To assess if blood flow in dogs could be accurately measured with 64-CT, researchers compared the new scanner with an existing test that is considered to be the gold standard and relies on muscle absorption of microscopic beads in the heart muscle.
Six dogs had surgery to place a clamp around a main artery, cutting in half the blood flow to the heart. After surgery, the dogs were injected with the drug adenosine to speed up their heartbeat and maximize circulation. The dose, they note, was the same as that typically used in humans for routine stress testing: 140 micrograms per kilogram per minute, for five minutes.
When forced to pump faster, healthy heart tissue and surrounding blood vessels will adapt, while unhealthy, blocked ones will slow blood flow. These changes are not usually perceptible to the human eye from the scanned images but can be detected and quantified with CT imaging and computer analysis. Adenosine is commonly used in stress testing, Lardo says, to relax blood vessels in the muscle, which enhances the contrast between normal and abnormal regions of the heart.
After being injected, each of the dogs had a 64-CT scan of its heart and then underwent the standard test for blood flow with chemical beads. The beads, no bigger than 20 micrometers in diameter and called microspheres, were injected into the animal's bloodstream. Previous research has shown that they will lodge into the heart muscle at a fixed rate compared to how fast blood is flowing. Researchers can actually count the number of beads absorbed into the heart tissue to calculate blood flow.
However, calculating blood flow from the 3-D, scanned CT images was more complicated. Researchers used so-called deconvolution mathematical formulae to gauge the speed of blood flow through the heart and its feeding arteries and made separate cal
Source:Johns Hopkins Medical Institutions