The subject of last year’s Nobel Prize in Physiology/Medicine, magnetic
resonance imaging (MRI) is well known for making beautiful images of
the inside of the body. MRI is less recognized for its ability to track
movement, such as clinical studies of blood flow.
Now, researchers in Canada (Benedict Newling, University of New Brunswick,
email@example.com) have invented a new MRI method suitable for measuring
much faster fluid speeds, ten times more rapid than the fastest human
blood flow. Their approach uses a constant, shorter-than-usual measurement
interval (0.6 milliseconds).
In effect, the MRI scanner becomes a new type of practical wind tunnel,
one that's non-invasive too. An obstruction of any shape can be placed
in the flow at the center of the scanner. The resulting flow of liquid
or gas around the object is readily measured.
As an example, the researchers measure gas flow past a wing at realistic
speeds (corresponding to a stalled aircraft) and compare them with computer-based
calculations of the expected flow (see figure at Physics
The flows they measure are highly turbulent, which means the fluid
velocity at every position varies rapidly around some average value.
The MRI measurement contains information about both the average velocity
MRI is naturally three-dimensional and works just as well in opaque
or transparent fluids. Furthermore, MRI can measure several positions
simultaneously, unlike most conventional wind-tunnel measurements, and
therefore has the potential to deliver measurements in substantially
reduced times. (Newling
et al., Physical Review Letters, 8 October 2004)