New MRI technique quickly builds 3-D images of knees

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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.

University of Wisconsin-Madison