The standard CE-MRA approach relies on a venous injection of contrast agent with physiological dilution and transport to the target vessels. Another group of techniques use a direct injection of suitable concentration to fill the target vessels with contrast.
Conservative researchers employed the method to create direct MR venography (1), while others developed direct intra-arterial CE-MRA. (IACEMRA). Direct injection CE-MRA has obvious application in the development of interventional MR [ii],[iii] but it has been used initially to supplement equivocal X-ray DSA.
The only human studies comparing intra-arterial direct CEMRA (IACEMRA) with arterial X-ray DSA were published by two independent Australian groups.[iv],[v]
Laboratory and animal studies described two technical approaches (injected solution fully replacing blood, or using physiological flow to further dilute the injected solution) but there were discrepancies on the target concentration [vi],[vii]The concentration of injected concentration was thought to be of critical importance for successful direct CE-MRA, but the T1 response of the sequences used mean that a broad range of concentrations, 10 – 60 mM (dilutions of 1:50 and 1:8), give almost equal results.
This range means that direct MRA with a 1:10 solution and fast hand injections ( 3 – 6 cc/sec) will deliver effective results in all vessels outside the Aorta. Commercial contrast agents are not approved for direct arterial injection, but the safe use of intra-arterial Magnevist for X-ray angiography[viii],[ix] and CT angiography[x] has been reported.