JPS61227424A - Waveform generator for nmr-ct device - Google Patents

Abstract

PURPOSE:To control generation of a spike noise by a calculating forecast data at an optical time between the intermediate read times when sampling data is read at a prescribed period and adding the data to the original data as the time data. CONSTITUTION:Sampling data is read from a waveform memory 1, sent to an adder circuit 5, added to the data read precedingly and latched in a latch circuit 4 just before, the result is fed to a 1/2 multiplier 6, where the data is halved. Thus, the two adjacent data are added and averaged. A T flip-flop 8 repeates inversion every time a clock pulse CLOCK1 is inputted, and the output data of a latch circuit 4 and the added average data are selected alter nately by a multiplexer 7. Then the data selected by the multiplexer 7 is converted into an analog signal by a D/A converter 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an NMR-CT apparatus that creates images of the inside of a human body using NMR phenomena, and in particular to a waveform generator used to generate excitation pulses and gradient magnetic fields. Regarding improvements.

In a conventional NMR-CT apparatus, an excitation pulse is applied to the subject in order to tilt the spins of a selected slice plane by 90° or 180°, but this excitation pulse is generally applied by sampling a pre-recorded waveform. It is created by sequentially reading out data, performing D/A conversion, and modulating the resulting analog waveform signal with a carrier wave. In addition, the gradient magnetic field applied to add position information to the NMR signal from the subject is also applied to the D/A by sequentially reading pre-recorded waveform sampling data, as described above.
Controlled by converted analog waveform signals.

These waveform generators have conventionally been constructed as shown in FIG. The waveform memory 1 has waveform sampling data stored in advance as discrete digital values, and this sampling data is read out at regular intervals by the address counter 2. Read clock pulse CL
When OCKo (frequency fo) is applied to the address counter 2, the address counter 2 counts by +1, and the digital data stored in the address corresponding to the count value of the address counter 2 is output from the waveform memory l. The D/A converter 3 which is sequentially read out and operates with the same clock pulse CLOCKo receives this digital data.
The signal is D/A converted and output as an analog signal. The analog waveform output in this way is as shown in FIG. 4B. Here, the 0 mark is an analog value corresponding to the sampling data stored in the waveform memory l.

Problems to be Solved by the Invention In this way, when pre-recorded waveform sampling data is sequentially read out and D/A converted to create an analog signal, the clock pulse CLOCKo inevitably changes as shown in Figure 4B. It is unavoidable that the signal changes suddenly every cycle. In particular, if there is a large gap between adjacent digital data, the degree of this change will become especially large and strong spike noise will occur, causing the waveform signal to change as it should. Generally speaking, a filter can be used to remove spike noise, but if adjacent digital data are too far apart, the effect cannot be expected.

Furthermore, in order to reduce the gap between adjacent digital data, it is conceivable to make the sampling interval of the waveform finer, but this would inevitably increase the storage capacity of the waveform memory l.

An object of the present invention is to provide an improved waveform generator for an NMR-CT apparatus that can effectively reduce spike noise without increasing storage capacity.

Means for Solving the Problems A waveform generator for an NMR-CT apparatus according to the present invention includes a storage means in which waveform sampling data is stored in advance as digital data, and means for reading data from the storage means at a constant cycle. , a means for calculating predicted data at an intermediate discretionary time of each reading time, and a means for calculating predicted data at an intermediate discretionary time of each reading time, and a means for calculating predicted data at an intermediate discretionary time of each reading time; and means for converting the signal and outputting it as an analog signal at each corresponding time.

When reading out sampling data at a constant cycle,
Predicted data at an arbitrary time in between is calculated and added to the original data as data at that time, so when these digital data are D/A converted, sudden changes in the analog signal are avoided. Changes are suppressed, resulting in smooth changes, and the occurrence of spike noise is suppressed.

Embodiment 8 In FIG. 1, the waveform memory 1, address counter 2 and D/A converter 3 are the same as those in FIG. In addition to these, latch circuit 4. Addition circuit 5, patch multiplier 6. A multiplexer 7 and a T-flip-prop 8 are provided. Additionally, the read clock pulse CLOCKo
In addition to (frequency fo), there is a clock pulse CLOCK with twice the frequency.

(Frequency f1=2fo) is given.

When the clock pulse CLOCKo is applied to the address counter 2 and the address counter 2 counts +1, the sampling data stored at the address corresponding to the counted value is sequentially read out from the waveform memory 1. First, when one clock pulse CLOCKo is applied and certain sampling data is read out, this data is latched by the latch circuit 4. When the next clock pulse CLOCKa is applied and the address counter 2 increases by +1, the next sampling data is read out from the waveform memory 1 and sent to the adder circuit 5. The data read in and the data read just now are added,
The output of the adder circuit 5 is sent to a repair multiplier 6 and made into a station. In this way, two adjacent pieces of data are averaged.

The output data of the latch circuit 4 and the averaged data are sent to the multiplexer 7, and one of the inputs is selected under the control of the T-flip-flop 8.

This T-flip-flop 8 has a clock pulse CLO
The inversion is repeated every time CK is input, and the output data of the latch circuit 4 and the averaged data are alternately selected by the multiplexer 7. The data selected by the multiplexer 7 is then converted into an analog signal by the D/A converter 3.

In this way, as shown in FIG. 2A, the value corresponding to the read sampling data (indicated by 0) and the value corresponding to the automatically added average data (indicated by An analog signal waveform in which the following signals (as shown in FIG. 1) appear alternately is obtained. That is, by adding the averaged data, the gap between adjacent data is eliminated, the waveform becomes smoother, and as a result, the occurrence of spike noise is reduced.

In addition, here, the average value of adjacent sampling data is calculated and added at exactly the middle point of the adjacent sampling data, but at any multiple points in the middle, multiple values are added according to their internal division ratio. It is also possible to calculate and add pieces of data, and it is also possible to use three or more pieces of data instead of just two adjacent pieces of data as the basis for calculation.

Furthermore, in the above explanation, it is assumed that the waveform memory 1 stores sampling data created in advance.
In order to store data in this waveform memory 1, analog data collection and digitization can be performed using a sample hold circuit and an A/D converter operated by a clock pulse CLOfJa.

Effects of the Invention According to the present invention, it is possible to suppress the generation of spike noise even when adjacent pieces of read sampling data are far apart from each other.

Further, it is sufficient that the data is sampled within a range that satisfies the sampling theorem, and there is no need to sample it more finely due to the problem of spike noise, so there is no need to increase the storage capacity.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a time chart showing analog waveforms obtained by the same embodiment, Fig. 3 is a block diagram of a conventional example, and Fig. 4 is a conventional example. It is a time chart for showing the obtained analog waveform.

Claims (1)

[Claims] (1) A storage means in which waveform sampling data is stored in advance as digital data, a means for reading data from this storage means at a constant cycle, and predicted data at an arbitrary time between these reading times is calculated. and a D/
A waveform generator for an NMR-CT apparatus, comprising means for A-converting and outputting it as an analog signal at each corresponding time.