Gadolinium-enhanced off-resonance contrast angiography

Area of Science:

• Magnetic Resonance Imaging
• Vascular Imaging
• Medical Physics

Background:

• Standard contrast-enhanced MR angiography (CE-MRA) relies on T1 effects of gadolinium (Gd).
• A novel physical basis for Gd-enhanced MRA, termed Off-Resonance Contrast Angiography (ORCA), is introduced.
• ORCA leverages bulk magnetic susceptibility (BMS) effects of Gd, not T1 relaxation.

Purpose of the Study:

• To describe and validate the novel ORCA technique for MR angiography.
• To assess ORCA's capability for background suppression and catheter conspicuity.
• To evaluate ORCA's performance in imaging vascular structures in phantoms and human subjects.

Main Methods:

• ORCA methodology was developed and tested at 3 Tesla using phantoms with varying Gd-DTPA and ultrasmall iron oxide contrast agent concentrations.
• Image acquisition was performed in phantoms and human subjects, including forearm veins and extracranial carotid bifurcations.
• Gd-induced intravascular frequency shifts were measured in vivo.

Main Results:

• ORCA achieved complete background suppression without the need for image subtraction.
• Catheters filled with Gd dilutions were highly conspicuous in ORCA projection images, suggesting utility for passive catheter tracking.
• Angiograms of forearm veins comparable to CE-MRA were generated, and extracranial carotid bifurcations were successfully imaged during IV contrast administration.
• Gd-induced intravascular frequency shifts in human subjects were within expected ranges.

Conclusions:

• ORCA presents a novel approach to MR angiography based on Gd's bulk magnetic susceptibility effects.
• The method demonstrates potential for improved catheter conspicuity in MR-guided interventions.
• While promising, ORCA faces technical limitations including dependence on vessel orientation and field homogeneity, requiring further investigation for clinical utility.