Enhanced active MRI image of carpal bones (Abhijit Chaudhari, University of California – Davis)
Medical researchers at University of California in Davis designed a technique based on magnetic resonance imaging (MRI) that makes it possible to display the complex anatomy of the wrist in motion, offering a better method for diagnosing orthopedic injuries. A team led by Davis radiology professor Abhijit Chaudhari published the results of its first test of the technique, appearing earlier this week in the online journal PLoS One.
The wrist, say the authors, becomes unstable when carpal bones — the eight small bones connecting the fingers and thumb to the forearm — are misaligned, which disrupts functioning of the joints. These disruptions can lead to reduced mobility and weakness, as well as long-term and chronic conditions, such as osteoarthritis. Early diagnosis can catch these alignment problems, but the current choice of non-invasive imaging techniques either do not display all of the soft tissues (i.e., ligaments) or, like dynamic computed tomography and fluoroscopy, require radiation that can be harmful to some patients.
Individual MRI scans can get some, but not all, of the information needed for a completed diagnosis, say the researchers. “MRI scans provide detailed anatomical information of wrist structures without using ionizing radiation,” notes Chaudhari in a university statement, “but they cannot help diagnose problems with bone or tendon position that are best seen when the wrist is moving.”
To capture images of the wrist in motion, Chaudhari and colleagues devised a method of recording brief MRI scans of the wrist and assembling the images to display in sequence, almost like a video. The technique, called active MRI, had to overcome some slow speed of normal MRI scans. An MRI scan normally takes 30 to 45 minutes, with each set of images in the scan requiring at least three minutes.
The Davis team adapted an enhancement of MRI called balanced steady-state free precession, which in other applications was shown capable of capturing MRI pulse sequences quickly — 600 milliseconds or less — and with sufficient image quality for diagnostics. Using active MRI, the researchers could record an image every half-second, delivering a set of scans in about a half-minute.
Another problem was interference from the bones with the MRI’s magnetic field, which interrupts the signal and causes dark bands to appear on the images obscuring the bones in the wrist. To solve this problem, the researchers used dielectric pads, which have a chemical solution that when placed between the imaging coil and patient amplify the signals and minimize bands appearing on the images. The researchers report the only bands appearing were on the edges of the images, thus not obscuring the wrist anatomy.
In the test of the technique, the researchers scanned the wrists of 10 volunteers with no symptoms of wrist problems. The team was able to record videos of one or both wrists from the 10 volunteers performing motions such as clenching their fists, waving the hand from side to side, and rotating the wrist. Each session with the volunteers reportedly took about 10 minutes.
The video-like images offer advantages over conventional MRIs says Davis radiologist and first author Robert Boutin. “Now patients can reproduce the motion that’s bothering them while they’re inside the scanner,” says Boutin, “and physicians can assess how the wrist is actually working.”
Chaudhari says the next step is to test the technique with patients reporting wrist instability problems, particularly among women who report higher rates of hand osteoarthritis and carpal tunnel syndrome. The research was funded in part by a Building Interdisciplinary Research Careers in Women’s Health award from National Institutes of Health.
The following brief video shows active MRI images of a wrist cross-section while the wrist is rotated.
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