Simultaneous multi-orientation magnetic resonance imaging
Simultaneous multi-orientation (“SMO”) magnetic resonance imaging (“MRI”), in which arbitrarily-oriented slices are simultaneously imaged, is described. The SMO techniques can include any number of pulse sequences that are adapted to acquire data from two or more arbitrarily oriented slices. In general, an SMO acquisition includes sequentially exciting two or more arbitrarily rotated slices that share a common spatial encoding axis (e.g., a common frequency encoding direction) and simultaneously acquiring data from the excited slices.
1. A method for imaging a subject using a magnetic resonance imaging (MRI) system, the method comprising:
(a) performing a pulse sequence with the MRI system, wherein the pulse sequence includes in each repetition time (TR) period:
a first radio frequency (RF) excitation pulse that excites spins in a first slice;
a first set of spatial encoding gradients to provide slice encoding and phase encoding of the spins in the first slice oriented in a first imaging plane;
a second RF excitation pulse that excites spins in a second slice that is oriented in a second imaging plane that is non-orthogonal and non-parallel to the first imaging plane;
a second set of spatial encoding gradients to provide slice encoding and phase encoding of the spins in the second slice;
a single frequency encoding gradient that forms a first echo signal at a first echo time and a second echo signal at a second echo time, wherein the first echo signal is associated with spins in the first slice and the second echo signal is associated with spins in the second slice;
(b) acquiring first data from the first echo signal with the MRI system, the first data being associated with the first slice;
(c) acquiring second data from the second echo signal with the MRI system, the second data being associated with the second slice;
(d) reconstructing a first image from the first data and reconstructing a second image from the second data, wherein the first image depicts the first slice and the second image depicts the second slice; and
(e) outputting the first and second image to a computer system for at least one of display or storage.
2. A method for imaging a subject using a magnetic resonance imaging (MRI) system, the method comprising:
(a) performing a pulse sequence with the MRI system, wherein the pulse sequence includes in each repetition time (TR) period:
a plurality of radio frequency (RF) excitation pulses that each excite a different slice, such that a plurality of slices is excited in each TR period, wherein at least two of the plurality of slices are non-orthogonal and non-parallel to each other;
a plurality of spatial encoding gradients to provide slice encoding and phase encoding of spins in each of the plurality of slices;
a single frequency encoding gradient that forms a plurality of echo signals at a corresponding plurality of echo times, wherein each of the plurality of echo signals is associated with the spins in a corresponding one of the plurality of slices;
(b) acquiring data from the plurality of echo signals with the MRI system;
(c) reconstructing a plurality of images from the data, wherein the plurality of images depict the plurality of slices; and
(d) outputting the plurality of images to a computer system for at least one of display or storage.
3. The method as recited in claim 1 , wherein the first set of spatial encoding gradients and the second set of spatial encoding gradients each have a zeroth moment defined in part by a phase encoding step and a zeroth moment of the frequency encoding gradient.
4. The method as recited in claim 1 , wherein the pulse sequence further comprises in each TR period a set of spoiler gradients applied after the frequency encoding gradient.
5. The method as recited in claim 1 , wherein the first echo occurs before the second echo.
6. The method as recited in claim 1 , wherein the first echo occurs after the second echo.
7. The method as recited in claim 1 , wherein the first echo time and the second echo time are equal.
8. The method as recited in claim 1 , wherein the first echo time and the second echo time are not equal.
9. The method as recited in claim 1 , wherein the pulse sequence further comprises:
a third RF excitation pulse that excites spins in a third slice that is oriented in a third imaging plane non-orthogonal and non-parallel with at least one of the first imaging plane or the second imaging plane;
a third set of spatial encoding gradients to provide slice encoding and phase encoding of the spins in the third slice;
wherein the single frequency encoding gradient also forms a third echo signal at a third echo time, the third echo signal being associated with the spins in the third slice; and
further comprising acquiring third data from the third echo signal with the MRI system, the third data being associated with the third slice.
10. The method as recited in claim 1 , wherein the first data and the second data are acquired using an extended readout gradient.
11. The method as recited in claim 1 , wherein the first data and the second data are acquired using the frequency encoding gradient to form the first echo signal and the second echo signal as combined echo signals.
12. The method as recited in claim 3 , wherein the zeroth moment of the first set of spatial encoding gradients is also defined in part by a zeroth moment of a slice-select gradient.
13. The method as recited in claim 10 , wherein the first data and the second data are acquired using simultaneous image refocusing.
14. The method as recited in claim 12 , wherein the zeroth moment of the first set of spatial encoding gradients is defined by,
E
n
,
ℓ
=
[
ℓ
Δ
k
P
/
γ
M
0
,
n
,
F
0
]
;
wherein η is a slice number index, is a phase encoding line index, Δk p is a phase encoding step size, γ is a gyromagnetic ratio, and M 0,n,F is the zeroth moment of the frequency encoding gradient.