Magnetic resonance neurography
Magnetic resonance neurography (MRN) is the direct imaging of
History and physical basis
Magnetic resonance imaging (MRI) is based on differences in the physical properties of
In 1992, Aaron Filler and Franklyn Howe, working at
There are two main physical bases for the imaging discovery. Firstly, it was known at the time that water diffused preferentially along the long axis of neural tissue in the brain – a property called "
The endoneurial fluid compartment in nerve can be unmasked by similar techniques resulting in a "T2" based neurography[6] as well as the original diffusion based neurography technique. Endoneurial fluid increases when nerve is compressed, irritated or injured, leading to nerve image hyperintensity in an magnetic resonance neurography image. Subsequent research has further demonstrated the biophysical basis for the ability of MR Neurography to show nerve injury and irritation.[7]
Measurements of the T2 relaxation rate of nerve by Filler and Howe revealed that previous reports of a short relaxation time were wrong and that—once signal from
Within a few months of the initial findings on diffusion-based nerve imaging, the diffusion technique for nerve imaging was adapted to permit for visualization of neural tracts in the spinal cord and brain via Diffusion Tensor Imaging.
Clinical uses
The most significant impact of magnetic resonance neurography is on the evaluation of the large proximal nerve elements such as the
Neurography has also been helpful for improving image diagnosis in spine disorders. It can help identify which spinal nerve is actually irritated as a supplement to routine spinal MRI. Standard spinal MRI only demonstrates the anatomy and numerous
Many nerves, such as the median and ulnar nerve in the arm or the tibial nerve in the tarsal tunnel, are just below the skin surface and can be tested for pathology with electromyography, but this technique has always been difficult to apply for deep proximal nerves. Magnetic resonance neurography has greatly expanded the efficacy of nerve diagnosis by allowing uniform evaluation of virtually any nerve in the body.[14][15][16][17]
There are numerous reports dealing with specialized uses of magnetic resonance neurography for nerve pathology such as traumatic brachial plexus root avulsions,[18] cervical radiculopathy, guidance for nerve blocks,[19] demonstration of cysts in nerves,[20] carpal tunnel syndrome, and obstetrical brachial plexus palsy.[21] In addition several formal large scale outcome trials carried out with high quality "Class A" methodology[22][23][24] have been published that have verified the clinical efficacy and validity of MR Neurography.
Use of magnetic resonance neurography is increasing in neurology and neurosurgery as the implications of its value in diagnosing various causes of sciatica becomes more widespread.
Magnetic resonance neurography does not pose any diagnostic disadvantage relative to standard magnetic resonance imaging because neurography studies typically include high resolution standard MRI image series for anatomical reference along with the neurographic sequences. However, the patient will generally have a slightly longer time in the scanner compared to a routine MRI scan. Magnetic resonance neurography can only be performed in
References
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- ^ Filler AG, Tsuruda JS, Richards TL, Howe FA: Images, apparatus, algorithms and methods.GB 9216383 Archived 2009-06-26 at the Wayback Machine, UK Patent Office, 1992.
- ^ Filler AG, Tsuruda JS, Richards TL, Howe FA: Image Neurography and Diffusion Anisotropy Imaging[permanent dead link]. US 5,560,360, United States Patent Office, 1993.
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