Re: MRI Machines

On 25 Jun, 02:00, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Tue, 24 Jun 2008 19:26:57 -0400, RFI-EMI-GUY



<Rhyol...@xxxxxxxxxxxx> wrote:
John Larkin wrote:
On Tue, 24 Jun 2008 13:28:46 -0400, RFI-EMI-GUY
<Rhyol...@xxxxxxxxxxxx> wrote:

Well I spent a half hour of my life under the magnet of an "open" MRI
machine yesterday. Still a bit claustrophobic. While I sort of
understand the theory of the MRI, what I don't understand is what
creates all the noise and racket. Any experts out there that can tell me
whats going on?

Pulsed gradient coils. These are "small" 3-axis coils that sweep a
gradient field across your innards, modulating the nuclear resonant
frequencies of your molecules to produce the spatial resolution. These
are generally water-cooled, with ballpark 20 KW constant-current
drivers per axis, playing all sorts of weird waveforms.

They scanned my head last year, with the gradient coils around my head
like some horror mask: noisy and boring.

John

Are they inside the machine or are they in the frame clamped around my
head and neck?

They're in the horror mask around your head. For body stuff, there's
an equivalent rig.

John

Are you sure? I thought that the coils attached to the patient (mask
etc?) were for creating the RF field to excite the resonance and for
picking up the return signal, and the gradient coils were within the
magnet casing. The forces on the gradient coils must be quite large,
and that may explain the noise.

AFAIK the EU has decided to make more advanced MRI pretty much illegal
(or more precisely, approaching the MRI machine much faster than a
snail could travel subjects you to an "electromagnetic" field that
some guy with a nice tin hat told a credulous eurocrat might sprain
your Chi or something like that). So a bunch of people who know not
much about physics made up some laws and then when someone competent
finally read the directive it was too late so they just asked the
member states to not enforce it for a while or something. Anyway when
these eurocrats end up getting sick, they'll find out that they need
to go to the US for the most advanced diagnistic scans since they
banned it in the EU. The pity is that they will have been well enough
paid to afford it whereas others won't and will have to use nice safe
x-rays instead of those nasty magnetic fields.
http://www.theregister.co.uk/2007/10/30/em_mri_rethink_ec/

Chris
.

Relevant Pages

  • Re: MRI Machines
    ... machine yesterday. ... While I sort of ... They scanned my head last year, with the gradient coils around my head ...
    (sci.electronics.design)
  • Re: MRI Machines
    ... machine yesterday. ... While I sort of ... The forces on the gradient coils must be quite large, ... I think these are MRI gradient coils... ...
    (sci.electronics.design)
  • Re: MRI Machines
    ... machine yesterday. ... While I sort of understand the theory of the MRI, what I don't understand is what creates all the noise and racket. ... They scanned my head last year, with the gradient coils around my head ... "Treason doth never prosper: what's the reason? ...
    (sci.electronics.design)
  • Re: MRI Machines
    ... RFI-EMI-GUY wrote: ... machine yesterday. ... While I sort of understand the theory of the MRI, what I don't understand is what creates all the noise and racket. ...
    (sci.electronics.design)
  • Re: MRI Machines
    ... While I sort of ... understand the theory of the MRI, what I don't understand is what ... They scanned my head last year, with the gradient coils around my head ...
    (sci.electronics.design)