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Intravascular CE-MRA
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Overview:
A demonstrable ability to repeatedly obtain high quality MR angiograms is crucial for MR guided endovascular therapy. The presence of an intra-arterial catheter offers new opportunities for optimizing MR angiograms and minimizing the volume of contrast delivered. We have explored and optimized an assortment of intra-vascular CE-MRA parameters, including target arterial concentration, methods of mixing/dilution, and injection requirements with respect to acquisition durations.
Findings:
Gadodiamidum (brand name "Omniscan") was administered with a syringe infusion pump at constant rates through either a conventional or a "pigtail" 5F catheter. The catheter tip was positioned in the thoracic aorta, ~3 cm superior to the dome of the liver, and phase-contrast flow measurements were made at this level to determine aortic flow. Real time 2D projection angiograms or 4s volumetric acquisitions (with matching TR/TE/flip = 5/1.7/30) were acquired over the abdominal aorta and iliac vessels during an assortment of injection conditions. Optimal mixing was achieved with dilute contrast (10-20% of stock) and a diffuser (pigtail catheter). Optimal arterial concentration was investigated by perfoming 2D real time angiography during injection of contrast at varying rates.
Arterial enhancement was found to be optimal when injection rates aimed to achieve 20mM Gadodiamidum in blood (~4% stock contrast to blood). In order to minimize the delivered contrast dose, we also explored injection durations shorter than the full image acquisition duration. 3D volumes were acquired with optimal mixing, arterial concentration and acquisition delay times, and the injection duration was varied to be 25%, 50%, 75%, 87.5% or 100% of the acquisition duration.
Injection durations less than the scan times were associated with a substantial loss in image quality (above) as aortic SNR dropped by an average of 11, 27, 41 or 63% for injection durations of 87.5, 75, 50 or 25% of the acquisition duration respectively.
In Summary, intra-arterial injection of extracellular MR contrast media can provide high-resolution MR angiograms with a minimal amount of contrast. For our acquisition parameters, we found an arterial concentration of 0.02M Gadodiamidum provided optimal results.
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Last update: 11/20/02