Universal radio frequency coil system used for magnetic resonance imaging, and imaging method

Abstract

A universal radio frequency coil system used for magnetic resonance imaging, and an imaging method. The system comprises a transmitting coil (3), a universal pickup coil (4) and a radio frequency coil (5), wherein the universal pickup coil (4) and the radio frequency coil (5) form a radio frequency coil (5) combination, and the transmitting coil (3) is used for transmitting a magnetic resonance signal for a target part to be imaged, so that the target part is excited to generate an electromagnetic signal; the radio frequency coil (5) is composed of a plurality of radio frequency coil (5) units, and is used for amplifying the electromagnetic signal and transmitting the amplified electromagnetic signal to the universal pickup coil (4) by magnetic coupling; and the universal pickup coil (4) surrounds the radio frequency coil (5) and the target part wearing the radio frequency coil (5) to provide 360° coverage. The system can improve the sensitivity and parallel imaging performance of magnetic resonance imaging.

Description

A universal wireless radio frequency coil system for magnetic resonance imaging and imaging method TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic resonance imaging, and more particularly to a universal wireless radio frequency coil system for magnetic resonance imaging and imaging method. BACKGROUND

[0002] Magnetic resonance imaging technology has become an important means for human soft tissue imaging due to its non-invasive, non-radiation, high resolution, high contrast, and arbitrary orientation cross-sectional imaging advantages. The magnetic resonance signal acquisition process mainly includes two stages of radio frequency excitation and radio frequency reception. Referring to the traditional wired coil diagram in FIG. 1, in the radio frequency excitation stage, the magnetic resonance imaging system sends a magnetic resonance signal to the human tissue located in the wired coil 11 through the transmitting coil 3 (the transmitting coil 3 is a body coil, which can be used as a transmitting coil or a receiving coil, and in the example in FIG. 3, it is only used as a transmitting coil); in the radio frequency reception stage, the excited tissue sends electromagnetic signals to the surrounding space, which are received by the receiving coil 11 and fed back to the imaging system, and the signal acquisition process is completed. Since the electromagnetic signal is very weak, the performance of the receiving coil is very critical, which largely determines the final image quality.

[0003] The performance of the receiving coil mainly reflects in two aspects of sensitivity and parallel imaging capability. High sensitivity means being able to distinguish weak signals, and high parallel imaging capability determines that the magnetic resonance system can perform faster imaging in hardware. In order to obtain the best possible image quality, the prior art usually customizes special wired receiving coils 11 for different human body parts, such as head coils, knee coils, abdominal coils, etc. When performing magnetic resonance imaging of different parts, the doctor needs to change between different wired coils. Moreover, the traditional various receiving coils need to be composed of a large number of resonant units, matching / tuning circuits, preamplifier circuits, and transmission cables with wave traps. These structures result in a very heavy coil, for example, the weight of the common head coil, knee coil, and abdominal coil reaches several kilograms. The repeated replacement of such heavy coils and cables brings physical burden to the doctor's work. When the doctor replaces and carries the wired coil, the patient can only wait on the side, which greatly affects the efficiency of the examination. In addition, due to the heaviness of the existing wired abdominal coil, the patient needs to bear the pressure of the abdominal coil during the abdominal imaging, which not only has safety hazards for injured or weak patients, but also greatly affects the comfort, easily causing the patient to be uneasy and twist, resulting in image artifacts.

[0004] After analysis, the current wired or wireless radio frequency coil mainly has the following defects:

[0005] 1) Prior art uses spine coil as pickup coil. Spine coil is usually a multi-channel coil array laid on the bed. Spine coil loses signals in other directions because it is only distributed under the wireless radio frequency coil, thus affecting the overall sensitivity. Since the parallel imaging capability of the wireless radio frequency coil depends on the number of channels of the pickup coil and the spatial angle covered by the pickup coil, the spine coil (arranged on the bed) is only distributed under the wireless radio frequency coil, and its spatial angle covered is limited relative to the imaging target area and the wireless radio frequency coil, thus affecting the parallel imaging capability.

[0006] 2) Prior art uses body coil as pickup coil. Body coil is usually a birdcage coil integrated in the magnet, because the sensitivity of the birdcage coil is usually weaker than that of the same size surface coil array. However, the birdcage coil is usually too far away from the wireless radio frequency coil, so using the birdcage coil as the pickup coil reduces the sensitivity. In addition, the birdcage coil has only two channels, while the parallel imaging capability of the wireless radio frequency coil system depends on the number of channels of the pickup coil, the more channels, the stronger the parallel imaging capability, so the scheme of using the body coil (birdcage coil) also affects the parallel imaging capability.

[0007] SUMMARY

[0008] The purpose of the present application is to overcome the above-mentioned defects of the prior art, and to provide a universal wireless radio frequency coil system and an imaging method for magnetic resonance imaging.

[0009] According to a first aspect of the present application, a universal wireless radio frequency coil system for magnetic resonance imaging is provided, comprising a transmit coil, a universal pickup coil and a wireless radio frequency coil, the universal pickup coil and the wireless radio frequency coil forming a wireless radio frequency coil combination, wherein the transmit coil is used to emit a magnetic resonance signal for a target part to be imaged to excite the target part to generate an electromagnetic signal; the wireless radio frequency coil is composed of a plurality of wireless radio frequency coil units, used to amplify the electromagnetic signal and transmit the amplified electromagnetic signal to the universal pickup coil through magnetic coupling; the universal pickup coil surrounds the wireless radio frequency coil and the target part wearing the wireless radio frequency coil in a manner covering a range of 360°.

[0010] According to a second aspect of the present application, an imaging method is provided. The method comprises:

[0011] Performing magnetic resonance scanning on the target part using the provided universal wireless radio frequency coil system;

[0012] Obtaining the imaging result of the magnetic resonance scanning and displaying it.

[0013] Compared with the prior art, the universal wireless radio frequency coil system for magnetic resonance imaging can improve the sensitivity and parallel imaging performance of magnetic resonance imaging, and is especially suitable for high-sensitivity and high-parallel imaging of different organs of the human body.

[0014] Other features and advantages of the present application will become apparent from the following detailed description of illustrative embodiments thereof, which description should be taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the application.

[0016] Fig. 1 is a schematic diagram of a wired radio frequency coil in the prior art;

[0017] Fig. 2 is a front view of a universal wireless radio frequency coil system for magnetic resonance imaging according to an embodiment of the present application;

[0018] Fig. 3 is a schematic diagram of a cross-section 1 of the universal wireless radio frequency coil system of Fig. 2;

[0019] Fig. 4 is a schematic diagram of a cross-section 2 of the universal wireless radio frequency coil system of Fig. 2;

[0020] Fig. 5 is a flowchart of an imaging method based on the universal wireless radio frequency coil system according to an embodiment of the present application;

[0021] Fig. 6 is a flowchart of an imaging method of a wired radio frequency coil system in the prior art;

[0022] Fig. 7 is a schematic diagram of a wireless radio frequency coil unit according to an embodiment of the present application;

[0023] Fig. 8 is a schematic diagram of a wireless radio frequency coil array according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of the components and steps set forth in the embodiments, numerical expressions, and numerical values are not limiting to the scope of the present application unless otherwise specifically stated.

[0025] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the scope of the application, its application, or uses.

[0026] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein, but should be considered as part of the specification, where appropriate.

[0027] In all of the examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not limiting. Thus, other examples of the exemplary embodiments can have different values.

[0028] It should be noted that like reference numerals and letters refer to like items throughout the drawings, and once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0029] The present application proposes a general wireless radio frequency coil system for magnetic resonance imaging and a corresponding imaging method. In general, the general wireless radio frequency coil system takes a surface coil array as a pickup coil and is composed of wireless radio frequency coils for different parts. The imaging method based on the general wireless radio frequency coil system has higher imaging sensitivity and stronger parallel imaging capability compared with existing solutions.

[0030] Specifically, referring to FIG. 2, the provided general wireless radio frequency coil system mainly includes a transmit coil 3, a general pickup coil 4, and wireless radio frequency coils 5. The wireless radio frequency coils 5 can be designed to adapt to different imaging parts, i.e., different wireless radio frequency coils 5 are equipped for different human body parts to adapt to the corresponding shapes. The general pickup coil 4 and the wireless radio frequency coils 5 form a wireless radio frequency coil combination. FIG. 2 also shows a magnetic resonance patient bed 1 and a magnet 2.

[0031] In the present application, the wireless radio frequency coils 5 are not physically connected to the main body of the MRI device, and the combination of the general pickup coil 4 and the wireless radio frequency coils 5 replaces the wired receiving coil 11 of the prior art in FIG. 1, achieving higher imaging quality.

[0032] In one embodiment, the wireless radio frequency coil combination includes one general pickup coil 4 and several wireless radio frequency coils 5 for different parts. In use, the general pickup coil 4 surrounds the wireless radio frequency coils 5 and the imaging object in the radio frequency coil, covering a 360° range. This full- range spatial angle coverage for the imaging object or the imaging target part improves the parallel imaging capability. The wireless radio frequency coils 5 can send, receive, or transmit and receive radio frequency signals of the imaging target part. In this paper, the wireless radio frequency coil working in the radio frequency receiving stage is mainly taken as an example for illustration.

[0033] In one embodiment, in order to meet the high parallel imaging performance, the general pickup coil 4 is composed of a wired surface coil array for magnetic resonance imaging to realize the acquisition of magnetic resonance signals, and is provided to have more than 6 channels. In addition, the aperture of the pickup coil 4 is set to be large enough to accommodate a human body lying in it, thereby imaging different target parts.

[0034] In one embodiment, the wireless radio frequency coil 5 is arranged to be able to work in a detuned state or a resonant state. For example, in a transmitting phase of the magnetic resonance system, the wireless radio frequency coil 5 is in the detuned state, and in a receiving phase of the magnetic resonance system, the wireless radio frequency coil 5 is in the resonant state. The wireless radio frequency coil 5 can be composed of a single or multiple resonant units, and is able to realize electromagnetic resonance within 100 MHz positive and negative of the resonant frequency of the magnetic resonance system.

[0035] The transmitting coil 3 is used to transmit a magnetic resonance signal to the target site to be imaged to excite the target site to generate an electromagnetic signal. The transmitting coil 3 can be implemented by a body coil or other types of coils.

[0036] It should be noted that the wireless radio frequency coil combination proposed in the present application mainly works in the receiving phase, and therefore, in the transmitting phase, the wireless radio frequency coil needs to be in a parallel resonant state. When in parallel resonance, the wireless radio frequency coil is equivalent to an open circuit, and therefore, when electromagnetic excitation occurs in the transmitting phase, no induced current is generated on the wireless radio frequency coil, thereby avoiding interference with the magnetic field in the transmitting phase.

[0037] For the general wireless radio frequency coil system in the working state, the relative position relationship of the transmitting coil 3 (for example, a body coil), the general pickup coil 4, and the wireless radio frequency coil 5 is shown in FIGS. 2, 3, and 4.

[0038] FIG. 5 is a flowchart of an imaging method based on the general wireless radio frequency coil system provided in the present application, and the imaging method comprises the following steps:

[0039] In step S1, the general pickup coil 4 is placed on the magnetic resonance bed 1, and is connected to the magnetic resonance machine through a cable. When the scanning site is changed or the patient is changed, the general pickup coil 4 does not need to be removed or replaced.

[0040] In step S2, the patient wearing the wireless radio frequency coil 5 lies on the bed 1.

[0041] In step S3, the bed 1 is sent into the magnet 2 to perform magnetic resonance imaging.

[0042] In step S4, after the imaging is completed, it is determined whether the site needs to be changed or the patient needs to be changed.

[0043] If the determination is yes, step S5 is performed, and if the determination is no, step S6 is performed.

[0044] In step S5, while the previous patient is being examined, the next patient wears the wireless radio frequency coil 5 in the waiting area by himself / herself.

[0045] For example, while the previous patient is being examined, the next patient can wear the wireless radio frequency coil 5 corresponding to the site in the waiting area, and then places the site to be measured and the wireless radio frequency coil 5 into the general pickup coil 4, and sends the bed 1 into the magnet 2 to start the magnetic resonance scanning.

[0046] Step S6, exit the sickbed 1, remove the wireless radio frequency coil 5, and the scanning is completed.

[0047] Generally, when the magnetic resonance imaging system is working, the magnetic resonance signal is transmitted via the body coil 3, the tissue of the part of the patient to be imaged is excited to emit electromagnetic signals, the electromagnetic signals are amplified when passing through the wireless radio frequency coil 5, and the amplified signals are transmitted to the general pickup coil 4 through magnetic coupling to complete the signal acquisition.

[0048] For comparison with the prior art, Fig. 6 shows the imaging process based on the wired coil of Fig. 1. When the tissue of the part of the patient to be imaged is excited to emit electromagnetic signals, the electromagnetic signals are directly acquired through the wired coil. Under the premise of needing to replace the imaging part, the doctor needs to pull out the wired coil cable plug of the original part and remove the coil 11. It can be seen that, compared with the prior art, the present application eliminates the carrying process of the wired coil. While the previous patient is receiving examination, the next patient can simultaneously complete the wearing of the wireless coil in the waiting area and perform examination, which simplifies the process of the magnetic resonance examination and improves the efficiency. In addition, the wireless radio frequency coil used in the present application does not need a preamplifier circuit and a transmission cable with a wave trap, and thus is very thin, improving the safety and the comfort of use of the patient.

[0049] In actual use, the wireless radio frequency coil can contain multiple wireless radio frequency coil units, and Fig. 7 is a schematic view of a wireless radio frequency coil unit. Each wireless radio frequency coil unit includes a capacitor C1, a capacitor C2, a bidirectional diode D1, and an inductor L1, etc. The wireless radio frequency coil unit has a detuning circuit and a resonance circuit. The detuning circuit is composed of the inductor L1, the capacitor C2, and the bidirectional diode D1. When in the signal excitation stage, the diode is turned on, and the circuit is in a detuned state (or a parallel resonance state). When in the receiving stage, the diode is not turned on, and the circuit is in a resonance state. The wireless radio frequency coil satisfies the detuning within ±100 MHz of the working frequency of the system, and when in the signal receiving stage, the diode is not turned on, and the wireless radio frequency coil satisfies the resonance within ±100 MHz of the working frequency of the system. The wireless radio frequency coil array composed of multiple wireless radio frequency units is shown in Fig. 8.

[0050] It should be noted that, in the excitation stage, the wireless coil is detuned within ±100 MHz of the working frequency of the system, which reduces the interference of the wireless radio frequency coil on the transmission field in the transmission stage of the system; in the receiving stage, the wireless radio frequency coil is resonated within ±100 MHz of the working frequency of the system, which amplifies the signal, and thus the high sensitivity of the receiving coil can be achieved.

[0051] It should be understood that the above-mentioned embodiments can be appropriately changed or modified by those skilled in the art without departing from the spirit and scope of the present application. For example, the present application is not limited to human body imaging, but also applies to animal imaging. The general pickup coil is not limited to being placed on the bed, but can also be integrated into the magnet. In addition, the general pickup coil is not limited to the pattern shown in the figure, but can also use other surface coil arrays that play a signal pickup role. The resonant unit structure involved is not limited to circular, but also applies to other shapes that can meet the detuning and resonance requirements. And the wireless radio frequency coil is not limited to the resonant unit structure, but also applies to the array structure that meets the detuning and resonance conditions.

[0052] In order to further verify the effect of the present application, experimental verification is carried out, and the experiment shows that the general wireless radio frequency coil system designed by the present application not only can obtain higher sensitivity compared with the commercial knee coil, and has higher parallel imaging capability compared with the existing commercial coil, is a kind of practical imaging method.

[0053] In summary, compared with the prior art, the present application has the following advantages:

[0054] 1) Compared with the traditional wired coil, the wireless radio frequency coil of the present application has the characteristics of lightness and thinness, thus improving the patient comfort and the physical burden of the doctor.

[0055] 2) The pickup coil of the present application can be composed of a wired surface coil array to realize the collection of magnetic resonance signals, and more than 6 channels can be set to meet the needs of high parallel imaging performance.

[0056] 3) The pickup coil of the present application can be fixed in the bed or the magnet aperture, serving as the pickup coil of all wireless radio frequency coils, and when the scanning site is changed, the wired coil does not need to be pulled out, only the wireless coil corresponding to the scanning site needs to be replaced, thus improving the use comfort of the patient, reducing the workload of the doctor, simplifying the examination process, and improving the efficiency of magnetic resonance examination. Moreover, the present application can use a multi-channel overlapping coil array as a pickup coil, which has higher imaging sensitivity and stronger parallel imaging capability compared with the existing wireless radio frequency coil scheme.

[0057] 4) Because the present application uses a multi-channel surface coil array as a general pickup coil, compared with the existing scheme using a birdcage coil as a pickup coil or using a body coil, it has more channels, better imaging sensitivity and higher parallel imaging capability.

[0058] The present application can be a system, a method and / or a computer program product. The computer program product can include a computer readable storage medium having computer readable program instructions loaded thereon for causing a processor to implement various aspects of the present application.

[0059] Computer readable storage media can be tangible storage media which can retain and store instructions for use by an instruction execution device. Computer readable storage media can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer readable storage media include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

[0060] Computer readable program instructions described herein can be downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and / or a wireless network. The network can comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device.

[0061] Computer readable program instructions for carrying out operations of the present application can be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program instructions can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate array (FPGA), or programmable logic array (PLA) can execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present application.

[0062] The computer readable program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0063] These computer readable program instructions can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks. These computer readable program instructions can also be stored in a computer readable storage medium that can include random access memory (RAM), read only memory (ROM), electrically erasable programmable read only memory (EEPROM), flash memory or nonvolatile memory, or a suitable combination of the different types of computer readable storage media. The computer readable program instructions can also be downloaded to a computer, other programmable data processing apparatus, or other device from a computer readable storage medium or to an external computer or external storage device via a data signal that can be transmitted for example via a wired medium or a wireless medium such as the Internet or wireless media.

[0064] The computer readable program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0065] The computer readable program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0066] Embodiments of the present application have been described above, and the description is intended to be illustrative, and not restrictive, of the disclosed embodiments. Many modifications and variations of the described embodiments are possible, and all such modifications and variations are intended to be within the scope of the described embodiments. The description used herein is intended to best explain the principles of the embodiments, the practical application, and the best mode of the present application, to make this disclosure understood in the art. The scope of the present application is defined by the appended claims.

Claims

1. A universal wireless radio frequency coil system for magnetic resonance imaging, comprising a transmitting coil, a universal pickup coil and a wireless radio frequency coil, wherein the universal pickup coil and the wireless radio frequency coil constitute a wireless radio frequency coil assembly, wherein: The transmitting coil is used to transmit a magnetic resonance signal to the target part to be imaged so that the target part is excited to generate an electromagnetic signal; the wireless radio frequency coil is composed of a plurality of wireless radio frequency coil units, which are used to amplify the electromagnetic signal and transmit the amplified electromagnetic signal to the universal pickup coil through magnetic coupling; the universal pickup coil surrounds the wireless radio frequency coil and the target part wearing the wireless radio frequency coil in a manner covering a 360° range.

2. The universal wireless radio frequency coil system according to claim 1, wherein: The wireless radio frequency coil unit includes a first capacitor, a second capacitor, a bidirectional diode and an inductor, and by controlling the conduction or disconnection of the bidirectional diode, the wireless radio frequency coil unit is in a detuned state during the transmission phase and in a resonant state during the reception phase.

3. The universal wireless radio frequency coil system according to claim 2, wherein: In the detuned state, the wireless radio frequency coil is set to be detuned within a range of plus or minus 100 MHz of the operating frequency, and in the resonant state, the wireless radio frequency coil is set to be resonant within a range of plus or minus 100 MHz of the operating frequency.

4. The universal wireless radio frequency coil system according to claim 1, wherein: The universal pickup coil is formed by a wired surface coil array and is configured to have more than 6 channels.

5. The universal wireless radio frequency coil system according to claim 4, wherein: The universal pick-up coil is fixed in the patient bed or the magnet aperture of the magnetic resonance system and connected to the magnetic resonance machine via a cable.

6. The universal wireless radio frequency coil system according to claim 1, wherein: The aperture of the universal pickup coil is configured to accommodate a human body therein.

7. The universal wireless radio frequency coil system according to claim 1, wherein: The transmitting coil is a body coil.

8. The universal wireless radio frequency coil system according to claim 1, wherein: The number of the wireless radio frequency coil is set to be one or more.

9. An imaging method comprising: Performing magnetic resonance scanning on a target area using the universal wireless radio frequency coil system according to any one of claims 1 to 8; Obtain and display the imaging results of magnetic resonance imaging.

10. A computer-readable storage medium having a computer program stored thereon, wherein: When the computer program is executed by a processor, the steps of the method according to claim 9 are implemented.

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