Patent Description:
Sheath assemblies having an echogenic feature are known, for instance from <CIT>. See in particular figures <NUM> - 11B of <CIT> and the description related to these figures.

Such sheath assemblies can be used in conjunction with medical devices, such as needles. The echogenic structure allows a medical practitioner, such as physician or nurse to see the medical device on the screen of an ultrasound machine.

These sheaths may be used for various kinds of needles, for instance; biopsy needles, peripheral nerve block needles, microwave, cryogenic, radiofrequency ablation needles, vascular access needles, infusion needles. Obviously, this is a non-limiting list of examples.

<CIT> discloses another echogenic sheath (or cannula) assembly, see the sheath assembly <NUM> in <FIG> and paragraphs <NUM>-<NUM> of the description. This concept is based on the idea of adding a connector <NUM> to the sheath assembly <NUM>, wherein the connector is configured to be connected to the needle housing (hub) <NUM>.

<CIT> discloses another echogenic sheath (or cannula) assembly, see the sheath assembly <NUM> in <FIG> and paragraphs <NUM> of the description. This concept is also based on the idea of adding a connector <NUM> to the sheath assembly <NUM>, wherein the connector is configured to be connected to the needle housing (hub) <NUM>.

It was found in the present invention that all these sheaths have disadvantages. One relevant aspect that was recognized is that there are many different types of needles available on the market, in the order of hundreds or thousands of different types. As an example, for the biopsy system developed by the company BD/Bard, there are different versions called the Magnum and the Monopty. Each of these versions have a different housing (also called handle, luer lock, or hub) for the needle.

Many different suppliers of needles exist and each one generally manufactures its own versions. Therefore, a connector design which can be fixed to every needle handle is not possible from a practical point of view. Sheath assemblies could potentially be made separately for every single needle available on the market, and for every specified length and every found deviation in the specified length. However, this would result in having to produce hundreds if not thousands of different sheath types.

Furthermore, needle assemblies available on the market have different lengths. There is often a variation in needle length, e.g. a <NUM> needle from company X may be <NUM>, and a <NUM> needle from company Y maybe <NUM>. A further aspect is that the tip of the sheath should be positioned close to the tip of the needle. The medical practitioner uses the echogenic tip of the sheath to position the needle tip at the desired location in the human body. When the echogenic tip of the sheath is too far from the tip of the needle, accurate positioning is not possible. Therefore, ideally it should be possible for a medical practitioner to position the tip of the sheath close to the tip of the needle. It was recognized that preferably the tip of the sheath exactly lines up with the proximal end of the bevel, so the doctor knows exactly where the needle tip is.

Different needles have different bevel types and varying bevel angles. The variation in bevel length and bevel angles makes alignment of the echogenic tip with the proximal bevel edge challenging.

One way of overcoming the problem of the variation in needle lengths would be to provide a sheath assembly which can be cut to length by the medical practitioner just prior to the actual use. However, it was recognized that the cutting operation itself may result in mechanical properties of the sheath assembly which are undesirable. For example, the tip of the sheath assembly may comprise splinters or fragments as a result of the cutting, and these splinters or fragments may come loose during use and stay behind in the body of the patient.

Also, as result of the cutting, the mechanical strength of the sheath may be compromised resulting in deformations when the sheath assembly is inserted into the body. For example, the sheath may wrinkle or buckle.

Also, a cutting operation may negatively affect the echogenicity of the sheath assembly.

It is also conceivable to provide a sheath assembly with breaking zones or breaking lines, allowing a user to break off a certain length of the sheath assembly in order to trim the sheath assembly to the required length. However, this provides the risk that in use, a part of the sheath assembly would break off inside the body of the patient which is under treatment. This is also undesirable.

Also, as result breaking zones or breaking lines, the mechanical strength of the sheath may be compromised resulting in deformations when the sheath assembly is inserted into the body. For example, the sheath may wrinkle or buckle.

These circumstances make it difficult to develop an echogenic sheath assembly capable of being used with a variety of needles, from different manufacturers.

<CIT> also discloses a sheath but provides no insight on how to fixate the sheath to the device.

A further problem or rather challenge associated with echogenic sheath assemblies, is that if the sheath would come loose from the needle assembly during use, this brings along with it a risk that the sheath would stay inside the body of the patient. The connector <NUM> disclosed in <FIG> of <CIT> may have this problem. It provides a solid connection when the needle is inserted into the body, but much less when the needle is pulled from the body. The sheath <NUM> may come loose and stay inside the body.

Leaving the sheath behind in the body may result in tissue irritation, an infection or internal bleedings and exposing a patient to an unacceptable health risk. Therefore, a more "general" connector which connects to various different types of housing (handle, luer lock, or hub) could be problematic, as unless used with the specific needle, there is increased chance of coming loose in use.

In addition if the sheath assembly moves during the procedure, the echogenic tip of the sheath may no longer be aligned with the proximal end of the needle bevel, causing the clinician to misposition the needle.

Therefore the connection between the sheath assembly and the needle assembly should be strong enough that once attached, the sheath does not move. Clamps and connectors of various kinds are known from documents <CIT>,
<CIT>, <CIT>, <CIT> and <CIT>.

It is an object of the invention to provide an echogenic sheath assembly which is versatile and can be positioned over needles of different types, lengths and from different manufacturers. The echogenic sheath assembly should be safe in the sense that there is no risk or a negligible risk that the sheath comes loose from the needle assembly or catheter assembly. The sheath assembly should have good echogenic properties.

The invention provides a sheath assembly configured to be positioned over a needle of a needle assembly or over a needle of a catheter assembly, the sheath assembly comprising an elongated tube and a connector, wherein the elongated tube has a defined bore and comprises an echogenic structure, wherein the echogenic structure is configured to be inserted into a body of a patient and to provide echogenicity inside the body, wherein the connector is configured to be fixated to an outside of the cannula wall of the needle, thereby fixating the sheath assembly.

This advantageously allows the sheath assembly to be connectable to the needle assembly independently of the design of a housing (handle, luer lock, or hub) of the needle assembly. The echogenic sheath assembly which connects directly to the needle shaft, solves several problems. The sheath assembly fits any manufacturer's needle regardless of housing or length variation. Moreover, the sheath assembly can be positioned at any point along the needle shaft to line up with the proximal end of the bevel.

In some embodiments, the connector comprises a clamp. This allows a strong gripping force on the outside of the cannula wall.

The clamp may comprise at least a first clamping member and a second clamping member which are movable relative to one another and are configured to clamp the outside of the cannula wall of the needle. In another embodiment, the connector may comprise a single clamping member which has an annular shape and is configured to circumferentially engage the outside of the cannula wall and wherein a circumferential length of the single clamping member can be increased or decreased in order to vary the clamping force on the outside of the cannula wall.

When seen in axial view, the clamp may be configured to engage the cannula wall in three locations, in particular at about <NUM> degrees from one another in the circumferential direction. However, it is also possible that the clamp engages the outside of the cannula wall in more locations, for instance <NUM> - <NUM> locations, or more.

In some embodiments, the connector comprises a biasing member configured for exerting a biasing force which pushes the first and second clamping member towards one another. It was found that the biasing force advantageously provides a very secure fixation.

In some embodiments, the connector comprises an operating member configured to be operated by the user, wherein the operating member is movable between a first position and a second position. In some embodiments, in the first position the connector is not fixated to the needle, allowing the sheath assembly to slide over the needle in order to be positioned or removed from the needle, and in the second position the connector is fixated to the needle. The operating member advantageously allows the user to easily fixate the sheath assembly to the needle.

In some embodiments, the connector comprises a first connector part comprising:.

and a second, annular connector part comprising internal thread, wherein the second connector part is screwed onto the first connector part to press the first and second clamping member together against the outside of the cannula wall.

In some embodiments, the operating member is movable in a direction orthogonal to a main axis of the needle. This direction results in a simple and yet at the same time reliable connector.

In some embodiments, the operating member is configured to move the first and second clamping member away from one another against the biasing force of the biasing member when the operating member is moved to the first position. Advantageously, the user actively loosens the sheath assembly while the biasing force automatically fixates the connector to the needle when the operating member is let go by the user.

In some embodiments, the connector is configured to fixate the sheath assembly to the needle via friction. It was found that friction provides a secure connection.

In some embodiments, the first and second clamping member each have a curved, concave clamping surface. Advantageously, the curved concave clamping surface matches with the shape of the needle. This results in a high friction force. Alternatively, the clamping surface may be straight.

In some embodiments, the first and second clamping member are provided with sharp protrusions or with a covering layer of anti-slip material. The sharp protrusions or anti-slip material advantageously improve the fixation.

In some embodiments, the second clamping member is a housing and wherein at least a part of the first clamping member is movably arranged within the housing. This may provide a simple and robust connector.

In some embodiments, the connector comprises a housing having a first hole in a first housing wall and a second hole in an opposite, second housing wall, wherein the first and second hole have an edge, wherein the edges define the first clamping member,.

This configuration provides a user-friendly embodiment which is very practical and reliable. Also the combination of the housing and the clamping member which is movably arranged within the housing allows a strong gripping force.

In some embodiments, the second clamping member comprises a clamping hole, wherein the first clamping member is movable between:.

The needle of the needle assembly or catheter assembly can be inserted through the clamping hole and is and supported in all lateral directions. Also a very strong gripping force is possible with this embodiment.

In some embodiments, the connector is not capable of being connected to a casing, housing, base, handle, hub or luer lock of a needle assembly.

In some embodiments, the biasing member extends around the housing and is connected to the operating member outside of the housing and to the housing itself. This embodiment allows a small housing in combination with a large and strong biasing member capable of exerting a gripping strong force to keep the sheath assembly in place.

In some embodiments, the sheath assembly is constructed and intended to be positioned over a needle or catheter assembly for biopsy, vascular access orperipheral nerve block applications. These were found to be the usages in which the sheath assembly provides the most benefits.

In various embodiments the one or more clamping member and the biasing member are integrated into a single resilient member. This results in a simple yet strong connector.

In one such embodiment, the single resilient member is a spring which defines an opening and is biased to a gripping position, wherein the spring comprises a first handle and a second handle configured to be pushed toward one another by a user with his or her fingers, thereby deforming the spring against a spring force to a more open form, wherein after the user lets go of the handles, the resilient member deforms back to a clamped position under the influence of the spring force. In another embodiment, the clamp may for instance be a ratchet clamp. In yet another embodiment, the clamp may be a slit clamp as explained further below.

In another embodiment, the clamp may be a hose clamp. Hose clamps are known to be very reliable and easy to operate.

In some embodiments, the echogenic structure comprises a material with a different acoustic impedance than the tissue: fat, vein, artery, organ or muscle or any other body part into which the needle is inserted. The difference in acoustic impedance between the tissues fat, vein, organ or muscle and the echogenic structure causes the ultrasound signal to be reflected back to the ultrasound transducer, and an image of the device to appear on the ultrasound screen. The material of the echogenic structure may be harder than any tissue of the human body, e.g. glass which has an acoustic impedance of about <NUM> × <NUM><NUM> kg/m2. Alternatively, the material may be air or another gas. Air has an acoustic impedance <NUM> × <NUM><NUM> kg/m2. of Both a hard material and air or another gas have an acoustic impedance which is very different from the tissue of the human body.

In some embodiments, the echogenic structure is incorporated in a coating which is applied on the elongated tube.

In an embodiment, the coating comprises small particles, said small particles being manufactured from a material different than, the coating layer itself.

In some embodiments, the particles are gas, solid, gel or liquid particles.

In some embodiments, the particles are solid, gel or liquid particles, in particular glass, sand or crystal particles.

In some embodiments, the echogenic structure is not applied over the full length of the elongated tube, but only over a part of the length thereof. It was found that applying the echogenic structure over the distal end of the elongated tube improves the medical practitioner's ability to locate the tip.

In some embodiments, the coated echogenic structure has a length which at most extends over <NUM> percent of the length of the elongated tube, in particular over at most <NUM> percent, more in particular over at most <NUM> percent of the length of the elongate tubule. This ensures that the medical practitioner can clearly identify the needle tip.

In some embodiments, the echogenic structure is located at a distal end of the sheath and not at a proximal end of the sheath, in particular at the end of the elongated tube which is opposite to the end where the connector is located. It was advantageously found that the echogenic structure only needs to be applied at the tip of the elongated tube in order to allow the medical practitioner to accurately position the needle inside the body of the patient.

In some embodiments, the coated echogenic structure has a length of less than <NUM>. It was found that this length is sufficient for a medical practitioner to see the tip of the sheath assembly on the screen and to accurately position the needle on the basis of this information.

In some embodiments, the particles are solid microspheres. Solid microspheres advantageously reflect the sound waves in all directions. In this way, the sheath assembly is visible for the medical practitioner from all sides.

In some embodiments, the echogenic structure is manufactured from metal.

In some embodiments, the elongated tube comprises a tube wall which comprises a first, inner layer and a second, outer layer, and wherein the echogenic structure is:.

In some embodiments, the elongated tube is made from a polymer tubing, in particular Polyurethane, PolyEther Ketone, Polyether ether ketone, PEVAc, POM, PTSE, PEBAX, Nylon, PET, polyimide, polyamide, polyester, polycarbonate, PVC, polyethylene, polypropylene, FEP, silicone.

In some embodiments, the echogenic structure comprises gas bubbles inside the tube wall of the elongated tube or an echogenic structure adhesively bonded to the tube wall of the elongated tube.

In some embodiments, the echogenic structure comprises small particles, inside the tube wall of the elongated tube, the small particles being manufactured from a material different than the elongated tube wall itself.

In some embodiments, the particles are gas, solid, gel or liquid particles, preferably glass particles.

In some embodiments, the proximal end of the elongated tube at the connector tapers outwardly and distal end of the elongated tubed does not taper outwardly.

In some embodiments, the echogenic structure comprises a coating and solid microspheres embedded in the coating layer, wherein the echogenic structure is only provided at the distal end of the elongated tube, and wherein the connector comprises a clamp comprising a first clamping member and a second clamping member and a biasing member configured for exerting a biasing force which pushes the first and second clamping member towards one another.

The present invention further relates to a set of a sheath assembly according to the invention and a catheter assembly or needle assembly, wherein a shape of the connector corresponds with a radius of the outside of the cannula wall of the catheter assembly or needle assembly, wherein in particular a radius of the concave clamping surface of the first and second clamping member corresponds to a radius of the outside of the cannula wall.

In some embodiments of the set, the concave clamping surface of the first and second clamping member have a radius which is <NUM>-<NUM> percent of the radius of the outside of the cannula wall.

In some embodiments of the set, the connector is not capable of being connected to a casing, housing, base, handle, hub or luer lock of the needle assembly or catheter assembly.

The needle of the set may comprise notches in the outside of the cannula wall configured for providing grip for the connector of the sheath assembly. This may improve the fixation of the connector onto the needle.

The present invention further relates to a method for making a sheath assembly according to the invention, the method comprising:.

These and other aspects of the invention can be better understood by reference to the following detailed description and the accompanying drawings. In the accompanying drawings like reference symbols designate like parts.

Turning to <FIG>, a sheath assembly <NUM> is shown which is configured to be positioned over a needle <NUM> of a needle assembly <NUM> or over a needle of a catheter assembly. The sheath assembly <NUM> comprises an elongated tube <NUM> (also called sheath <NUM>) which defines a bore <NUM> and an echogenic structure <NUM>.

The sheath assembly further comprises a connector <NUM> configured to fixate the sheath assembly to the outside of the cannula wall <NUM> of the needle <NUM>. The connector is positioned at a proximal end of the sheath assembly.

The connector <NUM> is relatively small in order not to hinder the user or the patient. The outer dimensions may be smaller than <NUM> (length) by <NUM> (width) by <NUM> (height). In this way almost the full needle length or catheter length can be used.

With particular reference to <FIG>, the connector <NUM> comprises a clamp <NUM> comprising at least a first clamping member <NUM> and a second clamping member <NUM> and a biasing member <NUM> configured for exerting a biasing force which pushes the first and second clamping member towards one another.

The connector <NUM> further comprises an operating member <NUM> configured to be operated by the user, wherein the operating member <NUM> is movable in a direction <NUM> between a first position and a second position, wherein in the first position the connector <NUM> is not fixated to the needle <NUM>, allowing the sheath assembly to slide over the needle in order to be positioned or removed from the needle, and wherein in the second position the connector is fixated to the needle.

The operating member <NUM> is movable in a direction <NUM> orthogonal to a main axis <NUM> of the elongated tube <NUM>.

The operating member <NUM> is configured to move the first and second clamping member <NUM>, <NUM> away from one another against the biasing force of the biasing member <NUM> when the operating member is moved to the first position.

The connector <NUM> is configured to fixate the sheath assembly to the needle via friction.

At least one of the first and second clamping member <NUM>, <NUM> may have a curved, concave clamping surface <NUM>, <NUM>.

The first and second clamping member <NUM>, <NUM> may be provided with sharp protrusions or with a covering layer of anti-slip material.

The connector comprises a housing <NUM> having a first hole <NUM> in a first housing wall <NUM> and a second hole <NUM> in an opposite, second housing wall <NUM>. The elongated tube <NUM> is connected to the second housing wall <NUM>.

The first hole <NUM> and second hole <NUM> each have an edge, wherein the edges define the second clamping member <NUM>, wherein the first clamping member <NUM> is movably arranged inside the housing <NUM>, wherein the biasing member <NUM> comprises a spring, wherein the operating member moves the first clamping member from a clamping position to a disengaged position, wherein the spring biases the movable gripping member toward the clamping position.

The first clamping member <NUM> comprises a clamping hole <NUM>, wherein the first clamping member is movable between:.

When seen in side view, see <FIG>, the second clamping member <NUM> comprises a first clamping surface <NUM> and a second clamping surface <NUM> located at a distance from one another and associated with respectively the first hole <NUM> and the second hole <NUM>. The first and second clamping surface <NUM> engage the outside of the cannula wall from one side. The clamping surface <NUM> of the first clamping member <NUM> engages the outside of the cannula wall from the opposite side. In side view, the clamping surface <NUM> of the first clamping member <NUM> is located between the first and the second clamping surface <NUM>. In this way the clamp provides a three point clamping arrangement. Obviously, the clamp may engage the outside of the cannula wall in more than three locations, when seen in side view.

The connector <NUM> is not capable of being connected to a casing <NUM>, housing, base, handle, hub or luer lock of a needle assembly, only to the needle <NUM> itself. The connector may abut the casing, housing, base, handle, hub or luer lock of a needle assembly, though.

The sheath assembly <NUM> may in particular be constructed and intended to be positioned over a needle of a needle assembly for vascular access, or over a needle of a catheter assembly for a biopsy or for a peripheral nerve block.

The echogenic structure <NUM> comprises a coating which is applied on the elongated tube <NUM>.

The echogenic structure <NUM> comprises the coating and small particles, said small particles being manufactured from a material with an different acoustic impedance than the coating layer itself, the tissue, fat, vein, artery, organ or muscle or any other body part into which the needle is inserted, wherein the ultrasound signal is reflected back to the ultrasound transducer, and an image of the device appears on the ultrasound screen.

The particles are gas, solid, gel or liquid particles. The particles may in particular be glass, sand or crystal particles. The particles may be solid microspheres.

The echogenic structure <NUM> is not applied over the full length <NUM> of the elongated tube <NUM>, but only over a part <NUM> of the length thereof. The length <NUM> of the elongated tube may be <NUM>-<NUM>, in particular about <NUM> as shown in <FIG>. However, for different applications, different lengths may be used.

The echogenic structure has a length <NUM> which extends over at most <NUM> percent of the length of the elongated tube, in particular over at most <NUM> percent, more in particular over at most <NUM> percent of the length of the elongate tubule. The echogenic structure may have a length <NUM> of less than <NUM>.

The echogenic structure is located at a distal end <NUM> of the sheath and not at a proximal end <NUM> of the sheath, in particular at the end of the elongated tube <NUM> which is opposite to the end where the connector <NUM> is located.

In addition or in an alternative variant the echogenic structure or a part thereof is manufactured from metal.

The elongated tube <NUM> may comprise a tube wall <NUM> which comprises a first, inner layer <NUM> and a second, outer layer <NUM>, and wherein the echogenic structure is:.

This is further discussed in relation to <FIG>.

The elongated tube <NUM> may be made from a polymer tubing, in particular Polyurethane, PolyEther Ketone, Polyether ether Ketone, PEVAc, POM, PTSE, PEBAX, Nylon, PET, polyimide, polyamide, polyester, polycarbonate, PVC, polyethylene, polypropylene, FEP, silicone.

Additionally or alternatively, the echogenic structure may comprise gas bubbles inside the tube wall of the elongated tube or a echogenic structure adhesively bonded to the tube wall of the elongated tube.

The distal end <NUM> of the tube <NUM> does not taper outwardly.

The echogenic structure may comprise a coating and solid microspheres embedded in the coating layer, wherein the echogenic structure is only provided at one end, the distal end, of the elongated tube and has a length <NUM> of less than <NUM> percent of the length <NUM> of the elongated tube <NUM>, the length <NUM> being less than <NUM>. The connector <NUM> comprises a clamp comprising a first clamping member <NUM> and a second clamping member <NUM> and a biasing member <NUM> configured for exerting a biasing force which pushes the first and second clamping member towards one another.

The present invention also relates to a set <NUM> of a sheath assembly <NUM> according to any of the preceding claims <NUM> - <NUM> and a catheter assembly or needle assembly <NUM>, wherein a shape of the connector <NUM> corresponds with a radius r1 of the outside of the cannula wall <NUM> of the catheter assembly or needle assembly. In particular a radius r2 of the concave clamping surfaces <NUM>, <NUM> of the first and second clamping member corresponds to the radius r1 of the outside of the cannula wall.

The concave clamping surfaces <NUM>,<NUM> of the first and second clamping member <NUM>, <NUM> may have a radius which is <NUM>-<NUM> percent of the radius of the outside of the cannula wall.

The connector <NUM> may not be capable of being connected to a casing, housing, base, handle, hub or luer lock of the needle assembly or catheter assembly which is part of the same set.

A method for making a sheath assembly according to any the invention may comprise:.

Turning in particular to <FIG>, in operation, a medical practitioner may have a set as disclosed above comprising a needle assembly <NUM> or catheter assembly on the one hand and a sheath assembly <NUM> on the other hand.

The sheath assembly may come in a separate package and may not be specifically designed for the exact length of the needle of the needle assembly or catheter assembly. Instead, the sheath assembly <NUM> can be used for a range of needle assemblies <NUM> or catheter assemblies.

The medical practitioner holds the needle assembly <NUM> or catheter assembly with one hand 59A, takes the sheath assembly <NUM> with his other hand 59B, and pushes the operating member <NUM> downward and slides the elongated tube <NUM> over the needle <NUM> until the tip <NUM> (also called the distal end <NUM>) is positioned just at the edge <NUM> of the bevel <NUM> of the needle <NUM>. The medical practitioner can check this visually. In this position, the user releases the operating member <NUM> and the sheath assembly is fixated to the needle <NUM>.

The completed assembly is now ready for use. The medical practitioner can insert the needle <NUM> with the sheath into the patient. The ultrasound signal is reflected back to the ultrasound transducer, and an image of the device appears on the screen of an ultrasound imaging device. The echogenic structure allows the user to see where the needle tip is inside the body and to controllably move the needle tip inside the body.

When the medical practitioner is ready with the treatment, he or she can retrieve the completed assembly from the body by pulling back the needle, The sheath assembly <NUM> will automatically also be pulled back as a result of the connector <NUM> which provides the fixation.

Because the connector can be positioned anywhere along the needle <NUM>, there is no need for cutting the sheath <NUM> to length.

Turning to <FIG>, in another embodiment, the connector <NUM> comprises one or more finger grips <NUM> which protrude from the housing. The second hole <NUM> tapers outwardly.

The clamping hole <NUM> has a shape of a triangle or a triangle with a chamfered corner. The first and second holes <NUM>, <NUM> may have a similar shape but mirrored. As can be seen in <FIG> these two shapes together define a triangular through passage <NUM> which in use defines three contact points with the needle. In other words, the clamp is configured to engage the cannula wall in three locations. These three locations may in particular be located at about <NUM> degrees from one another in the circumferential direction.

Turning to the embodiment of <FIG>, this embodiment is essentially the same as the embodiment of <FIG>, except that the clamping hole <NUM> is oval. The first and second holes <NUM>, <NUM> are circular.

Turning to the embodiment of <FIG>, in this embodiment the biasing member <NUM> is located outside the housing <NUM>. The biasing member <NUM> extends around the housing <NUM> and is connected to the operating member <NUM> outside of the housing. The biasing member is also connected to the housing <NUM> itself, in particular to a bottom side <NUM> of the housing. The biasing member may have an oval shape. This makes it possible to apply a large and strong biasing member.

Turning to <FIG>, in another embodiment, the echogenic structure <NUM> may be a metal structure extending around the tube <NUM>. In particular the echogenic structure may be a metal coil which spirals around the tube <NUM>. The tube <NUM> may have a first inner layer and a second outer layer and the echogenic structure may be located between the first and second layer. The metal coil may only extend over a portion of the length of the tube <NUM>, or may extend over the entire length of the tube <NUM>.

Turning to <FIG>, in another embodiment, the connector <NUM> comprises first connector part <NUM> comprising:.

and a second, annular connector part <NUM> comprising internal thread <NUM>, wherein the second connector part is screwed onto the first connector part to press the first and second clamping member <NUM>, <NUM> together against the outside of the cannula wall. The tube <NUM> is connected to the first connector part <NUM>. This allows a very strong fixation of the sheath assembly onto the needle assembly or catheter assembly.

Turning to <FIG>, in another embodiment, the connector comprises a clamp having a single clamping member <NUM> which has an annular shape and is configured to circumferentially engage the outside of the cannula wall. A circumferential length of the single clamping member can be increased or decreased in order to vary the clamping force on the outside of the cannula wall. In this case the single clamping member <NUM> is a coiled spring <NUM>.

The spring <NUM> defines an opening and is biased to a gripping position. The spring comprises a first handle <NUM> and a second handle <NUM> configured to be pushed toward one another by a user with his or her fingers, thereby deforming the spring against a spring force to a more open form having a greater circumferential length, wherein after the user lets go of the handles <NUM>, <NUM>, the resilient member deforms back to a clamped position under the influence of the spring force. The handles are connected to opposite ends of the coiled spring.

Turning to <FIG>, in another embodiment, the clamp <NUM> is a hose clamp and comprises a strip <NUM> defining a circumference around an opening and an adjustment device <NUM>, in particular a rotary device. The adjustment device <NUM> engages a first portion of the strip and a second portion of the strip, wherein the adjustment device is configured to adjust a circumferential length of the strip, thereby controlling the fixation of the clamp <NUM> on the outside of the cannula wall.

Turning to <FIG>, in another embodiment, the connector <NUM> comprises a ratchet clamp <NUM>. The ratchet clamp <NUM> is self locking and comprises a single clamping member <NUM> which has an annular shape and is configured to circumferentially engage the outside of the cannula wall. The resilient body <NUM> defines an opening and extends at least partially around said opening. The ratchet clamp comprises a first ratchet member <NUM> and a second ratchet member <NUM> configured to engage one another and comprising respectively a first ratchet <NUM> and a second ratchet <NUM>. The user can simply press the first and second ratchet members together, thereby fixating the connector <NUM> onto the outside of the cannula wall.

Turning to <FIG>, in this embodiment, the clamp <NUM> comprises a body <NUM> comprising:.

The upper and lower slit part <NUM>, <NUM> extend from the tubular base towards the distal end <NUM> of the sheath assembly <NUM>. When viewed in an axial direction of the sheath assembly <NUM> the first and second slit part <NUM>, <NUM> are located within the bore of the elongated tube <NUM>. The first and second slit part <NUM>, <NUM> are resilient and allow the needle <NUM> to slide through the slit <NUM> in one direction but resist a sliding movement of the needle in an opposite direction.

Turning to <FIG>, in a further embodiment, the echogenic structure <NUM> comprises particles or gas bubbles <NUM> inside the sheath <NUM>. In case of gas bubbles, the gas may be air. In case of particles, the particles are manufactured from a material different than the tube wall itself, for instance glass particles. The bubbles or particles may have a same size or have different sizes. The bubbles or particles may have various shapes such as spheres, cubes, cylinders, polyhedrons or irregular shapes. The bubbles or particles may be arranged in an orderly manner.

Turning to <FIG>, in another embodiment, the echogenic structure comprises a metal material located between an inner layer <NUM> and an outer layer <NUM>. The echogenic structure can also be located on the outer side of the inner layer, or on the inner side of the outer layer. The metal echogenic structure can be in the shape of a coil or a braid.

Turning to <FIG>, in another embodiment the particles or bubbles <NUM> may have varying sizes and may be randomly dispersed in the cannula wall. Obviously, the particles and/or bubbles may also have uniform sizes (and shape).

Turning to <FIG>, in another embodiment, the needle of the needle assembly has ridges or grooves (<NUM>) or more generally a roughened surface for instance in the form of a pattern. This may further improve the gripping connection. The notches or grooves may extend circumferentially. A plurality of circumferential notches or grooves may be provided. The ridges, grooves or roughened surface extends over a limited length in the axial direction.

It will be clear to the skilled person that different embodiments of the connectors can be combined with different embodiments of the echogenic structure.

The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising i.e., open language, not excluding other elements or steps.

Claim 1:
Sheath assembly (<NUM>) configured to be positioned over a needle (<NUM>) of a needle assembly (<NUM>) or over a needle of a catheter assembly, the sheath assembly comprising an elongated tube (<NUM>) and a connector (<NUM>),
wherein the elongated tube has a defined bore (<NUM>) and comprises an echogenic structure (<NUM>), wherein the echogenic structure is configured to be inserted into a body of a patient and to provide echogenicity inside the body,
characterized in that
the connector (<NUM>) is configured to be fixated to an outside of the cannula wall of the needle, thereby fixating the sheath assembly.