JPH0686765A - Gradient power source of mr system - Google Patents

Abstract

PURPOSE:To improve the waveform quality of a gradient current, and also, to improve a frequency characteristic by converting a digital signal from a scan controller into an analog signal, and thereafter, adding an attenuated attenuation signal and a delay time, and eliminating a high-frequency component of an addition signal and outputting it as the gradient current. CONSTITUTION:A D/A converter 3 converts a digital signal SD from a scan controller 2 into an analog signal SA. Also, an attenuator 4 attenuates the analog signal SA to about 1/4 and sets it as an attenuation signal Vk. Moreover, a multi-delaying circuit 5 outputs delay signals V1, V2 and V3 obtained by delaying the attenuation signal Vk by delay time tau, 2tau, and 3tau. Furthermore, an adder 6 adds the attenuation signal Vk and the delay time tau, 2tau, and 3tau. Subsequently, an LPF 7 eliminates a high-frequency component of an addition signal VA from the adder 6, and outputs it as a gradient current 10. As a result, the waveform quality of the gradient current is improved, and also, a frequency characteristic can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradient power supply for an MR device, and more particularly to a gradient power supply for an MR device useful for improving the waveform quality of a gradient current and improving frequency characteristics.

[0002]

2. Description of the Related Art FIG. 4 shows a gradient power source 51 of a conventional MR device.
FIG. The D / A converter 3 converts the digital signal SD from the scan controller 2 into an analog signal SA. The waveform of the analog signal SA is schematically illustrated in FIG. This analog signal SA has a step voltage V = 80 for each step time T = 40 [μs].
It is a step-like waveform that rises by [mV].

The LPF 57 removes the high frequency component of the analog signal SA amplified by the preamplifier 8. The integrator 9 smoothes the stepwise waveform output by the LPF 57 to smooth the waveform and outputs it as a gradient current I0.
FIG. 5B schematically illustrates the waveform of the gradient current I0.

[0004]

In the gradient power supply 51 of the conventional MR device, the analog signal SA from the D / A converter 3 is smoothed by the integrating circuit 9 and output as the gradient current I0. However, since a large step-like waveform remains in the gradient current I0, there is a problem of poor waveform quality. Further, since the cutoff frequency of the LPF 57 needs to be lowered in order to remove a large step-like waveform from the analog signal SA as much as possible, there is a problem that the frequency characteristic is bad.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gradient power supply for an MR device which has improved waveform quality and frequency characteristics.

[0006]

A gradient power supply for an MR device according to the present invention converts a digital signal from a scan controller into an analog signal by a D / A converter and outputs a gradient current based on the analog signal. Of the gradient power supply, the signal input to the D / A converter after the predetermined delay time τ, 2τ, ..., (k-1)
A multi-delay circuit for delaying by τ is provided, and the input signal and delay time τ, 2τ, ..., (k-1) τ
, Vk-1 are added to the delayed signals V1, V2, ..., Vk-1, which are delayed only by the delay time, and further, the input signal is added between the D / A converter and the multi-delay circuit or at the subsequent stage of the adder. An attenuator that attenuates by a factor of 1 / k (an integer of k> 1) is provided, and a gradient current is output based on the output signal from the adder or the output signal from the attenuator. .

[0007]

In the gradient power source for the MR device according to the present invention, the digital signal from the scan controller is converted into an analog signal, and the analog signal is delayed by the delay times τ, 2τ ,.
Delay by (k−1) τ and add them. Also,
Before the delay or after the addition, it is attenuated by a factor of 1 / k (an integer of k> 1). When it is attenuated 1 / k times before delaying, a gradient current is output based on the output signal from the adder, and when it is attenuated 1 / k times after addition, it is the output signal from the attenuator. The gradient current is output based on.

As a result, the step-like waveform remaining in the gradient current can be made as small as 1 / k of the conventional one, so that the waveform quality can be improved. In addition, from analog signals, 1 / k of conventional
Since it is only necessary to remove the stepped waveform that has been made extremely small,
The cutoff frequency can be increased, and the frequency characteristics can be improved.

[0009]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 is an overall configuration diagram of a gradient power supply 1 of an MR device according to the present invention. In the gradient power supply 1 of this MR apparatus, the scan controller 2 outputs to the D / A converter 3 a digital signal SD that increases every step time T in order to raise the gradient current.

The D / A converter 3 converts the digital signal SD into an analog signal SA. In FIG. 2 (a),
The waveform of the analog signal SA is schematically illustrated. The analog signal SA has a step-like waveform in which the step voltage V increases by 80 [mV] every step time T = 40 [μs].

The attenuator 4 converts the analog signal SA into 1 /
An attenuation signal VK attenuated by k (an integer of k> 1) times is output. Here, for convenience of description, k = 4. The waveform of the attenuation signal VK is schematically illustrated in FIGS. 2B and 3A. This decay signal VK has a step time T
= 40 [μs] every step voltage V = 80/4 = 20
It is a step-like waveform that rises by [mV].

The multi-delay circuit 5 delays the input signal by a predetermined delay time τ, delay circuits 5a, 5b, ...
Are connected in series for (k-1) stages, and delay signals V1, V2, ... Are output from each delay circuit 5a, 5b ,. Here, k = 4, and delay times τ, 2τ, from delay circuits P1, P2, P3.
Delay signals V1, V2 and V3 delayed by 3τ are output. The delay time τ is 1 / k of the step time T. That is, τ = T / k. Here, T = 40
[Μs] and k = 4, delay time τ = 10 [μs]
Is. The waveform of the delayed signal V1 obtained by delaying the attenuated signal VK of FIG. 3 (a) by 10 [μs] is schematically illustrated in FIG. 3 (b). In addition, the attenuation signal VK of FIG.
The waveform of the delay signal V2 delayed by [μs] is schematically illustrated in FIG. The waveform of the delayed signal V3 obtained by delaying the attenuated signal VK of FIG. 3A by 30 [μs] is schematically illustrated in FIG. 3D.

When the step time T is fixed, the delay time τ may be fixed, but when the step time T changes, the setting of the delay time τ is changed according to the step time T by a controller (not shown).

The adder 6 has an attenuated signal VK and a delayed signal VK.
, V2, ... Are added to output an addition signal VA.
The attenuation signal VK of FIG. 3 (a) and the attenuation signal VK of FIG. 3 (b) (c)
The waveform of the addition signal VA obtained by adding the delay signals V1, V2 and V3 of (d) is schematically illustrated in (e) of FIG.

The LPF 7 removes the high frequency component of the addition signal VA and outputs it as a gradient current I0.

According to the gradient power supply 1 of the MR device, the step-like waveform affecting the gradient current I0 is the original analog signal S.
Since it becomes 1 / k times the stepwise waveform of D, the waveform quality of the gradient current I0 can be improved. Further, the cutoff frequency of the LPF 7 can be increased, and the frequency characteristic can be improved.

As another embodiment, the attenuator 4 shown in FIG.
Is moved to the subsequent stage of the adder 6.

[0018]

According to the gradient power supply of the MR device of the present invention, a large step waveform is not left in the gradient current, and the waveform quality of the gradient current can be improved. Since the LPF having a low cutoff frequency is not used, the frequency characteristic can be improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a gradient power supply of an MR device that is an embodiment of the present invention.

FIG. 2 is a waveform diagram of an analog signal and an attenuation signal in the gradient power supply of FIG.

FIG. 3 is a waveform diagram of each part in the gradient power supply of FIG.

FIG. 4 is an overall configuration diagram of an example of a gradient power source of a conventional MR device.

5 is a waveform diagram of an analog signal and a gradient current in the gradient power supply of FIG.

[Explanation of symbols]

 1 Gradient Power Supply 2 Scan Controller 3 D / A Converter 4 Attenuator 5 Multi Delay Circuit 5a, 5b, 5c Delay Circuit 6 Adder 7 LPF

Claims (1)

[Claims] 1. A gradient power supply for an MR device, which converts a digital signal from a scan controller into an analog signal by a D / A converter and outputs a gradient current based on the analog signal, and inputs the gradient power supply to a stage subsequent to the D / A converter. A multi-delay circuit for delaying the input signal by a predetermined delay time τ, 2τ, ..., (k-1) τ is provided, and the input signal and the delay time τ, 2τ, ..., (k-1) τ are provided. , Vk-1 are added to the delayed signals V1, V2, ..., Vk-1, which are delayed only by the delay time, and further, the input signal is added between the D / A converter and the multi-delay circuit or at the subsequent stage of the adder. 1 / k (k
A gradient power source for an MR device, comprising: an attenuator that attenuates by a factor of> 1) and outputs a gradient current based on an output signal from the adder or an output signal from the attenuator.