An ultrasonic imaging apparatus

Abstract: In an ultrasonic imaging apparatus for obtaining a tomogram image of an object to be diagnosed on a monitor, the apparatus includes electroacoustic transducers, a phasing unit, a phase detection unit, and an adding unit: electroacoustic transducers are provided in a line along with a surface of the object, emitting ultrasonic waves to the object, detecting the ultrasonic waves reflected therefrom, and converting them to electric signals as detection signals; a phasing unit is connected to the electroacoustic transducers for receiving the detection signals, delaying them in accordance with distance between the electroacoustic transducers and the object, and phasing them to match the phase of detection signals; a phase detection unit is connected to the electroacoustic transducers and the phasing unit for detecting the error of phase contained in the detection signals output from the electroacoustic transducers or the phasing unit and correcting the amount of delay previously set in the phase unit in accordance with the error of phase, the phase detection unit further comprising first and second binary units for binalizing the detection signals to detect the error of phase contained in the detection signals; and an adding unit is connected to the phasing unit to accumulate the detection signals phased by the phasing unit.

Description: The present invention relates to an ultrasonic imaging apparatus for obtaining a tomogram image of an object by using ultrasonic waves. The present invention is used mainly as a medical instrument for diagnosis. Recently, an ultrasonic imaging apparatus is widely used as a medical instrument for obtaining a tomogram image of an object, for example internal organs of a human body. Basically, the ultrasonic image apparatus has a plurality of electroacoustic transducers aligned along the surface of the object. The electroacoustic transducers emit ultrasonic waves to the object and detect the ultrasonic waves reflected therefrom. The detected ultrasonic waves are added to each other after a phasing process (i.e., matching all phases of detection signal) in accordance with a predetermined delay process for ultrasonic waves to obtain the phased detection signal, i.e., strengthened detection signal. After the above processes, it is possible to obtain an image signal focused to one particular point in the object. When electrically scanning the electroacoustic transducers, the focused point is straightly scanned so that it is possible to obtain the tomogram image of the object. Further, when controlling the time difference (below, the amount of delay), the focused point is curvedly scanned so that it is possible to obtain the tomogram image of the object. In this case, a propagation speed of the ultrasonic wave is slightly different within the object caused by the medium forming the object. That is, the propagation speed for the adipose tissue is different from that of the muscle tissue. Accordingly, the delay process is very important for adjusting the different propagation speed of the ultrasonic waves to obtain the clear tomogram image of the object. That is, when the propagation speed is not uniform within the object, it is impossible to obtain the clear tomogram image of the object. Accordingly, it is necessary to provide the means for preventing the deterioration of the tomogram image caused by non-uniformity of the propagation speed of the ultrasonic waves within the object. EP-A-256481 discloses a method of ultrasound imaging in which the delay times of signals from ultrasound transducers are adjusted to adapt to inhomogeneities in the sample. The correction values for the delay time are obtained in an adaption phase before the imaging. The object of the present invention is to provide an ultrasonic imaging apparatus enabling the prevention of deterioration of the tomogram image caused by non-uniformity of the propagation speed within the object and enabling a high precision tomogram image. In accordance with the present invention, there is provided an ultrasonic imaging apparatus for obtaining a tomogram image of an object to be diagnosed on a monitor, including: electroacoustic transducers provided in a line along a surface of the object, for emitting ultrasonic waves to the object, detecting the ultrasonic waves reflected therefrom, and converting them to electric signals as detection signals; a phasing unit operatively connected to the electroacoustic transducers for receiving the detection signals, delaying them in accordance with the distance between the electroacoustic transducers and the object, and phasing them to match the phase of detection signals; phase detection means operatively connected to the electroacoustic transducers and the phasing means for detecting the error of phase contained in the detection signals output from the electroacoustic transducers or phasing means and correcting the amount of delay previously set in the phasing means in accordance with the error of phase; the phase detection means further comprising first and second binary units for binarizing the detection signals to detect the error of phase contained in the detection signals; and adding means operatively connected to the phasing means to accumulate the detection signals phased by the phasing means. In the preferred embodiment, the phase detection unit further includes first and second shift registers connected to the corresponding binary units for sequentially latching and shifting the binary signals, the first shift register having more latch units than the second shift register, and an error detection unit for detecting mutual-relation values for binary signals from the first and second shift registers, and further detecting error of phase of the detection signals input to the first and second binary units so that errors of phases for all detection signals are detected by accumulating the error of phase. In another preferred embodiment, the phase detection unit further includes an input delay unit connected to the second binary unit for delaying the binary signals and outputting the delayed binary signals to the second shift register to correct the error of the phase detected by the error detection unit in accordance with the amount of delay at the input delay unit. In still another preferred embodiment, the error detection unit includes adder units and a decision unit; the former are provided for the same number as latch units of the second shift register to receive both latch signals from the first and second shift registers, and to accumulate the latch signals when both latch signals indicate the same level; the latter receives the accumulated latch signals and determines the maximum value from the accumulated latch signals. In still another preferred embodiment, the apparatus further includes a signal generating unit operatively connected to the phase detection unit for generating and supplying a reference signal to one of two binary units. In another example of the present invention, the ultrasonic imaging apparatus further includes a reference signal generating unit operatively connected to the phase detection unit for generating a reference signal; and one binary unit inputs the detection signal and the other binary unit inputs the reference signal having the same frequency as that of the detection signal; a multiplication unit is operatively connected to the first and second binary units for multiplying both binary signals from the first and second binary units; and a detection unit is operatively connected to the multiplication unit for extracting direct current components contained in the binary signal multiplied by the multiplication unit to detect the error of phase of the detection signals input to two binary units. Further, in the preferred embodiment, the first and second binary units set a threshold value for binarizing the detection signals to approximately the peak of the thermal noise level of the electroacoustic transducer. In this case, preferably, the first and second binary units output logic 1" when the detection signal is higher than the thermal noise level, and output logic "0" when the detection signal is equal to lower than the thermal noise level. BRIEF DESCRIPTION OF THE DRAWINGS In this drawing: Fig. 1 is a schematic block diagram of a conventional ultrasonic imaging apparatus; Fig. 2 is a schematic block diagram of a conventional coarse delay line shown in Fig. 1; Fig. 3 is a view for explaining amount of delay; Fig. 4 is a schematic sectional view of an object; Fig. 5 is a schematic block diagram of another conventional ultrasonic imaging apparatus; Fig. 6 is a detailed block diagram of a phase detection circuit shown in Fig. 5; Fig. 7 and 8 are graphs for explaining a mutual-relation value determined by the phase detection circuit shown in Fig. 6; Fig. 9 is a schematic block diagram of an ultrasonic imaging apparatus according to the present invention; Fig. 10 is a schematic block diagram of an ultrasonic imaging apparatus according to another aspect of the present invention; Fig. 11 is a schematic block diagram of an ultrasonic imaging apparatus according to one embodiment of the present invention; Fig. 12 is a detailed circuit of the phase detection unit shown in Fig. 11; Fig. 13 is a graph for explaining the effect of the present invention; Fig. 14 is a detailed circuit block of the phase detection circuit according to another embodiment of the present invention; Fig. 15 is a schematic block diagram of an ultrasonic imaging apparatus according to another embodiment of the present invention; Fig. 16 is a schematic block diagram of an ultrasonic imaging apparatus according to still another embodiment of the present invention; Fig. 17A is a view for explaining detection signals, thermal noise, and a threshold level at zero volt of the detection signal; Fig. 17B is a view for explaining binary signals for the detection signals and the thermal noise shown in Fig. 17A; Fig. 18A is a view for explaining detection signals, thermal noise, and a threshold level according to the present invention; Fig. 18B is a view for explaining binary signals for the detection signals and the thermal noise shown in Fig. 18A; Fig. 19A is a view for explaining the thermal noise shown in Fig. 17A; and Fig. 19B is a view for explaining the thermal noise shown in Fig. 18A. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the preferred embodiments, an explanation will be given of a conventional ultrasonic imaging apparatus. Figure 1 is a schematic block diagram of a conventional ultrasonic imaging apparatus. This ultrasonic imaging apparatus is known in the documents, for example, (1) Japanese Unexamined Patent Publication (KOKAI) No. 53-28989, and (2) Japanese Unexamined Patent Publication (KOKAI) No. 54-96286. The former application corresponds to U.S. Application (718721) by Richard D. Belling, filed on August 30, 1976, and the latter corresponds to U.S. Application (862454) by Samual H. Masrak, filed on December 20, 1977. In Fig. 1, reference numbers 1-1 to 1-n denote electroacoustic transducers, 2 a transmission circuit, 3-1 to 3-n pre-amplifiers, 4-1 to 4-n fine delay lines, 5-1 to 5-n coarse delay lines, 6 an adder, 7 a read only memory (ROM), and 8 a control circuit. The electroacoustic transducers 1-1 to 1-n are provided in a line (aligned) along the surface of the object, and the electroacoustic transducers 1-1 to 1-n emit the ultrasonic waves to the object and detect the ultrasonic waves reflected from the object (below, detection signal). The transmission circuit 2 generates electric pulses parallel to the electroacoustic transducers 1-1 to 1-n to control the emission of the ultrasonic waves. The pre-emplifiers 3-1 to 3-n amplify the detection signal from the electroacoustic transducers 1-1 to 1-n. The fine delay lines 4-1 to 4-n are formed by LC (inductor and capacitor) circuits for delaying the detection signal from the pre-amplifier based on an adjustable amount of delay. The coarse delay lines 5-1 to 5-n are also formed by LC circuits for obtaining a fixed amount of delay. By these delay lines, the detection signals are phased. The adder 6 adds all output from the coarse delay lines 5-1 to 5-n to obtain the tomogram of the object. The ROM 7 stores data of the fine and coarse amount of the delay previously determined in accordance with the difference of the distance between each electroacoustic transducer and the focused point. The amount of delay is shown by the formula (1) explained hereinafter. The control circuit 8 determines the fine delay amount and the coarse delay amount in accordance with the data stored in the ROM 7. Figure 2 is a schematic block diagram of a conventional coarse delay line shown in Fig. 1. The coarse delay line is formed by fixed delay lines DL-1 to DL-n each having taps T-1 to T-n connected to the fine delay lines 4-1 to 4-n to simultaneously perform the delay and adding operation. In this case, each of delay lines DL-1 to DL-n has the same amount of the delay Δt so that all amount of the delay Ti of the fixed delay line can be expressed by the formula (2) as explained hereinafter. Since all amounts of delay are accumulated by these delay lines dl-1 to dl-n, it is possible to delete the adder 6 shown in Fig. 1. Figure 3 is a view explaining the amount of delay. 1-1 to 1-n denote electroacoustic transducers, 1-c denotes a center transducer and 1-i denotes the transducer away from the center transducer 1-c by distance Xi. "P" denotes a point focused by emission of all transducers 1-1 to 1-n and this focused point is located by distance L from the center transducer 1-c. In this case, the amount of delay τi at the transducer 1-i is given as the following formula. τi = τ0 + ( L 2 + Xi 2 - L)/C Where C denotes a speed of ultrasonic waves, and τ0 denotes a constant value, the value τi of which becomes positive. Accordingly, the detection signal from the electroacoustic transducer 1-i is phased by the amount of delay τi. Similarly, all detection signals are phased by the corresponding amount, and after a phasing process by the delay lines, all phased detection signals are added by the adder 6. As is obvious from the formula (1), since the distance between the electroacoustic transducer 1-i and the focused point P is longer than the distance between the electroacoustic transducer 1-c and the focused point P, the amount of the delay of the transducer 1-i is set to a value smaller than that of the transducer 1-c. As explained above, when electrically scanning the electroacoustic transducers, the focused point is straightly scanned so that it is possible to obtain the tomogram of the object. When controlling the amount of delay, the focused point is curvedly scanned so that it is possible to obtain the tomogram of the object. Further, the amount of delay Ti at each coarse delay line 5-1 to 5-n is expressed by the following formula. Ti = int (τi/Δτ) × Δτ Where, Δτ is a fixed delay amount for unit length of the coarse delay line (so-called quantumaized error), and "int" is a positive integer. The amount of delay "ti" at each fine delay line 4-1 to 4-n is expressed by the following formula. ti = τi - Ti The amount of delay previously determined by the above formula (2) and (3) is stored in the memory (ROM) 7. The control circuit 8 reads the amount of delay from the memory to control the fine and coarse delay line. Figure 4 is a schematic sectional view of an object, for example, a human body. The electroacoustic transducers 1-1 to 1-n are aligned on the surface of the human body to diagnose the internal organ, for example, a liver. Of course, the adipose tissue and the muscle tissue exist between the transducer and the liver. In this case, the propagation speed of the ultrasonic waves for the adipose tissue is different from that of the muscle tissue. In general, the propagation speed in the muscle and liver tissues is 1570 per second, and the propagation speed in the adipose tissue is 1480 per second. As is obvious, the former is faster than the latter within the human body. Further, as shown in the drawing, each tissue has a different thickness. Accordingly, this is the reason for nonuniformity of the propagation speed within the object so that it is very difficult to obtain a clear and precise tomogram image of the object. Figure 5 is a shematic block diagram of another conventional ultrasonic imaging apparatus. This apparatus is superior to the structure shown in Fig. 1 in solving the above explained problem. The reference numbers used in Fig. 1 are attached to the same components in this drawing. In Fig. 5, reference number 9 denotes a phase detection circuit. The phase detection circuit 9 is added to the structure shown in Fig. 1, and detects the phase of the detection signal of each electroacoustic transducer 1-1 to 1-n and supplies resultant data to the control circuit 8 to adjust the amount of delay. Some phase detection circuits are known in the documents, for example, "U.S.P 4,817,614", "U.S.P 4,471,785", and "U.S.P 4,484,477". The phase detection shown in the documents is explained in detail hereinafter. Figure 6 is a detailed block diagram of the phase detection circuit shown in Fig. 5. In Fig. 6, reference number 10 denotes a wave memory, 11 a mutual-relation unit, 12 a difference detection unit, and 13 an integration unit. The wave memory 10 temporarily stores the detection signal from the pre-amplifier 3-1 to 3-n. The mutual-relation unit 11 calculates a mutual-relation value by selecting the detection signals of two adjacent electroacoustic transducers from the wave memory 10. The difference detection unit 12 detects the maximum time difference of the mutual-relation value calculated by the mutual-relation unit-11. The integration unit 13 integrates the time difference detected by the difference detection unit 12, deternimes the amount of delay for all detection signals, and informs the control circuit 8 of the amount of delay. In this case, if the wave memory 10 is formed by a digital memory, it is necessary to provide on analog-to-digital converter. Further, if the wave memory is formed by an analog memory, it is necessary to provide a sample-holding circuit. However, these circuits are omitted to simplify the explanation. Figures 7 and 8 are graphs explaining the mutual-relation value deternimed by the phase detection circuit shown in Fig. 6. In these drawings, u 1 (t) and u 2 (t) denote the detection signals from the two adjacent electroacoustic transducers, Δt denotes a sampling time interval, Q(τ) denotes the mutual-relation value, and τm denotes the maximum value of the mutual-relation value. The mutual-relation value Q(τ) is expressed by the following formula. Where, t1 to t2 denotes calculation time. Based on the above formula, the mutual-relation unit 11 calculates the mutual-relation value Q(τi) at each time difference (i.e., amount of delay) τi, the difference detection unit 12 detects the maximum time difference of the mutual-relation value τm. Further, the integration unit 13 integrates the time difference, determines the amount of delay for all detection signals, and informs the control circuit 8. As another known document, "U.S.P 4,835,689" discloses a method for correcting the deterioration of the image caused by nonuniformity of the propagation speed within the object by using a quadrature modulation. Further, "Phase-Aberration Correction Using Signals From Point Reflectora and Diffuse Scatterres" by S.W. Flax and M. O'Donnel, IEEE Vol. 35, No. 6, November 1988, PP 758-767. This document discloses an error of ultrasonic waves emitted from the electroacoustic transducer. There are, however, some problems in the above conventional ultrasonic imaging apparatus shown in Fig. 5. As explained above, the phase detection circuit 9 performs a calculation of the mutual-relation value of the detection signal to determine the amount of delay that prevents deterioration of the tomogram image caused by nonuniformity of the propagation speed within the object. As shown in Fig. 8, however, since the mutual-relation value is calculated from the time sampling interval Δt of the detection signal, the amount of delay determined by the phase detection circuit 9 includes an error contained in the time sampling interval Δt. That is, since the amount of delay depends on the sampling time interval Δt, the error in the sampling time interval Δt is included in the amount of delay determined by the phase detection circuit 9. Further, each error is accumulated when the integration unit 12 determines the amount of delay for all-detection signals so that it is very difficult to determine a precise amount of delay of the detection signal from the electroacoustic transducers 1-1 to 1-n. The above document of "S.W. Flax and M. O'Donnel" discloses the very high sampling frequency to solve the above problem. That is, in general, when the frequency of the ultrasonic waves is 3.5 MHz, the sampling time interval Δt is set to 20 MHz. However, in "S.W. Flax and M. O'Donnel", the sampling time interval Δt is set to a very high frequency, for example, 100 MHz to prevent the error accumulated in the sampling time interval. However, as is obvious, the higher the sampling frequency, the more sampling data. Accordingly, it is necessary to provide a very large and complex phase detection circuit to process bulky sampling data. Further, although the phase detection circuit performs a calculation of the mutual-relation for the detection signal to determine the amount of delay of the detection signal and prevent deterioration of the tomogram caused by nonuniformity of the propagation speed, this calculation of the mutual-relation needs many multiplications of the floating decimal point in both analog and digital signals. That is, the above convetional art requires bulky hardware, particularly, a very large and complex phase detection circuit. Therefore, the object of the present invention is to provide an ultrasonic imaging appratus that can prevent the deterioration of the tomogram image caused by nonuniformity of the propagation speed within the object and can achieve a high precision tomogram image with the ultrasonic imaging apparatus having a very simplified structure. Figure 9 is a schematic block diagram of a ultrasonic imaging apparatus according to one aspect of the present invention. Briefly, the feature of the present invention lies in the use of binary signals in the phase detection circuit. In Fig. 9, reference number 30 denotes an ultrasonic detector formed by a plurality of electroacoustic transducers 31-1 to 31-n, and 40 a body of a ultrasonic imaging apparatus. The electroacoustic transducers 31-1 to 31-n are provided in a line (aligned) along the object to be diagnosed. The electroacoustic transducers 1-1 to 1-n emit the ultrasonic waves to the object, detect them reflected therefrom, and convert them to electric signals as the detection signal. The body 40 is formed by a transmission unit 41, phasing units 42-1 to 42-n, a storage unit 43, a reference signal generating unit 44, a phase detection unit 45, an adder 46, a display signal generating unit 47, a display unit 48, and a control unit 49. The phase detection unit 45 further comprises a binary circuit 450, shift register 451, input delay circuit 452 and an error detection circuit 453. The transmission unit 41 supplies electric pulses parallel to the electroacoustic transducers 31-1 to 31-n to control the emission of the ultrasonic waves. That is, the electroacoustic transducers 31-1 to 31-n emit ultrasonic wavaes to the object in time with the eletric pulses. Each phasing unit 42-1 to 42-n performs the phasing process by delaying the detection signal from the corresponding electroacoustic transducer in accordance with the distance between the electrtoacoustic transducer and the object. The storage unit 43 stores the amount of delay previously determined based on the distancd between two adjacent electroacoustic transducers and the object. The reference signal generating unit 44 generates the reference signal having the same frequency as the detection signal. The phase detection unit 45 detects the error of the phase of the detection signal caused by nonuniformity of the detection signal. The adder 46 adds all detection signals phased by the phasing units 42-1 to 42-n. The display signal generating unit 47 generates the display signal after converting the brightness of the signals added by the adder 47. The display uint 48 displays the tomogram image of the object. Further, the control unit 49 controls all operations in above units 41, 43, 44, and 45. In the phase detection unit 45, the binary circuit 450 binarizes the detection signals from two adjacent electroacoustic transducers to detect an error of the detection signal caused by nonuniformity of the propagation speed. In this case, the reference signal from the reference signal generating unit 44 may be used instead of one of two detection signals. The shift register 451 sequentially shifts and latches a binary signal from the binary circuit 450. As shown in the drawing, a pair of binary circuits 450 and a pair of shift registers 451 are provided for the shifting and latching operation. One binary circuit 450 is directly connected to one shift register 451 and the other binary circuit 450 is connected to the other shift register 451 through the input delay circuit 452, which delays the binary signal. The error detection circuit 453 detects the error of the phase of the detection signal by obtaining the mutual-relation value of the binary signal shifted by the shift register 451. Further, although the shift register 451 delays the binary signal in one direction, the input delay circuit 452 is provided for detecting an error having an inverted phase. The error detection circuit 453 corresponds to the number of the latch of the shift register 451, and inputs one latch signal from one shift register 451 and the other latch signal is delayed by the input delay circuit 452. Accordingly, the error detection circuit 453 may be formed by an adding means and a decision means. The former increases the added values accumulated thereby when these latch signals indicate the same signal level, and the latter detects the maximum added value therein. In one aspect of the present invention, briefly, the binary circuit 450 binarizes two adjacent detection signals, the shift register 451 shifts two detection signals binarized by the binary circuit 450 in accordance with different delay times and the error detection circuit 453 calculates the mutual-relation value between two adjacent binarized detection signals. Further, the error detection circuit 453 determines the maximum mutual-relation value τm among the mutual-relation values. In this case, when using the detection signals from the electroacoustic transducers 31-1 to 31-n, the error detection circuit 453 detects the amount of delay of the phase caused by nonuniformity of the propagation speed by calculating the difference value between the amount of delay of the electroacoustic transducers and the amount of delay already set in the phasing units 42-1 to 42-n. Meanwhile, when using the detection signals from the phasing units 42-1 to 42-n, the error detection circuit 453 detects the amount of delay of the phase caused by nonuniformity of the propagation speed, and the control unit 49 corrects the amount of delay already set to the phasing unit 42-1 to 42-n in accordance with the amount of delay of the phase. Further, when the binary circuit 450 binarizes the reference signal from the reference signal generating unit 44, the error detection circuit 453 can determine the amount of delay for all detection signals without a calculation of accumulation for the amount of delay, since the common amount of delay is detected thereby. Accordingly, in one aspect of the present invention, since the mutual-relation values are calculated in accordance with the binary signals so that the amount of delay is determined at the phasing unit 42-1 to 42-n, it is possible to simplify the circuit arrangement of the phase detection circuit. As a result, it is possible to prevent deterioration of the tomogram image caused by nonuniformity of the propagation speed of ultrasonic waves within the object. Figure 10 is a schematic block diagram of an ultrasonic imaging apparatus according to another aspect of the present invention. The reference numbers used in Fig. 9 are attached to the same components in this drawings. In Fig. 10, the phase detection unit 45 comprises the binary circuits 450-1 and 450-2, a multiplication circuit 454 and a detection circuit 455. The multiplication circuit 454 multiplies both binary signals from the binary circuits 450-1 and 450-2. The detection circuit 455 detects the error of the phase of the detection signal by extracting the direct current components from the output of the multiplication circuit 454. In another aspect of the present invention, briefly, the binary circuit 450 binarizes two adjacent detection signals, the multiplication circuit 454 multiplies two detection signals binarized by the binary circuit 450, and generates two signal components, i.e., one signal component having double the frequency of the detection signal and the other signal component including the phase difference between two detection signals. The amplitude level corresponding to the binary signal can be clearly determined by two signal components. The detection circuit 455 receives two signal components and extracts the direct current component of the output signal from the multiplication circuit 454 so that the detection circuit 455 determines the difference of the amount of delay between two adjacent detection signals. In this case, when using the detection signals from the electroacoustic transducers 31-1 to 31-n, the detection circuit 455 detects the amount of delay of the phase caused by nonuniformity of the propagation speed by calculating the difference value between the amount of delay of the electroacoustic transducers and the amount of delay already set in the phasing units 42-1 to 42-n. Meanwhile, when using the detection signals from the phasing units 42-1 to 42-n, the detection circuit 455 detects the amount of delay of the phase caused by non-uniformity of the propagation speed, and the control unit 49 corrects the amount of delay already set to the phasing unit 42-1 to 42-n in accordance with the amount of delay of the phase. Further, when the binary circuit 450 binarizes the reference signal from the reference signal generating unit 44, the detection circuit 455 can determine the amount of delay for all detection signals without a calculation of accumulation for the amount of delay since the common amount of delay is detected thereby. Accordingly, in another aspect of the present invention, since the amount of delay of the detection signal is in accordance with the binary signals so that the amount of delay is determined at the phasing unit 42-1 to 42-n, it is possible to reduce the circuit arrangement of the phase detection circuit. As a result, it is possible to prevent deterioration of the tomogram image caused by nonuniformity of the propagation speed of ultrasonic waves within the object. Figure 11 is a schematic block diagram of an ultrasonic imaging apparatus according to one embodiment of the present invention. The reference numbers used in Fig. 1 are attached to the same components in this drawing. As shown in the drawing, "n-1" phase detection circuits 9-1 to 9-(n-1) are provided in this embodiment. That is, number of the phase detection circuits is equal to number of electroacoustic transducers minus one. The phase detection circuit 9-1 inputs both outputs of the pre-amplifiers 3-1 and 3-2. The phase detection circuit 9-2 inputs both outputs of the pre-amplifiers 3-2 and 3-3, and the phase detection circuit 9-(n-1) inputs both outputs of the pre-amplifiers 3-(n-1) and 3-n. That is, the phase detection circuit inputs two outputs of the adjacent pre-amplifiers and detects the amount of delay between detection signals output from two adjacent pre-amplifiers. The control circuit 8 receives the amount of delay parallel to the phase detection circuits 9-1 to 9-(n-1), detects the error of amount of delay caused by nonuniformity of the propagation speed, and corrects the deterioration of the tomogram image of the object. Figure 12 is a detailed circuit of the phase detection unit 9-i shown in Fig. 11. In Fig. 12, reference numbers 90-1 and 90-2 denote first and second binary circuits, 91 an input delay circuit, 92-1 and 92-2 first and second shift registers, 93-j (j=1 to p) an exclusive OR circuit (EOR), 94-j a register circuit, 95-j an adder circuit, 96-j a latch circuit, and 97 a delay detection circuit. The first and second binary circuits 90-1 and 90-2 binarize two detection signals input from the electroacoustic transducers 31-1 to 31-n or the phasing 42-1 to 42-n. The input delay circuit 91 is connected to the second binary circuit 90-2 and delays a binary signal from the second binary circuit 90-2. The first shift register 92-1 inputs the binary signal from the first binary circuit 90-1 and sequentially latches and shifts the binary signal. The second shift register 92-2 inputs the binary signal delayed by the input delay circuit 91 and sequentially latches and shifts the binary signal. In this case, the latch circuits of the second shift register 92-2 is alternately provided for the first shift register 92-1. The exclusive OR (EOR) circuit 93-j performs the exclusive OR operation between the binary signal from the first shift register 92-1 and the binary signal from the second shift register 92-2. The register circuit 94-j receives the output of the EOR circuit 93-j. The register circuit 94-j always sets the logic "1" for the least significant bit thereof. Further, the register circuit 94-j sets the logic "0" for other bits when the EOR circuit 93-j outputs the logic "1" and sets the logic "1" for other bits when the EOR circuit 93-j outputs the logic "1". The adder circuit 95-j receives the output of the register circuit 94-j and calculates accumulation values based on the output of the register 94-j. The latch circuit 96-j feedbacks the resultant value of the adder circuit 95-j to obtain the accumulation value in the adder circuit 95-j. The delay detection circuit 97 detects the amount of delay of two detection circuits by determining the latch circuit 96-j that holds the maximum value accumulated by the adder circuit 95-j. In this case, the number of the latch circuits for the first and second shift registers 92-1 and 92-2 and the number of bits for the register circuit 94-j are determined based on the calculation interval of the mutual-relation. The operation of the phase detection circuit 9-j is explained in detail hereinafter. The binary circuits 90-1 and 90-2 receive the detection signals output from two adjacent pre-amplifiers 3-j and 3-(i-1), and binarize each detection signal. The input delay circuit 91 adjust the binary signal from the second binary circuit (below, second binary signal) 90-2 to delay the binary signal from the first binary circuit (below, first binary signal) 90-1. Further, the first binary signal is delayed from the second binary signal since the latch circuits of the second shift register 92-2 is alternately provided for that of the first shift register 92-1. The EOR circuit 93-j outputs logic "0" when two signals from the first and second shift registers 92-1 and 92-2 indicate the same level, and outputs logic "1" when two signals from the first and second shift registers 92-1 and 92-2 indicate different values. The register circuit 94-j sets the bits "000---01", i.e., the bit "1" therein when the EOR circuit 93-j outputs logic "0", and sets the bits "111---11", i.e., the bit "1" therein when the EOR circuit 93-j outputs logic "1". The adder circuit 95-j adds the value set in the register circuit 94-j to the accumulated value latched in the latch circuit 96-j. The delay detection circuit 97 determines the latch circuit 96-j holding the maximum value and corrects the amount of delay for the input delay circuit 91 by using the maximum value determined by the latch circuit 96-j. Further, the delay detection circuit 97 informs the control unit 8 of the corrected amount of delay. When the control unit 8 receives the corrected delay, the control unit 8 sets the amount of delay to the fine delay lines 4-1 to 4-n. That is, the control unit 8 accumulates the amount of delay from the delay detection circuit 97 to determine the amount of delay for all detection signals. Further, the control unit 8 detects the error of phase caused by nonuniformity of the propagation speed within the object by calculating the difference between the above amount of delay and the amount of delay defined by the formula (1), and corrects the amount of delay already set in the fine delay lines 4-1 to 4-n by the corrected amount of delay corrected. Accordingly, in another aspect of the present invention, since the phase detection unit 9-i calculates the mutual-relation value by using the binarized detection signals and determines the amount of delay for the detection signal, it is possible to simplify the circuit arrangement of the phase detection circuit. Figure 13 is a graph explaining the effect of the present invention. This graph compares the actual measurement value for the present invention with that of the conventional art. The ordinate denotes the amount of delay (nano-second ns) to be corrected, and the abscissa denotes number of the electroacoustic transducers. The solid line denotes the actual measurement value of the amount of delay of the conventional art based on the analog calculation, and the dotted line denotes the actual measurement value of the amount of delay of the present invention based on the binary calculation. As is obvious from the graph, the dotted line is very close to the solid line so that there is no difference between the analog calculation and the binary calculation. Figure 14 is a detailed circuit block of the phase detection circuit according to another embodiment of the present invention. In Fig. 13, reference numbers 100-1 and 100-2 denote first and second binary circuits, 101 a multiplication circuit, 102 a low-pass filter, 103 a average value calculation circuit, and 104 a delay detection circuit. The first and second binary circuits 100-1 and 100-2 binalize two detection signals. The multiplication circuit 101 multiplies the first binary signal by the second binary signal. The low-pass filter 102 extracts the direct current component in the values multiplied by the multiplication circuit 101. The average value calculation circuit 103 levels the signals output from the low-pass filter 102. The delay detection circuit 104 detects the amount of delay for two detection signals in accordance with the sinal output from the average value calculation circuit 103. In this case, although the binary signals obtained by the binary circuits 100-1 and 100-2 are provided by square waves, the sine waves are used for this calculation instead of the square waves to simplify the explanation. The multiplication circuit 101 performs the following calculation. sin (ωτ + ) × sinωτ = -1/2 [cos(2ωτ + ) - cosωτ] Where, the first binary signal is "sin ωτ", and the second binary signal is "sin (ωτ + )". The low-pass filter 102 extracts the direct current component "cos /2". The delay detection circuit 104 obtains the phase difference "" between two detection signals from the direct current component calculated by the average value calculation circuit 103, and converts the phase difference "" into the amount of delay. Further, the delay detection circuit 104 informs the resultant data of the amount of delay to the control unit 8. The control unit 8 detects the error of the phase caused by non-uniformity of the propagation speed and corrects the amount of delay already set in the fine delay lines 4-1 to 4-n to the detected amount of delay. Figure 15 is a schematic block diagram of an ultrasonic imaging apparatus according to another embodiment of the present invention. The same reference numbers as used in Fig. 11 are attached to the same components in this drawing. In this embodiment, the number of phase detection circuits 9-1 to 9-n is equal to that of the pre-amplifiers 3-1 to 3-n. Further, a reference signal generating unit 20 is added to the circuit shown in Fig. 11. The reference signal generating circuit 20 generates the reference signal having the same frequency as that of the detection signal from the electroacoustic transducers 1-1 to 1-n, and outputs the reference signal parallel to each phase detection circuit 9-i. Accordingly, each phase detection circuit 9-i receives the detection signal from the pre-amplifier 3-i and the reference signal from the reference signal generating circuit 20. According to this embodiment, it is not necessary to perform the calculation of accumulation explained in Fig. 11 because the amount of delay at each phasing unit is compared with the reference signal. Figure 16 is a schematic block diagram-of an ultrasonic imaging apparatus according to still another embodiment of the present invention. In Fig. 16, reference numbers 21-(i-1) and 21-i denote analog-to-digital (A/D) converters, and 22-(i-1) and 22-i denote storage units. The A/D converters 21-(i-1) and 21-i convert the detection signals from the pre-amplifiers 3-(i-1) and 3-i to the digital values, and these digital values are stored in the storage units 22-(i-1) and 22-i. The control unit 8 can detect the amount of the delay by controlling read out timing from the storage units 22-(i-1) and 22-i. In this embodiment, since the detection signals are detected for the input stage of the adder 6, the phase detection circuit 9-i can directly detect the amount of delay to be corrected so that the control unit 8 does not perform the calculation of the difference between the amount of delay from the detection signal and the amount of delay. Figure 17A is a view for explaining detection signals, thermal noise, and a threshold level Thl at zero volt of the detection signal, and Figure 17B is a view for explaining binary signals for the detection signals and the thermal noise shown in Fig. 17A. Further, Figure 18A is a view for explaining detection signals, thermal noise, and a threshold level Th2 according to the present invention, and Figure 18B is a view for explaining binary signals for the detection signals and the thermal noise shown in Fig. 18A. Still further, Figure 19A is a view for explaining the thermal noise shown in Fig. 17A, and Figure 19B is a view for explaining the thermal noise shown in Fig. 18A. In the first and second aspect of the present invention, the first and second binary units set a threshold value for binarizing the detection signals to approximately the peak of the thermal noise level of the electroacoustic transducer. In this case, preferably, the first and second binary units output logic "1" when the detection signal is higher than the thermal noise level, and output logic "0" when the detection signal is equal to or lower than the thermal noise level. This reason is explained as follows. That is, when the threshold level is set to the zero volt of the detection signal as shown in Fig. 17A, the thermal noises are also binarized by the binary units so that it is difficult to obtain precise binary signals. Accordingly, in the present invention, the threshold level is set to approximately the peak of the thermal noise so that it is possible to obtain precise binary signals without influence of the thermal noise.

Claims: An ultrasonic imaging apparatus for obtaining a tomogram image of an object to be diagnosed on a monitor, comprising: electroacoustic transducers (31-1 to 31-n) provided in a line along a surface of the object, emitting ultrasonic waves to the object, detecting the ultrasonic waves reflected therefrom, and converting them to electric signals as detection signals; phasing means (42-1 to 42-n) operatively connected to the electroacoustic transducers for receiving the detection signals, delaying them in accordance with the distance between the electroacoustic transducers and the object, and phasing them to match the phase of detection signals; and adding means (46) operatively connected to the phasing means to accumulate the detection signals phased by the phasing means; characterised by phase detection means (45) operatively connected to the electroacoustic transducers and phasing means for detecting the error of phase contained in the detection signals output from the electroacoustic transducers or phasing means and correcting the amount of delay previously set in the phasing means in accordance with the error of phase, the phase detection means further comprising first and second binary units (450, 90-1, 90-2), for binarizing the detection signals to detect the error of phase contained in the detection signals. An ultrasonic imaging apparatus as claimed in claim 1, wherein the first and second binary units set a threshold value (Th2) for binarizing the detection signals to approximately the peak of the thermal noise level of the electroacoustic transducer. An ultrasonic imaging apparatus as claimed in claim 2, wherein the first and second binary units output logic "1" when the detection signal is higher than the thermal noise level, and output logic "0" when the detection signal is equal to or lower than the thermal noise level. An ultrasonic imaging apparatus as claimed in claim 1, wherein the phase detection means further comprises first and second shift registers (451, 92-1, 92-2) connected to the corresponding binary units for sequentially latching and shifting the binary signals, the first shift register (92-1) having more latch units than the second shift register (92-2), and error detection unit (453) for detecting mutual-relation values for binary signals from the first and second shift registers, and further detecting the error of phase of the detection signals input to the first and second binary units so that the errors of phases for all detection signals are detected by accumulating the error of phase. An ultrasonic imaging apparatus as claimed in claim 4, wherein the phase detection means further comprises an input delay unit (452, 91) connected to the second binary unit for delaying the binary signals and outputting the delayed binary signals to the second shift register to correct the error of phase detected by the error detection unit in accordance with the amount of delay at the input delay unit. An ultrasonic imaging apparatus as claimed in claim 4, wherein the error detection unit comprises adder units (95-j) and a decision unit (97); the former provided for the same number as latch units of the second shift register (92-2), receiving both latch signals from the first and second shift registers, and accumulating the latch signals when both latch signals indicate the same level; and the latter receiving the accumulated latch signals and determining the maximum value from the accumulated latch signals. An ultrasonic imaging apparatus as claimed in claim 1, further comprising reference signal generating means (44) operatively connected to the phase detection means for generating and supplying a reference signal to one of the two binary units. An ultrasonic imaging apparatus as claimed in claim 1, further comprising reference signal generating means (44) operatively connected to the phase detection means (45) for generating a reference signal; one binary unit inputting the detection signal and the other binary unit inputting the reference signal having the same frequency as that of the detection signal; a multiplication unit (454) operatively connected to the first and second binary units for multiplying both binary signals from the first and second binary units; and detection means (455) operatively connected to the multiplication unit for extracting direct current components contained in the binary signal multiplied by the multiplication unit to detect the error of phase of the detection signals input to two binary units. An ultrasonic imaging apparatus as claimed in claim 8, wherein the first and second binary units set a threshold value (Th2) for binarizing the detection signals to approximately the peak of the thermal noise level of the electroacoustic transducer. An ultrasonic imaging apparatus as claimed in claim 9, wherein the first and second binary units output logic "1" when the detection signal is higher than the thermal noise level, and output logic "0" when the detection signal is equal to or lower than the thermal noise level.

Inventors: IIDA ATSUO, NODA TAKUYA, IIDA, ATSUO, NODA, TAKUYA, IIDA, ATSUO, C/O FUJITSU LIMITED, Noda, Takuya, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: G01S15
IPC codes: G01S7, A61B8, G01S15