Methods, systems, circuits, and computer program products for determining polarization of a gas
A system for determining polarization of a gas comprises a container that contains the polarized gas. An oscillator circuit comprises an NMR coil that is positioned adjacent to the container. A pulse generator circuit is configured to generate an electrical pulse that may be transmitted to the optical cell through the NMR coil to excite the polarized gas responsive to a control processor. A Q-reduction circuit that is independent of the pulse generator circuit is configured to reduce oscillations in the oscillator circuit from the transmitted electrical pulse responsive to the control processor. A receive circuit is responsive to an electrical signal that is induced in the oscillator circuit due to the electromagnetic excitation of the polarized gas. The control processor is configured to determine the polarization of the gas based on the output signal of the receive circuit. A polarimetry circuit for determining polarization of a gas includes an NMR coil that may be configured to excite a polarized gas and be responsive to an electromagnetic signal generated by the excited, polarized gas. The polarimetry circuit has a reproducible polarization measurement variability of less than 2% when the NMR coil is exposed to a temperature in a range of about 0° C. to about 200° C. Moreover, circuit-to-circuit polarization measurement variability may be less than about 3%.
1. A method of determining a polarization of a gas, comprising:
analyzing a decaying electrical signal having an initial voltage that is proportional to the polarization of a polarized gas;
determining a plurality of intermediate voltage levels, the intermediate voltage levels corresponding to voltage levels of the decaying electrical signal at intermediate portions of a plurality of time segments;
determining the initial voltage of the decaying electrical signal based on the plurality of intermediate voltage levels; and
determining the polarization based on the initial voltage.
2. The method of claim 1 , wherein determining the plurality of intermediate voltage levels, comprises:
sampling a noise signal to obtain a plurality of samples noise i ;
sampling the decaying electrical signal to obtain a plurality of samples signal i ; and
calculating a plurality of strength values strength k , each corresponding to a respective time segment as follows:
strength
k
=
2
×
∑
i
[
(
(
signal
i
k
)
2
-
(
noise
i
k
)
2
)
Δ
t
]
,
wherein Δt is a time difference between samples, signal i k are signal i samples in time segment k and noise i k are noise i samples in time segment k.
3. The method of claim 1 , wherein the electrical signal has an associated voltage over time g(t) as follows:
g
(
t
)
=
ⅇ
-
(
t
/
A
)
B
wherein A is a time constant associated with the gas and 1≦B≦2.
4. The method of claim 1 , wherein the gas comprises at least one of 129 Xe, 3 He, 13 C compounds, and 15 N compounds.
5. The method of claim 1 , wherein the gas is polarized via spin-exchange with an alkali metal.
6. The method of claim 1 , wherein the gas is polarized via dynamic nuclear polarization (DNP).
7. The method of claim 1 , wherein the gas is polarized via para-hydrogen induced polarization.
8. A system for determining a polarization of a gas, comprising:
means for analyzing a decaying electrical signal having an initial voltage that is proportional to the polarization of a polarized gas;
means for determining a plurality of intermediate voltage levels, the intermediate voltage levels corresponding to voltage levels of the decaying electrical signal at intermediate portions of a plurality of time segments;
means for determining the initial voltage of the decaying electrical signal based on the plurality of intermediate voltage levels; and
means for determining the polarization based on the initial voltage.
9. The system of claim 8 , wherein the means for determining the plurality of intermediate voltage levels, comprises:
means for sampling a noise signal to obtain a plurality of samples noise i ;
means for sampling the decaying electrical signal to obtain a plurality of samples signal i ; and
means for calculating a plurality of strength values strength k , each corresponding to a respective time segment as follows:
strength
k
=
2
×
∑
i
[
(
(
signal
i
k
)
2
-
(
noise
i
k
)
2
)
Δ
t
]
,
wherein Δt is a time difference between samples, signal i k are signal i samples in time segment k and noise i k are noise i samples in time segment k.
10. The system of claim 8 , wherein the electrical signal has an associated voltage over time g(t) as follows:
g
(
t
)
=
ⅇ
-
(
t
/
A
)
B
wherein A is a time constant associated with the gas and 1≦B≦2.
11. The system of claim 8 , wherein the gas comprises at least one of 129 Xe, 3 He, 13 C compounds, and 15 N compounds.