JP6708578B2 - Magnetic resonance imaging apparatus and signal transmission apparatus - Google Patents

Description

The present invention relates to a magnetic resonance imaging (MRI) technique.

The MRI apparatus induces nuclear magnetic resonance (NMR) by irradiating an atomic nucleus in an arbitrary cross section that crosses an inspection target with a high-frequency magnetic field, and obtains a tomographic image in the cross section from the generated nuclear magnetic resonance signal (NMR signal). It is a medical image diagnostic apparatus.

In MRI imaging, a receiving coil that receives an NMR signal is connected to a main body device by a cable, and data communication is performed with the main body device via the cable. Patent Document 1 proposes a configuration in which a wireless device is used instead of such a wired cable to make the connection between the receiving coil and the main body device cableless. In the wireless MRI apparatus, when the RF signal obtained by digitizing the received signal in the receiving coil is wirelessly transmitted to the main unit, if the communication speed of the wireless device is lower than the received data rate, the data is transmitted. It takes extra time for imaging. Therefore, in Patent Document 1, by performing thinning processing on the received signal, the data rate is compressed to a wirelessly transmittable rate and then wirelessly transmitted, and the main signal restores the original signal from the thinned signal, Methods have been proposed for constructing MRI images.

JP, 2011-92553, A

In the technique of Patent Document 1, the process of thinning out the received signal is an irreversible compression process, and therefore there is a problem that the SNR of the reconstructed image deteriorates depending on the degree of the thinning process.

On the other hand, the received signal of the MRI apparatus is characterized in that the amplitude greatly changes within one received signal, and therefore the data compression also has to deal with the change in the dynamic range of the received signal.

An object of the present invention is to perform image reconstruction by wirelessly transmitting bit data obtained by digitizing a reception signal of an MRI apparatus and restoring it without deterioration.

In order to achieve the above object, the MRI apparatus of the present invention obtains bit data by sampling a received signal, which receives an NMR signal emitted by a subject, at a predetermined cycle and digitizes the received signal, and sequentially arranges the bit data. A receiving coil unit that generates a bitstream and wirelessly transmits it, and a bitstream wirelessly transmitted by the receiving coil unit are received, the bitstream is cut out for each bit length to obtain bit data, and the bit data is arranged and digitized. And a main unit that reconstructs an image of the subject using the received signal. The receiving coil unit changes the bit length of the bit data according to the signal strength of the received signal, and inserts a changed position bit string indicating the position where the bit length changes into the bit stream.

According to the present invention, by adopting a variable bit length, the transfer rate of received signal data can be increased and wireless transmission can be performed as compared with the case of a fixed bit length, and image reconstruction can be performed by restoring without deterioration. Therefore, it is possible to obtain an image without SNR deterioration.

The block diagram which shows the whole structure of the MRI apparatus of 1st Embodiment. The block diagram which shows the detailed structure of the receiving coil unit and main body apparatus of the MRI apparatus of 1st Embodiment. The graph which shows the typical NMR signal (echo) which a test object generate|occur|produces. (A) is explanatory drawing which shows the bit stream which arranged the bit data of an NMR signal, (b) is explanatory drawing which shows the bit stream after compression. The figure explaining the bit stream which inserted the header code of 1st Embodiment. FIG. 3 is an explanatory diagram showing an example of an imaging pulse sequence of the first embodiment and a time relationship of compression processing. Explanatory drawing which respectively shows (a) fixed bit length bit data, (b) variable bit length bit data after compression, and (c) fixed bit length bit data after decompression. The block diagram which shows the detailed structure of the echo compression part of 1st Embodiment. The flowchart which shows operation|movement of the maximum value determination part of 1st Embodiment. 6 is a flowchart showing the operation of the echo compression unit of the first embodiment. The figure explaining the header code of 1st Embodiment. The block diagram which shows the detailed structure of the echo restoration part of 1st Embodiment. 6 is a flowchart showing the operation of the echo restoration unit of the first embodiment. Explanatory drawing which shows the time relationship of the imaging pulse sequence of 2nd Embodiment, and a compression process. The block diagram which shows the detailed structure of the receiving coil unit and main body apparatus of the MRI apparatus of 2nd Embodiment. The block diagram which shows the detailed structure of the echo compression part of 2nd Embodiment. The figure explaining the bit stream of 3rd Embodiment. The block diagram which shows the detailed structure of the receiving coil unit and main body apparatus of the MRI apparatus of 4th Embodiment.

An MRI apparatus according to an embodiment of the present invention will be described.

<<First Embodiment>>
FIG. 1 is a block diagram showing an overall configuration of the MRI apparatus of the first embodiment, and FIG. 2 is a block diagram showing detailed configurations of a receiving coil unit 200 and a main body apparatus 300 of the MRI apparatus. FIG. 3 shows a typical NMR signal generated by the subject. 4A and 4B show a bit stream in which bit data of NMR signals are arranged. FIG. 5 shows a bitstream with a header code inserted.

As shown in FIGS. 1 and 2, the MRI apparatus of this embodiment includes at least a receiving coil unit 200 and a main body apparatus 300. The receiving coil unit 200 receives an NMR signal emitted by the subject 103 as shown in FIG. 3, obtains bit data by sampling and digitizing the obtained reception signal at a predetermined cycle, and sequentially obtains the bit data. By arranging them side by side, a bit stream as shown in FIGS. 4A and 4B is generated and wirelessly transmitted. The main body device 300 receives the bit stream wirelessly transmitted by the receiving coil unit 200, extracts the bit stream for each bit length to obtain bit data, arranges the obtained bit data, and restores a digitized reception signal. Then, the image of the subject 103 is reconstructed using the restored received signal. At this time, as shown in FIG. 4B, the receiving coil unit 200 makes the bit length of the bit data variable according to the signal strength of the received signal, and the change position bit string (hereinafter referred to as the change position bit string) indicating the position where the bit length changes. , Header code) 51 into the bitstream as shown in FIG.

By varying the bit length according to the signal strength of the received signal in this way, when transmitting an NMR signal with a large dynamic range as a bit stream, the unnecessary bit length for expressing the signal strength as bit data is reduced. can do. As a result, the unnecessary bit length of the bit stream represented by the fixed bit length as shown in FIG. 4(a) can be reduced, and the bit stream compressed as shown in FIG. 4(b) without damaging the bit data. Can be converted to.

The main body device 300 grasps the bit length set from the bit stream of the variable bit data by reading the header code 51, and changes the bit length for cutting out the bit stream according to the header code 51. It is possible to appropriately cut out stream data and restore the bit data indicating the signal strength of the received signal.

Therefore, in the MRI apparatus of the present embodiment, compared with the case of a fixed bit length, the transfer rate of received signal data can be increased and wireless transmission can be performed, and image reconstruction can be performed without deterioration, and thus SNR of It is possible to obtain an image in which deterioration is suppressed.

The variable bit length set by the receiving coil unit 200 is configured such that the receiving coil unit 200 determines and changes the bit length required to represent the signal intensity of the received signal at the time of sampling, for example. The receiving coil unit 200 has a compression unit, and when the first code bit of the data string of the bit data representing the signal strength of the reception signal at the time of sampling is 0, the compression unit outputs consecutive 0s after the code bit. , If the sign bit is 1, it is possible to compress the bit length by determining that consecutive 1s after the sign bit are unnecessary bits and removing them. On the other hand, the main body device 300 includes a restoration unit, and when the leading code bit of the bit data obtained by cutting out the bit stream for each bit length is 0, the restoration unit sets consecutive 0s after the code bit to the code bit. Is 1, the consecutive 1s after the code bit can be added to restore the predetermined fixed bit length.

In the present embodiment, the header code (change position bit string) is inserted before or after the bit data at the position where the bit length changes.

The header code may include information indicating the changed bit length. Thereby, main device 300 can change the bit length to be cut out in accordance with the bit length indicated by the header code when the bit stream is cut out and the bit string is generated.

Further, the receiving coil unit 200 discriminates the data having the maximum signal value among the bit data obtained by sampling the reception signal, and reverses the plurality of bit data sampled at a timing later than the maximum value bit data. The rearrangement may be performed to generate a bitstream. By rearranging in the reverse order as described above, it becomes possible to set the bit length of the received signal which actually gradually decreases after reaching the maximum amplitude by detecting only the gradually increasing.

Hereinafter, the MRI apparatus of the embodiment will be described more specifically.

As shown in FIG. 1, the MRI apparatus 100 of the present embodiment applies a static magnetic field generator 101 that generates a static magnetic field to an imaging space in which an imaging region of the subject 103 is arranged, and applies a gradient magnetic field to the imaging space. The gradient magnetic field coil 102, the transmission coil 107 that irradiates the subject 103 with a high-frequency magnetic field pulse, the receiving coil unit 200, the bed 115 on which the subject 103 is mounted, and the main body device 300 are configured.

As is clear from FIGS. 1 and 2, the main body device 300 includes a gradient magnetic field power supply 105 for supplying a current for generating a gradient magnetic field to the gradient magnetic field coil 102, and a high frequency signal for generating a high frequency magnetic field pulse in the transmission coil 107. , A sequencer 104 that controls these operations, a wireless communication unit 301 that wirelessly receives the bit stream transmitted from the receiving coil unit 200, an echo restoration unit 302, and an image configuration unit 303. A display device 304, a storage device 112, and an input device 116.

As shown in FIG. 2, the receiving coil unit 200 includes a receiving coil 201, a receiving circuit 202, a signal processing unit 203, an echo compression unit 204, a wireless communication unit 205, and a timing control unit 206.

When capturing an image in the MRI apparatus having such a configuration, the sequencer 104 executes the imaging pulse sequence 601 designated by the user via the input device 116 or the like, and the NMR signal (hereinafter, also referred to as an echo signal or a reception signal). To get. First, the user operates the bed 115 to place the subject 103 in the imaging space. For example, when the imaging pulse sequence 601 is a spin echo sequence as shown in FIG. 6, the sequencer 104 applies the slice encode gradient magnetic field from the gradient magnetic field coil 102 while applying the high frequency magnetic field pulse (hereinafter referred to as the high frequency magnetic field pulse) from the transmission coil 107. , RF pulse) 611 to excite spins of the subject 103 and apply a phase-encoding gradient magnetic field 612, and then an echo signal 613 is received by the receiving coil 201 while applying a readout gradient magnetic field.

In the spin echo sequence, the waveform of the reception signal (echo signal) output from the reception coil 201 has an amplitude that increases toward a certain maximum peak, although there is a slight increase or decrease, as shown in FIG. After that, it decreases. The amplitude at the position (3) which is the maximum peak and the amplitude at the position (1) which is the minimum are largely different, and the ratio (dynamic range) is large.

The receiving circuit 202 of FIG. 2 samples the echo signal received by the receiving coil 201 at a predetermined sampling period, and thereby the amplitude (hereinafter, also referred to as signal strength) at the time of sampling is represented by a digital signal having a fixed bit length. Is obtained (FIG. 4(a)). The signal processing unit 203 performs filter processing, down conversion, and the like on the bit data as necessary. The echo compressing unit 204 compresses the bit data by deleting unnecessary bit lengths from the bit data representing the amplitude of the received signal at the time of sampling to represent the amplitude at that time, and then arranges the compressed bit data into bits. A stream is generated (FIG. 4(b)).

7A and 7B show the basic concept of compression performed by the echo compression unit 204. The reception circuit 202 converts the reception signal into bit data represented by a binary number having a fixed bit length (8 bits in FIG. 7A) at the time of sampling the reception signal. At this time, the first bit is the sign bit 71, which indicates the sign (positive or negative) of the amplitude value, and the remaining 7 bits are data bits 72 which indicate the amplitude (signal strength) in binary. The echo compression unit 204 leaves the sign bit 71 for this bit data, deletes unnecessary bits from the data bit 72 indicating the amplitude, and changes to a variable bit length of a fixed bit length (8 bits) or less. (FIG. 7B).

Specifically, the echo compression unit 204 reads by determining whether the most significant code bit 71 is 1 or 0, and when the code bit 71 is 0 (amplitude value is positive), the bit next to the code bit 71 is determined. It is determined whether (that is, the first bit of the data bit 72) is 0. When the next bit is 0, it is further determined whether or not the next bit is 0, and each bit is repeatedly determined in order until the 1 bit appears. As a result, when one or more 0s are consecutive from the beginning of the data bit 72, one or more consecutive 0s are unnecessary bits 73 and are removed.

On the other hand, when the sign bit 71 is 1 (the amplitude value is negative), it is determined whether the bit next to the sign bit 71 (that is, the first bit of the data bit 72) is 1. If the next bit is 1, it is further determined whether or not the next bit is 1, and each bit is repeatedly determined in order until a 0 bit appears. As a result, if one or more 1's are consecutive from the beginning of the data bit 72, one or more consecutive 1's is an unnecessary bit 73 and is removed.

In this way, the echo compression unit 204 can delete the unnecessary bit 73 from the data bit 72 representing the amplitude value, and thus the length of the data bit 72 can be shortened without affecting the bit representing the amplitude value. And can be compressed. The echo compression unit 204 arranges the bit data from which the unnecessary bits 73 are deleted to generate a bitstream (FIG. 4B).

The wireless communication unit 205 transmits the compressed bitstream generated by the echo compression unit 204 to the main device 300. The timing control unit 206 controls the start and end of reception of a reception signal and the start and end of wireless communication according to the timing signal transmitted from the main body device 300.

A more detailed configuration and operation of the echo compression unit 204 will be described. As described above, in the waveform of the echo signal, the amplitude (3) at the maximum peak position is significantly different from the amplitude (1) at the minimum amplitude position. Therefore, these amplitudes (signal strengths) are used to represent bit data. The required number of bits is different. The echo compression unit 204 compresses the data in consideration of this.

FIG. 8 shows a detailed configuration of the echo compression unit 204. As shown in FIG. 8, the echo compression unit 204 includes a maximum value determination unit 803, a reception buffer 804, a code determination unit 805, an effective bit length counter 806, a comparator 807, a header code generation unit 808, and a radio. And a transmission buffer 809. The maximum value determination unit 803 is connected to the continuous zero number storage unit 810 and the maximum value address storage unit 811, and the reception buffer 804 is connected to the position determination unit 812. A bit length storage unit 814 is connected to the comparator 807. Further, a variable length bit generation unit 814 is connected in parallel from the code determination unit 806 to the comparator 807.

The reception signal received by the reception coil 201 is AD-converted by the reception circuit 202 at a predetermined sampling period to be sequentially converted into bit data having a fixed bit length (for example, 8 bits) as shown in FIG. The signal processing unit 203 performs filter processing and the like as necessary, and then outputs to the echo compression unit 204. As described above, the amplitude of the received signal is small (amplitude (1)) in the initial stage, but gradually increases (amplitude (2)), reaches the maximum value (amplitude (3)), and then gradually decreases. There is a feature (Fig. 3). The echo compression unit 204 of the present embodiment sets the variable bit length required to represent the amplitude of the received signal that gradually increases and then gradually decreases, so that the amplitude has the maximum value so that it is sufficient to detect only the incremental increase. The signal read direction is reversed before and after reaching. Specifically, the maximum value determination unit 803 sequentially receives fixed-bit-length bit data indicating the amplitude at the time of sampling from the signal processing unit 203, and outputs the bit data with the maximum amplitude value indicated by the data bit 72 in FIG. Determine according to the flow.

That is, when the maximum value determination unit 803 receives the bit data from the signal processing unit 203, the maximum value determination unit 803 compares the amplitude value with the temporary maximum value (initial value is 0) stored in the maximum value address storage unit 811. (Step 901) If it is larger than the temporary maximum value, the temporary maximum value stored in the maximum value address storage unit 811 is updated with the amplitude value of the current bit data, and then the bit data is stored in the reception buffer 804 ( Step 902). At this time, the data address of the reception buffer 804 is also stored in the maximum value address storage unit 811. On the other hand, in step 901, when the amplitude value of the current bit data is equal to or less than the provisional maximum value stored in the maximum value address storage unit 811, the provisional maximum value in the maximum value address storage unit 811 is not updated. Not performed. This is repeated until the time for reading the echo signal by the receiving circuit 202 ends, that is, until the reception of the bit data from the signal processing unit 203 ends (step 903). After that, the maximum value determination unit 803 resets the provisional maximum value of the maximum value address storage unit 811 to zero which is the initial value (step 904).

Further, the maximum value determination unit 803 counts the number of consecutive 0s in the bit data forming the bit data received from the signal processing unit 203 in parallel with steps 901 to 904. If the counted number of consecutive zeros is greater than the provisional maximum consecutive zero number stored in the consecutive zero number storage unit 810, the maximum value determination unit 803 updates the provisional maximum consecutive zero number. This maximum number of consecutive zeros is used to indicate that the header code 51 is different from bit data of variable bit length.

As shown in the flow of FIG. 10, the position determination unit 812 determines that the data address in the reception buffer 804 of the bit data to be read next by the code determination unit 805 is the maximum value stored in the maximum value address storage unit 811. Is determined (step 911). If the address is not the maximum value bit data address, the address is sampled before the maximum value, or is sampled after the maximum value. It is determined whether the address is the address of the bit data that has been sampled (step 913). If the address is the address of the bit data sampled before the maximum value, the process proceeds to step 914. In step 914, the code determination unit 805 reads the bit data (amplitude value) of the next data address from the reception buffer 804 (FIG. 7A). Then, the code determination unit 805 reads and determines whether the most significant code bit 71 of the read bit data is 1 or 0 (step 916). When the code bit 71 determined by the code determination unit 805 is 0 (amplitude value is positive), the effective bit length counter 806 indicates that the bit next to the code bit 71 (that is, the first bit of the data bit 72) is 0. If the next bit is 0, the process of further determining whether the next bit is 0 is repeated until the 1 bit appears. As a result, when one or more 0s continue from the beginning of the data bit 72, the number of 0s that continue one or more is counted as the number of unnecessary bits 73, and the number of unnecessary bits 73 is subtracted from the fixed bit length. The calculated bit length is calculated as the bit length required to represent the bit data (amplitude) of this time (step 917). Similarly, in step 916, when the sign bit 71 is 1 (the amplitude value is negative), the valid bit length counter 806 has the value 1 next to the sign bit 71 (that is, the first bit of the data bit 72). If the next bit is 1, the process of further determining whether the next bit is 1 is repeated until a 0 bit appears. As a result, when one or more 1's are consecutive from the beginning of the data bit 72, the number of 1's of 1 or more consecutive 1's is counted as the number of unnecessary bits 73, and the number of unnecessary bits 73 is subtracted from the fixed bit length. The calculated bit length is calculated as the bit length required to represent the bit data (amplitude) of this time (step 917).

The comparator 807 compares the required bit length calculated by the valid bit length counter 806 with the provisional bit length (initial value 0) stored in the bit length storage unit 814 (step 918). If the required bit length is long, the provisional bit length is updated to the required bit length calculated in step 917, and the required bit length is output to the header code generation unit 808. The header code generation unit 808 generates the header code 51 indicating that the required bit length is different from that of the previous time, and writes it in the wireless transmission buffer 809 (step 919).

FIG. 11 shows an example of the header code 51. The header code 51 includes a header identification bit string 111 and a bit length string 113. The header identification bit string 111 is a bit string that indicates the header code 51 because the number of consecutive 0s is larger than the number of consecutive 0s than the fixed bit length bit data output from the signal processing unit 203. The number of consecutive 0s in the header identification bit string 111 is set to be larger than the maximum value of consecutive 0s in the bit data of the received signal stored in the consecutive zero number storage unit 810. Thus, when the main body device 300 that has received the bitstream detects that a sequence of 0s that is longer than the number of consecutive 0s in the data indicating the amplitude of the received signal is included, that is the header identification bit sequence. It can be determined to be 111. The bit length string 113 indicates the bit length of the variable length data string 41 after the header code 51.

Next, the variable length bit generation unit 815 receives the bit data of the same address as the code determination unit 805 performed the code determination in step 916 from the reception buffer 804 and the number of unnecessary bits 73 via the comparator 807. , The unnecessary bit 73 is deleted from the head of the data bit 72 of the bit data. As a result, compressed bit data having a variable bit length is generated and written in the wireless transmission buffer 809 (step 920).

On the other hand, in step 911 described above, the position determination unit 812 determines that the data address in the reception buffer 804 of the bit data to be read next by the code determination unit 805 is the maximum value address stored in the maximum value address storage unit 811. If it is, the maximum value marker code 52 (see FIG. 5) is generated and written in the wireless transmission buffer 809. Then, the process proceeds to step 913, and if the data address to be read next is one sampled after the maximum value, the process proceeds to step 915, where the bit data is stored in the receiving buffer in the reverse order of the time series from the end of the address. Is read (step 915), and steps 916 to 920 are sequentially performed on the read bit data. In this way, by sequentially reading the bit data whose amplitude is after the maximum value from the end, as shown in FIG. 3, the amplitude data of the received signal that gradually decreases from the maximum value in the case of a time series is read from the end to the minimum value. Since the data can be treated in the same manner as the data gradually increasing from the maximum value to the maximum value, it can be processed in the same manner as the first half of the received signal. The data read from the end may be rearranged in the main body device 300 after being rearranged, and then image reconstruction may be performed.

The wireless communication unit 205 reads the bit data written in the wireless transmission buffer 809 in the order in which they were written, concatenates them in time series to generate a bit stream, and wirelessly transmits the bit stream. As a result, as shown in FIG. 5, a bit stream in which the header code 51 indicating the bit length of the variable length data string, the variable length data string 41, and the maximum value marker code 52 are connected is wirelessly transmitted.

FIG. 6 shows a time chart of echo signal reception and compression processing. The signal processing in the reception circuit 202 and the signal processing unit 203, and the maximum value determination processing by the maximum value determination unit 803 are performed in parallel with the reception of the echo signal. The compression process by the sign determination unit 805, the effective bit length counter 806, the header code generation 808, and the variable length bit generation 815 is performed after the echo signal of the pulse sequence 601 is received and before the next echo signal is received.

The wireless communication unit 301 (FIG. 2) of the main device 300 receives the data (bit stream) transmitted by the wireless communication unit 205 of the receiving coil unit 200. The echo decompression unit 302 decompresses the bit data compressed by the echo compression unit 204 and performs a process of decompressing the reception signal (echo) of FIG. The image composing unit 303 reconstructs an image using the restored received signal. The timing control unit 305 sends a timing signal to the timing control unit 206 of the receiving coil unit 200, while instructing the start and end of reception of the wireless communication unit 301.

FIG. 12 shows a detailed configuration of the echo restoration unit 302. The echo restoration unit 302 includes a wireless reception buffer 121, a maximum value marker determination unit 302, a header code determination unit 303, a code restoration unit 304, and a write buffer 305. A maximum value address storage unit 306 and a read control unit 309 are connected to the maximum value marker determination unit 302. A bit length storage unit 307 is connected to the header code determination unit 303, and a write control unit 308 is connected to the code restoration unit 304.

The operation of each unit of the echo restoration unit 302 will be described with reference to the flowchart of FIG. The wireless reception buffer 121 stores the bitstream received by the wireless communication unit 301. The read control unit 309 cuts out variable-length data (bit string) from the beginning of the bit stream stored in the wireless reception buffer 121 with the bit length stored in the bit length storage unit 307, and the maximum value marker determination unit 302. (Step 131). The maximum value marker determination unit 302 determines whether or not the read bit string is the maximum value marker code 52 (FIG. 5) (step 132), and when it is not the maximum value marker code, the header code determination unit 303 It is determined whether the read data is the header code 52 (step 134). Specifically, the header code determination unit 303 determines whether the header identification bit string 111, which is a string of 0s in which the number of consecutive 0s is longer than the number of consecutive 0s in the data indicating the amplitude of the received signal, is included. If the header identification bit string 111 is included, it is determined that the read data is the header code 51. Then, in step 135, the numerical value of the bit length string 113 after the header identification bit string 111 of the header code 51 is read as the variable bit length set in the bit string thereafter. The header code determination unit 303 updates the variable bit length stored in the bit length storage unit 307 with the read variable bit length. On the other hand, in step 134, when the bit string is not the header code 51, the process proceeds to step 136, and the code restoring unit 304 sets between the sign bit 71, which is the most significant bit of the bit string, and the second and subsequent data bits 72. The compressed bit string is restored by inserting the decompression bit 74 of the 0 column or the 1 column as shown in FIG. 7C. The restoration bit 74 is a sequence of 0 if the sign bit 71 is 0, and is a sequence of 1 if the sign bit 71 is 1. The number of bits of 0 or 1 added by the restoration bit 74 is the number of bits of the difference between the variable bit length and a predetermined fixed bit length. The code restoration unit 308 writes the restored bit string in the write buffer 305 of the address indicating the write control unit 308, and increments the address indicated by the write control unit 308. As a result, a variable bit length bit string can be restored to a predetermined fixed bit length and written in the write buffer 305.

On the other hand, in step 132, the maximum value marker determination unit 302 stores the maximum value address in the maximum value address storage unit 306 when the read bit string is the maximum value marker code 52, and returns to step 131.

The read control unit 309 repeats reading the bit string until all the data streams in the wireless reception buffer 121 are read (steps 138 and 131).

The image configuration unit 303 reads the maximum value address stored in the maximum value address storage unit 306, and after this maximum value address, the data indicating the received signal in the write buffer 305 is the reverse of the time series. Recognize that they are arranged in order, and rearrange the received signals. The data before the maximum value address is in the same order. As a result, the received signal (echo) in FIG. 3 is restored, and the image is reconstructed using this. The reconstructed image is displayed on the display device 304 and stored in the storage device 112.

As described above, the MRI apparatus of the present embodiment compresses the bit string by reducing the unnecessary bit length for expressing the signal strength of the received signal as bit data, so that the necessary bit data is compressed without being damaged. it can. Therefore, it is possible to perform image reconstruction by accurately restoring the compressed bit stream that can be wirelessly transmitted.

The echo compression unit 204 and the echo decompression unit 302 may be configured such that their functions are executed by software when the CPU executes a program, or a part or all of them may be implemented by an ASIC (Application Specific Integrated). It may be configured by hardware such as a custom IC such as a circuit) or a programmable IC such as an FPGA (Field-Programmable Gate Array).

<<Second Embodiment>>
FIG. 13 shows an embodiment of the MRI apparatus according to the second embodiment.

The second embodiment includes a plurality of echo compression units 204 of the first embodiment arranged in parallel. As a result, even when the compression processing is not completed before the next echo signal is received, as shown in FIG. 13, the plurality of echo compression units 204 perform the compression processing in parallel, so that the compression processing can be performed in real time. is there. Other configurations and operations are the same as those in the first embodiment, and thus the description thereof will be omitted.

<<Third Embodiment>>
FIG. 15 shows the configurations of the receiving coil unit 200 and the main body device 300 of the MRI apparatus according to the third embodiment. 16 shows the configuration of the compression device, and FIG. 17 shows the configuration of the bit stream. As shown in FIGS. 15 and 16, the MRI apparatus of the third embodiment includes change point map storage units 151 and 152 instead of the header code generation unit 808 of the first embodiment.

In the third embodiment, as in the first embodiment, the variable length data string 41 is generated by the same operation as in FIG. 10, but instead of generating the header code 51 in step 919, the change point address 170 is used. Are generated and sequentially stored in the change point map storage unit 151. The change point address 170 includes a write address 170a to the transmission buffer 809 of the variable length data string 41 at the time when the variable bit length is changed, and a bit string 170b that sequentially shows the changed variable bit length. Then, as shown in FIG. 17, at the end of all the variable length data strings 41, a change point map string 171 in which change point addresses 170 in the change point map storage unit 151 are sequentially arranged is transmitted.

The change point map storage unit 152 of the main device 300 reads and stores the change point map sequence 171 from the bitstream received by the wireless communication unit 301. The data restoration unit 302 performs the restoration process as in the flow of FIG. 13, but the bit string read in Step 131 is stored in the change point map storage unit 152 instead of determining whether the header code is in Steps 134 and 135. It is determined whether or not it is the address of the stored change point address 170. If it is the change point address 170, the variable bit length indicated by the change point address 170 is read, and the process proceeds to step 136 to set the restoration bit 74. Insert into a bit string and restore to a fixed length bit string.

Other configurations and operations are the same as those in the first embodiment, and therefore description thereof will be omitted.

The MRI apparatus of this embodiment can also achieve the same effects as those of the first embodiment.

<<Fourth Embodiment>>
FIG. 18 shows an embodiment of the MRI apparatus according to the fourth embodiment. As shown in FIG. 18, the MRI apparatus of the fourth embodiment includes a receiving coil unit 200 with a sequence profile storage unit 181 and a main body device 300 with a sequence profile generating unit 182.

In the present embodiment, the receiving coil unit 200 changes the bit length according to a predetermined change pattern (sequence profile) of the signal strength of the received signal. Specifically, main device 300 generates a sequence profile that defines information as to when to change the bit length. For example, the sequence profile can be the envelope shape of the received signal (echo) of FIG. 3 which is obtained in advance by calculation or experiment.

The receiving coil unit 200 receives the sequence profile generated by the main body apparatus and wirelessly transmitted, performs compression processing based on the sequence profile, and the main body apparatus 300 performs decompression processing based on the sequence profile. Specifically, in this embodiment, in the flow of FIG. 10 of the first embodiment, the calculation of the bit length necessary to represent the amplitude of the received signal is not performed in step 917, and the bit length is calculated in step 920 according to the sequence profile. Change the length. When the bit length defined by the sequence profile is insufficient to represent the amplitude of the received signal, the largest value that can be represented by the bit length defined by the sequence profile is generated. Also, in steps 918 and 919, no header code is generated.

As a result, the apparatus of the present embodiment does not need to calculate the bit length, and does not need to generate or insert the header code, so that the data can be compressed in a short time.

Other configurations and operations are the same as those in the first embodiment, and therefore description thereof will be omitted.

Since the amplitude of the received signal changes not only according to the imaging conditions and the subject, but also according to the value of the phase encoding gradient magnetic field 612, the value of the imaging condition and the value of the phase encoding gradient magnetic field 612 are stored in advance in the main device 300. It is preferable to prepare a plurality of sequence profiles according to the above, select a sequence profile according to the imaging condition and phase encoding, and transmit the selected sequence profile to the receiving coil unit. Alternatively, prescan may be performed in advance to measure the amplitude of the received signal, and the sequence profile may be selected according to the result.

51... Header code, 52... Maximum value marker code, 71... Sign bit, 72... Data bit, 73... Unwanted bit, 74... Restoration bit, 100... MRI apparatus, 101... Static magnetic field generator, 102... Gradient magnetic field coil, 103... Subject, 104... Sequencer, 105... Gradient magnetic field power supply, 106... High frequency generator, 107... Transmission coil, 112... Storage device, 115... Bed, 116... Input device, 200... Reception coil unit, 201... Reception coil , 202... Receiving circuit, 203... Signal processing section, 204... Echo compression section, 205... Wireless communication section, 206... Timing control section, 300... Main unit, 301... Wireless communication section, 302... Echo restoration section, 303... Image Configuration unit, 304... Display device, 305... Timing control unit

Claims (12)

A receiving coil unit that receives bit signals obtained by sampling a received signal that has received an NMR signal emitted from the subject at a predetermined period and digitizing the bit signals, sequentially arranging the bit data to generate a bit stream, and transmitting wirelessly.
The receiving coil unit receives a bit stream wirelessly transmitted, cuts out the bit stream for each bit length to obtain the bit data, arranges the bit data to restore the digitized reception signal, and the reception signal And a main body device for reconstructing an image of the subject using
The receiving coil unit changes the bit length of the bit data according to the signal strength of a received signal, and inserts a change position bit string indicating a position where the bit length changes into the bit stream. Imaging equipment. The magnetic resonance imaging apparatus according to claim 1, wherein the reception coil unit determines, for each signal intensity of the sampled reception signal, a bit length required to represent the signal intensity, and the bit length is determined. A magnetic resonance imaging apparatus characterized in that The magnetic resonance imaging apparatus according to claim 2, wherein the receiving coil unit has a compression unit, and the compression unit is a head of a data string of bit data representing a signal strength of the reception signal at the time of sampling. If the sign bit of 0 is 0, consecutive 0's after the sign bit, and if the sign bit is 1, consecutive 1's after the sign bit are determined to be unnecessary bits, respectively. , A magnetic resonance imaging apparatus characterized by compressing a bit length. The magnetic resonance imaging apparatus according to claim 3, wherein the main body device has a restoration unit, and the restoration unit has a leading code bit of the bit data obtained by cutting out the bit stream for each bit length from 0. Is added, consecutive 0's after the sign bit are added, and consecutive 1's after the sign bit are added to restore the magnetic field to a predetermined fixed bit length. Resonance imaging device. The magnetic resonance imaging apparatus according to claim 1, wherein the change position bit string is inserted before or after the bit data at the position where the bit length changes. The magnetic resonance imaging apparatus according to claim 1, wherein the change position bit string includes information indicating a changed bit length, and the main body device cuts out the bit stream to generate the bit string, A magnetic resonance imaging apparatus, wherein the bit length to be cut out is changed according to the bit length indicated by the change position bit string. The magnetic resonance imaging apparatus according to claim 1, wherein the receiving coil unit determines bit data having a maximum signal value among the bit data obtained by sampling the reception signal, and the bit data having the maximum value is detected. A magnetic resonance imaging apparatus characterized in that a plurality of the bit data sampled at a timing later than the bit data is rearranged in a reverse order of time series to generate the bit stream. The magnetic resonance imaging apparatus according to claim 1, wherein the changed position bit string is added to the end of the bit stream. The magnetic resonance imaging apparatus according to claim 1, wherein the reception coil unit changes the bit length according to a predetermined change pattern of the signal intensity of the reception signal. apparatus. The magnetic resonance imaging apparatus according to claim 9, wherein a plurality of types of change patterns of the signal intensity are prepared in advance, and the main body apparatus selects a change pattern to be used from the plurality of types of change patterns, and receives the reception pattern. A magnetic resonance imaging apparatus, which transmits to the coil unit by the wireless transmission. A signal transmitting device that obtains bit data by sampling and digitizing a reception signal that receives an NMR signal emitted by a subject at a predetermined cycle, sequentially arranges the bit data to generate a bit stream, and wirelessly transmits the bit stream. There
A signal transmitting apparatus comprising: a compression unit that changes a bit length of bit data according to a signal strength of the received signal and inserts a change position bit string indicating a position where the bit length changes into the bit stream. The signal transmission device according to claim 11, wherein, when the first code bit of the data string of the bit data representing the signal strength of the received signal at the time of sampling is 0, the compression unit is after the code bit. When the consecutive 0's and the sign bit are 1, the consecutive 1's after the sign bit are determined as unnecessary bits and are removed, thereby compressing the bit length. ..

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