EP0206129A2 — NMR magnetization inversion by non-linear adiabat…

Claim 1

Independent Claim 155 words

A method for complete inversion of magnetization by adiabatic fast passage during an NMR investigation of a sample having a selected nuclear specie with a Larmor frequency w 0 , comprises the steps of: (a) generating a radio-frequency (RF) magnetic field having an amplitude B 1 and an instantaneous frequency w(t); (b) controlling the frequency w(t) to non-linearly sweep, as a function of time during a preselected time interval, from a first frequency, selected from one of a minimum frequency ω 1 substantially at a maximum offset frequency Δω below the Larmor frequency ω 0 , and a maximum frequency w h substantially at the maximum offset frequency Δω above the Larmor frequency, through the Larmor ω 0 frequency, to a second frequency which is the remaining one of the minimum and maximum frequencies; and (c) applying the non-linearly swept RF signal to the sample-being-investigated to substantially invert the magnetization of the selected nuclear specie.

Claim 2

Independent Claim 155 words

A method for complete inversion of magnetization by adiabatic fast passage during an NMR investigation of a sample having a selected nuclear specie with a Larmor frequency w 0 , comprises the steps of: (a) generating a radio-frequency (RF) magnetic field having an amplitude B 1 and an instantaneous frequency w(t); (b) controlling the frequency w(t) to non-linearly sweep, as a function of time during a preselected time interval, from a first frequency, selected from one of a minimum frequency ω 1 substantially at a maximum offset frequency Δω below the Larmor frequency ω 0 , and a maximum frequency w h substantially at the maximum offset frequency Δω above the Larmor frequency, through the Larmor ω 0 frequency, to a second frequency which is the remaining one of the minimum and maximum frequencies; and (c) applying the non-linearly swept RF signal to the sample-being-investigated to substantially invert the magnetization of the selected nuclear specie.

Claim 3

Dependent Claim 50 words

The method of claim 1, wherein the swept frequency w(t) is substantially equal to a first form tangential function, ω(t) = (ω 0 ±γB 1 tan(arcsin(ω s t))), where γ is the gyromagnetic constant of the selected nuclear specie and ω s = αγB 1 , where O < α≤1.

Claim 4

Dependent Claim 15 words

The method of claim 2, wherein ω 0 is on the order of 2πx (63Mhz.)

Claim 5

Dependent Claim 17 words

The method of claim 2, wherein Δω is on the order of 2 1 x (10 KHz.)

Claim 6

Dependent Claim 56 words

The method of claim 2, wherein the magnetization is substantially completely inverted at each of a plurality of nodes of the first form tangential function, each node occurring at a different time after commencement of the sweep; and step (c) includes the step of terminating the non-linear-swept RF signal substantially at a selected node occurrence time.

Claim 7

Dependent Claim 12 words

The method of claim 5, wherein the second node time is selected.

Claim 8

Dependent Claim 14 words

The method of claim 6, wherein Δω is about 2 1 rx (10 KHz.)

Claim 9

Dependent Claim 15 words

The method of claim 7, wherein ω 0 is on the order of 2πx (63MHz.)

Claim 10

Dependent Claim 49 words

The method of claim 1, wherein the swept frequency ω(t) is substantially equal to a second form tangential function, ω(t) = (ω 0 ±γB 1 tan (w s t), where γ is the gyromagnetic constant of the selected nuclear specie and ω S = αγB 1 , where 0<α≤1.

Claim 11

Dependent Claim 15 words

The method of claim 9, wherein ω 0 is on the order of 2πx (63MHz.)

Claim 12

Dependent Claim 15 words

The method of claim 9, wherein Δω is on the order of 2πx (20 KHz.)

Claim 13

Dependent Claim 42 words

The method of claim 9, wherein the magnetization is substantially completed inverted for a sweep time at least as long as a known sweep time; and step (c) includes the step of selecting the sweep time to exceed the known sweep time.

Claim 14

Dependent Claim 59 words

The method of claim 9, wherein the magnetization is substantially completely inverted for a sweep time greater than a known sweep time at a known RF magnetic field amplitude B l ; and step (a) includes the step of overdriving the RF magnetic field to an amplitude greater than known amplitude B 1 during the frequency sweep time interval.

Claim 15

Dependent Claim 42 words

The method of claim 13, wherein the magnetization is substantially completely inverted for a sweep time at least as long as a known sweep time; and step (c) includes the step of selecting the sweep time to exceed the known sweep time.

Claim 16

Dependent Claim 18 words

The method of claim 9, wherein the non-linear-swept RF signal is present for about one and one-quarter milliseconds.

Claim 17

Dependent Claim 189 words

Apparatus for generating an RF magnetic field excitation signal, for obtaining a complete magnetization inversion by adiabatic fast passage during an NMR investigation of a sample having a selected nuclear specie with a Larmor frequency ω 0 , comprising: means for generating an RF signal having an instantaneous frequency responsive to the amplitude of a control signal during a sweep time interval; means for generating said control signal as a non-linear ramp signal having initial, mid and final, values, said initial value causing said frequency to be at a selected one of a minimum frequency w 1 substantially at a maximum offset frequency Δω below the Larmor frequency ω 0 and a maximum frequency w h substantially equal to said maximum offset frequency Aw above said Larmor frequency ω 0 , said mid-value causing said frequency sweep to be substantial at said Larmor frequency ω 0 , and said final value causing said frequency sweep to be at the remaining one of said minimum and maximum frequencies; and means for applying said RF signal to said sample as an RF magnetic field with a selected amplitude B 1 .

Claim 18

Dependent Claim 189 words

Apparatus for generating an RF magnetic field excitation signal, for obtaining a complete magnetization inversion by adiabatic fast passage during an NMR investigation of a sample having a selected nuclear specie with a Larmor frequency ω 0 , comprising: means for generating an RF signal having an instantaneous frequency responsive to the amplitude of a control signal during a sweep time interval; means for generating said control signal as a non-linear ramp signal having initial, mid and final, values, said initial value causing said frequency to be at a selected one of a minimum frequency w 1 substantially at a maximum offset frequency Δω below the Larmor frequency ω 0 and a maximum frequency w h substantially equal to said maximum offset frequency Aw above said Larmor frequency ω 0 , said mid-value causing said frequency sweep to be substantial at said Larmor frequency ω 0 , and said final value causing said frequency sweep to be at the remaining one of said minimum and maximum frequencies; and means for applying said RF signal to said sample as an RF magnetic field with a selected amplitude B 1 .

Claim 19

Dependent Claim 75 words

The apparatus of claim 16, wherein said control signal generating means and said RF generating means cooperate to cause said RF magnetic field signal to have a swept frequency w(t) essentially equal to one of the equations: w(t) = ω 0 ±γB 1 tan (arcsin(wst)) and w(t) = ω 0 ±γB 1 tan (w s t), where ω S = αγB 1 , t is the gyromagnetic ratio for the selected nuclear specie and O<α≤1.

Claim 20

Dependent Claim 115 words

The apparatus of claim 17, wherein said RF generating means includes: VCO means for generating a first RF signal responsive to said control signal and having a frequency F' RF responsive to said mid value of said ramp signal and outside the band of frequencies within said maximum offset frequency Δω from said Larmor frequency ω 0 ; oscillator means for providing a second RF signal at a frequency F K selected such that one of the sum and difference products of F' RF and FK is essentially at said Larmor frequency; and means, receiving said first and second signals, for providing said RF signal as the selected product of said first and second signals.

Claim 21

Dependent Claim 25 words

The apparatus of claim 18, further including means for reducing the amplitude of said RF signal substantially to zero except during said sweep time interval.

Claim 22

Dependent Claim 67 words

The apparatus of claim 18, wherein said control signal generating means includes a ramp generator having a monotonic non-linear ramp signal output and having means for adjusting the sweep time of said output signal to essentially equal the desired sweep time interval and means for adjusting the ramp amplitude variational value for controlling the RF generating means over a contiguous range of frequencies essentially equal to 2Aw.

NMR magnetization inversion by non-linear adiabatic fast passage

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