362 MHz for NMRI - Why?

Would anyone happen to know why 362 MHz is a standard frequency for
NMRI?

IOW what atomic or molecular function, etc. does it relate to?

Bruce Condine

On 7 mar, 11:56, brucecond...@optoplex.com (Bruce Condine) wrote:

Would anyone happen to know why 362 MHz is a standard frequency for
NMRI?

IOW what atomic or molecular function, etc. does it relate to?

Bruce Condine

Hello Bruce,

The required frequency to excite the protons is given by the larmor
formula

f = B0*(Gamma), f [Hz], B0 = magnetic field [T],
gamma = larmor constant, for hydrogen about 42.57 MHz/T
So there are no specific frequencies that have to be used.

Your frequency probably belongs to a B0 field of 8.5 T. (85000
Gauss).

When you classify the NMR/MRI devices by their strength of the B0
field, the required RF frequency follows from the larmor constant.  In
MRI scanners for humans, the required volume is that large that it is
technically/economically spoken not possible to generate very large
magnetic fields. Therefore these devices use lower frequencies.
Small volume NMR devices can reach up to about 20 T and therefore
require 900 MHz to excite the nuclei.

Wimpie <wimabctel_at_tetech.nl> wrote:
: On 7 mar, 11:56, brucecond...@optoplex.com (Bruce Condine) wrote:
: > Would anyone happen to know why 362 MHz is a standard frequency for
: > NMRI?

: gamma = larmor constant, for hydrogen about 42.57 MHz/T
: So there are no specific frequencies that have to be used.

: Your frequency probably belongs to a B0 field of 8.5 T. (85000
: Gauss).

8.5 teslas sound quite high for a MRI system with a significantly
sized magnet bore, like those made for medical imaging. An example
of a device of such caliber is the french Neurospin facility
http://tinyurl.com/yahy59o . We happen to collaborate with them,
although not in the high-field MRI stuff.

For small sample sizes 8.5T is approximately the highest field
that can be obtained by simple Nb-Ti superconducting magnets operated
at 4.2K . For higher fields you'd need more expensive and hard-to-
manufacture materials and/or lower temperature. Maybe the 8.5T is
adopted as some sort of a standard, eg. in MRI-based chemical
analysis.

Regards,
Mikko

On Sun, 7 Mar 2010 18:01:31 +0200 (EET), Okkim Atnarivik
Okkim.Atnarivik_at_twentyfour.fi.invalid> wrote:

Wimpie <wimabctel_at_tetech.nl> wrote:
: On 7 mar, 11:56, brucecond...@optoplex.com (Bruce Condine) wrote:
: > Would anyone happen to know why 362 MHz is a standard frequency for
: > NMRI?

: gamma = larmor constant, for hydrogen about 42.57 MHz/T
: So there are no specific frequencies that have to be used.

: Your frequency probably belongs to a B0 field of 8.5 T. (85000
: Gauss).

8.5 teslas sound quite high for a MRI system with a significantly
sized magnet bore, like those made for medical imaging. An example
of a device of such caliber is the french Neurospin facility
http://tinyurl.com/yahy59o . We happen to collaborate with them,
although not in the high-field MRI stuff.

For small sample sizes 8.5T is approximately the highest field
that can be obtained by simple Nb-Ti superconducting magnets operated
at 4.2K . For higher fields you'd need more expensive and hard-to-
manufacture materials and/or lower temperature. Maybe the 8.5T is
adopted as some sort of a standard, eg. in MRI-based chemical
analysis.

Regards,
Mikko

NMR and FTMS use smaller bore magnets, which generally aren't used for
imaging (although micro-imaging gets close to optical microscope
resolution.) The NMR magnets have about a 2" room-temp bore and the
highest field magnets have their hydrogen resonance around a GHz. A
21T FTMS magnet has a (roughly) 8" bore and costs around $8M.

I think that NMR s/n goes up with the square of field strength, so the
high-field magnets can be worth it. FTMS is linear, so the payoff is
less.

One application for small-bore high-field magnets is MRI of lab
animals. One can feed a rat or a rabbit some drug and image them
regularly, as opposed to lopping off their heads and dissecting them.
An animal-care person is usually present when they are imaged.

This is neat stuff.

John

In article <k7q7p5903i2lbotfvsmljepf7qp8tmg...@4ax.com>, John Larkin



jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sun, 7 Mar 2010 18:01:31 +0200 (EET), Okkim Atnarivik
Okkim.Atnari...@twentyfour.fi.invalid> wrote:

Wimpie <wimabc...@tetech.nl> wrote:
: On 7 mar, 11:56, brucecond...@optoplex.com (Bruce Condine) wrote:
: > Would anyone happen to know why 362 MHz is a standard frequency for
: > NMRI?

: gamma = larmor constant, for hydrogen about 42.57 MHz/T
: So there are no specific frequencies that have to be used.

: Your frequency probably belongs to a B0 field of 8.5 T. (85000
: Gauss).

 8.5 teslas sound quite high for a MRI system with a significantly
sized magnet bore, like those made for medical imaging. An example
of a device of such caliber is the french Neurospin facility
http://tinyurl.com/yahy59o. We happen to collaborate with them,
although not in the high-field MRI stuff.

 For small sample sizes 8.5T is approximately the highest field
that can be obtained by simple Nb-Ti superconducting magnets operated
at 4.2K . For higher fields you'd need more expensive and hard-to-
manufacture materials and/or lower temperature. Maybe the 8.5T is
adopted as some sort of a standard, eg. in MRI-based chemical
analysis.

 Regards,
          Mikko

NMR and FTMS use smaller bore magnets, which generally aren't used for
imaging (although micro-imaging gets close to optical microscope
resolution.) The NMR magnets have about a 2" room-temp bore and the
highest field magnets have their hydrogen resonance around a GHz. A
21T FTMS magnet has a (roughly) 8" bore and costs around $8M.

I think that NMR s/n goes up with the square of field strength, so the
high-field magnets can be worth it. FTMS is linear, so the payoff is
less.

One application for small-bore high-field magnets is MRI of lab
animals. One can feed a rat or a rabbit some drug and image them
regularly, as opposed to lopping off their heads and dissecting them.
An animal-care person is usually present when they are imaged.

This is neat stuff.

John

I had occasion to be the sample in a MRI device last year.  As one of
the servants of The Machine explained I'd hear a clack-clack-clack
noise, I told them that was the field gradient coil.

When asked if I was familiar with the technology, I replied that when I
had studied it, it was known as NMR, but I understood that term was no
longer palatable.

The staff agreed -- the n-word is no longer used.

...but that doesn't change how the device works!