MRI system and method for generating RF pulses for an MRI system

Abstract

The present invention relates to RF pulse generation for MRI applications. According to the present invention, an RF transmitter for an MRI system (1) is provided, the RF transmitter comprising: an RF amplifier (9) for generating RF pulses and for forwarding these RF pulses to an RF transmitting coil (5) of the MRI system (1); a capacitor bank (10) coupled to the RF amplifier (9) for storing electrical energy and for providing the RF amplifier (9) with current for generating the RF pulses; a main power supply (11) coupled to the capacitor bank (10) for generating a charging current for charging the capacitor bank (10) with electrical energy; and a power supply control unit (12) coupled to the main power supply (11) for controlling the generation of the charging current for the capacitor bank (10), wherein the power supply control unit (12) is adapted to receive an indication signal indicative of an actual current and / or an upcoming current drawn from the capacitor bank (10) and to control the generation of the charging current for the capacitor bank (10) based on the indication signal. In this way, the generation of RF pulses for MRI applications becomes more efficient, enabling the use of smaller capacitor bank values ​​at the same performance level.

Description

Technical Field

[0001] The present invention relates to the field of magnetic resonance imaging (MRI), and in particular to an RF (radio frequency) transmitter for an MRI system, the MRI system comprising an RF transmitter for generating RF pulses and for forwarding these RF pulses to an RF transmitting coil of the MRI system. In addition to an RF amplifier, the RF transmitter also comprises a capacitor bank and a main power supply, the capacitor bank is coupled to the RF amplifier, for storing electrical energy and for providing current to the RF amplifier for generating RF pulses; the main power supply is coupled to the capacitor bank, for generating a charging current for charging the capacitor bank. The present invention also relates to a method for generating RF pulses for an MRI system having an RF transmitter, the RF transmitter comprising a main power supply, a capacitor bank and an RF amplifier, the method comprising the following method steps: generating a charging current in the main power supply and charging the capacitor bank with the charging current, providing current to the RF amplifier through the capacitor bank for generating RF pulses, and generating RF pulses in the RF amplifier and forwarding these RF pulses to the RF transmitting coil of the MRI system. Background Art

[0002] Current RF amplifiers in magnetic resonance imaging applications utilize large capacitor banks to store the pulse energy that needs to be generated. These RF amplifiers typically include a main power supply, a capacitor bank for energy storage, and an RF amplifier that uses the stored energy. Typically, the capacitor bank is recharged between pulses from the main power supply. Typically, RF transmission occurs in very short pulses, and there is a considerable time between manipulating gradient fields and / or receiving RF signals.

[0003] The main power supply that charges the capacitor bank in the RF amplifier often uses switch mode power supply technology. When the capacitor bank voltage is below a threshold voltage, the switch mode power supply starts to recharge the capacitor bank. The charging current in the power supply is limited, and some control algorithm can be added to limit the charging current when the capacitor bank voltage is only slightly below the threshold voltage. Therefore, the charging starts with some delay relative to the start of discharge of the RF amplifier. Therefore, the full supply current is not available during short high power RF pulses.

[0004] US2017 / 261573 A1 describes a magnetic resonance imaging device, which includes an amplifier, a capacitor bank, and a processing circuit. The amplifier supplies RF pulses to an RF coil that generates a radio frequency magnetic field based on an imaging sequence. The capacitor bank supplies power to the amplifier. The processing circuit determines whether imaging through the imaging sequence can be performed based on the conditions of the RF pulses in the imaging sequence and the output efficiency of the amplifier. Summary of the invention

[0005] It is an object of the present invention to make RF pulse generation for MRI applications more efficient.

[0006] According to the invention, this object is solved by the subject matter of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

[0007] Therefore, according to the present invention, there is provided an RF transmitter for an MRI system, the RF transmitter comprising:

[0008] an RF amplifier for generating RF pulses and for forwarding these RF pulses to an RF transmit coil of the MRI system,

[0009] a capacitor bank coupled to the RF amplifier for storing electrical energy and for providing current to the RF amplifier for generating the RF pulses,

[0010] a main power source coupled to the capacitor bank for generating a charging current for charging the capacitor bank with electrical energy, and

[0011] a power control unit coupled to the main power supply for controlling the generation of the charging current for the capacitor bank, wherein

[0012] The power supply control unit is adapted to receive an indication signal indicative of an actual current and / or an upcoming current drawn from the capacitor bank and to control the generation of the charging current for the capacitor bank based on the indication signal.

[0013] Thus, the present invention solves the problem of power supply control for an MRI RF transmitter by using additional information. This information can be used so that a recharging current for the capacitor bank can be activated even if the voltage drop is still small. This will allow the use of smaller capacitor bank values ​​at the same performance level. According to the present invention, there are different possibilities for determining when the capacitor bank recharging current should start and how large it should be.

[0014] In this respect, according to a preferred embodiment of the invention, a capacitor bank current sensor is provided, which is coupled to the capacitor bank and is adapted to measure the actual current drawn from the capacitor bank and to generate the indication signal based on this current. In this way, the control of the charging current fed from the main power supply to the capacitor bank is directly affected by the actual current drawn from the capacitor bank. In other words: the actual current drawn from the capacitor bank directly triggers a corresponding recharging of the capacitor bank.

[0015] Additionally or alternatively, according to a preferred embodiment of the present invention, there is provided an RF amplifier power sensor coupled to the RF amplifier and adapted to measure the actual RF power used in the RF amplifier, the actual RF power being able to form a basis for calculating the current drawn. According to this preferred embodiment of the present invention, the actual RF power generated in the RF amplifier triggers the recharging of the capacitor bank.

[0016] Typically, the RF amplifier may only be coupled to the capacitor bank for feeding current to the RF amplifier. However, according to a preferred embodiment of the present invention, the RF amplifier is also directly coupled to the main power supply for drawing current directly from the main power supply. Ideally, the current from the main power supply is available during the maximum part of the RF pulse. Therefore, according to this preferred embodiment of the present invention, not only the current from the capacitor bank can be used to generate the RF power in the RF amplifier, but also the current directly obtained from the main power supply can be used to generate the RF power in the RF amplifier. This will also allow the use of smaller capacitor bank values ​​at the same performance level.

[0017] For the main power supply, the invention allows the use of different types of power supplies. However, according to a preferred embodiment of the invention, the main power supply is a switch mode power supply.

[0018] The invention also relates to an MRI system having an RF transmitter as described above. In this respect, according to a preferred embodiment of the invention, the MRI further comprises a transmitting coil and an information unit, the information unit being coupled to the power supply control unit and being adapted to generate the indication signal based on an upcoming current drawn from the capacitor bank based on an upcoming RF power demand for the transmitting coil of the MRI system. Thus, information about the MRI power demand can also be provided by the MRI system via a separate communication to the power supply control unit and thus to the RF amplifier, thereby informing the RF amplifier when to draw current from the capacitor bank and how much current will be drawn (which are based on and derived from the RF power demand).

[0019] The invention also relates to a method for generating RF pulses for an MRI system having an RF transmitter, the RF transmitter comprising a main power supply, a capacitor bank and an RF amplifier, the method comprising the following method steps:

[0020] generating a charging current in the main power supply and charging the capacitor bank with the charging current,

[0021] providing the current generated by the capacitor bank to the RF amplifier for generating the RF pulses,

[0022] generating RF pulses in the RF amplifier and forwarding these RF pulses to the RF transmit coil of the MRI system,

[0023] estimating the actual and / or upcoming current drawn from the capacitor bank, and

[0024] The generation of the charging current for the capacitor bank is controlled based on the estimated actual current and / or upcoming current drawn from the capacitor bank.

[0025] Preferred embodiments of the method described above relate to preferred embodiments of the RF transmitter described further above. In this respect, preferably, the method further comprises the method step of controlling the generation of the charging current for the capacitor bank based on the estimated upcoming current drawn from the capacitor bank, such that the charging current is fed directly to the capacitor bank before RF pulses are generated and forwarded to the RF transmit coil.

[0026] Additionally or alternatively, according to a preferred embodiment of the present invention, the method further comprises the method step of estimating the actual current drawn from the capacitor bank by measuring the actual current drawn from the capacitor bank.

[0027] As an alternative, the method step of measuring the actual current drawn from the capacitor bank can be avoided if the actual current drawn from the RF amplifier can be estimated based on different information, such as: the time-varying current drawn by (part of) the RF amplifier or the time-varying RF amplifier output power. The RF amplifier output power is closely related to the drawn current, but it also depends on other component values, such as temperature, actual bias currents in different parts of the RF amplifier, transistor efficiency and capacitor bank voltage.

[0028] According to a preferred embodiment of the invention, the RF amplifier is also fed directly by the charging current from the main power supply. As further elaborated above, according to this preferred embodiment of the invention, not only the current from the capacitor bank can be used to generate the RF power in the RF amplifier, but also the current obtained directly from the main power supply can be used to generate the RF power in the RF amplifier, which allows the use of smaller capacitor bank values ​​at the same performance level.

[0029] Additionally, according to a preferred embodiment of the present invention, the method comprises the method step of estimating the upcoming current drawn from the capacitor bank based on an upcoming RF power demand for the RF transmit coil of the MRI system.

[0030] A further preferred option of the present invention is to track and store the efficiency of the RF amplifier over time and also control the generation of the charging current for the capacitor bank based on the efficiency of the RF amplifier. In this regard, additional information about the actual RF amplifier efficiency can be utilized and the RF amplifier efficiency can be tracked over time (e.g. during changes in conditions such as temperature, aging, etc. and thus using more complete information about the RF sequence from the MRI system).

[0031] The present invention also relates to a non-transitory computer-readable medium, comprising instructions stored thereon, which, when executed on a processor, cause the processor system to perform the method as described above.

[0032] The present invention can also be used in any application where large amounts of energy are buffered and then drawn on a very short time scale. In such cases, the energy replenishment mechanism may be too late. The present invention combines a continuous time control algorithm (known from the power supply) with discrete time information from the rest of the application and can measure the output power value from the energy storage device in real time. Therefore, the control system can learn to accurately estimate the power drawn in the system and use it to fill the energy buffer.

[0033] Additionally, the present invention can also work in situations where multiple components draw power from the same energy storage, as long as all the drawn powers can be estimated with reasonable accuracy. For example, in the case of a single capacitor bank with two RF amplifier channels, the drawn power of each channel can be determined independently. The total drawn power can be used to determine the recharge current for the capacitor bank. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] These and other aspects of the invention will become apparent and elucidated with reference to the embodiments described hereinafter. However, such embodiments do not necessarily represent the full scope of the invention and therefore reference is made herein to the claims for interpreting the scope of the invention.

[0035] In the attached picture:

[0036] Figure 1 schematically depicts an MRI system with an RF transmitter according to a first preferred embodiment of the present invention,

[0037] Figure 2 Schematically depicting in more detail an RF transmitter of a first preferred embodiment of the present invention,

[0038] Figure 3 schematically depicts an RF transmitter according to a second preferred embodiment of the present invention,

[0039] Figure 4schematically depicts an RF transmitter according to a third preferred embodiment of the present invention,

[0040] Figure 5 schematically depicts an MRI system with an RF transmitter according to a fourth preferred embodiment of the present invention, and

[0041] Figure 6 The RF transmitter of a fourth preferred embodiment of the present invention is schematically depicted in more detail.

[0042] Reference numerals list

[0043] 1 MRI system

[0044] 2 Patients

[0045] 3 Superconducting magnets

[0046] 4 Gradient coils

[0047] 5 RF Transmitter Coil

[0048] 6 RF receiving coil

[0049] 7 Patient Support

[0050] 8 RF Transmitter

[0051] 9 RF Amplifier

[0052] 10 Capacitor Bank

[0053] 11 Main power supply

[0054] 12 Power Control Unit

[0055] 13 Capacitor bank current sensor

[0056] 14 RF amplifier current sensor

[0057] 15 Current lines

[0058] 16 MRI control unit

[0059] 17 Information Unit

[0060] 18 Inspection Area DETAILED DESCRIPTION

[0061] exist Figure 1In FIG. 1 , an MRI system according to a first preferred embodiment of the present invention is shown. The MRI system 1 is used to perform an MRI examination on a patient 2 in an examination region 18 in a bore of a superconducting magnet 3, which is used to generate a high static magnetic field. In order to position the patient 2 in the examination region 18, the patient 2 is positioned on a patient support 7, which can be driven into and out of the examination region 18 in the bore of the superconducting magnet 3.

[0062] Here, the MRI system 1 is shown only with its most relevant components, i.e., components having some relevance to the present invention. In this regard, the MRI system 1 according to the first preferred embodiment of the present invention includes a gradient coil 4 and an RF transmitting coil 5 and an RF receiving coil 6 in the bore of the superconducting magnet 3. The RF transmitting coil 5 transmits RF pulses supplied from the RF transmitter 8 and generates a radio frequency magnetic field in the bore of the superconducting magnet 3.

[0063] As is well known to those skilled in the art, by transmitting RF pulses having orthogonal polarization to the magnetic field generated by the superconducting magnet 3 and matching the Larmor frequency of the nucleus of interest, it is possible to excite the spins of the nuclei and make the nuclei in phase, and obtain a deflection of the net magnetization of the nuclei relative to the magnetic field direction of the superconducting magnet 3, so that a transverse component relative to the longitudinal component of the net magnetization is generated. After the RF pulse is terminated, the relaxation process of the longitudinal component and the reverse component of the net magnetization begins until the net magnetization returns to its equilibrium state. The magnetic resonance signal generated by the precessing magnetization is detected by means of the RF receiving coil 6. The received magnetic resonance signal is a time-based amplitude signal, which is further Fourier transformed into a frequency-based magnetic resonance spectrum signal and is further processed to generate a magnetic resonance image of the nucleus of interest.

[0064] According to a first preferred embodiment of the invention described herein, there is provided an RF transmitter 8, Figure 2 . The RF transmitter 8 comprises an RF amplifier 9 for generating RF pulses and for forwarding these RF pulses to the RF transmitting coil 5 of the MRI system 1. In addition, the RF transmitter 8 comprises a capacitor bank 10, which is coupled to the RF amplifier 9 for storing electrical energy and for providing the RF amplifier 9 with current for generating the RF pulses. A main power supply 11 is coupled to the capacitor bank 10 for generating a charging current for charging the capacitor bank 10 with electrical energy.

[0065] An essential aspect of the first preferred embodiment of the present invention is that a power supply control unit 12 is coupled to the main power supply 11 for controlling the generation of a charging current for the capacitor bank 10. The generation of the charging current for the capacitor bank 10 is controlled in the following manner: the power supply control unit 12 receives an indication signal, which indicates the actual current drawn from the capacitor bank 10, and the power supply control unit 12 is used to control the generation of the charging current for the capacitor bank 10 based on the indication signal. The indication signal is generated by a capacitor bank current sensor 13, which is coupled to the capacitor bank 10 and measures the actual current drawn from the capacitor bank 10 and generates the indication signal based on the measured current, which is forwarded to the power supply control unit 12. Therefore, the control of the charging current fed to the capacitor bank 10 from the main power supply 11 is directly governed by the actual current drawn from the capacitor bank 10. Therefore, the actual current drawn from the capacitor bank 10 directly triggers a corresponding recharging of the capacitor bank 10 by the main power supply 11.

[0066] According to an alternative second preferred embodiment of the present invention, instead of measuring the current drawn from the capacitor bank 10, an RF amplifier current sensor 14 is provided, which is coupled to the RF amplifier 9. The RF amplifier current sensor 14 measures the actual current used in the RF amplifier 9 for generating RF pulses. Based on this current, the RF amplifier current sensor 14 generates an indication signal, which is sent to the power supply control unit 12 for controlling the generation of electrical energy in the main power supply 11. Therefore, according to the second preferred embodiment of the present invention, the actual current used in the RF amplifier 9 triggers the recharging of the capacitor bank 10.

[0067] It should be noted that although the second preferred embodiment of the present invention is described here as an alternative to the first preferred embodiment of the present invention described previously, the options according to the first preferred embodiment and the options according to the second preferred embodiment may also be combined accordingly. This means that the RF transmitter 8 may be provided with a capacitor bank current sensor 13 as well as an RF amplifier current sensor 14 for generating a signal indicating the required current in the RF transmitter 8 and therefore for corresponding recharging of the capacitor bank 10 by the main power supply 11, which is controlled by the power supply control unit 12.

[0068] Figure 4A RF transmitter 8 according to a third preferred embodiment of the present invention is schematically depicted. This third preferred embodiment of the present invention is similar to the previously described second preferred embodiment of the present invention, wherein, in addition to charging the RF amplifier 9 by the capacitor bank 10, the RF amplifier 9 can also be charged directly by the main power supply 11, since there is a direct current line between the main power supply 11 and the RF amplifier 9. Therefore, not only the current from the capacitor bank 10 can be used to generate RF power, but also the current directly obtained from the main power supply 11, which allows the use of a smaller capacitor bank 10 at the same performance level.

[0069] exist Figure 5 As is generally known for MRI systems, the present MRI system 1 according to the fourth preferred embodiment of the present invention is also controlled by an MRI control unit 16, which is Figure 1 is omitted in Figure 5 The MRI control unit 16 is coupled to an information unit 17, which is further coupled to an RF transmitter 8 according to a fourth preferred embodiment of the present invention. Figure 6 The RF transmitter 8 is described in more detail in FIG. Figure 6 It can be seen that the information unit 17 is coupled to the power supply control unit 12. In practice, the information unit 17 receives information about the MRI procedure performed by the MRI system 1 from the MRI control unit 16. In this way, the information unit 17 generates an indication signal based on the upcoming current, which is drawn from the capacitor bank 10 based on the upcoming RF power demand for the transmit coil 5 of the MRI system, which RF power demand is fed to the information unit 17 by the MRI control unit 16. In this way, the charging current can be fed directly to the capacitor bank 10 even before the RF pulses are generated and forwarded to the RF transmit coil 5. Thus, this embodiment makes it possible to prevent a conceivable drop in the available RF power based on the planned MRI procedure performed by the MRI system 1.

[0070] In summary, the present invention addresses power control of the RF amplifier 9 of the RF transmitter 8 of the MRI system 1 by using additional information about the required charging current of the capacitor bank 10. This information is used to initiate recharging of the capacitor bank 10 in a timely manner and in some cases even before a drop in RF energy has occurred. In this way, RF pulse generation for MRI applications becomes more efficient, enabling the use of smaller capacitor bank values ​​at the same performance level of the system.

[0071] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered illustrative or exemplary, not restrictive; the present invention is not limited to the disclosed embodiments. Those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention by studying the drawings, the disclosure, and the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the words "one" or "an" do not exclude multiple. Although certain measures are recorded in different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage. Any figure marks in the claims should not be interpreted as limiting the scope. In addition, for the sake of clarity, not all elements may be provided with figure marks in the drawings.

Claims

1. An MRI system having an RF transmitting coil (5) and an RF transmitter (8), the RF transmitter comprising: an RF amplifier (9) for generating RF pulses and for forwarding these RF pulses to the RF transmitting coil (5) of the MRI system (1), a capacitor bank (10) coupled to the RF amplifier (9) for storing electrical energy and for providing the RF amplifier (9) with current for generating the RF pulses, a main power source (11) coupled to the capacitor bank (10) for generating a charging current for charging the capacitor bank (10) with electrical energy; as well as a power control unit (12) coupled to the main power source (11) for controlling the generation of the charging current for the capacitor bank (10), wherein an information unit (17) coupled to the power supply control unit (12) and adapted to generate an indication signal based on an upcoming current drawn from the capacitor bank (10) based on an upcoming RF power demand for the RF transmit coil (5) of the MRI system (1), and The power supply control unit (12) is adapted to receive the indication signal indicative of an upcoming current drawn from the capacitor bank (10), and to control the generation of the charging current for the capacitor bank (10) based on the indication signal.

2. The MRI system according to claim 1, further comprising: A capacitor bank current sensor (13) is coupled to the capacitor bank (10) and is adapted to measure an actual current drawn from the capacitor bank (10) and to generate the indication signal based on the current.

3. The MRI system according to claim 1 or 2, further comprising: An RF amplifier current sensor (14) is coupled to the RF amplifier (9) and is adapted to measure an actual current used in the RF amplifier (9) for generating the RF pulses based on the current and for generating the indication signal.

4. The MRI system according to claim 1 or 2, wherein: The RF amplifier (9) is also directly coupled to the main power supply (11) for drawing current directly from the main power supply (11).

5. The MRI system according to claim 1 or 2, wherein: The main power supply (11) is a switch mode power supply.

6. A method for generating RF pulses for an MRI system (1) having an RF transmitter (8), the RF transmitter (8) comprising a main power supply (11), a capacitor bank (10) and an RF amplifier (9), the method comprising the following method steps: generating a charging current in the main power source (11) and charging the capacitor bank (10) with the charging current, providing the current from the capacitor bank (10) to the RF amplifier (9) for generating the RF pulses, generating RF pulses in the RF amplifier (9) and forwarding these RF pulses to the RF transmit coil (5) of the MRI system (1), estimating an upcoming current drawn from the capacitor bank (10) based on an upcoming RF power demand for the RF transmit coil (5) of the MRI system (1), and The generation of the charging current for the capacitor bank in the main power supply (11) is controlled based at least on the estimated upcoming current drawn from the capacitor bank (10).

7. The method according to claim 6, comprising the following additional steps: The generation of the charging current for the capacitor bank (10) is controlled based on the estimated upcoming current drawn from the capacitor bank (10) such that the charging current is fed directly to the capacitor bank (10) before RF pulses are generated and forwarded to the RF transmit coil (5).

8. The method according to claim 6, comprising the following additional steps: estimating the actual current drawn from the capacitor bank (10), and The generation of the charging current for the capacitor bank in the main power supply (11) is controlled based on the estimated actual current drawn from the capacitor bank (10) and the upcoming current.

9. The method according to claim 8, comprising the following additional steps: The actual current drawn from the capacitor bank (10) is estimated by measuring the actual current drawn from the capacitor bank (10).

10. The method according to claim 8, comprising the following additional steps: The actual current drawn from the capacitor bank (10) is estimated by measuring the actual current used in the RF amplifier (9).

11. The method according to any one of claims 6 to 10, wherein: The RF amplifier (9) is also fed directly by the charging current from the main power supply (11).

12. A non-transitory computer readable medium comprising instructions stored thereon, which when executed on a processor cause an MRI system (1) to perform the method according to any one of claims 6 to 11.

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