Saturday, March 22, 2014

Enginerds - For The Unfamiliar

I've had a minor medical thing going on this year.  It really goes back a long time, and it's one of those annoying things rather than the kind of thing that makes you think "I've got to get to the Emergency Room now!".  Years ago, let's say 2004, I started to notice that if I stood up too long without moving around, the outer (left) side of my left thigh would start going numb.  Then it would turn into the "pins and needles" sensation, and eventually get pretty painful.  As it seemed to be taking less time to get there lately, I started to get concerned about it maybe becoming permanent or at least getting to where I couldn't stand for more than a few minutes, so I thought I'd mention it to my GP. 

The Doc had lots of "do you have...?" questions ranging from the unpleasant to the really scary, and I could thankfully say "no" to all of it.  He said it was probably a pinched nerve and suggested a few weeks of physical therapy followed by an X-Ray.  Sparing you some of the details, the x-ray came back and said I had a fractured vertebra, either L4 or L5 (don't recall).  The PT had said she could isolate the place where the pinched nerve would be, and it would have been between L4 and L5.  I went back to the GP and told him I had a hard time believing it.  I've had this problem for 10 years; if this is an old, healed fracture - that's one thing, but they didn't say "old fracture".  If they think it's new, that's two problems.  First - it's not causing the reason why I'm there; second, I sure haven't hit my back hard enough to break something.  If they had said I had a bad disk, yeah, I'd probably believe that, just not the fracture.  Doc suggested I get an MRI.  Finally had it Thursday after work. 

A friend and I got talking about it.  One of the questions they ask is if you're claustrophobic, and I know some people who have really freaked out in one of those things.  I found it pretty comfortable, if a little tight at the shoulders, and probably could have taken a nap if wasn't so dang loud!  They give you earplugs, the little foam shooters' plugs, and I swear the bangs out of the machine were around the loudness of a 9mm in your hands.  I'm not claustrophobic, but I was lying there a little while with my eyes open and there's just plain nothing to see.  It's dimly lit and there's just a little speaker panel about four inches in front of my face, so I left my eyes closed most of the time.

Both of us, though, said that we found the loud noises and frequency sweeps interesting, and we spent our time in the tube trying to figure out what the system was doing.  We both do radar and have some familiarity with synthetic imaging, and an MRI does synthetic imagaing very much like a radar or the fish finding sonars small boaters use.  The Magnet in Magnetic Resonance Imaging is a superconducting electromagnet, with the coils submerged in liquid helium - producing a field 40,000 times stronger than the earth's magnetic field.  Are the loud noises from relief of mechanical stress from the modulation of the coils in the strong magnetic field, or from something else?  And what kind of weird electromagnetic and mechanical considerations come into play in such large fields with superconducting magnets bathed in liquid helium?  (This is a pretty good explanation of how MRIs work)

If you haven't seen this Dilbert clip, it explains engineers as well as can be:

Doctor: "It's worse than I feared."
Mother: "What is it?"
Doctor: "I'm afraid your son has ... the Knack."
Mother: "The knack?"
Doctor: "The Knack. It's a rare condition characterized by an extreme intuition about all things mechanical and electrical ... and utter social ineptitude."
Mother: "Can he lead a normal life?"
Doctor: "No. He'll be an engineer."
Mother: "Oh, no!"  (sobs)

As my friend said, "I can see trying to do PET scans of engineer's heads. Hey you! Stop trying to figure out the details of what's going on dammit! You're ruining the scan! Think soft kittens. Soft kittens."


  1. look up meralgia paresthetica

  2. I've got the same thing, but in my right thigh.

    I have a referral to the neurology department, and have to get some X-rays and ultrasound scans done to pin it down.

    My Doctor thinks it's a pinched nerve somewhere, so we're going to start as soon as this nutty work schedule I'm on settles down.

  3. It certainly seems that meralgia paresthetica would be the name for what's going on. Fits it quite well.

    The PT was somewhat uncomfortable with making zero progress, but after various things, she'd have me stand around and stay still to see if the onset was always the same delay. It was.

    DrJim, my GP has already referred me to a neurosurgeon. Probably will see him next month.

    It's probably residual from getting hit by a pickup truck while riding my bike, back in 1999.

  4. Numbness and tingling are symptoms of paresthesia....not at all uncommon as we age and gravity has it's way with our spines. An MRI is the single best method of determining if there is a structural defect compressing a nerve root from the spine or in the case of the lower lumbar the Cauda Equina.

    And the loud knocking noises in an MRI are the sounds of the gradient coils that produce the RF signal that causes the hydrogen atoms in your body to shift out of and back into precessional alignment with the
    magnetic field that is aligned along the axis of the magnet bore. It takes a fair amount of energy to create enough RF to cause the atoms to respond....this causes the coils to heat up and cool down which is where the noise comes from. The variation in the noises are determined by machine settings that involves which coils are energized.....this determines which image plane is visualized....and for how long they are energized. The physics behind signal creation and acquisition is complex but relatively straightforward. Where it gets really complex is the 2D and 3D Fournier calculations used to translate signal data into pixels on an image that represent signal intensity.

  5. Concerning MRIs: I'm not claustrophobic, but on the one and only occasion I had to get one, the damned thing very nearly cooked me. I don't know of anyone else who's ever had that reaction.

    Apropos of MRIs, Damadian had nothing to do with the development of Nuclear Magnetic Resonance Imaging. The entire development of the procedure belongs to Nobel Laureate Dr. Paul Lauterbur, during his years at SUNY Stony Brook -- and I know this for a fact, because I worked on the project with him.

    Damadian has been trying to appropriate Lauterbur’s accomplishment ever since.

  6. The energy from the RF coils in a magnet is definitely not insignificant. All modern machines require a weight be input as part of the process so that inherently programmed safeguards in the software can limit the energy input. A good but not perfect process. As an aside people with tattoos that have ink with lots of metallic content can absorb enough RF to get real skin burns.....prison tattoos that use iron filings/rust are highly susceptible to this issue.

    As for Raymond Damadian he did not "invent" NMR.....he did however discover that using the technology behind NMR allowed for the differentiation between different tissue types with a high degree of specifity. This phenomenon which he realized just as modern computing was becoming available and affordable allowed engineers to take the fundamental principles being learned in creating cross sectional images in CAT scanning and apply it to machines that collect data from RF signals used on tissues in a magnetic field....and voila MRI was born.