Patent Description:
In X-ray imaging techniques such as x-ray computed tomography, fluoroscopy, and X-ray imaging medical imaging data is acquired from a subject and used to reconstruct a medical image. This enables physicians or other health care professionals to accurately image a subject's internal anatomy. A disadvantage of these techniques is that the subject can move during the acquisition of the medical imaging data, which can lead to the addition of artifacts in the medical image or X-ray.

The European patent application <CIT> concerns an MRI system with a pilot tone generator for generating a cardiac movement signal. This known pilot tone emitter is formed as a separate single radio frequency source that generates a single pilot tone signal.

The invention provides for an X-ray system, a computer program product and a method in the independent claims. Embodiments are given in the dependent claims.

Embodiments of the invention may provide for an improved method of determining the motion state of a subject for an X-ray system. Embodiments may provide this by using a pilot tone system. In a pilot tone system, a pilot tone signal (a radio frequency signal) is transmitted using a transmit coil and then pilot tone data is received using at least one receive coil. The pilot tone data is the signal in the receive coil caused by the transmission of the pilot tone signal. As the subject moves the RF coupling between the transmit coil and the receive coil changes. The change in the RF coupling causes a change in the pilot tone data which can be used to determine a motion state of the subject.

In one aspect the invention provides for an X-ray system configured for acquiring medical imaging data from a subject at least partially within an imaging zone. The X-ray system comprises a memory storing machine-executable instructions. The X-ray system further comprises a processor for controlling the X-ray system. The X-ray system further comprises a pilot tone system. The pilot tone system comprises a radio-frequency system comprising at least one transmit channel and at least one receive channel. The at least one transmit channel is configured for transmitting the at least one pilot tone signal via at least one transmit coil. The at least one receive channel is configured for receiving pilot tone data via at least one receive coil. The pilot tone system is based on transmission of the pilot tone signal as an electromagnetic signal e.g. in the radio frequency range of e.g. <NUM>-<NUM>. The pilot tone signal is transmitted in a continuous wave (cw) mode and the pilot tone data are due to impedance response to the transmitted pilot tone signal. This response is represented by the changes in amplitude and phase of the pilot tone data relative to that of the transmitted pilot tone signal. That is the pilot tone data represent a frequency domain response to the pilot tone signal and spectrally resolved information is carried by the pilot tone data.

Execution of the machine-executable instructions further cause the processor to transmit the at least one pilot tone signal, notably multi-channel pilot toen signals by controlling the at least one transmit channel. Execution of the machine-executable instructions further causes the processor to acquire the pilot tone data, notably multi-channel pilot tone data by controlling the at least one receive channel to receive the pilot tone data. Execution of the machine-executable instructions further causes the processor to determine a motion state of the subject using the pilot tone data. This embodiment may be beneficial because it may provide for an effective means of monitoring the motion state of the subject during an X-ray examination.

The X-ray system may take different forms in different examples. In one example the X-ray system is a computed tomography system or CT system. In another example the X-ray system is a fluoroscope.

In another embodiment the X-ray system is an X-ray imaging system that is configured for acquiring two-dimensional X-rays. All of the previously mentioned X-ray systems may benefit from the use of a pilot tone system.

In another embodiment the at least one transmit channel is multiple transmit channels. The at least one transmit coil has multiple transmit coils. The transmitting of the at least one pilot tone signal by controlling the at least one transmit channel comprises transmitting multi-channel pilot tone signals by controlling at least a portion of the multiple transmit channels. The acquisition of the pilot tone data by controlling the at least one receive channel to receive the pilot tone data comprises acquiring multi-channel pilot tone data by controlling at least a portion of the multiple receive channels to receive the pilot tone data.

The determination of a motion state of the subject using the pilot tone data comprises determining a motion state of the subject using the multi-channel pilot tone data. This embodiment may be beneficial because multiple transmit channels and multiple receive channels are used. This enables a larger degree of information on the motion of the subject.

The radio-frequency system is configured for encoding each of the multi-channel pilot tone signals using any one of the following: frequency encoding, phase encoding, complex modulation, CDMA encoding, and combinations thereof. This embodiment may be beneficial because it may provide for an effective means of differentiating the source of a pilot tone signal when receiving multiple signals. This may improve the ability to determine the motion state of the subject.

In another embodiment the at least one receive channel is multiple receive channels. The at least one receive coil is multiple receive coils. This embodiment may be beneficial because a number of receive coils may be placed in different locations and then the placement of the subject with respect to the pilot tone system is less sensitive.

In another embodiment the motion state is any one of the following: a subject motion location, a motion vector, a subject motion classification, a breathing state, a heart motion state, a translation vector descriptive of at least a portion of the subject, a rotation descriptive of at least a portion of the subject, and combinations thereof.

In another embodiment execution of the machine-executable instructions further causes the processor to determine the motion state using a recurrent neural network that is configured for receiving the pilot tone data and the at least one pilot tone signal and then for outputting the motion state. This embodiment may be beneficial because it may be trained to recognize complex patterns.

In another embodiment execution of the machine-executable instructions further causes the processor to determine the motion state by detecting a distance between the subject and each of the at least one receive coils. As a subject comes closer to a particular receive coil the coupling may increase. This may provide a model which may be used to efficiently yet simply determine the position of the subject.

In another embodiment execution of the machine-executable instructions further causes the processor to determine the motion state by detecting using digital filtering. Various periodic motion such as breathing or heartbeat will produce a pilot tone that has a characteristic frequency. The digital filtering enables the accurate and easy detection of such motion as heart or breathing.

In another embodiment execution of the machine-executable instructions further cause the processor to determine the motion state using principle component analysis. This embodiment may be beneficial because it may be possible to use large amounts of previously acquired pilot tone signals and pilot tone data to form the principle component analysis model.

In another embodiment execution of the machine-executable instructions further cause the processor to control the X-ray system to acquire the medical imaging data during acquisition of the pilot tone data. This embodiment may be beneficial because then the pilot tone data may be used for example controlling the function and operation of the X-ray system and/or later used for reconstructing an X-ray or medical image.

In another embodiment execution of the machine-executable instructions further cause the processor to reconstruct a medical image using the medical imaging data. Execution of the machine-executable instructions further cause the processor to correct the reconstruction of the medical image using the motion state of the subject. This embodiment may be particularly beneficial in cases where the X-ray system is a tomographic system such as a CT system. A knowledge of the position of the subject may help to account for motion of the subject during the reconstruction of the medical image.

In another embodiment execution of the machine-executable instructions further cause the processor to gate acquisition of the medical imaging data using the motion state of the subject. For example, if the motion state is a breathing phase or heart phase the gating of the subject may be useful for producing heart or breathing phase result images of the subject.

In another embodiment execution of the machine-executable instructions further causes the processor to modify acquisition of the medical imaging data using the motion state of the subject. For example, in a tomographic medical imaging technique such as CT the determination of the motion state may be used to change the style and position of the where the coordinate system for acquired medical imaging data is. This may for example be useful in compensating for motion of the subject during the acquisition of the medical imaging data.

In another embodiment the pilot tone system further comprises the at least one transmit coil and/or the at least one receive coil.

In another embodiment the X-ray system further comprises a subject support for supporting at least a portion of the subject in the imaging zone. The at least a portion of the at least one transmit coil and at least a portion of the at least one receive coil are integrated into the subject support. This may be beneficial because it may provide for an efficient means of incorporating the pilot tone system into the X-ray system.

The processor used to control the pilot tone system could be integrated into the subject support also. For example, the pilot tone system could be completely contained within the subject support. This could for example enable the addition of a pilot tone system to the X-ray system by the use of the subject support. The subject support could also be used for different imaging techniques such as magnetic resonance imaging. A single subject support could be moved to different imaging system as well as different types of imaging systems.

In another embodiment the X-ray system is an X-ray computed tomography system. This may be beneficial because the exact location of the subject may be beneficial in controlling the X-ray computed tomography system and/or during the reconstruction to improve the quality of medical images or X-rays from the X-ray system.

In another aspect the invention provides for a computer program product comprising machine-executable instructions for execution by a processor configured for controlling an X-ray system. The X-ray system is configured for acquiring medical imaging data from a subject at least partially within an imaging zone. The X-ray system comprises a pilot tone system. The pilot tone system comprises a radio-frequency system comprising at least one transmit channel and at least one receive channel. The at least one transmit channel is configured for transmitting at least one pilot tone signal via at least one transmit coil. The at least one receive channel is configured for receiving pilot tone data via at least one receive coil.

Execution of the machine-executable instructions further causes the processor to transmit the at least one pilot tone signal by controlling the at least one transmit channel. Execution of the machine-executable instructions further causes the processor to acquire the pilot tone data by controlling the at least one receive channel to receive the pilot tone data. Execution of the machine-executable instructions further causes the processor to determine a motion state of the subject using the pilot tone data.

In another aspect the invention provides for a method of operating an X-ray system configured for acquiring medical imaging data from a subject at least partially within an imaging zone. The X-ray system comprises a pilot tone system. The pilot tone system comprises a radio-frequency system comprising at least one transmit channel and at least one receive channel. The at least one transmit channel is configured for transmitting at least one pilot tone signal via at least one transmit coil. The at least one receive channel is configured for receiving pilot tone data via at least one receive coil. The method comprises transmitting the at least one pilot tone signal by controlling the at least one transmit channel. The method further comprises acquiring the pilot tone data by controlling the at least one receive channel to receive the pilot tone data. The method further comprises determining a motion state of the subject using the pilot tone data.

Disclosed herein if a magnetic resonance imaging system that comprises a memory storing machine-executable instructions and pulse sequence commands that are configured for controlling the magnetic resonance imaging system to acquire magnetic resonance imaging data. The magnetic resonance imaging system further comprises a processor for controlling the magnetic resonance imaging system.

The magnetic resonance imaging system further comprises a pilot tone system. The pilot tone system comprises a radio-frequency system comprising at least one transmit channel and at least one receive channel. The multiple receive channel is configured for receiving pilot tone data via the at least one transmit channel. Execution of the machine-executable instructions cause the processor to transmit the at least one pilot tone signal by controlling the at least one transmit channel. Execution of the machine-executable instructions further cause the processor to acquire pilot tone data by controlling the at least one receive channel to receive the pilot tone data. Execution of the machine-executable instructions further cause the processor to determine a motion state of the subject using the multi-channel pilot tone data.

Execution of the machine-executable instructions further cause the processor to determine a current gradient pulse frequency using the pulse sequence commands. Execution of the machine-executable instructions further cause the processor to detect subject motion with a periodicity within a predetermined range of the current gradient pulse frequency using the pilot tone data. Alternatively, subject motion may be detected by determining or detecting a correlation between the gradient pulse frequency and the pilot tone data. Execution of the machine-executable instructions further cause the processor to provide a peripheral nerve stimulation warning signal if the subject motion is detected.

The matching of the subject motion and the gradient pulse frequency could be determined in several different ways. In one case a frequency is determined from the periodicity of the gradient pulse waveform. This can be used to define a bandwidth where if the motion is detected using the pilot tone data then the peripheral nerve stimulation warning signal is provided. There may also be a threshold level or predetermined threshold level that is set to determine if the peripheral nerve stimulation is significant enough to warrant the providing of the warning signal.

The processor used to control the pilot tone system could be integrated into a subject support also. For example, the pilot tone system could be completely contained within the subject support and be used to add PNS detection to existing magnetic resonance imaging systems by using the subject support with the integrated pilot tone system.

Further disclosed is that execution of the machine-executable instructions further causes the processor to perform any one of the following if the peripheral nerve stimulation warning signal is provided: select alternative pulse sequence commands, modify the pulse sequence commands, and cancel execution of the pulse sequence commands. All of these alternatives may be beneficial because they may be used to reduce or eliminate the peripheral nerve stimulation. This may result in a higher degree of comfort for the subject in the magnetic resonance imaging system as well as reduce motion and thereby improve the quality of any resulting magnetic resonance image.

Further disclosed the magnetic resonance imaging system further comprises a magnetic resonance imaging coil. The magnetic resonance imaging coil comprises the at least one pilot tone transmit coil and/or the at least one receive coil. In various examples the coils can be integrated into the subject support of the magnetic resonance imaging system as well as being integrated into the magnetic resonance imaging coils or antennas that are used.

Further disclosed is that the magnetic resonance imaging system is configured for acquiring magnetic resonance imaging data within an imaging frequency range. The multiple transmit channels are configured for transmitting the unique pilot tone signals outside of the imaging frequency range. For example the pilot tone signals may be at a frequency higher than what is used for the magnetic resonance imaging. This may be beneficial because it may enable the simultaneous use of the magnetic resonance imaging system to acquire magnetic resonance imaging data as well as monitor subject motion using the pilot tone signals.

Further disclosed is that the at least one transmit channel is multiple transmit channels. It should be noted that all of the embodiments which were disclosed related to the multi-channel pilot tone signals and the multi-channel pilot tone data may also be applied to the magnetic resonance imaging system. For example there may be multiple transmit and receive channels.

Further disclosed is that the at least one receive channel is multiple receive channels. This may be particularly beneficial because the distance from the subject to the receive channels is very sensitive in determining the signal strength. If there are multiple receive channels then it is easier to properly place the subject such that a receive channel will receive a pilot tone signal which can be interpreted as subject motion.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as an apparatus, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module" or "system. " Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer executable code embodied thereon.

A `computer-readable storage medium' as used herein encompasses any tangible storage medium which may store instructions which are executable by a processor of a computing device. The computer-readable storage medium may be referred to as a computer-readable non-transitory storage medium. The computer-readable storage medium may also be referred to as a tangible computer readable medium. In some embodiments, a computer-readable storage medium may also be able to store data which is able to be accessed by the processor of the computing device. Examples of computer-readable storage media include, but are not limited to: a floppy disk, a magnetic hard disk drive, a solid state hard disk, flash memory, a USB thumb drive, Random Access Memory (RAM), Read Only Memory (ROM), an optical disk, a magneto-optical disk, and the register file of the processor. Examples of optical disks include Compact Disks (CD) and Digital Versatile Disks (DVD), for example CD-ROM, CD-RW, CD-R, DVD-ROM, DVD-RW, or DVD-R disks. The term computer readable-storage medium also refers to various types of recording media capable of being accessed by the computer device via a network or communication link. For example a data may be retrieved over a modem, over the internet, or over a local area network. Computer executable code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wire line, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

`Computer memory' or 'memory' is an example of a computer-readable storage medium. Computer memory is any memory which is directly accessible to a processor. `Computer storage' or 'storage' is a further example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. In some embodiments computer storage may also be computer memory or vice versa.

A 'processor' as used herein encompasses an electronic component which is able to execute a program or machine executable instruction or computer executable code. References to the computing device comprising "a processor" should be interpreted as possibly containing more than one processor or processing core. The processor may for instance be a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed amongst multiple computer systems. The term computing device should also be interpreted to possibly refer to a collection or network of computing devices each comprising a processor or processors. The computer executable code may be executed by multiple processors that may be within the same computing device or which may even be distributed across multiple computing devices.

Computer executable code may comprise machine executable instructions or a program which causes a processor to perform an aspect of the present invention. Computer executable code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages and compiled into machine executable instructions. In some instances the computer executable code may be in the form of a high level language or in a pre-compiled form and be used in conjunction with an interpreter which generates the machine executable instructions on the fly.

Aspects of the present invention are described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It is understood that each block or a portion of the blocks of the flowchart, illustrations, and/or block diagrams, can be implemented by computer program instructions in form of computer executable code when applicable. It is further under stood that, when not mutually exclusive, combinations of blocks in different flowcharts, illustrations, and/or block diagrams may be combined.

A `user interface' as used herein is an interface which allows a user or operator to interact with a computer or computer system. A `user interface' may also be referred to as a `human interface device. ' A user interface may provide information or data to the operator and/or receive information or data from the operator. A user interface may enable input from an operator to be received by the computer and may provide output to the user from the computer. In other words, the user interface may allow an operator to control or manipulate a computer and the interface may allow the computer indicate the effects of the operator's control or manipulation. The display of data or information on a display or a graphical user interface is an example of providing information to an operator. The receiving of data through a keyboard, mouse, trackball, touchpad, pointing stick, graphics tablet, joystick, gamepad, webcam, headset, pedals, wired glove, remote control, and accelerometer are all examples of user interface components which enable the receiving of information or data from an operator.

A `hardware interface' as used herein encompasses an interface which enables the processor of a computer system to interact with and/or control an external computing device and/or apparatus. A hardware interface may allow a processor to send control signals or instructions to an external computing device and/or apparatus. A hardware interface may also enable a processor to exchange data with an external computing device and/or apparatus. Examples of a hardware interface include, but are not limited to: a universal serial bus, IEEE <NUM> port, parallel port, IEEE <NUM> port, serial port, RS-<NUM> port, IEEE-<NUM> port, Bluetooth connection, Wireless local area network connection, TCP/IP connection, Ethernet connection, control voltage interface, MIDI interface, analog input interface, and digital input interface.

A 'display' or `display device' as used herein encompasses an output device or a user interface adapted for displaying images or data. A display may output visual, audio, and or tactile data. Examples of a display include, but are not limited to: a computer monitor, a television screen, a touch screen, tactile electronic display, Braille screen,.

Cathode ray tube (CRT), Storage tube, Bi-stable display, Electronic paper, Vector display, Flat panel display, Vacuum fluorescent display (VF), Light-emitting diode (LED) displays, Electroluminescent display (ELD), Plasma display panels (PDP), Liquid crystal display (LCD), Organic light-emitting diode displays (OLED), a projector, and Head-mounted display.

Medical imaging data is defined herein as two- or three-dimensional data that has been acquired using a medical imaging scanner such as a X-ray system. A medical imaging scanner is defined herein as an apparatus adapted for acquiring information about the physical structure of a patient and construct sets of two dimensional or three dimensional medical image data. Medical image data can be used to construct visualizations which are useful for diagnosis by a physician. This visualization can be performed using a computer.

Magnetic Resonance (MR) imaging data is defined herein as being the recorded measurements of radio frequency signals emitted by atomic spins using the antenna of a Magnetic resonance apparatus during a magnetic resonance imaging scan. Magnetic resonance data is an example of medical imaging data. A Magnetic Resonance Imaging (MRI) image or MR image is defined herein as being the reconstructed two- or three-dimensional visualization of anatomic data contained within the magnetic resonance imaging data. This visualization can be performed using a computer.

<FIG> illustrates an example of an X-ray system. In this example the X-ray system is a computed tomography system or CT system. However, this system depicted in <FIG> may also be for example a system for acquiring two-dimensional X-ray images such as a conventional X-ray system or a fluoroscope. The X-ray system <NUM> further comprises a computed tomography gantry <NUM> which has a bore <NUM>. Within the bore is shown a subject <NUM> reposing on a subject support <NUM>. The computed tomography gantry <NUM> has an imaging zone <NUM> where medical imaging data can be acquired.

The X-ray system <NUM> is shown as having a pilot tone system <NUM>. The pilot tone system <NUM> comprises a radio-frequency system <NUM> that has at least one transmit channel <NUM> and at least one receive channel <NUM>. The at least one transmit channel <NUM> is connected to at least one transmit channel <NUM>. The at least one receive channel <NUM> is connected to at least one receive coil <NUM>. In this example the at least one transmit coil <NUM> and the at least one receive coil <NUM> are built into the subject support <NUM>. In other examples the coils <NUM>, <NUM> could be placed in alternative locations such as supports surrounding the subject <NUM> or even in some instances adjacent or on the subject.

The X-ray system <NUM> is shown as further comprising a computer <NUM>. The computer <NUM> comprises a processor <NUM>. The processor <NUM> is intended to represent one or more processor or processing cores. The processor <NUM> could also be distributed amongst multiple computer systems <NUM>. The processor <NUM> is shown as being connected to a hardware interface <NUM>. The hardware interface <NUM> enables the processor <NUM> to send and receive commands and data to other components of the X-ray system <NUM>. In some instances, the hardware interface <NUM> may for example be a network interface and enable the processor <NUM> to exchange data with other computer systems. The processor <NUM> is further shown as being connected to a user interface <NUM> and a memory <NUM>.

The memory <NUM> may be any combination of memory which is accessible to the processor <NUM>. This may include such things as main memory, cached memory, and also non-volatile memory such as flash RAM, hard drives, or other storage devices. In some examples the memory <NUM> may be considered to be a non-transitory computer-readable medium.

The memory <NUM> is shown as having machine-executable instructions <NUM>. The machine-executable instructions <NUM> enable the processor <NUM> to control the operation and function of the X-ray system. The memory <NUM> is shown as containing control commands <NUM>. The control commands may for instance be the specific commands for a particular imaging protocol to acquire medical imaging data <NUM>. The memory <NUM> is shown as containing medical imaging data <NUM> that was acquired by controlling the X-ray system with the control commands <NUM>. In some examples the control commands <NUM> may be incorporated into the machine-executable instructions <NUM>. The memory <NUM> is further shown as containing a pilot tone signal <NUM> that may be transmitted using the at least one transmit channel <NUM>.

The memory <NUM> is further shown as containing pilot tone data <NUM> that was received within the at least one receive channel <NUM> in response to transmitting the pilot tone signal <NUM>. In some examples the pilot tone signal <NUM> may be multiple unique pilot tone signals <NUM> that may for example be encoded differently as was disclosed previously. The pilot tone data <NUM> may likewise be multi-channel pilot tone data. The memory <NUM> is further shown as containing a motion state <NUM> that was derived from at least the pilot tone data <NUM>. The memory <NUM> may for example contain a motion state model <NUM>.

The motion state model <NUM> may for example take the pilot tone <NUM> as input and optionally the pilot tone signal <NUM> to determine the motion state <NUM>. The motion state model <NUM> may be implemented in different ways. In one example it may for example be a recurrent neural network, a convolutional neural network, a filter or other various models. The memory <NUM> is further shown as containing a medical image <NUM>. The medical image <NUM> was reconstructed from the medical imaging data <NUM>.

<FIG> shows a flowchart which illustrates a method of operating the X-ray system <NUM> of <FIG>. First in step <NUM> the X-ray system is controlled to acquire the medical imaging data <NUM>. As step <NUM> is performed steps <NUM>, <NUM>, and <NUM> are also performed. In step <NUM> the at least one pilot tone signal <NUM> is transmitted by controlling the at least one transmit channel <NUM>. Next in step <NUM> the pilot tone data <NUM> is acquired by controlling the at least one receive channel <NUM>. Finally, in step <NUM>, the motion state <NUM> of the subject <NUM> is determined using the pilot tone data <NUM>.

<FIG> illustrates an alternative method of operating the X-ray system <NUM> of <FIG>. The method illustrated in <FIG> is similar to the method illustrated in <FIG> with the addition of several additional steps. Steps <NUM>, <NUM>, <NUM>, <NUM> are performed as before. In this example step <NUM> may be performed after steps <NUM>, <NUM>, <NUM> are completely performed. Next in step <NUM> the medical image <NUM> is reconstructed using the medical imaging data <NUM>. Finally, in step <NUM> the reconstruction of the medical image <NUM> is corrected using the motion state <NUM>. This may for example be performed in different ways.

The motion state <NUM> could for example, if it is monitoring the heart or breathing phase, to divide the medical imaging data <NUM> into different bins and produce different images <NUM>. In other examples if the motion state <NUM> is more detailed various portions of the medical imaging data <NUM> may be corrected and using during the reconstruction of the medical image <NUM>. The method in <FIG> is an example of using the motion state <NUM> to perform retrospective correction of the medical image <NUM>.

<FIG> illustrates a further example of a method of operating the X-ray system <NUM> of <FIG>. The method in <FIG> is also similar to the method illustrated in <FIG>. Steps <NUM>, <NUM>, <NUM>, <NUM> are performed as before. In the example in <FIG> the determination of the motion state is done during the acquisition of the medical imaging data <NUM>. In step <NUM> the medical imaging data is used to modify the acquisition of the medical imaging data. This could for example be used for changing the alignment or region which is imaged as well as to gate the acquisition of the medical imaging data.

Disclosed is a motion detection method, which may use distinct frequency, multi frequency or broadband signal sources for x-ray or computed tomography (CT) scanners to correct for motion and synchronize the scanner for cardiac imaging using multi-RF reference signals. The proposed method can substitute ECG triggering or the additional data is used to improve reconstruction, reduce radiation dose and improve workflow for autonomous imaging.

CT scans may use a number of input parameters and proper scan preparation. Depending on body size, body weight, patient position and anatomy to be scanned a protocol is chosen and modified to fit the patient. Typically, these data have to be entered manually. Physiology parameters (e.g. necessary for triggering scans or gating) are typically measured using dedicated sensors. It has been demonstrated recently, that relevant parameters can be deduced from live video-streams of a camera observing the patient during scanning. During a CT procedure the patient is covered by clothes.

Consequently, camera images are of limited use.

Pilot Tones are a contactless, electromagnetic navigators that offers monitoring of motion independently of the MR or CT acquisition. Generation and acquisition of Pilot Tone signals, can be done using, already existing, system integrated parts, such as MR local coils which would be used for magnetic resonance imaging.

Potential benefits and/or applications may include one or more of the following:.

Examples may use pilot tone signals for X-Ray or CT scanner. In one example, the digital pilot signal antennas are located/integrated in the patient table.

For autonomous imaging using X-Ray the system may continuously monitor the 3D position. X-Radiation/imaging is triggered when there is no motion/movement detected or expected. The system allows body positioning during imaging or between imaging sequences or replacing a certain position.

For CT X-Ray beam is switched off during motion and system detects displacements from original position resulting in less dose.

In one example, the pilot tone signal may be monitored for active patient feedback. The patient/subject can reposition himself or the patient can align his position using a motion/position feedback monitor/sensor.

In another example, the 3D/4D information from the pilot tone data may be included in the reconstruction.

In another example separate transmit and receive antennas and digital transmitters and receivers are used to allow to translate motion into complex <NUM> D datasets.

In another example, the data can also feed a convolution neuronal network or a recurrent neuronal network.

In another example, the pilot tone system is used with one or more additional motion detection system such as an optical camera, a radar, or ultrasonic acoustic detection.

<FIG> illustrates an example of multi-channel pilot tone data <NUM>. The pilot tone data <NUM> shown shows a number of plots of individual pilot tone signals that were measured. Cardiac signals and breathing motion are well detected, but strongly depends on individual antenna channel.

In examples, Local antennas (at least one receive coil <NUM>) receive the narrow band signals (pilot tone signals). Each antenna feeds a preamplifier an individual software defined receiver. Complex signals are processed and the motion appears differently in the individual signals as changes in magnitude or phase. The data is further processed and the 3D/4D information is translated into motion parameters.

The data (pilot tone data) can also feed a convolution neuronal network or a recurrent neuronal network. A recurrent neural network (RNN) is a class of artificial neural network where connections between nodes form a directed graph along a sequence. This allows it to exhibit dynamic temporal behavior for a time sequence. Unlike feedforward neural networks, RNNs can use their internal state (memory) to process sequences of inputs (here different frequencies). This makes them applicable to tasks such as unsegmented, connected motion recognition or camera motion recognition.

<FIG> illustrates a functional diagram of an X-ray system <NUM>. In this example the X-ray system <NUM> comprises a CT or X-ray tube <NUM>. Adjacent to a head of the subject <NUM> are a number of pilot reference receivers or multiple receive channels <NUM>. Further away from the subject <NUM> is a single pilot reference transmitter which is a single transmit channel <NUM> or at least one transmit coil <NUM>. There may also be multiple transmit coils <NUM> also. There is a supplementary motion feedback monitor <NUM>. The motion feedback monitor <NUM> may be used to display to the subject <NUM> the current motion state and may help the subject <NUM> remain still. The X-ray system comprises an RF and SDR transceiver and feedback control which comprises the pilot tone system <NUM>. This pilot tone system provides data to a feedback patient monitor <NUM>. The feedback patient monitor <NUM> provides the image which is rendered by the motion feedback monitor <NUM>. The pilot tone system <NUM> also provides data to ECG triggering and breathing triggering <NUM>. The pilot tone system <NUM> also provides information to the reconstruction algorithm <NUM>. An artificial or machine learning module <NUM> may be used for aiding during the reconstruction <NUM> as well as be trained with the data that is received via the pilot tone system <NUM>.

<FIG> illustrates examples of a motion state <NUM> which can be derived from multi-channel pilot tone data <NUM>. <FIG> shows several position measurements that were used with multi-channel pilot tone data <NUM>. In the examples illustrated in <FIG> a simple model was used to determine the distance of a subject's head from multiple receive coils <NUM>. Plot <NUM> shows the position of a subject's head using this model. Plot <NUM> shows the direction of the subject's nose from the data in plot <NUM>. Likewise plot <NUM>' also shows a head position as measured using multiple receive coils. Plot <NUM>' shows a change in the subject's nose orientation.

<FIG> illustrates a simple example of how a set of pilot tone transmitters and receivers can be used to detect motion of the head. The images <NUM> and <NUM>' show a very simple head model in form of the vector pointing form the back of the head to the tip of the nose in the real coordinate system. The origin of the coordinate system denotes the isocenter of the CT scanner. The back of the head is assumed to be fix to the patient table and cannot move.

The images <NUM> and <NUM>' show a wire frame model of a <NUM>-node pilot tone system. The positions of the nodes were derived from the spatial distribution of the pilot tone transmitters and receivers around the subject's head.

The coordinate system in these images is zeroed once the patient is placed on the patient table. Any movement will now affect the signal strength and phase among the different pilot tone transmitters and receivers. In the given model, a signal increase is mapped to the wire frame model by increasing the distance of the corresponding wire frame node from the (virtual) origin.

As a result, the wire frame gets distorted. The kind of distortion is characteristic for the head movement, e.g. shaking the head will lead to a signal increase for certain pilot tone transmitters and receiver combinations while others encounter a decrease. This insight was used for the simplified head model. The position of the nose tip is calculated by the spatially weighted average of the signals of the <NUM> pilot tone nodes. In the given example the volunteer turned his head from middle position (<NUM>, <NUM>) to the right (negative y). In the wire frame model (<NUM>', <NUM>'), this this resulted in a tilt-like distortion. Accordingly, the head vector model moves its tip to negative y.

<FIG> illustrates an example of a magnetic resonance imaging system <NUM>. Reference numerals reused in this figure indicate features or components which are equivalent to previously described features or components. Previously described components may not necessarily be described again.

The magnetic resonance imaging system <NUM> comprises a magnet <NUM>. The magnet <NUM> is a superconducting cylindrical type magnet with a bore <NUM> through it. The use of different types of magnets is also possible; for instance it is also possible to use both a split cylindrical magnet and a so called open magnet. A split cylindrical magnet is similar to a standard cylindrical magnet, except that the cryostat has been split into two sections to allow access to the iso-plane of the magnet, such magnets may for instance be used in conjunction with charged particle beam therapy. An open magnet has two magnet sections, one above the other with a space in-between that is large enough to receive a subject: the arrangement of the two sections area similar to that of a Helmholtz coil. Open magnets are popular, because the subject is less confined. Inside the cryostat of the cylindrical magnet there is a collection of superconducting coils.

Within the bore <NUM> of the cylindrical magnet <NUM> there is an imaging zone <NUM> where the magnetic field is strong and uniform enough to perform magnetic resonance imaging. A region of interest <NUM> is shown within the imaging zone <NUM>. The magnetic resonance data that is acquired typically acquried for the region of interest. A subject <NUM> is shown as being supported by a subject support <NUM> such that at least a portion of the subject <NUM> is at least partially within the imaging zone <NUM> and the region of interest <NUM>.

Within the bore <NUM> of the magnet there is also a set of magnetic field gradient coils <NUM> which is used for acquisition of preliminary magnetic resonance data to spatially encode magnetic spins within the imaging zone <NUM> of the magnet <NUM>. The magnetic field gradient coils <NUM> connected to a magnetic field gradient coil power supply <NUM>. The magnetic field gradient coils <NUM> are intended to be representative. Typically magnetic field gradient coils <NUM> contain three separate sets of coils for spatially encoding in three orthogonal spatial directions. A magnetic field gradient power supply supplies current to the magnetic field gradient coils. The current supplied to the magnetic field gradient coils <NUM> is controlled as a function of time and may be ramped or pulsed.

Within the bore <NUM> of the magnet <NUM> is a magnetic resonance imaging antenna <NUM>. The magnetic resonance imaging antenna <NUM> is shown as comprising the multiple transmit coils <NUM> and the multiple receive coils <NUM>. The magnetic resonance imaging antenna <NUM> also comprises a number of radio-frequency coils <NUM> which are used for performing the magnetic resonance imaging. The radio-frequency system <NUM> is also connected to the radio-frequency coil <NUM>. The arrangement shown in <FIG> enables the acquisition of magnetic resonance imaging data simultaneous with the use of the pilot tone system. In other examples the radio-frequency coils <NUM> may also function as the multiple transceiver coils <NUM> and/or multiple receive coils <NUM>.

The radio frequency coils <NUM> may also be referred to as a channel or antenna. The magnetic resonance antenna <NUM> is connected to a radio frequency system <NUM>. The magnetic resonance antenna <NUM> and radio frequency system <NUM> may be replaced by separate transmit and receive coils and a separate transmitter and receiver. It is understood that the magnetic resonance antenna <NUM> and the radio frequency system <NUM> are representative. The magnetic resonance antenna <NUM> is intended to also represent a dedicated transmit antenna and a dedicated receive antenna. Likewise the system <NUM> may also represent a separate transmitter and receivers. The magnetic resonance antenna <NUM> may also have multiple receive/transmit elements and the radio frequency system <NUM> may have multiple receive/transmit channels. For example if a parallel imaging technique such as SENSE is performed, the radio-frequency system <NUM> could have multiple coil elements.

The radio frequency system <NUM> and the gradient controller <NUM> are shown as being connected to the hardware interface <NUM> of the computer system <NUM>.

The memory <NUM> is shown as containing machine executable instructions <NUM>. The machine executable instructions <NUM> enable the processor to control the magnetic resonance imaging system <NUM> as well as perform various data processing and image processing tasks. The memory <NUM> is further shown as containing pulse sequence commands <NUM> instead of control commands. The pulse sequence commands <NUM> are commands or data which may be converted into such commands which are used for controlling the operation of the magnetic resonance imaging system <NUM>. The memory <NUM> is further shown as containing magnetic resonance imaging data <NUM> that was acquired by controlling the magnetic resonance imaging system with the pulse sequence commands <NUM>.

The memory <NUM> is further shown as containing a magnetic resonance image <NUM> that was reconstructed from the magnetic resonance imaging data <NUM>. The motion state <NUM> may be used in different ways. For example, the motion state <NUM> may be used for gating the acquisition of the magnetic resonance imaging data <NUM> as well as being used in the reconstruction of the magnetic resonance image <NUM>.

The memory <NUM> may further contains a time-dependent gradient pulse frequency <NUM> that was determined from the pulse sequence commands <NUM>. The motion state <NUM> may be compared with the time-dependent gradient pulse frequency <NUM> to determine if there is peripheral nerve stimulation in the subject <NUM>. If the motion state correlates above a certain degree or above a certain amplitude within the same frequency range as motion detected, there may be a peripheral nerve stimulation warning signal <NUM> that is generated.

<FIG> shows a flowchart which illustrates a method of operating the magnetic resonance imaging system <NUM> of <FIG>. First in step <NUM> the magnetic resonance imaging system <NUM> is controlled with the pulse sequence commands <NUM> to acquire the magnetic resonance imaging data <NUM>. As step <NUM> is performed steps <NUM>, <NUM>, and <NUM> are also performed.

Next in step <NUM>, the at least one pilot tone signals <NUM> are transmitted by controlling at least a portion of the multiple transmit channels <NUM>. Next in step <NUM>, the pilot tone data <NUM> is acquired by controlling the at least one receive channel <NUM>.

Then in step <NUM>, the motion state <NUM> of the subject <NUM> is determined using the pilot tone data <NUM>. This could for example be performed using a recurrent neural network. In a recurrent neural network both the pilot tone data <NUM> and the pilot tone signals <NUM> could be input. In other cases, the motion state <NUM> can be determined from the multi-channel pilot tone data <NUM> alone. For example, the periodic breathing or heart motion of a subject <NUM> may cause the pilot tone data <NUM> to have a frequency component which is equal to or about equal to the heart rate and/or breathing rate. The heart and/or breathing motion may therefore be determined by the pilot tone data <NUM> alone.

In step <NUM>, the time-dependent gradient pulse frequency <NUM> is determined using the pulse sequence commands <NUM>. Next in step <NUM> subject motion with a periodicity within a predetermined range or correlation of the time-dependent gradient pulse frequency is detected using the motion state <NUM>. For example, the motion state can be compared to the time-dependent gradient pulse frequency <NUM> or there can for example be a correlation that is calculated on the fly. Finally, in step <NUM> the peripheral nerve stimulation warning signal <NUM> is generated if the subject motion is detected.

Another application is the detection of Peripheral Nerve Stimulation during magnetic resonance imaging. It is possible to use the pilot tone signals acquired by the receive coil array and correlate it with gradient waveform signal to detect and trigger for PNS detection. The full matrix of the receive coil is measured and correlated with the gradient waveform to detect PNS.

If certain thresholds are reached, the MR sequence is adapted to reduce PNS. The sequence automatically adapts for patient comfortable parameters. Measure: change readout direction, change sequence, gradient strength, reposition patient. The data (multi-channel pilot tone data) can also feed a convolution neuronal network or a recurrent neuronal network.

Strong gradients applied during MRI exams can trigger peripheral nerve stimulation resulting in motion of muscle fibers or whole muscles.

In general, PNS induced effects on the Pilot tone signals are expected to be lower than that of e.g. breathing. Due to this, and to distinguish from other motion the Pilot tone signals acquired by the receive coil may be correlated with the gradient waveform.

If certain thresholds are reached, the MR sequence is adapted to reduce PNS. The sequence automatically adapts for patient comfortable parameters. Possible measures are to change.

Additional supplementary data may also be used such as optical, camera, radar, and ultrasonic acoustic detection.

Current MRI scanners feature a low-power transmit path independent from the transmit chain of the body coil for calibration purposes. Here, a small off-resonant coil is attached to the RF screen to the body coil. The transmit power for this coil was adjusted so that RF signals are in the same order of that originating from the spin system. Standard MRI coils are used for reception.

Pilot tone measurements can be interleaved or merged with the MR sequence. Tests showed that this setup allows to detect motion induced by breathing. Further tests were performed to increase the sensitivity of the set-up.

The <FIG> above shows an example of pilot tone magnitude signals. Additional information can be gained when simultaneously observing the phase of the acquired signals. The ideal position of the off-resonant coil was determined in tests to provide most sensitive outcome for breathing and heart motion. In the given experiments, the best setup was to place the coil on top of the patient's sternum. The acquisition of the pilot tone using all available RX coils allows for (limited) spatial sensitivity.

This insight can be used to distinguish different motion types.

It is likely that for PNS detection another position is more suitable, e.g., close to the long muscles of the patients back.

The data (multi-channel pilot tone data) can also feed a convolution neuronal network or a recurrent neuronal network. A recurrent neural network (RNN) is a class of artificial neural network where connections between nodes form a directed graph along a sequence. This allows it to exhibit dynamic temporal behavior for a time sequence. Unlike feedforward neural networks, RNNs can use their internal state (memory) to process sequences of inputs (here different frequencies). This makes them applicable to tasks such as unsegmented, connected motion recognition or camera motion recognition (see Fig13 below).

<FIG> illustrates a software algorithm and functional building blocks of a system that may for example be incorporated into a magnetic resonance imaging system such as the medical system <NUM> illustrated in <FIG>. Block <NUM> represents the pilot tone system and the radio-frequency reference coil array. Block <NUM> represents the gradient waveform from the pulse sequence commands. Block <NUM> represents a software component that is a peripheral nerve stimulation detector and/or correlator <NUM>. The detector or correlator <NUM> is able to take information about the gradient waveform <NUM> and information from the pilot tone data <NUM> to detect if there is peripheral nerve stimulation. This is then fed into the controller <NUM>.

For example, the controller <NUM> may be equivalent to the processor <NUM>. This information could then be forwarded or processed from the controller and fed to a neural network <NUM> that may for example be equivalent to a neural network. The controller <NUM> can use a detection of the peripheral nerve stimulation for example to modify behavior of the gradient amplifier <NUM>, and possibly even modify the behavior or change the pulse sequence commands <NUM>. This data may also be provided to a peripheral nerve stimulation monitor <NUM>. This for example may be provided via the user interface <NUM>.

The following scheme illustrated in <FIG> shows how the Pilot Tone data may be processed and used.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claim 1:
An X-ray system (<NUM>, <NUM>) configured for acquiring medical imaging data (<NUM>) from a subject (<NUM>) at least partially within an imaging zone (<NUM>), wherein the X-ray system comprises:
- a memory (<NUM>) storing machine executable instructions (<NUM>);
- a processor (<NUM>) configured for controlling the X-ray system; and
- a pilot tone system (<NUM>), characterized in that the pilot tone system comprises a radio frequency system (<NUM>) comprising multiple transmit channels (<NUM>) and multiple receive channel (<NUM>), wherein the multiple transmit channels are configured for transmitting multi-channel pilot tone signals (<NUM>) via multiple transmit coils (<NUM>); wherein the multiple receive channels are configured for receiving multi-channel pilot tone data (<NUM>) via multiple receive coils (<NUM>);
wherein execution of the machine executable instructions causes the processor to:
- transmit (<NUM>) the multi-channel pilot tone signals by controlling the multiple transmit channels;
- acquire (<NUM>) the multi-channel pilot tone data by controlling the multiple receive channels; and
- determine (<NUM>) a motion state (<NUM>, <NUM>, <NUM>', <NUM>, <NUM>') of the subject using the multi-channel pilot tone data.