JP6479359B2 - Coil driving apparatus and magnetic resonance imaging apparatus - Google Patents

Description

  Embodiments described herein relate generally to a coil driving apparatus and a magnetic resonance imaging apparatus.

  The period in which a current flows through the gradient magnetic field coil of a magnetic resonance imaging (MRI) apparatus is a period in which a predetermined constant current flows (constant current period), and a period in which the polarity of the current is reversed (current sudden change period). And are repeated alternately. The current sudden change period is required to be as short as possible. In order to reverse the polarity by rapidly changing the current flowing through the gradient coil in a short time, it is preferable to apply a large reverse bias to the gradient coil.

  For this reason, it is preferable to use a high-voltage power supply as a drive device for the gradient magnetic field coil (G-AMP, hereinafter referred to as a coil drive device) during the sudden current change period. For example, by using a gradient coil drive device that has a high-voltage power supply capable of outputting a large current and a switch (power element) with a high breakdown voltage and a large current, the current flowing in the gradient coil can be rapidly changed in a short time. Polarity can be reversed. Further, when this type of coil driving device is used, the current flowing through the gradient coil becomes a predetermined constant current by controlling the duty ratio of the switching operation of the high withstand voltage and large current switch in the constant current period. DC current control can be performed.

JP 2001-292979 A

  However, a high voltage power supply capable of outputting a large current has a larger power supply power than a low voltage power supply. For this reason, when using a high voltage power supply, the size of a coil drive device will become large. Moreover, since the high withstand voltage switch has a large power loss of the element itself, a large-scale cooling mechanism such as a water cooling device is required.

  In the constant current period, it is required to perform low voltage and large current direct current control with high stability and high accuracy. However, when a high voltage power supply is used as a drive power supply for the gradient magnetic field coil, it is difficult to control a low voltage and a large constant current with high accuracy by a switching operation.

  In order to solve the above-described problem, a coil drive device according to an embodiment of the present invention includes a high voltage power supply and a high voltage switch connected to an output of the high voltage power supply, and includes a gradient magnetic field of the magnetic resonance imaging apparatus. A high-voltage supply unit that supplies the output power of the high-voltage power supply to the coil via the high-voltage switch, and is connected to the low-voltage power supply and the output of this low-voltage power supply, and has a higher power loss when turned on than the high-voltage switch A low voltage supply unit that has a small low withstand voltage switch and supplies the output power of the low voltage power supply to the gradient magnetic field coil via the low withstand voltage switch, and a gradient coil in the current sudden change period that suddenly changes the current flowing through the gradient magnetic field coil While supplying power from the high voltage supply unit to the gradient coil, power is supplied from the low voltage supply unit to the gradient coil in a constant current period in which the current flowing through the gradient coil is kept constant. To supply, in which and a drive control unit for controlling the high pressure supply and the low pressure supply unit.

1 is a block diagram showing an example of an MRI apparatus including a coil driving apparatus according to a first embodiment of the present invention. The block diagram which shows an example of the conventional coil drive device. The functional block diagram which shows an example of the coil drive device which concerns on 1st Embodiment. The figure which shows an example of the output part circuit of the coil drive device which concerns on 1st Embodiment. The timing chart which shows an example of ON / OFF operation | movement of switch Q1-Q4 controlled by the drive control part which concerns on 1st Embodiment. (A) is a figure which shows an example of the circuit which implement | achieves a positive high voltage power supply, (b) is a figure which shows an example of the circuit which implement | achieves a negative high voltage power supply. The figure which shows an example of the circuit which implement | achieves a positive low voltage power supply and a negative low voltage power supply. The functional block diagram which shows an example of the coil drive device which concerns on 2nd Embodiment. The figure which shows an example of the output part circuit of the coil drive device which concerns on 2nd Embodiment. The timing chart which shows an example of ON / OFF operation | movement of switch Q1-Q6 controlled by the drive control part which concerns on 2nd Embodiment.

  Embodiments of a coil drive device and a magnetic resonance imaging apparatus according to the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a block diagram showing an example of an MRI apparatus 1 including a coil driving apparatus 10 according to the first embodiment of the present invention.

  The static magnetic field magnet 101 is formed in a hollow cylindrical shape, and generates a uniform static magnetic field in an internal space by a current supplied from a static magnetic field power source (not shown). For example, the static magnetic field magnet 101 is composed of a permanent magnet, a superconducting magnet, or the like.

  The RF coil 102 is a transmission / reception coil disposed so as to face the subject P within the opening of the static magnetic field magnet 101. The RF coil 102 receives an RF pulse supplied from the transmitter 103 and generates an RF magnetic field. Further, the RF coil 102 receives a magnetic resonance signal emitted from the hydrogen nucleus of the subject P by excitation and gives it to the receiving unit 104.

  The couch device 105 includes a top plate 106 on which the subject P is placed, and the top plate 106 on which the subject P is placed is inserted into the cavity (imaging port) of the RF coil 102. Normally, the bed apparatus 105 is installed so that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 101.

  The couch controller 107 is controlled by the computer system 201 via the sequence controller 200 to control the couch device 105. The couch control unit 107 drives the couch device 105 to move the couchtop 106 in the longitudinal direction and the vertical direction.

  The gradient coil 11 is formed in a hollow cylindrical shape and generates a gradient magnetic field in the internal space. Specifically, the gradient magnetic field coil 11 is arranged inside the static magnetic field magnet 101 and receives a current supplied from the coil driving device (gradient magnetic field power source) 10 to generate a gradient magnetic field.

  The coil drive device 10 supplies a current to be supplied to the gradient coil 11 so as to alternately repeat a current sudden change period in which the current supplied to the gradient coil 11 is suddenly changed and a constant current period in which the current supplied to the gradient coil is kept constant. Control.

  The computer system 201 performs overall control of the MRI apparatus 1, collection of MR signal data, image reconstruction, and the like.

  The interface unit 210 controls input / output of various signals transmitted / received to / from the sequence control unit 200. For example, the interface unit 210 transmits sequence information to the sequence control unit 200 and receives MR signal data from the sequence control unit 200. Further, when receiving MR signal data, the interface unit 210 stores the received MR signal data in the storage unit 250. When the interface unit 210 receives feedback information from the transmission unit 103, the interface unit 210 inputs the received feedback information to the main control unit 260.

  The input unit 220 includes a general input device such as a keyboard, a touch panel, a numeric keypad, a mouse, or a trackball, and outputs an operation input signal corresponding to a user operation to the main control unit 260. For example, the input unit 220 cooperates with the display unit 230 to provide a GUI (Graphical User Interface) for accepting various operations to the operator of the MRI apparatus 1. The display unit 230 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, and displays various types of information such as image data according to the control of the main control unit 260.

  The image reconstruction unit 240 reconstructs an MRI image by performing reconstruction processing such as Fourier transform on the MR signal data stored in the storage unit 250 and stores the reconstructed MRI image in the storage unit 250. To do.

  The storage unit 250 stores MR signal data received by the interface unit 210, MRI images stored by the image reconstruction unit 240, and other data used in the MRI apparatus 1. The storage unit 250 includes a recording medium that can be read by the main control unit 260, such as a magnetic or optical recording medium or a semiconductor memory.

  The main control unit 260 comprehensively controls the MRI apparatus 1 by controlling the units 200 and 210-250. For example, the main control unit 260 generates sequence execution data based on the imaging conditions input from the operator via the input unit 220 and transmits the generated sequence execution data to the sequence control unit 200, thereby causing the MRI apparatus 1. Controls scanning with. The main control unit 260 is configured by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or an electronic circuit such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit). be able to. The main control unit 260 may be configured by a plurality of processors.

Here, a conventional coil driving device (gradient magnetic field power supply) will be described.
FIG. 2 is a configuration diagram illustrating an example of a conventional coil driving device.

  In the conventional coil driving device, in order to change the current flowing in the gradient magnetic field current suddenly in a short time during the current sudden change period, for example, a plurality of high voltage / high current power supplies (three 1000 V power supplies in the example shown in FIG. 2), It is composed of high withstand voltage and large current switches. Here, the breakdown voltage of the switch refers to the maximum rated voltage when the switch is off.

  However, the high voltage / high current power source requires output power corresponding to output voltage × output current. For example, if the power supply has an output voltage of 3000 V and an output current of 300 A, a power capacity of 900 kW is required. The power supply becomes larger as the output power increases. For this reason, the size of the power supply of the conventional coil drive device becomes large.

On the other hand, the higher the element of the switch, the higher the power loss of the element when it is on. For example, when a power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used as a switch, a high breakdown voltage element has a large on-resistance (RON), and when current I flows when the element is on, I ^2. Loss of RON occurs. In addition, when an IGBT (Insulated Gate Bipolar Transistor) is used as a switch, the collector-emitter saturation voltage (VCEsat) of a high breakdown voltage element is high, and if current I flows when the element is on, I · VCEsat Loss.

In general, a high voltage is required to change the current flowing through the gradient coil 11. The inductance E of the gradient magnetic field coil 11 is LC [H], and the voltage E applied to the coil necessary for changing the current from zero to I [A] at time t [sec] is E = LC · I / t [ V]. For example, when LC = 1 [mH], t = 100 [μs], and I = 300 [A], E = LC · I / t = 1 × 10 ⁻³ × 300 / (100 × 10 ⁻⁶ ) = 3000 [V] (see FIG. 2).

  On the other hand, in order to pass a constant current I [A] through the gradient coil 11, a voltage of E = RC · I [V] is applied from the coil resistance RC [Ω] and the current I [A] flowing through the coil. That's fine. For example, when RC = 0.1 [Ω] and I = 300 [A], E = RC · I = 0.1 × 300 = 30 [V].

  For example, when an IGBT is used as a high breakdown voltage switch, the on-state voltage of the IGBT having a breakdown voltage required in the conventional coil driving device shown in FIG. 2 is about 2 [V]. For this reason, when a constant current is passed through the gradient coil, the power loss per switch element is 2 × 300 = 600 [W]. In the example shown in FIG. 2, since there are six elements that are turned on when a current flows through the gradient magnetic field coil 11, the loss in the entire circuit is as large as 600 × 6 = 3600 [W]. For this reason, in the conventional coil drive device, the heat generation of the switch cannot be ignored, and a large-scale cooling mechanism such as a water cooling device is required, which increases the size of the entire device.

  In the conventional coil drive device, the voltage applied to the gradient coil 11 when the current flowing through the gradient coil 11 is kept constant is obtained by switching the switch. For example, in order to obtain a voltage of 30 [V] by switching from a 3000 [V] high-voltage power supply as in the above example, assuming that the ON time of the switch is TON and the OFF time is TOFF, 30 [V] / 3000 [V ] The ON time and the OFF time are adjusted so as to satisfy TON = (TON + TOFF). However, in this example, the on-time must be reduced to 1/100 with respect to the switching period (TON + TOFF). In addition, in order to control the current flowing through the gradient coil 11 with an accuracy of 0.1%, the control circuit is required to have a resolution of 1 / 100,000 or less of the switching period (1/100 × 0.001 = 1/100000). For this reason, in the conventional coil drive apparatus, since a high voltage power source must be used even during the constant current period, it is very difficult to control the current with high accuracy during the constant current period.

  Therefore, the coil drive device 10 according to the present embodiment uses a high voltage power supply and a high withstand voltage switch in the current sudden change period to suddenly change the current, and uses a low withstand voltage switch with the low voltage power supply in the constant current period. By making it possible, the current loss of the switch element is reduced.

  FIG. 3 is a functional block diagram illustrating an example of the coil drive device 10 according to the first embodiment.

  As shown in FIG. 3, the coil driving apparatus 10 according to the present embodiment includes a high-pressure supply unit 12, a low-pressure supply unit 13, and a drive control unit 14.

  The high voltage supply unit 12 includes a high voltage power source 21 and a high voltage switch 22 connected to the output of the high voltage power source. The high voltage supply unit 12 supplies the output power of the high voltage power supply 21 to the gradient coil 11 via the high voltage switch 22.

  The low voltage supply unit 13 includes a low voltage power supply 31 and a low withstand voltage switch 32 connected to the output of the low voltage power supply. The low voltage supply unit 13 supplies the output power of the low voltage power supply 31 to the gradient magnetic field coil 11 via the low withstand voltage switch 32. The high breakdown voltage switch 22 and the low breakdown voltage switch 32 are connected in series, and the gradient coil 11 is connected to the low breakdown voltage switch 32 side.

  The high withstand voltage switch 22 and the low withstand voltage switch 32 can be configured by MOSFETs, IGBTs, or the like. As the low withstand voltage switch 32, a switch with lower power loss when turned on than the high withstand voltage switch 22 is used. When a MOSFET element is used as the low breakdown voltage switch 32, a substantial on-resistance can be reduced by connecting a plurality of MOSFETs in parallel.

  The drive control unit 14 supplies power from the high voltage supply unit 12 to the gradient coil 11 during the sudden current change period, and supplies power from the low voltage supply unit 13 to the gradient coil 11 during the constant current period. The high pressure supply unit 12 and the low pressure supply unit 13 are controlled. The drive control unit 14 can be configured by a microcontroller including a processor, for example. The drive control unit 14 may be configured by a plurality of processors. Further, the drive control unit 14 may be a function realization unit of the main control unit 260. In this case, the drive control unit 14 controls the high pressure supply unit 12 and the low pressure supply unit 13 via the sequence control unit 200.

  FIG. 4 is a diagram illustrating an example of an output unit circuit of the coil driving apparatus 10 according to the first embodiment.

  The high voltage supply unit 12 is connected to a positive high voltage power supply 21p and a high voltage switch Q1 connected to the output of the positive high voltage power supply 21p, and to the negative high voltage power supply 21m and the output of the negative high voltage power supply 21m. High withstand voltage switch Q2. On the other hand, the low voltage supply unit 13 includes a positive low voltage power supply 31p and a low withstand voltage switch Q3 connected to the output of the positive low voltage power supply 31p, a negative low voltage power supply 31m, and an output of the negative low voltage power supply 31m. And a high voltage switch Q4 connected to the.

  A high voltage is applied to V1 (V2) from a positive (negative) high-voltage power supply 21p (21m). On the other hand, a low voltage is applied to V3 (V4) from a positive (negative) low-voltage power supply 31p (31m).

  As the switches Q3 and Q4, those having a smaller power loss when turned on than the switches Q1 and Q2 are used.

  When the switch Q3 is on, a positive current flows through the gradient coil 11. When the switch Q4 is on, a negative current flows through the gradient coil 11. When the switches Q1 and Q3 are both on, a positive high voltage is applied to the gradient coil 11 to increase the current in the gradient coil 11 in a short time. When both the switches Q2 and Q4 are on, a negative high voltage is applied to the gradient coil 11, and the current in the gradient coil 11 is reduced in a short time.

  FIG. 5 is a timing chart showing an example of the on / off operation of the switches Q1-Q4 controlled by the drive control unit 14 according to the first embodiment.

  First, the operation of increasing from 300 (A) in a current sudden change period T1 = 100 [μs] from a state in which no current flows through the gradient coil 11 (time t = t1) will be described. In order to simplify the explanation of the operation, voltage drops of the switches Q1 to Q4 and the diodes D1 to D6 are not considered.

A voltage of 3000 [V] is applied to V1. When Q1 and Q3 are turned on at time t = t1, a voltage of 3000 [V] is applied to the gradient coil 11, and the current I flowing through the gradient coil 11 increases with time t. If the inductance of the gradient coil 11 is LC, the current I increases according to I = (V1 / LC) · t. If LC = 1 [mH], the current reaches 300 [A] 100 [μs] after Q1 and Q3 are turned on (t = t2).
I = (3000/1 × 10 ⁻³ ) × 100 × 10 ⁻⁶ = 300 [A]

  The current flowing through the gradient coil 11 is detected by a current detector (not shown). The drive control unit 14 turns off Q1 when the target current is reached. The current detector may be provided, for example, on the coil driving device 10 side in the vicinity of the gradient coil 11. When Q1 and Q3 are on, the diode D5 is reverse-biased and no current flows from V3.

  Next, in the period T2 (constant current period) after the current flowing through the gradient coil 11 reaches the target current, the drive control unit 14 turns on only Q3 and passes the gradient coil 11 from V3 through D5 and Q3. Continue to pass current through. When the resistance RC of the gradient magnetic field coil 11 is 0.1 [Ω] and the current I flowing through the gradient magnetic field coil 11 is 300 [A], the voltage of V3 is V3 = RC · I = 0.1 × 300 = 30 [30]. V].

Next, when changing the direction of the current flowing through the gradient coil 11 in order to change the gradient direction of the gradient magnetic field, the drive control unit 14 first turns off the switch Q3 (t = t3). Then, the energy stored in the gradient coil 11 is regenerated to the capacitor C2 through the diodes D2 and D4 connected in antiparallel to the switches Q2 and Q4, respectively. At this time, since −3000 V is applied to V2, a voltage of −3000 V is applied to the capacitor C2. If a capacitance is selected such that the voltage of C2 is hardly affected by the energy regeneration of the gradient coil 11, the current in the gradient coil 11 becomes zero after a period T3 = 100 [μs] after Q3 is turned off (t = t4).
I = 300 + (V2 / LC) · t
= 300 + (− 3000/1 × 10 ⁻³ ) × 100 × 10 ⁻⁶
= 0 [A]

When the drive control unit 14 detects that the current flowing through the gradient magnetic field coil 11 has become zero (t = t4), the drive control unit 14 turns on the switches Q2 and Q4 and causes a current in the negative direction to flow through the gradient magnetic field coil 11. Since V2 is −3000 [V], the current I flowing through the gradient coil 11 decreases according to I = (V2 / LC) · t, where t is the time after the switches Q2 and Q4 are turned on. Therefore, at time t = t5 after the period T4 = 100 [μs] from the time t = t4,
I = (V2 / LC) · t
= (− 3000/1 × 10 ⁻³ ) × 100 × 10 ⁻⁶
= -300 [A]

  It becomes. When Q2 and Q4 are on, the diode D6 is reverse-biased and no current flows from V4.

  When the drive control unit 14 detects that the target current value = −300 A is reached, the drive control unit 14 turns off the switch Q2 (t = t5). Then, current continues to flow from the gradient coil 11 to V4 through Q4 and D6. Assuming that the resistance of the gradient coil 11 is RC = 0.1 [Ω] and the constant current I = −300 [A] that flows through the gradient coil 11, the voltage of V4 is V4 = RC · I = 0.1 × ( −300) = − 30 [V].

Next, the drive control unit 14 turns off the switch Q4 after the constant current period of the period T5 (t = t6). Then, the energy stored in the gradient magnetic field coil 11 is regenerated in the capacitor C1 through the diodes D3 and D1 connected in antiparallel to the switches Q3 and Q1, respectively. At this time, V1 is 3000 V, and a voltage of 3000 V is applied to the capacitor C1. If a capacitance is selected such that the voltage of C1 is hardly affected by the energy regeneration of the gradient coil 11, the current in the gradient coil 11 becomes zero after a period T6 = 100 [μs] after Q4 is turned off (t = t7). ).
I = −300 + (V1 / LC) · t
= −300 + (3000/1 × 10 ⁻³ ) × 100 × 10 ⁻⁶
= 0 [A]

  During the data collection period of the MRI apparatus 1, the above sequence of time t = t1 to t7 is repeated.

  FIG. 6A is a diagram illustrating an example of a circuit that realizes a positive high-voltage power supply 21p, and FIG. 6B is a diagram illustrating an example of a circuit that realizes a negative high-voltage power supply 21m.

  The high voltage applied to V1 and V2 can be generated using a converter (flyback converter) using a flyback transformer as shown in FIG. 6, for example. According to the flyback converter, a high voltage can be generated with a simple circuit.

  The drive control unit 14 can control the change rate of the current during the sudden current change period by controlling the output voltages V1 and V2 of the high voltage power supply 21 by controlling the high voltage generation circuit shown in FIG.

  Further, as the capacitance of the capacitors C1 and C2, by selecting a capacitor with little power fluctuation even when the energy stored in the gradient coil 11 is regenerated, a period of changing the direction of the current flowing in the gradient coil 11 in a short time ( The energy stored in C1 or C2 can be used in the current sudden change period (see periods T1, T3, T4, and T6 in FIG. 5). For this reason, the flyback transformer and its drive circuit elements can be of a small rating. Therefore, coil energy can be utilized by appropriately selecting the capacitances of the capacitors C1 and C2, and the power supply circuits for V1 and V2 can be made small.

  FIG. 7 is a diagram illustrating an example of a circuit that realizes the positive low-voltage power supply 31p and the negative low-voltage power supply 31m.

  The low voltage applied to V3 and V4 can be made by a full-bridge forward converter as shown in FIG. 7, for example. According to the full-bridge forward converter, a large-current power source can be efficiently produced.

  The drive control unit 14 controls the output voltage V3 and V4 of the low voltage power supply 31 by controlling the low voltage generation circuit shown in FIG. 7, so that the current of the gradient magnetic field coil 11 in the constant current period is a set value (predetermined value). Constant current value). For this reason, it is possible to easily cope with the individual difference of the gradient magnetic field coil 11 and the change in the resistance value Rc caused by the temperature change due to continuous use or the like, and maintain the constant current.

  Further, the drive control unit 14 may control the current of the gradient magnetic field coil 11 in the constant current period by controlling the switching operation of the low breakdown voltage switch 32 (Q3, Q4). For example, if the secondary winding voltage of the transformer used in the power supply circuit is designed to be 120 [V], in a period in which a constant current flows through the gradient coil 11 (constant current period, see periods T2 and T5 in FIG. 5). In order to obtain 30 [V], the duty ratio of the switching element may be about 0.25. For this reason, the coil drive apparatus 10 can adjust the voltages of V3 and V4 with higher accuracy than a conventional coil drive apparatus (duty ratio of 0.01 in the above example).

  The coil drive apparatus 10 and the MRI apparatus 1 according to the present embodiment use a low voltage power supply 31 and a low breakdown voltage switch 32 with small power loss when a constant current is applied to the gradient coil 11. For this reason, compared with the conventional coil drive device, a cooling device can be made very simple. Further, when the current of the gradient magnetic field coil 11 is changed, the high voltage power supply 21 and the high breakdown voltage switch 22 are used. However, since the current sudden change period is short, the amount of heat generated by the high breakdown voltage switch 22 can be small.

The coil driving device 10 and the MRI apparatus 1 control the low-voltage power supply 31 when a constant current is passed through the gradient coil 11, but as described above, the switching element (the primary in FIG. 7) of the low-voltage power supply 31. The side ratio) can be designed so that the duty ratio (ratio between the ON time TON of the switching element and the switching period (TON + TOFF)) is about 0.25. For this reason, when the current flowing through the gradient coil 11 is controlled with an accuracy of 0.1%, the resolution required for the control circuit is only 1/4000 of the switching period, so a highly accurate control circuit can be easily realized. (1/4 × 0.001 = 1/4000).

  Therefore, according to the coil drive device 10 and the MRI apparatus 1, the current flowing through the gradient magnetic field coil 11 can be kept constant with high accuracy and can be reversed in a short time, and the heat generated by the switches 22 and 32 can be reduced. Therefore, the cooling device can be simplified.

(Second Embodiment)
Next, a second embodiment of the coil driving apparatus and the MRI apparatus according to the present invention will be described. FIG. 8 is a functional block diagram illustrating an example of a coil drive device 10A according to the second embodiment. FIG. 9 is a diagram illustrating an example of an output unit circuit of the coil drive device 10A according to the second embodiment.

  The coil drive device 10A shown in the second embodiment is different from the coil drive device 10A shown in the first embodiment in that the adjustment circuit 42 is provided and current control is performed by the switching operation of the output side circuit of V1-V4. Since other configurations and operations are not substantially different from those of the coil drive device 10 shown in FIG. 1, the same components are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, the drive control unit 14A does not require the drive control unit 14A to control the high voltage power supply 21A and the low voltage power supply 31A. For this reason, the high voltage power supply 21A of the high voltage supply unit 12A and the low voltage power supply 31A of the low voltage supply unit 13A may have a very simple configuration as compared to the circuits shown in FIGS. 6 and 7 of the first embodiment. it can.

  The adjustment switch 41 (see Q5 and Q6 in FIG. 9) of the adjustment circuit 42 is necessary for returning the current of the gradient coil 11. The adjustment switch 41 is preferably a high voltage switch.

  FIG. 10 is a timing chart illustrating an example of an on / off operation of the switches Q1-Q6 controlled by the drive control unit 14A according to the second embodiment. Hereinafter, differences from FIG. 5 will be described.

  As shown in FIG. 10, the drive control unit 14A controls the current flowing through the gradient coil 11 by the switching operation (SW operation) of the output side circuit of V1-V4.

  In the period T1, the drive control unit 14A turns on the switches Q1, Q3, and Q5 and performs current acceleration control by the switching operation of Q1 and Q5. In the period T2, constant current control is performed by switching operations of the switches Q3 and Q5. In the period T3, deceleration control is performed by the switching operation of the switch Q5. In the period T4, the switches Q2, Q4 and Q6 are turned on, and current acceleration control is performed by the switching operation of Q2 and Q6. In the period T5, constant current control is performed by the switching operation of the switches Q4 and Q6. And drive control part 14A performs deceleration control by switching operation of switch Q6 in period T6.

  Also with the coil drive device 10A according to the present embodiment, the current flowing through the gradient magnetic field coil 11 can be kept constant with high accuracy and can be reversed in a short time, and the heat generation of the switches 22 and 32 can be suppressed. The cooling device can be simplified.

  In addition, the coil driving apparatus 10A according to the present embodiment does not need to control the high voltage power supply 21A of the high voltage supply unit 12A and the low voltage power supply 31A of the low voltage supply unit 13A, and thus the configuration may be simplified. it can.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10, 10A Coil drive device 11 Gradient magnetic field coil 12, 12A High voltage supply unit 13, 13A Low voltage supply unit 14, 14A Drive control unit 21, 21A High voltage power supply 22 High voltage switch 31, 31A Low voltage power supply 32 Low voltage switch 41 Adjustment Switch

Claims (7)

A high-voltage power supply and a high-voltage switch connected to the output of the high-voltage power supply, and a high voltage that supplies output power of the high-voltage power supply to the gradient magnetic field coil of the magnetic resonance imaging apparatus via the high-voltage switch A supply section;
A low-voltage power supply and a low-voltage switch that is connected to the output of the low-voltage power supply and has lower power loss when turned on than the high-voltage switch, and is connected to the gradient magnetic field coil via the low-voltage switch A low voltage supply unit that supplies output power of a low voltage power supply;
In the current sudden change period in which the current flowing through the gradient coil is suddenly changed, the gradient magnetic field is supplied with electric power from the high-voltage supply unit, while in the constant current period in which the current flowing in the gradient coil is kept constant, the gradient magnetic field is supplied. A drive control unit for controlling the high-pressure supply unit and the low-voltage supply unit so as to supply power from the low-voltage supply unit to the coil;
With
The low voltage power supply is
Consists of a converter having a switch element,
The drive control unit
In the constant current period, the high voltage supply unit and the low voltage supply unit are controlled to supply low voltage power output from the low voltage power supply to the gradient magnetic field coil via the low voltage switch, and a predetermined constant voltage is supplied. Controlling the switching operation of the switch element of the low-voltage power supply so that a current flows through the gradient coil.
Coils drive. A high-voltage power supply and a high-voltage switch connected to the output of the high-voltage power supply, and a high voltage that supplies output power of the high-voltage power supply to the gradient magnetic field coil of the magnetic resonance imaging apparatus via the high-voltage switch A supply section;
A low-voltage power supply and a low-voltage switch that is connected to the output of the low-voltage power supply and has lower power loss when turned on than the high-voltage switch, and is connected to the gradient magnetic field coil via the low-voltage switch A low voltage supply unit that supplies output power of a low voltage power supply;
In the current sudden change period in which the current flowing through the gradient coil is suddenly changed, the gradient magnetic field is supplied with electric power from the high-voltage supply unit, while in the constant current period in which the current flowing in the gradient coil is kept constant, the gradient magnetic field is supplied. A drive control unit for controlling the high-pressure supply unit and the low-voltage supply unit so as to supply power from the low-voltage supply unit to the coil;
An adjustment switch provided between the low-pressure supply unit and the gradient coil;
Bei example,
The drive control unit
In the constant current period, the high-voltage supply unit, the low-voltage supply unit, and the adjustment switch are controlled so that low-voltage power output from the low-voltage power supply is supplied to the gradient coil through the low-voltage switch. And controlling the switching operation of the low withstand voltage switch and the adjustment switch so that a predetermined constant current flows through the gradient coil.
Coils drive. A high-voltage power supply and a high-voltage switch connected to the output of the high-voltage power supply, and a high voltage that supplies output power of the high-voltage power supply to the gradient magnetic field coil of the magnetic resonance imaging apparatus via the high-voltage switch A supply section;
A low-voltage power supply and a low-voltage switch that is connected to the output of the low-voltage power supply and has lower power loss when turned on than the high-voltage switch, and is connected to the gradient magnetic field coil via the low-voltage switch A low voltage supply unit that supplies output power of a low voltage power supply;
In the current sudden change period in which the current flowing through the gradient coil is suddenly changed, the gradient magnetic field is supplied with electric power from the high-voltage supply unit, while in the constant current period in which the current flowing in the gradient coil is kept constant, the gradient magnetic field is supplied. A drive control unit for controlling the high-pressure supply unit and the low-voltage supply unit so as to supply power from the low-voltage supply unit to the coil;
With
The high-pressure supply unit is
A positive high-voltage power supply and a first high-voltage switch connected to the output of the positive high-voltage power supply; a negative high-voltage power supply and a second high-voltage switch connected to the output of the negative high-voltage power supply And
The low-pressure supply unit is
A positive low-voltage power supply and a first low-voltage switch connected to the output of the positive low-voltage power supply; a negative low-voltage power supply and a second low-voltage switch connected to the output of the negative low-voltage power supply And
The first low withstand voltage switch and the second low withstand voltage switch are:
The power loss at the time of ON is smaller than the first high voltage switch and the second high voltage switch,
The drive control unit
The positive low-voltage power source and the first low withstand voltage switch are used for a period in which a constant current having a positive predetermined current value flows through the gradient coil in the constant current period, while a negative in the constant current period is used. Controlling the high-voltage supply unit and the low-voltage supply unit to use the negative low-voltage power source and the second low-voltage switch during a period in which a constant current having a predetermined current value is passed through the gradient coil.
Coils drive. A high-voltage power supply and a high-voltage switch connected to the output of the high-voltage power supply, and a high voltage that supplies output power of the high-voltage power supply to the gradient magnetic field coil of the magnetic resonance imaging apparatus via the high-voltage switch A supply section;
A low-voltage power supply and a low-voltage switch that is connected to the output of the low-voltage power supply and has lower power loss when turned on than the high-voltage switch, and is connected to the gradient magnetic field coil via the low-voltage switch A low voltage supply unit that supplies output power of a low voltage power supply;
In the current sudden change period in which the current flowing through the gradient coil is suddenly changed, the gradient magnetic field is supplied with electric power from the high-voltage supply unit, while in the constant current period in which the current flowing in the gradient coil is kept constant, the gradient magnetic field is supplied. A drive control unit for controlling the high-pressure supply unit and the low-voltage supply unit so as to supply power from the low-voltage supply unit to the coil;
With
The high withstand voltage switch and the low withstand voltage switch are connected in series, and the gradient coil is connected to the low withstand voltage switch side,
The drive control unit
In the current sudden change period, the high-voltage supply unit and the low-voltage supply unit are controlled to supply the high-voltage power output from the high-voltage power supply to the gradient magnetic field coil via the high-voltage switch and the low-voltage switch. ,
The high voltage supply unit includes a first diode connected in antiparallel to the high voltage switch,
The low-voltage supply unit includes a second diode connected in antiparallel to the low-breakdown-voltage switch;
When both the high withstand voltage switch and the low withstand voltage switch are off, energy stored in the gradient coil is regenerated to the high voltage power source through the first diode and the second diode.
Coils drive. The high withstand voltage switch and the low withstand voltage switch are connected in series, and the gradient coil is connected to the low withstand voltage switch side,
The drive control unit
In the current sudden change period, the high-voltage supply unit and the low-voltage supply unit are controlled to supply high-voltage power output from the high-voltage power supply to the gradient coil via the high-voltage switch and the low-voltage switch. ,
The coil drive device according to any one of claims 1 to 4 . The current sudden change period is
A period in which the current polarity is reversed from one of the positive predetermined current value and the negative predetermined current value to the other,
The constant current period is
A period in which a constant current of one of the positive predetermined current value and the negative predetermined current value is passed through the gradient coil after inversion in the current sudden change period;
The coil drive device according to any one of claims 1 to 5 . A gradient coil for applying a magnetic field corresponding to a current passed through the subject to the subject;
A coil driving device according to any one of claims 1 to 6 ;
A magnetic resonance imaging apparatus comprising:

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