Oct. 9, 2013: As Nebuloni et al. have just published in Academic Radiology, Nanoprobes' gold nanoparticle X-ray contrast agent, AuroVist™-15 nm, demonstrates the highest contrast, the highest resolution, and the longest blood pool residence of any contrast agent commercially available for micro-CT.
In the study, which compared commonly used X-ray contrast agents containing iodine, alkaline earth metals and gold, AuroVist also received high marks for its minimal toxicity.
Rising to the challenge of micro-CT
X-ray imaging of the vascular system is challenging because blood vessels provide low levels of intrinsic contrast, unlike bone and other hard tissues. X-ray contrast agents are needed to enhance the visibility of vasculature for X-ray observation and reconstruction, in both clinical use and research applications.
Clinical computed tomography (CT) scans are usually acquired rapidly, but the lower-energy micro-CT used in research can take much longer. Micro-CT is an important method for studying both structural features and dynamic processes in the vascular system, which often require lengthy scanning and data acquisition times. For micro-CT contrast agents, in addition to contrast and resolution, a long blood residence time is critical.
To find the X-ray contrast agent best suited to the unique needs of micro-CT, Nebuloni et al. evaluated commercially available contrast agents in mice. After injection into the tail vein, in vivo micro-CT scans were acquired at three regions of interest (neck, head, right lower hind limb). A vivaCT 40 instrument from Scanco Medical AG was used, operated at 45 kVp and 150 mA.
After three-dimensional reconstruction of the scanned projections, a Gaussian filter was applied to the images to reduce noise; they then aligned and subtracted the pre-contrast from the post-contrast images. After segmenting, contrast parameters were calculated on the blood itself.
AuroVist proves best suited for vascular studies with micro-CT
20µm blood vessels in a live mouse around legs and pelvic region after IV injection of AuroVist™-15nm.
Once these parameters were calculated, AuroVist™ showed the highest linear attenuation in blood (2.33/mm) as compared to both iodine (iomeprol) (1.97/mm) and alkaline earth (ExiTron nano 12000) (1.58/mm) formulations. Its contrast resolution was also the highest, at 60 µm, compared with 100 µm for the next best agent. Just as significantly, its blood pool residence time was also the highest in the group, with data indicating that its half life in the blood was longer than 24 hours.
Nebuloni et al. concluded that AuroVist™ 15 nm is the best contrast agent for anatomical investigation of the vascular network in micro-CT.
"We're happy to see such great results, even when just half the recommended dose of AuroVist was used in the study," said its inventor, Dr. James F. Hainfeld. He notes that a full dose delivers even greater contrast and resolution. "We developed AuroVist as a theranostics tool in the course of our cancer research here at Nanoprobes," he said, "and we're really glad that other scientists are finding it helpful in their research, too."
A Comparative Analysis of Water-Soluble and Blood-Pool Contrast Agents for in vivo Vascular Imaging with Micro-CT.
Laura Nebuloni, Gisela A. Kuhn, Ralph Müller.
Academic Radiology, 2013:20, 1247-1255. doi: 10.1016/j.acra.2013.06.003. PMID: 24029056.