UW-Madison: New MRI Technique Quickly Builds 3-D Images of Knees

MADISON – A faster magnetic resonance imaging (MRI) data-acquisition technique will
cut the time many patients spend in a cramped magnetic resonance scanner, yet
deliver more precise 3-D images of their bodies.

Developed at the University of Wisconsin-Madison, the faster technique will enable
clinics to image more patients – particularly the burgeoning group of older adults
with osteoarthritis-related knee problems – and can help researchers more rapidly
assess new treatments for such conditions.

Magnetic resonance has long been touted as the ideal method for capturing 3-D images
of the human body. “But unfortunately, it is kind of a slow technique,” says Walter
Block, an associate professor of biomedical engineering and medical physics. “You
can only sample a few pieces of information needed to build the image at a time.”

Consequently, most magnetic resonance technicians acquire images as a series of 2-D
slices, which yield high resolution in a single plane and poor resolution in the
remaining direction, he says.

To capture an image, a magnetic resonance scanner commonly conducts hundreds to
thousands of little “experiments,” or encodings, that help to make up the big
picture. Block’s data-acquisition technique capitalizes on recent magnetic resonance
hardware advances that, coupled with a novel way of maintaining a high-level
magnetic resonance signal throughout the scan, will speed an MRI session. “But to
maintain the high-level signal,” he says,” you need to be able to complete each of
these smaller encodings within a couple of milliseconds.”

Rather than using the conventional approach, which sweeps horizontally to gather
magnetic resonance data, Block’s technique acquires the body’s signals radially, in
a way that looks somewhat like a toy Koosh ball. “We can essentially acquire data
during the whole experiment, where in the (conventional) case, a lot of time was
spent either prepping for the experiment or returning it to the steady state so that
you could do the next experiment,” Block says. “What we’re doing now is capable of a
study that you can visualize in any plane in about the same time as people are doing
one plane.”

For example, when imaging a joint like the knee – Block’s inspiration for developing
the new technique – suppressing the fat signal in bone provides image contrast
between bone and the cartilage surface. The conventional data-acquisition method
would spend half its scan time suppressing the signal from fat, instead of imaging
cartilage. However, Block’s technique exploits the difference in resonant
frequencies between fat and water. During the scan time, then, the technique
maximizes each component of the image, so that a technician can view any aspect.

High-resolution 3-D images are important not only from diagnostic and clinical
standpoints, but also to help patients better understand their health conditions,
says Block. “If you could actually look at a 3-D model from different perspectives,
you’d have a much better chance to make sense of the pain you’re feeling, your
doctor’s diagnosis and your treatment options,” he says.

The technique, which Block patented through the Wisconsin Alumni Research
Foundation, also will make it easier to image parts of the body, such as the heart
or abdomen, in which motion is a factor.

In related research, Block also has developed an algorithm that, within less than a
second, can calibrate a magnetic resonance system to use nonconventional methods of
data acquisition, yet produce clearer images.

Grants from the National Institutes of Health, the Coulter Foundation and the
UW-Madison Graduate School support Block’s research.