US 9,519,039 B2Granted

Determining the form of RF pulses for selective excitation in magnetic resonance imaging

AssigneeSiemens Healthcare GmbH

InventorsRene Gumbrecht, Kaveh Vahedipour, Tony Stoecker, Nadim Joni Shah

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Abstract

The invention relates to a magnetic resonance method involving the generation of high-frequency pulses and magnetic gradients (gx, gy, gz) for the selective excitation of an object to be examined. According to the invention, the magnetic resonance method is characterized in that a magnetic resonance signal s(t) according to the following signal equation is generated: s ⁡ ( t ) = ∫ V ⁢ m ( r r , T ) ⁢ exp ⁡ [ t ⁢ / ⁢ T 2 ] ⁢ exp ⁡ [ ⅈ ⁢ ⁢ t ⁢ ⁢ ω s ] ⁢ exp ⁡ [ - ⅈ ⁢ ⁢ k r ⁡ ( T - t ) · r r ] ⁢ ⁢ ⅆ 3 ⁢ r wherein stands for a desired transversal magnetization after the selective excitation, t stands for a time, {right arrow over (r)} stands for a position vector and T stands for a duration of a pulse, and whereby s(t) stands for a magnetic resonance signal, V stands for a volume that is to be examined, T2 stands for a transversal relaxation time, and ωs stands for a shift of the resonance frequency. The invention also relates to a nuclear spin tomograph for carrying out the magnetic resonance method.

A magnetic resonance method involving the generation of high-frequency pulses and magnetic gradients (gx, gy, gz) for the selective excitation of an object that is to be examined, whereby the magnetic resonance method comprises the following steps:

providing a transversal magnetization m({right arrow over (r)}, T) which is described by
m
(
r
->
,
T
)
=
ⅈγ
⁢
⁢
m
0
⁢
exp
⁡
[
-
T
⁢
/
⁢
T
2
]
⁢
exp
⁡
[
-
ⅈ
⁢
⁢
T
⁢
⁢
ω
s
]
⁢
∫
0
T
⁢
exp
⁡
[
t
⁢
/
⁢
T
2
]
⁢
exp
⁡
[
ⅈ
⁢
⁢
t
⁢
⁢
ω
s
]
⁢
b
1
⁡
(
t
)
⁢
exp
[
ⅈ
⁢
⁢
k
->
⁡
(
t
)
·
r
->
]
⁢
⁢
ⅆ
t
wherein i stands for an imaginary unit, γ stands for a gyromagnetic ratio, m0 stands for an equilibrium magnetization, t stands for a time, {right arrow over (r)};
stands for a position vector and T stands for a duration of a pulse, T2 stands for a transversal relaxation time, ωs stands for a shift of the resonance frequency, b1(t) stands for a high-frequency pulse, and {right arrow over (k)}(t) stands for a vector of the k-space trajectory that is given by the magnetic gradients,
determining the high-frequency pulse by means of a signal equation s(t) according to:
s
⁡
(
t
)
=
∫
V
⁢
m
(
r
->
,
T
)
⁢
exp
⁡
[
t
⁢
/
⁢
T
2
]
⁢
exp
⁡
[
ⅈ
⁢
⁢
t
⁢
⁢
ω
s
]
⁢
exp
⁡
[
-
ⅈ
⁢
⁢
k
->
⁡
(
T
-
t
)
·
r
->
]
⁢
⁢
ⅆ
3
⁢
r
wherein V stands for a volume that is to be examined, so that, except for factors, the high-frequency pulse is obtained as:
b
1
⁡
(
t
)
=
J
⁡
(
t
)
ⅈγ
⁢
⁢
m
0
⁢
s
⁡
(
T
-
t
)
wherein J(t) is a Jacobi determinant that, under the premise of the bijectivity of k(t) onto a value range of t, yields the dependence of the coordinate transformation between the time parameterization and the k-space parameterization,
using the high-frequency pulse to excite the volume that is to be examined,
detecting the measured signal generated by the high-frequency pulse in the volume that is to be examined, and
evaluating the measured signal.

191 more elements

Facts

Application

14/000,493Filed 15 Feb 2012

Priority

DE 10 2011 004 43220 Feb 2011

Published

US 2015/0042330 A112 Feb 2015

Granted

13 Dec 2016

Term ends

Not estimatedThe source records don’t support an estimate.

Classification5 codes

G01R 33/4833
With selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy: using spatially selective excitation of the…
G01R 33/385
Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field: using gradient magnetic field coils
G01R 33/4818
NMR imaging systems: mR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g.…
G01R 33/56
Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console: image enhancement or…

Abstract

Claims8