Magnetic resonance imaging apparatus and SAR estimation method
View Patent ↗In order to further improve the accuracy of SAR estimation by accurately estimating, for each object, the energy of RF pulses absorbed into a part of an object, for example, a head, on the basis of measurement performed before main imaging, a nuclear magnetic resonance imaging apparatus estimates a head SAR by calculating a signal S h generated from the head and a signal S b generated from the whole object, calculating the ratio α between the signal generated from the head and the signal generated from the whole object, and calculating the energy E h absorbed into the head using the ratio of the signals.
1. A nuclear magnetic resonance imaging apparatus comprising:
a static magnetic field generator configured to generate a static magnetic field in a space where an object is placed;
a gradient magnetic field application section configured to apply a gradient magnetic field to the object;
a high frequency magnetic field generator configured to apply an RF pulse with a magnetic resonance frequency to the object;
a signal detector configured to detect an echo signal generated from the object;
an image reconstruction section configured to reconstruct an image using the detected echo signal; and
a controller configured to control the gradient magnetic field application section, the high frequency magnetic field generator, and the signal detector,
wherein the controller estimates a partial body SAR regarding a part of the object by calculating an amount of the echo signal received by the signal detector and generated from the part of the object expressed by ( 14 a ) below and calculating an amount of the echo signal received by the signal detector and generated from a wide region of the object including the part of the object expressed by ( 14 a ) below,
S
h
=
∫
L
head
ⅆ
r
→
[
f
-
1
(
MRIsignal
(
r
→
)
)
]
2
(
14
a
)
S
b
=
∫
L
coil
ⅆ
r
→
[
f
-
1
(
MRIsignal
(
r
→
)
)
]
2
(
14
b
)
calculating a ratio between the signal generated from the part of the object and the signal generated from the entire wide region expressed by α=S h /S b , and calculating energy absorbed into the part of the object using the ratio of the signals, wherein a head region is defined by L head , and {right arrow over (r)} is a position vector, f −1 is a function determined by an imaging function, MRIsignal ({right arrow over (r)}) is an MRI signal strength of {right arrow over (r)}.
2. The nuclear magnetic resonance imaging apparatus according to claim 1 ,
wherein the part of the object is a head of the object.
3. The nuclear magnetic resonance imaging apparatus according to claim 2 ,
wherein the controller is configured to acquire an FID signal and is configured to calculate a signal, which is generated from the head, and a signal, which is generated from the entire wide region, from the FID signal.
4. The nuclear magnetic resonance imaging apparatus according to claim 2 ,
wherein the controller is configured to acquire projection data in a body axis direction and is configured to calculate a signal, which is generated from the head, and a signal, which is generated from the entire wide region, from the projection data signal.
5. The nuclear magnetic resonance imaging apparatus according to claim 2 ,
wherein the controller is configured to capture a 3D image with the inside of an entire TR-body coil as an imaging field of view and is configured to calculate a signal, which is generated from the head, and a signal, which is generated from the entire wide region, from a pixel value of the 3D image.
6. The nuclear magnetic resonance imaging apparatus according to claim 2 ,
wherein the controller is configured to calculate a signal, which is generated from the head, and a signal, which is generated from the whole object, from a B1map.