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University of Washington Researchers Make Major Advances in New MRI Technique That Produces Clear Images of Nerves and Nerve Injuries
In a major advance, researchers at the University of Washington School of Medicine have shown they can create clear images of nerve compressions and injuries, using a technique called magnetic resonance (MR) neurography. They believe the breakthrough will alter the way pain and nerve-related disorders are diagnosed in the future. Results of the study are published in the Aug. 1 issue of the Journal of Neurosurgery.
The new imaging technique can be achieved with standard commercial MRI scanners already in use in most hospitals, using modified computer programs and signal-enhancing devices to bring out the weaker signals produced by nerve tissue.
Magnetic resonance imaging (MRI) allows doctors to look within the human body, producing images of soft tissues and organs by detecting radio signals from hydrogen atoms in water molecules within tissue. However, until the current breakthrough in imaging at the UW, nerve tissue has not stood out clearly because its signals are overwhelmed by signals from adjacent soft tissue.
In an initial breakthrough three years ago, the UW group published the first medical image to show a detailed view of a human nerve by rendering invisible other tissues around the nerve. Their further research has shown that neurography can show images of normal nerves, as well as nerves that are compressed or injured. The injury sites display as "hyperintensities" or bright regions in the image.
"The discovery that specific injury sites can be imaged transforms the technique from an anatomical or educational tool into a powerful new means of neurologic diagnosis," said Dr. Aaron Filler, lead author. Filler was a resident in neurosurgery at the UW at the time of the studies and has since joined the neurosurgery faculty at UCLA Medical Center. "We have already found that we can make diagnoses and offer surgical treatment in some cases where all other diagnostic methods had proven ineffective."
Co-authors include Drs. H. Richard Winn, Robert Goodkin and Michel Kliot of the UW Department of Neurological Surgery; and Drs. Cecil Hayes and Jay Tsuruda of the UW Department of Radiology. Tsuruda is now on the radiology faculty at the University of Utah.
A preliminary study of a patient whose sciatic nerve injury was imaged using the new technology was originally reported in March, 1993 in The Lancet, and received widespread press coverage.
"In most imaging techniques, nerves look similar to tendons, blood vessels, fat and other tissue," said Filler. "Diagnosis and treatment have relied on images of the structures near the nerves, such as bone, muscles and ligaments, as well as electrical tests and the traditional physical exam. Neurography can localize nerve injuries without surgery, with a precision never before possible."
In the current article, the researchers describe the results of 242 imaging studies that evaluated nerves in various regions of the bodies of both healthy volunteers and of patients with nerve injuries. They have produced detailed images of the complete array of cervical spinal nerves, the entire extent of an injured brachial plexus (the web of nerves extending from the neck to the arm), and the course of the inferior alveolar nerve through the jaw to the lip and teeth.
They have imaged a variety of nerve problems, including herniated disc, nerve entrapment (carpal tunnel syndrome and ulnar nerve entrapment across the elbow), sciatica, diabetic neuropathy, cervical radiculopathy (disease of the spinal nerve root), and mass lesions such as tumors involving peripheral nerves.
"This technique may well have a significant impact on patient care as well as on health care costs, since it may eliminate the need for other investigations," said Richard Winn, professor and chair of the Department of Neurological Surgery at the UW.
The UW scientists have been able to make images of nerves stand out by filtering out the image signals from other tissues, until only the signals from nerve tissue remain, making the nerve fibers the brightest structures in the image. The new technique can also block out the sheathing tissue, allowing individual nerve bundles, called fascicles, to be clearly imaged.
"As the surrounding tissues disappear, we are left with a three-dimensional picture of the nerve remaining in the image, like the smile of the Cheshire cat in 'Alice in Wonderland,'" said Filler.
The concept of neurography was initially developed by Filler and colleagues while he was at the University of London as part of his UW residency training. The imaging techniques were made possible in large part by the development of special phased array coils fabricated at the UW Diagnostic Imaging Center (DISC) by Hayes under the guidance of Tsuruda and Dr. Kenneth Maravilla, head of the division of Neuroradiology. The coils pick up the signal from the scanner.
Scanners at other medical centers can be retrofitted fairly readily to use the new technique. The new findings are expected to significantly accelerate the pace at which MRI manufacturers make the specially designed equipment and major software more widely available.
"Within five years these image techniques may be in use for hundreds of thousands of patients annually," said Filler. "The impact will be to reduce the number of exploratory surgeries done to evaluate nerve injury and to identify patients who have treatable lesions, who might otherwise be sent to pain clinics or psychiatrists for treatment of pain whose source could not be diagnosed."
"Our goal has been to evolve MRI technology to the point that images of peripheral nerve structures are of sufficient detail to aid in both diagnosis and treatment," said Kliot. "We're attempting to extend to the peripheral nervous system the enormous impact MRI has already had on diagnosing and treating disorders of the brain and spinal cord."
The investigators believe that neurograms, as they are calling the new images, will be key to a new form of surgery called "interventional MRI," where the surgeon will see real-time images of the surgical site on a screen and will be able to make surgical repairs endoscopically, in place of open surgery. The images, colorized to clarify detail if necessary, will help the surgeon work on structures close to nerves without injuring the nerves.
Photos of the nerve compression images suitable for publication are available.
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