Patent ID: 12186105

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the scope of the appended claims. In the embodiments, a plurality of features are described. However, not all the plurality of features are necessarily essential to the present invention, and the plurality of features may arbitrarily be combined. In addition, the same reference numerals denote the same or similar configurations in the accompanying drawings, and a repetitive description will be omitted.

Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.

The present invention relates to a technique for detecting high-frequency reflections incident on the antenna installed on the subject, and generating and acquiring information on a state and a behavior of the subject, and can be regarded as a subject information acquisition apparatus, a control method thereof, or a subject information acquisition method or a signal processing method. The present invention can also be regarded as a program for causing an information processing apparatus including hardware resources such as a CPU to execute the subject information acquisition method and the signal processing method, or as a storage medium storing such a program. Furthermore, the invention can be regarded as a magnetic resonance imaging apparatus including these.

First Embodiment

Configuration of Subject Information Acquisition Apparatus

FIG.1is a diagram schematically showing a configuration of a subject information acquisition apparatus according to a first embodiment. The subject information acquisition apparatus1includes an antenna110and an apparatus main body120constituting the subject information acquisition apparatus1.

The antenna110is a configuration of an antenna apparatus. In the present embodiment, since the subject information acquisition apparatus1in principle has one antenna, the antenna apparatus is configured by a single antenna. In the embodiment described later, the subject information acquisition apparatus1may include a plurality of antennas, and in this case, the antenna apparatus is configured by a plurality of antennas. The antenna apparatus (irradiation unit) irradiates the subject with a high-frequency signal from at least one antenna.

The measurement target of the subject information acquisition apparatus1is a subject100, and the subject information acquisition apparatus1mainly aims to acquire movement of the subject100due to heart rate, respiration, or the like. As the subject100, for example, a site of a living body, specifically, a heart, a lung, an abdomen in a human body or an animal, or a vicinity thereof, is assumed. However, the present invention is not necessarily limited to such sites, and any site where the movement of the subject100occurs can be targeted.

FIG.2is a diagram schematically showing the connection relationship of the constituent elements of the apparatus main body120. Each component of the apparatus main body120is interconnected via a bus200as inFIG.2. Each component of the apparatus main body120can exchange information via the bus200. The signal processing circuit160(signal processing unit) functions as a control unit to control the operation of each component of the apparatus main body120via the bus200. Further, the signal processing circuit160holds a program in which a subject information acquisition method to be described later is recorded in an internal memory, and the signal processing circuit160can read the program from the memory, control each component of the apparatus main body120, and cause the subject information acquisition apparatus1to execute the subject information acquisition method.

A power amplifier (PA)142or a directional coupler (DC)143, and the antenna110for which settings are seldom changed after operating characteristics have been set and for which operation is passive are not explicitly described inFIG.2, but in the case where active control by the apparatus main body120is required, these may be connected to the bus200.

Antenna110

The antenna110is disposed close to the subject100, which is a human body. The antenna110does not need to be directly attached to the skin of the subject100as in the case of an electrode of an electrocardiometer, and may be placed on the clothing of the subject100, for example. AlthoughFIG.1shows an example in which the antenna110is disposed on the chest of the subject100who is lying on a top board101of the bed, a posture of the subject when the antenna110is arranged and the site of the subject where the antenna110is disposed are not limited to the example shown inFIG.1. For example, the antenna110may be disposed on the chest or the back of the subject in a standing position, or may be disposed on the chest or the back of the subject in a sitting position, for example, during driving of a vehicle.

Apparatus Main Body120

The apparatus main body120includes, as components, a high-frequency signal generator130, a transmission circuit140, a coupling amount detecting circuit150, and a signal processing circuit160.

High-Frequency Signal Generator130

The high-frequency signal generator130(signal generation unit) generates a high-frequency signal of continuous waves based on a predetermined frequency. The frequency of the high-frequency signal is not particularly limited, but a frequency, such as one in the VHF band and UHF band, for example, is selected using the dimensions and the like of the antenna110. For example, it is possible to set different frequencies in the high-frequency signal generator130(signal generation unit) and generate a high-frequency signal corresponding to the respective frequencies.

Transmission Circuit140

The transmitting circuit140, after causing the high-frequency signal generated by the high-frequency signal generator130to pass through a band-pass filter (BPF)141, amplifies the signal to a predetermined power by a power amplifier (PA)142, and outputs the result to the antenna110via a directional coupler (DC)143.

Coupling Amount Detecting Circuit150

The coupling amount detecting circuit150(coupling amount detecting unit) has a function of detecting a coupling amount of near-field coupling due to an electric field between the subject100and the antenna110, for example, and is configured to include a band-pass filter (BPF)151, a low-noise amplifier (LNA/AGC)152with an automatic-gain adjusting function, and, a wave detection circuit153. The coupling amount detecting circuit150functions as an acquisition unit, and acquires a plurality of detection signals based on a reflection signal or a transmission signal when the subject is irradiated with a high-frequency signal corresponding to respective frequencies from at least one antenna110. Then, the coupling amount detecting circuit150detects the coupling amount of the near-field coupling due to the electric field between the antenna110and the subject100based on the acquired detection signal.

The high-frequency signal generator130, the transmission circuit140, and the coupling amount detecting circuit150, for example, can be mounted on a printed circuit board which is housed in a single casing.

The high-frequency signal outputted from the directional coupler143of the transmission circuit140is inputted to the antenna110, but a portion of the high-frequency signal is not directed to the subject100and bounces back (is reflected) at the input terminal of the antenna110, returns to the directional coupler143, and branches into the coupling amount detecting circuit150.

The coupling amount detecting circuit150measures the magnitude of the reflection signal from the antenna110by detecting the signal (reflection signal) output from the branch terminal of the directional coupler143by the wave detection circuit153. Here, the magnitude of the reflection signal varies in accordance with the distance between the antenna110and the subject100, and a change in the state of the subject100included in the electric field created by the antenna110, such as a change in the shape or a change in the composition of inside or outside of the subject due to heartbeat or respiration. For example, as the subject100and the antenna110approach each other, the subject100absorbs a large amount of power from the antenna110, and the reflected power decreases (i.e., the coupling amount of the near-field coupling becomes large).

On the other hand, when the subject100and the antenna110are separated from each other, the opposite occurs, i.e., the coupling amount of the near-field coupling becomes small. That is, the coupling amount detecting circuit150detects the coupling amount of the near-field coupling based on the magnitude of the reflection signal.

Although the above describes a configuration in which the reflection signal of the antenna110is inputted to the coupling amount detecting circuit150by the directional coupler143, but configuration may be taken to make the antenna110a transmission-only antenna, and have a reception-only antenna (not shown) in addition to the antenna110, and to input the output (transmitted signal) of the reception-only antenna to the band-pass filter151. In this case, configuration may be such that the directional coupler143is removed from the configuration, and the output of the reception-only antenna (transmitted signal) may be configured to be inputted to the band-pass filter151. As shown inFIG.1, the reception-only antenna may be disposed on the same side as the antenna110with respect to the front side of the subject100, or may be disposed on the back side of the subject100(e.g., inside the top board101of the bed). Similar to the case of the reflection signal, the magnitude of the transmission signal changes in accordance with a change in the distance between the subject100and the two antennas and a change in the state of the subject100in the electric field between the two antennas. That is, the coupling amount detecting circuit150detects the coupling amount of the near-field coupling based on the magnitude of the transmission signal. Thereafter, the signal by which the reflection signal or transmitted signal is detected is referred to as a detection signal.

Also, in the present invention, it is possible to use a reflection signal that reflects back from the input terminal and a transmission signal between a plurality of antennas among the high-frequency signals inputted to the input terminal of the antenna110. In the case of using the transmission signal, there is the possibility that the electromagnetic waves that propagate through the subject100will be detected as a result, but the frequency characteristics of the antenna110change with the distance between the subject100and the antenna110.

Note that there are various methods for detecting the change in the state of the subject100of the present invention, and there is no limitation to the embodiment above.

Signal Processing Circuit160

The signal processing circuit160has a displacement detection circuit161(displacement detecting unit) and a signal selection circuit162(signal selection unit). The signal processing circuit160is typically configured by an element such as a CPU, a GPU, or an A/D converter, a circuit such as an FPGA, an ASIC, or the like. Further, the signal processing circuit160may be configured as a dedicated printed circuit board having a processor, or may be configured as an information processing apparatus such as a personal computer or a tablet terminal device having a display. The signal processing circuit160may be such that it is not only composed of only one element or circuit, but rather a plurality of elements and circuits. In addition, any of the elements or circuits may execute the respective processes performed in the subject information acquisition method. Incidentally, the signal processing circuit160has a non-transitory recording medium, and each process performed in the subject information acquisition method can be stored as a program that the signal processing circuit160executes itself.

Displacement Detection Circuit161

The displacement detection circuit161extracts a signal (displacement signal) corresponding to a predetermined movement of the subject100from the detection signal detected by the wave detection circuit153based on the coupling amount of the near-field coupling (for example, a change in the coupling amount of the near-field coupling). The displacement signal extracted by the displacement detection circuit161is, for example, a signal corresponding to movement of the subject100due to respiration (respiration signal), a signal corresponding to movement of the subject100due to heartbeat (heart-rate signal), a signal corresponding to blinking, a signal corresponding to nodding, a signal corresponding to convulsion, or the like. As a process of extracting these signals (displacement signals), the displacement detection circuit161can use Fourier transform, short-time Fourier transform, wavelet transform, an infinite impulse response filter, a finite impulse response filter, a Kalman filter, principal component analysis, independent component analysis, a neural network or the like.FIG.3shows an example of the detection signal detected by the wave detection circuit153, i.e., the input signal to the displacement detection circuit161, and the respiration signal and the heart-rate signal are extracted from the detection signal as displacement signals.

The signal processing circuit160may display an extracted displacement signal as a waveform on a display or the like, or may acquire and display a respiration rate, a respiration cycle, a heart rate, a heartbeat cycle, or the like by analyzing the displacement signal. Further, the signal processing circuit160may detect the presence or absence of an abnormality in respiration or heartbeat from a waveform, a respiration rate, a heart rate, or the like. Similarly, blinking, nodding, convulsions, and the like of the subject100may be detected. Based on the detected information of the subject100, the signal processing circuit160can control the apparatus for inspecting the subject100to synchronize with the movement, give a warning to the subject100or a third party, or provide feedback to a machine or a vehicle operated by the subject100to enhance safety.

Signal Selection Circuit162

The signal selection circuit162, based on an index value of the plurality of acquired detection signals corresponding to different frequencies set in the high-frequency signal generator130, selects at least one detection signal from the plurality of detection signals. Here, the signal selection circuit162, based on an index value calculated for each of the plurality of detection signals, selects an index value signal evaluated to be of high accuracy (detection signal) as a signal well-suited to acquiring the subject information, and selects the frequency of the high-frequency signal that was set in the high-frequency signal generator130when that detection signal was acquired. That is, the signal selection circuit162selects a signal well-suited for acquiring subject information (detection signal) and the frequency of the high-frequency signal corresponding to the detection signal based on the index values calculated for each of the plurality of detection signals.

Case Where a Correlation Value that Correlates With a Template Signal is Used as the Index Value

First, processing in which a correlation value (a similarity) that correlates with a template signal indicating a reference signal waveform is initially used as an index (selection index) for the selection of the detection signal by the signal selection circuit162will be described. The signal selection circuit162using a similarity between a template signal indicating a reference signal waveform and a plurality of detection signals acquired in correspondence with different frequencies set in the high-frequency signal generator130, selects, as the index value, at least one detection signal from a plurality of detection signals based on the similarity.

FIG.4is a view illustrating an example of a heart-rate signal corresponding to one period in the detection signal. When compared to an electrocardiogram of the same time phase as the heart-rate signal, for example, the peak or inflection point of the heart-rate signal is located in the vicinity of an R wave of the electrocardiogram, and the heart-rate signal has temporal relationship to the waveform of the electrocardiogram. That is, if the heart-rate signal as shown inFIG.4can be acquired, the behavior and state of the heart can be grasped similarly to a conventional method in which an electrocardiogram is taken. The peak and inflection point of the heartbeat waveform are only examples, and other feature points may be used as long as they correspond to the movement of the subject. Therefore, the accuracy of the detection signal including the heart-rate signal generated by the displacement detection circuit161can be evaluated by obtaining correlation values (similarity) with respect to an ideal template using the template signal (hereinafter, also referred to as the ideal template) as a reference heart-rate signal as shown inFIG.4.

FIG.5is a diagram showing an outline of a process in which a correlation value (similarity) with respect to an ideal template is used as an index value. As shown inFIG.5, the signal selection circuit162performs a normalized cross-correlation calculation on the heart-rate signal and the ideal template to generate a correlation waveform, and uses the maximum value of the absolute value of the correlation waveform as the index value. That is, the signal selection circuit162compares the index values calculated for each of a plurality of detection signals, and evaluates the heart-rate signal (the detection signal including the heart-rate signal) to be more accurate the larger an index value for similarity to the ideal template is. A plurality of detection signals are each for different settings of the frequency of the high-frequency signal, and a frequency of the high-frequency signal for which a detection signal of an index value evaluated to be of high accuracy was acquired is selected, and the high-frequency signal generator130generates a high-frequency signal based on the frequency selected by the signal selection circuit162. As a result, measurement can be performed using a detection signal that is well-suited to acquiring subject information.

Since the heart-rate signal (a detection signal including the heart-rate signal) may have a shape in which the ideal template is inverted depending on the frequency of the high-frequency signal and the characteristics of the subject100, the signal selection circuit162uses the absolute value of the correlation waveform in the signal processing. The present invention is not limited to such signal processing, and the signal selection circuit162may, before taking the absolute value of the correlation waveform, respectively calculate the average value of the maximum value and the average value of the minimum value of the correlation waveform, and use the larger absolute value as the index value, and the index value may be anything as long as it reflects similarity to the ideal template.

In the example shown inFIG.5, a normalized cross-correlation calculation is used, but it is also possible to use any calculation method that can calculate similarity to the ideal template, such as a sum of absolute differences (SAD) or a sum of squared differences (SSD). Note that the ideal template is not limited to that ofFIG.4, and any signal that reflects a behavior or state of the heart, or a predetermined body movement may be used. Alternatively, the cycle of the heart-rate signal may be detected, and the ideal template may be enlarged or reduced in the time direction in accordance with the detection cycle.

Case Where the Signal-To-Noise Ratio of the Detection Signal is Used as the Index Value

Next, a process of using an SN ratio (signal to noise ratio) of the detection signal as an index (selection index) for selecting the detection signal will be described.

FIG.6shows an outline of a process for using a signal-to-noise ratio of a detection signal as an index value. The signal selection circuit162sets a signal ratio between a signal component indicating a coupling amount of a near-field coupling corresponding to a predetermined movement of the subject100and a noise signal component to be an index value, and based on a signal ratio, in a plurality of detection signals acquired in correspondence to different frequencies set in the high-frequency signal generator130, selects at least one detection signal from a plurality of detection signals. As shown inFIG.6, the signal selection circuit162Fourier-transforms the detection signal (input signal to the displacement detection circuit161), and sets the signal ratio (SN ratio) Is/In between the signal component (Is) corresponding to the predetermined movement of the subject100and the noise signal component (noise floor: In) as the index value. That is, the signal selection circuit162evaluates a better SN ratio as more accurate. For example, since the component corresponding to a heartbeat is around 1 [Hz] and the component corresponding to respiration is around 0.3 [Hz], peak component values around these frequencies may be defined as Is. The present invention is not limited to the Fourier transform and any method, such as wavelet transform or Kalman filter, may be used if an SN ratio can be acquired.

The signal selection circuit162, as described above, calculates an index value for selecting a detection signal from a plurality of detection signals, selects a signal (detection signal) for which the index value is large, and outputs the frequency of the high-frequency signal corresponding to the detection signal as the selection result. The signal selection circuit162outputs, as a selection result, an index for identifying a signal (detection signal) for which the index value is large among the plurality of detection signals, for example, and the selected signal (detection signal).

The signal selection circuit162selects the frequency of the high-frequency signal corresponding to the selected detection signal, and sets the frequency selected in the high-frequency signal generator130. The high-frequency signal generator130generates a high-frequency signal based on the frequency set by the signal selection circuit162. The displacement detection circuit161generates a displacement signal indicating the displacement of the subject100based on the coupling amount of the near-field coupling detected by the coupling amount detecting circuit150.

Method of Acquiring Subject Information

FIG.7is a diagram showing a processing flow in the first embodiment, and each step of the method of acquiring the subject information according to the present embodiment will be described with reference toFIG.7. Incidentally, the signal processing circuit160executes each step by controlling the operation of each configuration of the apparatus main body120.

Step S110: Step of Setting the High-Frequency Signal Frequency

In this step, the signal processing circuit160sets, to the high-frequency signal generator130, the frequency of the high-frequency signal irradiated from the antenna110to the subject100. The signal processing circuit160sets, to the high-frequency signal generator130, a different frequency for each loop process that occurs at the condition branch of step S130. Typically, the frequency of the high-frequency signal can be set in a range from 100 [MHz] to 1 [GHz], but a suitable range for measurement of the subject information may be selected in accordance with the geometry of the antenna110and the site and composition of the subject100. For example, in the case of a heart-rate signal or a respiration signal, the frequency of the high-frequency signal can be set in the range of 400 [MHz] to 650 [MHz]. Within this frequency range, the signal processing circuit160sets, to the high-frequency signal generator130, a different frequency for each loop process. As the increment of the frequency, it is possible to set the frequency at intervals of a predetermined frequency (e.g., 5 [MHz]) in order to capture a high-precision detection signal, but it is also possible to set an interval larger than 5 [MHz] for the purpose of shortening the measurement time.

Step S120: Step of Acquiring a Detection Signal

In this step, a high-frequency signal of the frequency set in step S110is irradiated from the antenna110to the subject100via the transmission circuit140, and the coupling amount detecting circuit150acquires a detection signal based on the high-frequency signal. A duration over which to acquire the detection signal is a duration within which it is possible to calculate an index value in the signal selection circuit162. By setting a shorter duration, the measurement time can be shortened. The signal processing circuit160stores the detection signal acquired from the coupling amount detecting circuit150in the internal storage medium.

Step S130: Step of Determining Whether a Detection Signal Has Been Acquired for All Frequencies

In this step, the signal processing circuit160determines whether it has acquired a detection signal based on the high-frequency signal for all frequencies. When the acquisition of the detection signals is completed, the processing proceeds to step S140(step S130—Yes), and when the acquisition of the detection signal has not completed, the processing returns to step S110(step S130—No). When returning to the processing of step S110, a different frequency is set in step S110. Then, in step S120, the coupling amount detecting circuit150acquires a detection signal based on the high-frequency signal of the set frequency, and the signal processing circuit160stores the detection signal acquired from the coupling amount detecting circuit150and the frequency of the high-frequency signal corresponding to the detection signal in the internal storage medium. The signal processing circuit160performs such loop processing until a detection signal based on the high-frequency signal has been acquired for all frequencies. By the processing of step S110to step S130, a plurality of detection signals for which the setting of the frequency of the high-frequency signal differs respectively are acquired.

Step S140: Step of Selecting/Setting the High-Frequency Signal Frequency

In this step, the signal selection circuit162calculates an index value for each of the plurality of detection signals having different frequencies of the high-frequency signal acquired in step S110to step S130, selects a detection signal having the largest index value from the index values of the plurality of detection signals thus calculated, and selects the frequency of the high-frequency signal set to the high-frequency signal generator130when the detection signal was acquired. That is, the signal selection circuit162selects a signal well-suited for acquiring subject information (detection signal) and the frequency of the high-frequency signal corresponding to the detection signal based on the index values calculated for each of the plurality of detection signals. In this step, the signal selection circuit162may select the frequency of the high-frequency signal corresponding to one detection signal based on the magnitude of the index value from the calculated plurality of index values, and it is also possible to select a plurality of frequencies of the high-frequency signal corresponding to the highest ranked detection signals in the order of highest to lowest index values.

For example, when a principal component analysis or an independent component analysis is used in the detection process of the displacement signal in step S170, a plurality of frequencies of the high-frequency signal corresponding to the highest ranked detection signals in order of largest to smallest index values may be selected. The signal processing circuit160sets the frequency of the high-frequency signal selected by the signal selection circuit162to the high-frequency signal generator130.

Incidentally, this step may be performed between step S120and step S130, and rather than saving the detection signal in the storage medium in step S130, the index value may be acquired from the detection signal acquired in step S120, and the acquired index value may be saved in the storage medium. In this case, the signal selection circuit162may acquire the index values of the detection signals from the storage medium and select a single frequency of a high-frequency signal corresponding to a detection signal based on the magnitude of the index value, and the signal selection circuit may select a plurality of frequencies of the high-frequency signal corresponding to the highest ranked detection signals in order of the largest to the smallest index value of the detection signals. The signal processing circuit160sets a frequency selected by the signal selection circuit162to the high-frequency signal generator130.

Step S150: Step of Acquiring a Detection Signal

In this step, the high-frequency signal of the frequency set in the high-frequency signal generator130in step S140is irradiated from the antenna110via the transmission circuit140to the subject100, the coupling amount detecting circuit150acquires a detection signal based on the high-frequency signal of the set frequency. The coupling amount detecting circuit150inputs the acquired detection signal to the displacement detection circuit161of the signal processing circuit160.

Step S160: Step of Detecting a Displacement Signal

In this step, the displacement detection circuit161of the signal processing circuit160acquires a displacement signal corresponding to a predetermined movement of the subject100from the detection signal acquired in step S150.

Step S170: Step of Analyzing the Displacement Signal

In this step, the signal processing circuit160analyzes the displacement signal acquired by the displacement detection circuit161in step S160to acquire information about the behavior and state of the subject100.

It should be noted that, among the processing flows described with reference toFIG.7, by executing the processing of step S150, step S160, and step S170in parallel, the displacement signal may be acquired in real time to acquire information on the behavior and the state of the subject100.

As described above, according to the present embodiment, by selecting the frequency of a high-frequency signal well-suited to acquiring the subject information, it is possible to perform measurement with a detection signal well-suited to acquiring the subject information, and it is possible to detect movement with high accuracy and to acquire information related to the behavior and state of the subject with high accuracy.

Second Embodiment

In the present embodiment, a subject information acquisition apparatus having a configuration for correcting a detection signal and a displacement signal will be described. Components identical to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

Configuration of Subject Information Acquisition Apparatus

FIG.8is a diagram schematically showing a configuration of the subject information acquisition apparatus according to the second embodiment, andFIG.9is a diagram schematically showing a connection relationship of components in the apparatus main body120of the second embodiment. Similar to the connection relationship described in the first embodiment, as shown inFIG.9, each component of the apparatus main body120can exchange information via the bus200, and the signal processing circuit160controls operation of each component of the apparatus main body120via the bus200. In the second embodiment, the signal processing circuit160differs from the connection relationship of the components described in the first embodiment (FIG.2) in that it has a signal correction circuit163for correcting the detection signal and the displacement signal (signal correction unit).

Signal Correction Circuit163

The signal correction circuit163corrects at least one of the detection signal selected by the signal selection circuit162and the displacement signal detected by the displacement detection circuit161. Here, as an example of the inversion of the displacement signal (e.g., the heart-rate signal), a case where a correction for inverting the code of the displacement signal is performed in the signal correction circuit163will be described. The heart-rate signal may have a shape in which an ideal template is inverted depending on the frequency of the high-frequency signal and the characteristics of the subject100.

In a case where the signal correction circuit163detected an inversion of the displacement signal, for example, the signal correction circuit163generates a non-inverted correction signal obtained by multiplying a correction value (−1) with the displacement signal. Thus, it is possible to suppress a decrease in analysis precision even when the signal processing circuit160analyzes the displacement signal in the case of non-inversion. For example, in the case of analysis processing for detecting a maximum value from the displacement signal, it may be impossible to detect that the maximum value is a minimum value when the displacement signal is inverted but possible to detect a maxima to be detected if it is a non-inverted correction signal.

FIG.10shows an outline of a process of signal inversion detection. As shown inFIG.10, the signal correction circuit163respectively performs normalized cross-correlation calculation on the heart-rate signal (inverted or non-inverted) and the ideal template to generate a correlation waveform, and calculates a local maximum average value Ipeakand a local minimum average value Ivalley. For a correlation waveform1010for non-inverted heart-rate signals, |Ipeak|>|Ivalley|, and for a correlation waveform1020when the heart-rate signals are inverted, |Ipeak<|Ivalley|; therefore, it is possible for the signal correction circuit163to determine inversion and non-inversion of the signals from the magnitude relationship between |Ipeak| and |Ivalley|.

If signal inversion occurs in the displacement signal and correction of the displacement signal is required, the signal correction circuit163multiplies a correction value (−1) with the displacement signal to produce a correction signal that is non-inverted.

Next, correction of the detection signal will be described. For example, even if the detection signal corresponds to the periodic movement of the subject100, the detection signal may be subject to a disturbance or the like originating from the living body. The signal correction circuit163corrects for disturbances in the waveform in such detection signals. Here, correction of the detection signal will be described as an example of correction of the signal, but the signal correction circuit163can similarly perform the correction of a signal in relation to the displacement signal.

FIG.11is a diagram that illustrates an outline of processing for correcting a disturbance originating in a living body. An IQ plot1110ofFIG.11is a diagram in which an In-phase signal (I signal) and Quadrature signal (Q signal) which are detected by the wave detection circuit153are plotted on in two-dimensional plane over a plurality of periods of a detection signal (e.g., the heart-rate signal). The length of a straight line connecting each point and the origin on the IQ plot1110represents the detection amplitude. The angle formed by the line connecting each point and the origin on the IQ plot1110and the I signal axis represents the detection phase.

An IQ statistic plot1120inFIG.11plots the mean value m (solid line) and standard deviation σ (dashed line) of the detection amplitude for each detection phase. Further, a disturbance detection plot1130ofFIG.11is a diagram showing a state in which a disturbance is detected. Here, the signal correction circuit163performs statistical processing of the signal (detection signal, displacement signal), and if the value of the signal obtained by the statistical processing is outside of a condition regarding the reference value, corrects the value of the signal so as to satisfy the condition regarding the reference value. Since the detection amplitude for a black circle1140is within a reference value (within the standard deviation σ) in the disturbance detection plot, the signal correction circuit163determines that the disturbance is small, and does not perform correction of the signal.

On the other hand, since the value of a broken-line circle1150is outside of the condition regarding the detection amplitude of the reference value (standard deviation σ), the signal correction circuit163determines that the disturbance of the signal value indicated by the broken-line circle1150is larger than the reference value (standard deviation σ), and corrects the value of the signal (the value of the circle1150of the broken line) to be the average value m indicated by the solid-line white circle1160so as to satisfy the condition regarding the reference value, for example. In this way, the correction process by the signal correction circuit163can reduce the influence of disturbance in the signal. Incidentally, in addition to using the value of the reference value (standard deviation σ) as a reference for the criteria for determining whether to perform the correction process for reducing the influence of disturbance, the value of 2σ or 3σ may be used as the reference value.

An example in which the disturbance of the signal is determined to be larger than the reference value (standard deviation σ) is described in the disturbance detection plot1130ofFIG.11, but the present embodiment is not limited to this example. For example, if the standard deviation −σ is used as a reference value, and the disturbance of the signal is smaller than the reference value (standard deviation −σ), and is outside of a condition regarding the reference value (standard deviation −σ) (e.g., the circle1170of the broken line), the signal correction circuit163corrects the value of the signal (the value of the broken-line circle1170) to become the value of the average value m indicated by white circle1160of the solid line, for example, so as to satisfy the condition regarding the reference value. In this way, the correction process by the signal correction circuit163can reduce the influence of disturbance in the signal. In addition to using the value of the standard deviation −σ as a reference, the value of −2σ or −3σ may be used as a reference.

A reference value other than the standard deviation (−σ, σ), such as an experimentally obtained arbitrary threshold value, may be adopted as criteria for determining the necessity of correction. Further, in the example shown inFIG.11, the value of the broken-line circle1150which is outside of the condition regarding the reference value (standard deviation σ) is corrected to the average value m as the correction value (correction target value), but an arbitrary experimentally obtained correction value or a boundary value of the standard deviation σ may be adopted as a correction value (correction target value). Furthermore, it is also possible to perform correction using a frequency component of the displacement signal or the detection signal. For example, it is possible for the signal correction circuit163to deconvolve the frequency component of the displacement signal or the detection signal with a frequency component of an envisioned ideal signal waveform, and to perform correction by deconvolving the signal (displacement signal or the detection signal).

In the case of a heartbeat waveform, the frequency component as shown inFIG.6is deconvolved with the frequency component of an ideal template as shown inFIG.4. Specifically, it is possible to perform a Fourier transform, perform a deconvolution, and then perform an inverse Fourier transform to obtain a corrected signal. It is also possible to generate a deconvolution waveform by inverse Fourier transform of the inverse of the frequency component of the ideal template, and to configure a deconvolution FIR filter from the deconvolution waveform and apply it to the displacement signal and the detection signal. In the above deconvolution, a Wiener filter can be used.

The displacement detection circuit161generates a displacement signal based on the signal corrected by the signal correction circuit163, and the signal processing circuit160acquires information indicating movement of the subject based on the generated displacement signal.

Method of Acquiring Subject Information

FIG.12is a diagram showing a processing flow in the first embodiment, and each step of the subject information acquisition method according to the present embodiment will be described with reference toFIG.12. InFIG.12, two types of processing flows are shown: a processing flow1210for correcting the displacement signal, and a processing flow1220for correcting the detection signal. Note that each step in the processing flow1210and the processing flow1220is executed by the signal processing circuit160controlling the operation of the respective components of the apparatus main body120. Description of the same steps as those in the processing flow of the first embodiment (FIG.7) is omitted.

First, a processing flow1210for correcting the displacement signal will be described. The processing of step S110to step S160is the same as in the processing flow of the first embodiment (FIG.7).

Step S210: Step of Determining Whether to Correct the Displacement Signal

In this step, the signal correction circuit163determines whether to correct the displacement signal detected in step S160. The content of the correction of the displacement signal may be the inversion of the waveform in the displacement signal, for example. As described inFIG.10, if an inversion occurs in the waveform of the displacement signal according to the magnitude relation between the local maximum average value Ipeakand the local minimum average value Ivalley, the signal correction circuit163determines to correct the displacement signal (step S210—Yes), and the process proceeds to step S220.

Step S220: Step of Correcting a Displacement Signal

In this step, the signal correction circuit163multiplies a correction value (−1) with the displacement signal to generate a non-inverted correction signal. Then, in the next step (step S170), the signal processing circuit160analyzes the displacement signal corrected by the signal correction circuit163in step S220to acquire information about the behavior and state of the subject100.

On the other hand, in the determination process of step S210, if no inversion occurs in the waveform of the displacement signal, the signal correction circuit163determines that the displacement signal is not corrected (step S210—No), and the process proceeds to step S170. In this case, the signal processing circuit160analyzes the displacement signal acquired by the displacement detection circuit161in step S160to acquire information about the behavior and state of the subject100.

Next, a processing flow1220for correcting the detection signal will be described. The processing of step S110to step S150is the same as in the processing flow of the first embodiment (FIG.7).

Step S230: Step of Determining Whether to Correct the Detection Signal

In this step, the signal correction circuit163determines whether to correct the detection signal acquired in step S150. The content of the correction of the detection signal may be disturbance of the waveform in the detection signal, for example. As described inFIG.11, if the value of the waveform in the detection signal (e.g., the value of the circle1150of the broken line) is outside of a condition regarding the reference value (e.g., the standard deviation σ, the value 2σ or 3σ, any threshold obtained experimentally, etc.), the signal correction circuit163determines to correct the detection signal (step S230—Yes), and the process proceeds to step S240.

Step S240: Step of Correcting the Detection Signal

In this step, the signal correction circuit163corrects the detection signal to a predetermined correction value (e.g., the average value m of the signal, the boundary value of any correction value or standard deviation σ obtained experimentally, etc.). Then, in the next step (step S160), the displacement detection circuit161acquires the displacement signal corresponding to predetermined movement of the subject100from the detection signal corrected by the signal correction circuit163in step S240. Then, the signal processing circuit160analyzes the displacement signal acquired by the displacement detection circuit161in step S160to acquire information about the behavior and state of the subject100.

On the other hand, in the determination process of step S230, if no disturbance is detected in the waveform of the detection signal, the signal correction circuit163determines that the detection signal is not corrected (step S230—No), and the process proceeds to step S160. In this case, the signal processing circuit160acquires a displacement signal corresponding to a predetermined movement of the subject100from the detection signal acquired in step S150. Then, in step S170, the signal processing circuit160analyzes the displacement signal acquired by the displacement detection circuit161in step S160to acquire information regarding the behavior and state of the subject100.

Note that the correction of the signal is not limited to the above example, and in the processing flow1210for correcting the displacement signal, for example, the disturbance included in the displacement signal may be corrected in the same manner as the processing of the processing flow1220. Also, in the processing flow1220for correcting the detection signal, the inversion of the waveform included in the detection signal may be corrected in the same manner as the processing of the processing flow1210. That is, any correction may be performed as long as it is a correction to the detection signal acquired under a condition selected/set in step S140or a displacement signal extracted therefrom. A waveform inversion and disturbance correction may also be combined.

Further, the processing of step S210and step S220may be executed in parallel with the processing of step S150and step S160and step S170, and the processing results may be outputted in real time. Similarly, the processing of step S230and step S240may be executed in parallel with the processing of step S150and step S160and step S170. Further, the processing of step S210or step S230may be executed prior to the processing of step S150to determine in advance whether the correction is necessary or not, and the determination processing during the execution of the correction in real time may be omitted.

Variation

In the second embodiment, a configuration in which the signal correction circuit163corrects at least one of the detection signal and the displacement signal has been described. Here, the detection signal is a signal selected by the signal selection circuit162based on the index value of a plurality of detection signals. Further, a displacement signal indicating a displacement of a subject is a signal generated by the displacement detection circuit161based on the coupling amount of the near-field coupling by an electric field between the antenna110and the subject100, and the coupling amount of the near-field coupling is detected based on the detection signal selected by the signal selection circuit162. That is, the signal to be corrected by the signal correction circuit163(detection signal and displacement signal) is a signal acquired based on a selection process of the signal selection circuit162.

Note that the processing of the signal correction circuit163is not limited to this example, and it is possible for the signal correction circuit163to correct at least one signal among the detection signal inputted to the coupling amount detecting circuit150(input detection signal) and the displacement signal, regardless of the selection process of the signal selection circuit162. In this case, the high-frequency signal generator130(signal generation unit) generates a high-frequency signal based on a set frequency. The coupling amount detecting circuit150functions as an acquisition unit, and when high-frequency signals are irradiated to the subject100from at least one antenna110, the coupling amount detecting circuit150acquires a detection signal (input detection signal) based on a reflection signal or a transmission signal from the subject100.

Also, the coupling amount detecting circuit150(coupling amount detecting unit) detects a coupling amount of near-field coupling due to the electric field between the antenna110and the subject100based on the detection signal (input detection signal). The displacement detection circuit161generates a displacement signal indicating the displacement of the subject100based on the coupling amount of the near-field coupling detected by the coupling amount detecting circuit150. The signal correction circuit163corrects at least one of the detection signal (input detection signal) and the displacement signal detected by the displacement detection circuit161. Signal correction processing by the signal correction circuit163is the same as the processing described previously, and the displacement detection circuit161generates a displacement signal based on the signal corrected by the signal correction circuit163.

As described above, according to the present embodiment, by performing correction on the detection signal and the displacement signal, movement of the subject can be detected with high accuracy, and information on the behavior and state of the subject can be acquired with high accuracy.

Third Embodiment

In the present embodiment, a subject information acquisition apparatus having a plurality of antennas will be described. Components identical to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

Configuration of Subject Information Acquisition Apparatus

FIG.13is a diagram schematically illustrating a configuration of the subject information acquisition apparatus according to the third embodiment, andFIG.14is a diagram schematically illustrating a connection relationship of components in the apparatus main body120of the third embodiment. Similar to the connection relationship described in the first embodiment, as shown inFIG.14, each component of the apparatus main body120can exchange information via the bus200, and the signal processing circuit160controls operation of each component of the apparatus main body120via the bus200. The connection relationship (FIG.2) of the components is different to that described in the first embodiment in that an antenna group111is configured by a plurality of antennas, and a switching unit for switching the plurality of antennas (hereinafter, a switch (SW)112) is connected to the bus200inFIG.14.

Antenna Group111

Different frequencies are set in the high-frequency signal generator130and a high-frequency signal corresponding to the respective frequencies is generated. The high-frequency signal generated by the high-frequency signal generator130is irradiated to the subject100from the antenna group111composed of a plurality of antennas. The antenna group111includes, for example, a plurality of antennas113,114, and115. The plurality of antennas are arranged to irradiate the high-frequency signal generated by the high-frequency signal generator130to different sites of the subject100. Thus, any one of the plurality of antennas is configured to capture a reflection signal (transmission signal) corresponding to a predetermined movement of the subject100. AlthoughFIG.13exemplarily shows three antennas as the plurality of antennas, the present embodiment is not limited to this example.

In addition, a plurality of antennas may be virtually configured by mechanically scanning a single antenna along the subject100. For example, the subject information acquisition apparatus1may include a scanning unit capable of moving a single antenna in a body axis direction of the subject100, and may irradiate a high-frequency signal generated by the high-frequency signal generator130from the single antenna to a different site of the subject100at a position moved to by scanning of the scanning unit.

The plurality of antennas113,114, and115may be configured to have different shapes depending on the site of the subject100. For example, a plurality of antennas having different physical lengths and shapes may be disposed so as to irradiate high-frequency signals to the same site. In this case, an antenna having a physical length or shape corresponding to an individual difference of the subject100, for example, the size of the heart, lung, or abdominal cavity, can be selected from a plurality of antennas.

Switch112

The switch112selects at least one antenna that illuminates a high-frequency signal from each of the antennas113to115that compose antenna group111. For example, the switch112can select and switch an antenna to be irradiated with a high-frequency signal from the antenna group111.

It is also possible to set the switch112so that high-frequency signals with different frequency settings are irradiated simultaneously from each antenna113to115. The wave detection circuit153, when detecting the inputted detection signal (input detection signal) based on the simultaneous irradiation of different high-frequency signals, the wave detection circuit153separates the input detection signal into detection signals corresponding to the high-frequency signals irradiated from each antenna. In this case, the switch112is configured to be virtually switched.

The configuration of the switch112may be any configuration, such as an electrical switch or a mechanical switch. The high-frequency signal generator130, the transmission circuit140, and the coupling amount detecting circuit150may be provided for each of a plurality of antennas constituting the antenna group111.

Signal Selection Circuit164

The signal selection circuit164of the present embodiment (signal selection unit) selects a signal well-suited for acquiring the subject information from a plurality of detection signals similarly to in the first embodiment (detection signal), but selects a frequency of the high-frequency signal so that it is possible to acquire an index value for each antenna and acquire an optimal detection signal for each antenna. For example, with respect to the antenna113near the chest, the signal selection circuit164selects a frequency suitable for acquisition of the heart-rate signal. Further, the signal selection circuit164can select a frequency suitable for acquisition of the respiration signal with respect to the antennas114and115in the vicinity of the abdomen.

Further, the signal selection circuit164can select an antenna suitable for acquiring a displacement signal corresponding to a predetermined movement of the subject100based on the index value of each of the antennas113to115. For the antenna that the signal selection circuit164selects, it is possible to select a plurality of the highest ranked antennas in order of largest to smallest acquired index values.

For example, when performing processing based on a plurality of signals such as principal component analysis and independent component analysis in the displacement detection circuit161, by excluding a low-precision detection signal in which the detection signal corresponding to the predetermined movement of the subject100is mostly not included, it is possible to improve precision in the displacement signal that is extracted and reduce the calculation amount. Further, even when the apparatus main body120processes the detection signals of all the antennas without selecting an antenna, since the optimum frequency for each antenna is selected by the processing of the signal selection circuit164, improved precision in the displacement signal that is extracted can be expected.

Method of Acquiring Subject Information

FIG.15is a diagram showing a processing flow in the third embodiment, and each step of the subject information acquisition method according to the present embodiment will be described with reference toFIG.15. Incidentally, the signal processing circuit160executes each step by controlling the operation of each configuration of the apparatus main body120. Description of the same steps as those in the first embodiment is omitted. The processing of step S110to step S140is the same as in the processing flow of the first embodiment (FIG.7).

Step S310: Step of Determining Whether a Detection Signal Has Been Acquired for All Antennas

In this step, the signal processing circuit160determines whether the processing for all the antennas113to115has been completed. That is, the signal processing circuit160determines whether the processing for acquiring the detection signal for all the antennas (step S130) and the process for selecting the optimum frequency for each antenna based on the index value of the detection signal (step S140) have been completed. If it is determined that the processing for all antennas has been completed, the signal processing circuit160advances the processing to step S320. On the other hand, if it is determined that the processing for all antennas has not been completed, the signal processing circuit160returns the processing to step S110.

In the case where processing returns to step S110, the signal processing circuit160controls the switch112to switch to the next antenna configuring the antenna group111.

In step S110, the initial value of the frequency range set for each antenna is set to the high-frequency signal generator130. The signal processing circuit160performs the loop processing of step S130until a detection signal based on the high-frequency signal has been acquired for all frequencies. Then, the signal processing circuit160selects the frequency of the optimal high-frequency signal for each antenna based on the index value of the detection signal. The signal processing circuit160performs looping of step S310until the processing for all the antennas113to115is completed.

Step S320: Step of Selecting the Antenna

In this step, the signal selection circuit164selects an antenna for irradiating a high-frequency signal based on the index value for the respective antennas acquired in the step S110to step S310. For example, the signal selection circuit164compares the index value at each antenna, and selects the antenna with the largest index value.

In this step, the signal selection circuit164may be select one antenna based on the magnitude of the index value, from the index values for the plurality of antennas, and may select a plurality of the highest ranked antennas in the order of largest to smallest index value.

When the antenna is selected by the signal selection circuit164, the signal processing circuit160controls the switch112so that the high-frequency signal is irradiated from the selected antenna.

Further, when a single antenna is moved along the body axis of the subject100by a scanning unit, the signal selection circuit164may select an irradiation position for irradiating the high-frequency signal based on the index value acquired at each scanning position of the scanning unit, and control the scanning unit to move the antenna to the irradiation position.

If the high-frequency signal generator130, the transmission circuit140, and the coupling amount detecting circuit150are provided for each antenna, the signal processing circuit160selects the high-frequency signal generator130, the transmission circuit140, and the coupling amount detecting circuit150corresponding to the selected antenna to control operation.

When scanning a single antenna, the signal selection circuit164selects the position where the largest index value is obtained as the antenna position based on an index value acquired at each scanning position of the scanning unit which can move the antenna, and the signal selection circuit164moves the antenna to the selected antenna position. When all the antennas are used, this step can be omitted.

As described above, according to the present embodiment, by selecting the antenna shape and the measurement site well-suited to acquiring the displacement signal corresponding to the predetermined movement, the movement of the subject can be detected with high accuracy, and the information on the behavior and state of the subject can be acquired with high accuracy.

Fourth Embodiment

In this embodiment, a configuration relating to a magnetic resonance imaging apparatus including a subject information acquisition apparatus according to each of the above-described embodiments will be described.

Configuration of Magnetic Resonance Imaging Apparatus

FIG.16is a schematic diagram of a magnetic resonance imaging apparatus according to the present embodiment. The magnetic resonance imaging apparatus has a static magnetic field magnet312, a gradient magnetic field coil310, a WB (Whole Body) coil320or the like, and these components are housed in a cylindrical housing. The magnetic resonance imaging apparatus further includes a bed600including a bed body620and a top plate101, and a local coil400disposed in close proximity to the subject100.

Additionally, the magnetic resonance imaging apparatus includes a gradient magnetic field power supply410, an RF receiver420, an RF transmitter430, and a sequence controller440. The magnetic resonance imaging apparatus also includes a computer having a processing circuit500, a storage circuit510, a display520, and an input device530, in other words a console.

The antenna110is preferably disposed in close proximity to the subject100, and is incorporated in the local coil400in this embodiment. In addition, the antenna110may be disposed inside the top plate101, or may be disposed close to the subject100as a separate device independent of these magnetic resonance imaging apparatuses. Further, a coil provided in a magnetic resonance imaging apparatus such as the gradient magnetic field coil310or the WB (Whole Body) coil320may be used as the antenna110.

A processing circuit500(imaging control unit) controls the imaging sequence of the magnetic resonance imaging apparatus based on information about the state and behavior of the subject100acquired by analyzing the detection signal and the displacement signal outputted from the apparatus main body120of the subject information acquisition apparatus1.

FIG.17shows an overview of imaging control in a magnetic resonance imaging apparatus.FIG.17shows an example of a time phase relationship in the case of controlling an imaging sequence (MR imaging sequence) of the magnetic resonance imaging apparatus using the diastolic phase of the heart-rate signal and the expiratory phase of the respiration signal as information on the state and behavior of the subject100. As shown inFIG.4, since the inflection point of the heart-rate signal is close in time phase to the R wave, it becomes the diastolic phase after a predetermined time from the inflection point. A period after a predetermined time has elapsed from the extraction of the inflection point is regarded as the diastolic phase of the heartbeat, and a signal for indicating that it is possible to image a heartbeat for this period is set to high.

In addition, a threshold value is provided for the respiration signal, and a period of time equal to or less than the threshold value can be regarded as the expiratory phase. During the expiratory phase, a signal for indicating that it is possible to image respiration is set to high. Furthermore, an AND operation of a signal for indicating that it is possible to image a heartbeat and a signal for indicating that it is possible to image respiration is performed to generate a signal indicating that imaging is possible. The signal processing circuit160executes the above signal processing, and outputs the signal indicating that imaging is possible to the processing circuit500of the magnetic resonance imaging apparatus. The processing circuit500performs an MR imaging sequence during which the signal indicating that imaging is possible is high. In the diastolic phase, cardiac movement is small, and in the expiratory phase, chest and abdominal movement due to respiration is small. Therefore, by executing an MR imaging sequence during the periods when both signals indicating that imaging is possible are high overlap, it is possible to ameliorate deterioration of the image quality of MR images due to the movement of the subject100, such as artifacts and resolution deterioration. Further, in the present invention, since the heart-rate signal and the respiration signal can be acquired with high accuracy, the accuracy of signals indicating that imaging is possible generated therefrom is also high, and the image quality of the MR image can be further improved.

Although both the diastolic phase and the expiratory phase have been considered above, a signal indicating that imaging is possible may be based (at least) on only one of the diastolic phase and the expiratory phase. Further, a signal indicating that imaging is possible is not limited to movement due to pulse or respiration, and may be generated based on arbitrary movement of the subject100.

According to the present embodiment, by controlling the imaging of the magnetic resonance imaging apparatus based on information about the behavior and state of the subject100acquired with high accuracy, it is possible to acquire a highly accurate MR image.

Other Embodiments

Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2020-206972, filed Dec. 14, 2020, which is hereby incorporated by reference herein in its entirety.