NMR magnetization inversion by non-linear adiabatic fast passage

Claim 3

The method of claim 1, wherein ω O is on the order of 2πx (63 Mhz.)

Claim 4

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

Claim 5

The method of claim 1, wherein the magnetization is substantially completely inverted at each of a plurality of nodes of the 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 6

The method of claim 4, wherein the second node time is selected.

Claim 7

The method of claim 5, wherein Δω is about 2πx (10 KHz.)

Claim 8

The method of claim 6, wherein ω O is on the order of 2πx (63 MHz.)

Claim 9

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 O , 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 nonlinear ramp signal having initial, mid and final values, said initial value causing said frequency to be at a selected one of a minimum frequency ω 1 substantially at a maximum offset frequency ωw below the Larmor frequency ω O and a maximum frequency ω h substantially equal to said maximum offset frequency Δω above said Larmor frequency ω O mid-value causing said frequency sweep to be substantially at said Larmor frequency ω O 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 ; said control signal generating means and said RF generating means cooperating to cause said RF magnetic field signal to have a swept frequency ω(t) essentially equal to one of the equations: ω(t)=ω O ±γB 1 tan (arcsin (ω S t)) and ω(t)=a O ±γB 1 tan (ω S t), where ω S =αγB 1 , γ is the gyromagnetic ratio for the selected nuclear specie and 0<α≦1.

Claim 10

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 O , 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 nonlinear ramp signal having initial, mid and final values, said initial value causing said frequency to be at a selected one of a minimum frequency ω 1 substantially at a maximum offset frequency ωw below the Larmor frequency ω O and a maximum frequency ω h substantially equal to said maximum offset frequency Δω above said Larmor frequency ω O mid-value causing said frequency sweep to be substantially at said Larmor frequency ω O 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 ; said control signal generating means and said RF generating means cooperating to cause said RF magnetic field signal to have a swept frequency ω(t) essentially equal to one of the equations: ω(t)=ω O ±γB 1 tan (arcsin (ω S t)) and ω(t)=a O ±γB 1 tan (ω S t), where ω S =αγB 1 , γ is the gyromagnetic ratio for the selected nuclear specie and 0<α≦1.

Claim 11

The apparatus of claim 8, 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 O ; 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 F K 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 12

The apparatus of claim 9, further including means for reducing the amplitude of said RF signal substantially to zero except during said sweep time interval.

Claim 13

The apparatus of claim 9, 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 2Δω.