GB2469839A

GB2469839A - Echogenic instruments using micro-bubbles formed between galvanic electrodes

Info

Publication number: GB2469839A
Application number: GB0907364A
Authority: GB
Inventors: John Cockburn
Original assignee: NORFOLK AND NORWICH UNIVERSITY
Current assignee: NORFOLK AND NORWICH UNIVERSITY
Priority date: 2009-04-29
Filing date: 2009-04-29
Publication date: 2010-11-03
Anticipated expiration: 2029-04-29
Also published as: GB0907364D0; CA2760256A1; GB2469839B; WO2010125377A1; CA2760256C

Abstract

Echogenic instruments needles for use in medical procedures including biopsy, drainage, tissue ablation, anaesthesia, cannula, catheter or central line insertion can be located and guided in using ultrasound techniques. The needles are made echogenic, ie reflective to ultrasound, by forming microscopic gas bubbles in any electrolyte material that is between two electrodes carried on the needle. The two electrodes on the needle are preferably dissimilar metals or metal oxides and separated by an insulator to enable a galvanic current to pass through the intervening electrolyte, which may be bodily fluids or tissues. The electrodes on needle 14 comprise an anode 24 and cathode 26 separated by insulator 28. The electrodes may be adjacent rings on the needle shaft (fig 3), sectors on the needle opening (figs 4, 5) or concentric rings on the needle opening (fig 6,7). The anode may be Fe, Al, Mg, Mn, Ag or alloys of Al or Mg, while the cathode may be Zn, Ni or Ta.

Description

MEDICAL INSTRUMENT

The present invention relates to medical instruments, and in particular to echogenic medical instruments for use in ultrasonography, which can be guided into place using ultrasound. The invention especially relates to echogenic needles for use in a wide range of medical applications, such as for biopsy, drainage, tissue ablation, anaesthesia, cannula, catheter or central line insertion, and in cosmetics.

Ultrasonography has many applications in medicine, and is an ultrasound-based imaging technique that is used to visualize body structures, such as tendons, muscles, joints, vessels and internal organs with a view to detecting pathology or lesions. In addition, ultrasound is of great benefit in helping to guide interventional procedures, for example when carrying out biopsies. Historically, ultrasound has been used to guide the placement of needles, cannula, catheters and guidewires by radiologists performing vascular access, drainage of fluid collections, and biopsy. It is now being increasingly used by anaesthetists for guiding regiona' nerve-block anaesthesia and more recently for percutaneous tracheostomy. Furthermore, ultrasound devices have seen a massive growth in recent years, due to the fact that they can be made smaller (hand-held), and cheaper with high resolution, and this has led to a much wider application of ultrasound, for example for central line and cannula insertion at the bedside.

Figure 1 illustrates a typical ultrasound imaging apparatus 2 used by a medical practitioner. The apparatus 2 consists of a transducer 4 capable of emitting and detecting ultrasound energy. In use, the transducer 2 is held against the body of a patient 6 and emits ultrasound energy thereto. Some of the emitted ultrasound energy is reflected back from the body structures and is received by the transducer 4. The reflected ultrasound is converted into electrical signals which are then transmitted along cable 8 to a signal processor 11. This decodes the interference pattern of the reflected ultrasound waves and displays it on a monitor 12, thereby creating a real-time video image of the body parts from which the ultrasound has been reflected.

Some medical procedures require the operator to obtain a tissue sample from the patient (e.g. from a tumour located in the body) for diagnostic purposes in a process so known as a biopsy. Typically, the sample is obtained by inserting a biopsy needle into the target area within the body (e.g. the liver), and observing the position of the needle and its surroundings on the video monitor. Ultrasound therefore allows the identification of the target tissue and adjacent structures, and provides real-time guidance to precisely position needles inside the patient's body.

However, a significant limitation of sonographic guidance is the difficulty in visualising the needle when it is inserted into the patient. This is due to the poor sonar reflectivity of needles, since the needle has many interfaces from which the sonar waves are reflected, thereby resulting in the needle being essentially invisible to ultrasound.

Furthermore, it becomes harder to visualise needles for target sites which are smaller and deeper inside the patient's body. Clearly, needle visualisation during a medical procedure is essential, particularly when inserting needles into tissues that are in close proximity to important structures such as blood vessels, nerves and pleura. Therefore, difficulty in locating the needle tip inside a patient is a major problem. As a consequence, there is a continuing need to make ultrasound-guided procedures safer, quicker, easier and less painful by improving the conspicuity of the inserted needle.

A number of methods have been attempted to increase the conspicuity of biopsy needles to ultrasound. For example, needles have been developed with undulations or dimples at the needle tip, in an attempt to increase the reflectivity of sound waves. This has also been attempted by roughening the tip, or by providing a tiny hole(s) near the tip of the needle. However, each of these efforts has been met with limited success, since, although such needles tend to have improved conspicuity to ultrasound, this only tends to be when the needle is positioned at about 90° to the transducer, and it has been found that the echogenicity markedly drops as the angle of the needle is varied with respect to the transducer. Another problem with using needles which do not have a smooth surface is that they are prone to catching and pulling on cells as the needle is inserted into, and removed from, the patient. In cases where the target site is a tumour, transfer of tumour cells from the tumour to a neighbouring unaffected area can theoretically cause tumour seeding, which clearly should be avoided.

Another method by which manufacturers have tried to increase the conspicuity of biopsy needles to ultrasound is by providing the needle with a thin biocompatible coating of resin in which tiny gas bubbles are trapped. A variation of such needles is to provide a coating of effervescent material which, upon contacting with fluid upon insertion into the patient's body, produces tiny bubbles of gas which become trapped within the resin coating. The gas bubbles trapped in the resin coatings provide an acoustic impedance differential, and therefore enhance the echogenicity of the needle to ultrasound.

However, a problem with using such "resin-coated needles" is that the coatings become less visible after multiple passes, for example when taking repeated biopsies from the target site within the patient. This happens because fewer bubbles are created with each pass, and furthermore, any bubbles that are trapped within the coating fill up with liquid, which reduces their acoustic impedance differential meaning that they are less conspicuous to ultrasound. Another problem with "resin-coated needles" is that they are not smooth in the coated region(s), and so are also prone to catching on cells as the needle is inserted into, and removed out of, the patient. Thus, tumour seeding is also a problem with using coated needles.

The inventor of the present invention has considered the various problems inherent with known needles, and devised an improved needle, which exhibits increased conspicuity to ultrasound, as shown in Figure 10. The inventor has found that the newly developed needle can be used in a wide variety of medical applications using ultrasonography.

Therefore, according to a first aspect of the invention, there is provided an echogenic needle comprising an anode and a cathode, wherein, in use, current flows between the anode and cathode, thereby producing a plurality of bubbles.

In use, the needle may be immersed into a subject's body containing firstly fluid, which acts as an electrolyte, and secondly neighbouring cells, tissues or vessels etc., which form around the needle. As the cells position around the needle, they form an electrically conducting bridge between the anode and cathode. The cells and the electrolyte therefore complete an electrical circuit with the needle, and the resulting electrolytic action produces an electric potential between the anode and cathode, such Jo that current flows through the bridging structure. As ionic current flows through the electrolyte, and electrical current flows through the bridge, gas bubbles are formed at the anode and cathode, i.e. effervescence.

The bubbles may be gas bubbles which are detectable by ultrasonic imaging apparatus.

The gas will depend on the composition of the fluid in which the needle has been inserted.

By way of example only, in embodiments where the needle is inserted into body tissue, the needle electrolyses the bodily fluid (i.e. saline), thereby releasing microscopic bubbles of chlorine at the anode and bubbles of hydrogen at the cathode. As shown in Figure 10, the inventor has found that the needle of the invention increases the ease with which it can be visualised when inserted inside a patient's body using ultrasound guidance. Although the inventor does not wish to be bound by any hypothesis, he believes that this increase in conspicuity with ultrasound is due to the gas bubbles that are generated by the needle having a higher degree of echogenicity compared to the needle alone. When the bubbles are insonated by an incident ultrasound beam, they generate a highly reflective signal. Accordingly, the needle of the invention is much easier to visualise and guide during medical procedures.

Furthermore, since the needle has a smooth external surface, unwanted cells are not picked up as the needle is inserted and removed from the body, and tumour seeding is therefore less of a problem compared to coated or roughened needles. In addition, the composition of the needle is such that the bubbles are produced to approximately the same extent upon repeated passes into the subject, and so, unlike "resin-coated needles", there is little or no decrease in conspicuity when repeatedly using the needle of the invention.

The inventor has found that the needle of the first aspect is particularly useful for carrying out biopsies on a patient when guided by ultrasound. Hence, the needle may be a biopsy needle. In one embodiment, the needle may be a simple hollow needle comprising a lumen which, after guided insertion into a target tissue (e.g. a tumour), is subjected to a suction force thereby drawing sample cells into the needle lumen for subsequent cytological analysis. This is referred to as fine needle aspiration biopsy (FNAB).

Alternatively, in another embodiment, the needle may be capable of yielding a core of tissue for subsequent histological analysis by virtue of an integral spring-loaded mechanism, for example a stylet. Cutting needle biopsies have an inner stainless steel solid stylet which has a sharpened end, and an outer stainless steel cutting sheath which is forced over the stylet by a spring. The biopsy is trapped in a longitudinal cavity or lumen in the stylet which is situated about 5mm from the sharpened stylet tip. Firstly, in use, the outer needle sheath and stylet are introduced into a patient together (stylet inside sheath) and directed towards a target site (e.g. a tumour). Secondly, when the target is reached, the inner stylet is advanced through the target for a distance of 1 or 2cm. The outer sheath stays behind at the edge of the target. Tissue naturally falls' into the longitudinal cavity which has been ground out of the stylet during manufacture.

Thirdly, the spring is activated or fired', and the outer cutting sheath snaps forwards over the stylet cutting the sample which now lies free in the longitudinal cavity. The needle and sample may then be removed from the patient.

The calibre of the needle may be between about 8G and 30G. The calibre may be 1 OG, 12G, 14G, 16G, 18G, 20G, 22G, or 24G. The length of the needle may be between about 1cm and about 50cm, between about 1cm and about 30cm, or between about 2cm and about 20cm. Preferably, the outer surface of the needle is substantially smooth to facilitate its insertion into, and its withdrawal out of, a patient's body without the risk of detaching unwanted cells.

The inventor has also found that the needle may be used for the insertion or attachment of a cannula to a patient. Cannulas are frequently used in medicine for the administration of injectable medicines and fluids into blood vessels. They comprise an outer plastic sheath to which a syringe or bag of fluid can be attached after placement.

A removable central needle allows placement to occur by facilitating puncture of the target and tracking of the plastic cannula over it. Thus, the needle of the invention may be incorporated into a cannula. By increasing the reflectivity of the needle after bubble generation by an electric current, the ease, speed, safety and tolerance of the cannulation procedure may be optimised.

so Preferably, the anode and the cathode are spaced apart. The needle may comprise a separator or insulator material, which is disposed between the anode and cathode.

Preferably, the insulator material electrically isolates the anode and cathode from each other, i.e. the insulator material ensures that the anode and cathode are physically separated from each other, thereby avoiding a short circuit and creating a potential difference therebetween, such that, upon insertion in electrolyte, current flows therebetween.

The insulator material may extend around the circumference of the needle, for example forming an annulus. The insulator material may be tubular-shaped, or in the form of a mesh. The insulator material may be semi-permeable or perforated. The insulator material may comprise a plurality of apertures extending therethough, through which electrolyte may pass. The insulator material may form a substrate upon which the anode and cathode may be disposed. The insulator material is preferably substantially non-conductive. It should be appreciated that the insulator material is compatible within a biological environment, i.e. physiologically inert and non-toxic to the subject.

It is generally preferred to use a polymer material, with at least one or more layer of the polymer being effective without unduly impairing the voltage. Thus, for example, the insulator material may comprise a polymer, for example polyethylene, polytetrafluoroethylene, polysulfide, polymethyl methacrylate, cellulose, alkyl cellulose ethyl cellulose, cellulose acetate, glass, or ceramic.

The anode and/or the cathode may extend around the circumference of the needle, for example forming an annulus. The anode and/or cathode may be tubular-shaped. The anode and/or the cathode may form a layer or coating on a suitable substrate material, which may be inert. For example, the substrate material may be a polymer, for example polyethylene, polytetrafluoroethylene, polysulfide, polymethyl methacrylate, cellulose, alkyl cellu'ose ethyl cellulose, cellulose acetate, glass, or ceramic. The substrate may comprise the insulator material. It will be appreciated that the layer of anode/cathode and the interface with the insulator material should form a smooth outer surface to the needle.

Figures 2 to 8 illustrate various embodiments of the needle of the invention. In each embodiment, the needle is echogenic due to the materials with which it is made. In one embodiment, the needle may comprise an anode and cathode of electrically conductive materials of different electrochemical potentials. The anode and cathode are preferably compatible within a biological environment, i.e. physiologically inert and non-toxic to the subject. The skilled person will appreciate that different metals have different electrochemical potential values, and lists of these values are readily available in standard chemical textbooks. For example, for the following metals, the electrode potential is given in volts. For calcium: -2.87V, barium: -2.80V, sodium: -2.7 1V, magnesium: -2.34V, aluminium: -1.67V, zinc: -O.76V, chromium:-O.74V, iron: -O.44V, nickel: -O.24V, tin: -O.24V, copper: O.34V, silver: O.80V, and gold: O.80V, and so on.

The skilled person will appreciate that pairings of any of these suitable metals (or oxide thereof) may be combined to form the anode and cathode, such that a suitable potential difference is created for electrolysis to occur when the needle is inserted into a patient's body. For example, the anode may comprise iron, cadmium, aluminium, magnesium, aluminium/magnesium alloy, manganese, or silver. As described in the example, the cathode may comprise tantalum, zinc or nickel. In one preferred embodiment, the anode may comprise iron, and the cathode may comprise tantalum. In another preferred embodiment, the anode may comprise cadmium, and the cathode may comprise nickel. In another preferred embodiment, the anode may comprise zinc, and the cathode may comprise silver oxide. In another preferred embodiment, the anode may comprise zinc, and the cathode may comprise manganese dioxide/carbon.

In one embodiment, the anode and cathode may form spaced apart sections which are disposed along a longitudinal axis of the needle, which sections are preferably separated by a section of insulator material. This embodiment is illustrated in Figures 2 and 3.

For example, the anode may be disposed at a distal end of the needle, and the cathode may be disposed at a proximal end of the needle, preferably with a section of insulator material being disposed therebetween. Alternatively, the anode may be disposed at a proximal end of the needle, and the cathode may be disposed at a distal end of the needle, preferably with the insulator material being disposed therebetween. Provided that the anode and cathode are separated by the insulator, either arrangement will result io in a potential difference being created, such that a current flows therebetween upon insertion into an electrolyte (i.e. in a subject's body). The inventor believes that the provision of the insulator material prevents the electrical circuit formed upon insertion of the needle into the electrolyte from shorting', which would other wise prevent electrolysis from occurring.

The length of the sections of anode, cathode and insulator material are such that a current of sufficient voltage is created to produce the gas bubbles. For example, the sections of anode, cathode and insulator material may be approximately equal in length.

The anode and/or the cathode may be provided as a coating on a suitable substrate material, forming a smooth outer surface. The substrate is preferably inert (such as ceramic), and may comprise the insulator material. Hence, in some embodiments, the anode and cathode may adhere to the inert substrate, leaving a space therebetween, which acts as the insulator section.

In another embodiment, the anode and cathode may form spaced apart sections which are disposed around the circumference of the needle, preferably separated by a section of insulator material. This embodiment is shown in Figures 4 and 5. For example, the anode section may be disposed on one side of the circumference of the needle, and the cathode may be disposed on a mutually opposing side of the needle's circumference.

Preferably, the needle comprises at least two sections of insulator material disposed in between the anode and cathode around the circumference of the needle. As with the embodiment discussed above, the anode and/or the cathode may also be provided as a coating on a suitable substrate material, which is preferably inert. The substrate may comprise the insulator material itself, such that, in some embodiments, the anode and cathode may adhere to the substrate material, leaving a space (and preferably two spaces) therebetween, which acts as the insulator sections. It is preferred that the coatings on the substrate form a smooth surface over the external surface of the needle.

In still another embodiment, the anode and cathode are arranged as radially spaced apart, concentric elements, preferably separated by an element comprising insulator material. This embodiment is depicted in Figures 6 and 7. For example, the needle may comprise an inner cathode, and an outer anode, and preferably an intermediate insulator material section, which separates the anode and cathode. Alternatively, the needle may comprise an inner anode, and an outer cathode, and preferably an intermediate insulator material section. It is believed to be important that the insulator allows electrolyte to flow between the anode and cathode. Thus, in this embodiment, the insulator may comprise a plurality of apertures extending therethrough, through which electrolyte may flow. For example, the insulator may comprise a mesh or a semi-permeable membrane.

In yet another embodiment, which is shown in Figure 8, the anode may comprise an outer hollow tube having a lumen extending therethrough, and the cathode may comprise a stylet slidably mounted through the lumen. The stylet may comprise cutting means at a distal end thereof. The cutting means may comprise a sharpened cutting edge capable of cutting into a target tissue within the subject's body. The needle may comprise an insulator material disposed between the anode and the cathode. The insulator material may be tubular-shaped. The needle may comprise an outer coating of semi-permeable material in the form of a cylinder having a lumen extending therethrough. The coating may be disposed around the cathode, and arranged, in use, to trap bubbles of gas therebetween.

In use, this embodiment of the needle may be inserted into a tissue of a subject, such as liver, in order to take a biopsy. Upon insertion into the tissue, the potential difference between the stylet acting as the anode, and the cathode cylinder, results in electrolysis taking place such that electrical current flows through the tissue, and ionic current flows through the fluid in the tissue. This results in the formation of bubbles of gas, many of which are trapped between the cathode and the outer semi-permeable coating. The bubbles ensure that the position of the needle is readily visible inside the patient. The operator may move the needle inside the patient, continuously checking its position on the monitor, until it reaches a target site, at which point, the operator may activate the stylet such that the cutting means cuts into, and removes, a biopsy. The cutting means may be withdrawn from the target site, thereby retaining the biopsy sample at the distal end of the needle. The needle may then be removed from the patient taking the biopsy with it.

In a further embodiment, the needle of the first aspect may comprise a power source, which generates electrical current which flows between the anode and cathode. Hence, -10 -in this embodiment, the anode and cathode may comprise the same or similar material having the same or substantially similar electrochemical potentials. For example, the anode and cathode may both comprise a'uminium, iron, iron alloy, silver, stainless steel, titanium or other alloys. In this embodiment, in contrast to the other embodiments, electrical current is provided by means of the power source, which provides the electromotive potential so that an anode and cathode are created, such that tiny bubbles of gas are produced, which increase the conspicuity of the needle by ultrasound. The power source may be integral with the needle, or it may be attached thereto via electrically conductive wires. For example, the power source may comprise a battery.

The inventor believes that he is the first to appreciate that ultrasonic imaging apparatus can be harnessed to visualise any medica' implement that has been designed to enable electrolysis to occur such that a current flows between an anode and a cathode, thereby producing microscopic gas bubbles. The inventor anticipates that this realisation may be applied not only to needles, but to any medical implement or device used in conjunction with ultrasound.

Therefore, according to a second aspect of the invention, there is provided an echogenic instrument for use in ultrasonography, the instrument comprising an anode and a cathode, wherein, in use, current flows between the anode and cathode, thereby producing a plurality of bubbles.

The echogenic instrument may be a needle, such as that according to the first aspect, e.g. a biopsy needle. However, the shape of the instrument is not confined to an elongated rod, such as a needle, and can vary depending on the intended application.

For example, in one embodiment, the instrument may be non-cylindrical in shape, and may be less than 2cm in length. The instrument may be any medical device, which is to be inserted into a subject's body, the presence of which is to be identified under ultrasound. For example, the medical device may be a stent, catheter, port, drug eluting element, or other implantable or insertable medical device, the position of which should be monitored during a medical procedure.

The instrument may be attached to an otherwise non-echogenic medical device, and may act as a beacon' for identifying the position of the medical device under -11 -ultrasound. The instrument can therefore be used to render non-echogenic devices, echogenic when attached thereto. Thus, the instrument may comprise attachment means by which it may be attached to the medical device. Suitable attachment means may comprise a clip, screw assembly or the like. Alternatively, the echogenic instrument may be shaped such that it can be attached to, or inserted into, the medical device.

According to a third aspect of the invention, there is provided an ultrasound imaging apparatus comprising the echogenic needle according to the first aspect or the echogenic instrument according to the second aspect, and means for generating ultrasound.

The means for generating the ultrasound may comprise a transducer. The apparatus may comprise means for detecting ultrasound. The means for detecting the ultrasound may comprise a transducer. The apparatus may comprise processing means for converting reflected sound into an electrical signal, which may be viewed on suitable display means, such as a monitor.

According to a fourth aspect of the invention, there is provided a method of carrying out ultrasonography on a subject, the method comprising the steps of: (a) introducing, into a subject, the echogenic needle according to the first aspect or the echogenic instrument according to the second aspect; (b) emitting an ultrasound signal in a direction substantially towards the needle or instrument; and (c) detecting ultrasound signal reflected from the needle or instrument.

According to a fifth aspect of the invention, there is provided a method of determining the position, in a subject, of the echogenic needle according to the first aspect, or the echogenic instrument according to the second aspect, the method comprising the steps of: (a) introducing, into a subject, the echogenic needle according to the first aspect or the echogenic instrument according to the second aspect; -12 - (b) emitting an ultrasound signal in a direction substantially towards the needle or instrument; (c) detecting ultrasound signal reflected from the needle or instrument; and (d) determining the position of the needle or instrument in the subject based on the detected ultrasound signal.

The methods may comprise inserting the needle or instrument into the subject, which contains fluid that acts as an electrolyte. The methods may comprise forming a conducting bridge comprising subject's cells between the anode and cathode. The methods may comprise creating a current which flows between the anode and cathode.

The methods may comprise creating an electrical current in the conducting bridge.

Preferably, the methods comprise creating an ionic current in the electrolyte. The methods may comprise creating gas bubbles at the cathode and/or anode.

The methods may comprise positioning an ultrasound transducer on a surface of the subject, and transmitting an ultrasonic signal thereto, to thereby cause at least some of the signal to be reflected by the bubbles. The methods may comprise detecting reflected ultrasound signal by the transducer. The methods may comprise converting reflected ultrasound signal into an electrical signal suitable for displaying on display means, such as a monitor.

The subject may be a vertebrate, mammal, or domestic animal, and is preferably a human being.

The apparatus of the third aspect, and the methods of the fourth and fifth aspects may be used for carrying out a wide range of medical applications, for example for obtaining a small cell sample from a tumour, or the like, i.e. a biopsy. The apparatus and methods may also be used for other medical applications in which a needle is inserted into a patient, for example inserting or attaching a cannula to a patient, inserting a catheter, insertion of a central line, in anaesthesia (e.g. regional or local anaesthetic), in keyhole surgery. The apparatus and methods may be used in cosmetics, such as injection of collagen, or botulinum toxin into a desired location while avoiding non-target structures, e.g. pleura, nerves and blood vessels, or in liposuction, in which the ability to -13 -retrace where a suction needle has been placed previously is thought to be particularly useful for removal of fat. Ultrasound guidance is also frequently used for sclerotherapy, i.e. a treatment for varicose veins.

The apparatus and methods of the invention may also be used during interventional procedures, such as nephrostomy, percutaneous biliary drainage, percutaneous gastrostomy insertion, abscess drainage, drainage of ascites, insertion of a catheter into the peritoneal cavity, artery or vein cannulation or catheterisation. The apparatus and methods may also be used for atherectomy (which feeds a catheter through the arm or groin to the heart), drainage and tissue ablation.

All of the features described herein (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which:-Figure 1 shows a schematic side view of ultrasound imaging apparatus, including a needle according to the invention, being used on a patient; Figure 2 shows a perspective view of a first embodiment of the needle shown in Figure 1; Figure 3 shows an enlarged cross-sectional side view of the first embodiment of the needle shown in Figure 2; Figure 4 shows an enlarged cross-sectional side view of a second embodiment of the needle; Figure 5 shows an end view of the second embodiment of the needle shown in Figure 4; -14-Figure 6 shows an enlarged cross-sectional side view of a third embodiment of the needle; Figure 7 shows an end view of the third embodiment of the needle shown in Figure 6; Figures 8(a) to (g) show cross-sectional side views of a fourth embodiment of the needle; Figure 9 is an ultrasound image showing a prior art 22G needle positioned about 10cm inside a body, which has been insonated by a 3.5MHz ultrasound probe; and Figure 10 is an ultrasound image showing a 22G needle according to the invention positioned about 10cm inside a body, which has been insonated by a 3.5MHz probe.

Example

Referring to Figure 1, there is shown an ultrasound imaging apparatus 2 according to the invention. The apparatus 2 may be used for carrying out a biopsy on a patient 6, for example for obtaining a small cell sample from a tumour, or the like. However, the apparatus 2 may also be used for a wide range of other medical applications in which a needle is inserted into the body of a patient 6, for example: (i) attachment of a cannula to a patient, (ii) in anaesthesia (i.e. administration of an anaesthetic to a patient, such as an epidural), (iii) insertion of a central line (i.e. a tube inserted directly into a major blood vessel, such as a vein or an artery near the heart), (iv) keyhole surgery, and (v) in cosmetics.

The apparatus 2 shown in Figure 1 includes an echogenic needle 14 which has a sharp tip, which, in use, pierces the skin of the patient 6 under investigation. Various embodiments of the needle 14 are described in detail below, and are illustrated in Figures 2 to 8. The apparatus 2 shown in Figure 1 further includes an ultrasound source which is connected to a transducer 4 via cable 8. The transducer 4 is capable of emitting and detecting ultrasound energy (e.g. 3.5MHz) that has been generated by the source 10. In use, the transducer 2 is held against the skin of the patient 6 adjacent the site of needle 14 insertion, and used to emit ultrasound energy thereto.

Referring to Figure 9, there is shown a prior art 22G needle exposed to 3.5MHz -15 -ultrasound via a transducer 4. As shown in Figure 9, it is not possible to see the prior art needle under ultrasound, and so is very difficult to use in most procedures.

However, with reference to Figure 10, since the needle 14 of the invention is echogenic, a proportion of the emitted ultrasound energy is reflected back from the needle 14 and, to a lesser degree, some internal body structures, and is received by the transducer 4.

The reflected ultrasound is converted into electrical signals which are then transmitted along cable 8 to a signal processor 11 and then displayed on a monitor 12, thereby creating a real-time video image of the needle 14, and any body parts from which the ultrasound has been reflected. As shown in Figure 10, the position of the needle 14 of the invention inside the patient 6 can be clearly seen via the video image on the monitor 12.

In each embodiment illustrated in Figure 2 to 8, the needle 14 of the invention is echogenic due to the materials with which it is made. The needle 14 comprises at least two metals having different electrochemical potentials, such that one of the metals forms an anode 24 and the other forms a cathode 26. The two metals forming the anode 24 and the cathode 26 are physically separated and therefore electrically isolated from each other by an insulator 28, which thereby creates a potential difference therebetween. Upon insertion of the needle 14 into a patient's body, liquid inside the body acts as an electrolyte, and conducting cells adjacent the needle 14 forms a conducting bridge between the anode 24 and cathode 26, such that current flows between the anode 24 and cathode 26. Ionic current is thought to flow through the electrolyte, whereas electrical current is thought to flow through the conducting bridge formed between the anode and cathode by neighbouring cells. The principle of the needle 14 therefore is that it acts as an electricity source capable of generating a voltage (of about 1 5mV) which is sufficient to electrolyse the liquid medium in the body (i.e. the electrolyte) surrounding the needle 14. For example, when inserted into subcutaneous fat and tissue of a patients body 6, the needle 14 electrolyses saline releasing chlorine gas at the anode 24, and hydrogen gas at the cathode 26. The gases are released as microscopic bubbles, and act as a focus of high impedance to the transmission of ultrasound, thereby rendering the needle 14, from which the gas is -16 -produced, highly visible (i.e. echogenic) using the transducer 4 of the ultrasound apparatus 2.

The needle 14 therefore acts as a battery, and so at least in some embodiments of the invention, does not requite the use of an external electrical source. The materials and construction of the needle 14 (i.e. the anode 24, cathode 26, and insulator 28) must meet a number of criteria. The primary criteria are that: (i) the materials forming the anode 24 and cathode 26 have different electrochemical potentials; and (ii) the insulatot 28 electrically isolates the anode 24 and cathode 26 from each other, to create the potential difference. When a needle 14 meeting these criteria is positioned inside the patient's body 6, it is effectively being immersed in an electrolytic fluid. For example, if the needle 14 is positioned in the body 6, the saline surrounding the organs constitutes the electrolytic liquid, and the organ in which the needle 14 has been inserted forms a conducting bridge between the anode 24 and cathode 26. If the needle 14 is positioned in a liver bile duct, for example if carrying out a biopsy from the bile duct, the bile itself constitutes the electrolytic liquid. If the needle 14 is inserted into the vascular network, for example when inserting a mainline or even a simple cannula, blood constitutes the electrolytic liquid, and so on. As the needle 14 is inserted into the patient's body, an electrical circuit is formed between the anode and cathode by the conducting bridge and the electrolyte. An electric potential difference between the anode 24 and cathode 26 is formed, such that a current flows therebetween.

Other material selection and construction criteria depend upon the specific application intended for the needle 14. For example, selected materials should be compatible within a biological environment, i.e. each material should be physiologically inert, neutral and non-toxic the patient 6. Electrolysis occurring inside the patient's body will erode the anode 24 and, provided that the anode, cathode and insulator materials are all physiologically neutral, any by-products of electrolysis will not have an adverse impact on the patient 6.

The inventor has found various combinations of materials that may be used for the anode 24 and cathode 26 of the needle 14 of the invention. One combination is Jo tantalum (as the cathode) with iron (as the anode). Another combination is nickel (as -17 -cathode) and cadmium (as anode). Aluminium-magnesium alloy or silver are further suitable anode 24 materials, but the generated output voltage with a silver anode may be less than with an iron anode. The intermediate insulator 28 can be formed of any physiologically inert or neutral non-conductive material, for example a polymer, such as polyethylene, or the like. The purpose of the insulator 28 is to electrically isolate the anode 24 from the cathode 26 so that a potential difference therebetween is created, such that tiny gas bubbles are formed, thereby increasing the conspicuity of the needle 14 with ultrasound.

Each of the various embodiments of the needle 14 according to the invention which can be used with the apparatus 2 shown in Figure 1 will now be described in detail.

Referring first to Figures 2 and 3, there are shown views of a first embodiment of the echogenic needle 14 for use in percutaneous procedures under ultrasound guidance. The needle 14 comprises an elongate shaft having proximal and distal ends 14a,14b, the latter of which is sharply pointed for piercing the skin of the patient 6.

The calibre of the needle 14 is between about 12G and 25G, and its length is between about 2cm and 20cm. The outer surface of the needle 14 is substantially smooth to facilitate its insertion into, and its withdrawal out of a patient's body without the risk of detaching unwanted cells. A smooth, internal, cylindrical lumen 16 extends between the ends 14a,14b along which fluid or bodily materials, such as a biopsy cell sample, may pass. In the first embodiment shown in Figure 2, the needle 14 includes a mounting 18 generally made of a plastic material which surrounds, and is secured to, the proximal end 14a. A stylet 20 is slidably and removably disposed within the lumen 16 of the needle 14, and substantially blocks the distal end 14b, and, as described hereinafter, helps form a cutting edge for use during the insertion process. When removed from the needle 14, the stylet 20 exposes a threaded or ribbed portion 22 within mounting 18 onto which a hypodermic syringe may be removably secured and used in a manner well-known in the art.

The needle 14 shown in Figures 2 and 3 is composed of three distinct sections disposed along a longitudinal axis of the needle 14, i.e. (i) the anode section 24 made of iron, which forms the distal end of the needle 1 4b, (ii) the cathode section 26 made of -18 -tantalum, which forms the proximal end of the needle 1 4a, and (iii) the intermediate insulator section 28 made of polyethylene, which physically separates the anode 24 and cathode 26, thereby creating a potential difference. Although not shown in the Figures, it should be appreciated that either the anode 24 or the cathode 26 can be disposed at either the distal end or the proximal end 14a of the needle 14b. Provided that the anode 24 and cathode 26 are separated by the insulator 28, either arrangement will result in a potential difference being created therebetween.

Once inserted into a patient's body, the needle 14 generates an electrolytic voltage of about 1 5mV by electrolysis. As electrolysis occurs, microscopic bubbles of gas are produced on the surface of the anode 24 and cathode 26, the bubbles sticking to the surface of the needle 14 by surface tension. As with all embodiments of the needle 14, the type of gas contained within the bubbles is determined by the composition of the electrolyte, which in turn depends upon the position of the needle 14 inside the patient's body. The bubbles act as a focus of high impedance to the transmission of ultrasound, thereby improving the visibility of the needle 14 to ultrasound guidance using apparatus 2. Once the needle 14 has been carefully guided into position, as viewed on the monitor 12, the operator then either takes a biopsy from, or delivers a medicine or the like to, the target site. The needle 14 may then be carefully removed from the target site in the patient 6, and, if necessary, re-inserted at a different position or angle. Due to the metallic composition of the needle 14, bubbles continue to be generated, thereby enabling the operator to view the needle in situ as many times as required.

Referring next to Figures 4 and 5, there are shown views of a second embodiment of the echogenic needle 14 for use in percutaneous procedures under ultrasound. As shown most clearly in Figure 5, the need'e 14 is composed of four distinct sections, which are disposed around the circumference of the needle 14, i.e. an anode section 24 made of cadmium on one side of the circumference of the needle 14, a cathode section 26 made of nickel on the opposite side of the needle's circumference, and two sections of insulator material 28 made of ceramic, which physically separates the anode 24 and cathode 26 sections, thereby creating the potential difference. The lumen 16 is shown in the centre of the needle 14. It will be appreciated that there is no physical contact -19 -between the anode 24 and cathode 26 due to the insulator 28, and because of the lumen 16.

Upon insertion of the needle 14 into the body of a patient, the needle 14 automatically generates an electrolytic voltage between the spaced-apart anode 24 and cathode 26, which in turn results in the formation of tiny bubbles of gas. As discussed above, the presence of the bubbles on the surface of the needle 14 improves its conspicuity to ultrasound, and greatly facilitates an operator in guiding the needle 14 through the patient's body.

Referring to Figures 6 and 7, there are shown views of a third embodiment of the needle 14 according to the invention. As shown most clearly in Figure 7, the needle 14 is arranged with a series of nested or concentric elements, i.e. an inner cathode 26 (tantalum), an outer anode 24 (silver), and an intermediate insulator 28, which separates the anode 24 and cathode 26, which sections collectively form a three-layer cylindrical structure. The lumen 16 is shown in the centre of the needle 14. Although not shown in the Figures, it will be appreciated that either the anode 24 or the cathode 26 can form the inner of outer layer of the needle 14. Provided that the anode 24 and cathode 26 are separated by the insulator 28 layer, either arrangement will result in a potential difference being created. In this embodiment, the insulator 28 is provided as a polymer mesh, or a semi-permeable membrane, having numerous apertures extending therethrough, through which electrolyte can flow. Thus, the insulator mesh 28 prevents the anode 24 and cathode 26 from contacting each other, as otherwise prevent a potential difference from being created. However, the mesh 28 also ensures that electrolyte can flow between the anode 24 and cathode 26 so that electrolysis can occur.

Once inserted into a patient's body, the needle 14 automatically generates an electrolytic voltage, which results in the production of tiny gas bubbles, which improve the visibility of the needle 14 to ultrasound guidance using apparatus 2. As with other embodiments of the needle 14, the operator can guide the needle 14 through the body of the patient by viewing its position on the monitor 12.

Referring to Figure 8(g), there is shown a fourth embodiment of the needle 14 according to the invention, and Figures 8(a) to (f) show the various components which -20 -collectively make up the needle 14. Figure 8(a) shows an elongate, inner stylet 20, at the distal end of which is located a sharp cutting edge 30. The stylet 20 is made of iron and acts as the anode of the needle 14. Figure 8(b) shows the polyethylene insulator 28 which is formed into a cylindrical mesh having lumen 16 extending therethrough. As shown in Figure 8(c), the stylet 20 is disposed within, and extends through, the lumen 16 of the insulator mesh 28. The mesh 28 has a plurality of apertures extending therethrough, through which electrolyte may flow.

Figure 8(d) illustrates the cathode made of tantalum, which is cylindrica' in shape having lumen 16 extending therethrough. As shown in Figure 8(e), the arrangement of the stylet 20 disposed within the insulator mesh 28 is in turn disposed within the cathode cylinder 26. Thus, the insulator mesh 28 prevents the cathode 26 contacting the anode stylet 20, but ensures that electrolyte can flow therethrough between the anode 24 and cathode 26. Finally, Figure 8(f) illustrates a semi-permeable coating, which in one embodiment, is made of plastic in the form of a cylinder 32 having a lumen 16 extending therethrough. As shown in Figure 8(g), the arrangement depicted in Figure 8(e) is disposed inside the semi-permeable coating 32 shown in Figure 8(f), thereby forming the complete needle 14.

In use, the needle shown in Figure 8(g) is inserted into a tissue of a patient 14, for example a lung, in order to take a biopsy. Upon insertion into the body 6, the potential difference between the stylet 20 acting as the anode, and the cathode cylinder 26 results in a 1 5mV current being created. The electrical current causes electrolysis inside the lung, resulting in the formation of tiny bubbles 34 of gas (chlorine and hydrogen), the majority of which are trapped between the cathode 26 and the semi-permeable coating 32, as shown in Figure 8(g). The bubbles 34 reflect the ultrasound energy to a greater extent than the patient's internal organs, such that the operator can easily see the position of the needle 14 inside the patient. The operator then moves the needle 14 inside the patient, continuously checking its position on the monitor 12, until it reaches the target site, i.e. the tumour, at which point, the operator activates the stylet 20 such that the cutting edge 30 cuts into, and removes, the biopsy. The cutting edge 30 is withdrawn from the target site, and insodoing, retains the biopsy sample at the distal end 1 4b of the needle 14. The needle 14 is then carefully removed from the patient -21 -taking the biopsy with it. Throughout the whole procedure, the operator is able to clearly see the position of the needle 14 inside the patient's body due to the production of microscopic gas bubbles which reflect the ultrasound. Therefore, the needle 14 can be accurately manoeuvred through the body 6.

Although not shown in the Figures, a fifth embodiment of the needle 14 is provided, which involves a needle in which the same metals (having the same or similar electrochemical potential) are used as the anode 24 and cathode 26. For example, the anode 24 and cathode 26 can both be made of stainless steel. However, in this embodiment, in contrast to the other embodiments, electrical current is provided by means of a separate power source, such as a battery (not shown). The battery provides the electromotive potential so that an anode 24 and cathode 26 are created, such that tiny bubbles 34 of gas are produced, which increase the conspicuity of the needle 11 by ultrasound.

In summary, the invention relates to a needle 14, which is capable of creating an electrical current upon insertion into a patient's body, and which exhibits increased conspicuity under ultrasound due to the automatic generation of tiny bubbles of electrolytic gas. The needle 14 can be inserted into the patient's body under ultrasound guidance using the apparatus 2 shown in Figure 1, and is clearly visible on an ultrasound image as shown in Figure 10 compared to the image viewed using a prior art needle (see Figure 9). In one embodiment, the needle 14 can be a simp'e Chiba'-style needle for gaining percutaneous access to an organ, or for the purpose of getting a tissue sample by fine needle aspiration (FNA). In another embodiment, the needle 14 could be a spring-loaded biopsy needle 14 capable of extracting a core of tissue when activated inside a target 2one, as shown in Figures 2 and 8. In another embodiment, the needle 14 can be a specialised needle 14 capable of delivering a substance (for example, a cell division inhibitor/promoter for use in chemotherapy, or a gene therapy product or an antibiotic etc), an electrical current (e.g. radiofrequency AC or DC), or some other means that is used to ablate a target tissue, for example a tumour. Such a needle 14 may have multiple self-expanding tines capable of ablating a large tissue volume.

-22 -The primary function of the needle 14 is not to kill cells or inhibit their growth, but rather to improve the ease, simplicity and accuracy of needle 14 insertion and positioning. In this way, non-target tissue can be avoided during insertion and withdrawal, and procedures can proceed more quickly and with a much greater degree of operator confidence. Thus, the needle 14 will lead to a significant reduction in operation training costs, and will improve the ease, speed, safety and patient tolerance of the procedure.

Claims

-23 -CLAIMS1. An echogenic needle comprising an anode and a cathode, wherein, in use, current flows between the anode and cathode, thereby producing a plurality of bubbles.
2. A needle according to claim 1, wherein the bubbles are gas bubbles produced by electro'ysis, and are detectable using ultrasonic imaging apparatus.
3. A needle according to either claim 1 or claim 2, wherein the needle is a biopsy needle.
4. A needle according to any preceding claim, wherein the needle is incorporated into a cannula.
5. A needle according to any preceding claim, wherein the needle comprises an insulator material, which is disposed between the anode and cathode.
6. A needle according to claim 5, wherein the insulator material is tubular-shaped, or in the form of a mesh.
7. A needle according to either claim 5 or claim 6, wherein the insulator material comprises a plurality of apertures extending therethough, through which electrolyte may pass.
8. A needle according to any one of claims 5 to 7, wherein the insulator material is substantially non-conductive to current.
9. A needle according to any one of claims 5 to 8, wherein the insulator material comprises a polymer, for example polyethylene, polytetrafluoroethylene, polysulfide, polymethyl methacrylate, cellulose, alkyl cellulose ethyl cellulose, cellulose acetate, glass, or ceramic.
10. A needle according to any preceding claim, wherein the anode and/or the cathode form a coating on a substrate material, which is inert.
11. A needle according to claim 10, when dependent on any one of claims 5 to 9, wherein the substrate comprises the insulator material. -24-
12. A needle according to any preceding claim, wherein the needle comprise an anode and cathode of electrically conductive materials of different electrochemical potentials.
13. A needle according to any preceding claim, wherein the anode comprises iron, cadmium, aluminium, magnesium, aluminium/magnesium alloy, manganese, or silver.
14. A needle according to any preceding claim, wherein the cathode comprises tantalum, zinc or nickel.
15. A needle according to any preceding claim, wherein the anode comprises iron, and the cathode comprises tantalum.
16. A needle according to any one of claims 1 to 15, wherein the anode comprises cadmium, and the cathode comprises nickel.
17. A needle according to any preceding claim, wherein the anode and cathode form spaced apart sections which are disposed along a longitudinal axis of the needle.
18. A needle according to claim 17, wherein the anode may be disposed at a distal end of the needle, and the cathode may be disposed at a proximal end of the needle, or vice versa, preferably separated by insulator material.
19. A needle according to any one of claims 1 to 17, wherein the anode and cathode form spaced apart sections which are disposed around the circumference of the needle.
20. A needle according to claim 19, wherein the anode section is disposed on one side of the circumference of the needle, and the cathode is disposed on a mutually opposing side of the needle's circumference, preferably separated by insulator material.
21. A needle according to claim 20, wherein the needle comprises at least two sections of insulator material disposed in between the anode and cathode around the circumference of the needle.
22. A needle according to any one of claims 1 to 17, wherein the anode and cathode are arranged as radially spaced apart, concentric elements.

-25 -
23. A needle according to claim 22, wherein the needle comprises an inner cathode, and an outer anode, or vice versa, preferably separated by insu'ator material.
24. A needle according to any one of claims 1 to 17, wherein the anode comprises an outer hollow tube having a lumen extending therethrough, and the cathode comprises a stylet slidably mounted through the lumen.
25. A needle according to claim 24, wherein the needle comprises an insulator material disposed between the anode and the cathode, and an outer coating of semi-permeable tubular material having a lumen extending therethrough, which coating is disposed around the cathode, and arranged, in use, to trap bubbles of gas therebetween.
26. A needle according to any preceding claim, wherein the needle comprises a power source, which in use is arranged to generate electrical current which flows between the anode and cathode.
27. A needle according to claim 26, when dependent on any one of claims 1 to 11, wherein the anode and cathode comprise the same or similar material having the same or substantially similar electrochemical potentials.
28. A needle according to either claim 26 or claim 27, wherein the power source is integral with the needle, or is electrically connected thereto via electrically conductive wires.
29. A needle according to any one of claims 26 to 28, wherein the power source comprises a battery.
30. An echogenic instrument, for use in ultrasonography, the instrument comprising an anode and a cathode, wherein, in use, current flows between the anode and cathode, thereby producing a plurality of bubbles.
31. An instrument according to claim 30, wherein the instrument is a needle according to any one of claims 1 to 29.

-26 -
32. An instrument according to claim 30, wherein the instrument is a stent, catheter, port, drug eluting element, or other implantable or insertable medical device, the position of which should be monitored during a medical procedure.
33. An instrument according to claim 32, wherein the instrument comprises attachment means by which it is attachable to a medical device, or is shaped such that it can be attached to, or inserted into, the medical device.
34. An instrument according to claim 33, wherein the medical device is a stent, catheter, port, drug eluting element, or other implantable or insertable medical device, the position of which should be monitored during a medical procedure.
35. An ultrasound imaging apparatus comprising the echogenic needle according to any one of claims 1 to 29, or the echogenic instrument according to any one of claims 30 to 34, and means for generating ultrasound.
36. A method of carrying out ultrasonography, the method comprising the steps of: (a) introducing, into a medium, the echogenic needle according to any one of claims 1 to 29, or the echogenic instrument according to any one of claims 30 to 34; ) emitting an ultrasound signal in a direction substantially towards the needle or instrument; and (c) detecting ultrasound signal reflected from the needle or instrument.
37. A method of determining the position, in a medium, of the echogenic needle according to any one of claims 1 to 29, or the echogenic instrument according to any one of claims 30 to 34, the method comprising the steps of: (a) introducing, into a medium, the echogenic needle according to any one of claims 1 to 29, or the echogenic instrument according to any one of claims 30 to 34; -27 - (b) emitting an ultrasound signal in a direction substantially towards the needle or instrument; (c) detecting ultrasound signal reflected from the needle or instrument; and (d) determining the position of the needle or instrument in the medium based on the detected ultrasound signal.
38. The method according to either claim 36 or 37, wherein the method comprises forming a conducting bridge comprising subject's cells between the anode and cathode, and creating an electrical current in the conducting bridge.
39. The method according to any one of claims 36 to 38, wherein the method comprises creating gas bubbles at the cathode and/or anode.
40. The method according to any one of claims 36 to 39, wherein the method comprises positioning an ultrasound transducer on a surface of the subject, and transmitting an ultrasonic signal thereto, to thereby cause at least some of the signal to be reflected by the bubbles.
41. The method according to claim 40, wherein the method comprises detecting reflected ultrasound signal by the transducer.
42. The method according to claim 41, wherein the method comprises converting reflected ultrasound signal into an electrical signal suitable for displaying on display means, such as a monitor.
43. The method according to any one of claims 36 to 42, wherein the subject is a vertebrate, mammal, or domestic animal, and is preferably a human being.
44. The apparatus according to claim 35, or the method according to any one of claims 36 to 43, for use in biopsy, inserting or attaching a cannula to a subject, insertion of a central line, in anaesthesia (e.g. regional or local anaesthetic), in keyhole surgery, in cosmetics, for sclerotherapy, for nephrostomy, percutaneous biliary drainage, percutaneous gastrostomy insertion, abscess drainage, drainage of ascites, -28 -insertion of a catheter into the peritoneal cavity, artery or vein cannulation or catheterisation, for atherectomy, or tissue ablation.