Optical sampling interface system for in vivo measurement of tissue

Abstract

An optical sampling interface system minimizes and compensates error resulting from sampling variations and measurement site state fluctuations. Components include: an optical probe placement guide having an aperture wherein the optical probe is received, facilitates repeatable placement accuracy on surface of a tissue measurement site with minimal, repeatable disturbance to surface tissue. The aperture creates a tissue meniscus that minimizes interference due to surface irregularities and controls variation in tissue volume sampled; an occlusive element placed over the tissue meniscus isolates the meniscus from environmental fluctuations, stabilizing hydration at the site and thus, surface tension; an optical coupling medium eliminates air gaps between skin surface and optical probe; a bias correction element applies a bias correction to spectral measurements, and associated analyte measurements. When the guide is replaced, a new bias correction is determined for measurements done with the new placement. Separate components of system can be individually deployed.

1 . A method for noninvasively sampling a targeted measurement site, comprising the steps of: 
 providing a mount having a contact surface, an aperture defined by said mount, and magnetic registration means along any of x-, y-, and z-axes; 
 at least a portion of said contact surface contacting a surface proximate said targeted measurement site during use;  
 said aperture receiving an optical probe;  
 wherein an area defined by said aperture comprises said measurement site; and  
   said mount coupling said optical probe to said targeted measurement site;    said coupling optical probe to said targeted measurement site being repeatable.    
     
     
         2 . The method of  claim 1 , wherein said measurement site comprises a tissue measurement site and wherein surface tissue at said measurement site comprises said skin surface comprising stratum corneum.  
     
     
         3 . The method of  claim 2 , further comprising the step of: 
 occluding said aperture when it is not occluded by the presence of said optical probe.    
     
     
         4 . The method of  claim 3 , wherein said step of occluding said aperture comprises using an occlusion plug.  
     
     
         5 . The method of  claim 4 , wherein shape and dimensions of a portion of said occlusion plug received by said aperture is substantially similar to shape and dimensions of said aperture.  
     
     
         6 . The method of  claim 4 , further comprising the step of: 
 removably attaching said plug to an exterior surface of said mount.    
     
     
         7 . The method of  claim 6 , wherein said step of removably attaching comprises using any of: 
 magnets attached to said plug and said mount;    hook and loop tape;    adhesives; and    snaps.    
     
     
         8 . The method of  claim 4 , wherein said plug fits snugly within said aperture without additional attachment means.  
     
     
         9 . The method of  claim 4 , wherein said mount induces a tissue meniscus within said aperture.  
     
     
         10 . The method of  claim 9 , wherein said plug stabilizes hydration level of the stratum corneum across surface of said meniscus.  
     
     
         11 . The method of  claim 1 , further comprising the step of: 
 removably attaching said mount at said measurement site.    
     
     
         12 . The method of  claim 11 , wherein said step of removably attaching comprises using an adhesive.  
     
     
         13 . The method of  claim 11 , wherein said step of removably attaching comprises using any of: 
 at least one strap;    at least one armband; and    at least one suction element.    
     
     
         14 . The method of  claim 1 , said magnetic registration means assessing location of said mount with respect to said measurement site.  
     
     
         15 . The method of  claim 1 , further comprising the step of: 
 monitoring surface temperature proximate to said measurement site.    
     
     
         16 . A method for coupling an optical probe to a targeted measurement site, comprising the steps of: 
 providing a mount having a contact surface, said mount defining an aperture; 
 contacting at least a portion of said contact surface to a surface proximate said measurement site during use;  
 said aperture receiving said optical probe;  
 wherein an area inside said aperture comprises said measurement site;  
 said mount providing a registration point along any of x-, y-, and z-axes; and  
   coupling said optical probe to said measurement site via said mount with a coupling medium;    said coupling of said optical probe to said targeted measurement site being repeatable.    
     
     
         17 . A method for optically sampling a targeted measurement site, comprising the steps of: 
 controlling variations in sample volume with an optical probe placement guide;    stabilizing surface hydration of a measurement site with an occlusion plug, said occlusion plug fitting into an aperture in said placement guide between measurements, wherein said occlusion plug is removably attached at an exterior surface of said guide.    
     
     
         18 . The method of  claim 17 , wherein said placement guide comprises: 
 a mount having a contact surface, at least a portion of said contact surface being in contact with a surface proximate to said measurement site during use; and    an aperture, defined by said mount, receiving said optical probe, wherein an area defined by said aperture comprises said measurement site;    removably attaching said guide at said measurement site to allow said guide to repeatably couple said optical probe to said measurement site.    
     
     
         19 . The method of  claim 18 , further comprising the step of: 
 attaching said guide to said measurement site using any of: 
 an adhesive;  
 at least one strap;  
 at least one armband; and  
 at least one suction element.  
   
     
     
         20 . The method of  claim 18 , wherein said probe fits snugly into said aperture, to allow mechanical registration in an x-y plane of said probe relative to said measurement site, said guide further comprising at least one mechanical stop for preventing over-penetration of said probe toward said measurement site, and providing registration along a z-axis of said probe relative to said measurement site.  
     
     
         21 . The method of  claim 18 , further comprising the step of: 
 using optical registration to register said probe relative to said measurement site along any of x-, y-, and z-axes.    
     
     
         22 . The method of  claim 17 , further comprising the step of: 
 using a coupling medium.    
     
     
         23 . The method of  claim 22 , wherein said coupling medium comprises an optical coupling fluid.  
     
     
         24 . The method of  claim 22 , wherein said coupling fluid comprises: 
 one or more perfluoro compounds, wherein a quantity of said coupling fluid is placed at an interface of an optical probe and a measurement site, so that said probe and said measurement site are tightly coupled.    
     
     
         25 . The method of  claim 17 , wherein shape and dimensions of a portion of said occlusion plug received by said aperture is substantially similar to shape and dimensions of said aperture.  
     
     
         26 . The method of  claim 17 , further comprising the step of: 
 monitoring surface temperature.    
     
     
         27 . The method of  claim 17 , wherein said measurement site comprises a tissue measurement site and wherein surface tissue at said measurement site comprises skin surface comprising stratum corneum.  
     
     
         28 . The method of  claim 27 , further comprising the step of: 
 correcting measurement bias resulting from any of variations in sampled volume and measurement conditions.    
     
     
         29 . The method of  claim 28 , wherein said step of correcting measurement bias comprises use of any of: 
 a noninvasive measurement system;    a tissue template; and    a calibration model;    wherein measurement bias is compensated by: 
 determining difference between a tissue measurement and a tissue template;  
 mapping resulting difference to a measurement of a target analyte according to a calibration model; and  
 applying a baseline adjustment to said analyte measurement.  
   
     
     
         30 . The method of  claim 29 , wherein variations in sampled volume result from differences in placement of either an optical probe or an optical probe placement guide between measurements.  
     
     
         31 . The method of  claim 29 , wherein said tissue template is determined through one or more tissue measurements combined according to a predetermined data selection criterion during a measurement period.  
     
     
         32 . The method of  claim 29 , further comprising the step of: 
 determining said calibration model from a calibration set of exemplary paired data points, each data point pair comprising a pre-processed and bias corrected tissue measurement and an associated reference analyte value determined from an analysis of a blood or interstitial fluid sample.    
     
     
         33 . The method of  claim 29 , wherein said baseline adjustment is associated with said tissue template and said calibration model.  
     
     
         34 . A method for minimizing optical sampling error at a tissue measurement site due to fluctuations of surface conditions, comprising the steps of: 
 providing an element defining a probe aperture, wherein at least a portion of said element is fabricated from a flexible material, wherein said element provides for stabilization of the measurement site and deformation of underlying tissue without applying undue force to a targeted tissue volume; and    inserting an occlusion plug into said aperture between measurements.    
     
     
         35 . The method of  claim 34 , wherein shape and dimensions of at least a portion of said occlusion plug is substantially similar to shape and dimensions of said aperture.  
     
     
         36 . The method of  claim 34 , wherein said plug fits snugly within said aperture without additional attachment means.  
     
     
         37 . The method of  claim 34 , further comprising the step of: 
 monitoring temperature near said tissue measurement site.    
     
     
         38 . The method of  claim 34 , further comprising the step of: 
 inducing a tissue meniscus within said aperture with said element bearing said probe aperture.    
     
     
         39 . The method of  claim 38 , further comprising the step of: 
 stabilizing hydration level of surface tissue across surface of said meniscus with said plug.    
     
     
         40 . The method of  claim 34 , wherein said element defining said aperture comprises an optical probe placement guide.  
     
     
         41 . A method for reproducibly coupling an optical probe to a tissue measurement site, comprising the steps of: 
 providing a mount having a contact surface and an aperture defined by said mount, for receiving said optical probe;    providing a plug for occluding said aperture when it is not occluded by the presence of said optical probe; and    removably attaching said plug at an exterior surface of said mount;    at least a portion of said contact surface contacting a skin surface proximate said measurement site during use;    wherein an area defined by said aperture comprises said measurement site; and    wherein said mount is contoured to approximate the surface of the measurement site.    
     
     
         42 . The method of  claim 41 , wherein said step of attaching comprises using any of: 
 a magnet attached to said plug    a magnet attached to said mount;    hook and loop tape;    an adhesive; and    a snap.    
     
     
         43 . The method of  claim 41 , wherein, said probe fits snugly into said aperture to probe mechanical registration in an x-y plane of said probe relative to said measurement site.  
     
     
         44 . The method of  claim 41 , further comprising the step of: 
 providing at least one mechanical stop on said mount, said stop preventing over-penetration of said probe toward said measurement site and providing registration along a z-axis of said probe relative to said measurement site.    
     
     
         45 . The method of  claim 41 , further comprising the step of: 
 optically registering said probe relative to said measurement site along any of x-, y-, and z-axes.    
     
     
         46 . A method for noninvasively sampling a targeted measurement site, comprising the steps of: 
 providing a mount having a contact surface and an aperture defined by said mount;    optically registering a sample probe relative to said measurement site along any of x-, y-, and z-axes;    contacting at least a portion of said contact surface to a surface proximate said targeted measurement site during use;    said aperture receiving an optical probe;    an area defined by said aperture comprises said measurement site; and    coupling said optical probe to said targeted measurement site using said mount and said optical registration, said coupling of said optical probe to said targeted measurement site being repeatable.