AU703770B2 - Medical needle for use in ultrasound imaging and method of enhancing the visability of such a needle to ultrasound - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): John Francis Cockburn AND Donald Cockburn ADDRESS FOR SERVICE: DAVIeS .LLIONAV-N

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-Patent Attorneys

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Or-, m\qm CO cu J0zzl i) s~b ~'o22,10 (2) U17o Q a~e~i-dT s' INVENTION TITLE: Medical needle for use in ultrasound imaging and method of enhancing the visibility of such a needle to ultrasound The following statement is a full description of this invention, including the best method of performing it known to me/us:e l The present invention relates to a hollow medical needle for use in ultrasonic imaging and to a method of enhancing the visibility of such a needle to a Doppler ultrasound imager.

The theory of ultrasonic transmission in biopsy needles is discussed in ULTRASONICS Vol. 26, No. 1, 1988 pp 27 to US 3,556,079 (Omizo) discloses a medical apparatus comprising a tubular needle within which is mounted an ultrasonic transducer which may be a transmitter, a receiver or a combined transmitter and receiver. This transducer is coupled to saline solution within the needle and transmits and/or detects ultrasound at considerable distances through body tissue at a frequency of e.g. 5MHz which is subsequently reflected off e.g. flowing blood in a blood vessel and sh:ted in frequency according to the Doppler equation. If the transducer in the needle is a transmitter only, then an external ultrasound receiver is arranged to detect the reflected Doppler-shifted ultrasound which is demodulated to generate an audio signal whose amplitude is a maximum when the needle is directed at the blood vessel. However the above arrangement merely enables the position of the blood vessel or other target to be detected and does not enable the position of the needle to be detected. It could not, for example, be used to direct a needle towards a portion of diseased static tissue.

Furthermore it is not an imaging system.

Ultrasound imaging utilises the principle of sound reflectivity in order to form images of body organs. These images are displayed on the monitor in grey-scale. Some ultrasound machines also incorporate the principle of Doppler frequency shift which S"allows moving objects eg red blood cells in a blood vessel to be imaged. Such vessels can then be assigned a colour according to the direction of movement within them, and they appear in colour against the grey-scale background of their environs.

It is often desirable to form such an image during treatment with an aspiration or a biopsy needle and it has been found difficult to produce a clearly defined image of the needle by this technique. It has been proposed to apply a transverse vibration to the needle in order to overcome this problem but this does not result in a clear image of the needle tip.

GB-A- 2,157,828 discloses an ultrasonic imaging apparatus comprising an inner needle having a miniature ultrasonic transducer mounted at its tip and an outer tubular puncture needle surrounding and supporting the inner needle. An ultrasonic imager generates an ultrasonic beam which impinges on the miniature transducer and the resulting electric output signal is either used to trigger a transponder which causes the transducer to emit a predetermined ultrasonic signal which is detectable and locatable by the imager or to enable circuitry in the imager to detect the position of the needle from the time interval between emission and detection of the ultrasonic beam. From this information the position of the needle can be superimposed on the image. However the above arrangement is complex and expensive and in general the needle can be used only with one design of imager.

Further background information is provided in US 5,131,394, EP-A-397,960, EP-A-83,973 (which teaches at p. 7 para 1 the desirability of contact between the stylet and the needle) and WO-A-82/03160, which however lies outside the technical field of the present invention.

EP-A-453,251 discloses a biopsy needle having a solenoid coil coupled to a core which is mounted directly on the proximal end of the stylet and arranged to reciprocate the stylet longitudinally at a frequency of e.g. up to 100 Hz in order to render the needle tip visibility to Doppler ultrasound. The amplitude of 20 vibration is such that the tip of the stylet oscillates between a position in which it is flush with the opening of the cannula and a position in which it is retracted about 1mm into the cannula./ However the above arrangement in which the vibratory transducer is directly coupled to the stylet has the disadvantage that movement of the stylet 25 inevitably causes motion of similar amplitude and frequency in the cannula, with the result that the motion is not confined to the needle tip and the Colour Doppler imager assigns a flare of colour to the entire needle. Furthermore the weight of the solenoid makes the needle harder to manipulate, an important point when one considers the degree of accuracy needed to perform certain biopsies.

Accordingly the present invention provides a medical apparatus comprising a tubular needle adapted for insertion into body tissue, a transducer, and a connection between the transducer and the tubular needle, the tubular needle having a hollow therein extending from a proximal end to a distal end, and the connection comprising a flexible tube connected at one end thereof to the transducer and at the other end to the proximal end of the tubular needle, the transducer being arranged to generate a longitudinal oscillation within the tubular needle at a b ultrasonic frequency via the connection which enhances the visibility of the distal end of the needle by Doppler ultrasound imaging, wherein the tube and the tubular needle are fluid filled.

In another aspect the invention may be said to reside in a medical apparatus for detecting the location of a hollow needle when inserted into a patient, wherein the apparatus comprises a first transducer external to the needle and mechanically isolated therefrom for producing longitudinal oscillations of fluid in the hollow region of the needle; and a Doppler imager comprising a second 15 transducer for receiving the longitudinal oscillations directly from the needle; and a monitor (apparatus) for directly displaying an image of the needle on the monitor.

In another aspect the invention provides a method of enhancing the visibility to a Doppler ultrasound imager of the tip of a tubular needle inserted into a 20 human or animal body, comprising generating a longitudinal oscillation of fluid within said needle at a frequency which is lower than the frequency of the ultrasound emitted by the said Doppler imager by means of a first transducer connected to the needle but mechanically isolated therefrom.

*Since the colour of a region of a Doppler ultrasound image is dependent on the velocity of the corresponding region of tissue and this velocity will vary with the amplitude of the oscillation of the end of the fluid column at the needle tip (assuming that the period of the oscillation is fixed) and this amplitude in turn is dependent on the mechanical properties of the tissue being vibrated by the fluid column, the apparatus of the present invention should enable the tissue at the needle tip to be characterised. For example, fatty tumours will vibrate differently from solid lesions and would be expected to generate a different colour response in the Doppler image of the needle tip.

Accordingly, in another aspect the invention provides a method of enhancing the visibility to a Doppler ultrasound imager of the tip of a tubular needle inserted into tissue of a human or animal body, comprising generating a longitudinal oscillation of a fluid within said needle at a frequency which is lower than a frequency of the ultrasound emitted by the said Doppler imager by means of a first transducer mechanically isolated from the needle and which is adjusted to vary the amplitude of said oscillation in dependence upon the mechanical properties of the tissue.

The transducer may for example comprise a moving coil loudspeaker coupled to the fluid column in the needle bore by a connecting tube whose cross section decreases towards the needle and thereby amplifies the motion of the loudspeaker diaphragm. Alternatively a thermal transducer such as a sparkgap chamber or a piezoelectric transducer may be used.

0*e0*0 S 1 5 The optimum frequency of the longitudinal oscillation generated by the transducer of the needle arrangement will depend on the Colour Doppler ultrasonic imager with which it is being used, in particular on the velocity range detectable by the imager. In a typical Colour Doppler ultrasonic imager the minimum detectable velocity will be 0 0 0 0 00 of 00 0

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of the order of ±0.001m/s and a maximum velocity of about ±3.8m/s, with a more usual range being from ±0.02m/s to ±0.6m/s. Accordingly it is believed that the frequency and amplitude of oscillation should be such that the maximum velocity is within the above ranges. With conveniently achievable amplitudes of oscillation, it is believed that the most useful frequencies will be in the audio range i.e. 20Hz to kHz but the invention is by no means limited to the above ranges.

Preferred embodiments of the invention are described below by way of example only with reference to the accompanying drawing, wherein: Figure 1 is a diagrammatic representation of a medical apparatus in accordance with the invention, and Figure 2 is a longitudinal cross-section of another needle arrangement for use in the arrangement of Figure 1.

Referring to Figure 1, which is a purely diagrammatic representation, a hollow needle 1 is shown inserted into body tissue 10. The needle comprises a 22 gauge tubular cannula 2 having an outside diameter of 0.711mm (0.028") and housing a stylet 3 of 0.457 mm (0.018") diameter within the cannula. The tip of the stylet projects about 2mm beyond the tip 31 of the cannula. The stylet is hollow and has an eccentric opening 32 immediately adjacent to its closed bevelled tip. The eccentric opening, which protrudes beyond the end of the 22 gauge housing cannula, allows the oscillating air column to deliver movement to adjacent tissue while minimising 25 the possibility of body tissue entering the stylet and occluding it. This arrangement allows the tip of the stylet to be rendered visible to Doppler ultrasound during the insertion of the needle through tissue. 8mm flexible pressure tubing 4 connects the hollow stylet with the neck of a funnel member 5 as shown. Alternatively the stylet 3 may optionally be solid and after passage of the needle through tissue, the solid stylet may be removed and the bore of the cannula 2 may be connected directly to the pressure tubing and funnel member as shown in phantom. The mouth of funnel member 5 is coupled in an airtight manner to a moving coil loudspeaker 7 whose diaphragm 6 is driven by a signal from a signal generator 8.

3 5 Preferably the signal which may be a pulsed or an oscillating signal, has a period of 0.03s to 0.001s More preferably the signal has a sine, square or triangular waveform of frequency 333Hz to 1kHz (ideally 400 to 800Hz e.g. 600Hz) and a power of a few 100) mW.

The body tissue is insonated with an ultrasonic beam 11 by a Doppler ultrasound imager 9, which may for example be an Acuson 128 XP10 imager. An image 13 of the needle tip 31 is formed on a screen 12 of the imager.

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Example A working model utilising a jelly phantom in place of the body tissue 10 was constructed generally as shown in Figure l.The components of the working model were as follows: hollow needles, a hollow stylet, a loudspeaker, signal generator and of 'pressure' tubing. The needles were standard 15cm Chiba needles (Cook Inc., Bloomington Indiana) in 18, 20, and 22G sizes and the 15cm hollow stylet was made of superelastic nickel titanium alloy with an inner diameter of 0.406mm (0.016") (Raychem Corp., Menlo Pk. Calif.). The speaker coil was modified from a io 127mm (5 inch) diameter plastic-coned loudspeaker (Tannoy Ltd., Strathclyde, Scotland) and was connected in an airtight arrangement via a funnel to the hollow stylet. The signal generator used was a Korg 770 synthesiser (Keio Electronic Laboratory Corporation, Tokyo, Japan). This instrument generates square, triangular and rectangular waveforms at a wide range of audio frequencies. The signal was amplified through a Realistic SA 1500 audio amplifier (Tandy Corporation, Fort Worth, Texas).

Colour Doppler ultrasound machines used to evaluate the device werc an Acuson XP10 (Acuson Ltd.),and a Diasonics Spectra VST (Diasonics Ltd. Milipitas Calif.

USA). Testing was done by applying a 3.5MHz probe to a jelly phantom and immobilising it in position. The pressure tubing was then connected directly to the needle barrel (minus its matching solid stylet). The needle was then inserted into the phantom as far as possible. 5MHz and 7.5MHz probes were also used with the needle 25 with similar results. Signal was applied to the needle starting at IHz and gradually increasing in frequency until colour signal was registered by the ultrasound machine at a selected pulse repetition frequency and gain setting.

Results 30 The needle tip was displayed as a beacon of colour regardless of the angle of incidence of the Doppler beam. Transverse, longitudinal and oblique projections displayed the beacon equally. The colour signal was not constant but was found to change hue and to flicker at varying rates depending on the frequency of the sound wave applied to the needle. This is believed to be caused by an interference pattern at the needle tip between the frequency of motion and the pulse repetition frequency of the incoming Doppler wave. The needle tip was readily detectable when inserted fully into the phantom. This corresponded to a depth of 15cm. No signal other than that at the tip of the needle was registered when the needle was stationary.

It was found that a frequency of 600Hz yielded a beacon of signal which was readily detectable at pulse repetition frequencies ranging from 800 to 2250 kHz using the Diasonics machine. Within this range, colour gain values of between 68 and 80 dB were required to demonstrate a visible beacon unaccompanied by colour noise on the screen. There was no visible diffcrence between sine, square, triangular or rectangular waveforms. Many other frequencies were found to generate detectable signal at various pulse repetition frequencies and colour gain settings but 600Hz was the single frequency most likely to be detectable in the range of pulse repetition frequencies described.

Increasing gain values above 80dB led to colour noise which could be mistaken for the needle tip. Below a pulse repetition frequency of 800kHz useful signal at the tip uncorrupted by colour noise was demonstrated only at 400Hz with this particular apparatus. Above 2,250 Hz a similar problem occurred with this particular apparatus. Because pulse repetition frequencies are not given a numerical value on the Acuson XPO10 display it was not possible to directly correlate the findings between it and the Diasonics Spectra VST. It was found that the Acuson machine was capable of displaying the colour beacon at the tip of the needle as well as the Diasonics although differences in frequency response between these two machines could not be ruled out because the frequency of pulse repetition is not displayed on the Acuson machine.

At higher pulse repetition frequencies (greater than 1000Hz) tissue motion 'flash' was not prominent and did not obscure the signal at the needle tip when Doppler interrogation was performed during the process of needle insertion. At pulse repetition frequencies lower than 1000Hz, an increasing amount of tissue flash was seen with needle movement which at the lowest settings e.g. 100Hz was very prominent.

SIt was found that when a tissue or agar phantom was used, the needle accumulated material within it and became blocked during insertion. When this occurred, no colour signal was visible at the tip. Blockage was prevented by using a phantom made of ultrasound coupling jelly.

The 0.406mm (0.016") internal diameter hollow stylet was connected to the pressure tubing and inserted into the 20G Chiba needle so that it protruded just beyond its tip to see if it was possible to conduct signal down a lumen of this diameter. Satisfactory colour signal was easily visible at the tip of this hollow stylet, although the size of the beacon was smaller than when the 20G needle barrel was connected directly to the pressure tubing.

The volume control of both amplifier and signal generator needed to be at maximum in order for good quality signal to be registered. Accordingly the speaker was housed in a cabinet to minimise unwanted sound output. Reducing thle volume caused a reduction in colour signal on the monitor. Of interest is the observation corresponding reduction in colour signal on the monitor. Of interest is the observation that slight movement of the transducer off the needle tip resulted in failure to detect any signal. This sensitivity allowed detection of the exact location of the tip of the needle in both colour Doppler and spectral modes. Furthermore the needle tip could be easily found when the probe was displaced far away from the insertion site and aligned randomly with respect to the needle shaft.

Referring now to Figure 2, the needle arrangement shown is designed to prevent occlusion of the oscillating fluid column during insertion into the body tissue and comprises a tubular outer cutting sheath 34 housing a trocar 21. Trocar 21 has a recess 14 at its distal end which exposes a retractable tubular stylet 30 which has a radially directed aperture 32 adjacent its forward (distal) tip. The bore of stylet communicates with the funnel arrangement shown in Figure 1 via flexible tubing 4 and consequently the Doppler signal is emitted at aperture 32 throughout the insertion and enables the precise position of the tip portian of the needle arrangement to be detected continuously.

In use, first the trocar 21 is advanced together with the stylet 30, the latter having its aperture 32 located in the recess 14 as shown and the outer cutting sheath being retracted as shown. When the recess 14 has been advanced to the required position, as determined with the aid of the Doppler ultrasound image of the stylet tip region, the stylet 30 is withdrawn from the trocar 21 to allow tissue to fill the recess 14 and outer cutting sheath 34 is advanced (from left to right relative to Figure 2) over the trocar to cut off the tissue lying in recess 14. The resulting tissue sample can then be extracted.

In this manner a tissue sample of a liver lesion) can be taken from an accurately 25 known region of the tissue.

.o In all the arrangements illustrated in the drawings, the stylet, cannula and trocar (if used) as well as the flexible tubing are sterilised and may be disposable.

The invention also provides a medical apparatus comprising a tubular needle which "is adapted for insertion into body tissue, the needle being provided with a transducer which is substantially mechanically isolated from the needle an l coupled to a fluid column within the needle, the transducer being arranged to generate a longitudinal oscillation of said fluid column at a non-ultrasonic frequency which enhances the visibility of the needle tip to Doppler ultrasound imaging.

The invention also extends to every novel combination or sub-combination disclosed herein.

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Claims (17)

1. A medical apparatus comprising a tubular needle adapted for insertion into body tissue, a transducer, and a connection between the transducer and the tubular needle, the tubular needle having a hollow therein extending from a proximal end to a distal end, and the connection comprising a flexible tube connected at one end thereof to the transducer and at the other end to the proximal end of the tubular needle, the transducer being arranged to generate a longitudinal oscillation within the tubular needle at a sub ultrasonic frequency via the connection which enhances the visibility of the distal end of the needle by Doppler ultrasound imaging, wherein the tube and the tubular needle are fluid filled.

2. Apparatus according to claim 1, wherein the transducer is a sub- ultrasonic transducer.

3. Apparatus according to claim 1 wherein the transducer comprises a moving coil loudspeaker coupled to the fluid column in the needle by a funnel member whose cross-section decreases towards the needle and thereby amplifies the motion of the loudspeaker diaphragm.

4. Apparatus according to claim 1, for use with a stylet adapted to be 20 extended from the distal tip of the needle.

5. Apparatus according to claim 4 wherein the stylet has an aperture at its distal end which communicates with its bore and is located and S: dimensioned to substantially prevent its occlusion by body tissue in use.

6. Apparatus according to claim 1 wherein the transducer is adjusted to vary the amplitude of the oscillation of the fluid contained in the needle in dependence upon the mechanical properties of the body tissue at the distal end of the needle. 9

7. Apparatus according to claim 1 further including a source for an electric signal adjusted to energize the transducer with a drive signal having a pulsed or oscillating waveform whose period is 0.03 second to 0.001 second.

8. Medical apparatus substantially as described herein above with reference to Figure 1 of the accompanying drawings.

9. Medical apparatus for detecting the location of a hollow needle when inserted into a patient, wherein the apparatus comprises a first transducer external to the needle and mechanically isolated therefrom for producing longitudinal oscillations of fluid in the hollow region of the needle; and a Doppler imager comprising a second transducer for receiving the longitudinal oscillations directly from the needle; and a monitor (apparatus) for directly displaying an image of the needle on the monitor. Apparatus according to claim 9, wherein the first transducer and the needle are adapted to be connected together by a fluid-containing flexible tube.

11. Apparatus according to claim 9, wherein the said first transducer is a sub-ultrasonic transducer.

12. Apparatus according to claim 9 wherein the said first transducer e comprises a moving coil loudspeaker coupled to the fluid column in the needle by a funnel member whose cross-section decreases towards the needle and thereby amplifies the motion of the loudspeaker diaphragm.

13. Apparatus according to claim 9, for use with a needle which comprises a stylet adapted to be extended from the distal tip of the needle, 25 said stylet being detectable by the second transducer of the Doppler Imager.

14. Apparatus according to claim 13, wherein the stylet has an aperture at its distal end which communicates with its bore and is located and dimensioned tr substantially prevent its occlusion by body tissue in use. 3 Th Apparatus according to claim 9, wherein said first transducer is adjusted to vary the amplitude of the oscillation of the fluid centained in the needle in dependence upon the mechanical properties of the body tissue at the needle tip.

16. Apparatus according to claim 9, comprising a source for an electric signal adjusted to energise said first transducer w;th a drive signal having a pulsed or oscillating waveform whose period is 0.03 second to 0.001 second.

17. Apparatus according to claim 9, comprising said Doppler ultrasound imager and its transducer positioned to insonate at least the region of said needle tip with ultrasound having a frequency higher than the frequency of said longitudinal oscillation and to form an image of the region of said needle *tip. 0000

18. A method of enhancing the visibility to a Doppler ultrasound imager 15 of the tip of a tubular needle inserted into a human or animal body, comprising generating a longitudinal oscillation of fluid within said needle at a frequency which is lower than the frequency of the ultrasound emitted by the said '"Doppler imager by means of a first transducer connected to but mechanically *0 *isolated from the needle. 20 19. A method of enhancing the visibility to a Doppler ultrasound imager of the tip of a tubular needle inserted into tissue of a human or animal body, comprising generating a longitudinal oscillation of a fluid within said needle at a frequency which is ower than a frequency of the ultrasound emitted by the said Doppler imager by means of a first transducer mechanically isolated from the needle and which is adjusted to vary the amplitude of said oscillation in dependence upon the mechanical properties of the tissue. A method as claimed in either of claim 18 or claim 19 when carried out using apparatus as claimed in any of the claims 9 to 17. I I 11

21. A method of making the tip of a hollow needle inserted into a human or animal body visible to a Doppler ultrasound 'mager, substantially as described hereinabove with reference to Figure 1 of the accompanying drawings. Dated this 7th day of January 1999 JOHN FRANCIS COCKBURN and DONALD COCKBURN By their Patent Attorneys COLLISON CO. eae l I Abstract Medical needle for use in ultrasonic imaging A needle inserted into body tissue (10) is rendered visible to a Doppler ultrasound imager by generating a longitudinal oscillation of the fluid column in the needle b-rrel by means of a transducer which is energised by a signal of frequency 100Hz to 2kHz, for example. An image (13) of the needle tip (31) is displayed on a screen (12). Figure 1. C 0. eoe e °l e L _I _I I