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We claim:
1. An apparatus for responding to a first transducer within an area of a body, said first transducer of the type which responds to ultrasonic energy impinging on a surface thereof
emitted by a second transducer, comprising:
an ultrasound imagining system for imaging an area of the body to cause said first transducer to provide return signals each time ultrasonic energy from said second transducer impinges thereon, said system including first means for providing a
display of said area by converting imaging information into a given number of scan lines to cover said area with said given number of scan lines indicative of a frame,
second means response to said return signals during said frame to analyze the amplitudes of said return signals on a frame to frame basis, said second means providing a control signal in each frame for controlling the analysis by said second
means of the next succeeding frame.
2. The apparatus according to claim 1, wherein said means responsive to said return signals includes means for dividing each scan line into a plurality of segments,
means for indicating the segment of each line where a return signal is present to provide a pixel number for each line having a returned signal.
3. The apparatus according to claim 2, further including means responsive to each of said return signals for providing and storing a representation of the amplitude of said return signals for each line during a frame.
4. The apparatus according to claim 3, including means responsive to each said representation stored to obtain an average of the amplitude of said return signals over a frame, and
means responsive to said average for reducing said representation as stored for each line.
5. The apparatus according to claim 4, further comprising:
selection means responsive to the reduced said representation stored for each line for selecting the largest stored amplitude for a given number of consecutive lines in a frame having pixel numbers which are less than a selected number from one
another, and
means responsive to said selection means to provide a line number and a segment number for the consecutive lines indicative of the position said first transducer.
6. The apparatus according to claim 5, including means responsive to said line number and segment number to indicate the position of said transducer on said display.
7. An apparatus for locating the position of a first transducer within an area of a body, said first transducer of the type which responds to ultrasonic energy impinging on a surface thereof emitted by a second transducer, comprising:
an ultrasound imaging system for imaging the area of the body to cause said first transducer to provide return signals each time ultrasonic energy from said second transducer impinges thereon, said imaging system including means for providing a
display of said area of said body by providing a given number of scan lines to cover said area with said given number of scan lines comprising a frame, and
means responsive to said return signals to analyze said return signals corresponding to each scan line within said frame to determine which ones of said return signals are of the highest amplitude and are indicative of the location of said first
transducer and to provide coordinate locations for said first transducer location.
8. The apparatus according to claim 7, wherein said means for providing a display of said area includes a scan controller to image said area with a given number of scan lines per frame, with a given number of frames per second, said scan
controller providing a frame start signal and a frame stop signal, with a plurality of FIRE signals located therebetween with each FIRE signal corresponding to one of said scan lines.
9. The apparatus according to claim 8, wherein said means responsive to said return signals includes,
line counting means operative to provide a line number during the presence of one of said return signals indicative of a first coordinate,
pixel generating means operative to divide each line into a plurality of segments,
means responsive to the presence of said return signals indicative of a first coordinate to provide a pixel number indicative of a second coordinate, whereby said first and second coordinates define said first transducer location during said
frame.
10. The apparatus according to claim 7, wherein said transducer is positioned on and secured to a catheter adapted to be located in said body tissue.
11. A method of locating the position of a first transducer present in a body, said first transducer of the type emitting a signal when ultrasonic energy from a second transducer impinges thereon, comprising the steps of:
detecting said signal emitted during a frame, and
defining the location of said signal in terms of a line contained within said frame and a position on said line to thereby define the location of said first transducer during said frame.
12. The method according to claim 11, wherein each line in said frame is indicative of the transmission of an ultrasonic pulse.
13. The method according to claim 11, wherein the step of defining said location includes the steps of dividing said line into a plurality of pixels and defining the pixel as said position on said line during a scan of said area.
14. Apparatus for locating the position of an object within a body, comprising:
first transducer means located on said object and capable of emitting a signal when ultrasonic signals emitted from a second transducer means impinges thereon,
an ultrasound imaging system for providing an imaged area of said body, said imaging system including means for scanning said image area nd to present a scanned area in terms of a plurality of scan lines with said plurality of scan lines
indicative of a frame,
means coupled to said first transducer means for measuring a predetermined signal characteristic from the signals emitted by said second transducer means during a frame, and
means responsive to signals emitted by said first transducer to provide an X and Y coordinate for a maximum measured value of said signal characteristic within said scanned area of each frame.
15. The apparatus according to claim 14, further comprising;
display means included in said imaging system for displaying the contents of said scanned area during each frame, and
means responsive to said X and Y coordinates for inserting a marker indication on the display for each frame indicative of the location of said maximum measured value and therefore said first transducer.
16. The apparatus according to claim 15, further including means responsive to said first transducer signal to compare the same with a threshold, wherein if any of said first transducer signal said threshold a control signal is provided and
means responsive to said control signal for storing the value of said first transducer signal as exceeding said threshold.
17. In an ultrasound imaging system operative to image an area of a patient's body with ultrasonic pulses, said imaging system including scan controller means for providing a given number of lines during a frame, with each line indicative of the
information received by said system during an associated pulse, the combination therewith of apparatus for locating the position of an object within said area of said patient's body comprising:
transducer means located on said object and operative to produce and emitted signal when ultrasonic energy impinges thereon,
first means coupled to said transducer means and responsive to said emitted signal to provide an output signal according to said emitted signal,
second means for comparing said output signal with other emitted signals to detect larger amplitude emitted signals during a line, and
third means responsive to said detection of said larger amplitude emitted signals during each line for providing an X and Y coordinate indicative of said larger amplitude emitted signals for each line in a frame,
fourth means responsive to said larger amplitude emitted signals and said X and Y coordinate to store said larger amplitude emitted signals during said frame, and
means responsive to the stored signals for selecting those signals indicative of the location of said transducer during said frame.
18. The apparatus according to claim 17, wherein said first means includes amplifier means for amplifying said emitted signal at an output terminal,
an analog to digital converter having an input coupled to said output terminal for providing a digital signal at an output of a value indicative of the amplitude of said emitted signal.
19. The apparatus according to claim 18, wherein said second means includes a first comparator having an input coupled to a noise level digital number and a second input coupled to the output of said analog to digital converter to provide an
output signal when said second input exceeds said first input, and latch means responsive to said output signal for storing the value of said emitted signal.
20. The apparatus according to claim 19, wherein said third means includes a second comparator having one input coupled to said transducer and another input coupled to the output of said analog to digital converter for comparing said emitted
signal stored within said latch means with new emitted signals from said analog to digital converter, and for providing an output signal when said new emitted signal exceeds said emitted signal stored within said latch means and means for causing said
latch means to store said new emitted signal whereby said latch means will have stored therein the largest emitted signal produced within said frame.
21. The apparatus according to claim 20, wherein said fourth means includes:
first counting means for counting each scan line during a frame and means coupled to said counting means for storing said counted line during the detection of said largest emitted signal, and indicative of said X coordinate, and
second means operative to divide each of said lines into segments and including means for storing said segments and including means for storing said segment during the detection of said largest emitted signal indicative of a Y coordinate.
22. The apparatus according to claim 19, further including a digital to analog converter having an input coupled to the output of said latch means for providing an analog signal at an output terminal, with said output terminal coupled to said
amplifying means for controlling the gain thereof according to the value of said emitted signal stored within said latch means.
23. The apparatus according to claim 17, further including video display means coupled to said scan converter means for providing a video display of each frame, and marker means coupled to said fourth means for highlighting said X-Y coordinate
location on said display to distinguish the location of said object from the remainder of said display.
24. The apparatus according to claim 23, wherein said marker means includes means for causing said X and Y coordinate location to blink.
25. The apparatus according to claim 23, wherein said marker means includes means for providing a color indication at said X and Y coordinate location.
26. The apparatus according to claim 17, further including means for comparing the X coordinates for the previous frame with the present frame and providing an output when they are equal, means responsive to said output for inserting a signal
into said imaging signal to mark the location of said transducer.
27. Apparatus for responding to a transducer located within an area of interest, said transducer of the type which responds to ultrasonic energy impinging thereon by producing return signals, comprising:
an ultrasonic imaging system of the type for imaging said area by providing a series of ultrasonic rays transmitted to said area for responding to reflected signals from said area, said system including display means for providing a display of
said area with at least each one of said rays indicative of one scan line of said display with a given number of scan lines constituting a frame, whereby said transducer returns said return signals from said rays which impinge thereon at said transducer
location within said area,
means responsive to said return signals for providing the maximum value of the returned signals during each ray for each frame and for storing the maximum values achieved for each ray,
means responsive to said stored signals for deriving an average value of said return signals stored for each frame, and
means responsive to said average value for providing the coordinate locations of said return signals stored during a frame.
28. The apparatus according to claim 27, further including:
means responsive to said series of rays to divide each ray into a plurality of segments to provide together with the location of each ray, a segment indication at the location indicative of the X, Y location of said return signals on said
display.
29. The apparatus according to claim 28, further including:
means responsive to the locations of each ray of signals returned to said transducer for displaying the locations on said display.
30. The apparatus according to claim 27, wherein said means responsive to the locations of each ray provides the magnitude and segment location of the maximum value returned signal for each ray. |
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Description |
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This invention relates to ultrasonic imaging systems and more particularly to the use of an ultrasound system for locating the position of an object within a body, for example a medical device, such as a catheter, within a living body.
BACKGROUND OF THE INVENTION
The accurate placement of catheters and other medical devices has become important in recent years for the treatment of a variety of illnesses, for example, the balloon angioplasty of coronary and peripheral arteries. There are many new uses
that will increase the need for precise catheter placement which include stricture dilation performed in the prostrate, selective infusion of drugs to specific sites, and a host of other applications. Catheter placement has been done almost exclusively
under x-ray guidance. In such techniques the contrast medium is sent through the catheter while it is being observed by x-ray fluoroscopy, the contrast moving through the catheter and the jet at the tip showing the location. The physician frequently a
"interventional radiologist" guides the catheter between x-ray sightings. Limitations on catheter placement by x-rays include the safety issues based on x-ray dosage which were received by the patient and physician and the contrast medium load on the
patient's kidneys. Other limitations are related to the need for the procedure to take place in a special room and the need for a radiologist to also be in attendance during the procedure. As one can ascertain both of these requirements add
inconvenience and expense to the procedure. Ultrasonic imaging can provide excellent images of many of the blood vessels and prostatic urethra in which these procedures take place. In addition to visualizing the vessels, the Doppler capability of
ultrasonic imaging allows measurements of flows achieved by the catheter, as to whether to augment flow or diminish it. There has not been any reliable method of localizing a catheter's position by ultrasonic imaging. This is because the ultrasonic
image of the catheter depends on the angle of the catheter to the ultrasonic beam as the catheter moves in the vessel. Some portion of it may become visible, but which portion and when it becomes visible depends on the exact path of the vessel imaged
and the particular location of a isonifying ultrasonic source. For these reasons no one uses ultrasound to try to accurately place a balloon catheter, for example, within a peripheral artery even though the artery and the blockage are visible by
ultrasonic imaging. The prior art was cognizant of the use of ultrasound imaging to locate the tip of a needle.
Reference is made to U.S. Pat. No. 4,249,539 issued on Feb. 10, 1981 to David H. R. Vilkomerson et al and entitled ULTRASOUND NEEDLE TIP LOCALIZATION SYSTEM. This patent describes a means for localizing a needle tip using an ultrasound
imaging system. The apparatus consists of a small transducer whose location was to be determined, receiving the transmitted pulse of an ultrasonic imaging system and sending it back to the imaging system to show its location. In particular, the patent
described the method whereby the return signal was generated electronically and returned directly to the imaging system rather than acoustically back through the body. More general uses of this technique, for example, locating interventional devices in
an artery by means of catheter carried transducers are being contemplated. Such uses require an accurate method of showing the position of the localizing transducer. The technique described had various associated problems. In the method described in
the patent, a comparator was employed to measure the received signal compared to a reference level. When the received signal was higher the apparatus would generate a pulse that would, after being delayed a time equal to that used in propagating from
the ultrasound system to the transducer (i.e., simulating the time required of a pulse reflected by the localizing transducer if direct reflection were used), be inserted into the signal stream of the ultrasonic imaging system, causing a "dot" to appear
at the location of the transducer. A problem with that method is that the reference level must be constantly re-adjusted for varying signal levels. When the transmitting transducer is close to the localizing transducer, not only the main lobe but the
side lobes of the imaging beam will exceed the reference level, causing a "dot" to appear in several beam positions of the image resulting in a smear in the image.
If the reference level is reduced to obtain the single beam position that represents the center of the imaging beam and which produces the most accurate location of the localizing transducer, a slight change in the position may reduce the signal
level at the localizing transducer enough to eliminate any signal whatsoever, thus erasing the "dot". Thus the prior art required a need for continuous readjustment of the reference level to achieve localization and is a serious drawback to system
operation. Also in regard to this particular technique, see an article entitled ULTRASONICALLY MARKED CATHETER--A METHOD FOR POSITIVE ECHOGRAPHIC CATHETER POSITION IDENTIFICATION by B. Breyer, et al and published in The Medical and Biological
Engineering and Computing Journal, May 1984, Pages 268-271. As one will understand from that article, the system described has the above-noted disadvantages.
It is therefore an object of the present invention to provide apparatus to be employed with an ultrasound system which eliminates the need for readjustment of any kind while achieving the optimum localization of the receiving transducer position.
A further object of the present invention is to provide an accurate and improved system for determining the position of an ultrasonic transducer.
SUMMARY OF THE INVENTION
An apparatus for responding to a transducer within an area of a body, said transducer of the type which responds to ultrasonic energy impinging on a surface thereof by returning a signal, comprising an ultrasound imaging system for imaging the
area of the body to cause said transducer to return a signal each time ultrasonic energy impinges thereon, said system including means for providing a display of said area by converting imaging information into a given number of scan lines to cover said
imaged area with said given number of scan lines indicative of a frame, and means responsive to said returned signals during said frame to analyze said signals on a frame to frame basis for providing a control signal enabling said means to optimally
respond to said returned signals.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a block diagram showing an ultrasonic imaging system incorporating processing circuitry according to this invention.
FIG. 2 is a detailed block diagram of an ultrasonic position indicating apparatus according to one embodiment of this invention.
FIG. 3 is a detailed block diagram of an ultrasonic position indicating apparatus according to another embodiment of this invention.
FIG. 4 is a flow chart useful in describing a mode of operation of another aspect of this invention.
FIG. 5 is a detailed block diagram of an alternate approach for locating a transducer according to this invention.
FIG. 6 is a timing waveform diagram showing fire pulses employed in this invention.
FIG. 7 is a format depicting the layout of the memory array useful in this invention.
FIGS. 8A and 8B are diagrams depicting the operation of a transducer having ultrasonic waves impinging thereon.
FIG. 9 is a flow chart depicting the sequence of operation performed by this system.
FIG. 10 is another flow chart useful in describing the fire interrupt mode implemented by this system.
FIG. 11 is a flow chart useful in describing a frame interrupt mode.
FIG. 12 is a flow chart useful in describing the operation of the frame interrupt mode.
DETAILED DESCRIPTION OF THE FIGURES
Referring to FIG. 1 there is shown a simple block diagram of an ultrasonic imaging system employing the present invention. The ultrasonic imaging system includes a display 21, which enables the practitioner or user of the system to visualize the
portion of a patient's body that is being scanned. Ultrasonic imaging systems have been widely used in medical applications because such systems enable imaging of internal structures of the body without the use of harmful forms of radiation. As seen,
the ultrasonic imaging system 20 is associated with a scanning head 10. The scanning head 10 is a hand held unit which the physician manually moves about the body of a patient to thereby perform imaging according to a particular ailment or complaint.
As is known in the prior art, it is desirable for hand held scanners as 10 utilizing ultrasound to provide a clear scan picture of the volume of tissue under investigation. The scan picture or display as indicated previously is presented on a display
21. As shown in FIG. 1 the hand held scanner 10 provides a beam of ultrasonic waves 14 which beam is directed into the body 15 of a typical patient under investigation.As indicated, it is a desire to utilize ultrasound to trace the progress of a
catheter which may be inserted into an artery, vein, or other body part of a patient under investigation. Such catheters are widely employed. As seen in the figure, a catheter 12 is inserted into an artery 11 of a patient and is moved by a
practitioner. As seen, the display 21 depicts the artery as well as the catheter in a conventional manner. In order to locate the catheter so that the physician in viewing the display 21 is able to determine the progress of the catheter, there is shown
a transducer 13 which is secured to the catheter and is capable of providing an electrical signal when the surface of the transducer is impinged upon by ultrasonic waves. In this manner the electrical signal provided by the transducer 13 is directed via
a wire 16 to the input of a receiving processing circuitry module 19. The circuitry module 19 as shown interfaces with the ultrasonic imaging system via input cable 18 and the ultrasonic imaging system interfaces with the receiving processing circuitry
via a cable 17. It is further indicated that the coupling can be done by many different techniques such as electromagnetic or electrostatic coupling. In this manner one can actually couple to, for example, the leads emanating from the scan head 10 to
the ultrasonic imaging system without actually making a direct connection to the lead but can do so by means of electromagnetic couplers, and so on. Coupling can also be acoustic by transponding via transducer 13. As will be further explained, it is an
objective of the present invention to enable a physician to accurately perceive the location of the catheter 12 in regard to the front of the catheter on the display. Accordingly the system determines the position of the transducer 13 which is located
at a predetermined position on the catheter. In this manner, the receiving processing circuitry 19, as will be explained, provides signals to the ultrasonic imaging system which determine the exact location of the catheter and cause the display to
display that location so the physician knows exactly where the catheter is being moved and knows the position of the catheter. The transducer 13, for example, may be the type of transducer described in a co-pending patent application entitled ANNULAR
ULTRASONIC TRANSDUCERS EMPLOYING CURVED SURFACES USEFUL IN CATHETER LOCALIZATION filed on Oct. 15, 1990 as Ser. No. 597,508 and assigned to the assignee herein. Before describing the particular system according to this invention, a brief description
of the operation will be given in conjunction with the block diagram of FIG. 1.
As indicated, the hand held scanner 10 emits ultrasonic waves 14 which essentially impinge upon the transducer 13 causing the transducer 13 to produce an electrical signal. This signal is transmitted along wire 16 where it is received by the
receiving processing circuitry 19. The receiving processing circuitry 19 is capable of determining the exact position of the transducer and therefore the catheter in regard to the image being displayed by the imaging system 20. Thus the receiving
processing circuit then produces an electrical signal which is directed to the ultrasonic imaging system causing the location of the transducer 13 to be clearly indicated on the display. This can occur by increasing the intensity of the display at that
location or by providing a symbol, or by causing the display to flash on and off or by numerous other techniques including adding a different color to the display to indicate the location of the transducer. In this manner by knowing the location of the
transducer with respect to the catheter as, for example, so many inches from the tip of the catheter or in the center of the catheter, the physician immediately knows the location of the catheter by viewing the display. For a general understanding of
ultrasonic imaging devices including a particular hand held scanner, reference is made to U.S. Pat. No. 4,508,122 entitled ULTRASONIC SCANNING APPARATUS AND TECHNIQUES issued on Apr. 2, 1985 to B. Gardineer, et al and assigned to Ultramed, Inc. of
New Jersey. As will be explained, the present invention provides a presentation of the location of the transducer associated with the catheter that enables the system to evaluate the received signal over the entire image frame so that the most accurate
localizing image is retrieved and introduced into the actual display. In this manner there is no need for readjustment of any kind to achieve the optimal localization of the receiving transducer position and none of the problems evidenced by the prior
art exist in the system according to the present invention.
Referring to FIG. 2 there is shown a block diagram of a catheter locating system in accordance with this invention. In FIG. 2 the catheter locating system will operate with an ultrasound system which essentially allows the circuit to interface
with the existing scan converter included in such a system. Most ultrasound systems employ scan converting apparatus which essentially enables one to generate a proper display. In ultrasound systems the returning echos from the transmitted pulse
provide one line of an ultrasonic image. That line in the ultrasonic image corresponds to the sequence of interfaces encountered by the sonic pulse as it propagates downwardly into the body of the patient. The term scan converter includes any scan
controlled system to enable one to format a video display by controlling the scan of the display from such lines. Hence the term scan controller is a broader concept than scan converter. The line information is typically stored in a scan converter that
assembles the information from the sequence of lines produced as the scanning head is moved along the body of the patient. The assembled image or frame is in a video format so that it can be displayed directly on a T.V. monitor or recorded on a video
recorder, and so on. In such systems the length of the image line or how far down the instrument collects the echo information is set by how long the system receives echo returns. Thus the scan converter must accurately assemble the lines into an
image. The determining factor in the accuracy and stability of the image is the positioning of the scan lines, and so on. Thus in FIG. 1, the image shown on display 21 consists of a predetermined number of lines whereby the predetermined number of
lines constitutes a frame. This frame is typical in video parlance and essentially determines a discrete number of lines which are implemented by the scan converter. Essentially the start of the frame is the start of the image and is, for example,
determined by the scan converter by means of a signal called "Image Start". This is a conventional signal and is shown in FIG. 2 as such. The "Image Start" signal as indicated is produced by all ultrasound systems employing scan converters and
basically determines the start of the image. In a similar manner, the end of the image or the end of the frame is also determined by a pulse which, for example, can be the same exact image start pulse, as the start of a new frame is indicative of the
end of the old frame. Between the "Image Start" pulses or frame pulses there are what is known in the art as FIRE pulses. Each FIRE pulse is a pulse which is being transmitted by the scanning head 10 and as indicated is indicative of one line of video
information. Thus between each "Image Start" or frame pulse there are a plurality of FIRE pulses which determine, for example, the total number of lines which comprise the picture 21. As one can immediately ascertain, in order to determine the location
of the transducer 13, one would therefore have to know the line that the transducer appears at in the video picture as well as the location of the transducer on that line as to whether it is in the center or towards the right or towards the left. Thus
as indicated in the video art, one would have to know the coordinates of the transducer 13, at the X-Y address defining the location of the catheter or the X and Y addresses in the video display to define that location. Thus the position of the catheter
on a line or on a ray (each pulse indicates a transmitted ray from the ultrasound system) and the exact position on that line or ray (pixel) is generated by this system to determine the location of the catheter in regard to the displayed image. Thus the
circuit of FIG. 2 operates to do so, as will be explained. Referring to FIG. 2, reference numeral 30 depicts the transducer as, for example, 13 of FIG. 1 which as indicated when impinged upon by an ultrasound signal emanating from the scanning head will
produce an electrical signal. Thus the electrical signal from the transducer 30 is coupled to the input of an amplifier 31. The output of the amplifier 31 is coupled to the input of an analog to digital (A/D) converter 32. The analog to digital
converter 32 is of conventional design and may, for example, be an 8 bit or 16 bit analog to digital converter. The A/D converter 32 has one output coupled to the input of an amplitude latch circuit 33. The purpose of the amplitude latch circuit as
will be explained is to store the largest amplitude emanating from the analog to digital converter 32 during a frame. The output of the A/D converter 32 is also directed to the P inputs of comparators 34 and 35. Each comparator 34 and 35 is a
conventional digital comparator which can operate to compare a signal at the P input with a signal at the Q input and provide an output when the signal at the P input exceeds or is equal to the signal at the Q input. The operation of such comparators is
well known. The output from the analog to digital converter 32 which is a digital output is applied to the P inputs of comparator 34 and comparator 35. The Q input of comparator 34 is derived from a noise level number which essentially is a digital
number indicative of a predetermined threshold above which the system will operate. In order to compensate for noise which is produced in any such ultrasonic system there must be a certain threshold level that has to be exceeded before the system will
operate. Thus the noise level number is a digital number which may be experimentally or empirically selected and applied to the Q input of comparator 34. Hence when the output signal from the analog to digital converter 32 at input terminal P exceeds
the noise level number at input terminal Q, the comparator 34 produces an output which is directed to one input of NOR gate 36. NOR gate 36 enables the amplitude latch 33 which amplitude latch 33 will then store the output signal from the analog to
digital converter 32. The P input of the comparator 35 is also coupled to the output of the analog to digital converter 32. The Q input of the comparator 35 is coupled to the output of the amplitude latch 33. In this manner the comparator 35 will
operate when the signal from the A/D converter 32 is greater than the signal stored in the amplitude latch 33. The amplitude latch 33 always has stored therein the level of the signal which exceeds the previously stored signal and also which exceeds the
noise level number. It is further seen that the gate 36 is enabled during the FIRE pulse. Thus during the FIRE pulse a clock oscillator 40 enables gate 36 to thereby assure that if either of the comparators 34 or 35 operate, that the amplitude latch
will store the output from the analog to digital converter 32 in proper digital form. The output of the amplitude latch as indicated and shown also goes to a digital to analog converter 39 which converts the digital signal into an analog signal, which
analog signal is used to control the gain of amplifier 31, amplifier gain control "AGC". The digital to analog converter 39 is latched at the "Image Start" to change the AGC signal, if necessary, each frame. Thus AGC is updated once per frame. Thus
the gain of amplifier 31 is controlled as a function of the signal stored in the amplitude latch 33. When NOR gate 36 is operated, this provides the dot enable signal. The dot enable signal essentially is the signal which indicates to the system that
the location of the transducer has been found. The dot enable signal now activates the dot found latch or flip-flop 37. The dot found latch is a normal DQ flip-flop which is always cleared at the "Image Start" pulse. It is of course understood that
the amplitude latch is also reset at the "Image Start" pulse. Thus when the dot enable signal is provided the flip-flop 37 activates the dot valid latch 38 which again is another DQ flip-flop. As one can ascertain at the presence of the "Image Start"
pulse, the dot valid output of flip-flop 38 will produce a high level indicating that a dot has been found during the last frame. The dot valid signal indicates that a symbol should appear in the image. The location of the dot is determined by
circuitry which will be now described. The clock oscillator 40 as indicated can provide a single enable pulse during the firing condition but can also operate to control the analog to digital and digital to analog converters 32 and 39 as well as provide
a clock for the up-down counters 41 and 51. As seen, up-down counter 41 is cleared at the "Image Start" pulse which means a clear at the beginning of the frame start. The input to up-counter 41 is the FIRE pulse. The FIRE pulse as indicated above
occurs when the ultrasound system emits a pulse indicative of a single line of information. Thus the up-counter 41 counts this pulse. As seen during the generation of the dot enable signal via gate 36 the ray latch or line latch 42 is enabled. In this
manner when the dot enable signal is provided, the contents of the up-counter 41 are stored in latch 42. This essentially determines the line in which the dot enable signal appeared. It is of course understood that as the amplitude varies or increases,
the contents of the ray latch 42 will also change to always store the line associated with the dot enable signal. The output from the ray latch 42 is directed to latch 43 which is a ray transfer latch. The latch 43 is enabled by the "Image Start"
signal. Hence at the end of a frame or the beginning of the next "Image Start" signal, the contents from the ray latch 42 are transferred and stored in the ray transfer latch 43. The output of the ray transfer latch 43 is coupled to the input of buffer
44 which essentially outputs the contents of the ray transfer latch 43 when commanded to do so by the Read Ray Number command present on the enable line of module 43. This Read Ray Number command is conventionally supplied by the scan converter of the
ultrasonic imaging system being controlled. Thus the Ray Number Out appears on line 46 and is directed to the scan converter of the ultrasonic imaging system notifying the scan converter that the largest signal during the last frame appeared on a given
line. The line has been defined and now the system must know where on the line the largest signal appeared. This coordinate is provided by means of up-counter 51. Up-counter 51 is cleared during each FIRE pulse and has its input coupled to the output
of the clock circuit. Thus in this manner each line is broken up into a series of segments determined by the clock input to the up-counter 51. Thus during each FIRE pulse up-counter 51 counts during the length of the line. For example, a typical line
may be broken up into many segments. During the dot enable the pixel latch 52 is enabled by means of the dot enable signal and hence the pixel latch stores the contents of the up-counter 51 during dot enable. The pixel transfer latch 53 operates in a
similar manner to the ray transfer latch and is enabled by the "Image Start" signal whereby at the end of a frame, the contents from the pixel latch 52 are transferred to the pixel transfer latch 53. The buffer 54 outputs the pixel number to the scan
converter of the ultrasonic imaging system when receiving the Read Pixel Number command. Hence in this manner the scan converter now receives the ray number out and the pixel number and therefore can now modulate that location by means of an increase in
the intensity or by color or by pulsing the display on and off. In this manner one accurately determines the largest signal produced by the transducer 30 during the frame and marks that signal on the image for exactly locating the position of the
catheter. It is of course understood that the largest signal may be indicative of the center position of the transducer 13. One knows the exact dimensions of the transducer 13 in regard to the overall display and hence one by using the ray number out
and the pixel number out information can accurately provide a display of the transducer over more than one line or over more than one ray in the display to thereby give the practitioner an absolute clear view of the exact dimension of the transducer and
the catheter with respect to the displayed image. It is, of course, understood that while the above-described system would produce the maximum output or the position of the maximum amplitude signal for a line and pixel it is of course understood that by
a simple modification of the system shown in FIG. 2, one could provide a plurality of signals all of which are associated with large amplitude and then from such signals make a more accurate determination of the exact location of the catheter. For
example, as one will ascertain the transducer 13 is essentially physically wider than one line of the image and may, for example, appear in four or five lines. The four or five lines all of which will have a large amplitude associated therewith, will
also be approximately located at about the same pixel in consecutive lines. For example, the catheter may be as wide as lines 100, 101, 102, and 103 and being approximately at the same pixel or at close pixels during each line. Therefore, one would
expect large signals during pixels for each of those lines. Thus it would become immediately apparent to one that the system can be accommodated to operate in this manner and store the four largest signals or a given number of large signals in
consecutive lines at about the same pixel locations. When one indicates at about the same pixel location, one is essentially saying that the transducer may not be perfectly vertically oriented and may, in fact, be at a positive or negative slope with
respect to the vertical or horizontal axis and therefore the pixel location associated with each of the lines may vary. As indicated above, the block diagram associated with FIG. 2 is pertinent when one has direct access to the scan converter of the
ultrasonic imaging system. The reason for this is that the scan converter when receiving a ray and pixel number would know exactly where to insert the image of the catheter on the display. As explained above, the amplified signal from the localization
transducer 30 is compared to the highest value previously experienced during the frame. The above discussion shows a digital implementation of the circuitry but as one can understand everything described above can be done in analog fashion as well,
utilizing for example capacitor storage devices, and so on and hence one can operate directly with analog signals. It is, of course, understood that the digital implementation is more reliable in regard to noise and other variations. As indicated
above, when a large amplitude is detected its position in both acoustic beam position representing the angle from the transmitting transducer and in time of occurrence representing the distance from the transmitting transducer is stored. Thus, at the
end of the frame where one has completed the scan of the area of interest, the exact position of the highest signal is stored in the registers 43 and 53. The signal must be higher than the noise level for the system to be enabled. As indicated above,
this information determines precisely the location of the dot in the image that represents the localizing transducer's position. In FIG. 2 the information is used to add the dot into the image by directly connecting to the scan converter whereby the
beam number and time are translated to the proper position in the image. This localizing dot as displayed in the image can be shown in color by means of what is known as graphic overlay on the image. There can be multiple transducers which can be
located and they can be coded differently, as one can ascertain.
Referring to FIG. 3 there is shown a technique which can be employed on ultrasonic imaging systems which do not have easy access to the scan converter. In the embodiment shown in FIG. 3 after the proper position is calculated, the dot is entered
into the next frame. Thus the stored ray number where the signal was the highest is compared to the present ray number. When they are equal, a pulse is introduced into that transmitting transducer line at a time equal to twice the time measured between
the transmit pulse and the maximum signal occurrence. The doubling in time compensates for the propagation time back from the localizing transducer to the transmitting transducer. Thus a bright dot is shown at the precise location of the localizing
transducer. This doubling in time would not be required if transducer transponding is implemented as by pulsing the transducer. It is, of course, understood that the transducer 60 can be located on any medical device. As shown in FIG. 3 the catheter
transducer 60 again is coupled to the input of the amplifier 61 whose output is supplied to A/D converter 62. The A/D converter 62 supplies inputs to the P input of comparator 64 and 65. Comparator 64 provides an output when the signal exceeds the
noise level number input to comparator 64 which amplitude is stored in the amplitude latch 63. The comparator 65 again produces an output when the input signal from A/D converter 62 exceeds the amplitude value stored in latch 63. The digital to analog
converter 67 controls the gain of amplifier 61. As noted, the digital to analog converter 67 is latched at "Image Start". Thus the AGC signal is updated once per frame. The output of NOR gate 66 again produces the enable signal which as indicated
above operates the dot found latch at the "Image Start" or at the beginning or end of frame signal via the latch 68. The output of latch 68 is coupled to latch 69 which is the dot transfer latch. The display dot signal is now applied to the input of
NOR gate 79 instead of to the scan converter. This will be further explained. In any event as indicated, the clock is applied to the analog to digital converter 62 and to the NOR gate 66 as well as to the up-counter 72 as previously indicated.
However, the clock is also applied to a divide by two 82 which is cleared during the presence of each FIRE signal. This clock 82 is supplied to the Data In Down-counter 78 which will be described further to explain how the dot is provided in the system
of FIG. 3. Similarly as described above, there is an up-counter 71 which up-counter 71 produces a count for each FIRE pulse occurring during the frame. The up-counter 71 is cleared by the "Image Start" signal. Thus the up-counter 71 counts each line
in the image display. In a similar manner, the up-counter 72 is | | |
