Patent Description:
An MRI apparatus is an imaging apparatus that magnetically excites nuclear spin of an object placed in a static magnetic field by applying a radio frequency (RF) pulse having the Larmor frequency and reconstructs an image on the basis of magnetic resonance (MR) signals emitted from the object due to the excitation.

In the MRI apparatus, the RF pulse is transmitted from a whole-body (WB) coil toward the object. The MR signal emitted from the object in response to the transmission is received by the WB coil or an RF coil. The RF coil receives the MR signal emitted from the object at a position close to the object. Depending on the anatomical imaging part of the object, there are various RF coils such as for the head, for the chest, for the spine, and for the lower limbs. The RF coil is also referred to as a local coil or a surface coil.

Conventionally, a wired RF coil has been widely used. The wired RF coil is configured to transmit an MR signal, which is received from the object, to the main body of the MRI apparatus by wire. On the other hand, a wireless RF coil has also been developed, which converts the received MR signal from an analog signal to a digital signal by using an A/D converter and wirelessly transmits the digitized MR signal to the main body of the MRI apparatus. The "main body of the MRI apparatus" may be hereinafter simply referred to as the "main body".

When using the wired RF coil, the main body performs A/D conversion on the MR signal transmitted as an analog signal from the wired RF coil to the main body by using an AD clock generated from the system clock in the main body. On the other hand, when using the wireless RF coil, an AD clock for performing A/D conversion on the MR signal is required on the RF coil side, and a system clock for generating the AD clock is also required on the RF coil side.

The digitized MR signal is transmitted to the main body, and various types of digital processing is performed on the digitized MR signal by using a system clock which is generated in the main body. Thus, it is required that the system clock used on the RF coil side and the system clock generated in the main body are synchronized with each other.

In order to synchronize both system clocks, it may be conceivable to wirelessly transmit the system clock in the main body to the RF coil. However, in a conventional remote wireless communication system, there may occur a situation in which stable transmission of the system clock becomes difficult due to the effects of fading occurring in the wireless propagation path (for example, <CIT>).

Apart from the situation about the transmission of the system clock described above, there is a strong demand to readily obtain biological information such as heartbeat and respiration of the object without imposing a burden on the object.

<CIT> relates to an MRI apparatus that includes a first radio communication unit, a second radio communication unit, an image reconstruction unit and a table for loading an object. The first radio communication unit obtains a nuclear magnetic resonance signal detected by an RF coil device, and wirelessly transmits the nuclear magnetic resonance signal in a digitized state via an induced electric field. The second radio communication unit receives the nuclear magnetic resonance signal via the induced electric field. The image reconstruction unit reconstructs image data based on the nuclear magnetic resonance signal. The table includes a supporting unit which detachably supports the first radio communication unit to the second radio communication unit so that an interval between the first and second radio communication units enables radio communication via the induced electric field.

<CIT> relates to a magnetic resonance coil device for receiving magnetic resonance signals. The magnetic resonance coil device includes a receiving antenna unit, a signal processing unit, a high-frequency unit, and a transmitting antenna unit for cable-free transmission of the received magnetic resonance signals and/or data to a data receiving unit. The magnetic resonance coil device includes at least one substantially uncovered region, and the transmitting antenna unit is arranged in the at least one substantially uncovered region.

The disclosed embodiments aim to provide an MRI technique that can stably transmit a system clock from the main body of the MRI apparatus to the wireless RF coil without being affected by fading. The disclosed embodiments further aim to provide an MRI technique that can readily acquire biological information such as heartbeat and/or respiration of the object without imposing a burden on the object.

A Magnetic Resonance Imaging (MRI) apparatus according to the present invention is recited in claim <NUM>.

Further, the MRI apparatus may be configured such that: the first communication circuitry includes a first electrode disposed close to the object; and the second communication circuitry includes a second electrode provided in the RF coil and disposed close to the object.

Further, the MRI apparatus may be configured such that: the second communication circuitry detects a phase fluctuation of the received system clock and transmit information on the detected phase fluctuation to the main body; and the main body sets a carrier frequency for transmitting the system clock from the first communication circuitry to the second communication circuitry so as to reduce the phase fluctuation.

Further, in the above-described MRI apparatus, the main body may be configured to estimate a propagation path length from the first communication circuitry to the second communication circuitry and correct a phase delay of the system clock corresponding to the propagation path length.

Further, in the above-described MRI apparatus, the second communication circuitry may further include a biological monitoring circuit that detects biological information including at least one of heartbeat and a respiratory motion of the object from change in signal intensity of the received system clock.

Further, the MRI apparatus may be configured such that: the first communication circuitry combines a first high-frequency signal for transmitting the system clock by the surface electric field communication and a second high-frequency signal for detecting biological information including at least one of heartbeat and a respiratory motion of the object by radiated electromagnetic field communication and transmits a combined signal of the first and second high-frequency signals to the second communication circuitry; and the second communication circuitry separates the first and the second high-frequency signals from the combined signal, reproduces the system clock from the separated first high-frequency signal, and detects the biological information from change in signal intensity of the separated second high-frequency signal.

Further, the MRI apparatus may be configured such that: the first communication circuitry is provided with a first plate-shaped dipole antenna disposed close to the object; the second communication circuitry is provided with a second plate-shaped dipole antenna provided inside the RF coil and disposed close to the object; the first and second plate-shaped dipole antennas perform communication corresponding to both of the surface electric field communication and the radiated electromagnetic field communication.

Further, in the above-described MRI apparatus, each of the first and second plate-shaped dipole antennas may be disposed in such a manner that the longitudinal direction of each of the first and second plate-shaped dipole antennas is orthogonal to a head-foot direction of the object.

Further, the MRI apparatus may be configured such that: the first communication circuitry is provided with a first circularly polarized antenna disposed close to the object; the second communication circuitry is provided with a second circularly polarized antenna provided inside the RF coil and disposed close to the object; and the first and second circularly polarized antennas perform communication corresponding to both of the surface electric field communication and the radiated electromagnetic field communication.

Further, the MRI apparatus may be configured such that: the second communication circuitry detects a phase fluctuation of the received system clock and transmits information on the detected phase fluctuation to the main body; and the main body sets a carrier frequency for transmitting the system clock from the first communication circuitry to the second communication circuitry so as to reduce the phase fluctuation.

Further, in the above-described MRI apparatus, a frequency of the second high-frequency signal may be set to a higher frequency than a frequency of the first high-frequency signal.

Further, in the above-described MRI apparatus, the second high-frequency signal may be generated from a signal source that is a generation source of a high-frequency transmission pulse for obtaining the MR signal, the signal source having a Larmor frequency of the object.

Further, the MRI apparatus may be configured such that: the second communication circuitry transmits the detected biological information to the main body; and the main body uses the received biological information for correcting a motion of the object in reconstruction processing of the MR signal.

A communication method of a Magnetic Resonance Imaging (MRI) apparatus according to the present invention is recited in claim <NUM>.

Hereinbelow, the first embodiment of the present invention will be described by referring to the accompanying drawings.

<FIG> is a block diagram illustrating an overall configuration of an MRI apparatus <NUM> according to the first embodiment. The MRI apparatus <NUM> of the first embodiment includes a gantry <NUM>, a control cabinet <NUM>, a console <NUM>, and a bed <NUM>.

The gantry <NUM> includes a static magnetic field magnet <NUM>, a gradient coil assembly <NUM>, and a whole body (WB) coil <NUM>, and these components are housed in a cylindrical housing. The bed <NUM> includes a bed body <NUM> and a table <NUM>. In addition, the MRI apparatus <NUM> includes at least one RF coil <NUM> to be disposed close to the object. As described above, the RF coil <NUM> is also referred to as a local coil <NUM> or a surface coil <NUM>.

The control cabinet <NUM> includes three gradient coil power supplies <NUM> (31x for an X-axis, 31y for a Y-axis, and 31z for a Z-axis), an RF receiver <NUM>, an RF transmitter <NUM>, and a sequence controller <NUM>.

The static magnetic field magnet <NUM> of the gantry <NUM> is substantially in the form of a cylinder, and generates a static magnetic field inside a bore, which is a space formed inside the cylindrical structure and serves as an imaging region of the object (for example, a patient). The gradient coil assembly <NUM> is also substantially in the form of a cylinder and is fixed to the inside of the static magnetic field magnet <NUM>. The gradient coil assembly <NUM> has a three-channel structure and includes an X-axis gradient coil, a Y-axis gradient coil, and a Z-axis gradient coil. Gradient magnetic fields Gx, Gy, and Gz are generated by respectively supplying the X-axis, Y-axis, and Z-axis gradient coils with electric currents from the gradient magnetic field power supplies 31x, 31y, and 31z, respectively.

The bed body <NUM> of the bed <NUM> can move the table <NUM> in the vertical direction and in the horizontal direction. The bed body <NUM> moves the table <NUM> with an object placed thereon to a predetermined height before imaging. Afterward, when the object is imaged, the bed body <NUM> moves the table <NUM> in the horizontal direction so as to move the object to the inside of the bore.

The WB body coil <NUM> is shaped substantially in the form of a cylinder so as to surround the object, and is fixed to the inside of the gradient coil assembly <NUM>. The WB coil <NUM> applies RF pulses to be transmitted from the RF transmitter <NUM> to the object, and receives MR signals emitted from the object due to excitation of hydrogen nuclei.

The RF transmitter <NUM> transmits an RF pulse to the WB coil <NUM> on the basis of an instruction from the sequence controller <NUM>. The RF receiver <NUM> detects an MR signal received by the WB coil <NUM> and/or the RF coil <NUM>, and then transmits raw data obtained by digitizing the detected MR signal to the sequence controller <NUM>.

The sequence controller <NUM> performs a scan of the object by driving the gradient coil power supplies <NUM>, the RF transmitter <NUM>, and the RF receiver <NUM> under the control of the console <NUM>. When the sequence controller <NUM> performs a scan so as to receive raw data from the RF receiver <NUM>, the sequence controller <NUM> transmits the raw data to the console <NUM>.

The sequence controller <NUM> includes processing circuitry (not shown). This processing circuitry is configured as, for example, a processor for executing predetermined programs or configured as hardware such as a field programmable gate array (FPGA) and an application specific integrated circuit (ASIC).

The console <NUM> is configured as a computer that includes processing circuitry <NUM>, a memory <NUM>, a display <NUM>, and an input interface <NUM>.

The memory <NUM> is a recording medium including a read-only memory (ROM) and a random access memory (RAM) in addition to an external memory device such as a hard disk drive (HDD) and an optical disc device. The memory <NUM> stores various programs to be executed by a processor of the processing circuitry <NUM> as well as various data and information.

The display <NUM> is a display device such as a liquid crystal display panel, a plasma display panel, and an organic EL panel.

The input interface <NUM> includes various devices for an operator to input various data and information, and is configured of, for example, a mouse, a keyboard, a trackball, and/or a touch panel.

The processing circuitry <NUM> is, for example, a circuit provided with a central processing unit (CPU) and/or a special-purpose or general-purpose processor. The processor implements various functions described below by executing the programs stored in the memory <NUM>. The processing circuitry <NUM> may be configured of hardware such as an FPGA and an ASIC. The various functions described below can also be implemented by such hardware. Additionally, the processing circuitry <NUM> can implement the various functions by combining hardware processing and software processing based on its processor and programs.

The MRI apparatus <NUM> includes at least one RF coil <NUM> in addition to the WB coil <NUM>. The RF coil <NUM> receives MR signals emitted from the object at a position close to the object. The RF coil <NUM> includes a plurality of coil elements, for example. Depending on the anatomical imaging part of the object, there are various RF coils <NUM> such as for the head, for the chest, for the spine, for the lower limbs, and for the whole body. Of these various RF coils, <FIG> illustrates the RF coil <NUM> for imaging the chest.

The RF coil <NUM> of the MRI apparatus <NUM> according to the embodiments is configured as a wireless RF coil, which converts an MR signal received from the object into a digital signal and transmits it to a main body <NUM> wirelessly. Note that, in this specification, the term of "main body <NUM>" herein is used for the configuration of the entire MRI apparatus <NUM> excluding the RF coil <NUM>, the first communication circuitry, and second communication circuitry described below.

The RF coil <NUM> converts the received analog MR signal into a digital signal by using an A/D converter and wirelessly transmits the digitized MR signal to the main body <NUM>, and thus, an AD clock for the A/D conversion is needed. Meanwhile, the main body <NUM> needs a processing clock that is synchronized with the AD clock used in the RF coil <NUM>, in order to acquire the wirelessly received MR signals as digital data at an appropriate timing.

Accordingly, in the MRI apparatus <NUM> of the present embodiment, the main body <NUM> is configured to generate a system clock, then transmits the system clock wirelessly and constantly to the RF coil <NUM>, while generating a processing clock therein from the system clock. The main body <NUM> and the RF coil <NUM> use this system clock in common, and thus can perform synchronized processing. In the present embodiments, the first communication circuitry <NUM> and the second communication circuitry <NUM> play a role of the wireless transmission of the system clock.

<FIG> are schematic diagrams for illustrating an arrangement of the first communication circuitry <NUM> and the second communication circuitry <NUM> with respect to the object. <FIG> further illustrates a wireless propagation from the first communication circuitry <NUM> to the second communication circuitry <NUM>. It should be noted that in the MRI apparatus <NUM> of the present embodiment, wireless transmission of the system clock from the first communication circuitry <NUM> to the second communication circuitry <NUM> is performed on the basis of surface electric field communication by using electric field propagation along the body surface of the object. The surface electric field communication is also called quasi-electrostatic field communication.

Electromagnetic fields can be classified into a radiated electromagnetic field, an induced electromagnetic field, and a quasi-electrostatic field. The radiated electromagnetic field decays in inverse proportion to the distance, the induced electromagnetic field decays in inverse proportion to the square of the distance, and the quasi-electrostatic field decays in inverse proportion to the cube of the distance. Among these three, the radiated electromagnetic field (so-called radio wave) having the smallest attenuation with respect to distance is used for ordinary long-distance telecommunication.

The quasi-electrostatic field does not have the property of propagating through space like the radiated electromagnetic field, and is a voltage phenomenon distributed like an electrostatic charge near a substance such as a human body and a vehicle. While the temporal change of the electrostatic field can be regarded as zero, the quasi-electrostatic field temporally changes, and has a frequency component.

In the present embodiment, this quasi-electrostatic field is used for the communication between the first communication circuitry <NUM> and the second communication circuitry <NUM>. Exciting an electric field due to capacitive coupling between the electrode <NUM> of the first communication circuitry <NUM> and the object (human body) and superimposing information of the system clock on the excited electric field enable the information of the system clock to be transmitted from the first communication circuitry <NUM> to the second communication circuitry <NUM> by using the surface of the human body as a transmission medium.

As shown in <FIG>, the first communication circuitry <NUM> having the first electrode <NUM> may be disposed, for example, inside the table <NUM> of the bed <NUM>, or at the top of the table <NUM>. In particular, it is preferred that the first electrode <NUM> of the first communication circuitry <NUM> is disposed close to the object. For example, as shown in <FIG>, the first electrode <NUM> is disposed close to the back of the object. The first electrode <NUM> can be coated with an insulating coating. The first electrode <NUM> is not necessarily required to contact the skin of the object, and thus, may be disposed near the object via clothing. The first electrode <NUM> is, for example, a flat metal plate. Although the first electrode <NUM> is not limited to a specific dimension, the first electrode <NUM> may be a flat metal plate having a side or a diameter ranging from several centimeters to several tens of centimeters, for example.

The second communication circuitry <NUM> is disposed inside the RF coil <NUM>. The second electrode <NUM> of the second communication circuitry <NUM> is disposed close to the object, similarly to the first electrode <NUM> of the first communication circuitry <NUM>. For example, the second electrode is disposed close to the chest or abdomen of the object. The second electrode <NUM> may be also, for example, a flat metal plate having a side or a diameter ranging from several centimeters to several tens of centimeters, similarly to the first electrode <NUM>.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> and the second communication circuitry <NUM> according to the first embodiment. <FIG> also shows the function of the main body <NUM> related to the communication and the communication information between the first communication circuitry <NUM> and the second communication circuitry <NUM>.

The main body <NUM> includes a system-clock generation circuit <NUM>, which generates the system clock. The system clock is used for the entire MRI apparatus <NUM>, and the AD clock is generated from the system clock when the RF coil <NUM> performs A/D conversion on each MR signal. At the same time, a clock for acquiring the digital MR signal, which is wirelessly transmitted from the RF coil <NUM>, to the main body <NUM> is also generated from the system clock.

As described above, the system clock is used for performing synchronized processing between the main body <NUM> and the RF coil <NUM>. Therefore, it is necessary to send the system clock generated by the main body <NUM> to the RF coil <NUM>.

Since the RF coil <NUM> of the present embodiment is configured as a wireless RF coil that transmits the MR signal to the main body <NUM> wirelessly, it is also necessary to wirelessly transmit the system clock generated by the main body <NUM> to the RF coil <NUM>. In the MRI apparatus <NUM> of the present embodiment, the wireless transmission of the system clock is performed by using the above-described surface electric field communication along the body surface. The wireless transmission of the system clock is performed by using the first communication circuitry <NUM> and the second communication circuitry <NUM> shown in <FIG>. In the following, while focusing on the wireless transmission of the system clock, the communication system of the present embodiment will be described.

The first communication circuitry <NUM> includes a first PLL (Phase Locked Loop) circuit <NUM>, a band-pass filter (BPF) <NUM>, and the first electrode <NUM>, as shown in <FIG>. The first PLL circuit <NUM> includes a phase comparator/charge pump (PFD/CP) <NUM>, a loop filter <NUM>, a VCO (voltage-controlled oscillator) <NUM>, and a frequency divider (M/N) <NUM>.

Although the clock frequency of the system clock generated by the main body <NUM> is not limited to a specific frequency, in the following, a description will be given of the case where the clock frequency of the system clock is <NUM>, as one example.

The first PLL circuit <NUM> of the first communication circuitry <NUM> multiplies the frequency of the system clock, which is transmitted by wire from the main body <NUM>, to generate a carrier signal for wirelessly transmitting the system clock from the first communication circuitry <NUM> to the second communication circuitry <NUM> by the surface electric field communication. Note that the carrier signal here is not a signal modulated by specific information or a specific waveform. Here, a clock signal obtained by simply multiplying the system clock is referred to as the carrier signal. In the following, the frequency of the carrier signal is referred to as the carrier frequency. Since the carrier signal is a signal obtained by multiplying the system clock by using the PLL circuit, the carrier signal and the system clock are signals synchronized with each other.

The band pass filter <NUM> removes unnecessary waves from the carrier signal, and the carrier signal after this filtering is wirelessly transmitted to the second electrode of the second communication circuitry <NUM> by the surface electric field communication with the use of the first electrode <NUM>. The carrier frequency of the carrier signal is determined by the frequency of the system clock and the frequency division ratio of the frequency divider (M/N) <NUM>. The clock frequency of the system clock is assumed to be <NUM> as described above. Thus, when the frequency division ratio of the frequency divider (M/N) <NUM> is <NUM>/<NUM>, the carrier frequency of the carrier signal will be <NUM>.

Although the carrier frequency of the carrier signal is not limited to a specific range, from the viewpoint of suppressing reflection from any structure or substance distant from the object (i.e., imaging target), and reducing fading by suppressing the radiated electromagnetic field, a too high frequency is not desirable for the carrier frequency of the carrier signal. On the other hand, if the carrier frequency is set to a too low frequency, the carrier signa is likely to be affected by noise around the object. From such viewpoints, the carrier frequency of the carrier signal is set, for example, in the range of <NUM> to several tens of MHz. In each embodiment, a description is given of the case where the carrier frequency of the carrier signal is <NUM>. However, it should be noted that this frequency is only one example, and other frequencies may be used for the carrier frequency.

The carrier signal, which is wirelessly transmitted from the first electrode <NUM> of the first communication circuitry <NUM>, is received by the second electrode <NUM> of the second communication circuitry <NUM>. The second communication circuitry <NUM> includes a band-pass filter (BPF) <NUM> and a second PLL circuit <NUM> in addition to the second electrode <NUM>. The second PLL circuit <NUM> includes a frequency divider (M/N) <NUM>, a phase comparator/charge pump (PFD/CP) <NUM>, a loop filter <NUM>, and a VCO <NUM>, similarly to the first PLL circuit <NUM>.

The second PLL circuit <NUM> performs the opposite operation of the first PLL circuit <NUM>. The first PLL circuit <NUM> generates the carrier signal by multiplying the system clock ten times, for example, from <NUM> to <NUM>. Conversely, the second PLL circuit <NUM> generates, or reproduces, the system clock by dividing the carrier signal by ten, for example, from <NUM> to <NUM>.

Since the divider (M/N) <NUM> of the first PLL circuit <NUM> and the divider (M/N) <NUM> of the second PLL circuit <NUM> have the same frequency dividing ratio (for example, <NUM>/<NUM>), the frequency of the system clock inputted to the first communication circuitry <NUM> can be completely coincident with the frequency of the system clock outputted from the second communication circuitry <NUM>, and thus, the respective phases of these two system clocks can be completely synchronized.

The second communication circuitry <NUM> is built in the RF coil <NUM> or is disposed close to the RF coil <NUM>. In the RF coil <NUM>, the MR signal received by the element coil <NUM> is converted into a digital signal by the A/D converter <NUM>. The AD clock to be used at this time is obtained by multiplying the system clock outputted from the second communication circuitry <NUM> with the use of the multiplier <NUM> of the RF coil <NUM>. Consequently, the AD clock used in the RF coil <NUM> becomes a clock signal that is synchronized with the system clock generated in the main body <NUM>.

The MR signal converted into a digital signal is further converted into a signal suitable for wireless transmission by a wireless modulation/transmitter <NUM>, and then is wirelessly transmitted from the transmission/reception antenna <NUM> to the transmission/reception antenna <NUM> of the main body <NUM>. This wireless transmission may be achieved by a remote communication method using a radiated electromagnetic field, for example.

Subsequently, in the main body <NUM>, each received MR signal is demodulated by the MR-signal demodulation circuit <NUM>. Thereafter, the reconstruction processing circuit <NUM> performs reconstruction processing on the demodulated MR signals so as to generate an MR image.

In the MRI apparatus <NUM> of the first embodiment described above, the system clock generated by the main body <NUM> is wirelessly transmitted to the RF coil <NUM> by the surface electric field communication using electric field propagation along the body surface of the object. Thus, the system clock can be stably wirelessly transmitted from the main body <NUM> to the RF coil <NUM> without being affected by fading due to reflection from any structure or substance around the object.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> and the second communication circuitry <NUM> according to the first modification of the first embodiment. As compared with the above-described first embodiment, the first modification of the first embodiment additionally has a function of detecting the phase fluctuation of the carrier signal and a function of setting the carrier frequency of the carrier signal so as to reduce the phase fluctuation.

The second communication circuitry <NUM> includes a fluctuation detection circuit <NUM> in order to implement the function of detecting the phase fluctuation of the carrier signal. Although the method of detecting fluctuation is not limited to a specific method, the fluctuation detection circuit <NUM> branches the carrier signal received by the second electrode <NUM> into the first path delayed by a delay element and the second path without delay, and then detects the phase difference between the respective output ends of the first path and the second path, for example. When no fluctuation is included in the phase of the carrier signal, this phase difference shows a constant value. By contrast, when fluctuation is included in the phase of the carrier signal, it is considered that this phase difference should fluctuate.

Information on the presence/absence and/or the degree of the phase fluctuation in the carrier signal detected by the fluctuation detection circuit <NUM> is sent to the main body <NUM> via the wireless modulation/transmitter <NUM>. The main body <NUM> according to the first modification of the first embodiment includes a clock carrier-frequency control circuit <NUM>. The clock carrier-frequency control circuit <NUM> adjusts the carrier frequency of the carrier signal such that the phase fluctuation is reduced, based on the presence/absence and/or the degree of the phase fluctuation in the carrier signal.

Specifically, the clock carrier-frequency control circuit <NUM> simultaneously changes the respective frequency dividing ratios of the frequency divider (M/N) <NUM> of the first communication circuitry <NUM> and the frequency divider (M/N) <NUM> of the second communication circuitry <NUM>, by sending a control signal so as to search for the carrier frequency that reduces the phase fluctuation, and then sets the searched appropriate carrier frequency for the carrier signal. The control signal for changing the frequency dividing ratio of the frequency divider (M/N) <NUM> of the second communication circuitry <NUM> is wirelessly transmitted from the main body <NUM> to the RF coil <NUM>, and then is sent to the frequency divider (M/N) <NUM> via the wireless receiver/demodulator <NUM> of the RF coil <NUM>.

According to the first modification of the first embodiment, in addition to the effects of the first embodiment, the phase fluctuation of the carrier signal can be reduced, and consequently, the phase fluctuation of the system clock can also be reduced.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> and the second communication circuitry <NUM> according to the second modification of the first embodiment. In <FIG>, the internal configuration of each of the first PLL circuit <NUM> and the second PLL circuit <NUM> is omitted in order to avoid complication.

In the second modification of the first embodiment, a function of shifting the phase of the system clock is added to the configuration of the first modification of the first embodiment. This additional function can be directly added to the first embodiment by removing the two functions added in the first modification.

In the second modification of the first embodiment, a phase-delay calculation circuit <NUM> is provided in the main body <NUM>, and the phase-delay calculation circuit <NUM> calculates a desired phase shift amount of the system clock. In the surface electric field communication used in the present embodiment, the propagation path length varies depending on the size of the body of the object. Thus, the phase difference between the system clock of the transmission source of the first communication circuitry <NUM> and the system clock reproduced by the second communication circuitry <NUM> (i.e., phase difference caused by the delay amount) has different values depending on the size of the object, such as the thickness of the trunk (body) of the object.

Thus, in the second modification of the first embodiment, the phase delay calculation circuit <NUM> estimates the size of the object such as the thickness of trunk of the object by using image recognition technology, estimates the propagation path length from the first communication circuitry <NUM> to the second communication circuitry <NUM>, and calculates the amount of phase correction.

The calculated phase correction amount is set in a phase shifter <NUM> provided in the first communication circuitry <NUM>. The phase shifter <NUM> adjusts the phase of the system clock of the transmission source so as to correct the amount of the phase delay due to the propagation path length.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> and the second communication circuitry <NUM> according to the third modification of the first embodiment. As compared with the second modification of the first embodiment, the third modification of the first embodiment additionally includes a function of detecting a body motion such as heartbeat and a respiratory motion.

The carrier signal transmitted from the first communication circuitry <NUM> to the second communication circuitry <NUM> propagates along the body surface of the object from the first electrode <NUM> toward the second electrode <NUM> as shown in <FIG>. Thus, when the body surface of the object fluctuates due to respiration and/or heartbeat, the carrier signal is subjected to amplitude modulation corresponding to the cycle of respiration and/or heartbeat and fluctuation range of respiration and/or heartbeat.

Thus, in the configuration of the third modification of the first embodiment, the second communication circuitry <NUM> is provided with a heartbeat/respiratory-motion detection circuit <NUM>. The heartbeat/respiratory-motion detection circuit <NUM> functions as a biological monitoring circuit. The carrier signal received by the second electrode <NUM> passes through the band-pass filter <NUM> to be sent to the second PLL circuit <NUM> where the system clock is reproduced. Meanwhile, the carrier signal also passes through the lowpass filter <NUM> to be sent to the heartbeat/respiratory-motion detection circuit <NUM>. The heartbeat/respiratory-motion detection circuit <NUM> detects the respiratory motion and/or heartbeat of the object on the basis of the amplitude fluctuation of the carrier signal and extracts information on the respiratory motion and/or heartbeat.

The heartbeat/respiratory-motion detection circuit <NUM> may detect biological information items such as a respiratory waveform, a heartbeat waveform, respiratory time-phase information based on the respiratory waveform, time-phase information of heartbeat based on the heartbeat waveform, a respiratory cycle, a respiratory rate, a heartbeat cycle, and/or a cardiac rate.

These biological information items detected by the heartbeat/respiratory-motion detection circuit <NUM> are transmitted to the wireless modulation/transmitter <NUM>, and then wirelessly transmitted to the main body <NUM>. The main body <NUM> can cause the display <NUM> to display the biological information items transmitted from the second communication circuitry <NUM>. The main body <NUM> can also perform ECG-gated imaging and respiratory-gated imaging by using the heartbeat waveform and the respiratory waveform.

In the reconstruction processing performed by the reconstruction processing circuit <NUM>, motion correction processing based on positional correction and/or phase correction may be performed by using the heartbeat waveform and the respiratory waveform transmitted from the second communication circuitry <NUM>.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> and the second communication circuitry <NUM> according to the second embodiment. In the second embodiment, the function of detecting a body motion such as heartbeat and a respiratory motion is added to the second modification of the first embodiment, similarly to the third modification of the first embodiment.

However, it should be noted that the configuration of the second embodiment detects a body motion, such as heartbeat and a respiratory motion, by a biological-information monitoring signal generated independently of the carrier signal of the system clock, while the configuration of the third modification of the first embodiment detects a body motion by using amplitude fluctuation of the carrier signal itself. The frequency of the biological-information monitoring signal of the second embodiments is selected so as to be different from the frequency of the carrier signal for transmitting the system clock.

The biological information monitoring signal is generated by a biological monitoring oscillator <NUM> provided in the first communication circuitry <NUM>. The frequency of the biological-information monitoring signal is, for example, <NUM>, and a frequency higher than the carrier frequency <NUM> of the carrier signal is selected as the frequency of the biological-information monitoring signal.

The biological-information monitoring signal and the carrier signal for clock transmission are combined by a combiner <NUM> and then wirelessly transmitted from the first electrode <NUM> to the second electrode <NUM> of the second communication circuitry <NUM>. In the second communication circuitry <NUM>, the combined signal of the biological-information monitoring signal and the carrier signal for clock transmission is divided into two by a divider <NUM>. One of the divided signals is transmitted to the second PLL circuit <NUM> through the band-pass filter <NUM> having the center frequency of <NUM>, and another of divided signals is transmitted to the heartbeat/respiratory-motion detection circuit <NUM> through the band-pass filter <NUM> having the center frequency of <NUM>.

The heartbeat/respiratory-motion detection circuit <NUM> detects a body motion such as heartbeat and a respiratory motion by detecting change in magnitude of the transmitted signal of the biological-information monitoring signal from the first electrode <NUM> to the second electrode <NUM>.

The block diagram of the second embodiment shown in <FIG> includes: the function (A), which is achieved by the components such as the fluctuation detection circuit <NUM> and the clock carrier-frequency control circuit <NUM>, of detecting the phase fluctuation of the system clock carrier signal and adjusting the carrier frequency to reduce the phase fluctuation; and the function (B), which is achieved by the components such as the phase shifter <NUM> and the phase-delay calculation circuit <NUM>, of correcting the phase delay attributable to the propagation path length of the system clock. However, the entire communication system may be configured such that one or both of the function (A) of adjusting the carrier frequency and the function (B) of correcting the phase delay may be omitted from the configuration of the second embodiment.

<FIG> are schematic diagrams illustrating how the first electrode <NUM> in the first communication circuitry <NUM> and the second electrode <NUM> in the second communication circuitry <NUM> according to the second embodiment are arranged, and how an electric field propagates between the first electrode <NUM> and the second electrode <NUM>. As shown in the right part of <FIG>, the first electrode <NUM> and the second electrode <NUM> are configured as a plate-shaped dipole antenna.

Note that the element of the dipole antenna is formed in a plate shape, instead of a usual rod shape. This configuration makes it easy to excite an electric field due to capacitive coupling with the object (human body) and can realize an antenna suitable for the surface electric field communication, in which an electric wave propagates on the body surface in a near field (quasi-electrostatic field) Es using a relatively low frequency. Meanwhile, a half-wave dipole antenna is formed by feeding power to the center of two plate-shaped elements, which achieves communication in the far field (radiation field) Er using a frequency (for example, <NUM>) higher than the carrier frequency at the same time.

It is known that the near field (quasi-electrostatic field) Es readily propagates in the longitudinal direction of the electrode when the plate-shaped electrode is rectangular. For this reason, it is preferred to dispose the plate-shaped dipole antenna such that the longitudinal direction thereof is orthogonal to the head-foot direction of the object (i.e., parallel to the right-left direction of the object). This is because the direction in which the carrier signal readily propagates coincides with the direction in which the propagation path length becomes shorter.

In the second embodiment, the heartbeat/respiratory-motion detection circuit <NUM> provided in the second communication circuitry <NUM> detects the change in magnitude of the transmitted signal of the biological-information monitoring signal from the first electrode <NUM> to the second electrode <NUM> so that a body motion such as heartbeat and a respiratory motion is detected.

Instead of detecting a body motion by the transmitted signal, the entire system may be configured such that a directional coupler (not shown) is provided between the combiner <NUM> and the first electrode <NUM> and the first communication circuitry <NUM> includes a heartbeat/respiratory-motion detection circuit (not shown) configured to detect the fluctuation of the reflected signal from the first electrode <NUM>. In this case, the heartbeat/respiratory-motion detection circuit of the first communication circuitry <NUM> detects change in coupling amount of the near-field coupling between the object and the first electrode <NUM>. That is, the coupling amount of the near-field coupling between the object and the first electrode <NUM> fluctuates due to the body motion of the object such as heartbeat and a respiratory motion, and thus, the matching situation of the first electrode <NUM> with respect to the biological-information monitoring signal fluctuates, resulting in that the reflected signal of the biological-information monitoring signal from the first electrode <NUM> fluctuates. Accordingly, in the first modification of the second embodiment, a body motion such as heartbeat and a respiratory motion is detected by detecting change in the reflected signal.

The second modification of the second embodiment is a configuration in which the second embodiment and the first modification of the second embodiment are combined as to detection of a body motion such as heartbeat and a respiratory motion. In other words, in the configuration of the second modification of the second embodiment, the second communication circuitry <NUM> is provided with the heartbeat/respiratory-motion detection circuit <NUM> and the first communication circuitry <NUM> is also provided with the heartbeat/respiratory-motion detection circuit.

The heartbeat/respiratory-motion detection circuit <NUM> of the second communication circuitry <NUM> detects the fluctuation of magnitude of the transmitted signal of the biological-information monitoring signal from the first electrode <NUM> to the second electrode <NUM>. Meanwhile, the heartbeat/respiratory-motion detection circuit of the first communication circuitry <NUM> detects the fluctuation of magnitude of the reflected signal of the biological-information monitoring signal from the first electrode <NUM>. Further, diversity processing is performed on the fluctuation of the transmitted signal and the fluctuation of the reflected signal to detect a body motion such as heartbeat and/or a respiratory motion. For example, the fluctuation width of the transmitted signal is compared with the fluctuation width of the reflected signal, and the body motion such as heartbeat and/or a respiratory motion is detected from the signal having the larger fluctuation width.

<FIG> are schematic diagrams illustrating the first electrode <NUM> and the second electrode <NUM> used in the first communication circuitry <NUM> and the second communication circuitry <NUM> according to the third modification of the second embodiment. In the second embodiment, a plate-shaped dipole antenna is used as the first electrode <NUM> and the second electrode <NUM> (<FIG>). In the third modification of the second embodiment, a microstrip circularly polarized antenna is used instead of the plate-shaped dipole antenna.

The use of the microstrip circularly polarized antenna for both the first electrode <NUM> and the second electrode <NUM> makes the quasi-electrostatic field Es approximately omnidirectional (or nondirectional) for the surface electric field communication. Thus, even if the first electrode <NUM> and the second electrode <NUM> are displaced with respect to the body surface or are misaligned (or misoriented) with each other, both electrodes <NUM> and <NUM> are less likely to be affected by the displacement or misalignment (misorientation).

In addition, the use of the circularly polarized waves makes it less likely to be affected by primary reflected signals from around the object. This is because the rotational direction of the circularly polarized wave in the case of the primary reflection signal is reversed.

Instead of the microstrip circularly polarized antenna, a cross dipole antenna in which two plate-shaped dipole antennas are arranged so as to be orthogonal to each other can be used. Circular polarization can be realized by the cross dipole antenna as well. The cross dipole antenna also has wide-angle directivity close to the microstrip circularly polarized antenna as compared with the dipole antenna, and can be made less susceptible to the displacement and misorientation of the first electrode <NUM> and the second electrode <NUM>.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> according to the fourth modification of the second embodiment. <FIG> focuses particularly on the components related to generation of the carrier signal of the system clock (center frequency fc1, for example, <NUM>) and the biological-information monitoring signal (center frequency fc2, for example, <NUM>).

The system clock (clock frequency fsys, for example, <NUM>) generated by the system-clock generation circuit <NUM> of the main body <NUM> is converted into a frequency fc1 (= <NUM>) of ten times by the first PLL circuit <NUM> of the first communication circuitry <NUM>.

The first communication circuitry <NUM> has a local oscillator with a local frequency fL (= <NUM>). The leftmost mixer in <FIG> mixes the output signal of the first PLL circuit <NUM> and the output signal of the local oscillator, and generates an intermediate signal of an intermediate frequency (fc1 + fL = <NUM>, fc1 - fL = <NUM>). As to these two frequencies (<NUM> and <NUM>), the intermediate signal having the frequency of <NUM> is selected by the band-pass filter having the center frequency Fc (= <NUM>), and further mixed with the output signal of the local oscillator by the second leftmost mixer. The output of this mixer includes: the sum frequency (fc1 + 2fL = <NUM>) of the intermediate frequency (fc1 + fL = <NUM>) and the local frequency fL (= <NUM>); and the difference frequency (fc1 = <NUM>) between the intermediate frequency (fc1 + fL = <NUM>) and the local frequency fL. The divider and two band-pass filters, which are connected to the output stage of the mixer, extract the signal corresponding to the sum frequency (= <NUM>) as the biological-information monitoring signal and also extract the signal corresponding to the difference frequency (= <NUM>) as the carrier signal of the system clock. Subsequently, these two signals are combined by a combiner and transmitted from the first electrode <NUM>.

<FIG> is a block diagram illustrating a configuration of the first communication circuitry <NUM> according to the fifth modification of the second embodiment. The configuration of the fourth modification of the second embodiment has the local oscillator of the local frequency fL (= <NUM>) in the first communication circuitry <NUM>. In the fifth modification of the second embodiment, without having a local oscillator in the first communication circuitry <NUM>, the output signal of the oscillator <NUM> provided in the main body <NUM> is used as a local signal of each mixer of the first communication circuitry <NUM>.

The output signal of the oscillator <NUM> of the main body <NUM> generates an RF pulse for exciting hydrogen nuclei of the object to emit an MR signal, and is outputted from the RF transmitter <NUM> via the WB coil <NUM> to the object. When the static magnetic field of the MRI apparatus <NUM> is <NUM> Tesla, the frequency of the output signal of the oscillator <NUM> is the Larmor frequency of <NUM>. Thus, in the fifth modification of the second embodiment, the Larmor frequency may be used as the local frequency fL (= <NUM>) in the first communication circuitry <NUM>.

According to the fifth modification of the second embodiment, the local oscillator in the first communication circuitry <NUM> is not required. Further, the frequency of the biological-information monitoring signal does not match the harmonics of the Larmor frequency, and thus, is not affected by harmonics of the RF pulse generated by the main body <NUM>.

According to the MRI apparatus <NUM> of each embodiment described above, the system clock can be stably transmitted from the main body of the MRI apparatus to the wireless RF coil without being affected by fading, and biological information such as heartbeat and/or respiration of the object can be readily obtained without imposing a burden on the object.

Claim 1:
A Magnetic Resonance Imaging "MRI" apparatus (<NUM>) comprising:
an RF coil (<NUM>) configured to perform A/D conversion on a magnetic resonance "MR" signal received from a human body and wirelessly transmit the MR signal;
a main body (<NUM>) configured to wirelessly receive the MR signal and generate a system clock signal; the apparatus being characterised by the following features:
first communication circuitry (<NUM>) configured to transmit the system clock signal by surface electric field communication using electric field wireless propagation along a body surface of the human body; and
second communication circuitry (<NUM>) disposed inside the RF coil (<NUM>) and configured to receive the system clock signal transmitted by the surface electric field communication using the electric field wireless propagation from the first communication circuitry (<NUM>),
wherein the RF coil (<NUM>) is configured to operate based on the received system clock signal.