JPH0659277B2 - Waveform generator for MRI - Google Patents

Description

The present invention relates to an MRI apparatus (nuclear magnetic resonance; imaging apparatus using NMR, so-called NMR-CT apparatus) for generating an excitation pulse and a waveform used for 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 read sequentially from sampling data of a waveform stored in a waveform memory in advance by D / A.
It is controlled by the converted analog waveform. Also,
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. 4, 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 a monotonous portion of a waveform can be stored by storing roughly sampled data so that the amount of data to be stored can be reduced.

Means for Solving the Problems The waveform generator for MRI according to the present invention stores peak value data sampled at a plurality of different sampling periods and also stores an index for distinguishing the plurality of sampling periods. Storage means, D / A conversion means for D / A converting the peak value data read from the storage means and outputting the same, and reference clocks for counting and respectively at a cycle corresponding to each of the above sampling cycles. A plurality of counter means that generate an output and are selected by the index read out together with the peak value data from the storage means, and a cycle of reading the peak value data from the storage means based on the outputs of the selected counter means. Read control means for controlling the.

Change the sampling period so that the operating waveform is fine when it changes sharply, and coarse when it changes slowly,
The peak value data obtained by a plurality of different sampling periods is stored. At the same time, the index for distinguishing the sampling period at that time is also stored. At the time of reading, the index is read along with the peak value data,
Select a counter by this index. The counter is
Since there are several units that produce outputs at a period corresponding to each sampling period, the original waveform is controlled by controlling the period at which the peak value data is read from the storage means based on the output of the selected counter. Is reproduced.

In this way, it is possible to reproduce the original waveform not only by uniformly sampling all of the waveforms, but by sampling only the necessary parts densely and coarsely sampling the others, thus reducing the amount of data to be stored. You can

Further, since it is sufficient to store an index for distinguishing a plurality of sampling periods (reading periods) instead of storing the data itself representing the time width of the sampling period (reading period), The storage capacity is small, which is good. Therefore, the index related to this sampling cycle (readout cycle) can be stored in the storage unit that stores the peak value data together with the peak value data. Further, when it is desired to change the read cycle, it is easy to change the output cycle of the counter independent of the storage means.

Example In FIG. 1, the memory 3 stores in advance the crest value data at each sampling point (circle) of the waveform of FIG. 3, and at each sampling cycle, that is, the sampling cycle T1 in the period A, Sampling period T2 in period B,
An index for distinguishing the sampling cycle T3 in the period C is stored in advance. In this waveform, period A
, The sampling period T1 and T3 are short, and the sampling period T2 is long. The data structure to be stored is, for example, as shown in FIG. 2, using two bits as an index,
The remaining bits are used for the peak value data, and the peak value data and the index are stored in order from the first sampling point. In this way, it is assumed that some waveform data is stored in the memory 3.

When generating one waveform from several waveform data stored in the memory 3, first, the controller 1 determines the start address where the waveform data is stored and the number of sampling data of the waveform. Is instructed. When the start is started and the operation is started at a predetermined timing, the controller 1 sets the address of the data to be read from the memory 3 in the address counter 2, and the first data is read from the memory 3. Thus, the first data in FIG. 2, that is, the index of “0” and “0” in the first and second bits and the third data
The data of the first peak value after the bit is read.
The peak value data is sent to the D / A converter 4, and the analog peak value at the first sampling point is reproduced.

On the other hand, the data of the indexes "0" and "0" are sent to the counter group 5 and the counter No0 is selected. In this embodiment, the index is composed of 2 bits and is associated with four counters No0 to No.3. Counter No 0
3 to 3 each generate a signal at a constant cycle by counting the reference clock, the counter No0 has a cycle T1, the counter No1 has a cycle T2, the counter No2 has a cycle T3, and the counter No3 has a cycle T4. To give a signal,
Each of the counter Nos. 0 to 3 is preset. Therefore, a signal generated from the counter No0 in a cycle equal to the cycle T1 is sent to the controller 1, the address counter 2 is advanced by 1, and the next address in which the second peak value data is stored is designated. Be done. Thus 1
The index and the peak value data are read out every cycle T1 from the second to the third, and so on.

Then, when the kth peak value data and the index are read out, since the indexes are "0" and "1", the counter No1 is selected, and the signal of the cycle T2 is sent to the controller 1. Given.

When the address counter 2 is advanced by 1 in the cycle T2,
The (k + 1) th peak value data and the index are read out, and the indexes at this time are "1" and "0", so the counter No2 is selected. As a result, after that, the reading is performed in the cycle T3, and the n-th step is advanced to reach the initially set number of data, so that the reading of this waveform is completed.

Although the index is composed of 2 bits and the counter is 4 in the above, the number of counters and the number of bits of the corresponding index can be arbitrarily changed. Further, in the above example, the index directly specifies the counter No. However, when the counter is specified by the index only when switching to a counter different from the previous counter, and the previous counter is used as it is, that is, the period A,
It is also possible to adopt a configuration in which designation by the index is not performed in B, ... In this case, for example, three counters are used, and one of those three counters is designated by the index of "0", "1" to "1", "1",
If the index is "0" or "0", the same counter as before is used.

Further, each of the counter Nos. 0 to 3 needs to be preset in correspondence with the sampling period of the waveform data, but it may be configured to be automatically reset according to the waveform to be read.

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. In particular, in the MRI apparatus, it is necessary to generate a number of waveforms having the same waveforms in the periods A and C shown in FIG. 3 but different only in the length of the period B as the waveforms of the gradient magnetic fields for phase encoding. In such a case, in the past, data was stored or the contents of the memory were rewritten corresponding to each waveform, but this is no longer necessary and only the sampling cycle T2 needs to be changed.

EFFECTS OF THE INVENTION According to the MRI waveform generator of the present invention, it is possible to reduce the amount of data to be stored together with the peak value data and the sampling period (readout period) (index). In particular, an MRI apparatus often generates waveforms that differ only in the length of a monotonous portion, and since it is often necessary to change only the time interval (readout cycle) of the peak value data to be output, the number of stored peak value data points. Can be reduced, and the amount of data can be significantly reduced. Further, since the index for distinguishing a plurality of sampling periods (reading periods) is stored instead of storing the data directly representing the sampling periods (reading periods), it is possible to reduce the storage capacity for the sampling periods (reading periods). It can be stored together with the peak value data in the storage means without preparing a memory. Furthermore, the output cycle of the counter that defines the read cycle of the peak value data to be output is easy to change and manage because the counter is independent of the storage unit that stores the peak value data and the like.

[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 waveform diagram showing data sampling points in the present invention, and FIG. It is a waveform diagram which shows the data sampling point of an example. 1 ... Controller, 2 ... Address counter 3 ... Memory, 4 ... D / A converter 5 ... Counter group

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 9219-2J G01N 24/02

Claims (1)

[Claims] 1. A storage unit for storing peak value data sampled at a plurality of different sampling periods and also storing an index for distinguishing the plurality of sampling periods, and a wave read from the storage unit. D / A conversion means for D / A converting high-value data and outputting the data,
A plurality of counter means for counting respective reference clocks, producing outputs at a cycle corresponding to each of the sampling cycles, and selected by an index read together with the peak value data from the storage means; And a read control means for controlling a read cycle of the peak value data from the storage means based on the output of the counter means.