# US 2014/0152308 A1 · Method and apparatus for acquiring b1 magnetic field information

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- Number: US 2014/0152308 A1
- Document ID: US20140152308A1
- Status: Published application
- Kind: A1
- Application number: 14/096,372
- Filed: 2013-12-04
- Published: 2014-06-05
- Earliest claimed: 2012-12-04
- Assignees: Industry Academic Cooperation Foundation Kyunghee University; Samsung Electronics Co., Ltd.
- Applicants: Industry Academic Cooperation Foundation Kyunghee University; Samsung Electronics Co., Ltd.
- Inventors: Ju-hyung LEE; Soo-yeol LEE
- Web page: https://patentgrep.com/patent/US20140152308A1

## CPC

- G01R 33/5659: {caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)}
- G01R 33/246: {Spatial mapping of the RF magnetic field B1}
- G01R 33/34092: {RF coils specially adapted for NMR spectrometers}
- G01R 33/586: {for optimal flip angle of RF pulses}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A method acquires RF magnetic field information (B1 magnetic field information) in response to generated radio frequency (RF) pulses in a magnetic resonance imaging (MRI) system. An RF excitation pulse sequence is generated, and the generated RF excitation pulse sequence includes a plurality of RF excitation pulses individually having different flip angles. The generated RF excitation pulse sequence is transmitted to a target object. RF echo response signals are received from the target object corresponding to the plurality of RF excitation pulses and B1 information is acquired by processing the received RF echo response signals.

## Claims

### Claim 1

A method of acquiring RF magnetic field information (B1 magnetic field information) in response to generated radio frequency (RF) pulses in a magnetic resonance imaging (MRI) system, the method comprising:
generating an RF excitation pulse sequence including a plurality of RF excitation pulses individually having different flip angles;
transmitting the generated RF excitation pulse sequence to a target object;
receiving RF echo response signals from the target object corresponding to the plurality of RF excitation pulses; and
acquiring B1 information by processing the received RF echo response signals.

### Claim 2 (depends on 1)

The method of claim 1, wherein the RF pulse sequence is generated, such that the plurality of RF pulses are interleaved at a predetermined time interval.

### Claim 3 (depends on 1)

The method of claim 1, wherein the RF pulse sequence comprises at least three RF pulses of different magnitude.

### Claim 4 (depends on 3)

The method of claim 3, wherein, a first RF pulse has a first flip angle α, a second RF pulse has a second flip angle β, and a third RF pulse has a third flip angle γ, and
the second flip angle β and the third flip angle γ are different real number multiples of the first flip angle α.

### Claim 5 (depends on 4)

The method of claim 4, wherein the acquiring of the B1 information comprises:
acquiring first ratio information determined using a magnitude of an echo response signal associated with the first RF pulse and a magnitude of an echo response signal associated with the second RF pulse;
acquiring second ratio information determined using a magnitude of an echo response signal associated with the second RF pulse and a magnitude of an echo response signal associated with the third RF pulse; and
acquiring a first flip angle α value of the first RF pulse by using the first ratio information and the second ratio information.

### Claim 6 (depends on 5)

The method of claim 5, wherein the first ratio information is acquired according to Equations (1) and (3) below,
the second ratio information is acquired according to Equations (2) and (3) below,
R
1
=
S
1
S
2
=
sin


β

(
1
+
cos


α
·
E
1
+
cos


γ
·
cos


α
·
E
1
2
)
sin


α

(
1
+
cos


γ
·
E
1
+
cos


β
·
cos


γ
·
E
1
2
)
,
(
1
)
R
2
=
S
3
S
2
=
sin


γ

(
1
+
cos


β
·
E
1
+
cos


α
·
cos


β
·
E
1
2
)
sin


β

(
1
+
cos


α
·
E
1
+
cos


γ
·
cos


α
·
E
1
2
)
,
(
2
)
E
1
=

-
T
1
TR
,
(
3
)
and
in Equations (1) through (3) above, T1 denotes a spin lattice relaxation time, and TR denotes a predetermined time interval at which the first RF pulse, the second RF pulse, and the third RF pulse are interleaved.

### Claim 7 (depends on 1)

The method of claim 1, wherein the acquired B1 information comprises a B1 map showing spatial distribution of B1 magnetic fields of the target object.

### Claim 8 (depends on 1)

The method of claim 1, wherein the different flip angles are selected to enable TR, comprising repetition time between successive RF excitation pulses, to be less than 20% of T1 the longitudinal relaxation time decay constant facilitating accelerated acquisition of a B1 map.

### Claim 9 (depends on 1)

The method of claim 1, wherein the RF excitation pulse sequence comprises a gradient echo sequence.

### Claim 10

A B1 information acquisition apparatus for acquiring magnetic field information (B1 magnetic field information) generated by radio frequency (RF) pulses in an MRI system, the B1 information acquisition apparatus comprising:
a pulse sequence generating unit, for generating an RF excitation pulse sequence including a plurality of RF excitation pulses individually having different flip angles;
an RF coil for transmitting the generated RF pulse sequence to a target object and receiving echo response signals from the target object corresponding to the plurality of RF pulses; and
a control unit configured for acquiring B1 information by processing the received RF echo response signals.

### Claim 11 (depends on 10)

The B1 information acquisition apparatus of claim 10, wherein the pulse sequence generating unit generates the RF pulse sequence, such that the plurality of RF pulses are interleaved at a predetermined time interval.

### Claim 12 (depends on 10)

The B1 information acquisition apparatus of claim 10, wherein the RF pulse sequence comprises at least three RF pulses of different magnitude.

### Claim 13 (depends on 12)

The B1 information acquisition apparatus of claim 12, wherein, a first RF pulse has a first flip angle α, a second RF pulse has a second flip angle β, and a third RF pulse has a third flip angle γ, and
the second flip angle β and the third flip angle γ are different real number multiples of the first flip angle α.

### Claim 14 (depends on 13)

The B1 information acquisition apparatus of claim 13, wherein the control unit comprises:
a first ratio information acquiring unit, which acquires first ratio information using a magnitude of an echo response signal corresponding to the first RF pulse and a magnitude of an echo response signal corresponding to the second RF pulse;
a second ratio information acquiring unit, which acquires second ratio information using a magnitude of an echo response signal corresponding to the second RF pulse and a magnitude of an echo response signal corresponding to the third RF pulse; and
a flip angle acquiring unit, which determines the first flip angle α of the first RF pulse by using the first ratio information and the second ratio information.

### Claim 15 (depends on 14)

The B1 information acquisition apparatus of claim 14, wherein the control unit acquires the first ratio information according to Equations (1) and (3) below,
the control unit acquires the second ratio information according to Equations (2) and (3) below,
R
1
=
S
1
S
2
=
sin


β

(
1
+
cos


α
·
E
1
+
cos


γ
·
cos


α
·
E
1
2
)
sin


α

(
1
+
cos


γ
·
E
1
+
cos


β
·
cos


γ
·
E
1
2
)
,
(
1
)
R
2
=
S
3
S
2
=
sin


γ

(
1
+
cos


β
·
E
1
+
cos


α
·
cos


β
·
E
1
2
)
sin


β

(
1
+
cos


α
·
E
1
+
cos


γ
·
cos


α
·
E
1
2
)
,
(
2
)
E
1
=

-
T
1
TR
,
(
3
)
and
in Equations (1) through (3) above, T1 denotes a spin lattice relaxation time, and TR denotes a predetermined time interval at which the first RF pulse, the second RF pulse, and the third RF pulse are interleaved.

### Claim 16 (depends on 10)

The B1 information acquisition apparatus of claim 10, wherein the control unit acquires the B1 information comprising a B1 map showing spatial distribution of B1 magnetic fields of the target object.

### Claim 17 (depends on 1)

A computer readable recording medium having recorded thereon a program for implementing the method of claim 1.

### Claim 18 (depends on 10)

The B1 information acquisition apparatus of claim 10, wherein the different flip angles are selected to enable TR, comprising repetition time between successive RF excitation pulses, to be less than 20% of T1 the longitudinal relaxation time decay constant facilitating accelerated acquisition of a B1 map.

### Claim 19 (depends on 10)

The B1 information acquisition apparatus of claim 10, wherein the RF excitation pulse sequence comprises a gradient echo sequence.