Ultrasonic imaging apparatus operating according to the impulse-echo method
BACKGROUND OF THE INVENTION 
     The invention relates to an ultrasonic imaging apparatus operating according to the impulse-echo method, particularly intended for medical diagnostics, comprising an ultrasonic applicator for the linear ultrasonic scanning of an examination subject and an image display device with a line generator for the reproduction of the echo impulses as lines, as well as an image generator for the displacement of the line as a function of the displacement of the ultrasonic beam in the subject, whereby, proceeding from a prescribable line sweep time of a picture tube as the image display installation, for example, from the standard line sweep time of a television picture tube, the period time of the ultrasonic transmission/reception cycles of the ultrasonic applicator is adjusted to a value which corresponds to a whole multiple of the line sweep time of the picture tube and whereby echo signals arising at the rate of these transmission/reception cycles are stored for each cycle in alternating memories until the next successive one and are only read out to the picture tube during this next succesive cycle, whereby the reading out ensues singly or mutliply in such reading-out times which correspond to the line sweep time of the picture tube. 
     Such an imaging apparatus is known for example from the German Offenlegungsschrift No. 2,629,895. It specifically renders possible a video-standard conversion with only a maxiumum of two memories for the intermediate storage of the echo signals of two respective successive scanning lines. Thereby, the conversion of the ultrasonic image ensues in the direct process. 
     In practice, not only the direct presentation of the image directly scanned at the current point in time is of interest; the reproduction of stored images is also of significance. By this means, one obtains a stationary image which facilitates the mensuration of the ultrasonic image on the picture screen. The diagnostic statement is also facilitated by means of stationary images, for example, upon later reproduction. 
     For the presentation of digitally stored images, particularly in the television standard, up to now total image memories (so-called orthogonal memories) which have a very high technical outlay were required, with whose help, thus, only an already converted, complete image could be stored and again polled. An ultrasonic image apparatus with such a memory system is already known, for example, from the German Offenlegungsschrift No. 2,619,684. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to create an imaging arrangement for the conversion of ultrasonic images into a prescribable image type, for example, in television standard, which, in addition to direct reproduction, also renders the reproduction of stored ultrasonic images possible with the smallest technical outlay. The reproduction of stored images should also preferably be able to ensure simultaneously with a current image. 
     The object is achieved with an ultrasonic imaging apparatus of the type initially cited in that, in addition to the alternating memories, at least one echo-line auxiliary memory is present which can be connected to the picture tube at the signal path between the ultrasonic applicator and the alternating memories via the alternating memories for reading in current echo lines of a ultrasonic image and for the later re-reading-out of stored lines. 
     Solely by the use of an echo-line auxiliary memory which requires little technical outlay in place of an extravagant and expensive total image memory, the invention renders possible the image recording of previously stored ultrasonic echo images in the reproduction manner desired. The recording of the stored images can ensue independently of the presentation of current images; as needed, however, the recording of stored images together with the presentation of a current image is just as easily possible. 
     Further advantages and details of the invention follow from the detailed description of an exemplary embodiment on the basis of the accompanying sheets of drawings in conjunction with the subclaims; and other objects, features and advantages will be apparent from this detailed disclosure and from the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, in a basic circuit diagram, shows an ultrasonic imaging apparatus according to the invention specifically for conversion into a television standard display; and 
     FIG. 2 shows a pulse diagram for explaining the implementation of a video-standard conversion according to the invention with the basic circuit diagram according to FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1, 1 designates the ultrasonic applicator which, in the present instance, is constructed in the form of an ultrasonic array. Accordingly, applicator 1 consists of a plurality of ultrasonic transducers W 1  through W n  (piezo-electric crystal lamellae), which are supported adjacently of one another in a row on a carrier section 2 consisting of a material having good ultrasonic wave-attenuating properties. The individual transducer elements W 1  through W n  are capable of being selectively energized individually or in groups by high frequency impulses of a high frequency pulse generator 3 in such a manner that they radiate ultrasonic impulses in the direction of arrows 4 into an examination subject 5, e.g. a human body. The actuation of the individual transducer elements W 1  through W n  individual or group formation proceeds by means of an actuating mechanism comprising, in the conventional manner, an actuating shift register 6 as well as actuating switches S 1  through S n  for the purpose of connecting transducer elements which are to be energized to high frequency impulse generator 3 in the transmit mode, or connecting them to an echo impulse receiving amplifier 7 in the receive mode. The actuating mechanism operates with shift register 6 in such a manner that the individual transducer elements W 1  through W n  can be switched to transmit or receive in continuous succession across the transducer row individually or in groups by means of correspondingly actuated switches S 1  through S n . In this manner, there is a resulting linear progression of the ultrasonic transmitting/receiving beam across the transducer row and a consequent corresponding linear ultrasonic scanning of the examination subject 5. A traditional (conventional) television monitor 8 serves for recording the echo signals of each ultrasonic scanning line as a corresponding image line. This television monitor comprises a television picture tube 9, to which a horizontal time-base generator 10 for a horizontal deflection coil 11 as well as a vertical sweep generator 12 for the vertical deflection coil 13 of the television picture tube 9 is allocated in the standard manner. The monitor 8 further comprises an intensity modulator 14 for intensity modulation of the image lines of the line scanning pattern in step with the occurring echo pulses as well as a synchronizing separator stage 15 for separating the different information contents of the composite video signal (BAS, FIG. 2E) supplied to the monitor 8. 
     The composite video signal develops at the output of a mixer stage 16, which is fed on its input side by the echo signal information, the horizontal (and vertical) blanking pulses as well as the line (and image) synchronizing pulses. Specifically in direct scanning operation, the echo signal information is conducted from the output of the echo signal reception amplifier 7 via a series connection consisting of a buffer memory 34 with switch 35 and mixer stage 31, to be explained later, to buffer memories 17 or, respectively, 18, which function in push-pull action by means of alternating switches 19 and 20 and are supplied from there, finally, to the composite video signal mixer stage 16 via a further amplifier 21 for the echo signals. A blanking pulse generator 22, 23 and respectively, a synchronizing pulse generator 24, serve for the generation of the horizontal (and vertical) blanking pulses and, respectively, of the line (and image) synchronizing pulses. The blanking pulse generator comprises two monostable flip-flops 22 and 23 which are triggered in temporal succession at the clock rate of clock pulses T G  of a basic cycle generator 25. The two pulse series T A  or, respectively, T ZI  according to FIG. 2 thus follow from the basic cycle of the basic cycle generator 25, which operates at the standardized line sweep frequency of the television picture tube 9 (of, for example, 15.625 kHz). Further, the basic cycle generator 25 also drives the synchronizing pulse generator 24 with clock pulses. The synchronizing pulse generator 24 is likewise designed as a monostable flip-flop which emits brief pulses according to the clock pulse waveform (T HS , FIG. 2B). The composite video signal (BAS signal) then results with a temporal waveform according to FIG. 2E which shows the superposition of the respective blanking pulses (e.g. FIG. 2D) with the synchronizing pulses (e.g. FIG. 2B) and the echo information. After separation in the synchronizing separator stage 15 of the television monitor 8, the line scanning voltage (Z K , FIG. 2F) is the respectively triggered by means of the horizontal synchronizing pulses. On the other hand, at the end of each image buildup, the image synchronizing pulse is generated in conjunction with an image blanking pulse which effects the return of the electron beam of the television picture tube 9 into the initial position and the retriggering of a further image sweep in conjunction with a further line scanning pattern sweep. On the other hand, a counter 26 into which the synchronizing pulses of the synchronizing pulse generator 24 are counted serves for setting the trasmission/reception times of the ultrasonic transmission/reception cycles. 
     In accord with the present exemplary embodiment, the counter 26 generates an output pulse T L , FIG. 2G, with each fourth developing synchronizing pulse, which output pulse on the one hand serves as a control clock pulse for effecting the forward shifting in the active register positions of the shift register 6 and, thus, the periodic sequencing of the switches S 1  through S n . On the other hand, with each occurrence of a control clerk pulse T L , the high frequency pulse transmitter 3 is at the same time activated to emit a high frequency pulse to the respective transducer element W 1  through W n  connected by means of a switch S 1  through S n . Thus, a line-by-line ultrasonic scanning of the examination object 5 is produced at the clock rate of the control clock pulses T L . Further, alternating changeover of the switches 19 and 20, also ensues via the control clock pulses T L . Thereby, the changeover times at the memory inputs and, respectively, the changeover times at the memory outputs are respectively designated in FIG. 2 with T E17  and T E18 , and T A17  and T A18 . The pulses illustrated with shading respectively designate the duration of the feeding of echo signal information into the one memory upon simultaneous read-out of the information of a preceding echo line from the other memory. The actual read-out of the information from the memory 17 or 18 respectively connected on the output side via the amplifier 21 to the mixer stage 16 ensues, on the other hand, at the synchronizing rate of the output pulses of the blanking pulse generator 22, 23 via the read-out control lines 27, 28. Since, for the duration of the selection of a memory 17 or, respectively, 18, by means of the output switch 20, a total of three blanking pulses of the blanking pulse generator 22, 23 always respectively develop in temporal succession, accordingly, an echo line rolled into the respectively connected memory 17 or 18 is read out a total of three times in temporal succession. Thus, an echo image with high line density and relatively high image frequency results on the picture screen of the television picture tube 9, whereby, however, each line is written three times. 
     As described, the operation up to now ensues only in the direct scanning process, i.e. such echo lines which develop directly at the examination object in the scanning operation are, correspondingly, directly (contemporaneously) converted into the video standard and illustrated on the television monitor as a direct image. 
     According to the present invention, however, there is also the possibility of reproducing and displaying stored images; the stored image can then serve as the actual television picture either alone or, as a variation, the stored image (or a plurality of stored images) can also represent the television picture in superposition together with a direct (contemporaneous) image now again developing in direct scanning operation. 
     Accordingly, in order to implement such processes, an auxiliary memory 29 (for example, a RAM memory) for the developing echo lines of an echo image is connected at the output of the echo pulse reception amplifier 7 in the basic circuit diagram of FIG. 1. The control of the auxiliary memory for reading-in or, respectively, again reading-out lines or entire images ensues by means of a control circuit 30 as a function of the basic cycle pulses T G  of the basic cycle generator 25 on the one hand and of the control pulses of the read-in or, respectively, read-out line 27, 28 for the buffer memory 17 or, respectively, 18, on the other hand. The read-out of stored lines from the auxiliary memory 29 to the alternately operating buffer memory 17 or, respectively, 18, ensues via a mixer stage 31 upon interpolation of a read-out buffer memory 32 with connection switch 33. As already initially described, the output signal of the echo pulse reception amplifier 7 is also supplied to the mixer stage 31 at a second input, again via a buffer memory 34 with switch 35, during line or image transmission in direct operation. 
     Thereby, the following mode of operation occurs: 
     Whereas with switch 35 closed, a television picture is generated in the direct process by the echo impulse reception amplifier 7 via the buffer memory 34 and the mixer stage 31, at the same time the current echo signals are written in succession line-by-line into the auxiliary memory 29 at the rate of control signals of the control circuit 30. The writing-in frequency in the auxiliary memory 29 exactly corresponds to the writing-in frequency of the corresponding lines in the buffer memory 17 or, respectively, 18. The capacity of the auxiliary memory 29 is limited to the number of the echo lines of at least one ultrasonic image multiplied by the scanning points of each line and (with digital storage of the amplitude of the echo signal at each scanning point) the number of bit positions used to encode each echo signal amplitude, i.e. the bit word length or bit depth. Depending on the position of switches 33 and 35, the mixer 31 then alternately receives in read-out operation echo signals either only from the echo impulse reception amplifier 7 via the buffer memory 34 or only from the auxiliary memory 29 via the read-out buffer memory 32 or from both at the same time. The television standard conversion, now as before, proceeds in all possible modes of operation via the alternating buffer memories 17, 18 in the mixer stage 16. 
     When the read-out frequency of the auxiliary memory 29 is the same as its write-in frequency, then the scale of the stored image corresponds to that which was registered in the direct scanning operation. With deviations of the read-out frequency to higher or lower values, a corresponding reduction or magnification of the scale ensues. Thus, for example, a stored, reduced total image, partial image or something similar or, respectively, such an image with magnification of a section can be mixed with the direct image (real time image). From a diagnostic standpoint, thus, any desired comparative measurements can be conducted on the basis of the direct image and the superimposed, stored partial image which, for example, is also altered in scale. 
     The parallel operation of the auxiliary memory 29 and the line alternating buffer memory 17 and 18 allows a simple line-wise organization of the auxiliary memory in the write and read mode and, thus, a simple addressing of the successive image points of each line. 
     The exemplary embodiments described works in the simple total image method. Of course, however, an interlaced scanning procedure can also be employed to the end that, with even-numbered multiples of the horizontal synchronizing pulses, ultrasonic scanning in the examination object and line image recording with the television picture tube occurs in, for example, two successive half-images, whereby the multiple writing of an echo line amounts to half of the even-numbered multiple of the horizontal sync. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts and teachings of the present invention.