Abstract:
The fiber optic pressure sensing system includes a sensor housing formed using MEMS processing. The sensor housing has ribs and grooves in both horizontal and vertical directions relative to the surface to allow the membrane to flex in a consistent manner. The flexing of the membrane allows the pedestal to be repeatedly positioned in response to pressure acting on the extension of the sensor head and membrane.

Description:
RELATED APPLICATION  
       [0001]    The present invention claims priority to provisional application No. 60/358,807 filed on Feb. 22, 2002. 
     
    
     FEDERAL RESEARCH STATEMENT  
       [0002] This invention was made with Government support under Grant Number 5R44HL62038 awarded by the National Institute of Health. 
     
    
     
       TECHNICAL FIELD  
         [0003]    The present invention relates generally to optical pressure sensors and, more specifically, to an ultra-miniature fiber optic pressure sensor embedded in an angioplasty guidewire.  
         BACKGROUND  
         [0004]    Each year in the United States, five million patients get initial diagnosis of a heart attack, and nearly one million patients undergo coronary angioplasty, or other interventional procedures, to open or restore flow through stenosed vessels. Angiography is the standard method for assessing lesion severity, but it only provides an anatomic view of the lumen of the vessel, often in only one plane. Clinical benefits, as well as other benefits, would result if a real-time assessment of the functional severity of the lesion and its effect on blood flow were possible. A current method for attempting to acquire this information is the Doppler guidewire via which flow (or flow velocity) can be measured at the lesion. For reliable measurements, a catheter must be accurately positioned and must be stable during the entire data collection interval. This is difficult to do and, consequently, this method is not widely used. In addition, the necessary equipment is expensive and requires an elaborate training program for proficient use. A method involving direct measurement of pressure, rather than velocity, will have distinct advantages. Direct pressure measurements are easier to interpret, more familiar to medical personnel, require less expensive recording instruments and signal processing devices, and the position of the catheter is less critical. In addition, velocity measurements assess flow only through the lesion, while pressure measurements also assess the effects of collateral flow from other sources. This collateral flow can mediate the effect of the lesion in some cases. A direct-reading pressure catheter system can be used during angioplasty to monitor the progress and the immediate effects of the procedure on pressure distal to the lesion.  
           [0005]    During angioplasty procedures, it is useful to be able to measure pressure distal to the lesions before, during, and after dilatation by the balloon. A procedure currently being investigated is the measurement of distal pressure during maximal vasodilatation. This is referred to as “functional flow reserve” and is a measure of the effect of the pressure drop across the lesion at maximal flow. This is currently measured through the lumen of the angioplasty catheter, but has limited fidelity, and can itself add to the severity of the lesion and the measured pressure drop. A narrow pressure sensor for direct pressure measurements was introduced in the U.S. market in February 1999, by RADI of Sweden called PressureWire™. The PressureWire™ sensor has a 360 micron diameter. However, there are several limitations with this sensor: (1) cost effectiveness, (2) mechanical characteristics, and (3) pressure measurement stability during angioplasty procedures. The current invention is related to a disposable sensor that reduces these limitations.  
           [0006]    With the advent of the RADI PressureWire™, many studies have been conducted to determine the specific usefulness of such a device for diagnosis and an assessment of the effectiveness of the treatment during angioplasty. The high interest in such a device is demonstrated with over 20 papers presented about the RADI PressureWire™ at the ACC meeting held March, 2000 in Anaheim Calif. A new index, the Fractional Flow Reserve (FFR), defined as FFR=Pa/Pd (Pa=aortic pressure and Pd=distal coronary pressure), can be obtained by such a device and is now considered to be an accurate, quantitative and cost effective method for diagnosis and assessment. In particular, the method is effective for accurately determining the clinical significance of moderate stenoses. These are difficult to determine with current angiography procedures.  
           [0007]    Presently the most common mass-produced disposable pressure sensors in the medical industry are silicon electronic devices with a typical size of several millimeters in diameter for the sensing area, usually used together with fluid-filled catheters as external pressure transducers. They are based on the piezoresistive or capacitive properties of silicon crystal and need complex circuitry for signal processing, drift compensation, and noise reduction before the information is made available to the medical personnel. These devices have an inherently high hysteresis and significant short-term creep (i.e., within a few hours) and thus need frequent re-calibration. They cannot easily perform static DC measurements. They also need to have a certain minimum size for the pressure-sensing mechanism to generate an adequate signal, so it is difficult to reduce the size down to the sub-millimeter region at a reasonable cost. The RADI PressureWire™ overcomes the size problem. However, it is an electronic sensor and the inherent problems described above remain, including a drift problem. In addition, the narrow (high impedance) cable must be adequately shielded to reduce RF interference. The desired feel (or stiffness) of the guidewire is therefore very difficult to achieve.  
           [0008]    Fiber-optic sensors for direct pressure measurements are generally known in the art. Fiber-optic sensors are of a relatively simple design, have an inherently smaller potential size, and offer other advantages. A fiber-optic sensor is safe, involving no electrical connection to the body; because the primary signal is optical it is not subject to electrical interference, is very small and flexible, and can be included in catheters for multiple sensing. In addition, fiber-optic devices lend themselves well to existing mass production techniques.  
           [0009]    U.S. Pat. No. 5,987,995 to the present assignee describes a fiber-optic pressure catheter that is suited to be low-cost and disposable. The sensor of the &#39;995 patent includes a ribbon reflector, in contact with a polyurethane window, as the key sensing element that translates mechanical deformation, due to pressure, to an optical intensity variation of a signal beam. For some applications, the sensor of the &#39;995 patent is undesirably large.  
           [0010]    It would therefore be desirable to provide a pressure sensing system that is capable of providing a sufficient amount of deflection for the membrane in order to improve the accuracy of the device, increase the sterility of the system, and provide a means for adjusting the sensitivity so that consistent pressure readings are obtained if the sensor is disconnected from the light source and monitoring system.  
         SUMMARY  
         [0011]    The present invention provides an improved pressure monitoring system particularly suited for use during angioplasty procedures.  
           [0012]    In one aspect of the present invention, an improved fiber-optic pressure includes an optical fiber and a sensor head that is coupled to the optical fiber. The sensor head has a first portion having a membrane and a second portion. The membrane comprises a substrate having a rectangular center portion having a pair of first sides having a first length and a pair of second sides having a second length. The membrane has a plurality of parallel grooves and ribs formed around the center portion to allow the membrane to deflect inward.  
           [0013]    In one constructed embodiment the grooves and ribs are formed parallel to the first sides and second sides. Two continuous rectangular grooves parallel to the center portion were used. The grooves have the ribs therebetween. The ribs are preferably discontinuous to facilitate flexing of the membrane.  
           [0014]    In a further aspect of the invention, a method of forming a pressures sensor comprises forming a top portion of a sensor housing; on a first substrate, etching a rectangular portion with a plurality of grooves defining a plurality of ribs around the center portion, and on a second side of the substrate etching to form a pedestal extending from the center portion.  
           [0015]    In yet another embodiment of the invention, an optical connecting system includes a housing having a central axis, a first optical fiber coupled to the housing having a first end and a second optical fiber coupled to the housing along the central axis having a second end. A lens and a lens scanning device movably coupled to the lens is also included within the housing. The lens is disposed on the central axis of the housing. The lens scanning device moves the lens relative to the housing to direct light from the first end to the second end.  
           [0016]    In yet another aspect of the invention a connector for connecting an optical fiber to the housing includes a collet having a flange portion and a hollow tube portion for receiving the guidewire, said tube portion having a taper. A cap portion having a channel therethrough has a second taper portion that corresponds to the first taper portion. A spring is used to couple the collet to the cap.  
           [0017]    Advantages of the invention include that the sensor measures blood pressures in the range of 0 to 300 mmHg with long-term stability and high fidelity. Also, the pressure sensor, imbedded in the guidewire, is stable for time periods compatible with prolonged guidewire implantation (up to 72 hours) although only 20 minutes is normally required in angioplasty use. Further pressure readings are independent of temperature over a range of at least 20° C. to 50° C. In addition to its functional properties, the pressure-sensor imbedded in a guidewire will be designed to be disposable and will, therefore, be available at a reasonable cost.  
           [0018]    Other advantages of the present invention are also apparent. By providing grooves and ribs in the membrane, the present invention allows the device to be fabricated using MEMS processing techniques while allowing a substantial amount of pedestal deflection.  
           [0019]    Yet another advantage of the invention is that repeatability is enhanced by the improved optical connecting system. That is, because a pressure sensor may be required to be decoupled during angioplasty, when the pressure sensor is reconnected, the optical connecting system adjusts the directional light between the two optical fiber ends so that consistent readings may be generated.  
           [0020]    The sterility of the system is also improved by providing an improved connector for connecting the optical fiber to the housing. The connectors are relatively inexpensive and provide a tight seal for mounting the optical fiber to the housing.  
           [0021]    Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a block diagrammatic view of the optical pressure sensing system according to the present invention.  
         [0023]    [0023]FIG. 2 is a simplified schematic view of a sensor head coupled to an optical fiber according to the present invention.  
         [0024]    [0024]FIG. 3 is a top view of a wafer used to form the present invention.  
         [0025]    [0025]FIG. 4 is a top view of a chip having various cells used in forming the housing of the present invention.  
         [0026]    [0026]FIG. 5 is a top view of the chip having a mask pattern thereon.  
         [0027]    [0027]FIG. 6 is an enlarged view of the mask pattern of both of the cell types of FIGS. 4 and 5.  
         [0028]    [0028]FIG. 7 is an enlarged mask of the first cell of FIG. 6.  
         [0029]    [0029]FIG. 8 is a cross-sectional view of the first cell after etching with the first mask.  
         [0030]    [0030]FIG. 9 is an elevational view of a second mask on the first and second cells.  
         [0031]    [0031]FIG. 10 is an enlarged elevational view of the mask on the first and second cells.  
         [0032]    [0032]FIG. 11 is a cross-sectional view of the first cell after etching with the second mask.  
         [0033]    [0033]FIG. 12 is an elevational view of the chip having a third mask thereon.  
         [0034]    [0034]FIG. 13 is a plot of the first cell having an enlarged view of the third mask of FIG. 12.  
         [0035]    [0035]FIG. 14 is a cross-sectional view of the hole created after etching using the mask of FIG. 13.  
         [0036]    [0036]FIG. 15 is a lateral cross-sectional view of the hole created by the mask of FIG. 13.  
         [0037]    [0037]FIG. 16 is an elevational view of the chip having a fourth mask thereon.  
         [0038]    [0038]FIG. 17 is an enlarged view of the first cell having the fourth mask thereon.  
         [0039]    [0039]FIG. 18 is a cross-sectional view of the rectangular hole created by etching using mask four.  
         [0040]    [0040]FIG. 19 is an elevational view of the chip having a fifth mask on the first cell.  
         [0041]    [0041]FIG. 20 is an enlarged elevational view of the first cell having the fifth mask thereon.  
         [0042]    [0042]FIG. 21 is an enlarged view of the mask of FIG. 20.  
         [0043]    [0043]FIG. 22 is a cross-sectional view of the first cell after etching using the masks  1 ,  2 ,  3 , and  5 .  
         [0044]    [0044]FIG. 23 is a cross-sectional view of the connector system of the present invention.  
         [0045]    [0045]FIG. 24 is an enlarged cross-sectional view of the lens scanning device of FIG. 23.  
         [0046]    [0046]FIG. 25 is a cross-sectional view of a guidewire cap formed according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0047]    In the following figures the same reference numerals will be used to illustrate the same components.  
         [0048]    Although the invention is illustrated in the context of a fiber-optic sensor suitable for use in the human body, it will be appreciated that this invention may be used with other applications requiring pressure sensing.  
         [0049]    Referring now to FIG. 1, a pressure sensing system  10  has a sensor unit  12  and a light transmitting and receiving unit  14 . Sensor unit  12  extends to the location in which the pressure is to be measured. Sensor unit  12  provides a spectral modulation of the light to light transmitting and receiving unit  14 . Light transmitting and receiving unit  14  converts the modulation into the spectral fringe pattern and also converts into a pressure reading with a microprocessor (or sends the digitized signal of the fringe pattern to a computer to convert a pressure reading).  
         [0050]    Sensor unit  12  comprises a sensor head  16 , an optical fiber  18  within a guidewire  20 , and a connecting system  24 . The sensor unit  12  further includes a coil tip  26  and a spring coil  28  that are typically associated with an angioplasty device. The sensor head  16  may, for example, be placed in a human artery to measure blood pressure or placed within the brain to measure fluid pressure. Optical fiber  18  is connected between the connector  24  and the sensor head  16 .  
         [0051]    Light transmitting and receiving unit  14  is connected through an optical fiber to the adaptive fiber connector  24 . The light transmitting and receiving unit  14  includes an optical coupler  32 , a spectrometer/CCD device  34 , a white light source  36 , an optical fiber  38 , and a second optical fiber  40 . Optical fibers  38  and  40  are used to couple the spectrometer/CCD  34  and the white light source  36 , respectively, to fiber coupler  32 . The coupler  32  is also used as a beam splitter to send light returned by the sensor head  16  to spectrometer  34 .  
         [0052]    Spectrometer  34  is used to analyze the light received from the sensor head  16 . Spectrometer  34  may divide the light into its wavelength components. Spectrometer  34  preferably uses a linear detector such as a series of charge coupling devices (CCD). Spectrometer  34  converts the detected light signal from the sensor  16  into a desirable output format such as digital signals.  
         [0053]    Light source  36  is preferably a wide band light source such as a white light source. One example of a desirable white light source is a tungsten-halogen source.  
         [0054]    Light transmitting and receiving unit  14  may also have a computer  42  associated therewith. Computer  42  is used to perform mathematical calculations with the digitized output of spectrometer  34  to determine the pressure and various calibrations and adjustments as will be further described below. A monitor  44  may be used to display the pressure as calculated by the computer  42 . The spectrometer  34  and optical coupler  32  may be contained on a compact computer board, which is inserted into computer  42 . Such a light digitizer is manufactured by Ocean Optics.  
         [0055]    One constructed embodiment of the invention includes guidewire  20  being formed of a hypo-allergenic tube of approximately five feet long having a 300 micron outer diameter. Spring coil  26  has the same outer diameter as the guidewire and is about eight to ten inches long. The sensor head  16  may be formed approximately two to three millimeters long. The coil tip may be tapered in diameter and be approximately one inch long. The coil tip is preferably made of platinum. The optical fiber  18  within the guidewire  20  with cladding and protective cover of polyimide has approximately a 90 micron outer diameter. The core of the optical fiber is a multi-mode optical fiber having a core diameter of approximately 60 microns.  
         [0056]    Referring now to FIG. 2, one embodiment of sensor head  60  is illustrated coupled to optical fiber  18  that has a cladding and polyimide casing  46 . Optical fiber  18  has a first end  48  that is polished smooth to be optically flat. The end  48  preferably has a coating  50  disposed thereon. The coating  50  is preferably formed of titanium dioxide (TiO 2 ) or zinc sulfide (ZnS). Coating  50  may be about 0.7 to 3 microns but is approximately 2 microns thick.  
         [0057]    Sensor head  16  has a housing  52 . Housing  52  has a top portion  54  and a bottom portion  56 . The top portion  54  includes a membrane  58 , a pedestal  60  and a cavity  62 . The optical fiber is positioned between the top portion  54  and the bottom portion  56 . Preferably, the top portion  54  has membrane  58 , pedestal  60  and cavity  62  integrally formed therewith. The housing  52  may be formed of a silicon material with a metallic material coating such as titanium grade  5 . The system works in a similar manner to that described in U.S. Pat. No. 5,987,995, which is incorporated by reference herein. A portion of light from the light source  36  never leaves optical fiber  18 . That is, the light reflects from end  48  and travels back through the optical fiber  18 . To increase and generate a desired pattern of reflectance of the end  48 , a portion of the light passes through the coating  50  and reflects from the end thereof: The coating  50  works as an Etalon so that the spectrum of the reflected light from the two surfaces is “spectrally” modulated (forming white light fringes). Some light leaves the coating  50  and bounces from the pedestal  60  back into the coating  50  and through the fiber core  18 . This bounced light is also spectrally modulated in such a way that the fringes are a complement of these of the reflected light by the coating  50 . As the pressure increases, the amount of the pedestal  60  in front of the optical fiber  18  varies. The amount varies from almost no pedestal in front of the reflective end to partially in front of the optical fiber  18 . Thus, it is the deflection of the membrane  58  that controls the amount of movement of the pedestal  60 . Thus, it is desirable to provide a suitable amount of movement of the pedestal  60 . The light returning from the sensor head consists of a superposition of two fringes: one from the coating  50  and the other from the pedestal  60 . The pressure is determined from a contrast of the superimposed fringes as is described in U.S. Pat. No. 5,987,995. It is to be noted that with this system the pressure is not directly determined by the amount of light reflected by the pedestal but is obtained as the contrast change of the superimposed fringes. Unlike the light variation measurements such as these taught in U.S. Pat. No. 5,018,529, this method of the measurement is a ratio measurement that makes the system robust against mechanical (fiber bending) and temperature fluctuations.  
         [0058]    Referring now to FIG. 3, the way in which the top of the sensor housing  54  and the bottom of the sensor housing  56  are made is described. In FIG. 3, a wafer  70  is illustrated having a chip  72  that is etched to form the present invention.  
         [0059]    Referring now to FIG. 4, chip  72  is illustrated in further detail. The chip is divided into a number of cells H 1  and H 2 . H 1  ultimately becomes the top portion  54  of the sensor housing and H 2  becomes the bottom portion of sensor housing  56 .  
         [0060]    In one constructed embodiment, the length of chip  72 , L 1  was 16 millimeters, the length of each cell, Lc is 3 millimeters, the width of each cell, Wc is 1000 microns, and the width of the end portions, Wes is approximately 2 millimeters. The system is illustrated with respect to a coordinate system having an origin C at 0, 0. Thus, an X axis  72  and a Y axis  74  are illustrated.  
         [0061]    Referring now to FIG. 5, a first mask  76  is provided. One mask for one H 1  cell and one H 2  cell is illustrated. The mask is repeated on each of the cells. The shaded areas illustrate the areas to be etched. The wafer from which the process is started is preferably about four or six inches in diameter and about 140 microns thick. Mask  1  is a lithographic mask that is applied to the surface except at the masked portions. Thus, when etching is performned, the illustrated shaded area will be etched.  
         [0062]    Referring now to FIGS. 6 and 7, mask  1  has various dimensions.  
         [0063]    Ltn=530  
         [0064]    Wtn=200  
         [0065]    Lup=700  
         [0066]    Lmb=1200  
         [0067]    Lfs=1100  
         [0068]    Wmb=205  
         [0069]    Wmb/2=205/2=102.5  
         [0070]    Wgv=25  
         [0071]    Wsp=4  
         [0072]    Lgl=Lmb−2*(Wgv+Wsp)=1200−2*(25+5)=1140  
         [0073]    Lgs=Lgl−2*(Wgv+Wsp)=1140−2*(25+5)=1080  
         [0074]    Wgp=85  
         [0075]    As can be seen, the mask  76  has various portions that correspond to the grooves in the surface. That is, a top view of the device after etching looks like FIG. 7 so the grooves and mask portions will be described together. Mask  1  has a center portion  78 , two vertical portions  80  and  81  on the left side of the center portion  78 , and two vertical portions  82  and  83  on the right side of the center portion  78 . It should be noted that right and left are described with respect to FIG. 7. That is, vertical portions  80 - 83  are parallel to the longitudinal sides of the center portion  78 . Mask  1  further includes horizontal portions  84 ,  85 ,  86 , and  87 . Horizontal portions  84  extend laterally and are parallel with the top and bottom sides of the center portion  78 . Thus, the grooves formed by the vertical and horizontal portions  80 - 87  include discontinuous outer grooves  80 ,  82 ,  84 , and  86  that are longer in size than their respective corresponding inner grooves  81 ,  83 ,  85 , and  87 . The lengths of the grooves formed by the masked portions  81  and  83  are preferably as long as the center portion  78 . The grooves formed by the horizontal portions  85  and  87  are as long as the center portion, two ribs and the width of the grooves  81  and  83 . The length of the grooves formed by the masked portions  80  and  82  are preferably as long as the longitudinal walls of the center portion  78  plus the width of two ribs and the width of the grooves  85  and  87 . The length of the grooves formed by the portions  84  and  86  are preferably as long as the lateral width of the center portion  78 , four ribs formed between the horizontal walls  81 ,  82 , and  83  and the width of the grooves formed by the portions  81 ,  82 , and  83 .  
         [0076]    The mask  76  and grooves are preferably elongated and rectangular in shape. Dimensions of the grooves and thus the widths of the ribs formed by the system are described below:  
         [0077]    Ltn=530  
         [0078]    Wtn=200  
         [0079]    Lup=700  
         [0080]    Lmb=1200  
         [0081]    Lfs=1100  
         [0082]    Wmb=205  
         [0083]    Wmb/2=205/2=102.5  
         [0084]    Wgv=25  
         [0085]    Wsp=4  
         [0086]    Lgl=Lmb−2*(Wgv+Wsp)=1200−2*(25+5)=1140  
         [0087]    Lgs=Lgl−2*(Wgv+Wsp)=1140−2*(25+5)=1080  
         [0088]    Wgp=85  
         [0089]    Referring now to FIG. 8, a cross-sectional view along line A—A of FIG. 7 is illustrated. The partially etched cell H 1  has a center portion  90 , a first longitudinal rib  92 , a second longitudinal rib  94 , a third longitudinal rib  96 , and a fourth longitudinal rib  98 . A first longitudinal groove  100  is disposed between the first rib  92  and the second rib  94 . A second longitudinal groove is positioned adjacent to the rib  94 . A third longitudinal groove  104  is disposed between the rib  96  and  98 . A fourth longitudinal groove is disposed adjacent to the rib  98 . Thus, the etching of the grooves  100 - 106  and the center portion  90  form the ribs  92 . Each groove  100 - 106  is preferably formed to have a flat portion  108 . The grooves in the lateral direction preferably have the same dimensions. Thus, the figure of a lateral direction would have the same dimensions except the width Wgp becomes Lgs. The dimensions of the ribs and grooves are:  
         [0090]    Wgv=25  
         [0091]    Wgb=5  
         [0092]    Wgp=85  
         [0093]    Wpb=65  
         [0094]    Wsp=5  
         [0095]    Dgv=15.7  
         [0096]    Referring now to FIG. 9, a second mask  110  is illustrated. As can be seen, mask  110  extends between cells H 1  and H 2 .  
         [0097]    Referring now to FIG. 10, the mask  110  is used to form breaking lines so that the various cells may be broken apart into their corresponding housing portions. The various dimensions with respect to the mask  2  are:  
         [0098]    Wc=1.0 mm  
         [0099]    We=400  
         [0100]    Lc=3.0 mm  
         [0101]    Lsl=500  
         [0102]    Wa=280  
         [0103]    Wan=210  
         [0104]    Referring now to FIG. 11, cross-sectional view of cell H 1  is illustrated. As can be seen, breaking lines  112  and  114  run longitudinally with respect to the cell H 1 . As mentioned above, the breaking lines  112  and  114  allow the top portion of housing  54  to be formed. The dimensions in the cross-sectional view are:  
         [0105]    Wwt=(Wa−Wmb)/2=(280−205)/2=37.5  
         [0106]    Wsn=(We−Wa)/2=(400−280)/2=60  
         [0107]    Dbl=about 110  
         [0108]    It should be noted that the etchings described above with respect to FIGS.  3 - 11  are formed on the first side (side A) of the cells (or the wafer). Later, the etching on the second sides will be illustrated. For the etching of the grooves and ribs, preferably KOH is used in the etching process. The breaking lines may be etched using a DRIE etching process. Because the edges of the etching may form sharp corners, a brief HNA etching may be used to round the corners. The entire side A after the etching process may be coated with titanium Grade  5 . The thickness of the film may, for example, be 1.5 microns on the flat surfaces. The titanium Grade  5  alloy consists of (Ti— 6 Al—4V) since an amorphous Ti film is desired.  
         [0109]    Referring now to FIG. 12, a third mask  120  is illustrated on chip  72 . This mask is used to determine the height of pedestal  60 . Mask  120  is on the opposite side of the device as FIGS.  3 - 11 .  
         [0110]    Referring now to FIG. 13, mask  120  is shown in an enlarged scale from that of FIG. 12. The dimensions of the mask correspond to the dimensions of the end of the pedestal  60  of FIG. 2. The dimensions are:  
         [0111]    Wc=1.0 mm  
         [0112]    Wc/2=0.5 mm  
         [0113]    Ls=1300  
         [0114]    LI=1700  
         [0115]    Wp=65  
         [0116]    Wpn=40  
         [0117]    The dimensions of the rectangular hole  122  shown in FIG. 14 and  15  are:  
         [0118]    Wp=65  
         [0119]    Wpn=40  
         [0120]    Dph=50  
         [0121]    Referring now to FIGS. 16 and 17, a fourth mask  124  is illustrated. Fourth mask  124  is also formed on the lower surface of the cell H 1 . The etching allows for the size of the optical fiber so that the optical fiber may be inserted within the top portion of housing  54 . The dimensions of mask  124  are:  
         [0122]    Lfs=1900  
         [0123]    Lls=1100  
         [0124]    Wfs=90  
         [0125]    Referring now to FIG. 18, the cell H 1  is illustrated with the rectangular slot  126  formed from mask  4 . Rectangular slot  126  as mentioned above is used to receive the optical fiber during assembly. The dimensions of the rectangular slot  126  are:  
         [0126]    Wfs=90  
         [0127]    Dfh=90  
         [0128]    The etching process uses a photolithography process, and DRIE etching as mentioned above.  
         [0129]    The cell H 1  is preferably planarized in a known manner before performing the fifth mask  128  described below.  
         [0130]    Referring now to FIG. 19, the chip  72  is illustrated having a mask  128 . Mask  128  has registration portions  130  and a rectangular portion  132 .  
         [0131]    Referring now to FIGS. 20 and 21, enlarged versions of the rectangular portion  132  are illustrated. The rectangular portion  132  has an opening  134  therein. The opening  134  corresponds to the pedestal so that the pedestal area is not further etched. The rectangular portion  132  is used to etch out the cavity  62  shown in FIG. 2. The dimensions of the etchings are:  
         [0132]    R1=R2=R3=R4=R5=70  
         [0133]    Rd=340  
         [0134]    Wsl=15  
         [0135]    Lue=700  
         [0136]    Lcl=1200  
         [0137]    Lls=1100  
         [0138]    Wcs=205  
         [0139]    Wp=65  
         [0140]    Wpn=40  
         [0141]    Referring now to FIG. 22, a cross-sectional view of the top portion  54  is illustrated. As can be seen, cavity  62  is illustrated while allowing the membrane and pedestal to remain fixedly thereto. As can be seen the titanium layer  135  remains while the silicon is etched away at the grooves. The dimensions illustrated on the cavity are:  
         [0142]    Wcs=205  
         [0143]    Dt=140 to the membrane.  
         [0144]    Referring now to FIG. 23, connecting system  24  is illustrated. Connecting system  24  has optical fiber  30  that is connected to fiber optic coupler  32  within the light transmitting and receiving unit  14 . The second optical fiber as shown in FIG. 1 is coupled to sensor head  16 . The connecting system  24  has a housing  140  that has a cavity  142  therein. Cavity  142  includes an imaging lens  144  and a lens scanning device  146 . The lens scanning device  146  positions the imaging lens  144  with respect to the optical fiber  30  and the optical fiber  18 . The scanning device is capable of moving the lens in a vertical direction illustrated by arrow  148 . The vertical direction corresponds to the lateral axis of the housing  140  which is perpendicular to the optical axis and the longitudinal axis of the housing  140 . The lens scanning device  146  is also capable of positioning the lens horizontally as indicated by arrow  151 . That is, the lens scanning device  146  is capable of moving the lens  144  in a horizontal direction perpendicular to the longitudinal axis (direction  148 ) and optical axis of the housing  140 . The optical fiber  18  may be positioned within the housing  140  using a sanitization cap  150 . Sanitization cap  150  is used to prevent the system from becoming contaminated during the angioplasty procedure. The cap  150  is removable from the housing  140  and is fixedly attached to the housing using a pin  152 . Pin  152  is removable and fits within a recess  154  in the cap  150 . The cap  150  has a channel  156  having a diameter sized to receive the optical fiber  18  and the guidewire  20 .  
         [0145]    Referring now to FIG. 24, lens scanning device  146  is illustrated in further detail. Lens scanning device  146  includes a lens holder  156  used to receive imaging lens  144  therein. Lens holder  146  has a vertical motion lever, arm  158  coupled thereto. Lens holder  156  also has a horizontal motion lever arm  160  coupled thereto. Vertical motion lever arm  158  is coupled to a screw  162  which in turn is moved by piezo device  164 .  
         [0146]    The horizontal motion lever arm  160  is coupled by way of a screw  166  to a piezo device  168 . Movement of the screw  166  caused by the piezo device  168  moves the lens holder  156  in a horizontal direction. Thus, the lens may be positioned in a horizontal direction and vertical direction by piezo devices  164  and  168  by pushing screws  162  and  166 .  
         [0147]    In the guidewire application, the sanitization cap end of the guidewire  120  cannot be larger than the diameter of the tube. For angioplasty procedures, a tube carrying a stent-balloon must be placed over the guidewire to place the stent in an injured part of a coronary artery. The end of the guidewire has to be removed from the fiber connector when the stent is applied. Thus, the connector has to be such that when a user of the connector disconnects or connects the guidewire to the fiber connector, the optical fiber  18  has to be reconnected in such a way that maintains consistent pressure readings. Because the connection takes place while the sensor is within the patient&#39;s artery, sensitivity or offset adjustments are not practical. The connector  24  is thus adapted by using the mechanism shown in FIG. 24. It is the desired goal of the system by monitoring the spectrometer  34  to form an image of the core of optical fiber  30  on the optical fiber  18 . If this is not achieved coupling efficiency is reduced and a signal offset level may be formed. This makes the system unreliable. The lens scanning device  146  is capable of moving the lens to compensate for the offset. The piezo devices  164  and  168  are capable of a displacement of 7 microns. Because of the leverage created by the lever arms  158  and  160 , up to 70 microns of movement may be achieved. Thus, an image formed by the lens may move up to 140 microns due to optical leverage. The lever arms may be formed using an electrode discharge machining process.  
         [0148]    In operation, the purpose is to project the image of the core of the source fiber  30  on the fiber. The visibility of the fringes from the coating  50  of FIG. 2 is used for this aim. The light in the core of the guidewire goes to the end of the fiber sensor  60  when it returns the spectrum modulated by the coating  50 . The light that strikes the other part of the end face of the guidewire does not contain any fringes and is reflected back to the detector  34 . By moving the piezo stacks, the lever arms are moved. This movement may be controlled by the computer  42 . By monitoring the visibility of the fringes, the position with the maximum visibility becomes the desired location. In a practical implementation, coarse scanning may be used followed by fine scanning. That is, the position of the system may be easily found using a 10 micron accuracy followed by 4 micron accuracy steps.  
         [0149]    Referring now to FIG. 25, a second embodiment of the sanitization cap connector  150 ′ is illustrated. In this embodiment, the connector  150 ′ is coupled to the housing  140 . The connector  150 ′ includes a collet  170 . The collet  170  has a flange portion  172  and a hollow tube portion  174 . Guidewire  18  is received within the hollow tube portion  174 . The connector  150 ′ also includes a cap  176  that is positioned within an angular opening  178 . The angular opening  178  corresponds to the conical shape of the cap  176 . The cap  176  has a flange  180  extending therefrom. A tension spring  182  is used to couple the cap  180  to the collet  170 . The spring is positioned between the flanges  172  and the flange  180  of cap portion  176 . The cap is preferably formed of stainless steel. The cap  176  has a channel  184  therein. The channel  184  has a tapered surface  186  therein. The tapered surface  186  corresponds to a taped surface  188  of the collet. Thus, as the hollow tube portion  174  is inserted within the cap, the tapered surfaces  186  and  188  act to hold the guidewire  20  therein. A guidewire stop  190  may also be coupled to the cap portion  176 . Guidewire stop  190  may be press fit and have a diameter smaller than the diameter of the guidewire  20 . This prevents the guidewire  20  from being positioned too far within the housing  140 .  
         [0150]    The tension spring  182  pulls the collet  170  in the cap  176  which holds the guidewire  20  in place. When the guidewire  20  is released, one pulls the flange out of the collet. This releases the guidewire holding force. The cap can be released from the housing  140  by pulling it outward. This helps prevent accidental release of the guidewire  20  from the fiber connector  24 .  
         [0151]    While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.