Neurography - MRI that can see nerves all over the body

[Justin]

The publication below is geared toward hips/knees. However, an MRI is an MRI--the specific location of the artificial joint doesn't change the technology, although different techniques may be employed to reduce artifact, etc.

Orthopedic Clinics of North America
Volume 37 • Number 3 • July 2006

Magnetic Resonance Imaging of Joint Arthroplasty

Hollis G. Potter, MD a, b, ∗
Li Foong Foo, MBBCh, FRCR a

a Division of Magnetic Resonance Imaging, Department of Radiology and Imaging, Hospital for Special Surgery, 535 East 70th Street New York, NY 10021, USA
b Department of Radiology, Weill Medical College of Cornell University, New York, NY 10021, USA

MRI has proved efficacious in the evaluation of native joints as a result of its multiplanar capabilities and superior soft tissue contrast. The application of MRI to joint arthroplasty traditionally has been limited, however, by artifact generated by the metallic components. This artifact is due to the close juxtaposition of the more easily magnetized, relatively ferromagnetic metallic components compared with the poorly magnetized diamagnetic soft tissue. This juxtaposition creates frequency shifts resulting in mismapping of spins and artifactual high signal intensity within the image (Fig. 1). The magnetic susceptibility, which is the relative tendency of the material to become magnetized when exposed to the magnetic field, is enhanced in the metallic components, distorting the local field and creating artifact [1]. In addition, the metallic components cause a regional degradation of signal as a result of rapid dephasing of the excited hydrogen nuclei, resulting in a low signal intensity void within the arthroplasty (see Fig. 1). The intensity of the artifact is related not only to the degree of relative ferromagnetism of the components, but also to their orientation relative to the external field, which in a clinical closed unit runs parallel to the long axis of the supine patient. Reduced artifact is encountered when imaging titanium components [2], [3]. Improved image quality also has been detected when imaging oxidized zirconium knee arthroplasty, owing to its lower magnetic moment [4]. In addition, the geometry of the implant is important because the rounded spherical shape of the femoral component of a total hip or shoulder arthroplasty creates more frequency shifts [5].

Because the composition of the metallic components is not a controllable variable at the time of imaging, modification of pulse sequence parameters is necessary to reduce the artifact. This modification can be accomplished with reproducible results using commercially available software. Strategies to reduce the artifact are twofold: (1) reduce the chemical shift generated by the metallic–soft tissue interface and (2) improve the signal-to-noise ratio. The former can be done by increasing the strength of the slice select and readout gradient because distortion is inversely proportional to the strength of these gradients. One of the easiest ways to reduce the artifact is the use of a wider receiver bandwidth [6]. In addition, high spatial resolution in the frequency direction is helpful in improving image clarity further [7]. With appropriate pulse sequence parameter modification, effective evaluation of the regional soft tissue and bone-metallic interface is possible. Suggested protocols for imaging of total hip and knee arthroplasty are provided in Tables 1 and 2.

Copyright © 2006 W. B. Saunders Company

[Bionic Michelle]

I HATE MRI's! HATE them. Lying flat on your back (OW!) with nothing to think about but a broken washing machine (you know, the noise it makes) for an eternally long hour. I was so excited that after my ADR, I thought I could no longer have them. Yeah! (I know, strange thing to get excited about-I know I'm weird, but after 6 of the damn things that never showed anything....) So, I was excited. Then my surgeon shot me down. Non-magnetic metal. Now I just have to hope that I don't need any more of them because the problem is fixed. It does seem weird that you can have metal and get in a giant magnet, but oh well.

[ZorroSF]

aha!
I guess iron is the key. I would think anything with steel or aluminum would also absorb a magnetic field.

Thanks Justin and Chuck for clearing that up. Time for me to setup a new appt. hopefully at that neurology clinic in L.A.

[David]

Very interesting! A friend of mine emailed me this link, as I was claiming that my two-level lumbar ADR precluded me from any future MRIs (not that I really want another MRI)

Thanks.

David

[Toebin]

Originally Posted by Trish

Perhaps not everyone has heard about Neurography. I thought I'd post some info here in case someone might find it helpful. You guys can decide for yourselves whether it's anything that you think might help.

Dr. Aaron Filler is a neurosurgeon in Cali. who has invented a new MRI method called Neurography. It is capable of imaging nerves very well. Regular MRI's are unable to see any nerves once they leave the immediate area of the spine.

www.neurography.com

For example, a few of his success stories are patients who had incurable back and/or leg pain. They went through several back surgeries only to find out that there is a nerve impingement from a benign tumor or pinched nerve that the regular MRI couldn't "see".

So far it looks like the only locations are in California and Pennsylvania.

Be prepared though, he is openly skeptical of implant surgeries due to conflicts of interest and the financial gain the surgeon benefits from when she/he choose to prescribe an implant (i.e. ADR) to a patient.

Hope this helps someone out there,
Trish

I know this is old, but I see the website is still operational.. I was wondering two things actually.

1. Why don't we hear more about this procedure if it truely is diagnostic of nerve problems? Seems so much easier than the guessing game many of us go through if our surgical outcome isn't all that great...

2. Does anyone have any experience with having this form of imaging? Has anyone had this done ?

Thanks !!

Inquiring minds want to know

[annapurna]

Originally Posted by Toebin

1. Why don't we hear more about this procedure if it truely is diagnostic of nerve problems? Seems so much easier than the guessing game many of us go through if our surgical outcome isn't all that great...

2. Does anyone have any experience with having this form of imaging? Has anyone had this done ?

2 - Nope, not me or Laura.

1 - Every MRI isn't equally capable even if the technique could be exported and it looked to me like they were not interested in training everyone on their new idea. Also, if they were to offer training, your local radiologist would have to decide that his/her equipment was capable and that he/she'd make back enough money using the technique to be worth their time to go to the seminar. We have this problem a lot where we live: the technique isn't available so local docs don't order it to be done and the local docs don't order it so the technique providers don't get training and equipment to make the technique available. You need to get a newbie who learned about it in school or someone recently acquainted with the technique to drive the local radiologists to get the technique in to your area.

[Toebin]

Thanks for the input annapurna,

It actually looks like this is available in my area and my Spine surgeon just left a practice in Santa Monica where the main MRN guy has his practice too. I'll have to ask him about it and see if it's a viable option. It certainly would be nice to have a direct picture of things going on rather than everyone guessing you have an inflammed/damaged nerve ....