SYSTEMS AND METHODS FOR DETECTING PATIENT MOTION DURING MAGNETIC RESONANCE IMAGING

1 . A magnetic resonance imaging (MRI) system configured to capture a magnetic resonance (MR) image, the MRI system comprising:

a B 0 magnet configured to provide at least a portion of a B 0 field;

at least one sensor configured to be capacitively coupled to a patient during MRI; and

at least one processor configured to:

while the patient is positioned within the MRI system:

measure a reflected signal value characteristic of a signal reflected by the at least one sensor in response to being driven by at least one radio frequency (RF) signal; and

determine, using the reflected signal value, whether the patient has moved.

2 . The MRI system of claim 1 , wherein the at least one sensor comprises an RF dipole antenna.

3 . The MRI system of claim 2 , wherein the RF dipole antenna comprises at least one inductor coupled to a lattice balun through at least a portion of a conductive arm of the RF dipole antenna, and wherein the at least one inductor is configured to reduce the electrical length of the RF dipole antenna.

4 . The MRI system of claim 3 , wherein the RF dipole antenna comprises at least one conductive arm, the at least one conductive arm including at least one 90-degree bend.

5 . The MRI system of claim 1 , wherein determining whether the patient has moved comprises:

calculating a ratio of the reflected signal value to a signal value of the at least one RF signal; and

comparing the calculated ratio to a threshold value.

6 . The MRI system of claim 1 , wherein the at least one sensor is calibrated prior to imaging the patient, and wherein calibrating the at least one sensor comprises:

driving the at least one sensor with a calibration RF signal, the calibration RF signal varying in frequency over time;

identifying a resonant frequency of the at least one sensor; and

setting a frequency of the at least one RF signal to be equal to the resonant frequency or within 5% of the resonant frequency.

7 . The MRI system of claim 6 , wherein identifying a resonant frequency of the at least one sensor comprises:

measuring, for each frequency in a plurality of frequencies, a reflected signal value characteristic of a signal reflected by the at least one sensor when driven by a signal having the frequency; and

identifying the resonant frequency of the at least one sensor to be that frequency from among the plurality of frequencies for which a smallest respective reflected signal value was measured.

8 . The MRI system of claim 1 , wherein the at least one sensor comprises a first sensor and a second sensor, the first sensor being disposed opposite the second sensor such the patient is positioned between the first sensor and the second sensor; and

the at least one processor is further configured to:

while the patient is positioned within the MRI system:

measure a first reflected signal value characteristic of a signal reflected by the first sensor in response to being driven by a first RF signal;

measure a second reflected signal value characteristic of a signal reflected by the second sensor in response to being driven by a second RF signal different from the first RF signal; and

determine, using the first and second reflected signal values, whether the patient has moved.

9 . The MRI system of claim 1 , further comprising an RF coil configured to provide a B 1 field and different from the at least one sensor.

10 . The MRI system of claim 1 , wherein the at least one processor is configured to measure the reflected signal value by measuring a voltage of the signal reflected by the at least one RF sensor in response to being driven by at least one RF signal.

11 . A method, comprising:

while a patient is positioned within a magnetic resonance imaging (MRI) system:

measuring a reflected signal value characteristic of a signal reflected by at least one sensor in response to being driven by at least one radio frequency (RF) signal; and

determining, using the reflected signal value, whether the patient has moved.

12 . The method of claim 11 , wherein the at least one RF signal comprises a frequency between 100 MHz and 250 MHz.

13 . The method of claim 11 , wherein determining whether the patient has moved comprises:

calculating a ratio of the reflected signal value from the at least one sensor to a signal value of the at least one RF signal; and

comparing the calculated ratio to a threshold value.

14 . The method of claim 11 , further comprising calibrating the at least one sensor, wherein calibrating the at least one sensor comprises:

driving the at least one sensor with a calibration RF signal, the calibration RF signal varying in frequency over time;

identifying a resonant frequency of the at least one sensor; and

setting a frequency of the at least one RF signal to be equal to the resonant frequency or within 5% of the resonant frequency.

15 . The method of claim 14 , wherein identifying the resonant frequency of the at least one sensor comprises:

measuring, for each frequency in a plurality of frequencies, a reflected signal value characteristic of a signal reflected by the at least one sensor when driven by a signal having the frequency; and

identifying the resonant frequency of the at least one sensor to be that frequency from among the plurality of frequencies for which a smallest respective reflected signal value was measured.

16 . The method of claim 11 , further comprising modifying how magnetic resonance (MR) data is acquired and/or used when it is determined that the patient has moved.

17 . The method of claim 16 , wherein modifying how the MR data is acquired and/or used comprises one of: discarding MR data collected during a time period during which the patient has moved, discarding an MR image formed using MR data collected during a time period during which the patient has moved, and/or correcting MR data collected during a time period during which the patient has moved.

18 . The method of claim 16 , wherein modifying how MR data is acquired and/or used comprises one or more of smoothing at least some of the MR data, rejecting at least some of the MR data, interpolating at least some of the MR data, and/or obtaining additional MR data to replace MR data collected during a time period during which the patient has moved.

19 . The method of claim 18 , wherein obtaining additional MR data comprises modifying a pulse sequence being used by the MRI system to obtain additional MR data at points in k-space that were obtained during a time period in which the patient has moved.

20 . The method of claim 16 , wherein modifying how MR data is acquired and/or used comprises:

after determining that the patient has moved:

grouping the MR data into first MR data collected prior to when the patient has moved and second MR data collected after the patient has moved; and

generating an MR image based on the first MR data and the second MR data.

21 . The method of claim 20 , wherein generating the MR image based on the first MR data and the second MR data comprises estimating a rigid transformation using the second MR data and the first MR data.

22 . At least one non-transitory computer-readable storage medium storing processor-executable instructions that, when executed by a magnetic resonance imaging (MRI) system, cause the MRI system to perform a method comprising:

while a patient is positioned within the MRI system:

measure a reflected signal value indicative of a signal reflected by at least one sensor in response to being driven by at least one RF signal; and

determine, using the reflected signal value, whether the patient has moved.

23 . The at least one non-transitory computer-readable storage medium of claim 22 , wherein determining whether the patient has moved comprises:

calculating a ratio of the reflected signal value from the at least one sensor to a signal value of the at least one RF signal; and

comparing the calculated ratio to a threshold value.

24 . The at least one non-transitory computer-readable storage medium of claim 22 , further comprising calibrating the at least one sensor, wherein calibrating the at least one sensor comprises:

driving the at least one sensor with a calibration RF signal, the calibration RF signal varying in frequency over time;

identifying a resonant frequency of the at least one sensor; and

setting a frequency of the at least one RF signal to be equal to the resonant frequency or within 5% of the resonant frequency.

25 . The at least one non-transitory computer-readable storage medium of claim 24 , wherein identifying the resonant frequency of the at least one sensor comprises:

measuring, for each frequency in a plurality of frequencies, a reflected signal value characteristic of a signal reflected by the at least one sensor when driven by a signal having the frequency; and

identifying the resonant frequency of the at least one sensor to be that frequency from among the plurality of frequencies for which a smallest respective reflected signal value was measured.

26 . The at least one non-transitory computer-readable storage medium of claim 22 , further comprising modifying how magnetic resonance (MR) data is acquired and/or used when it is determined that the patient has moved.

27 . The at least one non-transitory computer-readable storage medium of claim 26 , wherein modifying how MR data is acquired and/or used comprises one of: discarding MR data collected during a time period during which the patient has moved, discarding an MR image formed using MR data collected during a time period during which the patient has moved, and/or correcting MR data collected during a time period during which the patient has moved.

28 . The at least one non-transitory computer-readable storage medium of claim 27 , wherein correcting the MR data comprises one or more of smoothing at least some of the MR data, rejecting at least some of the MR data, interpolating at least some of the MR data, and/or obtaining additional MR data to replace MR data collected during a time period during which the patient has moved.

29 . The at least one non-transitory computer-readable storage medium of claim 26 , wherein modifying how MR data is acquired and/or used comprises:

after determining that the patient has moved:

grouping the MR data into first MR data collected prior to when the patient has moved and second MR data collected after the patient has moved; and

generating an MR image based on the first MR data and the second MR data.

30 . The method of claim 29 , wherein generating the MR image based on the first MR data and the second MR data comprises estimating a rigid transformation using the second MR data and the first MR data.