WO2008129249A2

WO2008129249A2 - Fiducial marker

Info

Publication number: WO2008129249A2
Application number: PCT/GB2008/001347
Authority: WO
Inventors: Mark De Langen; Stuart Green; Jorge Schlegel
Original assignee: Invibio Limited
Priority date: 2007-04-20
Filing date: 2008-04-17
Publication date: 2008-10-30
Also published as: WO2008129249A3; GB0707671D0; CA2684564A1; EP2139420A2

Abstract

A fiducial marker which is visible to a wide range of imaging techniques, comprises a radiopaque material, comprising zirconium moieties, encapsulated in a biocompatible polymeric material, for example a polyaryletherketone such as polyetheretherketone.

Description

Fiducial Marker

This invention relates to fiducial markers.

Visualisation techniques such as computer tomographic (CT) X-ray imaging and magnetic resonance imaging (MRI) machines are now well-known systems for imaging structures of the human body for subsequent assessment by a clinician to establish if any abnormalities are present. In the event of any abnormalities, for example a cancer, being noted the body may be subjected to focused treatment to remove or destroy the abnormality, for example using chemotherapy, radiation therapy and/or surgery.

In chemotherapy, drugs are used to destroy the abnormality. During the course of a treatment visualisation techniques are used to monitor the progress of the treatment and the effect of the treatment can be assessed by comparison of images taken over the course of ^'the treatment.

In radiation therapy, images of the abnormality are used by a radiologist to adjust the irradiating device and to direct radiation solely at the abnormality while minimizing or eliminating adverse effects to surrounding healthy tissue. During the course of the radiation treatment, visualization techniques are used to follow the progress of the treatment.

When surgery is used to remove an abnormality, the images of the lesion in the patient can guide the surgeon during the operation. By reviewing the images prior to surgery, the surgeon can decide the best strategy for reaching and biopsying, excising, or otherwise manipulating the abnormality. After surgery has been performed, further scanning is utilized to evaluate the success of the surgery and the subsequent progress of the patient.

It will be appreciated from the above that there is a need associated with the aforementioned - visualization techniques and/or treatments to provide a means of accurate selection and comparison of views of identical areas in images which have been obtained by imaging techniques at different times or at the same time using two or more different imaging techniques, such as both CT and MRI techniques. It is known to use fiducial markers to address the aforementioned problems. Such markers are artificial markers which are introduced into a human body and fixed in position by a surgeon at or adjacent an abnormality to provide a clear and accurate reference point which is visible on scans produced using visualization techniques such as CT and MRI techniques.

It is known to use markers in the form of wire or beads made of highly radiopaque materials such as gold or tantalum. However, there are problems associated with such materials. For example it is found that in a CT scan, the gold or tantalum marker may lead to production of artefacts in the image produced, for example information may be missing and/or "starbursts" may be present, leading to difficulties in accurately interpreting the images. Also, in MRI techniques, eddy currents may be produced in the gold or tantalum which again may result in the production of artefacts which render image interpretation more difficult. It is desirable that any fiducial marker is visible under MRI, CT and X-ray imaging so that, in any situation, one or more of the techniques may be used to visualize any marker .

It is also desirable to use fiducial markers which are as small as possible, to minimise patients' discomfort. On the other hand clinicians require markers to provide a strong signal which implies such markers should be as large as possible.

It is an object of the present invention to address problems associated with fiducial markers.

It is an object of the present invention to provide a fiducial marker which is small enough to be left in a patients' body with minimum discomfort and yet which is clearly visible under a range of imaging techniques, such as CT, MRI and conventional X-ray techniques with minimal artefacts such as starbursts.

According to a first aspect of the invention, there is provided a fiducial marker which comprises a radiopaque material encapsulated in a bio-compatible polymeric material, wherein said radiopaque material comprises zirconium moieties.

Said marker suitably has a maximum dimension measured in a first direction of less than 50mm. In this case, a marker may be elongate, for example in the form of a string or the like. Suitably, said marker has a maximum dimension measured in a first direction of less than 10mm, preferably less than 8mm, more preferably less than 6mm, especially less than 4mm. The maximum dimension may be at least lmm or at least 2mm. Typically, the maximum dimension in said first direction may be in the range 1.5 to 4mm.

Said marker preferably has a dimension in a second direction perpendicular to the first direction which is less than said maximum dimension in said first direction. The ratio of the maximum dimension in said first direction to said dimension in said second direction may be greater than 1, preferably greater than 1.1, more preferably greater than 1.3, especially greater than 1.5. The ratio may be less than 5, preferably less than 4, more preferably less than 3, especially less than 2.

The volume of the marker may be less than 20mm³, suitably less than 15mm³, preferably less than 10mm³, more preferably less than 8mm³, especially less than 6mm³. The volume may be at least 0.75mm³, preferably at least lmm³.

The density of the marker may be at least 1.1 g/cm³, suitably at least 1.2 g/cm³, preferably at least 1.3 g/cm³, more preferably at least 1.5 g/cm³, especially at lest 1.6 g/cm³. The density may be less than 3.5 g/cm³, suitably less than 3.2 g/cm³. Typically the density may be in the range 1.5 to 3 g/cm³.

Said marker preferably has a substantially constant cross- section along at least 50%, suitably at least 70%, preferably at least 90%, more preferably at least 95%, especially about 100%, of its extent in one direction, for example said first direction referred to. Said cross- section is preferably substantially symmetrical about a first plane which bisects the cross-section in one direction; preferably also it is symmetrical about two mutually orthogonal planes which bisect the cross-section. Said cross-section preferably includes a substantially circular outer wall. Said cross-section described may be substantially annular or circular. It preferably includes substantially no void areas.

Said cross-section preferably has an area of less than 5mm², preferably less than 4mm², more preferably less than 3mm², especially less than 2mm². The area may be less than 1.5mm². The area is preferably greater than 0.5mm².

Said cross-section is preferably of substantially constant shape on moving from one side of the marker to an opposite side thereof.

In an alternative embodiment, said marker may be substantially spherical.

Said fiducial marker may be in the form of an extruded tube, coil or solid member. Said marker preferably includes substantially no void areas; it is preferably substantially solid throughout.

Said radiopaque material is preferably an integral part of said marker. Said radiopaque material is preferably not fiowable within the marker. Said radiopaque material is preferably substantially immovably fixed in position in said marker so that its position relative to that of the polymeric material is substantially immovably fixed. Said radiopaque material is preferably covered, at least in part, by said bio-compatible polymeric material. Said radiopaque material is preferably substantially fully enclosed by said bio-compatible polymeric material.

Radiopaque material and polymeric material are preferably contiguous. Preferably substantially all of the radiopaque material is contiguous with bio-compatible polymeric material.

Said fiducial marker preferably includes no part which is arranged to be moved, for example pivoted, between predetermined first and second positions. Said marker preferably includes no moving parts. It should be appreciated however that this does not exclude the possibility of the marker being manipulated, for example bent, into any particular shape.

Said fiducial marker preferably comprises radiopaque material and polymeric material which have been extruded.

Said fiducial marker may have a weight of at least 3 mg, preferably at least 5 mg . The weight may be less than 100 mg, suitably less than 75 mg, preferably less than 50 mg, more preferably less than 25 especially less than 10 mg .

Said marker may include at least lwt%, suitably at least 3wt%, preferably at least 10wt%, more preferably at least 20wt%, especially at least 30wt% of radiopaque material. In some embodiments said marker may include at least 35wt% or at least 40wt% of said radiopaque material. Tne amount of radiopaque material may be less tnan 80wt%, suitably less than 70wt%, preferably less than 60 wt%, more preferably 55wt% or less, especially 50wt% or less.

Said marker may include at least 30wr%, preferably at least 40wt%, more preferably at least 45wt%, especially at least 50wt% of said bio-compatible material. The amount of bio-compatible polymeric material may be 97wt% or less, suitably 90wt% or less, preferably 80wt% or less, more preferably 70wt% or less, especially 65wt% or less.

The sum of the wt% of said bio-compatible polymeric material and said radiopaque material in said fiducial marker may be at least 60wt%, suitably at least 70wt%, preferably at least 80wt%, more preferably at least 90wt%, especially at least 99wt%.

Said bio-compatible polymeric material may be any polymeric material which is non-toxic and not otherwise harmful when introduced into the human or animal body as a fiducial marker.

Said bio-compatible polymeric material may have a Notched Izod Impact Strength (specimen 80mm x 10mm x 4mm with a cut 0.25mm notch (Type A), tested at 23°C, in accordance with ISO180) of at least 4KJm^"2, preferably at least 5KJm^"2, more preferably at least 6KJm^"2. Said Notched Izod Impact Strength, measured as aforesaid, may be less than 10KJm^"2, suitably less than 8KJm^"2.

The Notched Izod Impact Strength, measured as aforesaid, of the composite material of said fiducial marker may be at least 3KJm^"2, suitably at least 4KJm^"2, preferably at least 5KJm . Said impact strength may be less than 50 KJm^"2, suitably less than 30KJm^"2.

Said bio-compatible polymeric material suitably has a melt viscosity (MV) of at least 0.06 kNsrrf², preferably has a MV of at least 0.09 kNsπf², more preferably at least 0.12 kNsiτf², especially at least 0.15 kNsrrf².

MV is suitably measured using capillary rheometry operating at 400°C at a shear rate of 1000s^"1 using a tungsten carbide die, 0.5x3.175mm.

Said bio-compatible polymeric material may have a MV of less than 1.00 kNsrrf², preferably less than 0.5 kNsrrf².

Said bio-compatible polymeric material may have a MV in the range 0.09 to 0.5 kNsm^"2, preferably in the range 0.14 to 0.5 kNsm^"2.

Said bio-compatible polymeric material may have a tensile strength, measured in accordance with ISO527 (specimen type Ib) tested at 23°C at a rate of 50mm/minute of at least 20 MPa, preferably at least 60 MPa, more preferably at least 80 MPa. The tensile strength is preferably in the range 80-110 MPa, more preferably in the range 80-100 MPa.

Said bio-compatible polymeric material may have a flexural strength, measured in accordance with ISO178 (80mm x 10mm x 4mm specimen, tested in three-point-bend at 23°C at a rate of 2mm/minute) of at least 50 MPa, preferably at least 100 MPa, more preferably at least 145 MPa. The flexural strength is preferably in the range 145-180MPa, more preferably in the range 145-164 MPa.

Said bio-compatible polymeric material may have a flexural modulus, measured in accordance with ISO178 (80mm x 10mm x

4mm specimen, tested in three-point-bend at 23°C at a rate of 2mm/minute) of at least 1 GPa, suitably at least 2 GPa, preferably at least 3 GPa, more preferably at least 3.5

GPa. The flexural modulus is preferably m the range 3.5- 4.5 GPa, more preferably m the range 3.5-4.1 GPa.

Said bio-compatible polymeric material may be amorphous or semi-crystalline. It is preferably semi-crystalline . The level and extent of crystallinity in a polymer is preferably measured by wide angle X-ray diffraction (also referred to as Wide Angle X-ray Scattering or WAXS), for example as described by Blundell and Osborn (Polymer 24 , 953, 1983). Alternatively, crystallinity may be assessed by Differential Scanning Calerimetry (DSC).

The level of crystallinity of said bio-compatible polymeric material may be at least 1%, suitably at least 3%, preferably at least 5% and more preferaoly at least 10%. In especially preferred embodiments, the crystallinity may be greater than 25%.

The main peak of the melting endotherm (Tm) of said biocompatible polymeric material (if crystalline) may be at least 300⁰C.

Said bio-compatible polymeric material may include a polymeric moiety which is: an acrylate (e.g. it comprises or consists of methylmethacrylate moieties); a uretnaⁿe, a vinyl chloride; a silicone; a siloxane (eg comprising dimethylsiloxane moieties); a sulphone; a carbonate; a fluoroalkylene (e.g. a fluoroethylene) ; an acid (e.g. a glycolic acid or lactic acid); an amide (e.g. comprising nylon moieties); an alkylene (e.g. ethylene or propylene); an oxyalkylene (e.g. polyoxymethylene) ; an ester (e.g. polyethylene terephthalate) , an ether (e.g. an aryletherketone, an arylethersulphone (e.g. polyethersulphone or polyphenylenesulphone) or an ether lmide) .

Said bio-compatible polymeric material may be a resorbable polymer .

Said bio-compatible polymeric material may be selected from a polyalkylacrylate (e.g. polymethylmethacrylate), a polyfluoroalkylene (e.g. PTFE), a polyurethane, a polyalkylene (e.g. polyethylene or polypropylene), a polyoxyakylene (e.g. polyoxymethylene), a polyester (e.g. polyethylene terephthalate or polybutylene terephthalate) , a polysulphone, a polycarbonate, a polyacid (e.g. polyglycolic acid or polylactic acid) , a polyalkylene oxide ester (e.g. polyethylene oxide terephalate) a polyvmylchloride, a silicone, a polysiloxane, a nylon, , a polyaryletherketone, a polarylethersulphone, a polyether imide and any copolymer which includes any of the aforementioned .

Preferably, saj_d bio-compatible polymeric material is selected from resorbable polymers, polyethylene, polypropylene, silicone and polyetheretherkecone . More preferably, sa_i_d polymeric material is selecceα from polyethylene, polypropylene, silicone and polyetheretheketone .

Said bio-compatible polymeric material may be a homopolymer having a repeat unit of general formula

or a homopolymer having a repeat unit of general formula

or a random or block copolymer of at least two different units of IV and/or V

wherein A, B, C and D independently represent 0 or 1,

E and E' independently represent an oxygen or a sulphur atom or a direct link, G represents an oxygen or sulphur atom, a direct link or a -O-Ph-0- moiety where Ph represents a phenyl group, m, r, s, t, v, w, and z represent zero or 1 and Ar is selected from one of the following moieties (i) to (v) which is bonded via one or more of its phenyl moieties to adjacent moieties

Unless otherwise stated in this specification, a phenyl moiety has 1,4-, linkages to moieties to which it is bonded .

As an alternative to a bio-compatible polymeric material comprising units IV and/or V discussed above, said biocompatible polymeric material may be a homopolymer having a repeat unit of general formula

or a homopolymer having a repeat unit of general formula

or a random or block copolymer of at least two different units of IV* and/or V*, wherein A, B, C, and D independently represent 0 or 1 and E, E¹, G, Ar, m, r, s, t, v, w and z are as described in any statement herein.

Preferably, said bio-compatible polymeric material is a homopolymer having a repeat unit of general formula IV.

Preferably Ar is selected from the following moieties (vi) to (x)

In (vii), the middle phenyl may be 1,4- or 1, 3-substituted. It is preferably 1 , 4-substituted.

Suitable moieties Ar are moieties (ii) , (in), (iv) and (v) and, of these, moieties, (ii), (in) and (v) are preferred. Other preferred moieties Ar are moieties (vii) , (viii) , (ix) and (x) and, of these, moieties (vii), (viii) and (x) are especially preferred. An especially preferred class of bio-compatible polymeric materials are polymers (or copolymers) which consist essentially of phenyl moieties in conjunction with ketone and/or ether moieties. That is, in the preferred class, the first polymer material does not include repeat units which include -S-, -SO₂- or aromatic groups other than phenyl. Preferred bio-compatible polymeric materials of the type described include:

(a) a polymer consisting essentially of units of formula IV wherein Ar represents moiety (v) , E and E' represent oxygen atoms, m represents 0, w represents 1, G represents a direct link, s represents 0, and A and B represent 1 (i.e. polyetheretherketone) .

(b) a polymer consisting essentially of units of formula IV wherein E represents an oxygen atom, E¹ represents a direct link, Ar represents a moiety of structure (ii) , m represents 0, A represents 1,

B represents 0 (i.e. polyetherketone) ;

(c) a polymer consisting essentially of units of formula IV wherein E represents an oxygen atom, Ar represents moiety (ii), m represents 0, E' represents a direct link, A represents 1, B represents 0, (i.e. polyetherketoneketone) .

(d) a polymer consisting essentially of units of formula IV wherein Ar represents moiety (ii), E and E' represent oxygen atoms, G represents a direct link, m represents 0, w represents 1, represents 0, s represents 1 and A and B represent 1. (i.e. polyetherketoneetherketoneketone) .

e) a polymer consisting essentially of units of formula IV, wherein Ar represents moiety (v) , E and E¹ represents oxygen atoms, G represents a direct link, m represents 0, w represents 0, s, r, A and B represent 1 (i.e. polyetheretherketoneketone) .

;f) a polymer comprising units of formula IV, wherein Ar represents moiety (v) , E and E' represent oxygen atoms, m represents 1, w represents 1, A represents 1, B represents 1, r and s represent 0 and G represents a direct link (i.e. polyether- diphenyl-ether-phenyl-ketone-phenyl-) .

Said bio-compatible polymeric material may consist essentially of one of units (a) to (f) defined above. Alternatively, said polymeric material may comprise a copolymer comprising at least two units selected from (a) to (f) defined above. Preferred copolymers include units

(a) . For example, a copolymer may comprise units (a) and

(f) ; or may comprise units (a) and (e) .

Said bio-compatible polymeric material preferably comprises, more preferably consists essentially of, a repeat unit of formula (XX)

where tl, and wl independently represent 0 or 1 and vl represents 0, 1 or 2. Preferred polymeric materials have a said repeat unit wherein tl=l, vl=0 and wl=0; tl=0, vl=0 and wl=0; tl=0, wl=l, vl=2; or tl=0, vl=l and wl=0. More preferred have tl=l, vl=0 and wl=0; or tl=0, vl=0 and wl=0. The most preferred has tl=l, vl=0 and wl=0.

In preferred embodiments, said bio-compatible polymeric material is selected from polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone and polyetherketoneketone . In a more preferred embodiment, said polymeric material is selected from polyetherketone and polyetheretherketone. In an especially preferred embodiment, said polymeric material is polyetheretherketone.

Said radiopaque material is suitably such that when added to the bio-compatible polymeric material the radiopacity of the combination is increased. Said radiopaque material preferably improves the imageability of the bio-compatible polymeric material when imaged using both CT and MRI techniques .

Said radiopaque material may comprise a compound, for example a salt incorporating zirconium moieties.

Said radiopaque material preferably includes oxygen moieties .

Said radiopaque material may be a ceramic. It may be a zirconium ceramic salt. Said radiopaque material preferably includes zirconium moieties and oxygen moieties. Said material is preferably an oxide which comprises zirconium moieties. Said material is preferably zirconium dioxide.

Said radiopaque material preferably has a decomposition temperature which is greater than 300⁰C, suitably greater than 325°C, preferably greater than 350⁰C, more preferably greater than 500⁰C, especially greater than 700⁰C, suitably so it can be melt-processed with the preferred bio-compatible polymeric materials.

Said fiducial marker may include one or a plurality of bio-compatible polymeric materials. Where said marker includes a second or subsequent bio-compatible polymeric material, the second or subsequent material may have any feature of said bio-compatible polymeric material described herein.

The sum of the wt% of all organic polymeric materials

(including said bio-compatible polymeric material and any additional bio-compatible polymeric materials) in said fiducial marker is preferably in the range 50 to 80wt%, more preferably 55-75wt%.

Said fiducial marker may include one or a plurality of radiopaque materials.

The sum of the wt% of all radiopaque materials in said fiducial marker may be in the range 20 to 80wt%, suitably 20 to 70wt%, preferably 20 to 55wt%, more preferably in the range 20 to 50wt%, especially 25 to 50wt%. The sum of the wt% of all organic polymeric materials and all radiopaque materials in same fiducial marker is suitably at least 80wt%, preferably at least 90wt%, more preferably at least 95wt%, especially at least 99wt%.

In a first embodiment said fiducial marker may comprise a radiopaque material in particulate form dispersed within, preferably throughout, said bio-compatible polymeric material. Said fiducial marker preferably has a substantially constant density throughout. Said marker is preferably substantially homogenous. Suitably, said polymeric material defines a matrix in which particles of radiopaque material are substantially uniformly dispersed and embedded.

The total wt% of all particulate radiopaque materials in said marker may be at least 14wt%, suitably at least 20wt%, preferably at least 25wt%, more preferably at least 30wt%, especially at least 35wt%. The total may be 70wt% or less, suitably less than 60wt%, preferably less than 55wt% . If too much radiopaque material is included the integrity and/or strength of the marker may be compromised; if there is too little, the marker may not be satisfactorily visible in for example CT or MRI imaging techniques.

The total wt% of all bio-compatible polymeric materials in said marker may be at least 40wt%, preferably at least 50wt% . The total may be less than 85wt%, preferably less than 70wt%, more preferably less than 65wt%.

The sum of the wt% of all particulate radiopaque materials and all bio-compatible polymeric materials in said marker may be at least 80wt%, preferably at least 90wt%, more preferably at least 95wt%, especially at least 99wt%.

In a preferred example of said first embodiment, said fiducial marker includes 40 to 75wt% of bio-compatible polymeric material (preferably of formula [XX] above, especially polyetheretherketone) and 25 to 60wt% of radiopaque material (especially particulate material, for example zirconium dioxide) . In an especially preferred example, a fiducial marker includes 45 to 70wt% of polyetheretherketone and 30 to 55wt% of a particulate radiopaque material, especially zirconium dioxide.

In another preferred example of said first embodiment, said fiducial marker includes 60 to 85wt% of biocompatible polymeric material (preferably of formula [xx] above, especially polyetheretherketone) and 15 to 40wt% of a radiopaque material (especially particulate material, for example a zirconium oxide) . In preferred examples, said fiducial marker includes 15-30wt% of a zirconium compound as aforesaid and 70-85wt% of a polyaryletherketone, especially polyetheretherketone.

In a second embodiment, a wire, for example a metal wire may be encapsulated in said bio-compatible polymeric material. The wire may have a diameter in the range 10 to 200μm, suitably 20 to lOOμm, more preferably 25 to 75μm, especially about 50μm. The wire may be metal, for example selected from tantalum or another radiopaque wire. In a preferred embodiment, the wire is selected from stainless steel, tungsten and tantalum. Because the wire is very fine and is encapsulated in an inert and strong biocompatible polymeric material, the level of underdesirable artefacts noticeable on imaging may be significantly less than when thicker wire is used; and the bio-compatible polymeric material maintains the integrity of the marker.

In a preferred example of said second embodiment, a metal wire having a diameter in the range 0.1mm to 0.4mm (preferably in the range 0.1mm to 0.3mm) and preferably being selected from stainless steel, tungsten and tantalum defines a core which is encapsulated m a bio-compatible polymeric material as described herein (preferably one of formula [xx] and especially poletheretherketone) , wherein the bio-compatible polymeric material is filled with said radiopaque material, especially a zirconium oxide. The layer which encapsulates the wire may include 40 to 85wt% of said bio-compatible polymeric material and 15 to 60wt% of filler (e.g. one or more radiopaque fillers as described) . When a zirconium oxide is included, the layer may include 40 to 70wt% (preferably 45 to 60wt%) of said oxide with the balance being said bio-compatible polymer.

In a third embodiment, a fiducial marker may comprise first and second fillers encapsulated in said biocompatible polymeric material, which may be of formula [xx] and is preferably polyetheretherketone . A first filler may be a metal, suitably in powderous form, which may be selected from stainless steel, tantalum and titanium. A second filler suitably comprises said radiopaque material. Said fiducial marker may include 5- 20wt% of said first filler, 15-60wt% of said second filler and 20-80wt% of said bio-compatible polymeric material.

Accorαing to a second aspect of the invention, tnere is provided the use of a member which comprises a said radiopaque material encapsulated in a bio-compatible polymeric material as a fiducial marker.

The member may be a fiducial marker as described in said first aspect.

According to a third aspect of the invention, there is provided the use of a said radiopaque material encapsulated in a bio-compatible polymeric material in the manufacture of a fiducial marker for use in marking a position on a human or animal body.

The fiducial marker may be as described according to said first aspect.

According to a fourth aspect of the invention, there is provided a method of marking a position in the human or animal body, the method comprising positioning, preferably securing, within the body a fiducial marker as described according to the first aspect.

The method may include positioning a plurality, preferably at least four, markers in the body.

According to a fifth aspect of the invention, there is provided a method of obtaining images of predetermined positions of a human or animal body, the method comprising imaging a human or animal body in which has been positioned one or a plurality (preferably a plurality) of fiducial markers according to said first aspect.

The method may include imaging the body by CT or MRI scanning techniques. Preferably, the method involves imaging by both CT and MRI scanning techniques . The method may involve X-ray imaging. Advantageously, the fiducial markers are visible to X-ray imaging and compatible with CT and MRI methods.

The method may include the step of positioning one or a plurality of said fiducial markers in position within the body prior to said imaging.

According to a sixth aspect of the invention, there is provided a method of making a fiducial marker, the method comprising encapsulating a said radiopaque material in a bio-compatible material.

The method preferably includes the step of extrusion to encapsulate said radiopaque material. A mixture comprising radiopaque and polymeric materials may be extruded suitably to define a filament. Alternatively, a wire may be coated with extruded polymeric material.

The method may include chopping extruded material to define fiducial markers of appropriate dimensions.

The invention extends to a pack comprising a fiducial marker according to said first aspect contained in a packaging material. The packaging material could be sterile .

Preferably fiducial markers described herein are for use and/or use in relation to human bodies.

Any feature of any aspect of any invention or embodiment described herein may be combined with any feature of any aspect of any other invention or embodiment described herein mutatis mutandis.

Specific embodiments of the invention will now be described by way of example.

A fiducial marker may be prepared by selection of a polyetheretherketone (PEEK OPTIMA LT3 polymer obtained from Invibio Limited, UK) and a highly pure grade of zirconium dioxide of suitable particle size. The combination may then be introduced into a twin screw melt extrusion compounder and a lace produced having a diameter of 2 to 3 mm. The lace may then be passed to a conveyer, cooled and chopped into granules. The granules may be introduced into an extruder and monofilaments produced which may then be chopped to produce fiducial markers of predetermined lengths comprising polyetheretherketone polymer with zirconium dioxide substantially homogenously dispersed throughout the polymer.

The markers described can be imaged using CT, MRI and X- ray techniques. In each case, images include less distortion and/or starburst and/or other artefacts compared to other known markers.

Markers as described may be provided in a range of dimensions as shown in the table below. Furthermore, spherical markers, having diameters in the range 1 to 5 mm may be provided.

Diameter of ma r ker ( mm ) Length ( mm )

0 8 3

0 8 5

In another embodiment, a standard wire coating technique may be used to coat a 0.12mm diameter stainless steel wire with a homogenous mixture comprising PEEK OPTIMA LT3 polymer (50wt%) and zirconium dioxide (50wt%). The coated wire may be cut to size to define a fiducial marker comprising a wire core and an outer homogenous sheaf of PEEK OPTIMA LT3 polymer and zirconium dioxide.

The inclusion of the wire core improves visibility of the marker under MRI conditions, whilst the zirconium dioxide improves the visibility of the marker in other imagining techniques .

As variations on the example, the stainless steel wire core may be replaced with tantalum or titanium; or the amount of zirconium dioxide may be adjusted (e.g. in the range 30-70wt%) .

In a further alternative, the metal wire may be replaced with metal powder, for example of stainless steel, tungsten or tantalum, at up to 20wt% of the entire marker. An example of such a marker may include up to 20wt% of metal powder, 30 to 70wt% of zirconium dioxide and the balance being PEEK OPTIMA LT3. The materials are mixed to define a homogenous mass and extruded to define an elongate marker having a diameter of 1mm.

Claims

Cl a ims

1. A fiducial marker which comprises a radiopaque material encapsulated in a bio-compatible polymeric material wherein said radiopaque material comprises zirconium moieties.

2. A marker according to claim 1, wherein said marker has a maximum dimension measured in a first direction of less than 50mm.

3. A marker according to claim 1 or claim 2, which has a maximum dimension measured in a first direction of less than 10mm.

4. A marker according to claim 2 or claim 3, wherein said marker has a dimension in a second direction perpendicular to the first direction which is less than said maximum dimension in said first direction.

5. A marker according to any preceding claim which has a volume of less than 20mm³.

6. A marker according to any preceding claim, which has a density of less than 3.5g/cm³ and greater than 1.2g/cm³.

7. A marker according to any preceding claim, wherein said marker is elongate or spherical.

8. A marker according to any preceding claim, which includes substantially no void areas.

9. A marker according to any preceding claim, wherein said radiopaque material is substantially immovably fixed in position in said marker so that its position relative to that of the polymeric material is substantially immovably fixed.

10. A marker according to any preceding claim, wherein said radiopaque material is substantially fully enclosed by said bio-compatible polymeric material.

11. A marker according to any preceding claim, which comprises radiopaque material and polymeric material which have been extruded.

12. A marker according to any preceding claim which has a weight of at least 3mg and less than lOOmg.

13. A marker according to any preceding claim which includes at least 3wt% and less than 80wt% of radiopaque material .

14. A marker according to any preceding claim, which includes at least 30wt% of radiopaque material.

15. A marker according to any preceding claim which includes at least 30wt% of bio-compatible polymeric material .

16. A marker according to any preceding claim which includes at least 50wt% of bio-compatible polymeric material .

17. A marker according to any preceding claim, wherein the sum of the wt% of said bio-compatible polymeric material and said radiopaque material in said fiducial marker is at least 80wt%.

18. A marker according to any preceding claim, said biocompatible material having a Notched Izod Impact Strength (Specimen 80mm x 10mm x 4mm with a cut 0.25 mm notch (Type

A), tested at 23°C, in accordance with ISO180) of at least 4KJm^"2.

19. A marker according to any preceding claim, wherein said bio-compatible polymeric material is semi- crystalline .

20. A marker according to any preceding claim, wherein said bio-compatible polymeric material includes a polymeric moiety which is an acrylate, a urethane, a vinyl chloride, a silicone, a siloxane, a sulphone, a carbonate, a fluoroalkylene, an acid, an oxyalkylene, an ester or an ether .

21. A marker according to any preceding claim, wherein said bio-compatible polymeric material is selected from a polyalkylacrylate, a polyfluoroalkylene, a polyurethane, a polyalkylene, a polyoxyakylene, a polyester, a polysulphone, a polycarbonate, a polyacid, a polyalkylene oxide ester, a polyvinylchloride, a silicone, a polysiloxane, a nylon, a polyaryletherketone, a polarylethersulphone, a polyether imide and any copolymer which includes any of the aforementioned.

22. A marker according to any preceding claim, where said bio-compatible polymeric material comprises, a repeat unit of formula (XX)

where tl, and wl independently represent 0 or 1 and vl represents 0, 1 or 2.

23. A marker according to any preceding claim, wherein said bio-compatible polymeric material is polyetheretherketone .

24. A marker according to any preceding claim, wherein said radiopaque material comprises a salt incorporating zirconium moieties.

25. A marker according to any preceding claim, wherein said radiopaque material comprises a zirconium ceramic salt.

26 A marker according to any preceding claim, wherein said radiopaque material is zirconium dioxide.

27. A marker according to any preceding claim, wherein said marker includes 40-75wt% of bio-compatible polymeric material and 25-60wt% of radiopaque material.

28. A marker according to any preceding claim, wherein said marker includes 1 to 20wt% of metal, 15 to 60wt% of one or more radiodense salts and 20-84wt% of biocompatible polymeric material (s).

29. A marker according to claim 28, wherein said metal defines a core which is encapsulated by said biocompatible polymeric material or is in particulate form.

30. A marker according to claim 28 or claim 29, wherein said marker includes at least 5wt% of metal and at least 35wt% of bio-compatible polymeric material (s).

31. The use of a member which comprises a radiopaque material encapsulated in a bio-compatible polymeric material as a fiducial marker, wherein said radiopaque material comprises zirconium moieties.

32. The use of a radiopaque material encapsulated in a bio-compatible polymeric material in the manufacture of a fiducial marker for use in marking a position on a human or animal body, said radiopaque material comprising zirconium moieties.

33. A method of marking a position in the human or animal body, the method comprising positioning within the body a fiducial marker as described according to any of claims 1 to 30.

34. A method of obtaining images of predetermined positions of a human or animal body, the method comprising imaging a human or animal body in which has been positioned one or a plurality of fiducial markers according to any of claims 1 to 30.

35. A method of making a fiducial marker, the method comprising encapsulating a radiopaque material in a bio- compatible material, said radiopaque material comprising zirconium moieties.

36. A pack comprising a fiducial marker according to any of claims 1 to 30 in a packaging material.