JP7465623B2 - Magnetic resonance imaging equipment - Google Patents

Description

An embodiment of the present invention relates to a magnetic resonance imaging device.

A magnetic resonance imaging device is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with a radio frequency (RF) signal at the Larmor frequency, and generates an image by reconstructing the magnetic resonance signals (MR (Magnetic Resonance) signals) that are generated from the subject as a result of the excitation.

In a magnetic resonance imaging device, an RF coil receives an MR signal that is generated as a result of excitation by an RF signal. The received MR signal is then sampled at a predetermined sampling frequency by an AD converter provided in the receiving circuit, and is converted from an analog MR signal to a digital MR signal.

The MR signal converted to a digital signal is filtered by a digital filter to have the desired frequency characteristics, and is then supplied to subsequent reconstruction processing, etc.

In general, the bandwidth of the MR signal can vary depending on the set values of parameters such as pixel size, number of pixels, and FOV size in the readout direction. The set values of these parameters can be different depending on the type of pulse sequence being set.

For this reason, the bandwidth of the MR signal differs for each type of pulse sequence. Therefore, for example, the MR signal may be sampled and AD converted at a sampling frequency that is sufficiently higher than the expected bandwidth, and then a resampling process may be performed to convert the signal to a different sampling frequency according to the bandwidth of the MR signal (i.e., according to the type of pulse sequence). In addition, filtering is usually performed in conjunction with the resampling process. Filtering is a process for removing or reducing aliasing noise that overlaps with the band of the MR signal. In this filtering process, a digital filter with a cutoff frequency according to the bandwidth of the MR signal is used.

To change the cutoff frequency depending on the type of pulse sequence or the bandwidth of the MR signal, the coefficients of the digital filter must be changed depending on the type of pulse sequence or the bandwidth of the MR signal.

JP 2010-172383 A

The problem that this invention aims to solve is to develop a digital filter for magnetic resonance signals that is highly scalable and can flexibly accommodate parameter changes such as changes in the type of pulse sequence and changes in reception bandwidth.

The magnetic resonance imaging apparatus of one embodiment includes a digital filter circuit and a calculation and setting unit. The digital filter circuit is configured to exhibit different frequency characteristics depending on the setting of a filter coefficient. The calculation and setting unit calculates the filter coefficient from the bandwidth of a magnetic resonance signal corresponding to a pulse sequence to be executed each time the pulse sequence is executed, and sets the calculated filter coefficient in the digital filter circuit each time the pulse sequence is executed.

1 is a configuration diagram showing an example of the overall configuration of a magnetic resonance imaging apparatus according to an embodiment; FIG. 13 is a diagram showing a configuration example of an RF receiver in a comparative example. FIG. 2 is a diagram showing an example of the configuration of an RF receiver according to the embodiment. FIG. 2 is a functional block diagram of a processing circuit in the magnetic resonance imaging apparatus according to the embodiment. 4 is a flowchart showing an example of processing performed by the magnetic resonance imaging apparatus according to the embodiment. FIG. 13 is a diagram showing an example of a pulse sequence setting screen. FIG. 11 is a diagram illustrating a first example of a relationship between the time course during which each pulse sequence is executed and the time course during which a filter coefficient set is calculated and set. FIG. 11 is a diagram illustrating a second example of the relationship between the time lapse during which each pulse sequence is executed and the time lapse during which a filter coefficient set is calculated and set. 11 is a flowchart showing a processing example of an operation of registering and reusing a filter coefficient set.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus 1 according to an embodiment of the present invention, which includes a magnet gantry 100, a control cabinet 300, a console 400, a bed 500, and the like.

The magnet stand 100 has a static magnetic field magnet 10, a gradient magnetic field coil 11, a WB (Whole Body) coil 12, etc., and these components are housed in a cylindrical housing. The bed 500 has a bed body 50 and a tabletop 51. The magnetic resonance imaging device 1 also has an RF coil 20 that is disposed close to the subject.

The control cabinet 300 includes gradient magnetic field power supplies 31 (31x for the X-axis, 31y for the Y-axis, and 31z for the Z-axis), an RF receiver 32, an RF transmitter 33, and a sequence controller 34.

The static magnetic field magnet 10 of the magnet gantry 100 has a roughly cylindrical shape and generates a static magnetic field in a bore (the space inside the cylinder of the static magnetic field magnet 10), which is the imaging area of the subject (e.g., a patient). The static magnetic field magnet 10 has a built-in superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply (not shown) to the superconducting coil, and then, when the mode transitions to the persistent current mode, the static magnetic field power supply is disconnected. Once the mode transitions to the persistent current mode, the static magnetic field magnet 10 continues to generate a large static magnetic field for a long period of time, for example, for more than one year. The static magnetic field magnet 10 may be configured as a permanent magnet.

The gradient coil 11 also has a roughly cylindrical shape and is fixed inside the static magnetic field magnet 10. This gradient coil 11 applies gradient magnetic fields to the subject in the X-axis, Y-axis, and Z-axis directions by currents supplied from gradient magnetic field power supplies (31x, 31y, 31z).

The bed body 50 of the bed 500 can move the top plate 51 in the vertical direction, and the subject placed on the top plate 51 is moved to a predetermined height before imaging. Then, when imaging, the top plate 51 is moved horizontally to move the subject into the bore.

The WB coil 12 is fixed in a roughly cylindrical shape so as to surround the subject inside the gradient coil 11. The WB coil 12 transmits RF pulses transmitted from the RF transmitter 33 toward the subject, while receiving magnetic resonance signals (i.e., MR signals) emitted from the subject by excitation of hydrogen nuclei.

The RF coil 20 receives MR signals emitted from the subject at a position close to the subject. The RF coil 20 is composed of, for example, multiple element coils. There are various types of RF coils 20 depending on the part of the subject to be imaged, such as for the head, chest, spine, lower limbs, or whole body, but FIG. 1 shows an RF coil 20 for the chest.

The RF transmitter 33 transmits RF pulses to the WB coil 12 based on instructions from the sequence controller 34. Meanwhile, the RF receiver 32 detects the MR signals received by the WB coil 12 and the RF coil 20, and sends the raw data obtained by digitizing the detected MR signals to the sequence controller 34.

Under the control of the console 400, the sequence controller 34 drives the gradient magnetic field power supply 31, the RF transmitter 33, and the RF receiver 32 to scan the subject. After the sequence controller 34 performs a scan and receives raw data from the RF receiver 32, it sends the raw data to the console 400.

The sequence controller 34 includes a processing circuit (not shown). This processing circuit is composed of hardware such as a processor that executes a specific program, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit).

The console 400 is configured as a computer having a processing circuit 40, a memory circuit 41, a display 42, and an input device 43.

The memory circuitry 41 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), and an external storage device such as a HDD (Hard Disk Drive) or an optical disk device. The memory circuitry 41 stores various information and data, as well as various programs executed by the processor of the processing circuitry 40.

The display 42 is a display device such as a liquid crystal display panel, a plasma display panel, or an organic EL panel. The input device 43 is, for example, a mouse, a keyboard, a trackball, a touch panel, or the like, and includes various devices that allow the operator to input various information and data.

The processing circuit 40 is a circuit equipped with, for example, a CPU or a dedicated or general-purpose processor. The processor executes various programs stored in the memory circuit 41 to realize various functions described below. The processing circuit 40 may be configured with hardware such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). The various functions described below can also be realized by such hardware. The processing circuit 40 can also realize various functions by combining software processing by a processor and a program with hardware processing.

The console 400 controls the entire magnetic resonance imaging apparatus 1 using these components. Specifically, an operator such as a technician operates a mouse, keyboard, etc. (input device 42) to receive imaging conditions such as the type of pulse sequence, various information, and instructions such as starting imaging. The processing circuitry 40 then causes the sequence controller 34 to execute a scan based on the input imaging conditions, while reconstructing an image based on the raw data transmitted from the sequence controller 34, i.e., the digitized MR signals. The reconstructed image is displayed on the display 43, or stored in the memory circuitry 41.

Figure 2 is a diagram showing a configuration example of a comparative RF receiver 39. Also, Figure 3 is a diagram showing a configuration example of an RF receiver 32 of this embodiment. Both the comparative RF receiver 39 and the RF receiver 32 of this embodiment are configured to have an AD converter 320 and a digital filter 321.

The AD converter 320 converts the analog MR signal output from the RF coil 20 into a digital MR signal. Figures 2 and 3 show an example of a circuit configuration of a so-called direct sampling method in which the MR signal in the Larmor frequency band output from the RF coil 20 is directly sampled by the AD converter 320. In this case, for example, a frequency conversion function for converting from the Larmor frequency band to baseband is required between the AD converter 320 and the digital filter 321, but the frequency conversion function is not shown in Figures 2 and 3.

As mentioned above, the bandwidth of the MR signal can vary depending on the type of pulse sequence. More specifically, the bandwidth of the MR signal varies depending on the values of parameters that define the pulse sequence, such as the magnitude of the gradient magnetic field in the readout direction (readout direction) and the pixel size, number of pixels, and size of the FOV in the related readout direction.

In order to deal with such changes in the bandwidth of the MR signal, a process of changing the sampling frequency, i.e., a resampling process, is performed, while a filtering process for removing or reducing aliasing noise is realized by the digital filter 321. The digital filter 321 can be realized by a hardware circuit such as an FPGA (Field Programmable Gate Array), for example.

2 and 3 show an example of a FIR (Finite Impulse Response) type digital filter 321, but an IIR (Infinite Impulse Response) type digital filter may also be used. In the following, an FIR type digital filter 321 will be used as an example.

The FIR digital filter 321 is configured with a plurality of delay elements "Z ^-1 " corresponding to the number of taps N, a plurality of filter coefficients am,n (m=0 to M, n=0 to N) by which signals output between the delay elements are multiplied, and a plurality of adders indicated by "+". Here, (N+1) is the number of filter coefficients included in one digital filter 321, and M is the number of filter coefficient sets. One filter coefficient set is configured by (N+1) filter coefficients am,n (n=0 to N).

One frequency characteristic of the digital filter 321 is determined by one filter coefficient set. There are several types of parameters that should be specified as frequency characteristics, but one important parameter when configuring the digital filter 321 as an LPF (Low Pass Filter) is the cutoff frequency. In addition to this, parameters such as the amount of attenuation in the stopband and the amount of ripple in the passband are also specified as important frequency characteristics of the digital filter 321.

To realize a digital filter 321 having multiple different frequency characteristics, multiple different filter coefficient sets can be set in the digital filter 321. For example, to realize a digital filter 321 having M different cutoff frequencies, M different filter coefficient sets can be set in the digital filter 321. Once the frequency characteristics such as the cutoff frequency are specified, the filter coefficient set (i.e., the values of each of the multiple filter coefficients set in the digital filter 321) can be calculated using known techniques.

The RF receiver 39 shown in FIG. 2 is configured to have a memory 322 that stores multiple filter coefficient sets outside the circuit elements that make up the digital filter 321, for example, the digital filter 321 configured in the form of an FPGA. The memory 322 is, for example, a read-only semiconductor memory or a non-volatile semiconductor memory such as a flash memory.

Which filter coefficient set is selected from among the multiple filter coefficient sets (in the example of FIG. 2, M filter coefficient sets are indicated by filter coefficient 0 to filter coefficient M) is selected, for example, by a band designation signal sent from the console 32.

Then, the selected filter coefficient set is read from the memory 322 and set in the digital filter 321. In an RF receiver 39 having such a circuit configuration, if the number of filter coefficient sets increases due to a change in the type of pulse sequence or an associated change in bandwidth, the change and confirmation work becomes a heavy burden.

For example, when adding a new filter coefficient set in response to a change in bandwidth, it is necessary not only to calculate a filter coefficient set corresponding to the bandwidth to be changed, but also to a) remove the printed circuit board on which memory 322 is mounted, b) write the newly calculated filter coefficient set data to memory 322, c) check the operation of the printed circuit board alone, and d) further incorporate the printed circuit board into the device and check the operation of the magnetic resonance imaging device as a whole. In this way, the comparative RF receiver 39 cannot easily accommodate the addition of filter coefficient sets, and has low scalability and flexibility. In addition, the burden of the confirmation work etc. associated with changing the coefficient set is large.

In contrast, in the RF receiver 32 provided in the magnetic resonance imaging apparatus 1 of this embodiment, the digital filter 321 is configured to be highly scalable and to be able to flexibly respond to parameter changes such as changes in the type of pulse sequence and associated changes in the bandwidth of the MR signal.

Figure 3 is a diagram showing an example of the configuration of mainly the RF receiver 32 in this embodiment. As is clear from Figure 3, the RF receiver 32 in this embodiment is equipped with an AD converter 320 and a digital filter 321, similar to the RF receiver 39 in the comparative example described above, but the memory 322 in which multiple filter coefficient sets are stored is removed.

As described below, in many cases, the magnetic resonance imaging apparatus 1 sets up a pulse sequence group in which multiple types of pulse sequences are arranged in the order in which they are to be executed, and once imaging begins, imaging progresses while changing the type of pulse sequence in the set order.

Therefore, when imaging starts, the type of pulse sequence changes dynamically over time, and the bandwidth of the MR signal also changes dynamically with the change in the type of pulse sequence. Therefore, the magnetic resonance imaging apparatus 1 of this embodiment is configured to calculate a filter coefficient set in real time according to the type of pulse sequence or the bandwidth of the MR signal, which changes dynamically after imaging starts, and set the calculated filter coefficient set in real time to the digital filter 321 by the time the corresponding type of pulse sequence is executed. The calculation of the filter coefficients is performed, for example, by the processing circuit 40 of the console 400.

Figure 4 shows a functional block diagram of the magnetic resonance imaging apparatus 1, particularly the processing circuitry 40. As shown in Figure 4, the processing circuitry 40 of the magnetic resonance imaging apparatus 1 realizes each of the functions of a pulse sequence setting function 401, a filter coefficient calculation and setting function 402, a filter coefficient registration function 403, a reconstruction function 404, and an image processing function 405. Each of these functions is realized, for example, by a processor provided in the processing circuitry 40 executing a predetermined program.

Of the above functions, the pulse sequence setting function 401 sets a pulse sequence group by arranging multiple types of pulse sequences in the order of execution. For example, the user sets the pulse sequence group by operating the input device 43 such as a mouse or keyboard while looking at the setting screen SC1 (see FIG. 6) displayed on the display 42.

Information regarding the parameters of the pulse sequence set by the pulse sequence setting function 401 is sent to the sequence controller 34, and various signals such as the waveform of the gradient magnetic field in each of the X-axis, Y-axis, and Z-axis directions (including the magnitude and timing of the gradient magnetic field), the waveform of the RF signal (including the magnitude and timing of the RF signal), and the sampling timing of the MR signal are generated by the sequence controller 34.

On the other hand, information regarding the type of pulse sequence set by the pulse sequence setting function 401, or the bandwidth of the MR signal determined based on the type of pulse sequence, is also sent to the filter coefficient calculation setting function 402.

The filter coefficient calculation and setting function 402 calculates a filter coefficient set from the bandwidth of the MR signal corresponding to the pulse sequence to be executed each time a pulse sequence is executed. Then, the calculated filter coefficient set is set in the digital filter 321 each time a pulse sequence is executed.

The filter coefficient registration function 403 registers the filter coefficient set calculated by the filter coefficient calculation and setting function 402 in the memory circuit 41 in association with the type of the corresponding pulse sequence.

Figure 5 is a flowchart showing an example of processing performed by the magnetic resonance imaging apparatus 1 of this embodiment. The operation of the magnetic resonance imaging apparatus 1 will be explained in more detail with reference to the flowchart shown in Figure 5.

First, in step ST100, a pulse sequence group is set. The processing in step ST100 is mainly performed by the pulse sequence setting function 401.

Figure 6 is a diagram showing an example of a pulse sequence setting screen SC displayed on the display 42. From the right side, the setting screen SC has a window W1 for specifying the imaging site, a window W2 for specifying the PAS name, and a window W3 for displaying the pulse sequence group included in the specified PAS. It also has a window W4 for selecting multiple pulse sequences from the pulse sequence group included in the PAS and arranging them in the order of execution as the pulse sequence group to be executed in the imaging to be performed.

Here, PAS (Programmable Anatomical Scan) is a database that stores multiple pulse sequence groups corresponding to various anatomical imaging regions (e.g., head, legs, etc.). For example, as illustrated in FIG. 6, when a user selects "head" as an imaging target region in window W1, multiple PAS names (i.e., identification names given to multiple pulse sequence groups) corresponding to "head" are displayed in window W2. When a user selects, for example, "HEAD MRA" from among the multiple PAS names, the pulse sequence groups included in the selected PAS are displayed in window W3.

When the user selects a desired pulse sequence from the group of pulse sequences displayed in window W3, the selected pulse sequences are displayed in window W4 in the selected order. Then, when imaging begins, each pulse sequence is executed sequentially in the order arranged in window W4. Note that a pulse sequence is sometimes called a "protocol," and a group of pulse sequences is sometimes called a "protocol group."

Returning to FIG. 5, in step ST101 of FIG. 5, calculation of filter coefficient sets corresponding to the types of each pulse sequence in the selected pulse sequence group is started.

On the other hand, in step ST110 of FIG. 5, the calculation status of the filter coefficient set corresponding to each type of pulse sequence in the selected pulse sequence group is displayed on the display 42.

As shown in FIG. 6, window W4 of the setting screen SC displayed on the display 42 has a "No" column indicating the execution order, a "Sequence ID" column indicating the type of selected pulse sequence, as well as columns for "Calculation time" and "Calculation status."

When at least one pulse sequence is selected from the group of pulse sequences to be executed, the filter coefficient calculation and setting function 402 can determine the bandwidth of the MR signal corresponding to the type of selected pulse sequence and can start calculating the corresponding filter coefficient set.

The "Calculation Status" column of window W4 displays the calculation status of the filter coefficient set. For example, when the calculation of the filter coefficient set corresponding to the pulse sequence has been completed, the "Calculation Status" column displays "Completed", when the filter coefficient set is in the process of being calculated, it displays "Calculating", and when it has not yet been calculated, it displays "Not yet". This display makes it easy to grasp the calculation status of the filter coefficient set. The display in the "Calculation Status" column of window W4 can be performed, for example, by the filter coefficient calculation setting function 402.

On the other hand, in step ST102 of FIG. 5, the filter coefficient calculation setting function 402 may display the predicted calculation time of the filter coefficient set corresponding to each pulse sequence on the display 42. For example, the predicted calculation time of the filter coefficient set can be displayed in the "Calculation time" field of window W4. Once the type of pulse sequence or the band of the MR signal corresponding thereto is determined, it is possible to estimate the approximate predicted calculation time from past calculation results, etc., before actually calculating the filter coefficient set. The estimated predicted calculation time is displayed in the "Calculation time" field of window W4.

In step ST103, the user instructs the start of imaging. In response to this instruction, each pulse sequence in the pulse sequence group is executed sequentially according to the execution order of the set pulse sequence group.

In step ST104, before each pulse sequence is executed, a corresponding filter coefficient set is set in the digital filter 321. The processing of step ST104 is also performed by the filter coefficient calculation and setting function 402.

In step ST105, after the processing of step ST104, i.e., after the filter coefficient set corresponding to the pulse sequence to be executed is set in the digital filter 321, the pulse sequence is executed.

By executing this pulse sequence, the MR signals collected by the RF coil 20 are filtered by the digital filter 321 adapted to the bandwidth. The filtered MR signals are then imaged by the reconstruction function 404 shown in FIG. 4 to generate a diagnostic image. Furthermore, this diagnostic image is subjected to the desired image processing by the image processing function 405 and then displayed on the display 42.

In step ST106 in FIG. 5, a determination is made as to whether imaging has ended. If all pulse sequences in the set pulse sequence group have been executed, the process ends. On the other hand, if there are still pulse sequences to be executed, the process returns to step ST104, and the processes in steps ST104 and ST105 are repeated.

Figures 7 and 8 are schematic diagrams showing the relationship between the time it takes to set a pulse sequence group and execute each pulse sequence (shown in the upper parts of Figures 7 and 8) and the time it takes to calculate a filter coefficient set and set it in the digital filter 321 (shown in the lower parts of Figures 7 and 8).

Figure 7 shows a first example in which the user starts setting a pulse sequence group, filter coefficient sets are calculated immediately after at least one type of pulse sequence is set, and the calculation of all filter coefficient sets is completed during the period until imaging starts.

The "Pulse sequence group setting" period shown in the upper part of Figure 7 is a period during which the user selects the desired pulse sequence from the pulse sequence groups displayed in window W3 shown in Figure 6, thereby setting the pulse sequence group to be executed consecutively in one examination.

The "Editing the Pulse Sequence" period that follows "Setting the Pulse Sequence Group" is a period in which individual parameters, such as the flip angle and number of slices, within each pulse sequence in the set pulse sequence group are edited as necessary.

When "Editing the Pulse Sequence" is completed, the user instructs the start of imaging, and a series of pulse sequences are executed according to the set order. In the example shown in FIG. 7 and FIG. 8, a "pre-scan (1)" is followed by a "diagnostic scan (1)", and a "pre-scan (2)" is followed by a "diagnostic scan (2)". The "diagnostic scan (1)" is a diagnostic scan that acquires a diagnostic image using, for example, a pulse sequence for diffusion weighted imaging (DWI), and the "diagnostic scan (2)" is a diagnostic scan that acquires a diagnostic image using, for example, a pulse sequence for T2 weighted imaging (T2WI).

A prescan is a scan that, prior to a diagnostic scan, performs, for example, calibrating the gain of the amplifier equipped in the RF receiver 32 in order to adjust the signal level of the diagnostic scan. For example, "prescan (1)" is a prescan for gain calibration for "diagnostic scan (1)," and "prescan (2)" is a prescan for gain calibration for "diagnostic scan (1)."

Diagnostic scans require the generation of high-resolution images, so high performance is also required for the characteristics of the digital filters applied to the MR signals acquired in diagnostic scans. For example, a very large value is required for the attenuation in the stopband, while a very small value is required for the ripple in the passband. For this reason, the number of taps (i.e., the number of filter coefficients) of the FIR type digital filter is required to be large, for example, several hundred taps, and it takes time to calculate the filter coefficient set.

In contrast, the data collected in the prescan is not intended to directly generate an image, and therefore the performance of the digital filter, such as the attenuation in the stopband and the ripple in the passband, is not as high as that of the diagnostic scan. Therefore, in this embodiment, the number of taps (i.e., the number of filter coefficients) corresponding to the pulse sequence of the prescan is made smaller than the number of taps corresponding to the pulse sequence of the diagnostic scan. This shortens the calculation time for the entire set of filter coefficients, including the prescan and the diagnostic scan.

Figure 8 shows an example in which the calculation of all filter coefficient sets is not completed at the start of imaging, but the calculation of the filter coefficient set corresponding to the pulse sequence of the corresponding diagnostic scan is completed before the pulse sequence of this pulse sequence is executed.

For example, the filter coefficient (2) corresponding to the "diagnostic scan (1)" is calculated during the execution of the "pre-scan (1)", and the calculation is completed at the start of the "diagnostic scan (1)" and is set in the digital filter 321.

For example, the filter coefficient (4) corresponding to the "diagnostic scan (2)" is calculated during the execution of the "diagnostic scan (1)" which is executed before the "diagnostic scan (2)", and the calculation is completed at the start of the "diagnostic scan (2)" and is set in the digital filter 321.

A high-performance digital filter 321 has a large number of taps, and it may take several seconds, for example, to calculate the filter coefficient set. For this reason, it may be possible that the calculation of all filter coefficient sets is not completed at the time when the user instructs the start of imaging. Even in such a case, as described above, the calculation of the filter coefficient set corresponding to this pulse sequence can be completed before the pulse sequence of the corresponding diagnostic scan is executed by measures such as a) making the number of taps of the digital filter 321 for the prescan less than the number of taps for the diagnostic scan, thereby shortening the calculation time of the filter coefficient set for the prescan, b) calculating the filter coefficient set for the next diagnostic scan while the prescan is being executed, and c) calculating the filter coefficient set for the diagnostic scan to be executed after the diagnostic scan being executed while the diagnostic scan is being executed.

Furthermore, in the magnetic resonance imaging apparatus 1 of this embodiment, the filter coefficient registration function 403 can also reuse a filter coefficient set that has already been calculated. Figure 9 is a flowchart showing a processing example of the operation of registering and reusing a filter coefficient set.

In FIG. 9, the same processes as those in FIG. 5 are denoted by the same reference numerals. After starting calculation of the filter coefficient set for each pulse sequence in step ST101, in step ST200, it is determined whether or not the filter coefficient set corresponding to the set pulse sequence has been registered, for example, by referring to the memory circuitry 41. If it has been registered, in step ST201, the registered filter coefficient set is read from the memory circuitry 41, and the calculation process of the filter coefficient set corresponding to the pulse sequence is skipped.

If a filter coefficient set corresponding to the set pulse sequence is not registered, a new corresponding filter coefficient set is calculated in sequence as described above.

After the termination determination is made in step ST106, in step ST202, the newly calculated filter coefficient set is associated with the corresponding pulse sequence type and registered in the memory circuit 41.

The above-described process makes it possible to avoid repeatedly calculating filter coefficient sets corresponding to the same type of pulse sequence, and therefore makes it possible to reduce the overall calculation time for the filter coefficient sets.

As described above, the magnetic resonance imaging apparatus of each embodiment provides a digital filter for magnetic resonance signals that is highly scalable and can flexibly accommodate parameter changes such as changes in the type of pulse sequence and changes in reception bandwidth.

The pulse sequence setting function in the description of each embodiment is an example of a sequence setting unit in the description of the claims. The filter coefficient calculation setting function in the description of each embodiment is an example of a calculation setting unit in the description of the claims. The filter coefficient registration function in the description of each embodiment is an example of a registration unit in the description of the claims.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and gist of the invention.

1 Magnetic resonance imaging apparatus 32 RF receiver 34 Sequence controller 40 Processing circuit 41 Memory circuit 42 Display 43 Input device 320 AD converter 321 Digital filter 400 Console 401 Pulse sequence setting function 402 Filter coefficient calculation and setting function 403 Filter coefficient registration function 404 Reconstruction function 405 Image processing function

Claims (10)

A digital filter circuit configured to exhibit different frequency characteristics according to settings of a filter coefficient;
a calculation and setting unit that calculates the filter coefficient from a bandwidth of a magnetic resonance signal corresponding to a pulse sequence to be executed every time the pulse sequence is executed, and sets the calculated filter coefficient in the digital filter circuit every time the pulse sequence is executed;
A magnetic resonance imaging apparatus comprising: A digital filter circuit configured to exhibit different frequency characteristics according to settings of a filter coefficient;
a calculation and setting unit that calculates the filter coefficient from a type of a pulse sequence to be executed every time the pulse sequence is executed, and sets the calculated filter coefficient in the digital filter circuit every time the pulse sequence is executed;
A magnetic resonance imaging apparatus comprising: A sequence setting unit that sets a pulse sequence group by arranging a plurality of types of pulse sequences in an execution order,
the calculation setting unit calculates a filter coefficient corresponding to each type of the pulse sequence from when the pulse sequence group is set until when the type of the pulse sequence is executed, and sets the filter coefficient in the digital filter circuit.
3. A magnetic resonance imaging apparatus according to claim 1. the calculation setting unit starts calculating a filter coefficient corresponding to each type of the pulse sequence included in the pulse sequence group immediately after the pulse sequence group is set.
4. A magnetic resonance imaging apparatus according to claim 3. the group of pulse sequences includes a pulse sequence for a diagnostic scan for acquiring a diagnostic image and a pulse sequence for a prescan for preparing the diagnostic scan;
The calculation setting unit calculates the filter coefficients corresponding to a pulse sequence of the diagnostic scan following the prescan during execution of the prescan.
4. A magnetic resonance imaging apparatus according to claim 3. the number of filter coefficients corresponding to the pre-scan pulse sequence is less than the number of filter coefficients corresponding to the diagnostic scan pulse sequence;
6. A magnetic resonance imaging apparatus according to claim 5. the group of pulse sequences includes a pulse sequence of a first diagnostic scan for acquiring a diagnostic image and a pulse sequence of a second diagnostic scan executed after the first diagnostic scan;
the calculation setting unit calculates the filter coefficients corresponding to a pulse sequence of the second diagnostic scan during execution of the first diagnostic scan.
4. A magnetic resonance imaging apparatus according to claim 3. A storage unit;
A registration unit that registers the calculated filter coefficient in the storage unit in association with a type of a corresponding pulse sequence,
When the filter coefficients of the pulse sequence to be executed are registered in the storage unit, the calculation setting unit reads out the filter coefficients corresponding to the pulse sequence to be executed from the storage unit and sets them in the digital filter circuit.
8. A magnetic resonance imaging apparatus according to claim 1. a display;
the calculation setting unit displays on the display an expected calculation time of a filter coefficient corresponding to each pulse sequence of the pulse sequence group.
4. A magnetic resonance imaging apparatus according to claim 3. a display;
the calculation setting unit displays on the display a calculation status of a filter coefficient corresponding to each pulse sequence of the pulse sequence group.
4. A magnetic resonance imaging apparatus according to claim 3.

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