JP2006122344A - Ultrasonographic picture diagnostic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonographic picture diagnostic device for making the increase in the sound pressure of ultrasonic waves to be outputted compatible with the improvement of the receiving efficiency of ultrasonic reflection waves. <P>SOLUTION: This ultrasonographic picture diagnostic device is provided with: a plurality of C-MUT elements where a thin film and a board are provided having a gap between themselves and which transmit the ultrasonic waves by the vibration of the thin film and converts the vibration of the thin film by reception of the ultrasonic reflection wave to the echo signal of an electric signal; and a control means which gives variable bias voltage Vp where voltage is boosted gradually while going from a short distance reception period Rs for receiving the ultrasonic reflection wave reflected by the short distance section of a patient to a long distance reception period Re for receiving the ultrasonic reflection wave reflected by the long distance section in the receiving period T of the ultrasonic reflection waves, to the C-MUT element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic diagnostic imaging apparatus that uses a C · MUT (Capacitive Micromachining Ultrasound Transducers) device as an ultrasonic transducer.

  In recent years, an ultrasonic vibrator using an ultrasonic diagnostic imaging apparatus using a C / MUT element (capacitance coupled ultrasonic vibrator) has been proposed (for example, see Patent Document 1). In this C / MUT element, a DC (direct current) bias voltage is applied between a pair of electrode films arranged opposite to each other on a substrate such as silicon, and a drive pulse having a required frequency of an electric signal is superimposed on the applied voltage. As a result, the capacitance between the pair of electrode films fluctuates, and one electrode film vibrates to transmit ultrasonic waves having a required frequency. FIG. 17 shows a transmission waveform Ta of a drive signal transmitted to and driven by the C / MUT element and its DC bias voltage Va, and this DC bias voltage Va is fixed at about 80 V, for example. .

  In addition, when a reflected wave (echo wave) of an ultrasonic wave is received by one electrode film, the C · MUT element has a function of converting it into an echo signal of an electric signal. That is, the C · MUT element can reversibly convert ultrasonic waves into electrical signals.

The C · MUT element can appropriately control the resonance frequency by changing the electrostatic capacitance between the pair of electrode films by controlling the DC bias voltage. However, since this resonance frequency band is narrow, conventionally, the DC bias voltage of the C · MUT element is set to a value that uses a frequency band other than the resonance frequency to widen the ultrasonic frequency band.
US Pat. No. 6,443,901

  However, C / MUT elements generally have a problem that the sound pressure of ultrasonic waves is smaller than that of ultrasonic piezoelectric elements such as PZT.

  Therefore, the sound pressure of the ultrasonic wave is increased by increasing the DC bias voltage applied to the pair of electrode films of the C / MUT element or by amplifying the amplitude of the drive pulse superimposed on the DC bias voltage. It is possible.

  Further, by increasing the DC bias voltage, it is possible to improve the ultrasonic reception sensitivity or reception efficiency of the C · MUT element.

  However, if the DC bias voltage of the C / MUT element and the amplitude of the drive pulse are excessive, the amplitude of one vibrating electrode film may be excessive and may be damaged by hitting the other electrode film. is there.

  For this reason, it is necessary to reduce the DC bias voltage in accordance with the amplitude of the drive pulse. In other words, the conventional C / MUT element driving method has a problem that it is difficult to achieve both high sound pressure of ultrasonic waves and improvement in echo wave reception efficiency.

  In addition, when the DC bias voltage is increased rapidly, for example, in a staircase pattern, there are cases where a double image is generated by transmitting ultrasonic waves when the echo reception period is not intended.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic image diagnosis capable of achieving both an increase in the sound pressure of ultrasonic waves to be output and an improvement in the reception efficiency of ultrasonic reflected waves. To provide an apparatus.

  The present invention has been made paying attention to the point that the reception efficiency of the ultrasonic wave echo signal exponentially increases as the DC bias voltage of the C / MUT element increases as shown by the characteristic curve A in FIG. The DC bias voltage applied to the C / MUT element during the echo wave reception period is gradually increased from the short distance reception period to the long distance reception period, and is configured as follows.

  The invention according to claim 1 transmits an ultrasonic wave to a subject during a transmission period, and regenerates an ultrasonic image based on an echo signal of an ultrasonic reflected wave received from the subject during a reception period. An ultrasonic diagnostic imaging apparatus configured and displayed on a display means is driven by applying a DC bias voltage, receives a drive pulse and transmits the ultrasonic wave, while receiving the ultrasonic reflected wave and electrically A plurality of capacitively coupled ultrasonic transducers that convert the signal into an echo signal, and a short-distance reception of the ultrasonic reflected wave reflected at a short-distance portion of the subject during the reception period of the ultrasonic reflected wave A control means for applying a variable bias voltage having a gradually higher voltage to the capacitively coupled ultrasonic transducer as it goes from a reception period to a long-distance reception period for receiving an ultrasonic wave reflected at a long-distance site; It is characterized by having A ultrasound image diagnosis apparatus.

  According to a second aspect of the present invention, the control means includes a bias generation circuit that generates a drive bias voltage having a potential necessary for generating the drive pulse and the variable bias voltage applied during the reception period. A transmission control signal for outputting the driving bias voltage as a drive pulse from the bias generation circuit during the transmission period, and a transmission control signal for outputting the variable bias voltage from the bias generation circuit during the reception period. A transmission control unit that receives the transmission control signal from the transmission control unit that outputs the transmission control signal, and a transmission circuit that selectively applies the drive pulse and the variable bias voltage to the capacitively coupled ultrasonic transducer. The ultrasonic diagnostic imaging apparatus according to claim 1, further comprising:

  According to a third aspect of the present invention, the transmission control means includes means for outputting the transmission control signal so that the variable bias voltage applied during the reception period does not include the frequency component of the drive pulse. The ultrasonic diagnostic imaging apparatus according to claim 2, wherein:

  According to a fourth aspect of the present invention, a plurality of the capacitively coupled ultrasonic transducers are arranged in a row on the substrate to form an array element, and the plurality of array elements are scanned. The ultrasonic diagnostic imaging apparatus according to claim 1, wherein the ultrasonic diagnostic imaging apparatus is configured as a two-dimensional array element arranged in parallel in a direction.

  According to a fifth aspect of the present invention, the bias generation circuit is electrically connected to all the array elements, the transmission circuit is electrically connected to each of the array elements, and the transmission circuit control means includes the array 5. The ultrasonic diagnostic imaging apparatus according to claim 4, further comprising means for outputting a transmission control signal for electronic scanning of the element in the scanning direction.

  According to a sixth aspect of the invention, the transmission control means includes means for controlling the variable bias voltage in response to a manual operation of a gain operation tool of a console for controlling a gain of an amplifier that amplifies the echo signal. The ultrasonic diagnostic imaging apparatus according to claim 2, wherein the ultrasonic diagnostic imaging apparatus is provided.

  The invention according to claim 7 is characterized in that the transmission control means includes means for controlling the variable bias voltage in response to a manual operation of a frequency operation tool of a console for controlling the transmission frequency of the drive pulse. The ultrasonic diagnostic imaging apparatus according to claim 1, wherein the ultrasonic diagnostic imaging apparatus is characterized by the following.

  According to the present invention, during the reception period of the ultrasonic reflected wave, the variable bias voltage whose voltage gradually increases from the short-distance reception period to the long-distance reception period is applied to the thin film of the capacitively coupled ultrasonic transducer. Since it is applied between the substrates, it is possible to improve the reception efficiency or the reception sensitivity of the echo wave from this short distance reception period to the long distance reception period.

  Moreover, since the DC bias voltage of the capacitively coupled ultrasonic transducer is not increased during the transmission period of the ultrasonic transmission, a drive pulse having a large amplitude is applied to the capacitively coupled ultrasonic transducer and the ultrasonic wave is transmitted. Even if the sound pressure is increased, it is possible to effectively prevent the capacitively coupled ultrasonic transducer from being damaged. That is, it is possible to achieve both an increase in the sound pressure of ultrasonic waves and an improvement in reception sensitivity or reception efficiency of echo waves.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In these accompanying drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 2 is a block diagram showing the overall configuration of the ultrasonic diagnostic imaging apparatus 1 according to the first embodiment of the present invention. As shown in FIG. 2, the ultrasound diagnostic imaging apparatus 1 includes a probe head 200 and a main body apparatus 400 electrically connected to the probe head 200 via a signal cable 300.

  The probe head 200 includes a probe 201, a transmission circuit 202, a transmission control circuit 203, a bias generation circuit 204, a reception preamplifier 205, and a reception delay addition circuit 206, which are provided in a head case (not shown) and integrally configured. is doing.

  On the other hand, the main body device 400 includes a reception scanning circuit 401, a blood flow information detector 402, an amplitude detector 403, a data memory 404, a display processing unit 405, and a display monitor 406. Arranged integrally.

  FIG. 3 is a schematic diagram showing a principal plane of the probe 201. As shown in FIG. 3, the probe 201 is configured as a two-dimensional array element by arranging a plurality (for example, 64 elements) of array elements 211, 211,.

  Each array element 211 scans a plurality of C · MUT elements 231, 231... Having a planar shape such as a circle on an insulating substrate 221 made of silicon or the like in the horizontal slice direction in FIG. 3 and the vertical scan in FIG. For example, they are arranged in 3 rows and 12 columns, each with a required pitch in the direction.

  Each array element 211 forms a wiring conductor (not shown) that electrically connects a plurality of C / MUT elements 231 in parallel on the insulating substrate 221, and further includes this wiring conductor for each array element 211. The transmission circuits 202 are electrically connected to each other. Each transmission circuit 202 drives each C · MUT element 231 by outputting (transmitting) each C · MUT element 231 with the transmission signal 202S shown in FIG. The wave is transmitted to a subject (not shown).

  FIG. 4 is a longitudinal sectional view of each C · MUT element 231. As shown in FIG. 4, each C / MUT element 231 has a substrate-side conductive thin film 241 formed on the upper surface in FIG. 4 of an insulating substrate 221 made of silicon or the like as a substrate, and further this substrate-side conductive thin film. A frame-shaped insulating layer 251 made of non-conductive silicon nitride or the like is formed on 241, and a space 261 having a circular planar shape with a thickness of, for example, 1 μm or less is surrounded by the insulating layer 251. Is forming.

  Further, a non-conductive thin film 271 is formed on the insulating layer 251 on the gap layer 261. On the upper surface of the non-conductive thin film 271, a small circular radiation surface side conductive thin film of, for example, 100 μm or less is formed. The transmission signal 202S from the transmission circuit 202 is applied between the radiation surface side conductive thin film 281 and the substrate side conductive thin film 241. Thereby, the electrostatic force attracting each other acts between the conductive thin films 241 and 281 on the substrate side and the discharge surface side, and the electrostatic force between these conductive thin films 241 and 281 changes by controlling the DC bias voltage. Therefore, the discharge surface side conductive thin film 281 vibrates integrally with the non-conductive thin film 271, and ultrasonic waves having a required frequency are radiated from the radiation surface side conductive thin film 281.

  Further, in order to reduce the vibration resistance of the radiation surface side conductive thin film 281, the gap 261 is formed in a substantially vacuum.

  FIG. 1 is a waveform diagram showing a voltage waveform of a transmission signal 202S which is a drive signal given from the transmission circuit 202 to the C · MUT element 231. In FIG. 1, the horizontal axis indicates time (sec) t, the vertical axis indicates voltage (V), T is an ultrasonic transmission period having a period of, for example, 200 μsec, and R is an ultrasonic reflected wave (echo wave). A reception period for receiving, Rs is a short-range reception period for receiving an ultrasonic reflected wave reflected at a short-distance part of the subject, and Re is a long-distance reception period for receiving an ultrasonic reflected wave reflected at a long-distance part of the subject. , NR indicate non-reception (non-reception period), respectively.

  The waveform of the transmission signal 202S is configured by superimposing a drive pulse MP having a required frequency on a bias voltage. In the transmission period T during which the drive signal pulse MP is output, the bias voltage is about 80 V, for example, which is the lowest, but the upper side pulse Pu rising to the upper side, which is higher than the bias potential, and the same low potential. One lower side pulse Pd falling to the side. However, the upper and lower pulses Pu and Pd are not limited to one, but may be one or more each, or one of them.

  The transmission signal 202S has a variable bias voltage Vp component in the reception period R. This variable bias voltage Vp is a time-varying waveform that changes with time so that the bias voltage gradually increases from the short-distance reception period Rs to the long-distance reception period Re.

  The transmission signal 202S configured as described above is generated by the transmission circuit 202 receiving the transmission control signal 203S from the transmission control circuit 203, which is an example of a transmission control means, and the bias voltage 204S from the bias generation circuit 204. .

  The transmission control circuit 203 includes a clock generator, a frequency divider, a transmission delay circuit, and a switch circuit (not shown). The clock pulse generated by the clock generator is frequency-divided by a frequency divider to a predetermined frequency of about 5 KHz, for example. Then, the pulse is dropped into a rate pulse of a predetermined rate, which is given to the pulser through the transmission delay circuit, where a voltage pulse with a predetermined timing determined for each array element 211 is created, and this is used as the transmission control signal 203S as the transmission circuit 202. It is something to give to.

  The bias generation circuit 204 is commonly used for a plurality of (for example, 64 elements) array elements 211, and generates the driving upper voltage b1, the variable bias voltage b2, and the driving lower voltage b3 shown in FIG. Thus, the power is supplied to the power supply side of the upper first switch SW1, the variable second switch SW2, and the lower third switch SW3, which are bias selection means of the transmission circuit 202, respectively.

  As shown by the broken line in FIG. 5, the upper drive voltage b1 is constant at about 120 V, for example, and gives the maximum potential of the upper pulse Pu of the pair of upper and lower drive pulses MP shown in FIG. Further, the driving lower voltage b3 is constant at about 40 V, for example, as shown by a one-dot chain line in FIG. 5, and gives the potential of the lower pulse Pd of the driving pulse MP shown in FIG.

  The variable bias voltage b2 is a voltage that changes with time in the potential between the driving upper voltage b1 and the driving lower voltage b3 as shown by the solid line in FIG. It is. Further, the variable bias voltage b2 changes so that the voltage gradually increases from the short distance reception period Rs to the long distance reception period Re.

  FIG. 7 is a waveform diagram of the transmission control signal 203S. The transmission control signal 203S is given from the transmission control circuit 203 to the first to third switch circuits SW1 to SW3 of the transmission circuit 202, and the switch circuits SW1 to SW3 are controlled to be turned on only during the on-pulse width time. This is a switch control timing pulse for generating and outputting the signal 202S.

  The transmission control signal 203S has first, second, and third on-pulses P1, P2, and P3 having a pulse width with a predetermined duty ratio. The first on-pulse P1 turns on the first switch circuit SW1 for a predetermined time only during the transmission period T to output the upper driving voltage b1, and transmits this to the array element 211 as the upper-side pulse Pu in the driving pulse MP. This is a control pulse.

  The second on-pulse P2 is a control pulse that turns off the second switch circuit SW2 only during the transmission period T while turning on during the reception period R and continues to output the variable bias voltage b2 during the reception period R.

  In the transmission period T, the third on-pulse P3 turns on the third switch circuit SW3 for a predetermined time at the timing next to the first on-pulse P1 to output the driving lower voltage b3, which is output from the lower side of the driving pulse MP. This is a control pulse to be output as the pulse Pd.

  The transmission control signal 203S configured in this way is configured into 64 types of signals obtained by delaying the output timing of the first to third on pulses P1 to P3 by a predetermined time for each array element 211, for example, every 64 elements. Thus, each array element 211 can be electronically scanned in the scan direction in FIG. 3 by being given to each array element 211 from each transmission circuit 202.

  Next, the operation of the ultrasonic diagnostic imaging apparatus 1 according to this embodiment will be described.

  As shown in FIG. 6, from the bias generation circuit 204, the driving upper voltage b1, the variable bias voltage b2, and the driving lower voltage b3 shown in FIG. Are supplied to the voltage supply terminal side of the switch circuits SW1 to SW3.

  On the other hand, a transmission control signal 203S is given from the transmission control circuit 203 to the first to third switch circuits SW1 to SW3.

  For this reason, at the timing during the transmission period T, the first on-pulse signal P1 of the transmission control signal 203S is given to the first switch circuit SW1 and is turned on (active). Pu is output. Thereafter, the third on-pulse signal P3 is supplied to the third switch circuit SW3 and is turned on, so that the lower-order drive pulse Pd is output.

  On the other hand, during the reception period R, as shown in FIG. 7, a second on-pulse signal that is turned off only during the transmission period T and turned on during all other reception periods R is supplied to the second switch circuit SW2, and this is turned on. Therefore, during the reception period R, the variable bias voltage b2 having a time-varying waveform is output from the transmission circuit 202 as shown in FIG. The ON periods of these first to third switch circuits SW1 to SW3 are controlled so as not to overlap with each other, and so-called break before make is configured, and the plurality of switch circuits SW1 to SW3 are simultaneously turned on. Thus, an excessive current is prevented from flowing through the C · MUT element 211.

  From the transmission circuit 202, the transmission signal 202S having the waveform shown in FIG. 1 is applied to each C · MUT element 231.

  For this reason, during the transmission period T, a pair of conductive thin films 281 and 241 on the discharge surface side and the substrate side of the C / MUT element 231 are used as the driving pulse MP as the upper driving pulse Pu and the lower driving pulse Pd. Given in between.

  Thereby, the discharge surface side conductive thin film 281 is mechanically vibrated integrally with the non-conductive thin film 271. By repeating this transmission period T at a predetermined cycle (for example, 150 μsec), ultrasonic waves with a predetermined frequency are repeatedly output from the discharge surface side conductive thin film 271 at a predetermined cycle and transmitted to a subject (not shown).

  Further, during the reception period R, the variable bias voltage b 2 shown in FIGS. 1 and 5 is applied to the C · MUT element 231.

  The bias generation circuit 204 is used in common by each array element 211. Furthermore, the switch-on timing of the transmission control signal 203S is controlled independently, so that each array element 211 is electronically scanned in the scan direction by driving the C / MUT element 231 at a predetermined timing for each array element 211. can do.

  In this way, the ultrasonic wave transmitted into the subject is reflected at the boundary of different acoustic impedances within the subject during the reception period R, and is received by the C / MUT element 231 as a reflected wave (echo wave). Thus, stress is applied to the radiation surface side conductive thin film 281 and the non-conductive thin film 271 to be displaced.

  Also at this time, the variable bias voltage b2 is applied between the conductive thin films 281 and 241 on the radiation surface side and the substrate side, and an electromotive force is generated according to the displacement of the pair of conductive thin films 281 and 241. The electric signal is converted into an echo signal and input to the preamplifier 205.

  The echo signal is preamplified by the preamplifier 205 and input to the reception delay adding circuit 207 after the influence of the signal source impedance is reduced. In this reception delay adding circuit 207, the echo signal is partially delayed and added to be converted into a smaller number of echo signals than the number of elements of the array element 211, and then input to the reception scanning circuit 401 of the main unit 401 via the cable 300. Is done.

  The reception scanning circuit 401 performs beam forming by phasing and adding the echo signals, and in order to separately form reception directivities from a plurality of directions by a plurality of digital beam formers (not shown), a plurality of beam forming processes. To do.

  Therefore, an echo signal having directivity is generated, and this echo signal is given to the blood flow information detector 402 and the amplitude detector 403.

  The blood flow information detector 402 is a unit that realizes so-called color Doppler imaging (CDI). The blood flow information detector 402 extracts a Doppler signal that has undergone frequency shift from an echo signal. Further, only a specific frequency component is extracted from the Doppler signal using an MTI filter. And the frequency of the passed signal is obtained by an autocorrelator, and the average speed, dispersion, and power are calculated from the frequency by the calculation unit.

  It should be noted that by adjusting the pass band of the MTI filter, a general Doppler mode that mainly visualizes blood flow of a subject (image data in this mode is referred to as blood flow Doppler image data) and mainly myocardium. A tissue Doppler mode (image data in this mode is referred to as tissue Doppler image data) for imaging an organ such as the above can be appropriately switched. These image data are given to the data memory 404, respectively.

  On the other hand, the amplitude detector 403 detects the echo signal from the reception scanning circuit 401 and supplies it to the data memory 404 as image data.

  The data memory 404 stores the input image data. The data stored in the data memory 404 is read by the display processing unit 405 at the display timing of the display monitor 406, converted to an analog signal by a D / A converter (not shown), and then given to the display monitor 406, as an ultrasonic image. Is displayed.

  Therefore, according to the ultrasonic diagnostic imaging apparatus 1, the C · MUT element 231 is driven by the transmission signal 202S shown in FIG. 1, and the DC bias voltage applied to the C · MUT element 231 is applied during the transmission period T. Since it is reduced to the minimum, even when the amplitude of the drive pulse is increased in order to increase the sound pressure of the ultrasonic wave, it is integrated with the radiation surface side conductive thin film 281 of the C · MUT element 231 and this. It is possible to prevent the insulating thin film 271 from being damaged by hitting the other substrate-side conductive thin plate 241 with a large amplitude.

  In addition, since the bias voltage in the transmission period T is the lowest, the sound pressure of the ultrasonic waves can be increased by increasing the amplitude of the drive pulse MP.

  Further, the DC bias voltage applied to the C / MUT element 231 is higher during the reception period R than during the transmission period T as shown in FIG. The reception efficiency or reception sensitivity of the echo signal can be improved.

  That is, as shown by the characteristic curve A in FIG. 8, the relationship between the bias voltage and the reception efficiency of the echo signal is such that the reception efficiency increases exponentially as the bias voltage increases. For example, when the bias voltage is 80 V compared to 100 V, the reception amplitude decreases by −30% to 40%, and when the bias voltage is 40 V, the reception amplitude decreases by −70% to 80%. Decreases. That is, in the reception period R, since the bias voltage is set higher than that in the transmission period T, it is possible to improve reception efficiency or reception sensitivity.

  However, immediately after the transmission period T, that is, in the short distance reception period Rs, a strong reflected wave (echo wave) reflected from a shallow portion of the subject is received. The voltage is lower than the voltage during the reception period Re. Thereby, it is possible to prevent the reception sensitivity of the echo signal of the reflected wave from the shallow part of the subject received in the short distance reception period Rs from becoming too high and being saturated.

  On the other hand, since the bias voltage in the long-distance reception period Re is higher than the bias voltage in the short-distance reception period Rs, it is possible to increase reception efficiency or reception sensitivity in the long-distance reception period Re. That is, it is possible to improve the reception efficiency or the reception sensitivity of the ultrasonic wave reflected from the deep part of the subject received in the long-distance reception period Re.

  Therefore, it is possible to achieve both an increase in the sound pressure of the output ultrasonic wave and an improvement in reception efficiency or reception sensitivity of the reflected ultrasonic wave.

  Further, as shown in FIG. 5, the variable bias voltage b2 changes slowly immediately after the transmission period T, that is, from the short-distance reception period Rs to the long-distance reception period Re, and in the frequency spectrum diagram of FIG. Since the frequency component of the frequency band of the drive pulse MP indicated by the solid line C is not included as indicated by the broken line B, the C · MUT element 231 is driven during the reception period R, and unnecessary ultrasonic waves are output. It is possible to prevent an image from occurring.

  For example, in the case of the waveform of the transmission signal 203S shown in FIG. 9, the steep change in the waveform of the bias voltage is about 1 MHz, and includes only frequency components sufficiently separated from the frequency 3 MHz of the drive pulse MP. It is possible to prevent unnecessary output of ultrasonic waves that cause the multiple images.

  Further, as shown in FIG. 9, since the frequency spectrum of the waveform C of the transmission signal 203S is substantially flat in a region of approximately 1 MHz to 5 MHz and has a wide band, the SN ratio of the echo signal can be improved in a wide band.

  10 is a waveform diagram of about a half cycle of the transmission signal 202Sa according to the second embodiment of the present invention, FIG. 11 is a partial enlarged view of the transmission period T of the transmission signal 202Sa and its surroundings, and FIG. 12 is this transmission signal. FIG. 13 is a diagram showing the frequency characteristics of the ultrasonic wave Sa emitted from the C / MUT element 231 in response to the transmission signal 202Sa.

  As shown in FIG. 11, the transmission signal 202Sa includes two higher-order pulses Pu of the drive pulse MP compared to the transmission signal 202S shown in FIG. 1, and does not have the lower-order pulse signal Pd. Further, the potential Ve of the variable bias voltage b2a in the long-distance reception period Re immediately before the output of the high-order pulse Pu at the variable bias voltage b2 is higher than the potential Vs of the bias voltage in the short-distance reception period Rs immediately after transmission of the drive pulse MP. In the transmission period (T), the bias change and the drive pulse waveform are integrated so as to output the higher-order pulse Pu having a waveform that cancels the bias voltage Ve.

  The transmission signal 202Sa is, for example, 5 MHz, and the frequency distribution of the ultrasonic waveform output from the C / MUT element 231 driven thereby is approximately flat, for example, 3 MHz to 6 MHz as shown in FIG. Broadband ultrasonic transmission is possible.

  By the way, in the present invention, the variable bias voltage b2 is applied to an STC (Sensitive Time Control) knob, a transmission output (Gain) adjustment knob, and a transmission frequency selection knob of a console (not shown) provided in the main unit 400. You may comprise so that it may control in conjunction with each manual operation, and according to these, the dynamic range of the adjustment can be made small and power saving can be aimed at.

  FIG. 14 is a diagram showing an example of the waveform of the transmission signal 202Sb when the variable bias voltage b2b of the transmission signal 202Sb is controlled in conjunction with the adjustment operation of the STC knob.

  The transmission signal 202Sb is characterized in that the reception sensitivity at a short distance is lowered by lowering the bias voltage in the short distance reception period Rs as compared with the transmission signal 202S shown in FIG. For this reason, it is possible to prevent saturation of an echo signal based on a strong ultrasonic reflected wave reflected at a short distance portion of the subject.

  FIG. 15 is a diagram illustrating an example of a waveform of the transmission signal 202Sc when the variable bias voltage b2c of the transmission signal 202Sc is controlled in conjunction with the adjustment operation of the transmission output adjustment knob.

  The transmission signal 202Sc is characterized in that the amplitude of the transmission output is reduced and the bias b0 immediately after the output of the drive pulse MP is increased as compared with the transmission signal 202S shown in FIG. For this reason, it is possible to improve the reception efficiency or the reception sensitivity in the short distance reception period Rs.

  FIG. 16 is a diagram illustrating an example of a waveform of the transmission signal 202Sd when the variable bias voltage b2d of the transmission signal 202Sd is controlled in conjunction with the selection operation of the transmission frequency selection knob.

  This transmission signal 202Sd is characterized in that the rising of the bias voltage in the short-distance reception time Re is made steeper than the transmission signal 202S shown in FIG. 1 by controlling the frequency. For this reason, it is possible to sharply raise (improve) the reception efficiency or the reception sensitivity in the short distance reception period Re. For this reason, it is possible to receive echo waves that rapidly attenuate in the short-range reception period Rs with high sensitivity.

  In the above embodiment, the case where the bias generation circuit 204 is provided on the probe head 200 side has been described. However, the bias generation circuit 204 may be provided on the main device 400 side. Accordingly, the amount of heat generated on the probe head 200 side can be reduced by the amount of heat generated by the power loss of the bias generation circuit 204.

FIG. 3 is a voltage waveform diagram for almost one cycle of a transmission signal output from the transmission circuit shown in FIG. 2. 1 is a block diagram showing an overall configuration of an ultrasonic diagnostic imaging apparatus according to a first embodiment of the present invention. FIG. 3 is a partially cutaway plan view of the probe shown in FIG. 2. FIG. 4 is a longitudinal sectional view of the capacitively coupled ultrasonic transducer shown in FIG. 3. FIG. 3 is a voltage waveform diagram for almost one cycle of a bias component of a transmission signal shown in FIG. 1. FIG. 3 is a block diagram showing a configuration of a bias generation circuit and a transmission circuit shown in FIG. 2. FIG. 3 is a voltage waveform diagram for almost one cycle of a transmission control signal supplied from the transmission control circuit shown in FIG. 2 to the transmission circuit. The graph which shows the correlation between the bias voltage of a C * MUT element, and reception efficiency. The spectrum figure of the transmission signal shown in FIG. FIG. 6 is a voltage waveform diagram for almost one cycle of a transmission signal according to a second embodiment of the present invention. The elements on larger scale of the transmission period of FIG. 10, and its peripheral period. The spectrum figure of the transmission signal of FIG. The spectrum figure of the ultrasonic wave output from a C * MUT element based on the transmission signal of FIG. FIG. 6 is a voltage waveform diagram for almost one cycle of a transmission signal according to a third embodiment of the present invention. FIG. 10 is a voltage waveform diagram for almost one cycle of a transmission signal according to a fourth embodiment of the present invention. FIG. 10 is a voltage waveform diagram for almost one cycle of a transmission signal according to a fifth embodiment of the present invention. FIG. 6 is a voltage waveform diagram for almost one cycle of a conventional ultrasonic diagnostic imaging apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic imaging apparatus 200 Probe head 201 Probe 202 Transmission circuit 202S, 202Sa, 202Sb, 202Sc, 202Sd Transmission signal 203 Transmission control circuit 203S Transmission control signal 204 Bias generation circuit MP Drive pulse VP, b2 Variable bias voltage

Claims (9)

An ultrasonic wave is transmitted to the subject during the transmission period, while an ultrasound image is reconstructed based on the echo signal of the reflected ultrasonic wave received from the subject during the reception period and displayed on the display means. In the ultrasonic diagnostic imaging apparatus,
A thin film and a base are provided with an air gap therebetween, and a plurality of static waves are transmitted that transmit the ultrasonic wave by vibration of the thin film and convert the vibration of the thin film by reception of the reflected ultrasonic wave into an echo signal of an electric signal. A capacitively coupled ultrasonic transducer;
Long-distance reception for receiving an ultrasonic reflected wave reflected at a long-distance part from a short-distance reception period for receiving an ultrasonic reflected wave reflected at a short-distance part of the subject during the reception period of the ultrasonic reflected wave A control means for applying a variable bias voltage between the thin film and the substrate, the voltage of which gradually increases with time.
An ultrasonic diagnostic imaging apparatus comprising: The control means includes
A bias generation circuit for generating a pulse voltage applied to vibrate the thin film during the transmission period and the variable bias voltage applied during the reception period;
A transmission control means for outputting a transmission control signal for outputting the pulse voltage from the bias generation circuit during the transmission period, and outputting a transmission control signal for outputting the variable bias voltage from the bias generation circuit during the reception period;
A transmission circuit for selectively applying the pulse voltage and the variable bias voltage between the thin film and the substrate in response to the transmission control signal from the transmission control means for outputting the transmission control signal;
The ultrasonic diagnostic imaging apparatus according to claim 1, further comprising: The transmission control means includes means for outputting the transmission control signal so that the variable bias voltage applied during the reception period does not include a frequency component of the pulse voltage. Item 3. The ultrasonic diagnostic imaging apparatus according to Item 2. A plurality of the capacitively coupled ultrasonic transducers are arranged in a row on the substrate to form an array element, and a plurality of the array elements are arranged in parallel in the scanning direction to form a two-dimensional array. The ultrasonic diagnostic imaging apparatus according to claim 1, wherein the ultrasonic diagnostic imaging apparatus is configured as an array element. The bias generation circuit is electrically connected to all the array elements;
The transmission circuit is electrically connected to each of the array elements,
5. The ultrasonic diagnostic imaging apparatus according to claim 4, wherein the transmission circuit control means includes means for outputting a transmission control signal for electronically scanning the array element in the scanning direction.   The transmission control means includes means for controlling the variable bias voltage in response to a manual operation of a gain operating tool of an operation console for controlling a gain of an amplifier for amplifying the echo signal. The ultrasonic diagnostic imaging apparatus according to any one of 2 to 5. 7. The transmission control means comprises means for controlling the variable bias voltage in accordance with a manual operation of a frequency operation tool of an operation console for controlling a transmission frequency of the pulse voltage. The ultrasonic diagnostic imaging apparatus according to any one of the above. An ultrasonic wave is transmitted to the subject during the transmission period, while an ultrasound image is reconstructed based on the echo signal of the reflected ultrasonic wave received from the subject during the reception period and displayed on the display means. In the ultrasonic diagnostic imaging apparatus,
Capacitance in which a thin film and a base are provided with an air gap therebetween, and the ultrasonic wave is transmitted by vibration of the thin film, while the vibration of the thin film due to reception of the reflected ultrasonic wave is received as an echo signal of an electric signal. A combined ultrasonic transducer;
In the reception period, a bias voltage is applied between the thin film and the base so as to tension the thin film, and in the transmission period, the thin film and the base are generated so as to vibrate the thin film and generate ultrasonic waves. Control means for applying a pulse voltage between them and applying a bias voltage smaller than the bias voltage in the reception period;
An ultrasonic diagnostic apparatus comprising: An ultrasonic wave is transmitted to the subject during the transmission period, while an ultrasound image is reconstructed based on the echo signal of the reflected ultrasonic wave received from the subject during the reception period and displayed on the display means. In the ultrasonic diagnostic imaging apparatus,
Capacitance in which a thin film and a base are provided with an air gap therebetween, and the ultrasonic wave is transmitted by vibration of the thin film, while the vibration of the thin film due to reception of the reflected ultrasonic wave is received as an echo signal of an electric signal. A combined ultrasonic transducer;
In the reception period, a bias voltage is applied between the thin film and the base so as to tension the thin film, and in the transmission period, a pulse voltage having a waveform that cancels the bias voltage is applied between the thin film and the base. Control means to be applied to,
An ultrasonic diagnostic apparatus comprising:

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