/R coil. CEST data was acquired using a single slice parallel to the short axis of the cylindrical tube and was corrected for B0-inhomogeneities using a WASSR3 method. To provide proof-of-principle, angioCEST was performed on the intracranial vasculature of a healthy volunteer. Single axial WASSR and CEST slices were acquired of the brain superior to the ICA siphon using an 8-channel SENSE head coil. Regions of interest (ROIs) were manually drawn in WASSR data and automatically copied to corresponding CEST data (figure 1). Normalised Z-spectra were generated using the mean values per ROI and were filtered for noise and corrected for B0 inhomogeneities using WASSR. To quantify the generated CEST contrast, MTRasym was used2.
Results MTRasym analysis of the porcine blood samples showed a CEST effect of approximately 12% relative to surrounding saline at 2.5 ppm offset frequency. CEST experiments were performed on ACD confirmed that the observed CEST effect was due to blood and not generated by the anticoagulant. MTRasym plots (figure 1) of arterial blood (solid line) and white matter (dashed line) are shown in the bottom panel. Corresponding ROIs were drawn in WASSR data (top left) and copied to CEST data (top right) for analysis. Arterial blood shows a clear CEST effect of approximately 8% with respect to surrounding brain tissue.
Conclusion In-vitro and in-vivo experiments have shown feasibility to obtain CEST contrast from blood, which may enable development of a novel method for MR angiography that is less sensitive to flow artifacts than currently available non-invasive techniques.
Disclosures I. van der Bom: None. S. Zheng: None. M. Gounis: None.
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