JPH0741032B2 - Waveform generator for MRI - Google Patents

Description

Description: TECHNICAL FIELD The present invention generates an excitation pulse in an MRI apparatus (nuclear magnetic resonance; an imaging apparatus using NMR, so-called MNR-CT apparatus) and a waveform used when generating a gradient magnetic field. To improve the device.

2. Description of the Related Art In an MRI apparatus, a gradient magnetic field applied to add position information is generally controlled by an analog waveform obtained by sequentially reading out D / A conversion of waveform sampling data stored in advance in a waveform memory. To be done. An analog waveform obtained in the same manner is also used for the modulation signal of the high frequency excitation pulse.

In a conventional waveform generator, generally, as shown in FIG. 5, data obtained by sampling the wave height at a constant equal period T is stored in a waveform memory, and this is stored at a constant time interval T.
Are sequentially read out and output.

Problems to be Solved by the Invention However, when storing data sampled at a constant sampling period in the waveform memory as described above,
When the waveform consists of a part that changes sharply in a short time and a part that is monotonous in a long time, it is necessary to shorten the sampling period according to the sharp part of the waveform. The total amount of data to be stored increases.

An object of the present invention is to provide a waveform generator for MRI in which the amount of data to be stored is reduced by storing roughly sampled data in the monotonous part of the waveform.

Means for Solving Problems A waveform generator for MRI according to the present invention has a plurality of kinds of wave height data sequentially sampled at different sampling periods, at an address in the order thereof, together with an identification signal indicating that the wave height data is present. A storage unit that stores the period data representing the sampling period itself at an address corresponding to a transition of the sampling period together with an identification signal indicating that the period data is stored, and sequentially specifies an address of the storage unit. The reading means for reading the wave height data or the cycle data stored at each address together with the identification signal, and the wave height data and the cycle data read from the storage means are identified by the identification signals read at the same time, and If so, hold it until the next cycle data is read, Read control means for controlling the read cycle from the storage means by the read means according to the held cycle data.

The wave height is sampled while changing the sampling period into several types according to the degree of change, such as fine when the waveform changes abruptly and coarse when it changes slowly. The thus obtained wave height data and cycle data representing the sampling cycle are stored in the storage means. That is, the sequentially sampled wave height data is stored at the addresses in the order. In addition, the cycle data is stored in an address corresponding to the transition of the sampling cycle. Since these are stored in consecutive addresses in the same storage means, they are stored together with the identification signal indicating the wave height data or the periodic data. At the time of reading, the data is sequentially read from the storage unit for each address, so that the periodic data is read from time to time between a large number of wave height data. Since the wave height data or the periodic data can be discriminated by the discrimination signal, if it is the periodic data, it is held until the next periodic data is read. Then, if the read cycle from the storage means is controlled according to the held cycle data, the time interval at the time of sampling is reproduced and the original waveform is reproduced. In this case, since the previous cycle data is held and used as long as it has the same cycle, it is not necessary to store the cycle data together with the individual wave height data. As a result, the amount of stored periodic data is small, and the amount of stored pulse height data is not reduced. Further, since the wave height data and the period data are not separated and stored in the same storage means in order of address and only the order of address needs to be read at the time of reading, the structure of the storage means is simple and the reading means The configuration of is also simple. Further, the read control means for controlling the read interval also simply holds the cycle data up to the next cycle data and controls the read cycle according to the held cycle data, so that the configuration is simple.

Example In FIG. 1, the memory 3 stores the wave height data at each sampling point (circle) of the waveform in FIG. 4 and each sampling period, that is, the sampling period T1 in the period A and the sampling period T in the period B. The sampling cycle T2 and the sampling cycle T3 in the period C are stored in advance. In this waveform, the change is abrupt in the period A, but does not change in the period B and becomes a constant value.
Since it changes suddenly again in period C, the sampling cycle T
1, T3 is short and sampling period T2 is long. The data structure to be stored is as shown in FIG. 2, for example, and one bit (the first bit in this example) stores an identification signal of whether it is the data of the wave height or the data of the sampling period, and the other. The data of the wave height and the data of the sampling period are put in the bit of. The data of the sampling cycle is not inserted one by one for each wave height data but is stored only once immediately after the head wave height data of the period having the same sampling cycle. This suppresses an increase in the amount of data due to storing the data of the sampling period in the memory 3 as well. In this way, a plurality of waveform data are stored in the memory 3.

When trying to generate a specific waveform, the controller 1
The start address at which the data of the waveform is stored and the number of sampling data of the waveform are designated, and the operation starts at a predetermined timing. First, the address of the data to be read from the memory 3 is set in the address counter 2 from the controller 1, and the first data is read from the memory 3. In this way, the first data in FIG. 2, that is, the data of "0" in the first bit and the first wave height of the 2nd to mth bits is read. The 2nd to mth bits of data are sent to the multiplexer 4. The data of the first bit identifies the wave height data, and the multiplexer 4 sends this wave height data to the D / A converter 5 to reproduce the analog wave height value at the first sampling point. The controller 1 checks the data of the first bit, increments the address counter 2, and reads the next data. If the next data is the data of the sampling period T1, the multiplexer 4 sends it to the latch 6 to be latched. Then, the reference clock is counted based on the latched data of the sampling cycle T1, and the address counter 2 is advanced every sampling cycle T1 to obtain the next data.
It is read after the sampling period T1. If the read data is the wave height data, it is sent to the D / A converter 5 by the multiplexer 4 and an analog signal is obtained, and thus the period T1 changes, that is, the period A in FIG.
Until the end of, the pulse height data is sequentially read at the period T1 and an analog signal is obtained. When the cycle T2 of the period B is read, it is similarly latched by the latch 6 and the read operation and the analog conversion operation in this cycle T2 are sequentially performed. In this way, the reading of the wave height data and the analog conversion corresponding to the number of sampling data given in advance to the controller 1 are repeated, and the reading of one waveform is completed.

In the above, as shown in FIG. 2, the sampling cycle data is stored after the first wave height data of the same sampling cycle period. However, as shown in FIG. 3, the sampling cycle data is first stored and then the sampling cycle data is stored. It is also possible to store the data with a data structure in which wave height data are arranged until a new sampling period is reached.

As described above, since the sampling points can be reduced in the monotonous portion of the waveform, the amount of data to be stored in the memory 3 can be reduced. Especially, in the MRI apparatus, the period A in FIG.
It is necessary to generate several waveforms for the gradient magnetic field that have the same waveform in C but differ only in the length of the period B. However, since only the sampling period T2 needs to be changed, all the data of these waveforms must be changed. You can store it as it is,
It is not necessary to rewrite the contents of the memory 3 entirely.

EFFECTS OF THE INVENTION According to the waveform generator for MRI of the present invention, the number of sampling points of the wave height data is reduced in the gently changing portion, so that the amount of wave height data to be stored can be reduced.
In particular, since the MRI apparatus often generates waveforms that differ only in the length of the monotonous portion, it is possible to greatly reduce the storage amount of the wave height data. In exchange for this, the cycle data representing the sampling cycle must be stored, which is meaningless if the amount of memory is increased and the configuration such as reading and control is complicated, but the cycle data is It is stored in the same storage means in the same address order as the wave height data, and is only read in the address order. The control of the read cycle also holds the cycle data up to the next cycle data and determines the read cycle according to the held cycle data. It's just that, so it's a very simple configuration and does not increase the amount of memory.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing an example of a stored data structure, FIG. 3 is a diagram showing another example of the same data structure, and FIG. 5 is a waveform diagram showing data sampling points in FIG. 5, and FIG. 5 is a waveform diagram showing data sampling points in the conventional example. 1 ... Controller, 2 ... Address counter 3 ... Memory, 4 ... Multiplexer 5 ... D / A converter, 6 ... Latch

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H03M 1/66 B 9287-5L G06F 15/62 390 C

Claims (1)

[Claims] 1. An address corresponding to a transition of the sampling cycle, in which the data of the wave heights sequentially supplemented by a plurality of different sampling cycles are stored in an address in that order together with an identification signal indicating the wave height data. The storage means in which the cycle data representing the sampling cycle itself is stored together with an identification signal indicating that it is the cycle data, and the wave height data or the cycle data stored at each address is identified by sequentially specifying the addresses of the storage means. The reading means for reading out together with the signal and the wave height data and the cycle data read from the storage means are identified by the identification signal read at the same time. Is stored in the reading means according to the held periodic data. MRI waveform generator and a read control means for controlling the read cycle from the storage unit that.