FIELD OF THE INVENTION

The invention relates to a medical needle which incorporates optical waveguides to perform optical measurements at the tip of the medical needle. A method and a system for use in conjunction with the medical needle are also disclosed. The invention finds application in various medical fields including anesthesia and pain management, and in detection of tumors.

BACKGROUND OF THE INVENTION

In the fields of anaesthesia and pain management the need to accurately position a medical needle within the body is frequently encountered. Such needles may be used in the delivery of fluid, such as an anaesthetic reagent, wherein the position of the delivery of the fluid is important in achieving an optimal effect or in avoiding potentially damaging side effects. Likewise, medical needles that are used to perform a biopsy should be accurately positioned in order to ensure that the correct tissue sample is taken from the body.

Existing methods of positioning medical needles include the use of imaging systems to track the needle position. In one example a CT imaging system is used to track the tip of a needle. However this suffers from the drawback of risking exposure to the physician and poor positioning accuracy owing to the limited image quality that is achievable at an acceptable patient dose. Optical fibers have also been disposed in medical needles for the same purposes wherein the position of the needle is inferred from the optical characteristics of the tissue sensed by optical fibers at the needle tip. Patent application WO2013001394A details one approach. Improved positioning accuracy has been achieved with such optical techniques, but these are prone to trap tissue at the needle tip, thereby degrading their accuracy. In another known technique, optical measurements have been used to augment the so-called Loss Of Resistance technique in which the pressure at the tip of the needle is sensed by means of a fluidic or air connection to a syringe. Improved positioning has been achieved in such a system, although the optical measurements are likewise obscured in the event of trapped tissue. However, these solutions suffer from the drawback that tissue fragments that may become trapped at the needle tip during insertion where they interrupt optical measurements and may lead to poor reproducibility and therefore an inaccurate determination of the needle position. Pockets may be formed between and optical insert with optical fibers therein and the cannula in which it is inserted. Such pockets give rise to tissue stick when inserting the needle into tissue.

The reproducibility of the optical measurements in such systems also frequently hindered by the movement of the optical fibers with respect to the needle tip during insertion. Movement of the optical fibers with respect to the needle tip can change the illumination pattern of the tissue, and also changes in the detected signal which again leads to an inaccurate determination of the needle position.

It is important to ensure that measurement at a certain stage of the needle insertion reflects the actual position of the needle in the tissue, and that it is not influenced by the tissue penetrated just before. Hence it is important to prevent sticking of the tissue to the optical windows of the needle and/or take corrective actions when sticking occurs. One problem is thus how to integrate optical tissue sensing, i.e. optical fibers, into the elongated tube of the interventional device, while minimizing the effect of tissue stick, preventing pockets or protrusions and optimizing illumination and detection.

Consequently there remains room for improvement in terms of the incorporation of such optical fibers in a medical needle.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a medical needle with improved positioning accuracy. A method and a system are also disclosed in relation to the medical needle. It is further object to provide a medical needle having a needle tip with a reduced tendency to stick to the tissue or to trap tissue. It is a further object to optimize light coupling for illumination and detection. It is a further object to provide a medical needle should be possible to manufacture in a cost effective way, e.g. as disposable device. Still, it is a further object to detect sticking of tissue to the needle, and to take corrective actions when such sticking of tissue has been detected. A first aspect of the invention provides a medical needle comprising:

an elongate tube having a beveled distal end and a proximal end;

at least one optical fiber having a distal end surface; a stylet insert;

wherein the elongate tube is open at the distal end;

wherein the stylet insert has a bevel at the distal end that has substantially the same bevel angle as the beveled distal end of the elongate tube, and the stylet insert is arranged within the elongate tube such that a plane touching the beveled distal end of the elongate tube, and a plane touching the beveled distal end of the stylet insert are substantially parallel;

wherein the at least one optical fiber is arranged within the stylet insert such that a pocket is formed between the distal end surface of the optical fiber and the plane touching the beveled distal end of the stylet insert;

wherein an optically transparent material is arranged to cover at least a part of the distal end surface of the at least one optical fiber, so as to at least partly fill said pocket.

With such medical needle, sticking problems may be significantly reduced, since an optically transparent material, e.g. a glue or the like, is used to fill pockets that could otherwise trap tissue fragments, when the needle is inserted into the tissue. Thus, such needle has a reduced tendency to stick to the tissue. The optically transparent material may be such as an adhesive (glue), thus being possible to apply in a floating state so as to allow filling of the pocket(s), while being hard enough in a hardened state to be able to prevent sticking of biological tissue. In such way, the needle can be manufactured in a low cost manner.

Especially, the pocket may be filled, e.g. completely filled, with an optically transparent adhesive.

The pocket may be shaped in order to improve at least one of: the light delivery efficiency, and the light collection efficiency. The pocket may be surrounded by a light reflecting layer.

A channel may be formed within the elongate tube, so as to allow transport of a fluid through the medical needle. Especially, the channel may have a wall which comprises at least a portion of the inner bore of the elongate tube, alternatively or additionally the channel may have a wall which further comprises at least a portion of the outer bore of the stylet insert. As a still further option, the channel may be formed within the stylet insert.

The optically transparent material may comprise a coating covering the distal end surface of the at least one optical fiber. Such coating may comprise one of: Teflon®, Delrin®, silicon, and a lipophobic coating material. The thickness of a coating layer formed by such coating material may be such as 0.5-2 μπι.

The optically transparent material may comprise one type of material for filling said pocket, and another type of coating material for covering the distal end surface of the at least one optical fiber.

The distal end surface of the at least one optical fiber may have a slanting angle equal to or substantially equal to a slanting angle of the beveled distal end of the elongate tube. Especially, the slanting angle of the distal end surface of the at least one optical fiber is preferably equal to the slanting angle of the beveled distal end of the elongate tube, and arranged so as to form a plane coinciding with the plane touching the beveled distal end of the elongate tube. Hereby, an especially smooth surface of the medical needle can be provided, thus preventing sticking of tissue. Especially, the end surface of the at least one optical fiber has a polished surface, and wherein the said optically transparent material comprises a coating covering said end surface.

The pocket may be only partly filled with the optically transparent material, however still a sticking reduction may be reduced.

The medical needle may comprise two or more optical fibers arranged within the stylet insert. E.g. one optical fiber for transmitting light, and one optical fiber for receiving reflected and/or light from the tissue.

The optically transparent material may be one of: an adhesive, a and US curable resin. As further alternative types of materials are materials that can be delivered with ultrasonic welding such as any plastic, e.g. polycarbonate etc. Still further, doped glass may be used, preferably doped glass selected to match a refractive index to the optical fiber core and/or to the cladding. Especially, it is to be understood that the optically transparent material should be selected such that its optical loss of the actual light to be transmitted through the optical fiber is sufficiently low, so as to reduce the optical influence of the material being present.

In a second aspect, the invention provides an interventional device comprising a medical needle according to the first aspect.

In a third aspect, the invention provides a medical system comprising a medical needle according to the first aspect, and an optical console system comprising a light source and a light detector, and being arranged for optical connection to the at least one optical fiber, so as to allow optical interrogation of the at least one optical fiber. Especially, the medical system may comprise a stick detection module arranged for receipt of data from the optical console, and to calculate a likelihood that tissue is stuck to the medical needle by processing the data from the optical console in accordance with a predetermined algorithm. Such likelihood or a warning may be communicated to a user, e.g. by means of graphics on a display, such as a bar visualizing the sticking likelihood to the user.

It is to be understood that the advantages and embodiments apply as well for the second and third aspects, and the mentioned embodiments of the first aspect may be combined in any way with the second and third aspects.

In further aspects of the invention, various means for fixing the distal ends of the optical waveguides with respect to the distal end of the elongate tube are described in order to address one or more of the aforementioned problems. Still further, various means for fixing the distal ends of the optical waveguides with respect to the distal end of the elongate tube are described in order to address one or more of the aforementioned problems.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 A illustrates a prior art example of how fibers with straight cut fiber ends can be positioned in an elongated device as in WO2013001394A. In the FIG. 1 A pockets can be seen and are indicated by a and b. FIG. IB illustrates a prior art example of a space between cannula and optical insert which can also give rise to pockets that trap tissue.

FIG. 2 illustrates step index fiber with core and cladding light is internally reflected for rays with an angle Θ that is less than (9O-0 _C ), where 0 _C is the critical angle at which the rays still undergo total internal reflection at the core cladding interface.

FIG. 3 illustrates the use of reflecting coatings that around the optical fiber cladding at the distal end of the optical fibers in order to improve light delivery and collection.

FIG. 4 illustrates various methods for preventing the occurrence of pockets.

FIG. 5 illustrates an optical insert that is partly covering the needle cannula in plan view (to the left) and in a cross section view along A- A' (to the right).

FIG. 6 illustrates an optical insert having a convex surface at its distal end.

FIG. 7A illustrates an insert with a cone-shaped profile and FIG. 7B illustrates an insert with a rounded profile with fibers at either side. FIG. 8 illustrates the distal end of a needle having an insert in which the insert extends beyond the beveled surface at the distal end of the needle but not beyond the extreme distal end of the needle.

FIG. 9 illustrates a system for use with the present invention.

FIG. 10 illustrates the extinction coefficients and volume fraction of some absorbers.

FIG. 11 illustrates Intrinsic fluorescence curves for collagen, elastin, NADH and

FAD.

FIG. 12 illustrates an example of a system according to the invention wherein display bars indicates stuck tissue.

FIG. 13 illustrates an example of the incorporation of adhesively secured optical fibers in an elongate tube.

FIG. 14 illustrates the use of a stylet insert wherein adhesive is used to remove the sharp extrusion edges

FIG. 15 illustrates the use of an adhesive as a means for securing the optical fibers in the elongated tube.

FIG. 16 illustrates the distal end of a medical needle in which a fillet of adhesive remains after curing at the distal ends of the optical fibers.

FIG. 17 illustrates the distal end of a medical needle in which two optical fibers are secured at the distal end of an elongate tube by a non-circular cross section.

FIG. 18 illustrates the distal end of an elongate tube having an oval cross section used in the retention of two optical fibers.

FIG. 19 illustrates a deformed metal shaft with the fibers secured in the grooves at the outside of the needle.

FIG. 20 illustrates a cross section of the distal end of a medical needle having three separate elongate tubes at the distal end.

DETAILED DESCRIPTION OF THE INVENTION

In order to improve the positioning accuracy of a medical needle, the present invention comprising an elongate tube, at least one optical waveguide, and a stylet insert is described with reference to its use in the field of anaesthesia, wherein it is desirable to improve the determination of the needle position. However it is to be appreciated that the invention also finds application in other medical fields such as pain management, cardiology and oncology wherein the same need is encountered.

In order to include optical tissue sensing in an interventional device such as an optical needle or catheter, one or more illumination and detection fibers are integrated into the elongated tube of the device. Two situations give rise to the sticking of tissue at the tip of the needle during insertion. The first is present when an insert is used to mutually fix the distal ends of the optical fibers. In this situation, tissue may become trapped in the space between the insert and the inner bore of the needle. The second situation is also present when such an insert is used. Typically the distal ends of the optical fibers are polished perpendicular to the optical fiber axis in order to optimize their illumination properties. The insert by contrast typically has a beveled end which is flush with the beveled end of the needle tip, wherein the insert bevel acts to minimize the trapping of such tissue. However the pockets formed between the end of the optical fiber and the bevel of the insert act to trap tissue leading to a misinterpretation of the position of the needle.

In FIG. 1, FIG. 1 A illustrates a prior art example of how fibers FB with straight cut fiber ends can be positioned in an elongated device CN as in WO2013001394A. In FIG. 1 A pockets a, b can be seen. FIG. IB illustrates a prior art example of a space SP between cannula CN and optical insert OP_I which can also give rise to pockets that may trap tissue.

Slanted fiber ends could prevent such pockets; however, light output coupling with straight cut fibers is found to be more efficient compared to the light coupling with slanted fiber ends. Internal reflections at the slanted fiber interface cause light losses through the cladding CL and buffer BF of the fiber as now described with reference to FIG. 2. FIG. 2 illustrates step index fiber with core CR and cladding light is internally reflected for rays with an angle Θ that is less than (9O-0 _C ), where 0 _C is the critical angle at which the rays still undergo total internal reflection at the core cladding interface. Light coupling into or outwards from the fiber occurs for rays with angles Θ less than 0 _m . Internal reflection at a slanted fiber interface towards cladding CL and buffer BF causes reduced light output coupling for illumination and in coupling for detection since the angle Θ, for these rays will be Θ is greater than ( 90- 0 _C ) and do not undergo total reflection but is transmitted to the buffer BF and can be absorbed and scattered by the buffer material. Consequently, it is desirable to ensure that measurement at a certain depth of needle insertion reflects the actual position of the needle in the tissue, and that this is not influenced by tissue that has been previously penetrated. Hence it is important to prevent sticking of the tissue to the optical windows of the needle and/ or take corrective actions when sticking occurs. Several embodiments are proposed in order to prevent, detect and correct sticking of the tissue to the needle.

In accordance with a first aspect of the invention, various means for preventing the occurrence of such pockets whilst maintaining efficient illumination of the region in front of the optical fibers are provided. The sticking of tissue to the needle can be prevented in several ways. In a first example the shape of the needle tip may be adapted such that it does not contain any undesired ridges, thereby resulting in a smooth shape which permits the drainage of tissue and body fluids. This can be achieved by i) preventing any pockets by angled polished surfaces including the fibers, ii) filling pockets with optically transparent index matching materials such as Epotek optical fiber grade adhesive, iii) shaping and coating the optical insert surface to prevent tissue stick or drag. In a second example, non-absorbing, non-sticking materials may be used to construct either the entire needle tip, or to coat the needle tip, including the optical windows. In case the optical windows are coated, care should be taken that the light delivered and collected from the tissue can travel through the coating thereby preventing interference with the actual measurement. This may be achieved by i) adding reflecting layers or coatings to the fibers at positions where light losses can occur. In a third example a non-toxic washing liquid may be used that that can be flushed through the needle shaft continuously or at desired times or automatically. In a fourth example, the detection of tissue that is stuck in this way can be determined by monitoring the variation in parameters such as lipid content during insertion under image guidance from pre-recordings. If such parameters are outside typical boundaries a warming signal can be given to permit a user to take corrective action. Such corrective action may include i) discarding the optical information and withdrawing the needle, cleaning and repeating the insertion, ii) cleaning the needle whilst it is inserted, for example by flushing fluids, iii) vacuum suction, iv) rotating the needle or v) by mechanically moving the needle in an inward and outward motion.

In a first embodiment of the invention, FIG. 3 illustrates the use of reflecting coatings BF R that around the optical fiber cladding CL at the distal end of the optical fibers in order to improve light delivery and collection. Such a reflective coating BF R may be incorporated in a stylet which retains the optical fibers, or at the inside of the needle cannula. Alternatively, a reflecting coating BF R may be employed with polished pocket walls that are filled with index matching optically transparent material.

In a second embodiment of the invention, FIG. 4 illustrates various methods for preventing the occurrence of pockets P with an optical insert with optical fibers FB arranged within a cannula CN. In FIG. 4A: fiber pockets P are filled with a matching material like a transparent glue. In FIG. 4B: the fibers are polished at the slanted bevel angle. In FIG. 4C the slanted fibers have reflecting coating RC on the wall. In FIG. 4D the pocket walls are polished PH or alternatively have a reflecting coating applied and the pockets are optionally filled with index matching optically transparent material like a transparent adhesive.

In a third embodiment of the invention, FIG. 5 illustrates an optical insert OP I that is partly covering the needle cannula CN in plan view (to the left) and cross section along A- A' (to the right). Optical fibers FB are seen, and a cutting part of the cannula CP is also illustrated. The tip part TP partly covers the cannula CN. In order to maintain the needle's cutting behavior this insert OP I may only cover partly the needle cannula CN tip where no cutting faces are. Furthermore, in this configuration, the needle tip material could operate as fiber cladding or have polished reflecting coating on the inside of the fiber lumen.

In a fourth embodiment of the invention, FIG. 6 illustrates an optical insert with optical fibers FB within a cannula CN, wherein the optical insert has a convex surface at its distal end. The optical fiber FB ends are also polished along the same profile. Optionally an

illumination fiber, illustrated as the uppermost fiber in FIG. 6 has a substantially perpendicular distal end and the detection fiber has an end face with a non-perpendicular distal end, thus an end face with a plane that is less than 90 degrees to the fiber FB axis.

In a fifth embodiment of the invention, FIG. 7A illustrates an insert with optical fibers FB within a cannula CN, wherein the optical insert has a cone-shaped profile and FIG. 7B illustrates an insert with a rounded profile with fibers at either side. The optical fiber FB ends are polished along the same surface. During insertion these profiles force tissue in a lateral direction thereby preventing it from becoming stuck and consequently dragged into the body.

In a sixth, preferred embodiment of the invention, FIG. 8 illustrates the distal end of a needle CN having an insert OP I in which the insert extends with its end surface ES I beyond the beveled surface at the distal end of the needle CN but not beyond the extreme distal end of the needle CN. Optionally the surface between the fiber FB ends as a flat or a convex surface. An example is shown in FIG. 8B. The convex shape between the fibers FB ends (line A- A) and perpendicular to this line (line B-B) in FIG. 8B has a stronger bending radius in B-B line than for the A-A line.

Thus, the embodiment in FIG. 8 provides a medical needle comprising an elongate tube CN having a beveled distal end and a proximal end, at least one optical fiber FB, a stylet insert OP I, wherein the elongate tube CN is open at the distal end, wherein the distal end of the stylet insert ES I extends beyond a plane touching the beveled surface of the distal end of the needle CN, but not beyond the extreme distal end of the elongate tube CN. Especially, the distal end ES I of the stylet insert OP I may have a convex surface. Such convex stylet insert end ES I will help to prevent tissue sticking.

In a seventh embodiment of the invention the distal end of the needle insert, including the optical fibers, is coated with a thin layer of transparent material. The thin layer operates to prevent the sticking of tissue to the distal end of the needle. Preferably the thickness of this layer is one micrometer or less. Consequently the layer has minimal impact upon light absorption and therefore the optical characteristics of the optical fibers. Suitable coatings include Teflon®, Delrin®, silicon or lipophobic, thus fat-repelling coatings.

In an eighth embodiment of the invention the needle shaft comprises optical transport means such as optical fibers inside the shaft, or glued at the outside of the shaft.

Alternatively, the shaft material may be an optically transparent material such as a hard polymer that can both cut tissue and also guide light.

A system for use with the above-described medical needle is now detailed.

Needle with optical sensing: A typical needle according to the invention comprises an elongate tube and a needle hub. Optionally, tubing, or a syringe may be connected to the needle hub for injecting fluids. Furthermore the needle hub receives the fibers of which the distal ends of the fibers are ending at the tip of the needle. The fibers proximal ends are connected in a connector that can be attached to an optical console. The fibers between the connector and the needle hub are protected by tubing that prevents the fibers for being damaged during use. The needle hub forms also the holder for handling the needle. Console: FIG. 9 illustrates a system for use with the present invention. The optical fibers that are incorporated in the medical needle are connected to an optical console illustrated in FIG. 9. The first and second guide of the source-detector pair are understood to be light guides, such as optical fibers, such as optical waveguides. In a specific embodiment, the apparatus comprises a light source 104 in the form of a halogen broadband light source with an embedded shutter, a sleeve 112 around an interventional device with an optical detector 106. The optical detector 106 can resolve light with a wavelength substantially in the visible and infrared regions of the wavelength spectrum, such as from 400 nm to 1700 nm. The combination 104 and 106 allows for diffuse reflectance measurements. The console is designed such that a source- detector fiber pair results in a measured DRS. Each measured DRS is analyzed (see section "algorithm") and results in a signal whether tissue is reached.

In a more specific embodiment the console is capable of importing an image made by an imaging modality like X-ray, CT, MRI, US, PET-CT. Preferably in these images the needle tip is visible such that the information obtained by spectroscopy can be correlated with the image information. In this way the image can provide the coarse guidance to a certain tissue while the optical information provides the fine guidance. Although diffuse reflectance spectroscopy is described above to extract tissue properties also other optical methods can be envisioned like diffuse optical tomography by employing a plurality of optical fibers, differential path length spectroscopy, fluorescence and Raman spectroscopy (or SORS Spatially offset Raman Spectroscopy). A processor 110 transforms the measured spectra in 106 into

physiological parameters that are indicative for the tissue state for each source-detector pair. Optionally in order to translate the measured spectra into physiological parameters the processor 110 can make use of a database 114.

Algorithm: an example of extracting the physiological parameter is by fitting the acquired spectra using a custom made Matlab 7.9.0 (Mathworks, Natick, MA) algorithm. In this algorithm, a widely accepted analytical model was implemented, namely the model detailed in T.J. Farrel, M.S. Patterson and B.C. Wilson, "A diffusion theory model of spatially resolved, steady-state diffuse reflectance for the non-invasive determination of tissue optical properties, " Med. Phys. 19 (1992) p. 879-888 which is hereby incorporated by reference in entirety. The input arguments for the above model of the reference are the absorption coefficient, the reduced scattering coefficient and the center-to-center distance between the emitting and collecting fibers at the tip of the probe. For a complete description of the diffusion theory model, we refer to the above model. In the following part, the model will be explained briefly. The used formulas are described inR. Nachabe, B.H. W. Hendriks, M. V.D. Voort, A. E, and H.J. CM. Sterenborg, "Estimation of biological chromophores using diffuse optical spectroscopy : benefit of extending the UV-VIS wavelength range to include 1000 to 1600 nm, " Optics Express, vol. 18, 2010, pp. 879-888, and in R. Nachabe, B.H. W. Hendriks, A.E. Desjardins, M. van der Voort, M.B. van der Mark, and H.J.C.M. Sterenborg, "Estimation of lipid and water concentrations in scattering media with diffuse optical spectroscopy from 900 to 1600 nm, " Journal of Biomedical Optics, vol. 15, May. 2010, pp. 037015-10. which are hereby incorporated by reference in their entirety.

A double power law function can be used to describe the wavelength dependence of the reduced scattering, where the wavelength λ is expressed in nm and is normalized to a wavelength value λο of 800 nm. The parameter corresponds to the reduced scattering amplitude at this specific wavelength.

In this equation the reduced scattering coefficient is expressed as the sum of Mie and Rayleigh scattering where PMR is the Mie-to-total reduced scattering fraction. The reduced scattering slope of the Mie scattering is denoted b and is related to the particle size.

For a homogeneous distribution of absorbers, the total light absorption coefficient can be computed as products of the extinction coefficients and volume fraction of the absorbers as illustrated in FIG. 10, showing absorption of different biological chromophores as a function of wavelength λ for different materials.

M ₌ f i _ f 2 ^ £„s (Eq. l)

Instead of modeling the absorption coefficient as the sum of absorption coefficients weighted by the respective concentrations of the four chromophores of interest, it was decided to express the tissue absorption coefficient as ^"-* ?,) = £ ^; ) : ^■ ,. .. ₍ y * ^{: * *} " !. ) - :·-.·, , . ^{' ':} : .) [en; ^{"" 1} ! ( ^Ec L- ² ) , where ^iOS *{&) corresponds to the absorption by blood and corresponds to absorption by water and lipid together in the probed volume. The volume fraction of water and lipid is

%-£ whereas ¾ _0i33 represents the blood volume fraction for a

concentration of hemoglobin in whole blood of 150 mg/ml. The factor C is a wavelength dependent correction factor that accounts for the effect of pigment packaging and alters for the shape of the absorption spectrum. This effect can be explained by the fact that blood in tissue is confined to a very small fraction of the overall volume, namely blood vessels. Red blood cells near the center of the vessel therefore absorb less light than those at the periphery. Effectively, when distributed homogeneously within the tissue, fewer red blood cells would produce the same absorption as the actual number of red blood cells distributed in discrete vessels. The correction factor can be described as

, where R denotes the average vessel radius expressed in cm. The absorption coefficient related to blood is given by f . , = a .. - ^¾ - a - a _5: \ .< t i [_*»?: - ¹ ; ( ^Ec i- ⁴ )

, where μ^* ^®2 (A) and μ *(Χ) represent the basic extinction coefficient spectra of oxygenated hemoglobin Hb0 ₂ and deoxygenated hemoglobin Hb, respectively. The oxygenated hemoglobin fraction in the total amount of hemoglobin is noted = {HbO _z }/ -f- f fi¾j) and is commonly known as the blood oxygen saturation. The absorption due to the presence of water and lipid in the measured tissue is defined as

In this case the concentration of lipid related to the total concentration of lipid and water together can be written as f¾v _F = {Lipid f-$M i l -ϋ- where {Lipid] and { _∑ 0], correspond to the concentration of lipid (density of 0.86g/ml) and water, respectively.

This way of relating the water and lipid parameters in the expression of the absorption coefficient defined in Eq.6, rather than estimating separately the water and lipid volume fraction corresponds to a minimization of the covariance of the basic functions for fitting resulting in a more stable fit cf. reference Nachabe et al above.

Another way to discriminate differences in spectra is by making use of a principal components analysis. This method allows classification of differences in spectra and thus allows discrimination between tissues. It is also possible to extract features from the spectra. Apart from diffuse reflectance we could also measured fluorescence. Then for instance parameters like collagen CLG, elastin ELN, NADH and FAD could be measured too; see for instance FIG. 11 , which illustrates Intrinsic fluorescence F_I curves for these materials as a function of wavelength λ. Especially, the ratio NADH/FAD, which is called the optical redox parameter, is of interest because it is an indicator for the metabolic state of the tissue as detailed in Q. Zhang, M.G. Mueller, J. Wu and M.S. Feld, "Turbidity-free fluorescence spectroscopy of biological tissue " Opt. Lett. 25 (2000) pi 451., which is assumed to change upon effective treatment of cancer cells.

Display: The information regarding the insertion and tissue TS area in contact with the interventional device, or an interventional tool I T, can be provided in several ways to the physician. For instance a light indicator can be used that when showing a red light tissue is sticking to the needle CN tip and green light no tissue is sticking to the needle CN. Another way is using a sound signal when tissue stick occurs. Yet another method of showing tissue that is stuck in this way is by presenting the information as a bar on the screen. FIG. 12 illustrates an example of a system with an optical console connected to optical fiber(s) in the interventional device I T. A display shows the processed results to the user in response to data determined by the optical console. Especially, the display may show physiological parameters, i.e. translated results from measured spectral data, e.g. in the form of spectral data, and e.g. a bar indicating likelihood for tumor versus normal tissue. In one embodiment, a display bar (shown as a hatched bar on the display) indicates stuck tissue, or at least a likelihood for stuck tissue, a likelihood determined according to data from the optical console and processed in a stick detection module in accordance with a predetermined tissue sticking algorithm. Hereby an automatic warning can be given to the user, indicating that the results are less reliable, thus allowing the user to take corrective actions.

Another way is to integrate our signal into the image provided by an imaging modality capable of imaging the interior of the body such X-ray, CT, MRI, US, PET-CT etc.

An algorithm could be used to detect sticking: typically, when sticking occurs, the measured spectrum reacts less to movements of the needle than in case no sticking occurs.

Hence, the "sticking algorithm" uses as inputs the variations of the spectra over time, and variations in needle position. The latter could be obtained for instance from image information or from accelerometers positioned in the tip of the needle. A threshold for the ratio between of the "variation in spectra" and "variation in needle position" is used.

A warning that a chance of "sticking" is present could also be based on prior knowledge about the typical spectra or physiological parameters that are related to positioning the needle tip in certain tissues. For instance, if, based on image information, it is known that the needle resides in muscle tissue, but consistently a "too high" lipid content is measured, a warning could be given. Such a warning algorithm requires input related to the tissue type from another source than the optical information. A source could be image information, or information provided by the physician.

In case stuck tissue is detected, or detected to be most likely, a corrective action can be applied by a user. E.g. discarding optical information retrieved, and withdraw the needle, clean the needle, and redo the insertion. The needle can alternatively be cleaned while inserted in the tissue TS, e.g. by flushing fluids, vacuum pulling or by rotation of the needle or by mechanically moving needle in an out.

According to a second aspect of the invention various means for fixing the distal ends of the optical waveguides with respect to the distal end of the elongate tube are now described in order to address one or more of the aforementioned problems. These embodiments may likewise be used in accordance with the system described above.

In a ninth embodiment of the invention an adhesive is used to fix the distal end position of the fiber FB with respect to the distal end of the elongate tube E_T and an adhesive (glue) GL is used such that after curing, the adhesive GL forms a suspension for the fibers FB. Preferably the fibers FB are secured in such a way that there are no pockets or sharp protrusions. FIG. 13 illustrates an example of the incorporation of adhesively GL secured optical fibers FB in an elongate tube E_T. By applying the adhesive GL it will form connection to the fiber FB ends without giving rise to sharp protrusions (i.e. step like transitions). In a preferred embodiment the adhesive GL is used also as fixation means of the fibers FB with respect to the elongated tube E_T. In FIG. 13A a tip of an elongated interventional device, e.g. a tip of a medical needle, containing at least two optical fibers FB is shown in which a connector capable of connecting two or more fibers FB to an optical console, tubing around the fibers between the connector and the needle hub, a needle hub capable connecting the needle tubing containing the fibers FB and the elongated shaft and providing a coupling for fluid injection. The optical fibers FB are inserted within the elongate tube E_T and the distal end of the shaft is beveled, and the distal fibers FB ends are secured in the elongated tube E_T by a curable adhesive GL such that after curing there are no pockets and sharp protrusions between the fiber FB ends and the distal end of the interventional device formed by the glue GL. Preferably the glue GL form the fixation means to position the fibers FB with respect to the elongated tube E_T. Preferably the glue GL is a made of an optical transparent epoxy. Preferably the glue is made of a glue that complies with USP Class VI Biocompatibility standards. Preferably the needle hub provides a coupling for fluid injection into the elongated tube E_T and the fixation of the fibers FB by the glue GL is made such that there is an opening allowing fluid injection by the elongated device. Preferably the glue GL only extends part of the elongated tube. FIGs. 13B and 13C illustrate the entire medical interventional device comprising a hub allowing connection of a tube for applying the glue GL, e.g. by means of a syringe.

In a tenth embodiment of the invention the optical fibers FB are secured in an elongate tube E_T by a stylet insert ML I, a multi lumen insert ML I, and the curable glue GL is used to cover the pockets and extrusions that are consequent to the shape mismatch created through the use of straight cut fibers FB and a stylet insert ML I that has a beveled distal end. FIG. 14 illustrates the use of a stylet insert ML I wherein adhesive GL is used to remove the sharp extrusion edges. By removing the protrusions, or pockets, no tissue can be dragged along when inserting the needle. Dragging along tissue from another location would give rise to the erroneous tissue classification.

In an eleventh embodiment of the invention, FIG. 15 illustrates the use of an adhesive GL as a means for securing the optical fibers FB in the elongated tube E_T. In this embodiment the fiber FB desirably protrudes beyond a plane touching the beveled distal end of the needle E_T, illustrated by the dashed line in FIG. 15, but not beyond the extreme distal end of the needle E_T. When glue GL is applied no pockets can be formed and sharp edges are present.

In a twelfth embodiment of the invention, FIG. 16 illustrates the distal end of a medical needle in which a fillet of adhesive GL remains after curing at the distal ends of the optical fibers FB. The optically-transparent adhesive GL improves the optical collection and delivery efficiency. By arranging the shape of the distal end of the fillet the collection angle of the optical fiber FB can be modified depending on the desired sensing profile of the optical waveguide assembly. A suitable optically-transparent adhesive GL is epo-tek 3001 and epo-tek 301-2 form EPOXY TECHNOLOGY IINC. Desirably the adhesive GL may be used to reduce direct lateral optical cross-talk between an illumination fiber FB and a receiving fiber FB.

Furthermore, more preferred the glue GL forms a non-wetting surface.

Thus, the invention provides, as illustrated in FIGs. 13, 15 and 16, a medical needle comprising an elongate tube having a beveled distal end and a proximal end, and at least two optical fibers having distal end surfaces that are substantially normal to the longitudinal axes of the optical fibers, wherein the at least two optical fibers are fixed within the elongate tube by means of an adhesive material serving to fill a gap between the distal end surfaces of the at least two optical fibers, so as to smoothen an end surface of the medical needle. Said adhesive material may further serves to fix a position of the at least two optical fibers within the elongate tube. Especially, at least one of said optical fibers may have its distal end surface protruding in front of a plane touching the beveled distal end of the elongate tube, e.g. not protruding in front of an extreme distal end of the elongate tube.

According to an aspect of the invention various means for fixing the distal ends of the optical waveguides with respect to the distal end of the elongate tube are now described in order to address one or more of the aforementioned problems. These embodiments may likewise be used in accordance with the system described above. In accordance with this aspect various embodiments for fixing the distal ends of the optical fibers at the distal end of the elongate tube in the absence of adhesive are described. The unifying principle behind the securing means is that the distal end of the elongate tube, or needle, is deformed from the conventional circular cross section such that the deformation secures the distal end of the optical fibers, thereby preventing their movement with respect to the distal end of the elongate tube. In particular, rotational movement of the optical fibers is substantially inhibited, which movement would risk the shadowing of the optical fibers and thereby lead to inaccurate needle positioning. Such a deformation of the needle tip may be used with optical fibers in the absence of a stylet insert, or in the presence of a stylet insert. Advantageously a stylet insert may further incorporate a channel for the delivery of fluid such as an anaesthetic reagent from within the elongate tube, or for the sensing of the pressure at the distal end of the elongate tube in order to perform the Loss Of Resistance technique and thereby validate the optical measurements. In a thirteenth embodiment of the invention, FIG. 17 illustrate the distal end of a medical needle in which two optical fibers are secured at the distal end of an elongate tube by a non-circular cross section. FIG. 17A illustrates the distal end of a needle produced in accordance with this aspect of the invention in which the distal end of the elongate tube has a figure-of-eight cross section, and FIG. 17B illustrates the cross section through the distal end. Such a needle shape may be achieved by deforming the distal end of an elongate tube having an otherwise circular cross section by crimping, thus, applying pressure at two or more points at the distal end of the needle. Other shapes may likewise be formed for the retention of one or more optical fibers in this manner. The cross section may for example have a single indent rather than the two opposing indents illustrated in FIG. 17, or have an oval cross section, or in general have any non- circular cross section. Likewise a needle may be pre-fabricated with the cross section illustrated in FIG. 17B throughout a substantial portion of its length. In the example illustrated in FIG. 17 the cross section includes a channel for the delivery of fluid or sensing of pressure as described above. This preferred embodiment may therefore be used in the delivery of fluid.

Advantageously the fluid is in contact with the inner bore of the elongate tube, which simplifies cleaning and sterilization since prior to use only the outer surface of the optical fibers and the inner surface of the elongate tube require treatment. Other embodiments are also contemplated in which there is no channel and in which the inner cross section of the elongate tube is deformed or pre-shaped in order to match the outer cross section of a stylet insert. In so doing a stylet insert may be prevented from rotating. Alternatively the stylet insert may itself include a channel for use as described above.

In a fourteenth embodiment of the invention, FIG. 18 illustrates the distal end of an elongate tube having an oval cross section used in the retention of two optical fibers FB and an air void A_V around the optical fibers FB. In FIG. 18 A the elongate tube has a wall with substantially uniform thickness, and in FIG. 18B another option is shown in which the wall has a non-uniform thickness. The embodiment in FIG. 18B is advantageously less susceptible to bending in a direction parallel to the minor axis of the inner cross section of the elongate tube.

In a fifteenth embodiment of the invention, FIG. 19 illustrates a deformed metal shaft with the fibers secured in the grooves at the outside of the needle. A further channel for use in injecting fluid may also be secured on the outside groove and used to position the fiber inside the needle. In a sixteenth embodiment of the invention, FIG. 20 illustrates a cross section of the distal end of a medical needle having three separate elongate tubes at the distal end.

Additional tubes may be added in the same manner, wherein the tubes are secured through adhesive or welding techniques. In the example illustrated in FIG. 20, two elongate tubes may each comprise an optical fiber for optical measurements and the third may be used as a channel for the delivery of fluid or the sensing of pressure at the distal end of the elongate tube.

Thus, the above mentioned embodiments provide a medical needle comprising: an elongate tube having a beveled distal end and a proximal end;

at least one optical fiber;

wherein the elongate tube is open at the distal end;

wherein at least a portion of the bore of the distal end of the elongate tube has a non-circular cross section. Especially, at least a portion of the non-circular bore of the elongate tube may be in contact with a portion of at least one optical fiber such that the at least one optical fiber is immobilized within the bore. As a further option, the elongate tube may have a cross section in the form of an oval or a figure-of-eight. As a further option, the elongate tube may have a cross section with a notch.

Further, the invention provides a method of deforming a distal end of a medical needle through crimping. Especially, prior to crimping, the distal end of the medical needle may have a circular cross section. As a further option, the crimping may include application of force to the distal end of an elongate tube with an anvil having a concave recess on each of two opposing surfaces.

To summarize, a medical needle with improved position determining accuracy has been described. A system and a method for use in relation with the needle have also been described. Especially, the present invention relates to a medical needle comprising an elongate tube and at least one optical fiber for making optical measurements at the distal end of the needle. The one or more optical fibers are arranged within the elongate tube and are fixed with respect to the elongate tube in order to improve the repeatability of the optical measurements. Especially, the medical needle comprises an optically transparent material arranged to cover at least a part of the distal end surface of the optical fiber(s), so as to at least partly fill a pocket that may be present between a stylet insert and the elongate tube. Hereby, the medical needle will have a reduced problem with tissue sticking to the needle tip, thus the medical needle has an improved reliability and provides measurements with a higher certainty.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.