Systems and methods for multifrequency magnetic resonance electrical impedance tomography
View Patent ↗Disclosed herein are systems and methods for Magnetic Resonance Electrical Impedance Tomography (MREIT). A system for imaging biological tissue comprises a controller, a multifrequency arbitrary-waveform constant-current source, a Howland constant-current source, and a digital-to-analog converter. The controller is configured to generate a multifrequency magnetic resonance electrical impedance tomography sequence. The generation comprises producing, by the controller, a digital sequence, and converting, by the digital-to-analog converter, the digital sequence to an analog sequence. The generation may further comprise: producing, by the Howland constant-current source, a standard magnetic resonance electrical impedance tomography sequence based on the analog sequence; producing, by the multifrequency arbitrary-waveform constant-current source, a sine wave at one or more predetermined frequencies; and modulating the standard magnetic resonance electrical impedance tomography sequence with the sine wave. A method of measuring an electrical property of a biological tissue comprises imaging the biological tissue using this system.
1 . A system for imaging biological tissue, the system comprising:
a controller;
a multifrequency arbitrary-waveform constant-current source;
a Howland constant-current source; and
a digital-to-analog converter;
wherein the controller is configured to generate a multifrequency magnetic resonance electrical impedance tomography pulse sequence, wherein said generation comprises:
producing, by the controller, a digital sequence;
converting, by the digital-to-analog converter, the digital sequence to an analog sequence;
producing, by the Howland constant-current source, a standard magnetic resonance electrical impedance tomography pulse sequence based on the analog sequence;
producing, by the multifrequency arbitrary-waveform constant-current source, a sine wave at one or more predetermined frequencies; and
modulating the standard magnetic resonance electrical impedance tomography pulse sequence with the sine wave at a frequency between 100 Hz and 1 MHz.
2 . The system of claim 1 , further comprising a magnetic resonance imaging system, wherein the magnetic resonance imaging system is configured to produce a measurable signal based on the multifrequency magnetic resonance electrical impedance tomography pulse sequence.
3 . The system of claim 2 , wherein the measurable signal is interpreted using Bloch equations, wherein the Bloch equations are modified to include effects of external currents, wherein the modified Bloch equations are defined by
S
(
k
x
,
k
y
)
=
∫
∫
Ω
z
0
M
(
x
,
y
)
e
i
[
γT
c
B
z
(
x
,
y
)
]
e
-
i
2
π
(
k
x
x
+
k
y
y
)
dxdy
,
where M(x,y)>0 is a MR magnitude image of a slice Q located at z 0 , δ(x,y) is systematic phase artifact, γ is a gyromagnetic ratio of hydrogen, and T c is a total time for which the current is applied.
4 . The system of claim 1 , wherein a measurable signal of the sine wave comprises a lower power value than a measurable signal of the standard magnetic resonance electrical impedance tomography pulse sequence.
5 . The system of claim 4 , wherein the measurable signal of the sine wave is in a range of 15% to 30% of the power value corresponding to the measurable signal of the standard magnetic resonance electrical impedance tomography pulse sequence.
6 . The system of claim 1 , wherein the standard magnetic resonance electrical impedance tomography pulse sequence is a spin echo sequence.
7 . The system of claim 1 , wherein the multifrequency arbitrary-waveform constant-current source is configured to generate the sine wave.
8 . The system of claim 1 , wherein the multifrequency arbitrary-waveform constant-current source comprises a digital or analog multifrequency arbitrary-waveform signal source.
9 . The system of claim 1 , wherein the controller comprises a field programmable gate array (FPGA) controller or a function generator.
10 . A system for imaging biological tissue, the system comprising:
a controller or function generator; and
a multifrequency arbitrary-waveform signal source with a digital-to-analog converter;
wherein the controller or function generator is configured to generate a multifrequency magnetic resonance electrical impedance tomography pulse sequence, wherein said generation comprises:
producing, by the controller or function generator, a digital sequence;
converting, by the digital-to-analog converter, the digital sequence to an analog sequence;
producing, by the digital-to-analog converter, a standard magnetic resonance electrical impedance tomography pulse sequence based on the analog sequence;
producing, by the digital-to-analog converter, a sine wave at one or more predetermined frequencies; and
modulating the standard magnetic resonance electrical impedance tomography pulse sequence with the sine wave at a frequency between 100 Hz and 1 MHz.
11 . The system of claim 10 , wherein the multifrequency arbitrary-waveform signal source comprises a digital or analog multifrequency arbitrary-waveform signal source.
12 . The system of claim 10 , wherein the controller or function generator comprises a field programmable gate array (FPGA) controller or function generator.
13 . The system of claim 10 , further comprising a magnetic resonance imaging system, wherein the magnetic resonance imaging system is configured to produce a measurable signal based on the multifrequency magnetic resonance electrical impedance tomography pulse sequence.
14 . The system of claim 13 , wherein the measurable signal is interpreted using Bloch equations, wherein the Bloch equations are modified to include effects of external currents, wherein the modified Bloch equations are defined by
S
(
k
x
,
k
y
)
=
∫
∫
Ω
z
0
M
(
x
,
y
)
e
i
[
γT
c
B
z
(
x
,
y
)
]
e
-
i
2
π
(
k
x
x
+
k
y
y
)
dxdy
,
where M(x,y)>0 is a MR magnitude image of a slice Q located at z 0 , δ(x,y) is systematic phase artifact, γ is a gyromagnetic ratio of hydrogen, and T c is a total time for which the current is applied.
15 . The system of claim 10 , wherein a measurable signal of the sine wave comprises a lower power value than a measurable signal of the standard magnetic resonance electrical impedance tomography pulse sequence.
16 . The system of claim 15 , wherein the measurable signal of the sine wave is in a range of 15% to 30% of the power value corresponding to the measurable signal of the standard magnetic resonance electrical impedance tomography pulse sequence.
17 . The system of claim 10 , wherein the standard magnetic resonance electrical impedance tomography pulse sequence is a spin echo sequence.
18 . The system of claim 10 , wherein the multifrequency arbitrary-waveform constant-current source is configured to generate the sine wave.
19 . A method of measuring an electrical property of a biological tissue at a frequency, the method comprising
imaging the biological tissue using the system of claim 1 .
20 . A method of measuring an electrical property of a biological tissue at a frequency, the method comprising
imaging the biological tissue using the system of claim 10 .