Abstract
The objective of this study was to compare the blood pool agent Gadomer with a small contrast agent for the visualization of ultra-small, collateral arteries (diameter<1 mm) with high resolution steady-state MR angiography (SS-MRA) in a rabbit hind limb ischemia model. Ten rabbits underwent unilateral femoral artery ligation. On days 14 and 21, high resolution SS-MRA (voxel size 0.49×0.49×0.50 mm3) was performed on a 3 Tesla clinical system after administration of either Gadomer (dose: 0.10 mmol/kg) or a small contrast agent (gadopentetate dimeglumine (Gd-DTPA), dose: 0.20 mmol/kg). All animals received both contrast agents on separate days. Selective intra-arterial x-ray angiograms (XRAs) were obtained in the ligated limb as a reference. The number of collaterals was counted by two independent observers. Image quality was evaluated with the contrast-to-noise ratio (CNR) in the femoral artery and collateral arteries. CNR for Gadomer was higher in both the femoral artery (Gadomer: 73±5 (mean ± SE); Gd-DTPA: 40±3; p<0.01) and collateral arteries (Gadomer: 18±4; Gd-DTPA: 9±1; p = 0.04). Neither day of acquisition nor contrast agent used influenced the number of identified collateral arteries (p = 0.30 and p = 0.14, respectively). An average of 4.5±1.0 (day 14, mean ± SD) and 5.3±1.2 (day 21) collaterals was found, which was comparable to XRA (5.6±1.7, averaged over days 14 and 21; p>0.10). Inter-observer variation was 24% and 18% for Gadomer and Gd-DTPA, respectively. In conclusion, blood pool agent Gadomer improved vessel conspicuity compared to Gd-DTPA. Steady-state MRA can be considered as an excellent non-invasive alternative to intra-arterial XRA for the visualization of ultra-small collateral arteries.
Highlights
Therapeutic stimulation of the development of collateral arteries from pre-existent arterioles seems attractive as an alternative or adjuvant treatment for patients with peripheral arterial occlusive disease [1,2,3]
For Gadomer, thick-slab maximum intensity projection (MIP) provided the best overview of the vascular system, but for Gd-DTPA these images appeared too blurred to be of use
The number of collaterals identified on the steady-state images was equal for the two contrast agents, and closely mirrored the number of collaterals identified on high resolution invasive X-ray angiograms
Summary
Therapeutic stimulation of the development of collateral arteries from pre-existent arterioles (arteriogenesis) seems attractive as an alternative or adjuvant treatment for patients with peripheral arterial occlusive disease [1,2,3]. Further progress in the development of such treatment strategies relies strongly on the availability of non-invasive imaging methods that are able to evaluate the efficacy of treatment in terms of vascular changes at an early stage, even before clinical benefit can be noticed. Contrast-enhanced MR angiography (CE-MRA) has already proven to be a promising non-invasive tool to visualize collateral arteries in various parts of the body [4,5,6,7]. Visualization of small peripheral collateral arteries (diameter, mm) requires both a very high spatial resolution and a large spatial coverage. Meeting these requirements within the duration of the first pass period is a challenge. Correct timing of the first-pass acquisition is problematic in patients with severe stenoses and an extensive network of collateral arteries, whose filling occurs very slowly and varies considerably among and within patients [8,9]
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