Magnetic resonance imaging apparatus, Q-value calculation method, and specific absorption rate management method

Patent metadata

Field	Value
Publication number	US-10890632-B2
Application number	US-201716083969-A
Country	US
Kind code	B2
Filing date	Feb 14, 2017
Priority date	Mar 15, 2016
Publication date	Jan 12, 2021
Grant date	Jan 12, 2021

Abstract

To avoid the complication of an MRI apparatus and avoid the overestimation of a calculated value of SAR without extending a processing time and to perform accurate SAR management. To this end, the MRI apparatus is equipped with a high frequency antenna which has a plurality of channels and resonates at a predetermined frequency, and a measuring instrument which measures the amplitudes of a forward traveling and reflected waves of each high frequency signal supplied to the high frequency antenna. In the MRI apparatus, a reflection matrix S is determined based on the measured amplitudes. Diagonal terms of the determined reflection matrix S are used to calculate Q values for each of the channels. Each non-diagonal term of the reflection matrix S is used to correct the calculated Q value. The corrected Q value is used to calculate irradiation power consumed in a subject among irradiation power from the high frequency signals supplied to the high frequency antenna when imaging to thereby manage a specific absorption rate.

First claim

The invention claimed is:

1. A magnetic resonance imaging apparatus comprising:
a high frequency antenna which has a plurality of channels and resonates at a predetermined frequency;
a supply unit which supplies a plurality of high frequency signals having different frequencies to the high frequency antenna;
a measuring instrument which measures the amplitudes of a forward traveling wave and a reflected wave of each of the high frequency signals supplied from the supply unit to the high frequency antenna;
a Q-value calculation unit which calculates a Q value for each of the channels by fitting an absolute value of each diagonal term of a reflection matrix S calculated based on the amplitudes measured by the measuring instrument to a predetermined circuit model; and
a Q-value correction unit which corrects the Q value calculated by the Q-value calculation unit using an absolute value of each non-diagonal term of the reflection matrix S.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein the Q-value correction unit estimates the ratios of energy consumed by the high frequency antenna, of energy of the high frequency signals input to the high frequency antenna, and energy thereof consumed in a subject disposed near the high frequency antenna to thereby correct the Q value.

3. The magnetic resonance imaging apparatus according to claim 1 , wherein the Q-value correction unit corrects the Q value Q appear calculated by the Q-value calculation unit in accordance with the following formula to thereby acquire a Q value Q 0i :

Q

0
i

=

Q

appear
i

(

1
+

∑

k
=
1

,

(

k
≠
i

)

k
=
M

⁢

⁢

A
⁢

∑

j
=
1

M

⁢

⁢



S
jj

2
-
n



∑

m
=
1

M

⁢

⁢



S
mm

-
n



+
B

Q

a
⁢
p
⁢
p
⁢
e
⁢
a
⁢

r
i

⁢

Q

a
⁢
p
⁢
p
⁢
e
⁢
a
⁢

r
k

⁢

|

S

k
⁢
i

2

|

1
-

|

S
ii
2

|

)

where A, B, and n are constants determined according to the subject, in which n is a number greater than 0, and A and B are positive numbers. Further, i, j, k, and m

Assignees

• Hitachi Ltd

Inventors

• Habara Hideta
• Ono Masaharu
• Takahashi Tetsuhiko
• Takeuchi Hiroyuki

Classifications

• G01R33/288 Primary

  Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room · CPC title

• G01R33/3607

  RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal · CPC title

• G01R33/5608

  Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels (image data processing or generation, in general G06T) · CPC title

• G01R33/5612

  Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels · CPC title

• G01R33/4802

  Travelling-wave MR · CPC title