Abstract:
The present invention relates to a catheter head comprising: means ( 104, 108; 306, 304; 320, 322; 326; 338 ) for directing of radiation to a blood detection volume ( 220, 310 ), means ( 104, 108; 306, 304; 320; 322; 326; 332, 334, 330; 338 ) for receiving of return radiation from the blood detection volume, means ( 104; 306; 330 ) for transmitting of the return radiation to means ( 122 ) for analysis of the return radiation for determination of at least one property of the blood.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the field of catheters and imaging systems for catheterisation.  
       BACKGROUND AND PRIOR ART  
       [0002]     Catheterisation provides effective and quality service in significantly reducing patient discomfort, hospital stay, and medical cost. It often requires the ability to enter the vascular system through very small incisions and to manoeuvre therapeutic or diagnostic devices to the target region in a human body. With the smallest possible circular cross-sections, catheters are the most important device widely used in interventing procedures. More than any other type of interventing device, catheters are extremely diverse in shape and specific features. Each catheter is designed for its own purpose and is distinct from others with its own characteristics and configuration.  
         [0003]     The term catheter as used herein refers to any type of invasive surgical tool, used for insertion into a human or animal body for the purpose of providing remote access to a part of the body for performing some type of investigative and/or medical procedure.  
         [0004]     U.S. Pat. No. 6,208,887B1 shows a catheter-delivered low resolution Raman scattering analysing system for detecting lesions of a subject. The system uses a multi-mode laser attached to a catheter in making in-vivo Raman spectroscopic measurements of the lesion. The system includes a light collector and a light dispersion element as well as a detector to measure spectral patterns that indicate the presence of a lesion. In addition the components of the lesion can also be identified based on the unique Raman spectrum associated with each component of the lesion.  
         [0005]     Further, various catheter tracking techniques for remotely locating and tracking a catheter inside a human or animal body are known from the prior art. Currently, X-ray fluoroscopic imaging is the standard catheter tracking technique. For example the Philips Cath-Lab systems provide X-ray imaging during catheterisation for monitoring of the operation. (http://www.medical.philips.com/main/products/cardiovascular/)  
         [0006]     For example, in catheter based surgery a long and narrow plastic tube is inserted into the artery in the groin or arm. The physician then leads the catheter through the main artery to the heart During heart catherisation, the following diagnostic measurements can be made: 
        A small amount of contrast dye can be injected via the catheter. This contrast allows the blood vessels and heart chambers or valves, to be viewed using X-rays.     The pressure inside the heart chambers can be measured.     The concentration of oxygen and carbon dioxide in the blood can be measured locally.     The electrical signals inside the heart can be measured, or the response to applied electrical signals can be determined.        
 
         [0011]     Catheter based treatments include: 
        PTCA (percutane transluminale coronaire angioplasty) to widen the blood vessel locally.     Placement of an endovascular prostheses in the blood vessel.        
 
         [0014]     Typically various medical parameters are measured and monitored during catheterisation, such as heart frequency, blood pressure and others. This medical information is essential for permanently monitoring the state of the patients body.  
         [0015]     There is therefore a need for a catheter head enabling an improved monitoring of the state of a patient&#39;s body during catheterisation.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention provides for a catheter head which enables in vivo determination of at least one blood property by directing of radiation to a blood detection volume and analysing of return radiation which is returned from a blood detection volume.  
         [0017]     For example the catheter head has an optical wave guide for guiding radiation, such as laser radiation or infrared radiation, to a blood detection volume which is located in front of the catheter head; alternatively the blood detection volume can be located within an inlet or cavity inside the catheter head or at another suitable location. Radiation which is returned from the blood detection volume in response is captured by the catheter head and transmitted to an analyser. On the basis of the analysis of the return radiation at least one property of the blood is determined.  
         [0018]     In accordance with a preferred embodiment of the invention Raman spectroscopy is utilized. Laser radiation is directed into a blood detection volume which is located in front of or inside the catheter head. The resulting Raman scattered radiation is transmitted to a spectroscope for analysis of the Raman spectrum in order to determine one or more properties of the blood.  
         [0019]     Raman spectroscopy is based on inelastic scattering of light on molecules. In this scattering process, energy is transferred between the photon and the molecule, resulting in a wavelength shift of the light. The energy corresponding to the wavelength shift is equal to the energy difference of vibrational states of the molecule.  
         [0020]     By detecting the Raman signal in a sufficiently large wavelength region, the energy of a large number of molecular states can be calculated. Because this combination of energies is specific for each molecule, the Raman spectrum can be considered as a fingerprint of a molecular species. Blood analytes—for example glucose or lactate—can be detected using Raman spectroscopy. These analytes provide general and specific information about the patient&#39;s health.  
         [0021]     The integration of a Raman probe into a catheter in accordance with the present invention has the advantage, that blood analysis can be permanently performed during catheterisation for improved monitoring of the medical state of the patient during the operation. For example, this diagnostic tool can be used during catheterisation for the following purposes: 
        monitoring of the catheterisation procedure, for example by continuous monitoring of the patient&#39;s health by measurement of oxygenation or lactate;     measurement of local blood composition.        
 
         [0024]     This compares to prior art blood analysis, where blood is drawn from the arm using a needle and the blood sample is analysed in a chemical laboratory. This analysis and the transport take a considerable amount of time, varying between two days and typically 20 minutes in emergency situations. In contrast the present invention enables to continuously monitor the properties of the blood which provides the physician with up to date information on the medical state of the patient.  
         [0025]     In accordance with a preferred embodiment of the invention, confocal Raman spectroscopy using optical wave guides is used. Light from the Raman excitation laser is coupled into an optical fibre and this fibre is incorporated into the catheter. In the catheter head, light from the fibre is collected by a lens and is focussed into the detection area. Raman scattered light is collected by the same objective and coupled back into the optical fibre. The endpoint of the fibre serves as a pinhole to ensure confocal detection.  
         [0026]     In accordance with a further preferred embodiment two separate optical fibres are used: One optical fibre for transmitting the incident light to the blood detection volume and one for the return radiation.  
         [0027]     In accordance with a further preferred embodiment of the invention, a lens is used having a high numerical aperture (NA) in order to collect as much Raman scattered radiation as possible. The collected Raman light travels back through the optical fibre and is detected by a spectrum analyser to yield quantitative concentration measurements of the detected analyte(s).  
         [0028]     In accordance with a further preferred embodiment of the invention, the number of red and/or white blood cells in the detection volume is reduced in order to reduce absorption and scattering of light. For example a mesh with a shutter mechanism can be used for this purpose.  
         [0029]     In accordance with a further group of preferred embodiments of the invention, optical elements are used to enhance the collection efficiency of the Raman scattered radiation. This can be done by means of spherical or ellipsoidal mirrors.  
         [0030]     In accordance with a further preferred group of embodiments the blood detection volume is located in a cavity of the catheter head through which blood flows. In order to enhance the flow of blood through the detection volume the blood channel through the catheter head can be disposed such to make usage of the Pitot tube effect.  
         [0031]     As an alternative to the Raman effect other spectroscopic techniques can be used. For example this can be done by means of infrared light which is directed to the blood detection volume. In this instance the return radiation is analysed by means of infrared absorption spectroscopy which detects changes in the infrared light intensity.  
         [0032]     In accordance with a further preferred embodiment of the invention fluorescence spectroscopy is used. In this instance a laser beam or another kind of radiation is directed to the blood detection volume in order to excite molecules to emit induced fluorescence. The detected fluorescence forms the basis for the determination of the at least one property of the blood.  
         [0033]     In accordance with a further preferred embodiment of the invention elastic scattering spectroscopy is used. In this case the variations of the reflectance are used to perform the blood analysis.  
         [0034]     It is to be noted that the present invention is not restricted to any particular spectroscopic technique but that any type of optical spectroscopy can be used. This includes (i) infra-red spectroscopy, in particular infra-red absorption spectroscopy, Fourier transform infra-red (FTIR) spectroscopy and near infra-red (NIR) diffuse reflection spectroscopy, (ii) scattering spectroscopy techniques, in particularly Raman spectroscopy, stimulated Raman spectroscopy, coherent anti-Stokes Raman spectroscopy (CARS), fluorescence spectroscopy, multi-photon fluorescence spectroscopy and reflectance spectroscopy, and (iii) other spectroscopic techniques such as photo-acoustic spectroscopy, polarimetry and pump-probe spectroscopy. Preferred spectroscopic techniques for application to the present invention are IR absorbance spectroscopy and fluorescence spectroscopy.  
         [0035]     In accordance with a further preferred embodiment of the invention the catheter head has means for analysis of the return radiation being adapted to perform a spectroscopic analysis, such as Raman spectroscopic analysis, infra-red absorption spectroscopic analysis, scattering spectroscopic analysis, fluorescence spectroscopic analysis.  
         [0036]     In accordance with a further preferred embodiment of the invention the radiation that is directed to the volume of interest is selected to cause molecular vibrational scattering in order to provide the return radiation. For example, the radiation is laser radiation or infrared radiation.  
         [0037]     In accordance with a further preferred embodiment of the invention a remote controllable shutter is arranged in front of a mesh. The mesh has a size that prevents red and/or white blood cells to enter the detection volume.  
         [0038]     In accordance with a further preferred embodiment of the invention a mirror is used for the radiation and/or the return radiation, the mirror being a spherical mirror or an ellipsoidal mirror.  
         [0039]     In accordance with a further preferred embodiment of the invention the catheter head has a first optical wave guide for directing of the laser radiation to the blood detection volume and a second optical wave guide for receiving of the Raman scattered radiation for transmission to the means for spectroscopic analysis.  
         [0040]     In accordance with a further preferred embodiment of the invention the first optical wave guide determines an excitation light path and the second optical wave guide determines a detection light path, and further comprising means for decoupling the excitation light path and the detection light path.  
         [0041]     In accordance with a further preferred embodiment of the invention the catheter head has means for filtering out of the laser radiation in the detection light path.  
         [0042]     In another aspect the invention concerns a catheter system having a catheter head, the catheter comprising at least one optical wave guide for coupling of the catheter head to a Raman laser source and to means for spectroscopic analysis.  
         [0043]     In still another aspect the invention concerns an imaging system for catheterisation comprising a catheter system and having display means for display of a blood property being detected by the spectroscopic analysis. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]     In the following preferred embodiments of the invention will be described in greater detail by making reference to the drawings, in which  
         [0045]      FIG. 1  is a block diagram of a catheter system of the invention,  
         [0046]      FIG. 2  is illustrative of the catheter head of the catheter system of  FIG. 1  in a blood vessel,  
         [0047]      FIG. 3  to  13  show various embodiments of catheter heads,  
         [0048]      FIG. 14  shows a block diagram of an imaging system for catheterisation. 
     
    
     DETAILED DESCRIPTION  
       [0049]      FIG. 1  shows a catheter system  100  having a catheter head  102 . Catheter head  102  comprises optical fibre  104  which extends through catheter  106 . Further, catheter head  102  has objective lens  108  for directing of radiation towards a detection volume and for collecting of Raman scattered radiation.  
         [0050]     Optical fibre  104  is coupled to optical fibre  110 . Optical fibre  110  conducts laser beam  112  provided by Raman excitation laser  114  through connector  116  to optical fibre  104 . Laser beam  112  is directed towards a detection volume through objective lens  108 . The Raman scattered radiation is collected by objective lens  108  and coupled into optical fibre  104 .  
         [0051]     The Raman scattered radiation travels through optical fibre  104 , connector  116 , optical fibre  110  to mirror  118 , from where the Raman scattered radiation  120  is provided to Raman spectrum analyser  122 . Raman spectrum analyser  122  analyses the spectrum of the received Raman scattered radiation  120  in order to determine one or more blood properties such as the concentrations of glucose, glycohemoglobin, lactate, bilirubin, cholesterol, triglycerides, haemoglobin and blood gases.  
         [0052]     Further, a variety of other catheter inputs  124  can be connected to catheter head  102  via connector  116  and catheter  106  depending on the purpose of the catheterisation such as PTCA or others (cf. U.S. Pat. No. 5,938,582 or U.S. Pat. No. 6,302,866). Usually each application requires its own special catheter while some functionalities can be combined in specially designed catheters.  
         [0053]      FIG. 2  shows catheter head  102  of catheter system  100  of  FIG. 1  in operation. Catheter head  102  has been introduced into blood vessel  200  by means of catheter  106 . A laser beam is directed through optical fibre  104  to the confocal detection volume  202  which is defined by objective lens  108 . Raman radiation is scattered back by the blood flowing through the confocal detection volume  202  which is collected by objective lens  108  and coupled into optical fibre  104 .  
         [0054]     FIGS.  3  to  13  show various preferred embodiments of catheter heads for usage in a catheter system of the type as shown in  FIGS. 1 and 2 .  
         [0055]      FIG. 3  shows catheter head  300  which is similar to catheter head  102  of  FIGS. 1 and 2 . Catheter head  300  has an elongated housing  302  with an opening for receiving objective lens  304 . Optical fibre  306  (cf. optical fibre  104  of  FIGS. 1 and 2 ) serves to conduct laser radiation through catheter  308  which is directed through objective lens  304  towards the confocal detection volume  310 . Raman radiation which is back scattered from detection volume  310  into the direction of objective lens  304  is coupled back into optical fibre  306  for transmission to the Raman spectrum analyser (c.f. Raman spectrum analyser  122  of  FIG. 1 ). However, it is to be noted that the elongated form of the housing is not essential for the present invention.  
         [0056]     In the following preferred embodiments of FIGS.  4  to  12 , alike elements will be designated by the same reference numerals as in  FIG. 3 .  
         [0057]     In the embodiment of  FIG. 4 , a cavity  312  is formed in housing  302 . Through an opening which is formed in housing  302  blood can flow into cavity  312 . Confocal detection volume  310  is located inside cavity  312 . In the example considered here objective lens  304  is arranged on one of the side walls of cavity  312 . This way the surface of objective lens  304  is protected against contamination from the vessel walls as the catheter head  300  moves through the vessel.  
         [0058]     In the embodiment of  FIG. 5  mesh  314  is disposed at the opening of cavity  312  towards the blood vessel. Mesh  314  filters out red and/or white blood cells. When mesh  314  is closed only blood plasma enters cavity  312 . This reduces the absorption and scattering of the Raman laser light and Raman signal by the red and/or white blood cells.  
         [0059]     In order to filter out the red and/or the white blood cells a mesh size of below  5  microns is selected.  
         [0060]     In addition shutter  316  can be placed in front of the mesh  314 . This prevents the mesh from being contaminated while the catheter head  300  is moved through the blood vessels. Shutter  316  is remote controlled and is only opened before a blood measurement to enable blood flow through cavity  312 .  
         [0061]     In the embodiment of  FIG. 6 a  blood channel  318  is formed in housing  302  which enables a flow of blood through catheter head  300  passing by confocal detection volume  310 . This has the advantage that the surface of objective lens  304  can be protected against contamination and that the flow of blood through the detection volume  310  is enhanced at the same time.  
         [0062]     Channel  318  can be realised by means of a tube running through catheter head  300 . Alternatively, it is also possible to use a groove along the side of the catheter head  300 . In the preferred embodiment of  FIG. 7  the blood flow is further enhanced by using the Pitot tube effect. For this purpose channel  318  has one opening at the front of housing  302  and one opening at the side of housing  302 . This way an extra pressure difference is created when the blood flows along housing  302  which enhances the blood flow through channel  318  and through detection volume  310 .  
         [0063]     In the preferred embodiment of  FIG. 8 a  spherical mirror  320  is located opposite to objective lens  304 . Detection volume  310  is located within cavity  312  between objective lens  304  and spherical mirror  320 . The laser light which is directed towards detection volume  310  through objective lens  304  is reflected back into detection volume  310  by spherical mirror  320 . As a consequence Raman scattering takes place twice, once for the original laser beam and once for the reflected laser beam. Further the Raman scattered radiation is also reflected by spherical mirror  320  and collected by objective lens  304 ; as a result the sensitivity and the Raman signal to noise ratio are substantially increased.  
         [0064]     In the embodiment of  FIG. 9  an ellipsoidal mirror  322  is disposed within housing  302 . Distal end  324  of optical fibre  306  is located at one of the focal points of ellipsoidal mirror  322 . Detection volume  310  is located at the other focal point of ellipsoidal mirror  322 . Blood flows to the detection volume  310  through cavity  312  which extends into ellipsoidal mirror  322  and prevents a complete flooding of ellipsoidal mirror  322  with blood.  
         [0065]     In the embodiment of  FIG. 10  mirror  326  is completely filled with blood through opening  328  in housing  302 . Mirror  326  can be an ellipsoid or a spherical mirror. In this instance, detection volume  310  is located at the orifice of the optical fibre  306 .  
         [0066]     In the preferred embodiment of  FIG. 11  separate optical fibres  306  and  330  are used for guiding of laser radiation to detection volume  310  and for transmitting of the Raman scattered radiation back to the Raman spectrum analyser (cf. Raman spectrum analyser  122  of  FIG. 1 ), respectively. Raman scattered radiation is collected by objective lens  332  which is perpendicular to objective lens  304  for decoupling. Alternatively another angle can be used. This way the amount of laser light which is coupled into optical fibre  330  is reduced. For further reduction of the laser light in optical fibre  330  a filter  332  can be located between optical fibre  330  and objective lens  332  to suppress the excitation wavelength. This has the advantage that the Raman scattered radiation is not overlaid by fluorescence.  
         [0067]     When only a single optical fibre is used both for the Raman excitation laser beam and the Raman scattered radiation return beam the problem is that the excitation laser beam can create some amount of fluorescence in the optical fibre. This fluorescence has a negative influence on the signal to noise ratio of the Raman signal. By decoupling the Raman excitation laser beam and the return beam this problem is solved as the very low intensity Raman return beam does not create fluorescence in the return optical fibre  330 . As a consequence the signal to noise ration is improved in comparison to the embodiments using only a single optical fibre.  
         [0068]      FIG. 12  shows an alternative way of decoupling the Raman excitation laser beam and the return beam. Dichroic mirror  440  is positioned in the light path of the Raman excitation laser beam. At the wavelength of the Raman excitation laser beam, e.g.  785  nm, dichroic mirror  440  is transparent.  
         [0069]     The Raman scattered radiation is reflected from dichroic mirror  440  as dichroic mirror  440  is reflective at the wavelength of the Raman scattered radiation, e.g.  800  to  1000  nm. Dichroic mirror  440  reflects the Raman scattered radiation onto mirror  442 , which can also be dichroic. From mirror  440  the Raman scattered radiation is coupled into optical fibre  330 . No or only a limited fraction of the Raman excitation laser beam is coupled into optical fibre  330  as at least dichroic mirror  440  is transparent to the Raman excitation laser beam.  
         [0070]     In the embodiment of  FIG. 13  blood channel  336  which is arranged in housing  302  has half-round shape  338  around the detection volume  310 . The orifice of the optical fibre  306  is located at the centre of the flat side of half-round shape  338 . The half-round shape is covered with a reflective coating and acts as a spherical mirror. The diameter of the tubular portion of channel  336  is as small as possible to limit absorption of blood. Again using a Pitot type of tube form enhances the blood flow.  
         [0071]      FIG. 14  shows an imaging system  400  having an X-ray component  402  for acquisition of image data. X-ray component  402  is coupled to imaging component  404  for processing of the image data. The output of imaging component  404  is coupled to display unit  406 . Such imaging system are known from the prior art for monitoring of catheterisation. In addition to prior art imaging systems catheter system  100  (cf.  FIG. 1 ) is coupled to imaging component  404 . Catheter system  100  provides blood analysis data to imaging component  404 . The blood analysis data is integrated into the picture which is generated by imaging component  404  and displayed on display  406 . This way an operator is provided with both imaging data as well as chemical analysis data for improved monitoring of the state of the patient&#39;s body.  
       REFERENCE NUMBERALS  
       [0000]    
       
           100  catheter system  
           102  catheter head  
           104  optical fibre  
           106  catheter  
           108  objective lens  
           110  optical fibre  
           112  laser beam  
           114  raman excitation laser  
           116  connector  
           118  mirror  
           120  raman scattered radiation  
           122  raman spectrum analyser  
           124  catheter inputs  
           200  blood vessel  
           202  detector volume  
           300  catheter head  
           302  housing  
           304  objective lens  
           306  optical fibre  
           308  catheter  
           310  detection volume  
           312  cavity  
           314  mesh  
           316  shutter  
           318  channel  
           320  spherical mirror  
           322  ellipsoidal mirror  
           324  distal end  
           326  mirror  
           328  opening  
           330  optical fibre  
           332  objective lens  
           334  filter  
           336  channel  
           338  half-round spherical mirror  
           440  dichroic mirror  
           442  mirror  
           400  imaging system  
           402  x-ray component  
           404  imaging component  
           406  display unit