JPH01214350A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To simplify the constitution of a delay circuit by determining the interval between vibrators so that the vibrators of probes different in adapting frequency satisfy specific relation between the center intervals of the vibrators and the distance from the vibrator row to the converging point of an ultrasonic wave and mounting probes capable of using the delay circuit in common even if frequency is made different. CONSTITUTION:The center interval (d) of the vibrator of a probe of each adapting frequency is determined by setting the display possible max. distance of a tomographic image to L and adapting a formula (7). On the basis of a vibrator of d1=0.71mm and 3.5MHz, the center intervals d2, d3 of the vibrators of 5MHz, 7.5MHz are set to 0.62mm and 0.50mm. When a delay circuit for converging the ultrasonic wave of the probe having adapting frequency of 3.5MHz to a point F11 is used in the probe by determining the center intervals of the vibrators drive the probes of 5MHz, 7.5MHz, the ultrasonic waves transmitted from the probes are converged to a point F21 or F31 satisfying formula (7) or (8). When the delay circuit for converging an ultrasonic wave to F12, F13, F14 is used in common, the same result is obtained with respect to F12, F22, F23, F13, F23, F33 and F14, F24, F34.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic diagnostic apparatus that is equipped with a probe that transmits and receives ultrasonic waves to and from a living body and obtains tomographic images of the living body.

(Prior Art) In order to obtain a tomographic image with good resolution, an ultrasound diagnostic device selects a plurality of consecutive piezoelectric transducers from among a large number of piezoelectric transducers arranged in an array in a probe. , the ultrasonic waves are transmitted by pulse driving almost simultaneously.At this time, the end transducers of the selected transducers are driven temporally earlier, and the wave fronts emitted from each transducer are combined to improve focusing. It has been known for a long time that directivity can be improved by creating a wavefront with

FIG. 4 is a diagram showing the principle for performing the above transmission, which is known as electronic linear scanning.

- n oscillators E l arranged on a straight line with center spacing d
+... A plurality of consecutive items (n items) from IEII.

The transducer row 1 consisting of the transducers Elr . . . The center point on the transmission surface of each vibrator is assumed to be PI, . . . Pj+ . . . +Ps. A straight line passing through the center of this transducer row 1 and perpendicular to the transducer row 1 is taken as the Z-axis, and the left and rightmost transducers of the above-mentioned transducer row center points PI+ and P
, and draw an arc R (radius Xo).

The intersection point Qj ((j -2, ..., m-1
), and the distance MPJQj is divided by the speed of sound C in the medium to be measured to obtain the delay times T, wp, Q, /C. The delay time Tj is obviously longer for the central transducer of the transducer array 1, and the delay time Tj is longer for each transducer Ex-j-+(j-1, . . . ).

If m) is given these delay times Tj and driven simultaneously,
As described above, the wavefronts from each vibrator are combined into a circular shape and focused on point F, and a tomographic image with good resolution can be obtained in the vicinity of point F.

FIG. 5 is a block diagram of a circuit that performs the above driving. n oscillators E + + . . . that constitute the probe 2;
n connected with 0 signal cables 3 to each of E7
There is a switch group 4 comprising m switches, of which m
m switches connected to each vibrator of a vibrator array 1 consisting of vibrators E'i, . . . + E1*@-1 are in an ON state. The drive pulse 6 output from the clock pulse generation circuit 5 is sent to m delay circuits CT, . . .
CT'', ..., CT, predetermined delay time T+
,...,T, ,...,T, (where 'r, -T, -
0) is given, Pulsa pc+,...

pcj, . As explained with reference to FIG. 4, the central transducer of the transducer row 1 is given a long delay time, and an ultrasonic wave with a circular wavefront focused on the - point is transmitted. After this transmission is performed, the control circuit 7 controls the m oscillators Ei*1 in the switch group 4.
+...+The switch connected to Eis6 is turned on, and ultrasonic waves focused at a point slightly shifted in the direction of the transducer array are transmitted. Thereafter, the measurement target is scanned by repeating transmission one after another in the same manner.

The above description is for the case of transmission, but similar scanning is performed for reception as well.

The probes normally used in ultrasonic diagnostic apparatuses are not limited to one type, and probes with different common frequencies are used depending on the region to be diagnosed and the purpose. This is because the resolution and the degree of ultrasonic attenuation differ depending on the applied frequency.

When the applied frequencies are different, if the applied frequency is high and the wavelength λ of the ultrasound is relatively small compared to the center distance d of the transducer, the grating, which is an ultrasonic beam directed not only in front of the transducer but also to the side, Side ropes such as lobes will increase. For this reason, a target object that is not on the main beam is detected, and a false tissue image called an artifact is generated at a position where there should be nothing on the tomographic image. To prevent this, generally, in probes with different applicable frequencies, the center spacing of the transducers is made different, and the center spacing d of the transducers with a higher applicable frequency is made smaller. In addition, the higher the applied frequency, the greater the attenuation of ultrasonic waves, and the attenuation characteristic of the human body is 1 dB on average.
/MHz/cm, which is relatively large. For these reasons, a probe with a high applicable frequency generally has a small center-to-center spacing d between transducers, and at the same time shortens the distance between the transducer array and the focal point F of the ultrasonic waves. Therefore, the combinations of delay times given to transducer arrays of probes having different frequencies are different from each other. For this reason, conventional ultrasonic diagnostic apparatuses are provided with a plurality of types of delay circuits depending on the applicable frequency of the probe, and these delay circuits are switched for use.

[Problem to be solved by the invention]

The delay circuit occupies a large proportion of the cost of the circuit units that make up the main body of the diagnostic device, so having multiple delay circuits not only makes the diagnostic device expensive, but also complicates the circuit configuration of the device. There is a problem with making it.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic diagnostic apparatus in which the configuration of the delay circuit is simplified by including a probe that can share the delay circuit even if the frequencies are different.

[Means to solve the problem]

This invention includes a probe in which a large number of transducers are arranged in an array, and sequentially selects a plurality of continuous transducer rows from one end of the arranged transducers, and connects the transducer rows through a delay circuit. In a device that obtains tomographic images of a living body by transmitting and receiving ultrasonic waves through simultaneous electronic scanning, each transducer of a probe with a different applied frequency has a center spacing d between the transducers.
d7 between the transducer array and the distance to the focal point of the ultrasonic wave.
The transducer spacing d is determined so as to satisfy a Jτ-certain relationship.

[Effect]

The relational expression d/VT knee-constant between the center spacing d of the transducers and the distance from the transducer array to the focal point of the ultrasonic wave is based on the condition that the combination of delay times given to the transducer array remains unchanged. It has been derived.

d, which is determined to satisfy the above relationship, becomes small when the applied frequency is made high and L is made small, and becomes large when the applied frequency is made low and L is made large. This tendency coincides with the conventional tendency in which d is made small when the applied frequency is high, and d is made large when the applied frequency is low. In other words, by setting d to satisfy the above relationship,
It becomes possible to use probes with different applicable frequencies by sharing a delay circuit without impairing the characteristics of the diagnostic device.

〔Example〕

Prior to detailed description of this invention, the establishment of this invention will be explained.

Figure 1 shows m oscillators E driven simultaneously as in Figure 4.
E! ,..., EEt＊j−++・〜, E[! !
---1 schematically shows a transducer row 11 consisting of 1.

In FIG. 1, calculate the distance from the transducer array 11 to the ultrasonic focusing point F, and calculate the radius of the arc drawn to obtain the delay time to focus the ultrasound at point F from the center of the transducer array 11. Oscillator EEi or EEi at both ends. The distance to the center of m-1 is al + the distance from the center of transducer row 1 to the center Pj of a certain transducer EEi-J-1 is ak + the focal point F
Let the distance from to Pj be a I/ L <
1 r a w / L < 1, so X ,
w fL" + a + '# L (1 + 'A< a r / L)")
-------(t)b, -yu @ 4 a,! #LC1+'ACa*/L>"3 ----<2+. However, k is -j when j<m/2+1.

When j>II/2, it is given as -m-j+1.

Oscillator E [+1. The delay time Tj given to j-1 is Tj-PjQj/C, as described above. Therefore, fl), +21 leads to Pi Q.

jw − ” (X+ bm) ” (a% −am”) −・・・−・−・
・-(3) CL becomes. Also, the distance Ham is am ” where the center spacing is d.
l(j-1) d-%(m-1) dl-l (j
%(m+1) ) d l ---------(4). Also, in equation (4), a is j-1 or j-m, and a + -1'A (m -1) l a -...-
・－－－－－－(Given as 5+.

(3), (41, (From 51, TJ is Tj −−(m−j)(j −1) d” −−−−+
61CL Kinaru. Therefore, assuming that the j-th oscillator of several oscillator arrays consisting of m oscillators is given a common delay time T, then in equation (6), 77, C, m,
By treating J as a constant and L and d as variables, the following relationship is established between d and L: d* 2 CT J L (m-J) (j-1).

Equation (7) shows that when the distance from transducer example 11 to the focal point of the ultrasonic wave is changed, the transducer spacing at which the same delay time can be used is inevitably determined. In other words, such d makes L small (then it becomes small in proportion to the square root of L).

This is consistent with the fact that when the applied frequency is increased, the focal point is set at a shallower location, and the center spacing is reduced to avoid artifacts and perform appropriate transmission and reception. It is.

FIG. 2 is a comparative explanatory diagram schematically showing an embodiment of the present invention with respect to 2&ll vibrator arrays 12 and 13.

The vibrator array 12 shown in FIG. 2 [81] has a vibration frequency of f.

A probe 14 consisting of n transducers with a center spacing d,
Among them, m oscillators EEli, ..., EE1t re-
It is composed of 2゜..., EEli, , and T++
(-0),...

T l j + ..., T + - (-0) - sets of delay times are given to each transducer, and the distance L
An ultrasonic wave with a circular wavefront that is focused on one point F1 is transmitted. In this case, the delay time T+J given to the oscillator EE1j is T 1j-P +jQ IJ/ as explained in FIG.
Satisfies relationship C. Here, the P-th point is the center point on the transmitting surface of the transducer EE1j, and the Q-th point is the center point of the transducer EE1+ or EEl.
This is the intersection of an arc R8 whose radius is the distance rl between the center point pH or pHl on the transmission surface of , and F, and the extension of the line *F+jP+- that connects F and PIJ.

(bl is the probe 1 whose applied frequency is f and higher f8
m oscillators EE2i out of n oscillators of 5.

..., EEh-j-+ , ..., EE2=, -+
This figure shows a transducer row 13 consisting of the following. Since the applied frequency is higher than f, the attenuation of the ultrasonic waves is greater than that in the transducer array 12, so the distance Lt between the transmission surface of the transducer array 13 and the ultrasound focal point F2 is determined by considering the above attenuation characteristics. The value is determined to be L8 x Ll. Further, from this L2, the center distance d is determined so as to satisfy the condition of equation (7). In this case, considering d,,L, of the oscillator array in (a), d8 is given by eL! <Ll, so d, <d.

In this case, since the oscillator array 13 is driven through the same delay circuit as the oscillator array 12, the j-th oscillator EE2
i-J-1 is the j-th vibrator EE1z of the vibrator row 12;

The same delay time Tlj is given as .

Oscillator Eε2&. From the center point Ph of the transmitting surface of j-1 to C×
If we take point Q2j at the distance of T1j, then d, < d, so Q
It is clear that the radius of curvature r8 of the arc R8 created by the envelope of 2J is necessarily r, and the wavefront of the ultrasonic wave is focused on F, which is smaller than F1.

In Figure 3, the applicable frequency is 3.5 MHz, 5 Mllz
, 7.5 MHz, the embodiments of the present invention are compared in relation to the maximum displayable distance of a tomographic image.

As mentioned earlier, the higher the applied frequency, the greater the attenuation of the ultrasound, and the maximum distance at which a tomographic image can be displayed is generally about 20 cm for a 3.5Ml2 probe and about 151cm for a 5M) Iz probe. It is said to be about 10 cm with 7.5 Ml2. Obtaining a tomographic image by setting the ultrasound focal point at one point within this maximum distance is not preferable in terms of image resolution, so usually several focal points are set within the above maximum distance for diagnosis. It is common practice to select a focal point near the organ depending on its location. FIG. 3 shows four convergence points.

The center spacing d of the transducer of the probe for each applicable frequency is determined by applying formula 71 to L, which is the maximum distance that can display a tomographic image. 3.
5 MHz, respectively, based on a 5 MHz resonator.
Center spacing d of a 7.5 MHz oscillator, −0,62
fi.

d, -Q, and 5Qm are determined.

In the probe in which the center spacing of the transducers is determined in this way, the applied frequencies of 5 MHz and 7 MHz are used using a delay circuit to focus the ultrasonic waves of the probe with an applied frequency of 3.5 Ml (z) on the point F. When .5 MHz probes are driven, the ultrasonic waves transmitted from these probes are focused on points Ftl and F31 that satisfy equation (7) or (8). Point F+, respectively.
Fl! when a delay circuit for focusing on t+ F+s+ F+a is shared! ＋F! t+ Between Fxs+F
13+F! Between 3+F0+F+a+Fz
The same applies to 4+Fsa. If the maximum distance at which a tomographic image can be displayed becomes shorter in this way, the distance to the focal point becomes shorter, so a delay circuit can be shared to ensure proper transmission,
FIG. 3 shows that further reception is possible.

The above explanation relates to a linear type probe in which n transducers are arranged in a straight line with center spacing d, but it is also possible to use a linear probe in which multiple transducers are arranged at equal intervals on a curved line (usually on the circumference). The same holds true for convex probes. In addition, an electronic sector type probe that uses n transducers to perform sector scanning by swinging the ultrasonic beam in a fan shape by electronic scanning is equipped with a delay circuit for sector scanning and a delay circuit for focusing. Of these, the delay circuit that performs focusing can be shared. Further, if the difference in beam spread angle in sector scanning is not a problem, the delay circuit for sector scanning can also be shared.

〔Effect of the invention〕

According to this invention, the distance d between the centers of the transducers of probes with different applied frequencies is determined based on the condition that the same delay circuit can be used for the distance from the transducer row to the focal point of the ultrasonic waves. Since it is determined based on the relationship that d/J-L = constant, it is no longer necessary to use different delay circuits for each probe with a different frequency as in the past, and all probes can be used with just one type of delay circuit. It becomes possible to use the tentacle under appropriate conditions. As a result, it is possible to significantly reduce the number of delay circuits that account for a large proportion of the cost in the main unit circuit of the diagnostic device, which has a large effect not only on the economical side but also on simplifying the configuration of the device. effect can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a detailed explanatory diagram of the present invention, Fig. 2 is a comparative explanatory diagram showing the focusing points of ultrasonic waves of transducer rows with different center intervals of transducers in an embodiment of the invention, and Fig. 3 is a A graph showing the relationship between the focal point of ultrasonic waves and the maximum distance that can be displayed in three types of probes with different center spacings of transducers according to the embodiment of this invention, FIG. 4 is a delay given to the transducer array An explanatory diagram of time, FIG. 5 is a Pronk diagram of the probe drive circuit. 1.11, 12, 13: Transducer row, 2.14.15
: Probe, a, dl+dZ : Center distance, Et,・
..., El,... E,,,,,EE,,...,EEi,,-,,E
Eli,...,EEli,, -1°EE2. ,・
..., EE24. -I: Vibrator, CTC,...,C
T:? Distance d (mm) between 1st ÷ 1st interval d (mm)

Claims (1)

[Claims] 1) A probe is provided with a large number of transducers arranged in an array, and a plurality of continuous transducer rows are sequentially selected from one end of the arranged transducers, and the transducer row is In a device that obtains tomographic images of a living body by transmitting and receiving ultrasonic waves through electronic scanning, which is activated simultaneously via a delay circuit, each transducer of a probe with different applied frequencies has a center spacing d between the transducers. An ultrasonic diagnostic apparatus characterized in that a distance L between a transducer array and a focal point of ultrasound waves satisfies a constant relationship d/√L=.