Method and means for magnetic resonance spin-echo imaging using an adiabatic three pi pulse sequence

Claim 2

In spin-echo magnetic resonance imaging and spectroscopy, a method of refocusing dephased nuclei spins in an inhomogeneous RF magnetic field comprising the steps of applying a first selective adiabatic pulse for rotating nuclei spins 360 degrees (2π), and applying a second selective adiabatic pulse for rotating nuclei spins 180 degrees (π) for creating a spin echo, said first pulse producing no net nuclei rotation and compensating for phase variations of said second pulse.

Claim 3

The method as defined by claim 1 wherein said first pulse precedes said second pulse.

Claim 4

The method as defined by claim 1 wherein said second pulse precedes said first pulse

Claim 5

The method as defined by claim 1 wherein the duration of said second pulse is equal to the duration of said first pulse.

Claim 6

The method as defined by claim 4 wherein said first and second pulses are hyperbolic secants, B 1 (t) i0 (t) and defined by the following table: ______________________________________ Duration B.sub.1 (t) φ (t) ______________________________________ 2π T/4 μβ sech (βt) -μ ln sech (βt) T/4 -μβ sech (βt) μ ln sech (βt) π T/2 -μβ sech(βt/2) 2μ ln sech (βt/2) ______________________________________

Claim 7

The method as defined by claim 5 wherein the sampling schedule of said first and second pulses is given by the following table: ______________________________________ Pulse Interval i t [i] ______________________________________ 2π 0 ≦ i < n t.sub.0 + i/n n ≦ i < 2n t.sub.0 + (i - n)/n π 2n ≦ i < 4n t.sub.1 + (i - 2n)/n ______________________________________ where t o =-1/2+1/(2n) and t 1 =-1 +1/(2n).

Claim 10

The method as defined by claim 7 where the duration of said π pulse is equal to the duration of said 2π pulse.

Claim 11

The method as defined by claim 8 wherein said first and second pulses are hyperbolic secants, B 1 (t) i φ(t) and defined by the following table: ______________________________________ Duration B.sub.1 (t) φ(t) ______________________________________ 2π T/4 μβ sech (βt) -μ ln sech(βt) T/4 -μβ sech (βt) μ ln sech (βt) π T/2 -μβ sech (βt/2) 2μ ln sech (βt/2) ______________________________________

Claim 12

The method as defined by claim 9 wherein the sampling schedule of said first and second pulses is given by the following table: ______________________________________ Pulse Interval i t [i] ______________________________________ 2π 0 ≦ i < n t.sub.0 + i/n n ≦ i < 2n t.sub.0 + (i - n)/n π 2n ≦ i < 4n t.sub.1 + (i - 2n)/n ______________________________________ where t o =-1/2+1 (2n) and t 1 =-1 +1(2N).

Claim 13

Apparatus for magnetic resonant imaging a slice through an object using spin-echo techniques, comprising (a) means for establishing a static magnetic field said object, (b) means for superimposing a gradient magnetic field said static magnetic field, (c) means for applying a 90-degree RF pulse to said object at the Larmor frequency for a selected slice to be imaged, (d) means for applying a 3π adiabatic pulse to refocus dephased nuclei spins in selected slice, said 3π adiabatic pulse including a 2π pulse and a π pulse where said 2π pulse produces no net nuclei rotation and compensates for phase variations introduced by said π pulse, and (d) means for detecting a spin echo of the refocused spins in said selected slice.

Claim 14

Apparatus for magnetic resonant imaging a slice through an object using spin-echo techniques, comprising (a) means for establishing a static magnetic field said object, (b) means for superimposing a gradient magnetic field said static magnetic field, (c) means for applying a 90-degree RF pulse to said object at the Larmor frequency for a selected slice to be imaged, (d) means for applying a 3π adiabatic pulse to refocus dephased nuclei spins in selected slice, said 3π adiabatic pulse including a 2π pulse and a π pulse where said 2π pulse produces no net nuclei rotation and compensates for phase variations introduced by said π pulse, and (d) means for detecting a spin echo of the refocused spins in said selected slice.

Claim 15

Apparatus as defined by claim 11 wherein the duration of said π pulse is equal to the duration of said 2π pulse.

Claim 16

Apparatus as defined by claim 12 wherein said first and second pulses are hyperbolic secants, B 1 (t) i φ(t) and defined by the following table: ______________________________________ Duration B.sub.1 (t) φ (t) ______________________________________ 2π T/4 μβ sech (βt) -μ ln sech (βt) T/4 -μβ sech (βt) μ ln sech (βt) π T/2 -μβ sech (βt/2) 2μ ln sech (βt/2) ______________________________________

Claim 17

Apparatus as defined by claim 10 wherein the sampling schedule of said first and second pulses is given by the following table: ______________________________________ Pulse Interval i t [i] ______________________________________ 2π 0 ≦ i < n t.sub.0 + i/n n ≦ i < 2n t.sub.0 + (i - n)/n π 2n ≦ i < 4n t.sub.1 + (i - 2n)/n ______________________________________ where t 0 =-1/2+1/(2n) and t 1 =-1+1/(2n).