JPH0131151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving section of a receiving phasing device, such as an ultrasonic tomographic imaging device.

An electronic scanning ultrasonic tomography system achieves a function equivalent to an acoustic lens by processing electrical signals converted by multiple receiving elements that make up an array receiver, and obtains ultrasonic images. There is. That is,
As shown in FIG. 1, the time at which the wavefront WV _i that diffuses from the point of interest P _i in the field of view reaches each of the receiving elements E1 to E _o differs depending on each element. Therefore, in order to obtain the reception directivity for P _i , it is necessary to compensate for the time difference of the signals from each element and align the phases (this operation is generally called phasing), and then add them together using adder A. There is.

In the conventional method, in which each received signal is sampled and temporarily stored in memory M, and then the above-described phasing and addition is performed, a common sampling clock CL (clock pulse generator) is used for each received signal, as shown in Figure 1.
(obtained from CG) is used. Therefore, when the above-mentioned time difference compensation is performed only by memory addressing, the error determines the time accuracy due to time quantization in units of sampling clock cycles. In order to obtain higher time accuracy, values between sample points must be obtained by interpolation processing, and interpolators such as IP ₁ to _{IP o} in FIG. 1 are required. Therefore, the phasing accuracy often depends mainly on the accuracy of the interpolation process. In particular, in order to apply it to diagnostic ultrasound tomographic imaging devices that require high-speed signal processing, it is necessary to have a high-precision yet high-speed interpolator, which places a large burden on the hardware. .

SUMMARY OF THE INVENTION An object of the present invention is to perform focusing by simple electrical processing of received signals in a receiving device in which a plurality of receiving elements are arranged, particularly in an ultrasonic imaging device using an array type receiver.

The phasing principle of the present invention is based on a method in which signals from a plurality of receiving elements constituting an array receiver are sampled, temporarily stored in memory, and then phased and summed. The same phase front (..., WV _i ,...) of the wave front diffusing from the points (..., P _i ,...) _{arranged in}
A method of sampling each received signal at the time when it reaches (hereinafter referred to as phasing time sampling method)
It is. This method uses the sampling clocks CL ₁ to CL _o of each received signal to compensate for time differences in phasing processing.
This is done by controlling the Since the time difference-compensated value is written to the memory, interpolation processing after reading the memory, which is required in the conventional method, is essentially unnecessary. In particular, in the case of diagnostic ultrasound imaging devices that require high-speed signal processing,
It is a great advantage that interpolation processing is not required and signal processing is simplified.

By the way, in general, a signal with a center frequency _C , a maximum frequency _M , and a fractional bandwidth α=2( _M − _C )/ _C (<2), which has a spectrum as shown in Figure 3, can be sampled without loss of information. In order to do this, it is not necessarily necessary to have a sample rate of 2 _M or more, which is required by the usual sampling theorem. For example, as shown in Figure 4, a pair (hereinafter referred to as a 90° pair) is sampled with a time difference corresponding to a 90° phase difference for _C (the sampling points are shown as C _i and S _i , where i is an integer). Therefore, Figure 4 shows 5 pairs.)
If quadrature sampling (hereinafter referred to as 90° sampling method) is used, the sampling rate of the 90° pair only needs to satisfy the sampling theorem for the envelope band ±α _C /2, so the average sampling rate can be reduced to α _C. When applying this type of method that can use a sample rate of 2 _M or less to a conventional method that performs phasing processing using sampling to lower the sample rate, it is difficult to reduce the sample rate when using a sample rate of 2 _M or more. However, when combined with the phased time sampling method of the present invention, which essentially does not require interpolation processing, the sample The rate can be easily lowered to the above theoretical value.

Hereinafter, the present invention will be explained in detail with reference to Examples. FIG. 2 is a block diagram of an example in which the phasing time sampling method of the present invention is applied to a phasing section of an ultrasonic tomographic imaging apparatus. Sampling clocks CL ₁ to _{CL o} that control the times at which signals from each receiving element E ₁ to E _o configuring the array type receiver are sampled.
is generated by a clock generator CG which operates according to a value previously recorded in memory _M0 .
The values sampled by the sampling means SA ₁ -SA ₂ are written into the memory M, and the sample values of the respective received signals to be phased and added together are added by the adder A after they are all in the memory. By doing so, a value equivalent to the value obtained by virtually phasing and adding each unsampled received signal as it is by some method and sampling the signal is obtained as the output of the adder A. The feature of the phasing time sampling method of the present invention that essentially does not require interpolation processing in phasing processing is that
A further advantage is that the sample rate can be easily reduced to a logical value determined by the envelope bandwidth of the signal. Taking advantage of this advantage, the method of the present invention
FIG. 5 shows the configuration of an embodiment in which the present invention is applied to a phasing section of a diagnostic ultrasonic tomographic imaging device in combination with the 90° sample method. Sampling clock (CL _C1 ~ _{CL Co} ,
Each received signal sampled and held by sample and hold elements (SH _C1 - SH _Co , SH _S1 - SH _So ) in synchronization with CL _S1 - CL _So ) is sent to an A-D converter (AD _C1 - AD _Co , AD _S1) . 〜AD _So ) is converted into a digital value by the line memory ( _MC1 〜M _Co , M _S1 〜
M _So ). Note that PA ₁ , PA ₂ . . . are preamplifiers. Line memory (M _C1 ~ _{M Co} ,
The values read from each of the 90° pairs (hereinafter _referred to as the COS block and SIN block), that is, the _values read from the COS block (M _C1 ~ M _Co )
SIN blocks (M _S1 to _{M So} ) independently perform phasing and addition by adders _AC and _AS , respectively. next,
The arithmetic circuit RS calculates the sum of the squares of the COS amplitude and the SIN amplitude obtained from the adders A _C and A _S , and squares it to obtain the envelope amplitude.

The principle of operation will be explained with reference to FIG. Suppose that the emitted pulsed ultrasound is reflected by a point-like reflector at a point of interest P _i in the field of view, and an ultrasound wavefront WV _i is generated that spreads around that point. Generally, the time at which the same phase plane included in WV _i reaches each receiving element E ₁ to _{E o} making up the array receiver depends on the relative positional relationship between each receiving element and the point of interest P _i . Different. Therefore, if each received signal is sampled at the time when the same phase plane included in WV _i should reach each receiving element (time indicated by t) and added together, the reflected signal from P _i in particular will be This method provides reception directivity. For _c , select pairs of the same phase plane with a 90° phase difference at a frequency of about 1 to 3 pairs per pulse length,
By finding the square root of the sum of squares of the same phase plane addition values (COS amplitude, SIN amplitude) for each pair, a sampled envelope of the phased and summed signal can be obtained with sufficient accuracy. In addition, the 6th
In the figure, C1 ₁ to C1 _o and S1 ₁ to _{S1 o} indicate the first sampling points of the signals from the receiving elements E ₁ to E _o , and C4 ₁ to C4 _o and S4 ₁ to S4 _o indicate the first sampling points of the signals from the receiving elements E ₁ to E o. A fourth sampling point of the signal from ~E _o is shown, with the second and third sampling points following the first sampling point omitted. Further, the amplitude sums at the sampling points are indicated by A ₁ to _{A 4} .

Here, a comparison will be made between the conventional method of performing phasing using sampling and memory and the phasing time sampling method of the present invention with respect to the required sample rate in a specific device. center frequency
Taking as an example a receiving device that uses pulsed ultrasound with a 3 MHz envelope bandwidth of ±1 MHz and performs phasing processing with a time accuracy of 10 ns, a comparison will be made under the condition that it does not have an interpolator for phasing. The required sample rate for the conventional method is 100 MHz, whereas when using the phased time sampling method and following the normal sampling theorem, the required average sample rate is 8 MHz, and when combined with the 90° sampling method, the required average sample rate is 100 MHz. is 4MHz. In this way, according to the phasing time sampling method, the sampling rate can be significantly reduced.

In the circuit example shown in Figure 5, for the purpose of extracting the envelope amplitude, the same phase plane sum value (COS
We calculated the square root of the sum of squares for the amplitude (SIN amplitude, SIN amplitude), but if you do not require high envelope extraction accuracy and want to simplify the hardware,
The envelope amplitude can also be approximated by the sum of the absolute values of the COS amplitude and the SIM amplitude.

Generally, in order to obtain one point of the envelope amplitude value of the signal after phasing and addition, two or more real values equivalent to the two degrees of freedom of amplitude and phase are obtained for each received signal before phasing and addition. It would be good if it was. Therefore, the method of extracting the envelope amplitude of the signal after phasing and addition by sampling each received signal before phasing and addition is not limited to the above method. For example, the next method using high-speed adda is also possible. For each wavefront mentioned above, four identical phase planes having a phase difference of 90° are consecutively selected, and the values of each received signal are sampled as shown in FIG. The third value (C2) is subtracted from the first value (C1) by the high-speed adder (C1 - C2), and the second value (S ¹ ) is the COS width.
Subtract the fourth value (S ² ) from (S ¹ − ^{S 2} ).
It is written to the line memory as a SIN width, and the subsequent processing is performed in the same manner as in the case of FIG. According to this method, it is possible to eliminate the influence of DC drift in the circuit system in the preceding stage including the AD converter.

As explained above, according to the present invention, when sampling and phasing signals from a plurality of receiving elements constituting an array receiver, interpolation processing is essentially unnecessary, and this feature provides the following effects. will occur.

The sample rate can be easily reduced to the theoretically required sample rate determined by the envelope bandwidth of the received signal.

Interpolation processing for delay-and-sum is omitted, and the number of data to be processed can be kept to the minimum necessary, so the burden on hardware for subsequent data processing including delay-and-sum is reduced. I will come to live.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional device for phasing and adding received signals of an array type receiver, and FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. Figure 3 shows
This is a spectral diagram of a signal with a center frequency _C , a maximum frequency _M , and a fractional bandwidth α, FIG. 4 is an explanatory diagram of the sampling method used in the present invention, and FIG. 5 is a diagram showing the configuration of another embodiment of the present invention. The block diagram, FIG. 6, is an explanatory diagram of its operation, and FIG. 7 is another explanatory diagram of the sample method used in the present invention.

Claims (1)

[Claims] 1. A receiving device comprising a plurality of arrayed receiving elements and means for phasing and adding a plurality of received signals from the plurality of receiving elements so as to match the directivity to a point of interest within the field of view. , the phasing and addition means includes a sampling means for sampling the received signal of each receiving element at the time when the same phase front of the sound wave diffusing from the point of interest reaches each receiving element, and a sampling means for sampling each sampled received signal. 1. A receiving device comprising a memory that holds one part of each of the received signals, and an adding means that adds the held received signals to each other. 2. The phasing and addition means includes first and second phasing and addition means that respectively perform sampling with a 90° phase difference of the center frequency of the received signal, and the envelope band of the received signal is ±αc. 2. The receiving device according to claim 1, wherein the repetition frequency of sampling paired with a 90° phase difference is αc.