While humorists have gone to great lengths to describe the differences between men and pigs, scientists are more apt to focus on the similarities. In particular, the cardiovascular systems of the two species are very much alike -- not only genetically, but in their ability to develop high cholesterol levels and clogged arteries. At 60-90 kg, even the adult weight of the two species is roughly aligned, especially in the U.S.
Such attributes make swine ideal candidates for cardiovascular research, of course, to the point where a group from the University of Rome "La Sapienza" considered them ideal models for a study of a high-concentration iodinated contrast agent not yet approved for marketing.
Iomeprol (Iomeron, Bracco, Milan, Italy) is a nonionic iodinated contrast agent available commercially in concentrations as high as 400 mg of iodine per mL. An even higher concentration (500 mg/mL) is available for research, Dr. Carlo Catalano said in a presentation at the 2004 RSNA meeting in Chicago.
The group tapped the investigational Iomeron 500 agent in efforts to improve arterial contrast enhancement in CTA angiography with multidetector-row CT.
"CT angiography can be performed rapidly and safely for assessment of many vascular diseases," Catalano said, although "it relies on precise synchronization of the CT scan with the contrast media injection" -- a task growing ever more difficult with the addition of more detector rows on CT scanners, and the resulting shorter scan times.
"We can increase rate of injection, but 4 mL per second is recommended as maximum speed to avoid possible vessel damage," he added, suggesting the use of higher iodine concentrations as a solution.
To this end, the study used eight adult pigs to compare opacification in CTA between Iomeron 350 and 500. In the study, eight anesthetized adult pigs were injected at 3 mL/sec with Iomeron 350, then the 500 solution, in studies at least six hours apart.
Eight seconds after the contrast injection began, CT images of the heart were acquired every three seconds for 120 seconds on a HiSpeed scanner (GE Healthcare, Waukesha, WI). Transverse images included the abdominal aorta, hepatic artery, inferior vena cava, and portal vein.
At 5 g of iodine per kg/body weight, "each animal received 1.43 mL per kg of body weight of the 350 solution, and 1 mL per kg/(bw) of the 500 solution," Catalano said. "So the mean volume was 170 mL for (Iomeron) 350 and 175 ml for (Iomeron) 500. We didn't observe any adverse reactions, and there were no changes in vital signs."
Plotting arterial enhancement over time, the researchers found that opacification with Iomeron 350 (mean arterial value 70 HU) both rose and fell more gradually than with Iomeron 500, which peaked earlier and higher in both the aortic and hepatic arteries. In the vena cava, Iomeron 500's enhancement was longer lasting (p < 0.001) compared to the 350 solution.
"The 500 showed a (far) superior arterial peak, but also we got a very fast washout, while the 350 showed small rise and then a gradual fall," Catalano said. And while baseline HU was the same for both agents, "we probably increased CT imaging values up to 45% (with Iomeron 500), and when we considered just the arterial phase, we found a significant difference between the two solutions."
The increase in hepatic arterial enhancement with the 500 solution was not statistically significant, though breathing artifacts made hepatic artery evaluation difficult, he said. The substantial increase in enhancement with high-concentration iodine bodes well for future evaluations of the small arteries, though larger studies will be needed, Catalano concluded.
By Eric Barnes
AuntMinnie.com staff writer
March 10, 2005
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