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Wednesday, August 05, 2009

Google Ocean and the Animated MRI of a Horse's Foot

by Fran Jurga | 4 August 2009 | Fran Jurga's Hoof Blog

This blog post is comprised of three "aha!" moments.

It began back in February when I was intrigued by the launch of Google Oceans, an enhancement of Google Earth that allows us to look at the ocean floor, go inside the hull of a sunken ship, or explore the base of an iceberg in Antarctica. I imagine one day soon that the lobstermen around here won't have to go out and check their traps anymore; they will simply get on Google Ocean, type in the GPS coordinates of each trap, and see what they've caught. Then they would have to haul only those traps.

The image (above) that Google Ocean served up to promote its new program made me think of the horse's hoof, of course. The hoof has a lot in common with an iceberg. Everything is going on where we can't see it. Things are larger than they appear on the surface. And there's more to it than meets the eye. And as the history of the Titanic will tell you, a problem with an iceberg can ruin your day, or even end it. The same goes for a hoof.

Fast forward a couple of months and I'm lying inside an MRI unit in Massachusetts General Hospital. I'm determined to understand and appreciate this uncomfortable and deafening experience and use whatever I can get out of it to enhance my comprehension of magnetic imaging of the horse's foot.

Except no one on the staff wants to talk to me and the noise is too loud for conversation anyway.
I appreciate MRI images of the horse's foot because it is a new way to see inside the foot but I'm never sure what I'm looking at because I am trying to keep in mind that that is just a slice, unlike a radiograph. The MRI is like a strip of film negatives of a sequence of images in an old-fashioned filmstrip (albeit in 3D). When the radiologist looks at the MRI, he or she views the series mounted together on a sheet, not a single isolated image. Together, they make up the whole, but the isolated view reveals the injury.

MRI should be a collective noun, not a singular. That's what I brought out of that clanging tube that day at the hospital.

Fast forward again. Now it's the end of July and I'm in Columbus, Ohio, sitting in the back row at the AAEP's Focus on the Foot summer meeting. I'm really enjoying the speakers, taking notes like mad, and regretting missing the first day.

A change in the schedule brings North Carolina State University's Dr Rich Redding to the stage; he had been the victim of media glitches the day before, so his lecture was rescheduled. What a bonus for me! His lecture offers a hybrid approach to examining the foot and selecting the imaging modality for an injury diagnosis. All his images of the foot are lovely and explained very clearly but it all comes together for me when he compares four cases of foot injuries--puncture wound, two collateral ligament strains, and navicular zone pain by showing their MRIs.

The first thing that caught my attention was the should-be standard technique of showing a dissected foot cut at a specific point, and positioning an MRI "slice" at the same point next to it. That helped visualize the level in the foot where the injury was, and all the structures seen in the MRI, since the navicular bone can be viewed on so many different slices through the coffin joint.

Then, instead of showing an isolated MRI slice that showed the lesion site, he animated the slices into a fly-through of the entire MRI series.

Dr. Redding writes: "This was a horse that had a puncture to the navicular bone that damaged the Deep Digital Flexor (DDF) Tendon with a flap of tendinous tissue on the dorsal tendon proximal to the navicular bone. There is hemosiderin in the digital cushion where the nail penetrated the frog into the DDF and navicular bone." (Rough translation: the nail was in the back part of the foot so it grazed the upper surface of the navicular bone, which is at the level of the short pastern bone in the coffin joint. Watch the video and when the black square of P2 appears, you will see the injured area very briefly.)

It was Google Ocean all over again. You're beneath the surface, flying through; stop where you like and have a look around.

When they decide to do Google Hoof, I'm ready. Or maybe we're already doing it.

Thanks to Dr. Redding for the loan of this animation.

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Mike Miller said...

Yo, Fran

This is a very interesting posting. Yes, the MRI has a lot of potential for looking at the complex structures within the foot of the horse. But let's consider the following lessons from human medicine and the MRI:
1 - As you rightly point out, you need a familiar comparison model to understand what the image is showing you. In this case, an Allie Hayes type model of the same cross sections. Part of the learning curve for a new technology is relating it to what you already understand.
2 - The image generated by the MRI and also the CAT scan is not the same as a conventional x-ray; it is a computer reconstruction of an image from information on the density, and electromagnetic radiation from the object being studied. As such, it is more like an artist being blindfolded and allowed to feel a face, and then having the face taken away and making a drawing of it. The image quality is dependent on the machine, and on the complex formulae fed into the computer by the programmer. The man who figured out the original equations for the CAT scan rightly received a Nobel prize for his work. A conventional x-ray is a straightforward picture of the shadows made by an object on a film (or digital plate). All of this is important because it is a potential source of error in the image made by the computer.
3 - The findings in the MRI image must be calibrated against surgical or autopsy dissections to figure out what is true, and what is a false image. In the case of MRI of the human shoulder false positive and negative findings are common when the surgeon actually looks at the joint.
All of this is to say that equine MRI has a long shakedown cruise to go through, as has the MRI in human medicine. Also, in the horse MRI requires sedation or anesthesia, adding to the expense and complexity for the horse owner

Mike Miller

Fran Jurga said...

Hi Mike,

Thanks for checking in and making those points to clarify the essence and enigmatic factor of the MRI. (For anyone who doesn't know him, Mike is both a farrier and an M.D.) My guess is that Google Ocean has a similar culpability somewhere in its algorithm. Dr. Redding was very clear about comparing the benefits and limitations of each modality.

I might have daydreamed in this lecture on another day but the images were that much better than what I normally see and the animations of the MRIs were a great teaching tool.

He'll be speaking at the NEAEP conference in Connecticut in September.