Method and system for monitoring a motion of a subject, and corresponding computer program product

Abstract

The disclosure relates to a method for monitoring a motion of a subject, as well as to a corresponding system and computer program product. As part of the method, a monitoring signal is emitted towards a corresponding receiver. The motion of the subject is then detected based on a change in the received monitoring signal. Therein, the monitoring signal is emitted using a spread-spectrum technique and/or using an M-to-N and multi-antenna emitter-receiver system with a set of M transmitting antennas and a set of N receiving antennas.

Claims

1. A method for monitoring a motion of a subject, the method comprising: generating a monitoring signal; coupling out a part of the monitoring signal to provide a reference monitoring signal as intended for transmission; emitting, by an emitter, a respective remaining part of the monitoring signal towards a corresponding receiver; receiving, by the corresponding receiver, the emitted monitoring signal to provide a received monitoring signal; comparing, by a signal processing unit, the reference monitoring signal and the received monitoring signal; and detecting, by the signal processing unit, the motion of the subject based on a change between the reference monitoring signal and the received monitoring signal, wherein the respective remaining part of the monitoring signal is emitted toward the corresponding receiver: using a spread-spectrum technique, using an M-to-N multi-antenna emitter-receiver system with a set of M transmitting antennas and a set of N receiving antennas, or a combination thereof.

2. The method of claim 1, wherein a phase and an amplitude of the emitted monitoring signal are determined as a reference for the detecting of the motion of the subject.

3. The method of claim 1, wherein, when the monitoring signal is emitted using the spread-spectrum technique, the monitoring signal is generated through modulation with a predetermined pseudo-random spreading code.

4. The method of claim 1, wherein the motion monitoring is combined with a magnetic resonance imaging of the subject, and wherein a frequency of the monitoring signal is set to overlap a frequency band of a magnetic resonance imaging signal.

5. The method of claim 4, wherein a coil used for the magnetic resonance imaging of the subject is also used for the emitting of the monitoring signal, the receiving of the monitoring signal, or a combination thereof.

6. The method of claim 5, wherein the monitoring signal is emitted by at least one transmitting antenna, wherein the monitoring signal is received by at least one magnetic resonance local coil, wherein the at least one transmitting antenna is separate from at least one magnetic transmitting coil.

7. The method of claim 6, wherein the magnetic resonance local coil comprises an array of multiple spatially distributed magnetic resonance local coils.

8. The method of claim 4, wherein the monitoring signal is uniformly spread out over a predetermined frequency band using the spread-spectrum technique, wherein a signal level of the monitoring signal is set so that, at each frequency, the signal level is at or below a noise level of a received magnetic resonance echo signal, and wherein the received monitoring signal is separated from the received magnetic resonance echo signal through signal averaging over at least one time period that is longer compared to a measurement period defined in a respective MR imaging sequence.

9. The method of claim 8, wherein the at least one time period is at least 100 milliseconds.

10. The method of claim 4, wherein the received monitoring signal and a magnetic resonance echo signal are measured together and, for separating out the received monitoring signal, a weighting factor for minimizing a correlation between two signal parts is determined and applied to the measured signal.

11. The method of claim 4, wherein a signal reception chain through which a magnetic resonance echo signal is received and processed is continuously or regularly calibrated during the magnetic resonance imaging and the motion monitoring based on detected variations in the received monitoring signal that are not associated with the motion of the subject.

12. The method of claim 4, wherein a length of a predetermined pseudo-random spreading code used to spread out the monitoring signal as part of the spread-spectrum technique is set so that the monitoring signal is spread out across a full bandwidth of a magnetic resonance imaging receiving coil or coils or a full width of the frequency band used for the magnetic resonance imaging.

13. The method of claim 4, wherein the monitoring signal is emitted and received at least between pulses of a magnetic resonance imaging sequence that is applied for imaging the subject.

14. The method of claim 1, wherein the motion monitoring using the M-to-N multi-antenna emitter-receiver system is combined with a magnetic resonance imaging of the subject, and wherein a frequency of the monitoring signal is set to be outside of a frequency band used for the magnetic resonance imaging.

15. The method of claim 1, wherein the monitoring signal is emitted using the spread-spectrum technique and using multiple emitters of the M-to-N multi-antenna emitter-receiver system at a same time, and wherein different modulations that are orthogonal with respect to each are used for emitting the monitoring signal through the multiple emitters.

16. The method of claim 15, wherein the different modulations that are orthogonal with respect to each other are based on orthogonal spreading codes.

17. A system configured to monitor a motion of a subject, the system comprising: an emitter configured to emit a part of a monitoring signal to provide an emitted monitoring signal, wherein a remaining part of the monitoring signal is configured to be coupled out to provide a reference monitoring signal as intended for transmission; a receiver configured to receive the emitted monitoring signal to provide a received monitored signal; and a signal processor configured to compare the reference monitoring signal and the received monitoring signal detect the motion of the subject based on a change between the reference monitoring signal and the received monitoring signal, wherein the part of the monitoring signal is configured to be emitted towards the corresponding receiver: (a) using a spread-spectrum technique, (b) using an M-to-N multi-antenna emitter-receiver system with a set of M transmitting antennas and a set of N receiving antennas, or a combination thereof.

18. A non-transitory computer program product comprising instructions, wherein the instructions, when executed by a processor, cause a system to: emit a part of a monitoring signal towards a corresponding receiver to provide an emitted monitoring signal, wherein a remaining part of the monitoring signal is coupled out to provide a reference monitoring signal as intended for transmission; receive, by the corresponding receiver, the emitted monitoring signal to provide a received monitoring signal; compare, by a signal processing unit, the reference monitoring signal and the received monitoring signal; and detect, by the signal processing unit, a motion of a subject based on a change between the reference monitoring signal and the received monitoring signal, wherein the part of the monitoring signal is emitted towards the corresponding receiver: using a spread-spectrum technique, using an M-to-N multi-antenna emitter-receiver system with a set of M transmitting antennas and a set of N receiving antennas, or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features, and details of the present disclosure derive from the following description of embodiments as well as from the drawings. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone may be employed not only in the respectively indicated combination but also in other combinations or taken alone without leaving the scope of the present disclosure. In the drawings:

(2) FIG. 1 schematically illustrates an example of a flow chart for a method for monitoring a motion of a subject.

(3) FIG. 2 schematically illustrates an example of a system for carrying out the method.

(4) The examples described below refer to embodiments of the present disclosure. Therein, individual components and process acts of the embodiments each constitute individual, independent features of the present disclosure that may further develop the disclosure independently of each other as well as in combinations not explicitly described. The described embodiments may be further developed or supplemented by features, components, and/or acts already described above.

DETAILED DESCRIPTION

(5) FIG. 1 schematically depicts an example for a flow chart 1 for a method for monitoring a motion of a subject. This method is illustrated here by process acts S1 to S10 and program paths P1 to P6, both of which may represent corresponding instructions, routines, or program modules of a corresponding computer program or computer program product. This computer program and therefore the corresponding method may be carried out by a system which is schematically illustrated in FIG. 2 as an MRI device 2. Below, the method, (the flow chart 1), will be explained with reference to FIG. 1 and FIG. 2.

(6) The MRI device 2 is presently configured to image a patient 3 based on a magnetic resonance imaging technique. Here, the patient 3 serves as the subject whose motion is to be monitored using the mentioned method. In particular, the motion of the patient 3 shall be monitored while magnetic resonance imaging data (MR data) of the patient 3 is acquired by the MRI device 2. The MRI device 2 presently includes an imaging system 4, which is also only schematically represented here. The imaging system 4 includes at least a body coil 5 surrounding the patient 3 and configured to generate a magnetic field in a volume occupied by the patient 3. The imaging system 4 also includes multiple local coils 6 which are presently arranged in close proximity to the patient 3, in particular on and under him. Furthermore, the imaging system 4 also includes a signal processing unit 7, which is connected to some or all of the coils 5, 6.

(7) The signal processing unit 7 presently includes a processor 8 and connected thereto a data store 9, and is configured to process MR echo signals, e.g., MR data received or measured by the local coils 6. The signal processing unit 7 may also be configured to control the body coil 5 or a sequence of RF-pulses transmitted therewith as part of the magnetic resonance imaging process. Respective MR images of the patient 3 generated or reconstructed from the MR data by the signal processing unit 7 may be displayed using a connected display device 11.

(8) While the signal processing unit 7 is represented as a single unit this is to be understood as purely exemplary and schematically. In a practical implementation, the signal processing unit 7 may be divided into or include several individual units for the multiple functions or purposes of the signal processing unit 7 as described herein.

(9) The data store 9 may contain a computer program that may be executed by the processor 8 and that includes instructions representing the method for monitoring the motion of the patient 3, (e.g., the flow chart 1), to cause the processor 8 or the signal processing unit 7 or the MRI device 2 to execute the method.

(10) In process act S1, at least one pseudo-random spreading code is provided. Multiple orthogonal spreading codes may be provided. The spreading codes may be stored in or loaded into the data store 9.

(11) In process act S2, a spread-spectrum technique is performed to generate a spectrally spread out monitoring signal based on the provided pseudo-random spreading code. If multiple spreading codes are provided, multiple different corresponding modulations may be performed to generate multiple different monitoring signals or multiple differently modulated instances of the monitoring signal. This may be automatically performed by the signal processing unit 7.

(12) As indicated by a program path P1, a part of each monitoring signal is coupled out in process act S3 as a reference representing the original or unchanged monitoring signal as intended for transmission. Respective remaining parts of the monitoring signals are transmitted or emitted in process act S4 by dedicated transmission antennas 10. These transmission antennas 10 are presently integrated into or arranged in the body coil 5 but are actually individually controllable devices. Each of the transmission antennas 10 is used to emit a differently modulated one of the monitoring signals with orthogonal modulations towards the patient 3 and the local coils 6. The monitoring signals may be continuously or regularly emitted, which is indicated here by a looping program path P2.

(13) In process act S5, the parts of the monitoring signal is transmitted by the transmission antennas 10 are received by the local coils 6. At the same time, the patient 3 might be moving, (e.g., due to a breathing motion), which influences the received monitoring signal. Corresponding to the continuous or regular transmission of the monitoring signal, the signals may also be received continuously or regularly as indicated by a looping program path P3.

(14) The monitoring signals received by the local coils 6 are provided to the signal processing unit 7 via a wired connection. In process act S6, the signal processing unit 7 analyzes the received monitoring signals to determine a change corresponding to or indicating the motion of the patient 3.

(15) For this purpose, the monitoring signals received by the local coils 6 may be compared to the part of the original monitoring signal that was coupled out in process act S3. This coupled out part may be kept in the signal processing unit 7 or may be coupled out and the transmission antennas 10 and directly provided to the signal processing unit 7 through a wired connection without being subjected to any potentially signal changing influence of the patient 3 or his motion.

(16) In process act S7, it is determined if a detected change in the monitoring signal is consistent with possible motions of the patient 3. These possible motions and/or corresponding changes in the monitoring signals, (e.g., in terms of an amount of change, a speed of change, and/or a spatial distribution or a pattern of change), may be experimentally (pre-)determined and provided as input data for the signal processing unit 7. If it is determined that the detected change is inconsistent with a motion of the patient 3 or inconsistent with being caused by the motion of the patient 3, the flow chart 1 follows program path P4 to process act S8.

(17) In process act S8, the detected change might be discarded or stored as an indication of a possible error for later analysis. As indicated by program path P5, the method may then continue to detect any additional subsequent changes in the monitoring signals, because they may be continuously or regularly received or recorded. If at one point or in one iteration of process act S7 it is determined that a detected change in the monitoring signal is consistent with a motion of the patient 3 or with being caused by the motion of the patient 3, the flow chart 1 follows program path P7 to process act S9.

(18) In process act S9, the corresponding motion of the patient 3 is determined by the signal processing unit 7.

(19) In process act S10, the determined motion or corresponding motion data characterizing or describing this motion may be provided by the signal processing unit 7 or one of its functions or modules as an output, (e.g., to another function, module, subroutine, or device). For example, the motion data may be provided to an image reconstruction module of the signal processing unit 7 that is configured to reconstruct a motion-compensated MR image of the patient 3 based on the received MR data and the determined motion of the patient 3.

(20) While the method for monitoring or detecting the motion of the patient 3 has he been described in connection with magnetic resonance imaging of the patient 3, the method may also be performed independently thereof. It is also to be understood that the signal processing unit 7 may (depending on an implementation of the described method) be configured to separate different frequency bands used for the monitoring signals and/or the RF-pulses or MR echo signals, and/or be configured to separate corresponding different signal portions when overlapping frequencies or frequency bands are used. In particular, the concept of co-transmitting the monitoring signal in the frequency band used for the magnetic resonance imaging and using subtraction coefficients (wk or time-dependent: wk(t)) determined for separating signals and thereby cleaning or correcting the MR data or corresponding MR image as useful information, (e.g., for determining the motion of the patient 3), may analogously be used in or applied to other applications. Also, the broadband spreading out of the monitoring signal may enable additional ways of handling, using, or processing the monitoring signal for different types of applications and situations.

(21) In summary, the described examples show how a patient motion or movement may be monitored by a spread-spectrum modulated test signal and corresponding transmission and receiving antennas or arrays.

(22) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

(23) While the disclosure has been illustrated and described in detail with the help of the disclosed embodiments, the disclosure is not limited to the disclosed examples. Other variations may be deducted by those skilled in the art without leaving the scope of protection of the claimed disclosure.