Image: The forearm of a healthy volunteer in the wrist harness (Photo courtesy of Plos One).
Image: Extensor carpi ulnaris (ECU) tendon translation during wrist rotation (Photo courtesy of Plos One).
Scientists have created moving pictures of the wrist in motion using a series of short magnetic resonance imaging (MRI) scans. Called “Active MRI,” the technique could be useful in diagnosing subtle changes in physiology that indicate the onset of conditions such as wrist instability.
The findings of the University of California (UC) Davis Medical Center(Sacramento, CA, USA) radiologists, medical physicists, and orthopedic surgeons first assessment of the new technique was published online December 31, 2013, in the journal PLOS ONE
. “These fast images are like a live-action movie,” said Robert Boutin, professor of radiology at UC Davis and lead author of the study. “The movie can be slowed, stopped, or even reversed as needed. Now patients can reproduce the motion that’s bothering them while they’re inside the scanner, and physicians can assess how the wrist is actually working. After all, some patients only have pain or other symptoms with movement.”
Senior author Dr. Abhijit Chaudhari noted that wrist instability occurs when carpal bones become misaligned and affect joint function, frequently as a consequence of trauma that injures the ligaments between wrist bones. It causes abnormal mobility and chronic pain that can lead to osteoarthritis, a key socioeconomic liability to patients and healthcare systems. Good results in managing the condition are more probably with early diagnosis, when less-invasive treatments are possible.
Imaging technology such as dynamic computed tomography (CT) and fluoroscopy can visualize the moving wrist, but these approaches involve radiation and do not show soft tissue such as ligaments--a major part of the wrist’s intricate anatomy as well as MRI scans.
“MRI scans provide detailed anatomical information of wrist structures without using ionizing radiation, but they cannot help diagnose problems with bone or tendon position that are best seen when the wrist is moving,” said Dr. Chaudhari, assistant professor of radiology at UC Davis. “Active-MRI provides a detailed and ‘real time’ view of the kinesiology of the wrist in action using a widely available and safe technology.”
The researchers solved a number of hurdles in modifying MRI capabilities to providing moving images. A complete MRI scan typically takes 30 to 45 minutes, with each image set requiring at least three minutes—not nearly fast enough to make a video. The researchers developed a new MRI protocol that takes one image every 0.5 seconds, providing a set of images in a half minute.
Another hurdle to overcome was the presence of imaging errors called banding artifacts. Movement of the bones in the wrist area can impede the scanner’s magnetic field, creating signal drop-offs. The resulting dark bands can hide the moving wrist. The team overcame this difficulty with dielectric pads, which stabilize the magnetic field and move artifacts away from the area of interest and to the side, allowing clinicians to clearly see the wrist bones.
Active-MRI was evaluated for the study on 15 wrists of 10 study participants with no symptoms of wrist problems. The participants’ wrists were imaged as they performed motions such as clenching the fist, rotating the wrist, and waving the hand side-to-side. Each scan lasted 10 minutes. “It’s quite phenomenal that we can look inside the body while it’s in action using MRI,” said Prof. Boutin. “Routine MRI provides exquisite details, but only if the body is completely motionless in one particular position. But bodies are made to move. We think Active MRI will be a valuable tool in augmenting traditional, static MRI tests.”
“Our next step is to validate the technology by using it on patients with symptoms of wrist instability,” added Dr. Chaudhari. “We also want to use Active-MRI to study sex distinctions in musculoskeletal conditions, including why women tend to be more susceptible to hand osteoarthritis and carpal tunnel syndrome.”
University of California, Davis Medical Center