Patent Description:
Magnetic resonance imaging (MRI) provides an important imaging modality for numerous applications and is widely utilized in clinical and research settings to produce images of the inside of the human body. As a generality, MRI is based on detecting magnetic resonance (MR) signals, which are electromagnetic waves emitted by atoms in response to state changes resulting from applied electromagnetic fields. For example, nuclear magnetic resonance (NMR) techniques involve detecting MR signals emitted from the nuclei of excited atoms upon the realignment or relaxation of the nuclear spin of atoms in an object being imaged (e.g., atoms in the tissue of the human body). Detected MR signals may be processed to produce images, which in the context of medical applications, allows for the investigation of internal structures and/or biological processes within the body for diagnostic, therapeutic and/or research purposes.

<CIT> discloses a motion sensor for detecting movements of a patient in an imaging medical system, in particular in a magnetic resonance tomography system having at least one HF resonator for emitting an HF signal fed into the resonator from an HF signal source and for receiving a response signal, and a detection circuit for detecting movements of the patient derived from the received signal.

<CIT> discloses a method for measuring the breathing of a patient during a magnetic resonance examination with a magnetic resonance device, wherein the reflection properties of at least one coil element arranged beneath the patient are measured and evaluated to determine the breathing data that describes the respiratory situation at various times.

<CIT> is directed to a magnetic resonance imaging system with motion detection for examination of a patient, the magnetic resonance imaging system comprising an RF coil arrangement with an RF coil for transmitting and/or receiving an RF signal for generating a magnetic resonance image wherein the RF coil arrangement is provided with an additional RF sensor for transmitting an RF transmit signal which is adapted for interacting with the tissue of the patient allowing to sense motion signals due to motions of the patient simultaneously to transmitting and/or receiving the RF signal for generating the magnetic resonance image. In this way movements of a patient under examination in an MRI system may be detected in an efficient and reliable way.

<CIT> is directed to a magnetic resonance image recording system for recording at least part of a patient during a magnetic resonance examination, the magnetic resonance image recording unit having a first housing wall, a patient receiving area which is at least partially enclosed by the first housing wall, and a motion sensor unit for detecting a movement of the patient.

According to one aspect described herein, there is provided a device in accordance with claim <NUM>.

According to another aspect described herein, there is provided a device in accordance with claim <NUM>.

According to a further aspect described herein, there is provided a magnetic resonance imaging system in accordance with claim <NUM>.

The quality of acquired magnetic resonance (MR) images may be significantly impacted by a patient's motion during an MRI procedure, as movement by the patient during imaging may generate artefacts in the resulting MR images. Conventional approaches to mitigating this problem involve restraining patients in one or more directions of motion to reduce the introduction of artefacts into a resulting MR image. However, such restraints are uncomfortable for a patient or may cause a patient to feel claustrophobic during an MR imaging procedure.

Conventional methods of minimizing noise due to a patient's motion can be improved by detecting the patient's position and/or motion during MR imaging and using instances of detected changes in position to correct the resulting MR images. However, many off-the-shelf motion detectors do not function well when placed within the magnetic fields required for MRI and/or the detectors interfere with proper functioning of the MRI system. Other methods of patient motion detection rely on imaging the patient with an optical camera system while the patient is positioned within the MRI system, but such optical camera systems can be expensive to implement and too slow to detect the patient's motion instantaneously.

The inventors have appreciated that the resonant frequency of a sensor (e.g., an RF sensor such as an RF antenna) may change when in the presence of a subject (e.g., a patient) due to the parasitic capacitance between the sensor and the subject. For example, the resonant frequency of the sensor may decrease as the distance between the sensor and the patient decreases. Accordingly, the inventors have developed a system for detecting position and/or motion of a patient during an MR imaging procedure using at least one sensor configured to capacitively couple with the patient.

The inventors have recognized that detecting a resonant frequency shift of a sensor to detect patient motion may require bulky and costly electronics and may provide less sensitivity. For example, monitoring the sensor's resonant frequency could be achieved by performing a full frequency sweep and detecting the frequency which induces that maximum current in the sensor. However, performing such a frequency sweep requires additional electronics, which is expensive. Moreover, a frequency sweep may be time consuming to execute. To avoid these problems, the inventors have developed a technique for detecting patient position and/or motion by monitoring a reflected power at a set frequency from the sensor rather than detecting a change in the sensor's resonant frequency. The set frequency may be determined based on the resonant frequency of the sensor and set to a frequency such that the sensitivity of the sensor is increased (e.g., to a frequency such that the reflection curve has a maximum slope).

The inventors have developed a device for detecting motion of a patient while the patient is positioned within the MRI system. In some embodiments, the device includes at least one sensor (e.g., one or more RF antennas, for example, multiple RF dipole antennas) configured to be capacitively coupled to the patient during MR imaging. In some embodiments, while the patient remains positioned within the MRI system, the device may be configured to drive the at least one sensor with at least one radio frequency (RF) signal and measure a reflected signal value from the at least one sensor. The reflected signal value may be characteristic of a signal reflected by the at least one sensor in response to the at least one RF signal. For example, the reflected signal value may be a voltage. In some embodiments, a reflection coefficient calculated from the reflected signal value that is below a threshold reflection coefficient value may be indicative of a patient's motion. The threshold reflection coefficient value may be determined based on a previously measured reflection coefficient value (e.g., the threshold reflection coefficient value may be a previously measured reflection coefficient value plus and/or minus a percentage value indicative of noise). Accordingly, the reflected signal value and/or reflection coefficient obtained by using the device may be used to determine whether the patient has moved.

In some embodiments, a calibration procedure may be used to increase sensitivity of a sensor to the parasitic capacitance of the patient. The sensor may be most sensitive to parasitic capacitance when driven by at least one RF signal having a frequency different from the sensor's resonant frequency (e.g., within <NUM>% of the sensor's resonant frequency). In some embodiments, calibrating the sensor may include driving the sensor with a calibration RF signal whose frequency varies over time, identifying a resonant frequency of the sensor, and setting a driving frequency to be used for driving the sensor to be either the sensor's resonant frequency or within <NUM>% of its identified resonant frequency. As described herein, the driving frequency may be set to a frequency such that the sensitivity of the sensor is increased (e.g., to a frequency such that the reflection curve has a maximum slope).

In some embodiments, identifying the resonant frequency of a sensor may include measuring a reflected signal value from the sensor for each of multiple frequencies (e.g., of the calibration RF signal). In some embodiments, the resonant frequency of the sensor may be identified from among the multiple frequencies by identifying the frequency for which a smallest respective reflected signal value was measured.

In some embodiments, one or more sensors may be employed to measure patient movement and the one or more sensors may include at least one RF sensor (e.g., an RF antenna). In some embodiments, the sensor(s) may include at least one dipole antenna. In some embodiments, the dipole antenna may include at least one inductor coupled to a lattice balun. In some embodiments, each sensor or sensors may be configured to resonate at a frequency between <NUM> and <NUM>.

In some embodiments, the device may be configured to accommodate a patient's anatomy (e.g., the patient's head, leg, arm, foot, or other appendage) during an MR imaging procedure. For example, the device may include a helmet to accommodate the patient's head. In some embodiments, the device may include an attachment mechanism configured to securely mechanically couple the device to the MRI system, further reducing patient and/or device motion during MR imaging and reducing noise in resulting MR images.

The sensors used to detect patient motion are coupled to a surface of a helmet configured to accommodate the patient's head. To enable motion detection in multiple directions, four sensors are coupled to the device (to a surface of the helmet). The four sensors are grouped in pairs such that the patient's anatomy (the patient's head) is positioned between two sensors of each pair of sensors. Positioning the patient's anatomy between two sensors may maintain the patient's position within range of at least one sensor at all times and may allow for the detection of the patient's motion in both directions along an axis connecting the two sensors. The pairs of sensors are disposed along different axes (e.g., perpendicular axes) to detect motion of the patient in both directions along multiple axes.

In some embodiments, the device may further include at least one RF transmit and/or receive coil configured to provide a B<NUM> magnetic field during MR imaging and/or detect MR signals emitted by the subject. In some embodiments, the at least one sensor is different from the at least one RF transmit and/or receive coil. To prevent electromagnetic interference between the at least one sensor and the at least one RF transmit and/or receive coil, the at least one sensor may be configured to resonate at a different frequency than the RF transmit and/or receive coil. In some embodiments, where the at least one sensor includes two or more sensors, each of the two or more sensors may be configured to resonate at different frequencies from the RF transmit and/or receive coil as well as the other sensors of the two or more sensors.

In some embodiments, detecting a patient's motion during an MR imaging procedure may enable the MRI system and/or device to modify how MR data is acquired and/or used to reduce artifacts in resulting MR images. For example, in some embodiments, MR data collected during a time period during which the patient has moved (and/or MR images determined from such data) may be discarded. In some embodiments, MR data collected (and/or MR images determined from such data) during a time period during which the patient has moved may be corrected. Correcting MR data and/or images collected during a time period during which the patient has moved may include smoothing at least some of the MR data and/or images, rejecting at least some of the MR data and/or images, and/or interpolating at least some of the MR data and/or images.

In some embodiments, additional MR data may be acquired to replace MR data collected during a time period during which the patient has moved. For example, in some embodiments, obtaining additional MR data may include 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.

In some embodiments, correcting MR data may include generating MR images from spatial frequency data obtained by the MRI system in circumstances when the patient moves during imaging. In some embodiments, generating the MR images involves dividing the spatial frequency data into two sets of spatial frequency data, corresponding to two positions of the patient during imaging, with spatial frequency data collected during the patient's movement between the positions being discarded. Dividing the spatial frequency data into two sets of spatial frequency data may be performed based on additional information obtained by one or more sensors configured to detect and/or track motion of the patient being imaged. For example, one or more RF sensors as described herein may be used to obtain information indicating when a patient has moved during MR imaging and/or how the position of the patient has changed during MR imaging. In some embodiments, the first spatial frequency data may be identified as the spatial frequency data collected prior to the patient's motion (e.g., when the patient is in a first position) and the second spatial frequency data may be identified as the spatial frequency data collected subsequent to the patient's motion (e.g., when the patient is in a second position). In some embodiments, the spatial frequency data collected during the patient's motion (e.g., from the first position to the second position) may be removed.

In turn, the sets of spatial frequency data are used to estimate a transformation (e.g., a rigid transformation comprising a rotation and a translation) representing the patient's motion, and the transformation may be used to correct the spatial frequency data for the effect of motion. It should be appreciated that the spatial frequency data may be divided into any suitable number of sets of spatial frequency data corresponding to any suitable number of positions of the patient during MR imaging (e.g., <NUM>, <NUM>, <NUM>, <NUM>, etc.), and pairwise rigid transformations may be estimated therebetween for correcting spatial frequency data for the patient's motion, as aspects of the technology described herein are not limited in this respect.

Following below are more detailed descriptions of various concepts related to, and embodiments of, techniques for automatic messaging. It should be appreciated that various aspects described herein may be implemented in any of numerous ways. Examples of specific implementations are provided herein for illustrative purposes only. In addition, the various aspects described in the embodiments below may be used alone or in any combination and are not limited to the combinations explicitly described herein.

<FIG> is a block diagram of typical components of an MRI system <NUM>. In the illustrative example of <FIG>, MRI system <NUM> comprises computing device <NUM>, controller <NUM>, pulse sequences store <NUM>, power management system <NUM>, and magnetics components <NUM>. It should be appreciated that system <NUM> is illustrative and that an MRI system may have one or more other components of any suitable type in addition to or instead of the components illustrated in <FIG>. However, an MRI system will generally include these high-level components, though the implementation of these components for a particular MRI system may differ. It may be appreciated that the techniques described herein for detecting patient motion may be used with any suitable type of MRI systems including high-field MRI systems, low-field MRI systems, and ultra-low field MRI systems. For example, the techniques described herein may be used with any of the MRI systems described herein and/or as described in <CIT>, and titled "Low-Field Magnetic Resonance Imaging Methods and Apparatus,".

As illustrated in <FIG>, magnetics components <NUM> comprise B<NUM> magnet <NUM>, shim coils <NUM>, radio frequency (RF) transmit and receive coils <NUM>, and gradient coils <NUM>. B<NUM> magnets <NUM> may be used to generate the main magnetic field B<NUM>. B<NUM> magnets <NUM> may be any suitable type or combination of magnetics components that can generate a desired main magnetic B<NUM> field. In some embodiments, B<NUM> magnets <NUM> may be a permanent magnet, an electromagnet, a superconducting magnet, or a hybrid magnet comprising one or more permanent magnets and one or more electromagnets and/or one or more superconducting magnets. In some embodiments, B<NUM> magnets <NUM> may be configured to generate a B<NUM> magnetic field having a field strength that is less than or equal to <NUM> T or within a range from <NUM> mT to <NUM> T.

For example, in some embodiments, B<NUM> magnets <NUM> may include a first and second B<NUM> magnet, each of the first and second B<NUM> magnet including permanent magnet blocks arranged in concentric rings about a common center. The first and second B<NUM> magnet may be arranged in a bi-planar configuration such that the imaging region is located between the first and second B<NUM> magnets. In some embodiments, the first and second B<NUM> magnets may each be coupled to and supported by a ferromagnetic yoke configured to capture and direct magnetic flux from the first and second B<NUM> magnets. Additional details of such embodiments are described in <CIT>.

Gradient coils <NUM> may be arranged to provide gradient fields and, for example, may be arranged to generate gradients in the B<NUM> field in three substantially orthogonal directions (X, Y, Z). Gradient coils <NUM> may be configured to encode emitted MR signals by systematically varying the B<NUM> field (the B<NUM> field generated by magnet <NUM> and/or shim coils <NUM>) to encode the spatial location of received MR signals as a function of frequency or phase. For example, gradient coils <NUM> may be configured to vary frequency or phase as a linear function of spatial location along a particular direction, although more complex spatial encoding profiles may also be provided by using nonlinear gradient coils. In some embodiments, gradient coils <NUM> may be implemented using laminate panels (e.g., printed circuit boards). Examples of such gradient coils are described in <CIT>.

MRI is performed by exciting and detecting emitted MR signals using transmit and receive coils, respectively (often referred to as radio frequency (RF) coils). Transmit/receive coils may include separate coils for transmitting and receiving, multiple coils for transmitting and/or receiving, or the same coils for transmitting and receiving. Thus, a transmit/receive component may include one or more coils for transmitting, one or more coils for receiving and/or one or more coils for transmitting and receiving. Transmit/receive coils are also often referred to as Tx/Rx or Tx/Rx coils to generically refer to the various configurations for the transmit and receive magnetics component of an MRI system. These terms are used interchangeably herein. In <FIG>, RF transmit and receive circuitry <NUM> comprises one or more transmit coils that may be used to generate RF pulses to induce an oscillating magnetic field B<NUM>. The transmit coil(s) may be configured to generate any suitable types of RF pulses. The transmit and receive circuitry <NUM> may include additional electronic components of the transmit and receive chains, as described in <CIT>.

Power management system <NUM> includes electronics to provide operating power to one or more components of the low-field MRI system <NUM>. For example, power management system <NUM> may include one or more power supplies, gradient power components, transmit coil components, and/or any other suitable power electronics needed to provide suitable operating power to energize and operate components of MRI system <NUM>. As illustrated in <FIG>, power management system <NUM> comprises power supply <NUM>, power component(s) <NUM>, transmit/receive circuitry <NUM>, and thermal management components <NUM> (e.g., cryogenic cooling equipment for superconducting magnets). Power supply <NUM> includes electronics to provide operating power to magnetic components <NUM> of the MRI system <NUM>. For example, power supply <NUM> may include electronics to provide operating power to one or more B<NUM> coils (e.g., B<NUM> magnet <NUM>) to produce the main magnetic field for the low-field MRI system.

Amplifier(s) <NUM> may include one or more RF receive (Rx) pre-amplifiers that amplify MR signals detected by one or more RF receive coils (e.g., coils <NUM>), one or more RF transmit (Tx) power components configured to provide power to one or more RF transmit coils (e.g., coils <NUM>), one or more gradient power components configured to provide power to one or more gradient coils (e.g., gradient coils <NUM>), and one or more shim power components configured to provide power to one or more shim coils (e.g., shim coils <NUM>). Transmit/receive circuitry <NUM> may be configured to select whether RF transmit coils or RF receive coils are being operated (e.g., using a switch or switches).

As illustrated in <FIG>, MRI system <NUM> includes controller <NUM> (also referred to as a console) having control electronics to send instructions to and receive information from power management system <NUM>. Controller <NUM> may be configured to implement one or more pulse sequences, which are used to determine the instructions sent to power management system <NUM> to operate the magnetic components <NUM> in a desired sequence (e.g., parameters for operating the RF transmit and receive coils <NUM>, parameters for operating gradient coils <NUM>, etc.). As illustrated in <FIG>, controller <NUM> also interacts with computing device <NUM> programmed to process received MR data. For example, computing device <NUM> may process received MR data to generate one or more MR images using any suitable image reconstruction process(es). Controller <NUM> may provide information about one or more pulse sequences to computing device <NUM> for the processing of data by the computing device. For example, controller <NUM> may provide information about one or more pulse sequences to computing device <NUM> and the computing device may perform an image reconstruction process based, at least in part, on the provided information.

<FIG> illustrate views of a portable MRI system, in accordance with some embodiments. Portable MRI system <NUM> comprises a B<NUM> magnet <NUM> formed in part by an upper magnet 210a and a lower magnet 210b having a yoke <NUM> coupled thereto to increase the flux density within the imaging region. The B<NUM> magnet <NUM> may be housed in magnet housing <NUM> along with gradient coils <NUM> (e.g., any of the gradient coils described in <CIT>). According to some embodiments, B<NUM> magnet <NUM> comprises an electromagnet. According to some embodiments, B<NUM> magnet <NUM> comprises a permanent magnet.

Portable MRI system <NUM> further comprises a base <NUM> housing the electronics needed to operate the MRI system. For example, base <NUM> may house electronics including power components configured to operate the MRI system using mains electricity (e.g., via a connection to a standard wall outlet and/or a large appliance outlet). Accordingly, portable MRI system <NUM> can be brought to the patient and plugged into a wall outlet in the vicinity. In this manner, portable MRI system <NUM> can be transported to the patient and maneuvered to the bedside to perform imaging, as illustrated in <FIG>. For example, <FIG> illustrates a portable MRI system <NUM> that has been transported to a patient's bedside to perform a brain scan.

<FIG> illustrates a block diagram representing components of a device <NUM> configured to detect position and/or motion of a patient positioned within an MRI system, in accordance with some embodiments of the technology described herein. Device <NUM> may be communicatively coupled with a console <NUM> of an MRI system (e.g., one or more of the MRI systems <NUM> and/or <NUM> described in connection with <FIG> and <FIG>). Console <NUM> may be communicatively coupled with sensor controller <NUM> and sensor <NUM>. It should be appreciated that while only one sensor <NUM> is depicted in <FIG>, in some embodiments multiple sensors <NUM> (e.g., two, four, and/or six sensors) may be coupled to sensor controller <NUM>. It should further be appreciated that, while not shown in the example of <FIG>, additional DC components may be included in device <NUM>. For example, in some embodiments, additional filters (e.g., bandpass filters), bias tees, analog-to-digital converters (ADCs), and/or digital-to-analog converters (DACs) may be included in device <NUM>.

In some embodiments, sensor <NUM> may be configured to be capacitively coupled with a patient through a parasitic capacitance. In some embodiments, sensor <NUM> may be an RF sensor configured to resonate at an RF frequency. In some embodiments, sensor <NUM> may be an RF antenna (e.g., a loop antenna, a bowtie antenna, a dipole antenna, or any other RF antenna configured to resonate at a desired resonant frequency). In some embodiments, sensor <NUM> may be a dipole antenna, as described herein including with reference to <FIG> and <FIG> herein. In some embodiments, sensor <NUM> may have a resonant frequency between <NUM> and <NUM>.

In some embodiments, sensor controller <NUM> may include several components configured to drive sensor <NUM> with an RF signal and to measure a value of a reflected signal from sensor <NUM> in response to the RF signal. The value of the reflected signal from sensor <NUM> may indicate a degree of capacitive coupling between the sensor <NUM> and a patient positioned within the MRI system. The capacitive coupling between the sensor <NUM> and the patient may change in response to a change in the distance between the sensor <NUM> and the patient (e.g., as the patient moves toward or away from the sensor <NUM>), as is illustrated in <FIG>.

<FIG> shows simulated values of a ratio of reflected signal, Vref1, (e.g., voltage of the reflected signal from sensor <NUM>) to an input signal, Vfwd, (e.g., voltage of the RF signal from RF source <NUM>) as a function of frequency for different capacitive loads on a sensor, in accordance with some embodiments. As the capacitive load is increased (e.g., a patient is moved closer to the sensor in the helmet on the patient's head), the resonant frequency of the sensor may decrease. For example, curve <NUM> has a higher resonant frequency (represented by a minimum value of Vref1/Vfwd) than curve <NUM> because curve <NUM> was simulated with a lower capacitive load than curve <NUM>.

In some embodiments, device <NUM> may be configured to monitor an observation frequency corresponding to a resonant frequency of the unloaded sensor <NUM> (e.g., when the patient is not positioned within the MRI system, curve <NUM>). When a patient is positioned within the MRI system (e.g., curve <NUM>), the frequency response of the sensor <NUM> will decrease. The reflection coefficient, Vre1/Vfwd, measured at the observation frequency may accordingly change as a function of patient position. The measured reflection coefficient Vref1/Vfwd may be compared to a threshold value to determine whether the patient's motion is to a degree that may affect accurate acquisition of MR data and/or to determine whether the acquired MR data is to be post-processed to compensate for the motion. The threshold value may be determined based on a previous measured reflection coefficient. For example, the threshold value may be determined based on adding and/or subtracting a percentage of a previously measured reflection coefficient to the previously measured reflection coefficient (e.g., the threshold value may be a previously measured reflection coefficient ±<NUM>%, ±<NUM>%, and/or ±<NUM>%). The percentage of the previously measured reflection coefficient may be chosen to be representative of acceptable noise.

Returning to <FIG>, in some embodiments, sensor controller <NUM> may include a processor <NUM>. In some embodiments, the processor <NUM> may be a programmable system-on-a-chip (PSoC). Processor <NUM> may be communicatively coupled to console <NUM> (e.g., through serial communications). Processor <NUM> may receive instructions from console <NUM> (e.g., to initiate calibration of sensor <NUM>, to measure a reflected power value from sensor <NUM>). In some embodiments, processor <NUM> may send measurements from sensor <NUM> to console <NUM> for use in MR image reconstruction. Processor <NUM> may send data from sensor <NUM> to console <NUM> after (e.g., in response to) receiving it, without buffering for subsequent communication to maintain synchrony with the MRI system clock and to mitigate errors in the data stream from processor <NUM>. In other embodiments, data may be buffered and sent in packets. The packets may be sent at time intervals of less than <NUM> in width.

In some embodiments, console <NUM> may include software configured to use the data sent by processor <NUM> from sensor <NUM> to aid in reconstruction of MR images from the MRI system. In some embodiments, the software may be configured to compensate for patient motion by rejecting MR data acquired during a time period during which the patient has moved. Alternatively or additionally, the software may compensate for patient motion by, after rejecting some MR data, smoothing and/or interpolating the remaining MR data to compensate for the removal of some MR data. In some embodiments, the software may compensate for patient motion by sending instructions to the MRI system to acquire additional MR data to replace MR data acquired during a time period during which the patient has moved. For example, in some embodiments obtaining additional MR data may include modifying a pulse sequence for the RF transmit and receive coils of the MRI system to obtain additional MR data at points in k-space that were initially acquired during a time period in which patient motion was detected.

In some embodiments, processor <NUM> may be communicatively coupled with an RF source <NUM>. For example, processor <NUM> may be communicatively coupled with RF source <NUM> through an I2C bus. RF source <NUM> may be, for example, a programmable RF oscillator (e.g., Silicon Labs' Si514 frequency general purpose oscillator). RF source <NUM> may output an RF signal that was digitally synthesized by processor <NUM>.

In some embodiments, RF source <NUM> may output an RF signal to couplers <NUM>, which may couple with sensor <NUM>. Couplers <NUM> may be, for example, bi-directional couplers (e.g., ADCB-<NUM>-<NUM>+ SMT bi-directional couplers by Mini-Circuits). Couplers <NUM> may couple the output RF signal from RF source <NUM> to sensor <NUM>. Additionally, in some embodiments, couplers <NUM> may couple forward power from RF source <NUM> to RF detector <NUM> and reflected power from sensor <NUM> to RF detector <NUM>. For example, couplers <NUM> may additionally couple the output RF signal from RF source <NUM> to RF detector <NUM> to monitor the forward power of the output RF signal from RF source <NUM>. Monitoring the forward power of the RF source <NUM> may mitigate issues such as drift in the RF source power. Additionally, couplers <NUM> may couple the reflected signal from sensor <NUM> to RF detector <NUM> to monitor the reflected power. It should be appreciated that while the example of <FIG> shows two RF detectors <NUM> and <NUM>, in some embodiments, only a single RF detector may be present (e.g., either RF detector <NUM> or RF detector <NUM>).

In some embodiments, RF detectors <NUM> and <NUM> may convert a magnitude of the received waveform to a root mean square (RMS) voltage value. For example, RF detector <NUM> may convert a magnitude of the power of the output RF signal to an RMS value representing the forward power value from RF source <NUM>. Additionally, for example, RF detector <NUM> may convert a magnitude of the power of the reflected signal from sensor <NUM> to an RMS value representing the reflected power value from sensor <NUM>. The RMS values from either RF detector <NUM> or <NUM> may be digitized with a finite number of bits of resolution (e.g., <NUM> bits of resolution). In some embodiments, detectors <NUM> may be diode detectors, linear envelope detectors, and/or logarithmic power detectors. In some embodiments, detectors <NUM> may be, for example, LT5581 series RF detectors by Analog Devices Inc.

In some embodiments, the digitized RMS values may be sent from detectors <NUM> to processor <NUM>. Processor <NUM> may organize the digitized RMS values into data packets and transmit the data packets to console <NUM> of the MRI system. In some embodiments, processor <NUM> may send data packets to console <NUM> in response to signals from Tx/Rx trigger <NUM>. Signals from Tx/Rx trigger <NUM> may indicate Tx/Rx cycles of the MRI system, thereby maintaining synchronicity between device <NUM> and each Tx/Rx cycle of the MRI system.

In some embodiments, prior to positioning the patient within the MRI system, sensor <NUM> may be calibrated. To calibrate sensor <NUM>, its resonant frequency may be determined in order to determine a value of the output RF signal from RF source <NUM> which may increase the sensitivity of sensor <NUM>. For example, setting the frequency of RF source <NUM> to be different from the resonant frequency of sensor <NUM> but within <NUM>% of the resonant frequency may maximize the sensitivity of sensor <NUM>.

In some embodiments, setting the frequency of RF source <NUM> to be different from the resonant frequency of sensor <NUM> may involve setting the frequency of the RF source <NUM> to be a frequency at which the reflection curve of sensor <NUM> has a maximum slope. Accordingly, the frequency of RF source <NUM> may depend on the Q factor of the sensor <NUM>. For example, the sensor may be configured to have a Q factor of <NUM> and to resonate at <NUM>. The frequency of RF source <NUM> may be set to be at the steepest portion of the reflection curve of the sensor, or at <NUM>, which is <NUM>% higher than the resonant frequency <NUM>.

In some embodiments, during a calibration step, processor <NUM> may control RF source <NUM> to output an RF signal with a varying frequency. As the frequency of the RF signal output by RF source <NUM> is varied, processor <NUM> may monitor the reflected power from sensor <NUM>. When the output RF signal reaches the resonant frequency of sensor <NUM>, a maximum amount of the RF signal from RF source <NUM> may be delivered to sensor <NUM>, and the measured reflected signal value from sensor <NUM> may be at a minimum. Processor <NUM> may determine which output frequency from RF source <NUM> results in a minimum reflected signal value from sensor <NUM>. Processor <NUM> may then set the frequency of RF source <NUM> to be different from the resonant frequency of sensor <NUM> but within <NUM>% of the resonant frequency of sensor <NUM>.

<FIG> illustrates exemplary devices for detecting motion of a patient in communication with an MRI system, in accordance with some embodiments of the technology described herein. In some embodiments, sensor controller <NUM> may be coupled to one or more sensors <NUM>, as described in connection with <FIG> herein. The sensor controller <NUM> and sensors <NUM> may be disposed within a housing configured to accept a part of a patient's anatomy (e.g., head, limb, knee, foot, ankle, etc.). For example, the housing may be configured to fit within the MRI system and to accept a head of the patient, as described herein, including with reference to <FIG>, or to accept a foot of the patient, as described herein including with reference to <FIG>.

In some embodiments, one or more low noise amplifiers (LNAs) <NUM> may also be disposed within the housing adjacent the sensor controller <NUM>. The LNAs <NUM> may be configured to amplify MR signals detected by the RF coils (e.g., from RF transmit and receive coils <NUM> of <FIG>) while introducing a small or minimal level of noise to the measurements. The LNAs may be communicatively coupled to the MRI interface through system connector <NUM>.

In some embodiments, the sensor controller <NUM> may be communicatively coupled to the MRI system interface by a cable. For example, the sensor controller <NUM> may be digitally communicatively coupled to the MRI system interface through a universal serial bus (USB) cable (e.g., a USB-C cable, as shown in the example of <FIG>). It should be appreciated that the sensor controller <NUM> may, in some embodiments, be communicatively coupled to the MRI system using a different type of cable and/or using an analog connection. In some embodiments, the cables connecting the sensor controller <NUM> and the LNAs <NUM> to the MRI interface may be bundled to form a single cable bundle.

In some embodiments, the sensor controller <NUM> may be communicatively coupled to an interface board <NUM> configured to communicate with components of the MRI system interface. The interface board <NUM> may be a printed circuit board (PCB), in some embodiments, configured to communicate signals from various components of the MRI system interface to the sensor controller <NUM>. In some embodiments, the interface board <NUM> may be communicatively coupled to a host PC <NUM>, a console <NUM>, and/or a DC power supply (PSU) <NUM>. In some embodiments, the host PC <NUM> may be communicatively coupled to the interface board <NUM> with a USB to universal asynchronous receiver-transmitter (UART) cable for serial interfacing with the interface board <NUM>.

In some embodiments, the console <NUM> may be the same console as described in connection with <FIG> herein. The console <NUM> may be communicatively coupled to the sensor controller <NUM> (e.g., through the interface board <NUM>). In some embodiments, the console <NUM> may be configured to send one or more trigger signals to the sensor controller <NUM> through the interface board <NUM>. For example, the console <NUM>, in some embodiments, may send the Tx/Rx trigger signal <NUM> to sensor controller <NUM> through the interface board <NUM> to maintain synchronicity between the MRI system and the sensors <NUM>.

In some embodiments, the DC PSU <NUM> may provide power to components of the sensor controller <NUM> and/or sensors <NUM>. The DC PSU <NUM> may be configured to supply the interface board <NUM>, sensor controller <NUM>, and/or sensors <NUM> with DC power. For example, the DC power may be used to power components of the sensor controller <NUM>, including PSoC <NUM>, RF source <NUM>, couplers <NUM>, and/or detectors <NUM>.

<FIG> illustrates a sensor 600a, in accordance with some embodiments. Sensor 600a may be implemented as sensor <NUM> of device <NUM>, as described in connection with <FIG> and <FIG>. Sensor 600a may be formed as a dipole antenna including a lattice balun <NUM> and conductors <NUM>, according to some embodiments. Terminals of lattice balun <NUM> may be connected to a coaxial cable, the coaxial cable providing a driving RF signal to sensor 600a. Lattice balun may include inductors Lb and capacitors Cb enabling the driving of a symmetric differential voltage across capacitor Cd. Changing the value of capacitor Cd may change an impedance of sensor 600a. In some embodiments, sensor 600a has an impedance of <NUM> Ohms.

Lattice balun <NUM> may be coupled to two arms <NUM>, each arm <NUM> having lengths of conductors <NUM> separated by inductors Ld, in accordance with some embodiments. The length of sensor 600a may be determined by the desired frequency. A lowest resonant frequency of a dipole antenna such as sensor 600a may occur when the electrical length of the dipole is half as long as the desired wavelength. For example, the physical length of sensor 600a may be <NUM> to be sensitive to a signal with a frequency of <NUM>. Inductors Ld placed in series with conductors <NUM> may reduce the physical length of sensor 600a while maintaining a desired electrical length. By including inductors Ld, sensor 600a may be made much more physically compact.

<FIG> illustrates another example of a sensor 600b, in accordance with some embodiments of the technology described herein. Sensor 600b may be implemented as sensor <NUM> of device <NUM>, as described in connection with <FIG> and <FIG>. Sensor 600b may be the same as the sensor 600a but may include varactor diodes VDd1 placed in parallel with inductors Ld of sensor 600b. In some embodiments, the capacitance of the varactor diodes VDd1 may be electronically tuned (e.g., by changing a voltage applied to the varactor diode) to change a center frequency of the sensor 600b.

In some embodiments, sensor 600b may optionally include a second varactor diode VDd2. The second varactor diode VDd2 may be placed in parallel with capacitor Cd. In such embodiments, the capacitance of the second varactor diode VDd2 may be tuned electronically (e.g., by changing a voltage applied to the varactor diode) to perform impedance matching of the sensor 600b.

Alternatively or additionally, sensors 600a or 600b may be made in a compact form factor, as shown in <FIG> illustrates a simulated voltage distribution of a sensor <NUM>, in accordance with some embodiments. The gradient regions of sensor <NUM> indicate voltage distribution within sensor <NUM>. Sensor <NUM> may be implemented as sensor <NUM> of device <NUM>, as described in connection with <FIG>.

In some embodiments, sensor <NUM> may be a dipole antenna that is folded to fit within a <NUM> × <NUM> area. A lattice balun <NUM> is represented in the simulation of <FIG> as an input port for a driving RF signal. Conductors <NUM> may be coupled to lattice balun <NUM> by inductors <NUM>, which are simulated as areas of additional physical length.

In some embodiments, sensor <NUM> may detect a patient's presence when the patient is within approximately <NUM> of sensor <NUM>. A range of a dipole sensor may be related to a physical size of the dipole sensor, as shown in <FIG> illustrates the measured reflection coefficient, Vref1/Vfwd, as a function of distance between different sized sensors and a capacitive load, in accordance with some embodiments. Curve <NUM> was measured from a sensor with a configuration like that of sensor <NUM> while curve <NUM> was measured from a sensor with a configuration like that of sensor <NUM>. As a sensor becomes more compact in arrangement, its physical range may be reduced.

<FIG> is a flowchart of an illustrative process <NUM> for detecting whether a patient positioned within an MRI system has moved, in accordance with some embodiments of the technology described herein. For example, the process <NUM> may be performed by device <NUM> described with reference to <FIG>. In some embodiments, the process <NUM> may be performed by hardware (e.g., using an ASIC, an FPGA, or any other suitable circuitry), software (e.g., by executing the software using a computer processor), or any suitable combination thereof.

In act <NUM>, a reflected signal value may be measured from at least one sensor capacitively coupled to a patient positioned within an MRI system. The at least one sensor may be, for example, one or more of sensors <NUM>, <NUM>, and/or <NUM> as described in connection with <FIG>, <FIG>, and <FIG>. The measured reflected signal value may be characteristic of a signal reflected by at least one sensor in response to being driven by at least one RF signal. For example, the reflected signal value may be a voltage of the signal reflected by the at least one sensor. The measured reflected signal value may also be indicative of a distance between the patient and the sensor, as described in connection with <FIG>.

In some embodiments, a reflected signal value may be measured from the at least one sensor synchronously with processes performed by an MRI system. For example, a reflected signal value may be measured for each Tx/Rx pulse of an MR imaging procedure, as described in connection with <FIG>.

Next, in act <NUM>, it may be determined, using the reflected signal value, whether the patient has moved while positioned within the MRI system. In some embodiments, determining whether the patient has moved may be performed by at least one processor (e.g., a processor of console <NUM> as described in connection with <FIG>).

In some embodiments, determining whether the patient has moved may include calculating a ratio of the reflected signal value from the at least one sensor to a signal value of the RF signal driving the sensor. The calculated ratio may be compared to a threshold value to determine whether the patient has moved while positioned within the MRI system. The threshold value may be based on, for example, a measured ratio for the sensor when a patient is not positioned within the MRI system.

In some embodiments, sensors may be included in components configured to receive a portion of a patient's anatomy. <FIG> and <FIG> illustrate a helmet <NUM> to assist medical personnel in properly positioning a patient within helmet <NUM>, which is further described in <CIT>, and titled "Methods and Apparatus for Patient Positioning in Magnetic Resonance Imaging,". According to some embodiments, helmet <NUM> comprises an outer housing 1030a and a coil support 1030b for transmit and/or receive coils. Coil support 1030b may be adapted to accommodate a patient's head and provide a surface to which the transmit and/or receive coils are disposed. Housing 1030a may be attached to base <NUM> comprising a releasable securing mechanism <NUM> to releasably secure helmet <NUM> to an MRI system within the imaging region of the system.

<FIG> illustrates a radio frequency helmet <NUM> with a patient <NUM> positioned within coil support 1030b. Because outer housing 1030a and coil support 1030b are see-through (e.g., constructed from a transparent or semitransparent plastic material), the patient's head can be viewed through helmet <NUM>, thus facilitating proper positioning of patient <NUM> within helmet <NUM>.

<FIG> shows an interior view of a helmet <NUM> with sensors <NUM> disposed on a surface of the helmet <NUM>, in accordance with some embodiments. <FIG> shows a perspective view of helmet <NUM> showing sensors <NUM> positioned on a surface of the helmet and arranged around a patient's head. Sensors <NUM> may be RF sensors such as those described in connection with <FIG> and <FIG> herein (e.g., antennas or dipole antennas). In particular, in the embodiment illustrated in <FIG>, the sensors <NUM> may be disposed on opposing surfaces of helmet <NUM> so that the patient's head may be placed centrally between sensors <NUM>. In some embodiments, the sensors may be integrated within the helmet <NUM>.

It may be appreciated that the arrangement of sensors shown in <FIG> is only one example and that other arrangements of sensors may be implemented depending on the type and/or direction of motion that is desirable to detect. For instance, the arrangement of sensors <NUM> as shown in <FIG> and <FIG> may be used to detect motion of the patient's head when it makes side-to-side motions (e.g., shaking the head "no") and/or nodding motions (e.g., nodding the head "yes"). It may also be desirable to monitor up-down motion of the patient's head (e.g., into and out of the helmet), and sensors <NUM> may be placed at the top of the interior surface of helmet <NUM> to monitor such motion. In some embodiments, where it is desired to detect motion in six degrees of freedom (e.g., translation in three directions and rotations about three axes), there may be at least six sensors <NUM> included in the arrangement.

Additionally or alternatively, the sensor controller <NUM> may be located adjacent the sensors, in some embodiments, as shown in the example of <FIG> illustrates another example of a helmet <NUM> configured to accommodate a patient's head during MR imaging. The helmet <NUM> may include both sensors <NUM> for detecting motion by the patient during imaging and a sensor controller <NUM>, in accordance with some embodiments of the technology described herein. By placing the sensor controller <NUM> near the sensors <NUM>, cabling configured to transmit the analog signals from the sensors <NUM> to the sensor controller <NUM> may be shorter in length, reducing RF interference with the signals and improving performance of the motion detection system.

<FIG> illustrates another view of a helmet disposed within an MRI system, in accordance with some embodiments of the technology described herein. In some embodiments, the components of helmet <NUM> (e.g., sensor controller <NUM> and/or sensors <NUM>, not pictured) may be communicatively coupled from within the MRI system (e.g., within the imaging region of the MRI system) to an external MRI interface by a cable bundle <NUM>. The cable bundle may include portions 1090a, 1090b to provide communicative coupling from the MRI interface to different components of helmet <NUM> (e.g., as described in connection with <FIG> herein). For example, portion 1090a may include a USB cable to provide communicative coupling to the sensor controller <NUM>, and portion 1090b may include an analog connection to provide communicative coupling to LNAs <NUM>. In some embodiments, the portions 1090a, 1090b may be routed through a connector <NUM> that is configured to also provide electrical coupling between the RF coils disposed within the helmet <NUM> and the MRI interface.

As described above, techniques for detecting motion of a patient within an MRI system may also be applied to a device configured to accommodate an appendage, such as a leg or an arm, or a portion of an appendage such as an ankle, foot, wrist, hand, etc. <FIG> illustrates aspects of a foot coil adapted to accommodate a foot, configured to secure the foot coil to an MRI system so that the foot is positioned within the imaging region of the MRI system (e.g., within the imaging region of the exemplary low-field MRI systems described in the foregoing), and is coupled with sensors configured to capacitively couple with the patient's foot. According to some embodiments, a radio frequency apparatus is adapted to accommodate a foot and configured to be secured within the imaging region of an MRI system having a bi-planar B<NUM> magnet configuration in which the space between upper and lower B<NUM> magnets may be limited, some examples of which are described in further detail below.

<FIG> illustrates a view of a radio frequency apparatus <NUM> (referred to generally herein as a "foot coil," adapted to accommodate a foot for one or more MRI procedures). Foot coil <NUM> comprises transmit/receive housings or supports 1130t/r on or within which transmit and/or receive coils for the radio frequency apparatus are provided. According to some embodiments, foot coil <NUM> comprises a transmit housing for transmit coils and a receive housing for receive coils, as described in further detail in <CIT>.

Exemplary foot coil <NUM> also comprises an outer housing 1130a to at least partially cover transmit/receive housing(s) 1130t/r and to form a volume 1130c adapted to accommodate a foot. As illustrated in FIG. 11A, volume 1130c has a height h and a w that allows a foot to be inserted into the interior of foot coil <NUM>. <FIG> illustrates sensors <NUM> coupled to foot coil <NUM> of FIG. 11A, in accordance with some embodiments described herein. Sensors <NUM> may be RF sensors such as those described in connection with <FIG> and <FIG> herein (e.g., dipole antennas). In particular, in the embodiment illustrated in <FIG>, the sensors <NUM> may be disposed on opposing surfaces of foot coil <NUM> so that the patient's foot may be placed between sensors <NUM>.

It may be appreciated that the arrangement of sensors shown in <FIG> is only one example and that other arrangements of sensors may be possible depending on the type and/or direction of motion is desirable to detect. For instance, the arrangement of sensors <NUM> may be used to detect motion of the patient's foot along a latitudinal axis <NUM>, but additionally it may be desirable to detect motion of the patient's foot relative to a podal axis <NUM>. To detect motion of the patient's foot relative to the podal axis <NUM>, additional sensors may be arranged relative to the podal axis <NUM> (e.g., along an axis perpendicular to the podal axis <NUM> or along an axis at any other angle relative to the podal axis <NUM>).

<FIG> shows, schematically, an illustrative computer <NUM> on which any aspect of the present disclosure may be implemented.

In the embodiment shown in <FIG>, the computer <NUM> includes a processing unit <NUM> having one or more processors and a non-transitory computer-readable storage medium <NUM> that may include, for example, volatile and/or non-volatile memory. The memory <NUM> may store one or more instructions to program the processing unit <NUM> to perform any of the functions described herein. The computer <NUM> may also include other types of non-transitory computer-readable medium, such as storage <NUM> (e.g., one or more disk drives) in addition to the system memory <NUM>. The storage <NUM> may also store one or more application programs and/or resources used by application programs (e.g., software libraries), which may be loaded into the memory <NUM>.

The computer <NUM> may have one or more input devices and/or output devices, such as devices <NUM> and <NUM> illustrated in <FIG>. Examples of input devices that can be used for a user interface include keyboards and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, the input devices <NUM> may include a microphone for capturing audio signals, and the output devices <NUM> may include a display screen for visually rendering, and/or a speaker for audibly rendering, recognized text. As another example, the input devices <NUM> may include sensors (e.g., electrodes in a pacemaker), and the output devices <NUM> may include a device configured to interpret and/or render signals collected by the sensors (e.g., a device configured to generate an electrocardiogram based on signals collected by the electrodes in the pacemaker).

As shown in <FIG>, the computer <NUM> may also comprise one or more network interfaces (e.g., the network interface <NUM>) to enable communication via various networks (e.g., the network <NUM>). Examples of networks include a local area network or a wide area network, such as an enterprise network or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks. Such networks may include analog and/or digital networks.

Having thus described several aspects of at least one embodiment of this technology, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art.

The above-described embodiments of the technology described herein can be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers. Such processors may be implemented as integrated circuits, with one or more processors in an integrated circuit component, including commercially available integrated circuit components known in the art by names such as CPU chips, GPU chips, microprocessor, microcontroller, or co-processor. Alternatively, a processor may be implemented in custom circuitry, such as an ASIC, or semi-custom circuitry resulting from configuring a programmable logic device. As yet a further alternative, a processor may be a portion of a larger circuit or semiconductor device, whether commercially available, semi-custom or custom. As a specific example, some commercially available microprocessors have multiple cores such that one or a subset of those cores may constitute a processor. Though, a processor may be implemented using circuitry in any suitable format.

Also, the various methods or processes outlined herein may be coded as software that is executable on one or more processors running any one of a variety of operating systems or platforms. Such software may be written using any of a number of suitable programming languages and/or programming tools, including scripting languages and/or scripting tools. In some instances, such software may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine. Additionally, or alternatively, such software may be interpreted.

The techniques disclosed herein may be embodied as a non-transitory computer-readable medium (or multiple computer-readable media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other non-transitory, tangible computer storage medium) encoded with one or more programs that, when executed on one or more processors, perform methods that implement the various embodiments of the present disclosure described above. The computer-readable medium or media may be transportable, such that the program or programs stored thereon may be loaded onto one or more different computers or other processors to implement various aspects of the present disclosure as described above.

The terms "program" or "software" are used herein to refer to any type of computer code or set of computer-executable instructions that may be employed to program one or more processors to implement various aspects of the present disclosure as described above. Moreover, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that, when executed, perform methods of the present disclosure need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present disclosure.

Various aspects of the technology described herein may be used alone, in combination, or in a variety of arrangements not specifically described in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

Also, the technology described herein may be embodied as a method, examples of which are provided herein including with reference to <FIG>. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

Claim 1:
A device configured to accommodate a patient's anatomy during magnetic resonance, MR, imaging, the device comprising:
at least one radio frequency, RF, transmit and/or receive coil (<NUM>); and
at least one RF sensor (<NUM>, <NUM>), different from the at least one RF transmit and/or receive coil, configured to be capacitively coupled to the patient during MR imaging, wherein the at least one RF sensor comprises four RF dipole antennas coupled to a helmet (<NUM>) configured to accommodate a patient's head during MR imaging,
wherein:
the four dipole antennas are positioned on an inner surface of the helmet and arranged in two sets of two dipole antennas each;
the dipole antennas of each set of two dipole antennas are disposed along a respective axis and wherein the axis of the first of the two sets of two dipole antennas is different from the axis of the second of the two sets of two dipole antennas, for detecting motion of the patient in both directions along said respective axes; and
the patient's head is located on the respective axis between the dipole antennas of each set of two dipole antennas.