In patients with heart problems making blood flow abnormally fast, the threads appear red or yellow. In addition to flow velocity at various spots, the images show the direction the blood is flowing and the effect of any obstructions or deviations on blood flow, such as in patients with Tetralogy of Fallot, the condition snowboarder Shaun White had repaired as a child.
A 10-minute session in an MRI scanner is all it takes. Patients don’t need to hold their breath, the procedure is completely non-invasive and requires no contrast agent or general anesthesia. Squirmy children may need sedation to keep them still.
Physicians have measured blood velocity with standard MRIs for about 20 years, but it hasn’t been optimal. To acquire the 20 to 30 slices that are usually needed to scan the entire heart with an MRI, it can take between 45 and 90 minutes. Since patients must not move during the procedure, younger patients often require general anesthesia, which isn’t always desirable, especially for children with heart problems.
Ultrasound is another common technique used to look at blood flow in the heart, but the chest bone and other anatomy can make it hard to see some portions of the heart and vessels surrounding it.
What’s more, ultrasound and MRI images are typically two-dimensional representations, at times 3-D. But the new technique supplies 4-D information—three spatial dimensions plus time as the fourth dimension.
The new technique is known as PC VIPR (Phase Contrast Vastly undersampled Isotropic Projection Reconstruction).
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