JP2005312587A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide uniform sound field characteristics irrelevant to a beam deflection angle θ and a transmission focal depth r in an ultrasonic diagnostic apparatus. <P>SOLUTION: A transmission voltage coefficient is output from a power memory 36 to multipliers 24 provided in respective transmitters 16. The transmission voltage coefficients in the respective transmission channels are set to uniformize a sound pressure in the respective transmission focus points irrelevant to the beam deflection angle θ and the transmission focal depth r. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to transmission voltage control.

  In the ultrasonic diagnostic apparatus, a transmission beam is formed by setting a predetermined delay time relationship for a plurality of transmission signals applied to a plurality of vibration elements. The transmission beam is electronically scanned, and electronic sector scanning is known as the electronic scanning method. In the electronic sector scanning, generally, the transmission aperture is variably set according to the beam deflection angle, and the transmission voltage is weighted in the transmission aperture. As the weighting function, a Gaussian function, a Hamming function, or the like is well known.

  By the way, in the conventional ultrasonic diagnostic apparatus, if the transmission voltage is made constant irrespective of the beam deflection angle, the sound pressure decreases as the beam deflection angle increases, that is, the sensitivity at the left and right ends of the scanning surface increases. There is a problem that the sound field does not become uniform over the entire scanning surface. On the other hand, in the conventional ultrasonic diagnostic apparatus, if the transmission voltage is made constant regardless of the transmission focal depth, there is a problem that the amplitude of the received signal becomes excessive and the reception circuit is saturated.

  In the past, the electro-mechanical conversion efficiency of ultrasonic transducers was not very high, so it was desired to always set the maximum transmission voltage. However, recent technological advances have improved the conversion efficiency. However, maintaining the maximum transmission voltage at all times as in the conventional concept may cause the problem of non-uniform sound field. Incidentally, in the ultrasonic diagnostic apparatus, from the viewpoint of safety, an upper limit value is automatically set for the transmission voltage, and the transmission voltage can be variably set by the user. While taking these into consideration, the uniformity of the sound field and the like is required over the entire scanning plane as the two-dimensional space (or the three-dimensional echo data capturing area as the three-dimensional space).

  Even if the sound field at the time of transmission is non-uniform, it is not impossible to make the sensitivity uniform across the entire scanning plane by adjusting the sensitivity at the time of reception. However, adjusting the non-uniformity of the transmitted sound field on the receiving side requires complicated adjustment and control.

  Patent Document 1 listed below describes setting different transmission conditions (including transmission sound pressure) for each beam direction in order to make the transmission sound field uniform on the scanning plane. However, the relationship with the transmission focal depth is not described, and the condition under which the transmission voltage is actually controlled is not described. Patent Document 2 below describes that the local sound pressure is made equal for a plurality of regions of interest having different depths by adjusting the sound transmission sound pressure of an ultrasonic beam. However, this is for making the contrast effect of the contrast agent uniform, and the relationship with the beam scanning angle is not described.

JP 2001-327505 A JP 2003-093389 A

  An object of the present invention is to enable an ultrasonic diagnostic apparatus to form a good transmission sound field regardless of the beam scanning angle and the transmission focal depth.

  Another object of the present invention is to prevent the transmission output from being restricted more than necessary and prevent the receiving circuit from being saturated in the ultrasonic diagnostic apparatus.

(1) The present invention includes a plurality of vibration elements, a plurality of transmitters provided corresponding to the plurality of vibration elements, and a transmission control unit that controls the plurality of transmitters. The unit includes transmission voltage control means for setting a voltage of the transmission signal in accordance with at least a combination of a transmission beam azimuth and a transmission focal depth.

  According to the above configuration, the transmission voltage means controls the transmission voltage so as to improve the decrease in the transmission sound pressure due to the change in the transmission beam azimuth and the variation in the transmission sound pressure depending on the transmission focal length. Therefore, the transmission sound field can be made uniform, and in particular, a balanced transmission sound field can be constructed in the vicinity of each transmission focal point regardless of the beam deflection angle and the transmission focal depth.

  Desirably, the transmission voltage control means decreases the voltage of the transmission signal as the beam deflection angle as the transmission beam azimuth decreases and as the transmission focal depth decreases. According to this configuration, when the beam deflection angle becomes small or the transmission focal depth becomes shallow, the voltage of the transmission signal is reduced as described above, so that the problem of saturation of the reception circuit can be prevented.

  Preferably, the transmission voltage control means sets the voltage of the transmission signal so that the sound pressure is constant at the transmission focal point regardless of the beam deflection angle and the transmission focal depth.

  As described above, according to the present invention, a good transmission sound field can be formed regardless of the beam scanning angle and the transmission focal depth.

Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the transmission unit of the ultrasonic diagnostic apparatus according to the present invention.

  The array transducer 10 includes a plurality of transducer elements 12. In the present embodiment, in the array transducer 10, a plurality of vibration elements 12 are linearly arranged. An ultrasonic beam is formed by the array transducer 10, and the ultrasonic beam is scanned in the electronic sector in this embodiment. In the figure, an ultrasonic beam scanned in such an electronic sector is also represented by a beam deflection angle θ, and a transmission focus point (transmission focal point) on the ultrasonic beam (transmission beam) is represented by F. The distance from the transmission origin of the transmission focal point F is represented by r. Incidentally, the transmission aperture is variably set according to the deflection angle θ of the transmission beam. The present invention is also applicable when beam steering is performed in electronic linear scanning.

  The transmission unit includes a transmitter group 14 including a plurality of transmitters 16 and a transmission control unit 18 that controls them. One transmitter 16 is connected to one vibration element 12. In this embodiment, the transmitter 16 generates a transmission drive signal by converting a transmission signal as digital waveform data into an analog voltage signal, as described later with reference to FIG. 12 is output. An ultrasonic beam (transmission beam) is formed by setting a predetermined delay relationship for a plurality of transmission drive signals supplied to the plurality of vibration elements 12, and the ultrasonic beam is scanned in a predetermined direction. . The transmission control unit 18 controls the operation of the plurality of transmitters 16, and a control signal from a main control unit (not shown) is input to the transmission control unit 18.

  FIG. 2 shows a specific configuration example of the transmitter 16 shown in FIG. Each transmitter 16 shown in FIG. 1 has the configuration shown in FIG.

  The waveform memory 20 is constituted by, for example, a RAM or the like, and digital waveform data is stored on the waveform memory 20. The digital waveform data is read at a predetermined timing, and is input to the D / A converter 26 via the multiplier 22 and the multiplier 24. The D / A converter 26 converts the input digital waveform data into an analog signal. The analog signal is input to the linear amplifier 28, and linear amplification processing is performed in the linear amplifier 28, thereby generating the transmission drive signal.

  In the configuration example shown in FIG. 2, the transmission control unit 18 includes configurations such as a delay memory 32, an apodization memory 34, and a power memory 36. On the delay memory 32, delay data for each transmission channel, that is, each transmitter is stored. The delay data is set in a delay counter 30 provided for each transmission channel. The delay counter 30 counts a predetermined clock signal, and outputs a read trigger to the waveform memory 20 when the count value matches the delay data set therein. The digital waveform data is read from the waveform memory 20 with the timing at which the read trigger is input as the read start point. Incidentally, the digital waveform data stored in the waveform memory 20 can be rewritten by the transmission control unit. Alternatively, a plurality of digital waveform data may be stored in the waveform memory 20, and the digital waveform data to be actually used may be selected from them. On the apodization memory 34, weighting data provided for each transmission channel is stored. The weighted data is output to a multiplier 22 provided for each channel. In the multiplier 22, the input signal is multiplied by a weighting value, and the weighted signal is output. Weighting in the transmission aperture, that is, apodization can be performed by the data stored in the apodization memory 34. As the weighting function, various functions such as Gaussian distribution are known.

  In the present embodiment, a power memory 36 is provided, and transmission voltage data for each transmission channel is stored on the power memory 36. Specifically, an appropriate transmission voltage is set for each transmission channel in accordance with the combination of the beam angle θ and the transmission focus point depth r, and a voltage coefficient representing the transmission voltage is output to the multiplier 24. The multiplier 24 performs voltage correction on the input signal in accordance with such a voltage coefficient, and outputs the result. In the present embodiment, the transmission voltage coefficient is set so that a uniform transmission sound field is formed over the entire scanning plane regardless of the beam angle θ and the transmission focal depth r, particularly regardless of the position of the transmission focal point. It is set. Of course, the transmission voltage coefficient can also be determined according to other information such as the image forming mode, the type of probe, and the diagnostic part. In any case, if the transmission voltage is adjusted according to the combination of the beam angle θ and the transmission focal depth r, there is a problem such as saturation of the reception circuit at the time of short-distance transmission as in the past, and reception when the beam deflection angle is small. Problems such as circuit saturation can be prevented beforehand.

  Incidentally, a high voltage power supply 38 for bias application is connected to the linear amplifier 28. From the viewpoint of safety, when the transmission power is increased more than necessary, a limiter function (not shown) is operated to limit the transmission voltage.

  As described above, in this embodiment, the transmission voltage is adjusted according to the beam angle θ and the transmission focal depth r. This will be described with reference to FIGS. 3 to 7.

First, FIG. 3 conceptually shows the relationship between the beam angle θ and the transmission voltage. In the present embodiment, the transmission voltage when the beam angle θ is greater than or equal to a predetermined angle is 100%, and the transmission voltage is lowered as the beam angle θ decreases. Therefore, when attention is paid only to the beam angle θ, the transmission voltage becomes the smallest when the beam angle θ is 0 degree.

  FIG. 4 shows transmission sound field characteristics according to the transmission focal depth. The horizontal axis represents the distance from the transmission origin, and the vertical axis represents power (sound pressure). Further, the characteristic curves shown therein are for the cases where the distance of the transmission focal point is 10 mm, 15 mm, 20 mm, 25 mm, and 30 mm, respectively. As shown in FIG. 4, when transmission is performed without changing the transmission voltage in accordance with the transmission focal depth, the acoustic power becomes uneven at each transmission focal point (see the arrow line in the figure). The transmission aperture is variably set according to the depth of the transmission focus. Therefore, the sound pressure at the transmission focus is slightly lowered at the nearest transmission focus due to the effect of the limitation of the transmission aperture.

  FIG. 5 shows the relationship among the transmission focal length, the numerical aperture (the number of transmission channels constituting the transmission aperture), the transmission voltage, and the sound pressure ratio in the vicinity of the transmission focal point, as in FIG. When 100% is always set as the transmission voltage regardless of the transmission focal length as in the prior art, even when the numerical aperture is varied, as shown in FIG. 5 (or as shown in FIG. 4), in the vicinity of the transmission focal point. The sound pressure ratio becomes uneven.

  Therefore, as shown in FIG. 6, it is possible to make the sound pressure uniform at each focal depth by further adjusting the transmission voltage while varying the numerical aperture according to the depth of the transmission focal point. As a result, the uniformity of the sound field can be obtained even for the entire ultrasonic image. In the example shown in FIG. 6, the transmission voltage when the depth of the transmission focal point is 30 mm is 100%.

  In this embodiment, as a result of multiplying the transmission voltage coefficient (correction value) by the beam deflection angle θ and the transmission voltage coefficient (correction value) by the transmission focal depth, the transmission voltage correction value (correction coefficient) as a whole is obtained. It has been demanded. That is, as shown in FIG. 7, a plurality of voltage coefficient sets 40 are provided according to various situations such as a mode and a diagnosis part. In each voltage coefficient set 40, transmission is performed for each transmission channel. A corrected voltage coefficient is determined according to the combination of the depth of focus r and the beam deflection angle θ, and the voltage coefficient is output from the power memory 36 shown in FIG. 2 to the multiplier 24. Therefore, by setting such a voltage coefficient, it is possible to make the sound field uniform at each transmission focal position regardless of the beam deflection angle θ and the transmission focal depth r. Incidentally, as shown in FIG. 7, if an appropriate voltage coefficient set is selected according to the image forming mode or the like, there is an advantage that an appropriate transmission sound field can be formed according to various conditions. For example, when performing an ultrasound diagnosis of the carotid artery in the neck, the transmission is performed at a relatively short distance, and the sound pressure is greatly increased. Therefore, the appropriate voltage coefficient set is used, while the thyroid gland and In the case of mammary gland inspection or the like, since the signal attenuation is large and signal detection near the noise level is required, it is desirable to use a voltage coefficient set corresponding to it. In this case, for example, in the case of the above-described cervical ultrasonic diagnosis, a voltage coefficient set that changes the voltage coefficient according to the combination of the beam deflection angle θ and the transmission focal length r as shown in FIG. 7 is used. On the other hand, in the case of ultrasonic diagnosis of the thyroid gland, mammary gland, etc., a voltage coefficient set that makes the transmission voltage constant irrespective of the transmission focal depth may be selected as in the prior art.

  According to the above embodiment, in the electronic sector image, the luminance difference between the central portion and both end portions is reduced, and the image quality can be made uniform. Further, even when beam steering is partially performed in electronic linear scanning, the sensitivity can be made constant regardless of the steering angle. Furthermore, even when the transmission focus is set at a short distance, saturation in the receiving circuit can be prevented and the image quality of the ultrasonic image can be improved. Furthermore, since the transmission power is not limited more than necessary, there is an advantage that the S / N ratio of the ultrasonic image can be improved.

It is a block diagram which shows suitable embodiment of the transmission part in the ultrasonic diagnosing device which concerns on this invention. It is a block diagram which shows the specific structural example of the transmitter shown in FIG. It is a characteristic view which shows the relationship between beam deflection angle (theta) and transmission voltage. It is a figure which shows the sound field characteristic according to the transmission focal depth in the past. It is a table showing the characteristic shown in FIG. It is a table for demonstrating the voltage correction which concerns on this embodiment. It is a figure showing the voltage coefficient set according to a mode etc.

Explanation of symbols

  10 array transducers, 12 transducer elements, 16 transmitters, 18 transmission control units, 20 waveform memories, 22, 24 multipliers, 26 D / A converters, 32 delay memories, 34 apodized memories, 36 power memories.

Claims (3)

A plurality of vibration elements;
A plurality of transmitters provided corresponding to the plurality of vibration elements;
A transmission control unit for controlling the plurality of transmitters;
Including
The ultrasonic diagnostic apparatus, wherein the transmission control unit includes transmission voltage control means for setting a voltage of the transmission signal according to at least a combination of a transmission beam azimuth and a transmission focal depth. The apparatus of claim 1.
The transmission voltage control means reduces the voltage of the transmission signal as the beam deflection angle as the transmission beam azimuth decreases and as the transmission focal depth decreases. apparatus. The apparatus of claim 2.
The ultrasonic diagnostic apparatus, wherein the transmission voltage control means sets the voltage of the transmission signal so that the sound pressure is constant at the transmission focal point regardless of the beam deflection angle and the transmission focal depth.

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