Dynamic contrast enhanced (DCE) imaging is useful in evaluating the functional status of a vascular system¹. Gadofosveset is a clinically approved blood pool agent that binds to albumin resulting in a high effective molecular weight, only exiting the vessel lumen in areas of leaky neovessels and damaged endothelium². Studies have shown that gadofosveset is better able to discriminate atherosclerotic vessel wall in rabbits than Gd-DTPA³ and symptomatic patients showed increased contrast agent uptake into carotid plaque as characterized by gadofosveset⁴. However, changes in adventitial vasa vasorum density and permeability may not be characterized by gadofosveset if the neovessels have not yet disrupted. As a result, Gd-DTPA may be better suited to track initial disease progression and therapy outcomes⁵ whereas gadofosveset may detect highly inflamed, end-stage atherosclerotic plaque. In this work we propose the use of dual contrast agent injections in conjunction with a 3D DCE radial stack of stars sequence⁶.All imaging was performed on Siemens Trio and Prisma scanners with a 3D radial stack of stars sequence. Acquisition matrix was 192x304x12, resolution 0.8mmx0.8mmx1.5mm, TE/TR=2ms/5ms, 23 total measurements over 372s (16s per measurement). Data was reconstructed twice using the KWIC algorithm⁷. First the data is reconstructed into 16 temporal frames per measurement (1.3s effective temporal resolution) with the corresponding images being used to measure the AIF. The same data is then reconstructed a second time with a lower temporal resolution (4 temporal frames per measurement) to find the tissue contrast uptake curves. Following one minute of baseline measurement, 0.03 mmol/kg of Ablavar (Gadofosveset Trisodium, Lantheus Medical Imaging) was injected at 1.2 ml/s with a 20ml saline flush. Following another three minutes of measurements 0.1 mmol/kg of MultiHance (Gadobenate Dimeglumine, Bracco Diagnostics) was injected at 2ml/s with a 20 ml saline flush (Figure 1). All injections were performed with dual Medrad power injectors (Radiology Solutions, Bayer). Data was analyzed with Olea Sphere post processing software (Olea Medical). Image analysis

Evaluation of sequence improvements to DCE kinetic parameter estimation requires a reproducible set of tracer kinetic conditions. This was accomplished with an appropriate DCE phantom (Figure 3). Within the carotid plaque in Figure 4, there are areas of high k_trans as measured by low molecular weight Multihance along the juxtaluminal fibrous cap (red) and the adventitia (green). K_trans measurements with the high molecular weight Ablavar are decreased in comparison, reflecting differences in permeability between the two agents. Figure 5 compares contrast agent uptake with intraplaque hemorrhage as identified with a MPRAGE scan on the bottom right. In this case, there is increased uptake of MultiHance but not of Ablavar near the center of the hemorrhage indicating inflammation but not necessarily neovessel rupture.

We have demonstrated feasibility of performing dual contrast agent injection for clinical evaluation of carotid disease. Two different molecular weight contrast agents may allow further characterization of plaque permeability in vulnerable carotid plaque. The long term effect of this project will be a more reliable and inclusive DCE protocol to identify carotid plaque inflammation.