All right, and with that, I will turn it over to Dr. Aaron Filler from Santa Monica, who will be presenting part of a debate that we have set up on point-counterpoint session on MRI versus ultrasound in peripheral nerve surgery. Thanks very much. All right, thanks very much for the opportunity. I've got one, something overlay, some kind of overlay there, but hopefully it'll, oh, there it goes. So on comparing the MRI techniques, DTI, neurography, some of our high-resolution MRI axonal techniques versus ultrasound in relation to peripheral nerve surgery, and of course, so it was a little bit open-ended whether this referred to diagnostics, intraoperative guidance, say, for injections, and actual intraoperative procedures. And I've kind of framed the main issues. For MRI, the advantages would be linearity, so physical uniformity of an image in multiple dimensions over a larger volume, what I would call comprehensivity, if I can coin a word, which means that any tissue, fluid, bone, muscle, nerve, or structure can be made to be conspicuous and identifiable on a ready basis. So if we capture images, it's very easy to come back later, a year later, and any time for anybody and see what we did and where we were, whereas ultrasound, often you have to be there with the probe in your hand to really understand the image that you're generating. You know, patients have, we've all had the experience, a patient comes in to see you, they've got some nice ultrasound image to show you what they have, and you're looking at this thinking, what is this, even if it's a video. And then, effectiveness without contact, that is when you're working, there's nothing that has to be touching the surface, you don't have to put a probe in, fluid, gel, goo, it's open space, and the scanner is at some distance from where you're working. With ultrasound, some of the advantages, and there are many, it might be less expensive, although not quite so much, because a high-end, really good ultrasound probe can be $300,000, and you can get one used, right? And then, an open MRI system, these are now in the $500,000 range, so actually, the price is getting comparable for an open MR system versus an ultrasound, which really is very different from a perception in the past. Also, the ultrasound is really deployable in a standard operating room with all your standard equipment, and as soon as you go down the route of MRI, it's gonna be a special room and special devices and equipment. I would say, applicable upon arising issues, so you're working, you're doing a standard open surgery, and you realize you need some imaging. This is easy with ultrasound, you can get the probe, have them wheel it in, take a look. To decide in the middle of surgery, you need intraoperative MRI, just not really on, unless you're really prepared in advance for the possibility. And then, the other issue is real-time simultaneity, so with available ultrasounds, you have extremely short time base until far less than a second, so if you're palpating something, you can see in the image as you palpate. Now, I have one of the last built interventional MRI systems, it's 15 years old now, well, getting there, 13 years old, and we image in about 10 seconds, and it is possible to have fluoro MRI now, but there is no available system that actually lets you use it. That is, Jens Fromm invented this, it's possible, it's feasible, but you can't get it. I would say also, on the device side, the Chinese government has made one of these sort of moon-landing pushes to develop high-temperature superconductors to build MRI scanners of all shape and form that don't require liquids, liquid nitrogen, et cetera, and there's very little going on with Siemens, GE, Philips in this area, so there may be new devices coming down the road that transform the way that we have this opportunity. So going a little more quickly just through what we do with MRI, I won't say too much about, for me, the discovery of diffusion tensor imaging and neurography were together in 1991, 1992, although they're perceived as different things. We now sort of consider neurography, this is the T2 neurography that lets us down to see any detail, nerve elements, and then all the methods you take advantage of, the FAT suppression, diffusion methods, the fact that water diffusion in nerve is anisotropic versus isotropic in other tissues, and we can sensitize the scanner to it. And then, when we want to go around, Kurt, go follow this around, you can make the nerve the brightest structure in the image, you can make a pure nerve image, which was a neat finding, but before, we were always told you could barely see a nerve, but this is our inner rabbits. These are really small nerves. You make everything disappear except for the nerves, just the nerves in the upper arm. And then we want to follow the nerves around a curve, so it's nice enough we have a parallel and perpendicular gradient, and that led to the development of diffusion tensor imaging, which is just to apply tensor methodology, taking the image from a lot of directions, running some math on it, which was something that we used to do in the lab years ago for other reasons. And so now you can get very nice peripheral nerve DTI as well, which is very sensitive and has a big role diagnostically, and also it's a big role in nerve identification, so with a small nerve, sometimes I just run gradients in multiple directions, so if you want to see is it a vessel, is it a nerve, the vessel looks the same in any direction and the nerve changes intensity with direction of the gradient, so you're trying to identify a nerve in an image where you have small distal nerves. It's a nice way to do nerve identification, even if you don't actually run the tractography. General diffusion methods can let us get large views. Many of you may remember from the New England Journal, these whole body neurograms can be generated. The T2 neurography, which is focusing on endoneurial water and suppressing everything else. You have other imaging aspects of imaging strategies, such as your voxels need to be similar in size to the fascicles and oriented with them, so this is a voxel, an MRI, so it's got some depth, like a three millimeter slice thickness in the small end of it. You've got this set up so the fat's suppressed to be dark and the water's to be bright. If you produce a single dot on the image with this, it's going to be gray, it's mixing fat and water. This one will be a pure white dot, this one will be a pure black dot. So by orientation and size selection, you can make the nerve fascicular pattern stand out nicely. We saw this image earlier, so I'll skip along. Nerve fascicles swell when they're injured or affected, which is very helpful. We didn't know we would see that in advance, so an individual irritated nerve can really stand out nicely for a diagnosis. We can look at understanding where a brachial plexus impingement occurs, where along the brachial plexus we need to go and do a much more smaller focused operation. We can't do stimulation, which I know is always disappointing to Dr. Klein about these surgical designs, but we know exactly where to go, where the problem is, and make a smaller approach. And then here's this issue of being able to see larger areas, seeing the overall pattern of the nerve entrapment, a brachial plexus running in a straight line, a brachial plexus with a big curve in it, and seeing, oh, is it irritated at the point where it bends? Associated structures, osteophyte distorting a proximal root, again, these large overviews you can get. A problem like this, Dr. Zagor mentioned earlier about unusual issues. This is a split nerve, split muscle configuration in piriformis. When imaged correctly, we see the two parts of the piriformis, sciatic inside, sciatic beneath, and a comparable neurographic image. So we know when we're going to operate not to make a mistake and think you're cutting out the muscle and take half the sciatic nerve. And then, yes, you can do very nicely with ultrasound if you know where you are and are familiar. It's very much operator dependent, but you can get a lot of good data at high resolution out. There are pitfalls, of course. The orientation of the probe may fool you with regard to nerve size. So when there's nice measurements looking at swelling are affected by the orientation of the probe relative to the orientation of the nerve, and that's just one of those things to keep in mind. So that's a quick summary, and I'm sure we'll hear other viewpoints.

MRI

ultrasound

peripheral nerve surgery

diffusion tensor imaging

neurography