Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
  • G01R33/48—NMR imaging systems
  • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
  • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
  • G01R33/567—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution gated by physiological signals, i.e. synchronization of acquired MR data with periodical motion of an object of interest, e.g. monitoring or triggering system for cardiac or respiratory gating
  • G01R33/5673—Gating or triggering based on a physiological signal other than an MR signal, e.g. ECG gating or motion monitoring using optical systems for monitoring the motion of a fiducial marker
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
  • G01R33/34007—Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
  • G01R33/3692—Electrical details, e.g. matching or coupling of the coil to the receiver involving signal transmission without using electrically conductive connections, e.g. wireless communication or optical communication of the MR signal or an auxiliary signal other than the MR signal
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
  • G01R33/48—NMR imaging systems
  • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
  • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
  • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
  • G01R33/56509—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to motion, displacement or flow, e.g. gradient moment nulling
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
  • G01R33/341—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
  • G01R33/3415—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils comprising arrays of sub-coils, i.e. phased-array coils with flexible receiver channels

Definitions

• the invention relates to a magnetic resonance imaging (MRI) system for MRI 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, and especially to a magnetic resonance imaging system with the possibility to detect motions of the patient under examination.
• MRI magnetic resonance imaging
• a patient in a magnetic resonance imaging system, a patient, usually a human being or an animal, is exposed to a uniform main magnetic field (BO field) so that the magnetic moments of the nuclei within the patient form a certain net magnetization of all nuclei parallel to the BO field, which can be tilted leading to a rotation around the axis of the applied BO field (Larmor precession).
• the rate of precession is called Larmor frequency which is dependent on the specific physical characteristics of the involved nuclei, namely their gyromagnetic ratio, and the strength of the applied BO field.
• the gyromagnetic ratio is the ratio between the magnetic moment and the spin of a nucleus.
• an RF excitation pulse (B 1 field) which has an orthogonal polarization to the BO field, generated by means of an RF transmitting antenna or coil, and matching the Larmor frequency of the nuclei of interest, the spins of the nuclei can be excited and brought into phase, and a deflection of their net magnetization from the direction of the B0 field is obtained, so that a transversal component in relation to the longitudinal component of the net magnetization is generated.
• MR magnetic resonance
• gradient magnetic fields are superimposed on the B0 field, having the same direction as the B0 field, but having gradients in the orthogonal x-, y- and z-directions.
• the Larmor frequency of the nuclei Due to the fact that the Larmor frequency is dependent on the strength of the magnetic field which is imposed on the nuclei, the Larmor frequency of the nuclei accordingly decreases along and with the decreasing gradient (and vice versa) of the total, superimposed B0 field, so that by appropriately tuning the frequency of the transmitted RF excitation pulse (and by accordingly tuning the resonance frequency of the RF/MR receive antenna), and by accordingly controlling the gradient magnetic fields, a selection of nuclei within a slice at a certain location along each gradient in the x-, y- and z-direction, and by this, in total, within a certain voxel of the object can be obtained.
• the above described RF (transmitting and/or receiving) antennas can be provided in the form of coils which can be fixedly mounted within an examination space of an MRI system for imaging a whole patient, or which are arranged directly on or around a local zone or area to be examined.
• MRI scans need a number of input parameters and proper scan preparation. Depending on body size and body weight of a patient under examination, patient position and anatomy to be scanned, typically a protocol is chosen and modified to fit the patient. Usually, this data has to be entered manually. Physiology parameters, e.g. necessary for triggering scans, have to be measured using dedicated sensors. However, during a MRI procedure the patient is covered by clothes and for the most applications covered by RF coils such as head and/or (anterior) surface coils. Therefore, optical detection methods for detecting motions of the patient are difficult to realize.
• an apparatus and a method which provide signals corresponding to physiological motion of an imaging slice in an MRI system for use in synchronizing acquisition of MRI data with movement of the slice.
• the signals are generated by initiating an incident signal of a predetermined frequency which interacts with the imaging slice and returns a reflected signal of this frequency.
• a baseband signal is generated which is indicative of changes in the phase and magnitude relationships between the signals. Because changes in the phase and magnitude relationships between the signals are related in an approximately linear manner to movement of the imaging slice, the baseband signal provides an indication of movement of the imaging slice to serve as an accurate triggering signal to synchronize acquistion of MRI data with movement of the imaging slice.
• Such movement information is used for motion correction and cardiac triggering, but also for estimating a rough patient model, which can be calculated in real time. Further application is for triggering therapy devices (e.g. MR-LINAC).
• triggering therapy devices e.g. MR-LINAC
• a magnetic resonance imaging system for examination of a patient comprising an RF coil arrangement with an RF coil for transmitting and/or receiving an RF signal for generating a magnetic resonance image
• 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.
• the present invention relates to realizing a MRI system with an additional RF sensor to monitor motion signals like breathing and cardiac signals.
• additional relates to the fact that the additional sensor is provided in addition to the RF coil which may already be used as a sensor for such motion signals. Therefore, it is an essential feature of the invention, that further to the RF coil an additional sensor is provided 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.
• Clinical applications may use this additional information for simultaneous measurement and estimation of permittivity or conductivity (e.g. input for electrical properties tomography), real time electrical patient modelling and specific absorption rate control, motion
• RF monitoring has several advantages over other ways to monitor the patient: In contrast to optical monitoring, RF penetrates into the patient's body through clothing or other material covering the patient. In contrast to MR navigators, it can be operated simultaneously with the MR imaging. Thus sensor data are available continuously throughout the entire examination procedure independent of the sequence that is run on the system. It is contactless, i.e. no devices have to be attached to the patient by the MR operator, making it no burden on the workflow.
• motions of the patien does not only cover motions of the patient which are visible from outside but also motions within the patient like motions of internal organs of the patient. In most exams, the patient lies perfectly still but tracking the internal sources of motion is relavant for high quality imaging.
• such motion signals may be received by the RF coil itself.
• the additional RF sensor is also configured for receiving the motion signals which are due to motions of the patient.
• the RF coil arrangement is equipped with a preamplifier, and the additional RF sensor is arranged in the preamplifier.
• the additional RF sensor comprises an antenna which is located on a printed circuit board of the preamplifier.
• the additional RF sensor comprises an antenna which is integrated into the RF coil.
• the additional RF sensor may be used for transmitting different types of signals.
• the additional RF sensor is configured for transmitting continuous-wave radar signals and/or ultra wideband radar signals.
• the magnetic resonance imaging system further comprises a machine- learning module with deep learning capability adapted for receiving the sensed motion signals.
• Deep learning methods aim at learning feature hierarchies with features from the higher levels of the hierarchy formed by the composition of lower level features. They may include learning methods for a wide array of deep architectures, including neural networks with hidden layers and graphical models with levels of hidden variables.
• Unsupervised pre-training works to render learning deep architectures more effective. Unsupervised pre-training acts as a kind of network pre- conditioner, putting the parameter values in the appropriate range for further supervised training and initializes the model to a point in parameter space that somehow renders the optimization process more effective, in the sense of achieving a lower minimum of the empirical cost function.
• the additional RF sensors are part of the RF coil arrangement which also comprises the RF coil for transmitting and/or receiving the RF signal for generating a magnetic resonance image.
• the additional RF sensor may be provided independently from the RF coil.
• the additional RF sensor is arranged in a patient bed which is adapted for holding the patient during examination. Preferably, multiple such RF sensors are provided.
• the machine- learning module is also connected to the RF coil for receiving the RF signals for generating the magnetic resonance image.
• each RF coil arrangement comprising an RF coil for transmitting and/or receiving an RF signal for generating a magnetic resonance image and 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 of the patient, wherein each RF coil arrangement is connected to a separate machine- learning module for transmitting the respective sensed motion signals and the respective signals for generating the magnetic resonance image to the respective machine- learning module.
• the invention also relates to a method of operating a magnetic resonance imaging system for examination of a patient, the magnetic resonance imaging system comprising an RF coil arrangement with an RF coil and an additional RF sensor, the method comprising the following steps:
• an RF transmit signal which is adapted for interacting with the tissue of the patient by the additional RF sensor 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.
• Preferred embodiments of this method relate to the preferred embodiments of the MRI system described further above. Further, the invention also relates to a non-transitory computer-readable medium for controlling the operation of a magnetic resonance imaging system for
• the magnetic resonance imaging system comprising an RF coil arrangement with an RF coil and an additional RF sensor, the non-transitory computer- readable medium comprising instructions stored thereon, that when executed on a processor, perform the steps of any of the methods described herein.
• Fig. 1 schematically depicts a preamplifier printed circuit board with an integrated RF transceiver device for motion detection according to a preferred embodiment of the invention
• Fig. 2 schematically depicts a preamplifier printed circuit board with an integrated RF transceiver device for motion detection according to another preferred embodiment of the invention
• Fig. 3 schematically depicts an RF coil array with integrated RF motion detectors according to a preferred embodiment of the invention
• Fig. 4 schematically depicts RF coils with integrated RF motion detector antennas according to further preferred embodiments of the invention
• Fig. 5 schematically depicts anRF coil antenna with integrated distributed stub antennas according to a preferred embodiment of the invention
• Fig. 6 schematically depicts a MRI system with multiple RF sensors in a patient bed according to a preferred embodiment of the invention.
• FIG. 1 schematically a preamplifier printed circuit board 1 with an integrated RF transceiver device 2 for motion detection and an RF coil 4 according to a preferred embodiment of the invention can be seen.
• This is an RF coil arrangement with an RF coil 4 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 and receiving an RF transmit signal which is adapted for interacting with the tissue of a patient under examination 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.
• the antenna 3 of the RF transceiver 2 is integrated in the RF coil 4 but may also be located on the printed circuit board 1.
• the RF coil 4 itself may also be used as antenna device by the RF transceiver device 2 in a multi resonant design.
• the printed circuit board 1 comprises a radar and RF sensor 5 including a digital modulator 9 and an amplifier 10 from where signals are fed to the antenna 3. Signals received by the RF coil 4 are fed to the preamplifier 6 and further to the digitizer and compressor 7. I/O functionality is realized by a digital interface 8.
• Fig. 2 schematically depicts a preamplifier printed circuit board with an integrated RF transceiver device 2’ for motion detection according to another preferred embodiment of the invention.
• the general design is similar to the design shown in Fig. 1 and like devices are referred to with like reference signs.
• a carrier signal is generated which is either outside the MRI band or is a digital spread spectrum signal.
• the spread spectrum signal is removed from the MRI signal via decorrelator 11.
• the RF coil 4 is simultaneously used for MRI and the additional RF signal for motion detection.
• FIG. 3 An RF coil array with integrated RF motion detectors according to a preferred embodiment of the invention is schematically depicted in Fig. 3.
• Each individual coil 21 is equipped with a local motion detector device 22.
• the motion-detecting device 22 senses the motion in the tissue 23 of the patient, i.e. the motion of internal organs of the patient (heart, liver) or the body surface of the patient.
• the motion sensing field is referred to by reference sign 24. Either reflected wave or crosstalk between individual coil elements is used for further processing.
• Fig. 4 schematically depicts RF coils 4 with integrated RF motion detector antennas according to further preferred embodiments of the invention, i.e. a) an antenna array 41, b) a dipole 42, and c) a spiral Vivaldi design 43.
• Fig. 5 schematically an RF coil antenna 4 with integrated distributed stub antennas 44 according to another preferred embodiment of the invention is depicted.
• the MRI system 60 schematically depicted in Fig. 6 comprises a machine- learning module 51 with deep learning capability.
• Fig. 6 further shows a patient bed 52 for holding a patient 53 during MRI examination in an MRI bore 54 of the MRI system 60.
• the patient bed 52 comprises several RF sensors 55 for transmitting RF transmit signals which are adapted for interacting with the tissue of the patient 53 allowing to sense motion signals due to motions of the patient 53 simultaneously to transmitting and/or receiving the RF signal for generating the magnetic resonance image.
• the RF sensors 55 are controlled by a signal control and processing unit 56 which is coupled both to a MRI console 57 for operation by a user and the machine-learning module 51.
• the machine- learning module 51 receives the sensed motion signals and the RF signals for generating the magnetic resonance image.
• the machine- learning module 51 is identifying the relevant sensor attributes of the operating condition of the RF sensor 55, e.g.
• the signal control and processing unit 56 modifies the RF sensor coefficient setting continually and other parameters like the selection of sensors, frequency and antenna as the operating condition changes.
• the machine- learning module 51 monitors the present operating condition and, in response to abrupt changes, restores past coefficients that were successful under similar conditions beforehand.
• Successful coefficient settings are stored in a list that is indexed using a multi dimensional attribute vector derived from the measured operating condition. Unlike look-up- tables with array structures, the list generates elements automatically. The size of the list is dynamic, growing, as more operating conditions are experienced and contracting as neighbouring elements are recognized as redundant.
• Transceiver device 2 Antenna 3

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• 2017
  • 2017-11-16 EP EP17202078.6A patent/EP3486672A1/en not_active Withdrawn
• 2018
  • 2018-11-09 WO PCT/EP2018/080825 patent/WO2019096707A1/en not_active Ceased
  • 2018-11-09 CN CN201880081156.3A patent/CN111480089B/zh active Active
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