WO2008148165A1

WO2008148165A1 - Echogenic medical device

Info

Publication number: WO2008148165A1
Application number: PCT/AU2008/000812
Authority: WO
Inventors: Rowan Thomas Deam; David Tibor Julian Liley
Original assignee: Swinburne University Of Technology
Priority date: 2007-06-06
Filing date: 2008-06-06
Publication date: 2008-12-11

Abstract

A medical device which is provided over only part of its periphery with at least one indentation which in plan is non-circular with a major extent of greater than about a quarter of the wavelength of incident ultrasonic waves but less than the peripheral extension of the medical device, and which in cross-section has a depth and a width of about the quarter wavelength.

Description

ECHOGENIC MEDICAL DEVICE

FIELD OF THE INVENTION

The present invention relates to a medical device having enhanced ultrasonic reflectivity (or echogenicity).

BACKGROUND OF THE INVENTION

Medical devices, such as needles, are commonly positioned in vivo using ultrasonic imaging. It has previously been proposed to modify the surface of a needle to enhance diffuse specular reflection of incident ultrasonic waves from its periphery. Previously proposed echogenic surface modifications generally need to be made around the entire peripheral extension of the needle and/or need to be made with a precise shape in plan. Making echogenic surface modifications around the entire peripheral extension of a thin needle, and/or ensuring they are made on a thin needle with a precise plan shape is difficult and complex.

A need therefore exists for a medical device having a simple yet effective echogenic surface modification which does extend around the entire periphery of the medical device, and which does not have a precise plan shape.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a medical device which is provided over only part of its periphery with at least one indentation which in plan is non-circular with a major extent of greater than about a quarter of the wavelength of incident ultrasonic waves but less than the peripheral extension of the medical device, and which in cross- section has a depth and a width of about the quarter wavelength. The at least one indentation can be wholly or partially provided directly in the medical device itself and/or between at least two asperities provided on the medical device. The at least one indentation and/or the at least two asperities can be microtexturing and/or microstructures.

The present invention also provides a method of making a medical device including the step of providing the medical device over only part of its periphery with at least one indentation which in plan is non-circular with a major extent of greater than about a quarter of the wavelength of incident ultrasonic waves but less than the peripheral extension of the medical device, and which in cross-section has a depth and a width of about the quarter wavelength.

The at least one indentation can be wholly or partially formed directly in the medical device itself and/or between at least two asperities formed on the medical device. The at least one indentation and/or the at least two asperities can be microtexturing and/or microstructures.

The microtexturing and/or microstructures can be formed before, during or after fabrication of the medical device.

The microtexturing and/or microstructures can be formed using a microfabrication process selected from laser ablation, embossing, etching, injection moulding, casting, soft lithography, diamond turning, laser ablation, UV lithography, photolithography, e-beam lithography, ion-beam lithography, printing, spotting, electrode discharge machining, grinding, and combinations thereof.

The medical device can be generally elongate and the at least one indentation can be provided over only part of a transverse cross-section of the medical device. The transverse cross-section can be generally circular, elliptic, square or rectangular. The medical device can be generally hollow and the transverse cross-section can be defined by thin peripheral walls. The shape and size of the at least one indentation at least partially enhance diffuse specular reflection of incident ultrasonic waves from the periphery of the medical device. The at least one indentation can at least partially enhance diffuse specular reflection of incident ultrasonic waves towards an ultrasonic transducer when the at least one indentation faces either generally away from or generally towards the ultrasonic transducer.

The wavelength of incident ultrasonic waves can be in a range of about 100 μm to 1600 μm. The quarter wavelength can therefore be in a range of about 25 μm to 400 μm.

The at least one indention in cross-section can be generally U-shaped.

A plurality of spaced-apart indentations can be provided over only part of the periphery of the medical device in a regular or irregular surface pattern. The mutual spacing of the plurality of indentations can be greater than about the quarter wavelength, for example, in a range of about 100 μm to 500 μm.

The medical device can be selected from a needle, a biopsy needle, a cannula, a stylet, a stent, a guide wire, a dilator, an introducer, forceps, a tissue marker, a catheter, an angiography device, an angioplasty device, and a pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a side view of a needle having partially circumferential echogenic indentations made thereon;

Figure 2 is a cross-section view of the needle of Figure 1 with the partially circumferential echogenic indentions shown by grey shading and broken lines; and Figures 3 and 4 are perspective views of a needle and an ultrasonic transducer operating in respective long and short axis modes; - A -

Figures 5 to 10 are sequences of ultrasound images of indented and smooth needles at various angles of incidence to an ultrasonic transducer in long and short axis operating modes; and

Figures 11 to 13 are images of echogenic microtexturing and microstructures fabricated in or on needles using different microfabrication techniques.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 illustrates a needle 100 having a plurality of spaced-apart indentations 110 each of which only partially extends around the circumference of the needle 100. The indentations 110 can be made in the needle 100 using conventional techniques, for example, laser etching using a computer-controlled excimer laser.

In cross-section, the indentations 110 can be generally U-shaped with a depth and a width of about a quarter of the wavelength of incident ultrasonic waves from an ultrasonic transducer (not shown). For example, for incident ultrasonic waves having a wavelength range of about 100 μm to 1600 μm, the depth and width of the indentations can be in a range of about 25 μm to 400 μm. The mutual spacing of the indentations 110 can be greater than about the quarter wavelength, for example, in a range of about 100 μm to 500 μm.

Figure 2 illustrates that each indentation 110 in plan has a generally non-circular, elongate shape. The major extent of each indentation 110 in plan is less than the circumferential extension of the needle 100, but greater than about a quarter of the wavelength of incident ultrasonic waves. This obviates the need to make the indentations 110 over the entire circumference of the needle 100.

In use, the shape and size of the indentations 110 individually and/or collectively at least partially enhance diffuse specular reflection of incident ultrasonic waves from the circumferential surface of the needle 100. The indentations 110 can at least partially enhance diffuse specular reflection of incident ultrasonic waves towards an ultrasonic transducer when the indentations 1 10 face both generally away from and generally towards the ultrasonic transducer.

Figures 3 and 4 illustrate the needle 100 in use with an ultrasonic transducer 200 operating in respective long and short axis modes. The short axis mode provides easier clinical access, but the long axis mode provides enhanced images. Figures 5 to 10 are sequential example ultrasound images of an indented needle 100 and a smooth needle at a 10° angle of incidence to the normal of the emitting surface of an ultrasonic transducer 200 operating in long and short axis operating modes. Figures 6, 7, 9 and 10 illustrate that the acoustic signature of the indented needle 100 is at least partially enhanced relative to the acoustic signature of the smooth needle in both the long and short axis modes of the ultrasonic transducer 200 when the indentations 110 face both generally away from and generally towards the ultrasonic transducer 200.

An indented needle has been described and depicted by way of non-limiting example only. The echogenic indentations of the present invention can be alternatively implemented in any conventional medical device that is ultrasonically positioned, for example, a biopsy needle, a cannula, a stylet, a stent, a guide wire, a dilator, an introducer, forceps, a tissue marker, a catheter, an angiography device, an angioplasty device, and a pump. The echogenic indentations can be formed in medical devices and/or parts thereof made from metals, polymers, ceramics, and composites and combinations thereof.

The echogenic indentations can be provided as microtexturing in the medical device itself and/or as part of microstructures provided on the medical device. The microtexturing and/or the microstructure can include surface indentations and/or surface asperities. The microtexturing and/or the microstructure can be formed on the medical device before, during or after its fabrication. For example, microstructures can be fabricated on the needle shaft material at any stage of the needle fabrication process. That is, microstructures can be integrated into the needle as the first step of production or as the final step of production, prior to any cleaning and packaging, or at some point between. The fabrication of closely packed features with lateral dimensions in the order of 50μm, with a repeating period of the order lOOμm, and with a precisely controlled depth of the order of 25 μm eliminates many conventional machining processes, especially when these dimensions are combined with the need for a large volume of a low cost, disposable product. Microfabrication offers an attractive library of tools and processes which can produce features of this scale in large batch quantities, therefore offering significant cost savings as well as unique functionality.

In one embodiment, the echogenic indentations of the invention are formed on a needle using laser ablation. Figure 11 illustrates echogenic indentations formed by direct laser ablation of the needle material by frequency tripled Nd: YAG laser.

It will be appreciated that the microtexturing that is created in the shaft of the needle for the purpose of increasing the visibility of the needle during ultra-sound imaging can alternatively be formed using other conventional microfabrication tools and processes.

For example, in another embodiment the echogenic indentations of the invention are formed by microtexturing on a needle. The microtexturing is formed by creating an etch resistant mask on the needle shaft, patterning that mask to expose the stainless steel needle, and chemically etching microstructures into the needle. This process starts by dip coating the end of a pre-fabricated, commercially-available 22G x 65mm nerve block needle in a photo-resist material (AZ5214E). The dip coating creates a layer of material that, after baking for 30 minutes at ~ 120°C to cure the material, is approximately 15μm thick. The polymer coated needle is then presented to a frequency tripled Nd:YAG laser (Avia, Coherent Inc) with a spot size of ~30μm in diameter. The laser beam is scanned over the upper most surface of the needle to remove the photoresist in the desired pattern. The photoresist is completely removed over the irradiated areas so that the stainless steel needle material is exposed. The needle is then placed in a bath of hydrochloric acid at room temperature and etched for 45 minutes to achieve the 25μm deep and 50μm wide microtexturing illustrated in Figure 12. This microfabrication process can be improved, for example, the rate of the chemical etch can be increased by using an electrochemical etch process. One such process uses electrochemical etching to accelerate the pattern transfer process.

In another embodiment, microstructures can be fabricated by patterning a layer of polymer on the needle surface (i.e., not structuring the metallic needle at all). Figure 13 illustrates echogenic indentations between asperities formed as microstructures ablated by a frequency tripled Nd:YAG laser in a layer of photoresist material on the surface of the needle.

Other microfabrication processes can be used to form the echogenic microtexturing and/or microstructures of the invention. For example, echogenic indentations can be fabricated in a photoresist with a number alternative processes such as diamond turning, laser ablation (at various wavelengths, depending on the material being patterned), UV photolithography, e-beam and ion-beam lithography, and printing type processes. Most of these processes, in addition to electrode discharge machining, and grinding using custom cutting wheels can be used to create suitable microstructures directly into metal medical devices, such as needles. In addition, UV lithography, laser ablation, embossing, injection moulding, casting and soft lithography process are some of the processes suitable for creating a polymer structure directly onto metal medical devices, such as needles. The latter processes can also be used to integrate echogenic microtexturing and/or microstructures into polymer parts, such as stents, catheters, etc.

The embodiments have been described by way of example only and modifications are possible within the scope of the claims which follow.

Claims

1. A medical device which is provided over only part of its periphery with at least one indentation which in plan is non-circular with a major extent of greater than about a quarter of the wavelength of incident ultrasonic waves but less than the peripheral extension of the medical device, and which in cross-section has a depth and a width of about the quarter wavelength.

2. A medical device according to claim 1, wherein the at least one indentation is wholly or partially provided directly in the medical device itself and/or between at least two asperities provided on the medical device.

3. A medical device according to claim 2, wherein the at least one indentation and/or the at least two asperities are microtexturing and/or microstructures.

4. A medical device according to any preceding claim, wherein the medical device is generally elongate and the at least one indentation is provided over only part of a transverse cross-section of the medical device.

5. A medical device according to claim 4, wherein the transverse cross-section is generally circular, elliptic, square or rectangular.

6. A medical device according to claim 4 or 5, wherein the medical device is generally hollow and the transverse cross-section is defined by thin peripheral walls.

7. A medical device according to any preceding claim, wherein the shape and size of the at least one indentation at least partially enhances diffuse specular reflection of incident ultrasonic waves from the periphery of the medical device.

8. A medical device according to claim 7, wherein the at least one indentation at least partially enhances diffuse specular reflection of incident ultrasonic waves towards an ultrasonic transducer when the at least one indentation faces either generally away from or generally towards the ultrasonic transducer.

9. A medical device according to any preceding claim, wherein the wavelength of incident ultrasonic waves is in a range of about 100 μm to 1600 μm.

10. A medical device according to any preceding claim, wherein the quarter wavelength is in a range of about 25 μm to 400 μm.

1 1. A medical device according to any preceding claim, wherein the at least one indention in cross-section is generally U-shaped.

12. A medical device according to any preceding claim, wherein a plurality of spaced- apart indentations are provided over only part of the periphery of the medical device in a regular or irregular surface pattern.

13. A medical device according to claim 12, wherein the plurality of indentations are spaced apart from one another by greater than about the quarter wavelength.

14. A medical device according to claim 12 or 13, wherein the plurality of indentations are spaced apart from one another in a range of about 100 μm to 500 μm.

15. A medical device according to any preceding claim, wherein the medical device is selected from a needle, a biopsy needle, a cannula, a stylet, a stent, a guide wire, a dilator, an introducer, forceps, a tissue marker, a catheter, an angiography device, an angioplasty device, and a pump.

16. A method of making a medical device including the step of providing the medical device over only part of its periphery with at least one indentation which in plan is non- circular with a major extent of greater than about a quarter of the wavelength of incident ultrasonic waves but less than the peripheral extension of the medical device, and which in cross-section has a depth and a width of about the quarter wavelength.

17. A method according to claim 16, wherein the at least one indentation is wholly or partially formed directly in the medical device itself and/or between at least two asperities formed on the medical device.

18. A method according to claim 17, wherein the at least one indentation and/or the at least two asperities are microtexturing and/or microstructures.

19. A method according to claim 18, wherein the microtexturing and/or microstructures are formed before, during or after fabrication of the medical device.

20. A method according to claim 19, wherein the microtexturing and/or microstructures are formed using a microfabrication process selected from laser ablation, embossing, etching, injection moulding, casting, soft lithography, diamond turning, laser ablation, UV lithography, photolithography, e-beam lithography, ion-beam lithography, printing, spotting, electrode discharge machining, grinding, and combinations thereof.