in fig1 , illustrations of the splittable needle according to the invention are shown . the needle consists of two parts , i . e . a first shaft element 110 and a second shaft element 120 . the second shaft element is partly enclosed by the first shaft element . at the proximal end of the splittable needle , gripping portions are provided . a first holder part 112 is attached to the first shaft element 110 , whereas a second holder part 122 is attached to the second shaft portion 120 . by way of pulling the gripped holder parts away from each other , the shaft elements may be easily separated from each other . a reliable connection between the first and second shaft elements is realized by an overlap of the end portions 114 of the first shaft element 110 over the end portions 124 of the second shaft element 120 . additionally , inward - projections 116 are provided between each of the first end sections 114 and a middle section 118 of the first shaft element . furthermore , the second shaft element 120 includes bulks or projections 126 between the two end sections 124 and a middle section 128 , in order to make it robust and to provide stabilization so that the two shaft elements cannot rotate with respect to each other . furthermore , due to the construction of the invention , the two shaft elements 110 , 120 can be torn apart or can slide with respect to each other in the longitudinal direction . this enables that the needle can be split in two , the needle parts can be partially shifted with respect to each other to create an opening to the side or the two separate shaft elements can be reassembled if necessary . the holder parts 112 , 122 of the needle may contain additional functionalities apart from the functionality to be able to easily separate the two parts of the splittable needle . as can be seen in fig2 , the distal tip portion of the two shaft elements 110 , 120 as well as a probe body 210 are slanted to form a needle tip capable of being easily introduced into tissue . in the probe body 210 , a first optical fiber 220 is located adjacent to the distal end of the slanted front surface of the probe body , and a second optical fiber 220 is located at the proximal end of the slanted surface of the probe body . therefore , the two fibers may be arranged as far as possible away from each other on the slanted surface . one fiber may deliver light to the distal end of the probe body while the other fiber may collect the scattered light and may guide this light towards a detector in a console for spectroscopy . it is noted , that the optical fibers 220 may be directly embedded in the probe body 210 or placed in channels formed in the probe body , at the above described positions . alternatively each of the optical fibers 220 may be located within a duct 235 which is formed between an outward projection 126 of the second shaft element 120 and an outer surface of the probe body 210 , instead of within the probe body . it is noted that additional fibers or other functionality like ablation or suction may be easily integrated within the duct 235 . furthermore , the duct 235 may be utilized to extract a fluid , cells or tissue or to inject substances like pharmaceuticals . in fig3 , an exemplary illustration of the splittable needle is shown , with the second shaft element 120 slide ably pulled back relative to the first shaft element 110 , so that a portion of the side surface of the probe body 210 inside the splittable needle is exposed to the tissue surrounding the needle . this allows side way inspection of the tissue . this is of particular interest when tissue is sensitive to bleedings , for instance in the lung . in this case voids in front of the needle can easily fill up with blood making optical inspection of the tissue influenced by this bleeding . when looking to the side this effect is less apparent because the tissue is usually pressed firmly to the side of the needle avoiding voids filled with blood . in fig4 , both shaft elements 110 , 120 of the splittable needle are pulled back so that openings of channels 230 in the circumferential surface of the probe body 210 are exposed . such channels 230 with openings in the circumferential surface of the probe body 210 may be used for anchoring wires 240 . an end of a wire 240 may be moved out of such an opening to form a fixation means for fixation of the probe body 210 within a tissue . fig5 illustrates a tip portion of a splittable needle with fixation wires 240 protruding out of the probe body 210 . each fixation wire consists of a curved metal part that when moved with respect to the probe body will extrude to the side of the probe body away from the optical fiber ends . due to the curvature of the metal part the wire will curl into the tissue giving rise to a firm fixation of the probe . it is noted that the fixation wires may also be in the shape of a corkscrew . in this case the fixation wire is turned such that the corkscrew part screws inside the tissue again providing a firm fixation . in fig6 , a system according to the invention is shown including a splittable needle 100 and a device for tissue inspection 300 . within the two shaft elements 110 , 120 , an optical probe 200 is located , wherein the probe body 210 may be elastical or flexible . at the proximal end of a probe body 210 , a connector 250 is provided for a connection of especially the ends of the optical fibers provided within the probe body . additionally , for example at a side of the connector 250 , an actuation element 242 may be arranged for an actuation , i . e . a shifting of the fixation wire within the probe body in a longitudinal direction , so that the distal end of the fixation wire may protrude out of the distal end of the probe body , as shown in fig5 . the optical probe 200 is connected to a tissue inspection device 300 by way of a connector 250 at the probe body 210 which is connected with a connector 310 at an end of an optical cable 320 leading to a console 330 including a light source and a light detector . the light source of the console 330 enables light to be provided via one of the fibers to the distal end of the optical probe 200 . the light scattered by tissue is collected by the other fiber and is guided towards the light detector . the data are processed using a dedicated algorithm . for instance light is coupled out of the distal tip through at least one fiber , which serves as a source , and the wavelength is swept from e . g . 500 - 1600 nm . the corresponding wavelength - dependent reflection is measured by at least one other fiber , which is spatially separated from the source at e . g . 1 - 2 mm . the amount of reflected light measured at the “ detection ” fiber , is determined by the absorption and scattering properties of the probed structure ( e . g . tissue ). upon spatial and temporal ( wavelength - dependent ) multiplexing , reflections can be measured at multiple sites of the electrode tip . although diffuse reflectance spectroscopy is described above to extract tissue properties also other optical methods can be envisioned like fluorescence spectroscopy measurement , diffuse optical tomography by employing a plurality of optical fibers , differential path length spectroscopy , or raman spectroscopy . fig7 is a flow chart , showing the steps of a method of the use of the splittable needle together with an optical probe according to the invention . it will be understood , that the steps described with respect to the method are major steps , wherein these major steps might be differentiated or divided into several sub - steps . furthermore , there might be also sub - steps between these major steps . therefore , a sub - step is only mentioned , if that step is important for the understanding of the principles of the method according to the invention . in step s 1 , the splittable needle with the optical probe inside is introduced percutaneously through the tissue to a desired position within the tissue . in step s 2 , the signal from the optical probe is used to confirm that the probe tip is inside tumor tissue , for example . in step s 3 , at least one fixation wire is employed to firmly fixate the probe tip in the tissue . in step s 4 , the splittable needle is retraced back out of the tissue . in step s 5 , the splittable needle is split in two shaft elements and is removed , wherein the probe remains in the body . in step s 6 , the probe is used to measure the tissue properties over time when administering for example chemotherapy . in step s 7 , when the treatment shows a positive response , the optical probe is removed by first retracing the fixation wires and then the optical probe itself . in the following , an algorithm is described by means of which optical tissue properties such as the scattering coefficient and absorption coefficient of different tissue chromophores : e . g . hemoglobin , oxygenated haemoglobin , water , fat , etc . may be derived . these properties may be different for healthy tissue compared to diseased tissue such as tumor tissue and can be used to discriminate healthy from diseased tissue . this can be useful for positioning the optical insert at the correct location . for instance correct placement of the optical insert tip in the tumor for tumor response measurement on chemotherapy . another application may be when tissue is treated by for instance ablation . in this case the progress of the tissue ablation can be followed by the optical probe . in more detail the algorithm can be described as follows . the spectral fitting will be performed by making use of the analytically derived formula for reflectance spectroscopy ( see ref [ t . farrell et al . ‘ a diffusion theory model of spatially resolved steady - state diffuse reflectance for non - invasive determination of tissue optical properties in vivo ’, med . phys . 19 ( 1992 ), page 879 - 888 ]). a detailed description of the algorithm can be found in the paper by r . nachabe , et al ., “ estimation of lipid and water concentrations in scattering media with diffuse optical spectroscopy from 900 to 1600 nm ” in journal of biomedical optics volume 15 ( 3 ), 2010 , page 037015 that we include by reference . this reflectance distribution r is given by in this formula the three macroscopic parameters describing the probability of interaction with tissue are : the absorption coefficient μ a and the scattering coefficient μ s both in cm − 1 as well as by g which is the mean cosine of the scattering angle . furthermore , we have the total reduced attenuation coefficient μ t ′ that gives the total chance for interaction with tissue the albedo a ′ is the probability of scattering relative to the total probability of interaction a point source at a depth z 0 = 1 / μ t ′ and no boundary mismatch hence z b = 2 /( 3μ t ′) are assumed . furthermore , it is assumed that the scattering coefficient can be written as the main absorbing constituents in normal tissue dominating the absorption in the visible and near - infrared range are blood ( i . e . hemoglobin ), water and fat . in fig8 , the absorption coefficient of these chromophores as a function of the wavelength is presented . note that blood dominates the absorption in the visible range , while water and fat dominate in the near infrared range . the total absorption coefficient is a linear combination of the absorption coefficients of for instance blood , water and fat ( hence for each component the value of that shown in fig8 multiply by its volume fraction ). by fitting the above formula while using the power law for scattering we can determine the volume fractions of the blood , water and fat as well as the scattering coefficient . with this method we can now translate the measured spectra in physiological parameters that can be used to discriminate different tissues . another way to discriminate differences in spectra is by making use of multivariate statistical analysis methods such as principal component analysis which render classification of differences in spectra and thus allows discrimination between tissues . 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 . any reference signs in the claims should not be construed as limiting the scope .
a needle comprises an elongated first shaft element with a c - shaped cross section and an elongated second shaft element with a c - shaped cross section . the first shaft element and the second shaft element are adapted to be detachably connected to each other . this is achieved by an overlap of respective end sections of the first and second shaft elements . within the channel formed by the shaft elements , an optical probe may be accommodated from which the shaft elements may be removed by separating the two shaft elements from each other .