Vital Information Monitor and Magnetic Resonance Imaging Apparatus

Abstract

To detect biological information such as a heartbeat and respiration of a subject reliably and stably without imposing a burden on the subject.SOLUTION: A biological information monitoring device includes: an antenna device consisting of at least one antenna disposed close to a subject; a signal generation part for generating a high frequency signal; and a displacement detection part for detecting physical displacement of the subject using the high frequency signal. The antenna includes a dipole antenna, in the center of which an electric power supply part for supplying the high frequency signal is provided, a coaxial line for supplying the high frequency signal to the electric power supply part, and a conductor element of 1 / 4 wavelength, one end of which is short-circuited to an external conductor of the coaxial line.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a biological information monitoring device and a magnetic resonance imaging device. [Background technology]

[0002] In imaging using a magnetic resonance imaging apparatus, collected data fluctuates due to human body movements such as heartbeats (heartbeats), breathing, etc. Therefore, for example, with regard to heartbeats, a method is used in which electrodes of an electrocardiograph are attached to the human body, and the imaging timing is adjusted using the signal output from the electrocardiograph, or the collected data is corrected based on the signal from the electrocardiograph. However, attaching electrodes to the human body is a burden for the patient and also causes a decrease in the work efficiency of the imaging technician.

[0003] Also, a technique is known in which data (called navigation data) for monitoring body movements due to breathing is collected separately from data collection for generating diagnostic images, and the influence of body movements due to breathing is corrected using the navigation data. However, this method requires extra time to collect the navigation data, which lengthens the imaging time. From this perspective, there is a demand for a non-contact body movement monitoring device that does not impose a burden on the patient.

[0004] Non-contact body movement monitoring devices are in demand not only in the field of imaging using magnetic resonance imaging devices, but also in the field of healthcare in general. For example, there is a demand for body movement monitoring devices that can monitor the heart rate and breathing of a person while sleeping or driving a vehicle without contacting the person and without placing a burden on the human body.

[0005] Meanwhile, devices have been proposed that use radio waves to detect the movement of a subject and detect the heart rate and respiratory rate. These devices transmit radio waves from an antenna to the subject and detect the movement of the subject by detecting the fluctuation of the waves reflected from the subject.

[0006] However, in conventional detection devices using radio waves, fading occurs because reflected waves are received not only from the subject but also from various structures surrounding the subject, making it difficult to stably detect the subject's heart rate and respiration with high reliability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-55997 A Summary of the Invention [Problem to be solved by the invention]

[0008] One of the problems that the embodiments disclosed in this specification and the drawings aim to solve is to enable stable detection of a subject's biological information, such as heart rate and respiration, with high reliability, without imposing a burden on the subject.

[0009] However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. Problems corresponding to the effects of each configuration shown in the embodiments described later may be positioned as other problems. [Means for solving the problem]

[0010] A biological information monitoring device in one embodiment includes an antenna device having at least one antenna disposed adjacent to a subject, a signal generating unit that generates a high-frequency signal, and a displacement detecting unit that detects physical displacement of the subject using the high-frequency signal, the antenna including a dipole antenna having a power supply unit at its center to which the high-frequency signal is supplied, a coaxial line that supplies the high-frequency signal to the power supply unit, and a ¼-wavelength conductor element having one end shorted to the outer conductor of the coaxial line. [Brief description of the drawings]

[0011] [Figure 1]1 is a block diagram showing the overall configuration of a biological information monitoring device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram for explaining the operation concept of the biological information monitoring device according to the first embodiment. [Diagram 3] (a) is a graph showing an example of the measured value of the reflected signal from the antenna, (b) is a graph showing the respiration waveform extracted from the reflected signal, and (c) is a graph showing the heart rate waveform extracted from the reflected signal. [Figure 4] A diagram comparing a loop antenna and a dipole antenna as antennas used in a vital sign monitoring device. [Diagram 5] FIG. 2 is a diagram showing an example of the arrangement of antennas used in the first embodiment. [Figure 6] FIG. 11 is a block diagram showing the overall configuration of a biological information monitoring device according to a second embodiment. [Figure 7] FIG. 11 is a diagram for explaining the operation concept of the biological information monitoring device according to the second embodiment. [Figure 8] Graph (a) shows an example of a measured value of a transmitted signal from a transmitting antenna to a receiving antenna, graph (b) shows a respiration waveform extracted from the transmitted signal, and graph (c) shows a heart rate waveform extracted from the transmitted signal. [Figure 9] FIG. 11 is a diagram showing an example of the arrangement of a transmitting antenna and a receiving antenna used in the second embodiment. [Figure 10] FIG. 11 is a block diagram showing the overall configuration of a biological information monitoring device according to a third embodiment. [Figure 11] FIG. 1 shows an example of an arrangement of four antennas for performing diversity processing. [Figure 12] FIG. 1 is a diagram showing an example of the configuration of a magnetic resonance imaging apparatus equipped with a biological information monitoring device. [Figure 13] FIG. 2A is a diagram showing an example of the configuration of a biological information monitor used in a magnetic resonance imaging apparatus, and FIG. 2B is a diagram showing an example of a period for transmitting and receiving a high-frequency signal for the biological monitor. [Figure 14] 13A and 13B are diagrams showing examples of markings on a local coil and a tabletop that indicate the position of an antenna. [Figure 15] 1A and 1B are diagrams for explaining problems with conventional antennas. [Figure 16] 1A to 1C are diagrams showing an example of the appearance and structure of an antenna according to a first embodiment; [Figure 17] 4A to 4C are diagrams for explaining the effects of the antenna according to the first embodiment. [Figure 18] 5A to 5C are diagrams for explaining constraints on the structure of the antenna according to the first embodiment. [Figure 19] 5 is a graph showing the technical effect of the antenna of the first embodiment. [Figure 20] FIG. 11 is a first diagram showing an example of the structure of an antenna according to a second embodiment; [Figure 21] FIG. 2 is a second diagram showing an example of the structure of the antenna according to the second embodiment. [Figure 22] 13A and 13B are diagrams showing examples of the structure of an antenna according to another embodiment; [Figure 23] 1A and 1B are diagrams showing examples of the structure of an antenna having multiple conductor elements (L-shaped elements) of different lengths. [Figure 24] 1A and 1B are diagrams showing examples of the structure of an antenna having multiple conductor elements of different sizes (bowtie shape). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (First embodiment) A first embodiment of the present invention will now be described with reference to the accompanying drawings.

[0013] FIG. 1 is a block diagram showing the overall configuration of a biological information monitoring device 1 according to a first embodiment. The biological information monitoring device 1 includes an antenna 10 and a biological information monitoring device main body 20 (hereinafter simply referred to as the main body 20). The antenna 10 constitutes an antenna device (not shown). In the first embodiment, the biological information monitoring device main body 20 is basically configured to have one antenna, so the antenna device is composed of one antenna. On the other hand, in other embodiments described later, the biological information monitoring device main body 20 may have multiple antennas, in which case the antenna device is composed of multiple antennas.

[0014] The antenna 10 is disposed close to a subject, which is a human body. The antenna 10 does not need to be attached in direct contact with the subject's skin, as with the electrodes of an electrocardiograph, and may be disposed, for example, on the subject's clothes. In addition, while FIG. 1 shows an example in which the antenna 10 is disposed on the chest of a subject lying on a top plate 510 of a bed, the posture of the subject when the antenna 10 is disposed and the part of the subject on which the antenna 10 is disposed are not limited to the example shown in FIG. 1. For example, the antenna 10 may be disposed on the chest or back of a subject in a standing position, or on the chest or back of a subject in a sitting position while driving a vehicle. The main body 20 includes an RF signal generator 30, a transmission circuit 40, a coupling amount detection circuit 50, and a displacement detection circuit 60.

[0015] The RF signal generator 30 generates a continuous wave high frequency signal. The frequency of the high frequency signal is not particularly limited, but for example, a frequency in the VHF band or UHF band is selected based on the dimensions of the antenna, etc.

[0016] The transmission circuit 40 passes the high-frequency signal through a band-pass filter (BPF) 41 , then amplifies the signal to a predetermined power by a power amplifier (PA) 42 , and outputs the signal to the antenna 10 via a directional coupler (DC) 43 .

[0017] The coupling amount detection circuit 50 has a function of detecting the amount of near-field coupling due to the electric field between the subject and the antenna 10, and is configured with, for example, a band pass filter (BPF) 51, a low noise amplifier with automatic gain control function (LNA / AGC) 52, and a detection circuit 53. The RF signal generator 30, the transmission circuit 40, and the coupling amount detection circuit 50 can be mounted on, for example, a printed circuit board housed in a single casing.

[0018] The high-frequency signal output from the directional coupler 43 of the transmission circuit 40 is input to the antenna 10, but a portion of this high-frequency signal is not directed toward the subject, but is bounced off (reflected) at the input end of the antenna 10 and returns to the directional coupler 43, and is branched and input to the coupling amount detection circuit 50.

[0019] The coupling amount detection circuit 50 measures the magnitude of the reflected signal from the antenna 10 by detecting the signal output from the branch end of the directional coupler 43 with the detection circuit 53. Then, the coupling amount of the near-field coupling is detected based on the magnitude of the reflected signal.

[0020] Considering that the power output from the transmission circuit 40 to the antenna 10 is a constant value, the coupling amount detection circuit 50 is equivalent to detecting the S11 parameter indicating the reflection loss (that is, return loss) of the antenna 10.

[0021] Fig. 2 is a diagram for explaining the operation concept of the biological information monitoring device 1 according to the first embodiment. Fig. 2(a) is a diagram for explaining the operation when the distance D between the subject and the antenna 10 is small, and Fig. 2(b) is a diagram for explaining the operation when the distance D between the subject and the antenna 10 is large. Since the subject (human body) is an object having electrical conductivity, it becomes easier for the antenna 10 to absorb energy from the subject when the antenna 10 approaches the subject.

[0022] 2(a), when the distance D between the object and the antenna 10 is small, the energy absorbed by the object is large. This means that the amount of near-field coupling between the object and the antenna 10 is large. The power Sin input to the antenna 10 is mainly divided into the power Sb absorbed by the object and the power Sr reflected from the antenna end 10a of the antenna 10, and when the distance D is small, the power Sb absorbed by the object is large, and the power Sr reflected from the antenna end 10a is small by that amount. For example, when the power Sin input to the antenna 10 is 100, the power Sb absorbed by the object is 70, and the power Sr reflected from the antenna end 10a is 30.

[0023] This means that when the distance D between the object under test and the antenna 10 is small, the reflected signal from the antenna end 10a decreases, and the return loss of the antenna 10 also decreases. In other words, the S11 parameter, which is an index of the degree of mismatch of the antenna 10, exhibits a small value. The S11 parameter is an index expressed as the square root of the ratio of the reflected power to the input power to the antenna 10.

[0024] 2(b), when the distance D between the object and the antenna 10 is large, the energy absorbed by the object is small. This means that the amount of near-field coupling between the object and the antenna 10 is small. As a result, when the distance D is large, the power Sb absorbed by the object is small, and the power Sr reflected from the antenna end 10a is large accordingly. For example, when the power Sin input to the antenna 10 is 100, the power Sb absorbed by the object is 30, and the power Sr reflected from the antenna end 10a is 70.

[0025] This means that when the distance D between the object under test and the antenna 10 is large, the reflected signal from the antenna end 10a increases, increasing the return loss of the antenna 10. In other words, the S11 parameter, which is an index of the degree of mismatch of the antenna 10, will exhibit a large value.

[0026] In this way, when the input power to the antenna 10 is constant, the reflected signal from the antenna end 10a changes depending on the distance D between the subject and the antenna 10. In other words, the degree of mismatch of the antenna 10 or the value of the S11 parameter also changes depending on the distance D between the subject and the antenna 10. And since the distance D between the subject and the antenna 10 changes due to body movements such as heartbeat and breathing, the magnitude of the reflected signal from the antenna end 10a or the value of the S11 parameter changes according to changes in body movements such as heartbeat and breathing.

[0027] The biological information monitoring device 1 of the first embodiment utilizes such characteristics and detects bodily movements such as heart rate and breathing by detecting the magnitude of the reflected signal from the antenna 10 arranged near the subject or the value of the S11 parameter.

[0028] 3(a) is a graph showing an example of an actual measurement value of a reflected signal from antenna 10. The horizontal axis of the graph represents time, and the vertical axis represents the amplitude of the reflected signal. As shown in FIG. 3(a), the reflected signal from antenna 10 has a waveform in which a short-period vibration waveform (a waveform corresponding to a heartbeat) is superimposed on a relatively long-period vibration waveform (a waveform corresponding to breathing movement). The reflected signal from antenna 10 is detected by detection circuit 53 of coupling amount detection circuit 50, and output to displacement detection circuit 60.

[0029] The displacement detection circuit 60 may be configured, for example, as a dedicated printed circuit board equipped with a processor, or may be configured as an information processing device such as a personal computer or tablet terminal device equipped with a display.

[0030] The displacement detection circuit 60 performs filtering processing on the reflected signal detected by the detection circuit 53 to extract a frequency component corresponding to breathing and a frequency component corresponding to heartbeat, respectively, to generate the breathing waveform shown in Fig. 3(b) and the heartbeat waveform shown in Fig. 3(c). Alternatively, the displacement detection circuit 60 may perform a Fourier transform on the reflected signal from the antenna 10, extract the frequency component corresponding to breathing and the frequency component corresponding to heartbeat in frequency, and perform an inverse Fourier transform on each of the extracted frequency components to generate the breathing waveform shown in Fig. 3(b) and the heartbeat waveform shown in Fig. 3(c).

[0031] The displacement detection circuit 60 may display the generated respiratory waveform and heart rate waveform on an appropriate display, or may analyze the generated respiratory waveform and heart rate waveform. For example, the displacement detection circuit 60 may analyze the respiratory waveform and heart rate waveform to obtain the respiratory rate and respiratory cycle, or the heart rate and heart rate cycle, or may detect the presence or absence of abnormality in breathing or heart rate from the respiratory rate and heart rate. FIG. 4 is a diagram comparing a loop antenna and a dipole antenna as the antenna 10 used in the biological information monitoring device 1. In FIG.

[0032] Figure 4(a) shows a loop antenna whose loop length is the resonant length, i.e., a one-wavelength loop antenna. In a one-wavelength loop antenna, the current distribution on the opposing sides is in opposite phase, so the electric field is not cancelled out. Therefore, in the near field, the electric field component is larger than the magnetic field component. Although it depends on the frequency used, the antenna shape is relatively large.

[0033] Figure 4(b) shows a loop antenna whose loop length is shorter than the resonant length. In this type of loop antenna, the current distribution on the corresponding sides is not in opposite phase, so the electric fields are cancelled out. As a result, the magnetic field component is larger than the electric field component in the near field. Therefore, the coupling with the human body in the near field is magnetic field coupling. Magnetic field coupling tends to pass easily through the inside of the body. Figure 4(c) shows a half-wave dipole antenna. The half-wave dipole antenna has a large electric field component in the near field because there is no electric field cancellation.

[0034] Figure 4(d) shows a dipole antenna whose element length is shorter than the resonant length. Even if the element length is shorter than the resonant length (i.e., half the wavelength), the current distribution shape does not change. Therefore, like a half-wavelength dipole antenna, the electric field component is large in the near field. Naturally, it can be made smaller than a half-wavelength dipole antenna. Since the electric field component is large in the near field, coupling with the human body in the near field is electric field coupling. Electric field coupling tends to propagate easily along the surface of the body.

[0035] From the viewpoint of miniaturization, a loop antenna (FIG. 4(b)) whose loop length is shorter than the resonant length or a dipole antenna (FIG. 4(d)) whose loop length is shorter than a half wavelength is preferable, and either type of antenna can be used in the vital sign monitoring device 1. However, compared with a loop antenna, a dipole antenna tends to be able to extract finer electrocardiogram waveforms.

[0036] A normal antenna used for communication and the like is required to minimize the reflected signal from the antenna and maximize the power going out into space. For this reason, it is considered desirable for the voltage standing wave ratio (VSWR) of the antenna to be as close to 1.0 as possible. In contrast, in the biological information monitoring device 1 of the first embodiment, the heartbeat and breathing movements are detected by detecting the reflected signal from the antenna 10. For this reason, it is rather preferable that there is a certain amount of reflected signal from the antenna 10. Therefore, it is preferable that the voltage standing wave ratio (VSWR) of the antenna 10 used in the biological information monitoring device 1 of the first embodiment is set to, for example, 2.0 to 5.0.

[0037] 5 is a diagram showing an example of the arrangement of the antenna 10 used in the biological information monitoring device 1 of the first embodiment. In principle, the number of antennas 10 used in the first embodiment is one, but various variations are possible regarding the arrangement and orientation of the antenna 10. As a basic concept, it is preferable to arrange the antenna 10 in a part where the movement of the body is as noticeable as possible, and when detecting the heartbeat, it is preferable to arrange the antenna 10 as close as possible to the heart.

[0038] In Fig. 5, a dipole antenna is shown as an example of the type of antenna 10. It is said that the range of movement of the heart is greater in the head-foot direction than in the left-right direction of the subject. Therefore, in Fig. 5(a), the antenna 10 is placed near the heart so that the longitudinal direction of the dipole antenna is in the head-foot direction of the subject, and on the ventral side in the dorsal-ventral direction of the subject. On the other hand, in Fig. 5(b), the antenna 10 is placed near the heart on the dorsal side of the subject (the longitudinal direction of the dipole antenna is in the head-foot direction of the subject).

[0039] The placement of the antenna 10 may be subject to some physical constraints. For example, when the heart rate is measured using the biological information monitor 1 during imaging of the subject by the magnetic resonance imaging apparatus, the local coil 200 of the magnetic resonance imaging apparatus 100 is placed on the subject. When the local coil 200 is a chest coil, the antenna 10 is placed at a position that avoids the chest coil and is as close to the heart as possible, as shown in FIG. 5(c). Also, when the antenna 10 is placed on the back and the local coil 200 is a spine coil, the antenna 10 is placed at a position that avoids the spine coil and is as close to the heart as possible, as shown in FIG. 5(d).

[0040] As described above, in the biological information monitoring device 1 according to the first embodiment, bodily movements such as heartbeat and breathing are detected as a change in the amount of near-field coupling between the antenna 10 and the human body. Then, the change in the amount of near-field coupling is measured as a change in the reflected signal reflected from the input end of the antenna 10, or as a change in the value of the S11 parameter, which is the reflection loss of the antenna 10. Therefore, the biological information monitoring device 1 according to the first embodiment is less susceptible to fading caused by reflected waves from structures around the subject, such as the gantry structure of a magnetic resonance imaging device and various devices in an examination room, and can detect heartbeat and breathing movements with high reliability, despite being a non-contact detection method using radio waves.

[0041] Second embodiment 6 is a block diagram showing the overall configuration of a biological information monitoring device 1 according to the second embodiment. While the biological information monitoring device 1 of the first embodiment is basically equipped with one antenna 10, the biological information monitoring device 1 of the second embodiment has at least two antennas, a transmitting antenna 10 (first antenna) and a receiving antenna 11 (second antenna).

[0042] The biological information monitor main body 20 has a configuration similar to that of the first embodiment, and includes an RF signal generator 30, a transmission circuit 40, a coupling amount detection circuit 50, and a displacement detection circuit 60.

[0043] The main body 20 differs from the first embodiment in that the transmission circuit 40 of the second embodiment does not have a directional coupler (DC) 43. The power amplifier (PA) 42 of the transmission circuit 40 and the transmission antenna 10 are directly connected without the directional coupler (DC) 43, and the band pass filter (BPF) 51 of the coupling amount detection circuit 50 and the receiving antenna 11 are also directly connected without the directional coupler (DC) 43.

[0044] The coupling amount detection circuit 50 of the second embodiment detects the amount of near-field coupling based on the magnitude of a transmitted signal, which is a high-frequency signal output from the RF signal generator 30 and transmitted from the transmitting antenna 10 to the receiving antenna 11, using a detection circuit 53.

[0045] Considering that the power output from the transmitting circuit 40 to the transmitting antenna 10 is a constant value, the coupling amount detection circuit 50 equivalently detects the S21 parameter, which indicates the insertion loss (i.e., insertion loss) from the transmitting antenna 10 to the receiving antenna 11.

[0046] Fig. 7 is a diagram for explaining the operation concept of the biological information monitoring device 1 according to the second embodiment. Fig. 7(a) is a diagram for explaining the operation when the distance D between the subject and the antenna 10 is small, and Fig. 7(b) is a diagram for explaining the operation when the distance D between the subject and the antenna 10 is large. As described above, the subject (human body) is an object having electrical conductivity, and therefore, when the distance between the transmitting antenna 10 and the subject is small, it becomes easy to absorb energy from the transmitting antenna 10. Therefore, the energy absorbed by the subject from the transmitting antenna 10 becomes large. This means that the amount of near-field coupling between the subject and the transmitting antenna 10 is large.

[0047] Similarly, when the receiving antenna 11 approaches the subject, the energy input from the subject to the receiving antenna 11 also increases, which means that the amount of near-field coupling between the subject and the receiving antenna 11 is large. The power Sin input to the antenna 10 is absorbed by the subject as power Sb1, propagates inside and on the surface of the subject, and is transmitted to the receiving antenna 11 as power Sb2. When the distance D is small, the power Sb1 absorbed by the subject from the transmitting antenna 10 increases, and the power Sb2 transmitted from the subject to the receiving antenna 11 also increases accordingly. For example, when the power Sin input to the transmitting antenna 10 is 100, the power Sb absorbed by the subject from the transmitting antenna 10 is 70, the power Sb2 emitted from the subject to the receiving antenna 11 is 60, and therefore the power St output from the receiving antenna 11 is also 60.

[0048] This means that when the distance D between the subject and the transmitting antenna 10 and the receiving antenna 11 is small, the transmitted signal from the transmitting antenna 10 to the receiving antenna 11 increases, and the insertion loss from the transmitting antenna 10 to the receiving antenna 11 decreases. In other words, the S21 parameter (real value), which is an index of the insertion loss from the transmitting antenna 10 to the receiving antenna 11, will exhibit a large value.

[0049] On the other hand, as shown in FIG. 7(b), when the distance D between the transmitting antenna 10 and the subject increases, the subject is less likely to absorb the energy from the transmitting antenna 10. Therefore, the energy absorbed by the subject from the transmitting antenna 10 decreases. This means that the amount of near-field coupling between the subject and the receiving antenna 11 decreases. Similarly, when the distance D between the receiving antenna 11 and the subject increases, the energy input from the subject to the receiving antenna 11 also decreases. This means that the amount of near-field coupling between the subject and the receiving antenna 11 also decreases. For example, when the power Sin input to the transmitting antenna 10 is 100, the power Sb absorbed by the subject from the transmitting antenna 10 is 30, the power Sb2 emitted from the subject to the receiving antenna 11 is 20, and therefore the power St output from the receiving antenna 11 is also 20.

[0050] This means that when the distance D between the object under test and the transmitting antenna 10 or the distance D between the object under test and the receiving antenna 11 is large, the transmitted signal from the transmitting antenna 10 to the receiving antenna 11 decreases, and the insertion loss from the transmitting antenna 10 to the receiving antenna 11 increases. In other words, the S21 parameter (real value), which is an index of the insertion loss from the transmitting antenna 10 to the receiving antenna 11, will exhibit a small value.

[0051] 8(a) is a graph showing an example of an actual measurement value of a transmitted signal from the transmitting antenna 10 to the receiving antenna 11. The horizontal axis of the graph indicates time, and the vertical axis indicates the amplitude of the transmitted signal. The transmitted signal in the second embodiment is similar to the reflected signal in the first embodiment (FIG. 3(a)), and has a waveform in which a short-period vibration waveform (a waveform corresponding to a heartbeat) is superimposed on a relatively long-period vibration waveform (a waveform corresponding to breathing movement). This transmitted signal is also detected by the detection circuit 53 of the coupling amount detection circuit 50, and is output to the displacement detection circuit 60.

[0052] As in the first embodiment, the displacement detection circuit 60 performs filtering and Fourier transform processing on the reflected signal detected by the detection circuit 53 to extract frequency components corresponding to respiratory movement and heartbeat, respectively, to generate a respiratory waveform shown in FIG. 8(b) and a heartbeat waveform shown in FIG. 8(c).

[0053] 9 is a diagram showing an example of the arrangement of the transmitting antenna 10 and the receiving antenna 11 used in the biological information monitoring device 1 of the second embodiment. Various variations are possible regarding the arrangement and orientation of the transmitting antenna 10 and the receiving antenna 11 used in the second embodiment. As a basic concept, it is preferable to arrange the transmitting antenna 10 and the receiving antenna 11 so as to sandwich a part where the movement of the body is as noticeable as possible. For example, when detecting the heartbeat, it is preferable to arrange the transmitting antenna 10 and the receiving antenna 11 so as to sandwich the heart in any direction of the subject's back-ventral direction, left-right direction, or head-foot direction.

[0054] 9(a), 9(b), and 9(c) show a dipole antenna as an example of the type of antenna, and Fig. 9(d) shows a monopole antenna as an example. Fig. 9(a) shows an example of an arrangement in which the heart is sandwiched between the transmitting antenna 10 and the receiving antenna 11 from the posterior and ventral directions of the subject.

[0055] Fig. 9(b) shows an example of an arrangement in which the heart is sandwiched between the transmitting antenna 10 and the receiving antenna 11 from the left and right of the subject. Fig. 9(c) shows an example of an arrangement in which the heart is sandwiched between the transmitting antenna 10 and the receiving antenna 11 from the head-to-foot direction of the subject. Fig. 9(d) shows an example of an arrangement in which the heart is sandwiched between the transmitting antenna 10 and the receiving antenna 11, which are monopole antennas, from the head-to-foot direction of the subject.

[0056] It is not necessary to particularly distinguish between the transmitting antenna 10 and the receiving antenna 11, and in any of the examples shown in Figs. 9(a) to 9(d), the transmitting antenna 10 and the receiving antenna 11 can be arranged in an interchangeable manner.

[0057] The voltage standing wave ratio (VSWR) of the transmitting antenna 10 used in the biological information monitoring device 1 of the second embodiment is preferably set to, for example, 2.0 to 5.0, similar to the antenna 10 of the first embodiment. However, for the receiving antenna 11, a VSWR of, for example, 2.0 or less is preferable.

[0058] (Third embodiment) 10 is a block diagram showing the overall configuration of a biological information monitoring device 1 according to a third embodiment. The biological information monitoring device 1 of the third embodiment is an embodiment that combines the first embodiment and the second embodiment. Specifically, this embodiment is configured to be selectable between a first mode corresponding to the first embodiment and a second mode corresponding to the second embodiment.

[0059] In the first mode, a high-frequency signal is input to antenna 11, and the heart rate, respiratory movements, etc. of the subject are measured based on the reflected signal from antenna 11 (or the S11 parameter of antenna 11). Meanwhile, in the second mode, a high-frequency signal is input to antenna 10, and the heart rate, respiratory movements, etc. of the subject are measured based on the transmitted signal from antenna 10 to antenna 11 (or the S21 parameter from antenna 10 to antenna 11).

[0060] The RF signal generator 30 and the first transmission circuit 40 are components corresponding to the function of generating a high-frequency signal in the first mode. The RF signal generator 30a and the second transmission circuit 40a are components corresponding to the function of generating a high-frequency signal in the second mode. The coupling amount detection circuit 50 is a component commonly used in both the first and second modes.

[0061] The diversity determination circuit 70 monitors the reflected signal detected in the first mode and the transmitted signal detected in the second mode, and selects either the first mode or the second mode. When monitoring the reflected signal in the first mode, the diversity determination circuit 70 switches both the switch 44 of the first transmission circuit 40 and the switch 54 of the coupling amount detection circuit 50 to the directional coupler 43 side as shown in Fig. 10. When monitoring the transmitted signal in the second mode, the switches 44 and 54 are switched to the opposite side to the state shown in Fig. 10.

[0062] The diversity determination circuit 70 compares the fluctuation range of the reflected signal with the fluctuation range of the transmitted signal, and selects the mode with the larger fluctuation range. For example, if it is determined that the fluctuation range of the reflected signal is larger than that of the transmitted signal, the diversity determination circuit 70 selects the first mode. Also, for example, the diversity determination circuit 70 may perform a Fourier transform on each of the reflected signal and the transmitted signal, and select the mode with the larger frequency component corresponding to the heartbeat, or the mode with the larger frequency component corresponding to respiration.

[0063] After selecting either the first mode or the second mode, the diversity determination circuit 70 sets the switches 44 and 54 to a state corresponding to the selected mode, and measures the reflected signal or transmitted signal using the selected mode to detect body movement signals such as heart rate, respiratory movement, etc. (Modification of the third embodiment)

[0064] The biological information monitoring device 1 according to the modified example of the third embodiment performs diversity processing using two or more antennas 10, 11. In this diversity processing, one antenna capable of detecting a body movement signal best is selected, or a combination of two or more antennas capable of detecting a body movement signal best is selected.

[0065] Fig. 11 is a diagram showing an example of the arrangement of four antennas for performing diversity processing. In this case, for example, as shown in Fig. 11(a), four dipole antennas 10 and 11 may be arranged to surround the heart. Also, as shown in Fig. 11(b), antennas 10 and 11 of a type in which a dipole antenna is bent at a substantially right angle in the middle may be arranged to surround the heart using a dipole antenna.

[0066] When diversity processing is performed in the biological information monitoring device 1 of the first embodiment, or when diversity processing is performed in the first mode of the third embodiment, one antenna that can best detect the body movement signal is selected from the four antennas.

[0067] Furthermore, when diversity processing is performed in the biological information monitoring device 1 of the second embodiment, or when diversity processing is performed in the second mode of the third embodiment, for example, one transmitting antenna 10 is selected, and one antenna that can best detect a body movement signal is selected from the remaining three receiving antennas 11, or a synthesis process is performed on the remaining three receiving antennas 11 in any combination.

[0068] In a modification of the third embodiment, for example, a circuit having a function similar to that of the diversity determination circuit 70 shown in Fig. 10 may be provided. This circuit performs the above-mentioned antenna selection process and antenna combination process. (Magnetic Resonance Imaging Device) FIG. 12 is a diagram showing an example of the configuration of a magnetic resonance imaging apparatus 100 including the biological information monitoring device 1 according to each of the above-mentioned embodiments.

[0069] The magnetic resonance imaging apparatus 100 includes a static magnetic field magnet 118, a gradient magnetic field coil 119, a WB (Whole Body) coil 120, etc., and these components are housed in a cylindrical housing. The magnetic resonance imaging apparatus 100 also includes a bed 500 including a bed body 520 and a top board 510, and a local coil 200 disposed adjacent to the subject.

[0070] Furthermore, the magnetic resonance imaging apparatus 100 includes a gradient magnetic field power supply 310, an RF receiver 320, an RF transmitter 330, and a sequence controller 340. The magnetic resonance imaging apparatus 100 also includes a computer having a processing circuit 400, a memory circuit 410, a display 420, and an input device 430, i.e., a console.

[0071] The biological information monitor 1 has antennas 10 and 11 in addition to the main body 20 shown in Figures 1, 6, and 10. The antennas 10 and 11 are disposed close to the subject, but do not need to be directly attached to the subject's skin. The antennas 10 and 11 may be disposed separately near the subject, but may also be built into the local coil 200 or into the tabletop 510 as shown in Figure 12.

[0072] Fig. 13(a) is a diagram showing a configuration example of a biological information monitor 1 used in a magnetic resonance imaging apparatus 100. The magnetic resonance imaging apparatus 100 can be used in any of the above-mentioned embodiments, but Fig. 13 shows the biological information monitor 1 of the second embodiment as an example. In the magnetic resonance imaging apparatus 100, an MR RF pulse with very high power is output from the RF transmitter 330, and this RF pulse is radiated from the WB coil 120 toward the subject. Therefore, a very high RF power is input to the main body 20 of the biological information monitor 1 via the antennas 10 and 11.

[0073] Therefore, in the biological information monitor 1 used in the magnetic resonance imaging apparatus 100, protective switches 45 and 55 are provided at the output end of the transmission circuit 40 and the input end of the coupling amount detection circuit 50, respectively. The protective switches 45 and 55 are turned on and off using a control signal sent from the main body of the magnetic resonance imaging apparatus 100.

[0074] Fig. 13(b) is a diagram showing an example of a transmission / reception period of a high-frequency signal for a biological monitor. As shown in Fig. 13(b), the high-frequency signal for a biological monitor is transmitted / received during a period that avoids a transmission period of an MR RF pulse and a reception period of an MR signal in order to avoid interference between the magnetic resonance imaging apparatus 100 and the biological information monitor 1.

[0075] The repetition period T of the transmission and reception period of the high frequency signal for the vital sign monitor can be determined from the heart rate cycle and the respiratory cycle. The heart rate frequency can be assumed to be approximately 2 Hz or less, and the respiratory frequency can be assumed to be approximately 0.5 Hz or less. According to the sampling theorem, the heart rate waveform and the respiratory waveform can be measured by sampling at twice the higher frequency, i.e., at a frequency of 4 Hz or more. Therefore, the repetition period T should be set to 250 ms (= 1 / 4 Hz) or less.

[0076] The frequency of the high frequency signal for the biological monitor is preferably higher than the Larmor frequency used in the magnetic resonance imaging apparatus 100. By setting the frequency of the high frequency signal for the biological monitor higher than the Larmor frequency, it is possible to prevent not only the high frequency signal for the biological monitor itself but also its harmonics from entering the reception band of the MR signal of the magnetic resonance imaging apparatus 100.

[0077] 14 is a diagram showing an example of markings on the local coil 200 and the top board 510 indicating the positions of the antennas 10 and 11. As described above, the antennas 10 and 11 of the biological information monitor 1 can be embedded and mounted in the local coil 200 and the top board 510 of the bed 500. When measuring the heart rate, it is preferable to dispose the antennas 10 and 11 near the heart of the subject. Therefore, the user may attach markings to the antennas 10 and 11 embedded in the local coil 200 and the top board 510 so that they can be easily seen, and adjust the position of the subject and the position of the local coil 200 so that the markings are near the heart of the subject.

[0078] (First embodiment of antenna with conductive element) Up to this point, as shown in Figs. 5, 9 and 11, a configuration has been described in which a dipole antenna is used as a typical example of the antenna elements of the antennas 10 and 11 used in the biological information monitoring device 1.

[0079] Many of the conventional antennas that use a dipole antenna as an antenna element are configured so that a high-frequency signal is fed to the dipole antenna via a coaxial line (for example, a coaxial cable).

[0080] 15(a) to 15(c) are diagrams for explaining the problems of the conventional antenna having such a configuration. Fig. 15(a) is a diagram showing a situation in which the antenna (conventional antenna) of the biological information monitor 1 is placed on the chest of a subject to measure the pulse and respiratory motion of the subject.

[0081] Fig. 15(b) shows an example of the configuration of a conventional antenna, in which a high-frequency signal is supplied to a dipole antenna via a coaxial line. As is well known, a dipole antenna is a balanced circuit, whereas a coaxial line is an unbalanced circuit. Therefore, a leakage current generated at the boundary between the balanced circuit and the unbalanced circuit, i.e., at the power feed point which is the boundary between the dipole antenna and the coaxial line, flows into the outer conductor of the coaxial line.

[0082] When measuring the pulse or respiratory movement of a subject, the antenna is placed on the subject as described above. In this case, the coaxial line near the power feeder is placed on the subject (e.g., on the chest or abdomen of the subject) together with the dipole antenna.

[0083] For this reason, the leakage current flowing in the outer conductor of the coaxial line, together with the current on the dipole antenna, is coupled with the object under test, and the return loss (S11 parameter) of the antenna varies according to the movement of the object surface.

[0084] For example, as shown in FIG. 15(a), when the outer conductor of the coaxial line approaches the abdomen of the subject, the variation of the abdomen due to breathing is larger than the variation of the chest due to heartbeat, and therefore the influence of the abdomen on the S11 parameter caused by the leakage current described above becomes large.

[0085] For this reason, as shown in the graph of FIG. 15(c), the fluctuation in the S11 parameter due to breathing (fluctuations with a long period) overshadows the fluctuation in the S11 parameter due to heartbeats (fluctuations with a short period), making it difficult to capture the movement of the heartbeat.

[0086] In response to this, it has been found that by configuring the antenna used in the vital sign monitoring device 1 as an antenna 10 having a 1 / 4 wavelength conductor element 104, it is possible to reduce the leakage current flowing through the outer conductor, thereby solving the above problem.

[0087] Various embodiments of the antenna 10 with a 1 / 4 wavelength conductive element 104 will be described below with reference to Fig. 16 to Fig. 22. Note that, although Fig. 15(a) illustrates the antenna as a transmitting / receiving antenna for detecting the S11 parameter, it can also be used as a transmitting antenna 10 and a receiving antenna 11 for detecting the S21 parameter.

[0088] 16 is a diagram showing an example of the appearance and structure of the antenna 10 according to the first embodiment of the antenna 10 with a ¼ wavelength conductive element 104. The antenna 10 includes a dipole antenna 101, a coaxial line 103, and a conductive element 104.

[0089] A power supply section 102 is provided at the center of the dipole antenna 101. A high-frequency signal supplied from the biological information monitor main body 20 is fed to the power supply section 102 via a coaxial line 103.

[0090] The coaxial line 103 is, for example, a coaxial cable whose outer conductor is made of woven thin conducting wires called braided wires and whose outer conductor is covered with an insulating protective coating such as vinyl called a sheath. Alternatively, the coaxial line 103 may be a so-called semi-rigid cable, which uses a seamless metal tube as the outer conductor and has the outer conductor exposed to the outside.

[0091] The conductive element 104 is a linear conductor or a strip-shaped conductor whose length is approximately ¼ wavelength. One end of the conductive element 104 is configured as a short-circuited portion 105 that is short-circuited to the outer conductor of the coaxial line 103, and the other end of the conductive element 104 is configured as an open end (open end portion 106).

[0092] The conductor element 104 can be configured as, for example, an L-shaped element 104. The L-shaped element 104 has a short axis portion formed by bending one end of a linear conductor or a band-shaped conductor short, and a long axis portion that is the remaining portion. The tip of the short axis portion of the L-shaped element 104 is short-circuited to the outer conductor of the coaxial line 103, and the long axis portion is disposed approximately parallel to the coaxial line 103 with a predetermined gap therebetween.

[0093] Although not necessarily limited to, the conductor element 104 has an end closer to the power supply portion 102 of the dipole antenna 101 that is open, and an end farther from the power supply portion 102 of the dipole antenna 101 that is short-circuited to the outer conductor of the coaxial line 103, as exemplified in FIG. 16 .

[0094] Fig. 17 is a diagram for explaining the action and effect of the antenna 10 according to the first embodiment. Fig. 17 is a diagram in which a current distribution is added by dashed lines to the diagram of the antenna 10 shown in Fig. 16. The current distribution shown in Fig. 17 is a distribution of a current generated in a rectangular portion formed by the outer conductor and the L-shaped element 104.

[0095] In the rectangular section formed by the outer conductor and L-shaped element 104 having a length of 1 / 4 wavelength of the resonant frequency of dipole antenna 101, a current is generated which is maximum at short-circuited portion 105 of L-shaped element 104 and minimum at open end 106. Therefore, the impedance of the rectangular portion formed by the outer conductor and L-shaped element 104 as viewed from power supply 102 becomes maximum at the position of open end 106 of L-shaped element 104 . As a result, leakage current in the direction of the outer conductor is blocked at the open end 106, making it possible to suppress leakage current flowing to the outer conductor. Conventionally, a method called a Supertopf has been known as a method for suppressing leakage current from a dipole antenna to an outer conductor. The Supertopf is composed of a cylindrical conductor that covers the outer circumference of a coaxial line near the feeding point of the dipole antenna. While the conventional Supertopf has a three-dimensional structure, the L-shaped element 104 of this embodiment has a planar structure such as a linear conductor or a band-shaped conductor. Therefore, the manufacturing process of the antenna 10 of this embodiment is simplified compared to the conventional antennas using the Supertopf.

[0096] 18A and 18B are diagrams illustrating constraints on the structure of the antenna 10 according to the first embodiment. Among these, Fig. 18A is a diagram illustrating constraints on the height H of the L-shaped element 104 (i.e., the distance between the L-shaped element 104 and the outer conductor of the coaxial line 103).

[0097] 18(a), it is preferable that the height H of the L-shaped element 104 is 1 / 10 wavelength or less, because by making the height H of the L-shaped element 104 1 / 10 wavelength or less, it is possible to prevent the L-shaped element 104 from emitting radio waves as a monopole antenna. FIG. 18( b ) is a diagram showing constraints on the distance D between the open end 106 of the L-shaped element 104 and the power supply section 102 .

[0098] 18(b), it is preferable that the distance D between the open end 106 of the L-shaped element 104 and the power supply unit 102 is equal to or less than ¼ wavelength. This is because, by setting the distance D to ¼ wavelength or less, it is possible to prevent the occurrence of standing waves in the coaxial line 103, and as a result, it is possible to prevent near-field coupling between the coaxial line 103 and the subject.

[0099] Fig. 19 is a graph showing the technical effect of the antenna 10 of the first embodiment. Each graph shown in Fig. 19(a) and (b) is an example of actual measurement data showing the time variation of the S11 parameter measured by the biological information monitoring device 1. For comparison with the antenna 10 of the embodiment, Fig. 19(a) shows the time variation of the S11 parameter measured using a conventional antenna without the L-shaped element 104. Meanwhile, Fig. 19(b) shows the time variation of the S11 parameter measured using the antenna 10 of the embodiment having the L-shaped element 104.

[0100] 19(a) and (b), the time fluctuations with a long period of about 5 to 10 seconds are due to respiratory movement of the abdomen, etc. In contrast, the time fluctuations with a short period of 1 second or less are due to movement (pulsation) caused by heartbeat.

[0101] As shown in FIG. 19(a), in the S11 parameter measured using a conventional antenna without the L-shaped element 104, the signal fluctuation due to the heartbeat is buried in the signal fluctuation due to respiratory movement, making it difficult to detect.

[0102] In contrast, as is clear from FIG. 19(b), in the S11 parameter measured using an antenna 10 of an embodiment having an L-shaped element 104, the influence of respiratory motion is reduced, and signal fluctuations due to heart rate can be easily detected.

[0103] As described above, according to the embodiment of antenna 10 having conductive element 104 (for example, L-shaped element 104), leakage current occurring at power supply section 102, which is the boundary between dipole antenna 101 and coaxial line 103, is suppressed. As a result, the influence of respiratory motion is reduced, and signal fluctuations due to heartbeat can be easily detected.

[0104] (Second embodiment of antenna with conductive element) 20 and 21 are diagrams showing a structural example of the second embodiment of the antenna with conductive element. As shown in Fig. 20(a), the antenna 10 of the second embodiment is configured such that the parts other than the coaxial line 103, i.e., the dipole antenna 101 and the conductive element 104 (e.g., the L-shaped element 104), are formed on the substrate 107.

[0105] On the other hand, Fig. 20(b) shows a coaxial line 103 to be fixed to a substrate 107. The coaxial line 103 has an inner conductor 109 at the center and an outer conductor 110 on the periphery. The outer conductor 110 may be exposed to the outside like the coaxial cable (e.g., semi-rigid cable) shown in Fig. 20(b), or may be an insulating protective coating made of vinyl or the like provided on the outer periphery of the outer conductor. The substrate 107 is formed in a T-shape with a horizontal member corresponding to the position of the dipole antenna 101 and a vertical member corresponding to the position of the conductive element 104 .

[0106] The dipole antenna 101 and the conductor element 104 are each formed by, for example, etching a copper foil provided on one surface of the substrate 107 .

[0107] The dipole antenna 101 can be formed as a solid surface all over, but as shown in FIG. 20(a), in the area from the power supply 102 to a predetermined position toward both ends of the dipole antenna 101, the conductor (e.g., copper foil) of the dipole antenna 101 is formed in a meandering shape, and in the areas from the predetermined positions to both ends, the conductor (e.g., copper foil) of the dipole antenna 101 is formed as a solid surface.

[0108] Here, the region of the conductor formed in a meander shape refers to a pattern in which a thin conductor with a width sufficiently narrower than the width of the conductor in the short direction of dipole antenna 101 is bent multiple times into a crank shape, that is, a region of a pattern in which the conductor is formed as a so-called meander line. Also, the solid surface refers to a surface in which the entire surface of substrate 107 is covered with a conductor layer without any gaps, or a surface in which the entire surface of substrate 107 is covered with a conductor layer widely and continuously.

[0109] On the other hand, conductive element 104 is a conductive pattern formed on a vertical member of substrate 107. Conductive element 104 is formed so that its length (the length of conductive element 104 in a direction perpendicular to dipole antenna 101) is ¼ wavelength of the resonant frequency of dipole antenna 101.

[0110] The end of the conductive element 104 closer to the power supply portion 102 is an open end insulated from the dipole antenna 101. The end of the conductive element 104 farther from the power supply portion 102 is bent at a right angle. Then, by electrically connecting this bent area to the outer conductor of the coaxial line 103 by, for example, soldering, the outer conductor 110 of the coaxial line 103 and the conductive element 104 can be short-circuited.

[0111] The land 108 provided near the center of the conductive element 104 is provided to fix the coaxial line 103 to the substrate 107. The coaxial line 103 can be fixed to the substrate 107 by bonding the land 108, the coaxial line 103, and the outer conductor 110 together with, for example, solder or the like.

[0112] 21 is a diagram showing an example of the external appearance of antenna 10 in which dipole antenna 101 and conductor element 104 formed on substrate 107 are joined to coaxial line 103. The inner conductor and outer conductor of coaxial line 103 are connected to the left and right antenna elements of dipole antenna 101, respectively, at power feeding section 102, and a high-frequency signal is fed to dipole antenna 101.

[0113] Furthermore, the outer conductor 110 of the coaxial line 103 is shorted to the conductive element 104 at an end of the conductive element 104 farther from the power supply unit 102, thereby forming a shorted portion 105. Alternatively, the bond between the coaxial line 103 and the substrate 107 may be strengthened by bonding the land 108 shown in Fig. 20 and the outer conductor 110 of the coaxial line 103 with solder or the like.

[0114] In addition, if the coaxial line 103 is a type having an insulating protective coating on the outer periphery of the outer conductor 110, the insulating protective coating at the short-circuit portion 105 and the insulating protective coating at the joint with the land 108 may be removed before joining the coaxial line 103 to the substrate 107.

[0115] According to the antenna 10 of the second embodiment described above, the dipole antenna 101 and the conductive element 104 are formed on the same substrate 107, which makes it possible to improve ease of mounting and shorten the manufacturing time, thereby reducing the manufacturing cost.

[0116] (Other embodiments of antenna with conductive element) Fig. 22 is a diagram illustrating another embodiment of an antenna with a conductive element. Fig. 22(a) is a diagram illustrating an embodiment in which a bowtie-shaped element is used as the conductive element 104. The bowtie-shaped conductive element 104 is formed in a vertically elongated triangular shape with the short-circuit portion 105 as the base and the open end 106 as the apex. The length of the bowtie-shaped conductive element 104 is formed to be approximately ¼ wavelength, but by forming the conductive element 104 in a planar shape, it becomes possible for the effect of the conductive element 104 to be exerted over a wide band.

[0117] For example, when the shape of conductor element 104 is a right triangle, the length of the hypotenuse is L2 and the sum of the lengths of the opposite side and the base is L1 (L1 > L2), the conductor element 104 can achieve wideband characteristics determined by the lower limit frequency defined by length L1 and the upper limit frequency defined by length L2.

[0118] 22(b) is a diagram showing an embodiment in which the conductive element 104 has a spiral shape. In this embodiment, the conductive element 104 is a wire element, and this wire element is wound in a spiral shape around the outer periphery of the coaxial line 103. In this embodiment, at least one of the outer periphery of the conductive element 104 and the outer periphery of the wire element is covered with an insulating coating, and they are insulated from each other in areas other than the short-circuit portion 105.

[0119] In this embodiment, the length L3 from the short circuit portion 105 to the open end 106 of the conductive element 104 can be made shorter than a quarter wavelength, and the antenna 10 can be made smaller in size.

[0120] Fig. 23 is a diagram showing a modified example of the conductive element 104 of the antenna 10 shown in Fig. 21. In this modified example, the conductive element 104 is composed of a plurality of conductive elements, for example, three conductive elements 104a, 104b, and 104c, having different lengths.

[0121] Fig. 23(a) illustrates a conductor element 104 having three conductor elements (L-shaped elements) 104a, 104b, and 104c integrated at the base and short-circuited at one point with the outer conductor 110 of the coaxial line 103. On the other hand, Fig. 23(b) illustrates a conductor element 104 having three conductor elements (L-shaped elements) 104a, 104b, and 104c each independently short-circuited at three points with the outer conductor 110 of the coaxial line 103.

[0122] When the length of the conductive element 104 is uniform, it may not be the optimal length depending on the body type of the subject. In response to this, in the embodiment illustrated in Fig. 23, the lengths of the three conductive elements (L-shaped elements) are made different, such as short, medium, and long, so that the conductive element (short) 104a can be adapted to a thin subject, the conductive element (medium) 104b to a subject of normal body type, and the conductive element (long) 104c to an obese subject.

[0123] The antenna 10 of the embodiment shown in FIGS. 23(a) and 23(b) can be easily realized because the conductive element 104 has a planar structure, and it is considered difficult to realize it with the conventional three-dimensional structure of Supertop.

[0124] Fig. 24 is a diagram showing a modification of antenna 10 shown in Fig. 22(a) having bowtie-shaped conductive element 104. In this modification, conductive element 104 is composed of a plurality of conductive elements, for example, three conductive elements 104a, 104b, and 104c, which have roughly similar shapes but different sizes.

[0125] Although the bowtie-shaped conductive element 104 has a wideband characteristic, if the size is uniform, it may not be the optimal size depending on the body type of the subject. In contrast, in the embodiment illustrated in Fig. 24, the three bowtie-shaped conductive elements are made to have different sizes, such as small, medium, and large, so that the conductive element (small) 104a can be adapted to a thin subject, the conductive element (medium) 104b to a subject with a normal body type, and the conductive element (large) 104c to an obese subject.

[0126] The antenna 10 of the embodiment shown in FIG. 24 can also be easily realized because the conductive element 104 has a planar structure, but it would be difficult to realize with the conventional three-dimensional Supertop structure.

[0127] According to the biological information monitor 1 of each of the embodiments described above, biological information of a subject, such as heart rate and respiration, can be detected stably with high reliability without imposing a burden on the subject.

[0128] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. Regarding the above embodiment, the following supplementary notes are disclosed as one aspect and optional features of the invention. (Appendix 1) an antenna device including at least one antenna disposed adjacent to a subject; A signal generating unit that generates a high frequency signal; a displacement detection unit that detects a physical displacement of the subject by using the high frequency signal; Equipped with The antenna is a dipole antenna having a power supply portion at its center to which the high frequency signal is supplied; a coaxial line that supplies the high frequency signal to the power supply unit; a 1 / 4 wavelength conductor element, one end of which is shorted to the outer conductor of the coaxial line; The invention comprises: Vital sign monitoring device. (Appendix 2) The conductive element may be formed in an L-shape. (Appendix 3) The conductive element may be formed of a linear conductor. (Appendix 4) The conductive element may be formed of a strip-shaped conductor. (Appendix 5) The conductive element may have an open end closer to the power feed portion of the dipole antenna and an open end farther from the power feed portion and shorted to the outer conductor. (Appendix 6) The distance between the open end of the conductive element and the feed portion of the dipole antenna may be set to be shorter than 1 / 4 wavelength. (Appendix 7) The conductive element may be disposed so as to be substantially parallel to the coaxial line, and a distance between the conductive element and the coaxial line may be set to be shorter than 1 / 10 wavelength. (Appendix 8) The dipole antenna and the conductive element may be formed on the same substrate. (Appendix 9) The tip of the coaxial line may be connected to a power feed portion of the dipole antenna formed on the substrate, and the outer conductor of the coaxial line may be short-circuited to a predetermined portion of the conductive element formed on the substrate. (Appendix 10) The predetermined portion of the conductive element may be an end of the dipole antenna that is remote from the power feed portion. (Appendix 11) The dipole antenna is configured as a planar dipole antenna, and the conductor of the planar dipole antenna may be formed in a meandering shape in the area from the power supply part to which the high-frequency signal is supplied to a predetermined position toward both ends of the planar dipole antenna, and the area from the predetermined position to the both ends may be formed as a solid surface. (Appendix 12) The conductive element may be formed in a bowtie shape. (Appendix 13) The conductive element may be formed in a spiral shape. (Appendix 14) The conductive element may have an open end closer to the power feed portion of the dipole antenna and an open end farther from the power feed portion and shorted to the outer conductor. (Appendix 15) The distance between the open end of the conductive element and the feed portion of the dipole antenna may be set to be shorter than 1 / 4 wavelength. (Appendix 16) The conductive element may be configured to include a plurality of conductive elements having L-shaped major axis portions each having a different length. (Appendix 17) The conductive element may be configured to include a plurality of bowtie-shaped conductive elements having mutually different sizes. (Appendix 18) The present invention includes the biological information monitoring device as described above. Magnetic resonance imaging device. [Explanation of symbols]

[0129] 1. Biological information monitoring device 10 Antennas, Transmitting Antennas 11 Receiving antenna 20. Body of vital sign monitor (body) 30, 30a RF signal generator 40 Transmission circuit, first transmission circuit 40a Second transmission circuit 43 Directional coupler 50 Coupling amount detection circuit 53 Detector circuit 60 Displacement detection circuit 70 Diversity judgment circuit 100 Magnetic resonance imaging device 101 Dipole Antenna 102 Power supply unit 103 coaxial line 104 Conductor element (L-shaped element) 105 Short circuit 106 Open end 107 Substrate 109 Inner conductor 110 Outer conductor

Claims

1. an antenna device including at least one antenna disposed adjacent to a subject; A signal generating unit that generates a high frequency signal; a displacement detection unit that detects a physical displacement of the subject by using the high-frequency signal, The antenna is a dipole antenna having a power supply portion at its center to which the high frequency signal is supplied; a coaxial line that supplies the high frequency signal to the power supply unit; a conductor element having a length of ¼ wavelength, one end of which is shorted to the outer conductor of the coaxial line, the conductor element being configured as a planar structure of a linear conductor or a strip conductor; The invention comprises: Vital sign monitoring device.

2. The conductive element is formed in an L-shape.

2. The biological information monitoring device according to claim 1.

3. The conductive element has an end closer to the power feeder of the dipole antenna that is open, and an end farther from the power feeder that is shorted to the outer conductor.

3. The biological information monitoring device according to claim 1 or 2.

4. The distance between the open end of the conductive element and the power feed part of the dipole antenna is set to be shorter than 1 / 4 wavelength.

4. The biological information monitoring device according to claim 3.

5. the conductor element is disposed so as to be substantially parallel to the coaxial line, and a distance between the conductor element and the coaxial line is set to be shorter than 1 / 10 wavelength.

5. The biological information monitor according to claim 1.

6. The dipole antenna and the conductive element are formed on the same substrate.

6. The biological information monitor according to claim 1.

7. a tip end of the coaxial line is connected to a power supply portion of the dipole antenna formed on the substrate, and an outer conductor of the coaxial line is short-circuited to a predetermined portion of the conductive element formed on the substrate; 7. The biological information monitoring device according to claim 6.

8. The predetermined portion of the conductive element is an end portion of the dipole antenna that is farther from the power supply portion.

8. The biological information monitoring device according to claim 7.

9. The dipole antenna is configured as a planar dipole antenna, and a conductor of the planar dipole antenna is formed in a meandering shape in a region from a power supply part to which the high frequency signal is supplied to a predetermined position toward both ends of the planar dipole antenna, and a region from the predetermined position to both ends is formed as a solid surface.

9. The biological information monitor according to claim 6,

10. The conductive element is formed in a bowtie shape.

2. The biological information monitoring device according to claim 1.

11. The conductive element is formed in a spiral shape.

2. The biological information monitoring device according to claim 1.

12. The conductive element has an end closer to the power feeder of the dipole antenna that is open, and an end farther from the power feeder that is shorted to the outer conductor.

12. The biological information monitoring device according to claim 10 or 11.

13. The distance between the open end of the conductive element and the power feed part of the dipole antenna is set to be shorter than 1 / 4 wavelength.

13. The biological information monitoring device according to claim 12.

14. The conductive element is configured to include a plurality of conductive elements having L-shaped long axis portions with different lengths, or The conductive element is configured to include a plurality of conductive elements having bowtie shapes each having a different size.

2. The biological information monitoring device according to claim 1.

15. The biological information monitor according to any one of claims 1 to 14, Magnetic resonance imaging device.

Images