Patent Publication Number: US-2013232759-A1

Title: Method of Manufacturing a Transcutaneous Sensor

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of U.S. Provisional Application No. 61/755,273, filed 22 Jan. 2013, and also claims the priority of U.S. Provisional Application No. 61/609,865, filed 12 Mar. 2012, each of which are hereby incorporated by reference in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
       FIGS. 21A and 21B  show a typical arrangement for intravascular infusion. As the terminology is used herein, “intravascular” preferably refers to being situated in, occurring in, or being administered by entry into a blood vessel, thus “intravascular infusion” preferably refers to introducing a fluid or infusate into a blood vessel. Intravascular infusion accordingly encompasses both intravenous infusion (administering a fluid into a vein) and intra-arterial infusion (administering a fluid into an artery). 
     A cannula  20  is typically used for administering fluid via a subcutaneous blood vessel V. Typically, cannula  20  is inserted through skin S at a cannulation or cannula insertion site N and punctures the blood vessel V, for example, the cephalic vein, basilica vein, median cubital vein, or any suitable vein for an intravenous infusion. Similarly, any suitable artery may be used for an intra-arterial infusion. 
     Cannula  20  typically is in fluid communication with a fluid source  22 . Typically, cannula  20  includes an extracorporeal connector, e.g., a hub  20   a , and a transcutaneous sleeve  20   b . Fluid source  22  typically includes one or more sterile containers that hold the fluid(s) to be administered. Examples of typical sterile containers include plastic bags, glass bottles or plastic bottles. 
     An administration set  30  typically provides a sterile conduit for fluid to flow from fluid source  22  to cannula  20 . Typically, administration set  30  includes tubing  32 , a drip chamber  34 , a flow control device  36 , and a cannula connector  38 . Tubing  32  is typically made of polypropylene, nylon, or another flexible, strong and inert material. Drip chamber  34  typically permits the fluid to flow one drop at a time for reducing air bubbles in the flow. Tubing  32  and drip chamber  34  are typically transparent or translucent to provide a visual indication of the flow. Typically, flow control device  36  is positioned upstream from drip chamber  34  for controlling fluid flow in tubing  32 . Roller clamps and Dial-A-Flo®, manufactured by Hospira, Inc. (Lake Forest, Ill., US), are examples of typical flow control devices. Typically, cannula connector  38  and hub  20   a  provide a leak-proof coupling through which the fluid may flow. Luer-Lok™, manufactured by Becton, Dickinson and Company (Franklin Lakes, N.J., US), is an example of a typical leak-proof coupling. 
     Administration set  30  may also include at least one of a clamp  40 , an injection port  42 , a filter  44 , or other devices. Typically, clamp  40  pinches tubing  32  to cut-off fluid flow. Injection port  42  typically provides an access port for administering medicine or another fluid via cannula  20 . Filter  44  typically purifies and/or treats the fluid flowing through administration set  30 . For example, filter  44  may strain contaminants from the fluid. 
     An infusion pump  50  may be coupled with administration set  30  for controlling the quantity or the rate of fluid flow to cannula  20 . The Alaris® System manufactured by CareFusion Corporation (San Diego, Calif., US), BodyGuard® Infusion Pumps manufactured by CMA America, L.L.C. (Golden, Colo., US), and Flo-Gard® Volumetric Infusion Pumps manufactured by Baxter International Inc. (Deerfield, Ill., US) are examples of typical infusion pumps. 
     Intravenous infusion or therapy typically uses a fluid (e.g., infusate, whole blood, or blood product) to correct an electrolyte imbalance, to deliver a medication, or to elevate a fluid level. Typical infusates predominately consist of sterile water with electrolytes (e.g., sodium, potassium, or chloride), calories (e.g., dextrose or total parenteral nutrition), or medications (e.g., anti-infectives, anticonvulsants, antihyperuricemic agents, cardiovascular agents, central nervous system agents, chemotherapy drugs, coagulation modifiers, gastrointestinal agents, or respiratory agents). Examples of medications that are typically administered during intravenous therapy include acyclovir, allopurinol, amikacin, aminophylline, amiodarone, amphotericin B, ampicillin, carboplatin, cefazolin, cefotaxime, cefuroxime, ciprofloxacin, cisplatin, clindamycin, cyclophosphamide, diazepam, docetaxel, dopamine, doxorubicin, doxycycline, erythromycin, etoposide, fentanyl, fluorouracil, furosemide, ganciclovir, gemcitabine, gentamicin, heparin, imipenem, irinotecan, lorazepam, magnesium sulfate, meropenem, methotrexate, methylprednisolone, midazolam, morphine, nafcillin, ondansetron, paclitaxel, pentamidine, phenobarbital, phenytoin, piperacillin, promethazine, sodium bicarbonate, ticarcillin, tobramycin, topotecan, vancomycin, vinblastine and vincristine. Transfusions and other processes for donating and receiving whole blood or blood products (e.g., albumin and immunoglobulin) also typically use intravenous infusion. 
     Unintended infusing typically occurs when fluid from cannula  20  escapes from its intended vein/artery. Typically, unintended infusing causes an abnormal amount of the fluid to diffuse or accumulate in perivascular tissue P and may occur, for example, when (i) cannula  20  causes a vein/artery to rupture; (ii) cannula  20  improperly punctures the vein/artery; (iii) cannula  20  backs out of the vein/artery; (iv) cannula  20  is improperly sized; (v) infusion pump  50  administers fluid at an excessive flow rate; or (vi) the infusate increases permeability of the vein/artery. As the terminology is used herein, “tissue” preferably refers to an association of cells, intercellular material and/or interstitial compartments, and “perivascular tissue” preferably refers to cells, intercellular material and/or interstitial compartments that are in the general vicinity of a blood vessel and may become unintentionally infused with fluid from cannula  20 . Unintended infusing of a non-vesicant fluid is typically referred to as “infiltration,” whereas unintended infusing of a vesicant fluid is typically referred to as “extravasation.” 
     The symptoms of infiltration or extravasation typically include blanching or discoloration of the skin S, edema, pain, or numbness. The consequences of infiltration or extravasation typically include skin reactions (e.g., blisters), nerve compression, compartment syndrome, or necrosis. Typical treatment for infiltration or extravasation includes applying warm or cold compresses, elevating an affected limb, administering hyaluronidase, phentolamine, sodium thiosulfate or dexrazoxane, fasciotomy, or amputation. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments according to the present invention include a method of manufacturing a sensor to aid in diagnosing at least one of infiltration and extravasation in Animalia tissue. The method includes feeding an emission optical fiber through an emission aperture, feeding a detection optical fiber through a detection aperture, coupling first and second housing portions to define an interior volume, and disposing each individual point of the emission aperture with respect to each individual point of the detection aperture (i) a minimum distance not less than 3 millimeters; and (ii) a maximum distance not more than 5 millimeters. The emission and detection apertures penetrate a surface configured to confront an epidermis of the Animalia tissue, and the first housing portion includes the surface. The emission and detection optical fibers extend through the interior volume. The method further includes polishing (i) an emitter end face of the emission optical fiber; and (ii) a detector end face of the detection optical fiber. The emitter and detector end faces are substantially smooth with the surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features, principles, and methods of the invention. 
         FIG. 1  is a schematic view illustrating an electromagnetic radiation sensor according to the present disclosure. The electromagnetic radiation sensor is shown contiguously engaging Animalia skin. 
         FIGS. 2A-2C  are schematic cross-section views demonstrating how an anatomical change over time in perivascular tissue impacts the electromagnetic radiation sensor shown in  FIG. 1 . 
         FIG. 3  is a schematic exploded cross-section view of the electromagnetic radiation sensor shown in  FIG. 1 . 
         FIG. 4  is a schematic plan view illustrating a superficies geometry of the electromagnetic radiation sensor shown in  FIG. 1 . 
         FIGS. 5A-5C  are schematic cross-section views demonstrating the impact of different nominal spacing distances between emission and detection waveguides of the electromagnetic radiation sensor shown in  FIG. 1 . 
         FIG. 6  is a graph illustrating a relationship between spacing, depth and wavelength for the electromagnetic radiation sensor shown in  FIG. 1 . 
         FIG. 7  illustrates a technique for developing the superficies shown in  FIG. 4 . 
         FIG. 8  is a schematic plan view illustrating another superficies geometry according to the present disclosure. 
         FIG. 9  is a schematic plan view illustrating several variations of another superficies geometry according to the present disclosure. 
         FIG. 10  is a schematic plan view illustrating another superficies geometry according to the present disclosure. 
         FIG. 11  is a schematic plan view illustrating another superficies geometry according to the present disclosure. 
         FIG. 12  is a schematic plan view illustrating another superficies geometry according to the present disclosure. 
         FIG. 13  is a schematic plan view illustrating several variations of another superficies geometry according to the present disclosure. 
         FIGS. 14A-14D  illustrate distributions of spacing distances for examples of superficies geometries according to the present disclosure. 
         FIGS. 15-18  are schematic cross-section views illustrating topographies of superficies geometries according to the present disclosure. 
         FIG. 19  is a schematic cross-section view illustrating an angular relationship between waveguides of the electromagnetic radiation sensor shown in  FIG. 1 . 
         FIG. 20A  is a schematic cross-section view illustrating another angular relationship between waveguides of an electromagnetic radiation sensor according to the present disclosure. 
         FIG. 20B  illustrates a technique for representing the interplay between emitted and collected radiation of the waveguides shown in  FIG. 20A . 
         FIG. 21A  is a schematic view illustrating a typical set-up for infusion administration. 
         FIG. 21B  is a schematic view illustrating a subcutaneous detail of the set-up shown in  FIG. 21A . 
       In the figures, the thickness and configuration of components may be exaggerated for clarity. The same reference numerals in different figures represent the same component. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. 
     Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment according to the disclosure. The appearances of the phrases “one embodiment” or “other embodiments” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described that may be exhibited by some embodiments and not by others. Similarly, various features are described that may be included in some embodiments but not other embodiments. 
     The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Certain terms in this specification may be used to provide additional guidance regarding the description of the disclosure. It will be appreciated that a feature may be described more than one-way. 
     Alternative language and synonyms may be used for any one or more of the terms discussed herein. No special significance is to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and is not intended to further limit the scope and meaning of the disclosure or of any exemplified term. 
       FIG. 1  shows an electromagnetic radiation sensor  100  that preferably includes an anatomic sensor. As the terminology is used herein, “anatomic” preferably refers to the structure of an Animalia body and an “anatomic sensor” preferably is concerned with sensing a change over time of the structure of the Animalia body. By comparison, a physiological sensor is concerned with sensing the functions or activities of an Animalia body, e.g., pulse or blood chemistry, at a point in time. 
     Electromagnetic radiation sensor  100  preferably is coupled with the skin S. Preferably, electromagnetic radiation sensor  100  is arranged to overlie a target area of the skin S. As the terminology is used herein, “target area” preferably refers to a portion of a patient&#39;s skin that is generally proximal to where an infusate is being administered and frequently proximal to the cannulation site N. Preferably, the target area overlies the perivascular tissue P. According to one embodiment, adhesion preferably is used to couple electromagnetic radiation sensor  100  to the skin S. According to other embodiments, any suitable coupling may be used that preferably minimizes relative movement between electromagnetic radiation sensor  100  and the skin S. 
     Electromagnetic radiation sensor  100  preferably emits and collects transcutaneous electromagnetic radiation signals, e.g., light signals. Preferably, electromagnetic radiation sensor  100  emits electromagnetic radiation  102  and collects electromagnetic radiation  106 . Emitted electromagnetic radiation  102  preferably passes through the target area of the skin S toward the perivascular tissue P. Collected electromagnetic radiation  106  preferably includes a portion of emitted electromagnetic radiation  102  that is at least one of specularly reflected, diffusely reflected (e.g., due to elastic or inelastic scattering), fluoresced (e.g., due to endogenous or exogenous factors), or otherwise redirected from the perivascular tissue P before passing through the target area of the skin S. 
     Electromagnetic radiation sensor  100  preferably includes waveguides to transmit emitted and collected electromagnetic radiation  102  and  106 . As the terminology is used herein, “waveguide” preferably refers to a duct, pipe, fiber, or other device that generally confines and directs the propagation of electromagnetic radiation along a path. Preferably, an emission waveguide  110  includes an emitter face  112  for emitting electromagnetic radiation  102  and a detection waveguide  120  includes a detector face  122  for collecting electromagnetic radiation  106 . According to one embodiment, emission waveguide  110  preferably includes a set of emission optical fibers  114  and detection waveguide  120  preferably includes a set of detection optical fibers  124 . Individual emission and detection optical fibers  114  and  124  preferably each have an end face. Preferably, an aggregation of end faces of emission optical fibers  114  forms emitter face  112  and an aggregation of end faces of detection optical fibers  124  forms detector face  122 . 
     The transcutaneous electromagnetic radiation signals emitted by electromagnetic radiation sensor  100  preferably are not harmful to an Animalia body. Preferably, the wavelength of emitted electromagnetic radiation  102  is longer than at least approximately 400 nanometers. The frequency of emitted electromagnetic radiation  102  therefore is no more than approximately 750 terahertz. According to one embodiment, emitted electromagnetic radiation  102  is in the visible radiation (light) or infrared radiation portions of the electromagnetic spectrum. Preferably, emitted electromagnetic radiation  102  is in the near infrared portion of the electromagnetic spectrum. As the terminology is used herein, “near infrared” preferably refers to electromagnetic radiation having wavelengths between approximately 600 nanometers and approximately 2,100 nanometers. These wavelengths correspond to a frequency range of approximately 500 terahertz to approximately 145 terahertz. A desirable range in the near infrared portion of the electromagnetic spectrum preferably includes wavelengths between approximately 800 nanometers and approximately 1,050 nanometers. These wavelengths correspond to a frequency range of approximately 375 terahertz to approximately 285 terahertz. According to other embodiments, electromagnetic radiation sensor  100  may emit electromagnetic radiation signals in shorter wavelength portions of the electromagnetic spectrum, e.g., ultraviolet light, X-rays or gamma rays, preferably when radiation intensity and/or signal duration are such that tissue harm is minimized. 
     Emitted and collected electromagnetic radiation  102  and  106  preferably share one or more wavelengths. According to one embodiment, emitted and collected electromagnetic radiation  102  and  106  preferably share a single peak wavelength, e.g., approximately 940 nanometers (approximately 320 terahertz). As the terminology is used herein, “peak wavelength” preferably refers to an interval of wavelengths including a spectral line of peak power. The interval preferably includes wavelengths having at least half of the peak power. Preferably, the wavelength interval is +/−approximately 20 nanometers with respect to the spectral line. According to other embodiments, emitted and collected electromagnetic radiation  102  and  106  preferably share a plurality of peak wavelengths, e.g., approximately 940 nanometers and approximately 650 nanometers (approximately 460 terahertz). According to other embodiments, a first one of emitted and collected electromagnetic radiation  102  and  106  preferably spans a first range of wavelengths, e.g., from approximately 600 nanometers to approximately 1000 nanometers. This wavelength range corresponds to a frequency range from approximately 500 terahertz to approximately 300 terahertz. A second one of emitted and collected electromagnetic radiation  102  and  106  preferably shares with the first range a single peak wavelength, a plurality of peak wavelengths, or a second range of wavelengths. Preferably, an optical power analysis at the wavelength(s) shared by emitted and collected electromagnetic radiation  102  and  106  provides an indication of anatomical change over time in the perivascular tissue P. 
       FIGS. 2A-2C  schematically illustrate how an infiltration/extravasation event preferably evolves.  FIG. 2A  shows the skin S prior to an infiltration/extravasation event. Preferably, the skin S includes cutaneous tissue C, e.g., stratum corneum, epidermis and/or dermis, overlying subcutaneous tissue, e.g., hypodermis H. Blood vessels V suitable for intravenous therapy typically are disposed in the hypodermis H.  FIG. 2B  shows an infusate F beginning to accumulate in the perivascular tissue P. Accumulation of the infusate F typically begins in the hypodermis H, but may also begin in the cutaneous tissue C or at an interface of the hypodermis H with the cutaneous tissue C.  FIG. 2C  shows additional accumulation of the infusate F in the perivascular tissue P. Typically, the additional accumulation extends further in the hypodermis H but may also extend into the cutaneous tissue C. According to one embodiment, an infiltration/extravasation event generally originates and/or occurs in proximity to the blood vessel V, e.g., as illustrated in  FIGS. 2A-2C . According to other embodiments, an infiltration/extravasation event may originate and/or occur some distance from the blood vessel V, e.g., if pulling on the cannula C or administration set  30  causes the cannula outlet to become displaced from the blood vessel V. 
       FIGS. 2A-2C  also schematically illustrate the relative power of emitted and collected electromagnetic radiation  102  and  106 . Preferably, emitted electromagnetic radiation  102  enters the skin S, electromagnetic radiation propagates through the skin S, and collected electromagnetic radiation  106  exits the skin S. Emitted electromagnetic radiation  102  is schematically illustrated with an arrow directed toward the skin S and collected electromagnetic radiation  106  is schematically illustrated with an arrow directed away from the skin S. Preferably, the relative sizes of the arrows correspond to the relative powers of emitted and collected electromagnetic radiation  102  and  106 . The propagation is schematically illustrated with crescent shapes that preferably include the predominant electromagnetic radiation paths through the skin S from emitted electromagnetic radiation  102  to collected electromagnetic radiation  106 . Stippling in the crescent shapes schematically illustrates a distribution of electromagnetic radiation power in the skin S with relatively lower power generally indicated with less dense stippling and relatively higher power generally indicated with denser stippling. 
     The power of collected electromagnetic radiation  106  preferably is impacted by the infusate F accumulating in the perivascular tissue P. Prior to the infiltration/extravasation event ( FIG. 2A ), the power of collected electromagnetic radiation  106  preferably is a fraction of the power of emitted electromagnetic radiation  102  due to electromagnetic radiation scattering and absorption by the skin S. Preferably, the power of collected electromagnetic radiation  106  changes with respect to emitted electromagnetic radiation  102  in response to the infusate F accumulating in the perivascular tissue P ( FIGS. 2B and 2C ). According to one embodiment, emitted and collected electromagnetic radiation  102  and  106  include near infrared electromagnetic radiation. The power of collected electromagnetic radiation  106  preferably decreases due to scattering and/or absorption of near infrared electromagnetic radiation by the infusate F. The compositions of most infusates typically are dominated by water. Typically, water has different absorption and scattering coefficients as compared to the perivascular tissue P, which contains relatively strong near infrared energy absorbers, e.g., blood. At wavelengths shorter than approximately 700 nanometers (approximately 430 terahertz), absorption coefficient changes preferably dominate due to absorption peaks of blood. Preferably, scattering coefficient changes have a stronger influence than absorption coefficient changes for wavelengths between approximately 800 nanometers (approximately 375 terahertz) and approximately 1,300 nanometers (approximately 230 terahertz). In particular, propagation of near infrared electromagnetic radiation in this range preferably is dominated by scattering rather than absorption because scattering coefficients have a larger magnitude than absorption coefficients. Absorption coefficient changes preferably dominate between approximately 1,300 nanometers and approximately 1,500 nanometers (approximately 200 terahertz) due to absorption peaks of water. Therefore, the scattering and/or absorption impact of the infusate F accumulating in the perivascular tissue P preferably is a drop in the power signal of collected electromagnetic radiation  106  relative to emitted electromagnetic radiation  102 . According to other embodiments, a rise in the power signal of collected electromagnetic radiation  106  relative to emitted electromagnetic radiation  102  preferably is related to infusates with different scattering and absorption coefficients accumulating in the perivascular tissue P. Thus, the inventors discovered, inter alio, that fluid changes in perivascular tissue P over time, e.g., due to an infiltration/extravasation event, preferably are indicated by a change in the power signal of collected electromagnetic radiation  106  with respect to emitted electromagnetic radiation  102 . 
     Electromagnetic radiation sensor  100  preferably aids healthcare givers in identifying infiltration/extravasation events. Preferably, changes in the power signal of collected electromagnetic radiation  106  with respect to emitted electromagnetic radiation  102  alert a healthcare giver to perform an infiltration/extravasation evaluation. The evaluation that healthcare givers perform to identify infiltration/extravasation events typically includes palpitating the skin S in the vicinity of the target area, observing the skin S in the vicinity of the target area, and/or comparing limbs that include and do not include the target area of the skin S. 
     The inventors discovered a problem regarding accurately alerting healthcare givers to perform an infiltration/extravasation evaluation. In particular, healthcare givers may not be accurately alerted because of a relatively low signal-to-noise ratio of collected electromagnetic radiation  106 . Thus, the inventors discovered, inter alio, that noise in collected electromagnetic radiation  106  frequently obscures signals that alert healthcare givers to perform an infiltration/extravasation evaluation. 
     The inventors also discovered a source of the problem is emitted electromagnetic radiation  102  being reflected, scattered, or otherwise redirected from various tissues/depths below the stratum corneum of the skin S. Referring again to  FIG. 1 , the inventors discovered that a first portion  106   a  of collected electromagnetic radiation  106  includes emitted electromagnetic radiation  102  that is reflected, scattered, or otherwise redirected from relatively shallow tissue, e.g., the cutaneous tissue C, and that a second portion  106   b  of collected electromagnetic radiation  106  includes emitted electromagnetic radiation  102  that is reflected, scattered, or otherwise redirected from the relatively deep tissue, e.g., the hypodermis H. The inventors further discovered, inter alio, that second portion  106   b  from relatively deep tissue includes a signal that more accurately alerts healthcare givers to perform an infiltration/extravasation evaluation and that first portion  106   a  from relatively shallow tissue includes noise that frequently obscures the signal in second portion  106   b.    
     The inventors further discovered that sensor configuration preferably is related to the signal-to-noise ratio of a skin-coupled sensor. In particular, the inventors discovered that the relative configuration of emission and detection waveguides  110  and  120  preferably impact the signal-to-noise ratio of electromagnetic radiation sensor  100 . Thus, the inventors discovered, inter alio, that the geometry, topography and/or angles of emission and detection waveguides  110  and  120  preferably impact the sensitivity of electromagnetic radiation sensor  100  to the signal in second portion  106   b  relative to the noise in first portion  106   a.    
       FIG. 3  is an exploded schematic cross-section view illustrating the relative configuration between emission and detection waveguides  110  and  120  with respect to a housing  130  of electromagnetic radiation sensor  100 . Preferably, the housing  130  includes a first housing portion  130   a  and a second housing portion  130   b . The first and second housing portions  130   a  and  130   b  preferably are at least one of adhered, welded, interference fitted or otherwise coupled so as to define an internal volume  132 . Internal volume  132  preferably extends between first and second ends. Preferably, an entrance  134  is disposed at the first end of internal volume  132  and sets of passages through first housing portion  130   a  are disposed at the second end of internal volume  132 . Entrance  134  preferably provides emission and detection waveguides  110  and  120  with mutual access to internal volume  132 . Preferably, a set of emission passages  136  provides emission waveguide  110  with individual egress from internal volume  132 , and a set of detection passages  138  provides detection waveguide  120  with individual egress from internal volume  132 . Accordingly, sets of emission and detection passages  136  and  138  preferably separate emission waveguide  110  with respect to detection waveguide  120 . Preferably, emission passages  136  include emission apertures  136   a  that penetrate surface  130   c , and detection passages  138  include detection apertures  138   a  that penetrate surface  130   c . According to one embodiment, at least one of first and second housing portions  130   a  and  130   b  preferably includes an internal wall  130   d  for supporting, positioning and/or orienting at least one of emission and detection waveguides  110  and  120  in internal volume  132 . According to other embodiments, at least first housing portion  130   a  preferably includes a substantially biocompatible material, e.g., polycarbonate. 
     Electromagnetic radiation sensor  100  preferably is positioned in close proximity to the skin S. As the terminology is used herein, “close proximity” of electromagnetic radiation sensor  100  with respect to the skin S preferably refers to a relative arrangement that minimizes gaps between a surface  130   c  of first housing portion  130   a  and the stratum corneum of the skin S. Preferably, surface  130   c  confronts the stratum corneum of the skin S. According to one embodiment, surface  130   c  preferably contiguously engages the skin S. (See, for example,  FIG. 1 .) According to other embodiments, a film (not shown) that is suitably transparent to electromagnetic radiation preferably is interposed between surface  130   c  and the skin S. 
     A filler  140  preferably fixes the relative configuration of emission and detection waveguides  110  and  120  in housing  130 . Preferably, filler  140  is injected under pressure via a fill hole  142  so as to occupy voids in internal volume  132  and to substantially cincture emission and detection waveguides  110  and  120 . For example, filler  140  preferably occupies voids between (i) emission waveguide  110  and first housing portion  130   a , including emission passages  136 ; (ii) emission waveguide  110  and second housing portion  130   b ; (iii) detection waveguide  120  and first housing portion  130   a , including detection passages  138 ; (iv) detection waveguide  120  and second housing portion  130   b ; and (v) emission waveguides  110  and  120 . Preferably, filler  140  extends at least as far as entrance  134 , emission apertures  136   a , and detection apertures  138   a . Filler  140  preferably includes epoxy or another adhesive that is injected as an uncured liquid and subsequently cures as a solid. Thus, filler  140  preferably substantially fixes the relative positions/orientations of housing  130 , emission waveguide  110 , and detection waveguide  120 . According to one embodiment, filler  140  preferably couples first and second housing portions  130   a  and  130   b . According to other embodiments, filler  140  preferably includes first and second components. Preferably, the first component of filler  140  fastens at least one of emission and detection waveguides  110  and  120  with respect to first housing portion  130   a  and the second component of filler  140  packs internal volume  132 . The first and second components of filler  140  preferably are sequentially introduced to internal volume  132 . According to other embodiments, filler  140  preferably includes an electromagnetic radiation absorbing material. 
     Electromagnetic radiation sensor  100  preferably includes a superficies  1000  that overlies the skin S. Preferably, superficies  1000  includes surface  130   c , emitter face  112 , and detector face  122 . Superficies  1000  preferably may also include facades of filler  140  that occlude emission and detection apertures  136   a  and  138   a  around emitter and detector end faces  112  and  122 . Preferably, superficies  1000  is a three-dimensional surface contour that is generally smooth. As the terminology is used herein, “smooth” preferably refers to being substantially continuous and free of abrupt changes. 
       FIG. 4  shows an example of superficies  1000  having a suitable geometry for observing anatomical changes over time in the perivascular tissue P. In particular, the geometry of superficies  1000  preferably includes the relative spacing and shapes of emitter and detector faces  112  and  122 . According to one embodiment, a cluster of emission optical fiber end faces preferably has a geometric centroid  116  and an arcuate arrangement of detection optical fiber end faces preferably extends along a curve  126 . As the terminology is used herein, “cluster” preferably refers to a plurality of generally circular optical fiber end faces that are arranged such that at least one end face is approximately tangent with respect to at least three other end faces. Preferably, curve  126  has a radius of curvature R that extends from an origin substantially coincident with geometric centroid  116 . Curve  126  may be approximated by a series of line segments that correspond to individual chords of generally circular detection optical fiber end faces. Accordingly, each detection optical fiber end face preferably is tangent to at most two other end faces. The arcuate arrangement of detection optical fiber end faces preferably includes borders with radii of curvature that originate at geometric centroid  116 , e.g., similar to curve  126 . Preferably, a concave border  128   a  has a radius of curvature that is less than the radius of curvature R by an increment ΔR, and a convex border  128   b  has a radius of curvature that is greater than the radius of curvature R by an increment ΔR. According to one embodiment, increment ΔR is approximately equal to the radius of individual detection optical fiber end faces. According to other embodiments, detector face  122  preferably includes individual sets of detection optical fiber end faces arranged in generally concentric curves disposed in a band between concave and convex borders  128   a  and  128   b . As the terminology is used herein, “band” preferably refers to a strip or stripe that is differentiable from an adjacent area or material. 
       FIGS. 5A-5C  illustrate how different nominal spacing distances between emission and detection waveguides  110  and  120  preferably impact collected electromagnetic radiation  106 . Preferably, emitted electromagnetic radiation  102  enters the skin S from emission waveguide  110 , electromagnetic radiation propagates through the skin S, and collected electromagnetic radiation  106  exits the skin S to detection waveguide  120 . Emitted electromagnetic radiation  102  is schematically illustrated with an arrow directed toward the skin S and collected electromagnetic radiation  106  is schematically illustrated with an arrow directed away from the skin S. Preferably, the relative sizes of the arrows correspond to the relative powers of emitted and collected electromagnetic radiation  102  and  106 . Electromagnetic radiation in the near infrared portion of the electromagnetic spectrum preferably is measured in milliwatts, decibel milliwatts or another unit suitable for indicating optical power. The propagation is schematically illustrated with crescent shapes that preferably include the predominant electromagnetic radiation paths through the skin S from emitted electromagnetic radiation  102  to collected electromagnetic radiation  106 . Stippling in the crescent shapes schematically illustrates a distribution of electromagnetic radiation power in the skin S with relatively lower power generally indicated with less dense stippling and relatively higher power generally indicated with denser stippling. Referring to  FIG. 5A , a first nominal spacing distance D 1  preferably separates emitted electromagnetic radiation  102  and collected electromagnetic radiation  106 . At the first nominal spacing distance D 1 , the paths of electromagnetic radiation through the skin S generally are relatively short and predominantly extend through the cutaneous tissue C. Referring to  FIG. 5B , a second nominal spacing distance D 2  preferably separates emitted electromagnetic radiation  102  and collected electromagnetic radiation  106 . At the second nominal spacing distance D 2 , the paths of electromagnetic radiation preferably penetrate deeper into the skin S and extend in both the cutaneous tissue C and the hypodermis H. Referring to  FIG. 5C , a third nominal spacing distance D 3  preferably separates emitted electromagnetic radiation  102  and collected electromagnetic radiation  106 . At the third nominal spacing distance D 3 , the paths of electromagnetic radiation through the skin S generally are relatively long and predominantly extend through the hypodermis H. 
     The inventors discovered, inter alio, that varying the spacing distance between emission and detection waveguides  110  and  120  preferably changes a balance between the power and the signal-to-noise ratio of collected electromagnetic radiation  106 . The relative power of collected electromagnetic radiation  106  with respect to emitted electromagnetic radiation  102  preferably is greater for narrower nominal spacing distance D 1  as compared to broader nominal spacing distance D 3 . On the other hand, the signal-to-noise ratio of collected electromagnetic radiation  106  preferably is higher for broader nominal spacing distance D 3  as compared to narrower nominal spacing distance D 1 . Preferably, there is an intermediate nominal spacing distance D 2  that improves the signal-to-noise ratio as compared to narrower nominal spacing distance D 1  and, as compared to broader nominal spacing distance D 3 , improves the relative power of collected electromagnetic radiation  106  with respect to emitted electromagnetic radiation  102 . 
     The inventors designed and analyzed a skin phantom preferably to identify an optimum range for the intermediate nominal spacing distance D 2 . Preferably, the skin phantom characterizes several layers of Animalia skin including at least the epidermis (including the stratum corneum), dermis, and hypodermis. Table A shows the thicknesses, refractive indices, scattering coefficients, and absorption coefficients for each layer according to one embodiment of the skin phantom. Analyzing the skin phantom preferably includes tracing the propagation of up to 200,000,000 or more rays through the skin phantom to predict changes in the power of collected electromagnetic radiation  106 . Examples of suitable ray-tracing computer software include ASAP® from Breault Research Organization, Inc. (Tucson, Ariz., US) and an open source implementation of a Monte Carlo Multi-Layer (MCML) simulator from the Biophotonics Group at the Division of Atomic Physics (Lund University, Lund, SE). The MCML simulator preferably uses CUDA™ from NVDIA Corporation (Santa Clara, Calif., US) or another parallel computing platform and programming model. Preferably, a series of 1-millimeter thick sections simulate infiltrated perivascular tissue at depths up to 10 millimeters below the stratum corneum. The infiltrated perivascular tissue sections preferably are simulated with an infusate that approximates water, e.g., having a refractive index of approximately 1.33. Based on computer analysis of the skin phantom, the inventors discovered, inter alio, a relationship exists between (1) the spacing distance between emission and detection waveguides  110  and  120 ; (2) an expected depth below the stratum corneum for the perivascular tissue P at which anatomical changes over time preferably are readily observed; and (3) the wavelength of the electromagnetic radiation. 
       FIG. 6  shows a graphical representation of the spacing/depth/wavelength relationship based on a computer analysis of the skin phantom. In particular,  FIG. 6  shows a plot of spacing distances with the greatest signal drop at various perivascular tissue depths for certain wavelengths of electromagnetic radiation. The terminology “spacing distance with the greatest signal drop” preferably refers to the spacing distance between emission and detection waveguides  110  and  120  that experiences the greatest drop in the power signal of collected electromagnetic radiation  106 . The terminology “perivascular tissue depth” preferably refers to the depth below the stratum corneum of the perivascular tissue P at which anatomical changes over time are readily observed. According to the embodiment illustrated in  FIG. 6 , emission and detection waveguides  110  and  120  that preferably are separated between approximately 3 millimeters and approximately 5 millimeters are expected to readily observe anatomical changes at depths between approximately 2.5 millimeters and approximately 3 millimeters below the stratum corneum for wavelengths between approximately 650 nanometers and approximately 950 nanometers (between approximately 460 terahertz and approximately 315 terahertz). Preferably, the spacing distance range between emission and detection waveguides  110  and  120  is between approximately 3.7 millimeters and approximately 4.4 millimeters to observe an anatomical change over time in the perivascular tissue P at an expected depth of approximately 2.75 millimeters when the electromagnetic radiation wavelength is between approximately 650 nanometers and approximately 950 nanometers. The spacing distance between emission and detection waveguides  110  and  120  preferably is approximately 4.5 millimeters to observe an anatomical change over time in the perivascular tissue P at an expected depth of approximately 2.8 millimeters when the electromagnetic radiation wavelength is approximately 950 nanometers. Preferably, the spacing distance between emission and detection waveguides  110  and  120  is approximately 4 millimeters to observe an anatomical change over time in the perivascular tissue P at an expected depth of approximately 2.6 millimeters when the electromagnetic radiation wavelength is between approximately 850 nanometers (approximately 350 terahertz) and approximately 950 nanometers. 
     Electromagnetic radiation sensor  100  preferably aids in observing anatomical changes that also occur at unexpected depths below the stratum corneum of the skin S. Preferably, the expected depth at which an anatomical change is expected to occur is related to, for example, the thickness of the cutaneous tissue C and the location of blood vessels V in the hypodermis H. Relatively thicker cutaneous tissue C and/or a blood vessel V located relatively deeper in the hypodermis H preferably increase the expected perivascular tissue depth for readily observing an anatomical change. Conversely, relatively thinner cutaneous tissue C and/or a relatively shallow blood vessel V, e.g., located close to the interface between the cutaneous tissue C and the hypodermis H, preferably decrease the expected perivascular tissue depth for readily observing an anatomical change. There may be a time delay observing anatomical changes that begin at unexpected distances from electromagnetic radiation sensor  100 . The delay may last until the anatomical change extends within the observational limits of electromagnetic radiation sensor  100 . For example, if anatomical changes over time begin at unexpected depths below the stratum corneum, observing the anatomical change may be delayed until the anatomical change extends to the expected depths below the stratum corneum. 
     The shapes of emission and detection faces  112  and  122  preferably are related to the spacing distance range between emission and detection waveguides  110  and  120 . Preferably, each individual point of emission face  112  is disposed a minimum distance from each individual point of detector face  122 , and each individual point of emission face  112  is disposed a maximum distance from each individual point of detector face  122 . The minimum and maximum distances preferably correspond to the extremes of the range for the intermediate spacing distance D 2 . Preferably, the minimum distance is between approximately 2 millimeters and approximately 3.5 millimeters, and the maximum distance preferably is between approximately 4.5 millimeters and approximately 10 millimeters. According to one embodiment, each individual point of emission face  112  is disposed a minimum distance not less than 3 millimeters from each individual point of collection face  122 , and each individual point of emission face  112  is disposed a maximum distance not more than 5 millimeters from each individual point of collection face  122 . Preferably, the minimum distance is approximately 3.5 millimeters and the maximum distance is approximately 4.5 millimeters. According to other embodiments, each individual point of emission face  112  is spaced from each individual point of collection face  122  such that emitted electromagnetic radiation  102  transitions to collected electromagnetic radiation  106  at a depth of penetration into the Animalia tissue preferably between approximately 1 millimeter and approximately 6 millimeters below the stratum corneum of the skin S. Preferably, the transition between emitted and collected electromagnetic radiation  102  and  106  along individual electromagnetic radiation paths occur at the point of deepest penetration into the Animalia tissue. Emitted and collected electromagnetic radiation  102  and  106  preferably transition in the hypodermis H and may also transition in the dermis of relatively thick cutaneous tissue C. Preferably, emitted and collected electromagnetic radiation  102  and  106  transition approximately 2.5 millimeters to approximately 3 millimeters below the stratum corneum of the skin S. 
       FIG. 7  illustrates a technique for geometrically developing the shape of emission and detection faces  112  and  122  based on the spacing distance range between emission and detection waveguides  110  and  120 . According to one embodiment, a boundary  1010  delimits a portion of superficies  1000  for locating emitter face  112  relative to detector face  122 . The geometric development of boundary  1010  preferably is based on pairs of circles that are concentric with each individual end face of detection optical fibers  124 . Preferably, a radius of the inner circle for each pair corresponds to a minimum distance of the range for the intermediate spacing distance D 2  and a radius of the outer circle for each pair corresponds to a maximum distance of the range for the intermediate spacing distance D 2 . Boundary  1010  preferably is defined by a locus of points that are (1) outside the inner circles; and (2) inside the outer circles. Preferably, emitter face  112  is located within boundary  1010 . According to other embodiments, detector face  122  preferably is located within a boundary developed based on the end faces of emission optical fibers  114 . 
       FIGS. 8-13  show additional examples of superficies that also have suitable geometries for observing anatomical changes over time in the perivascular tissue P. According to one embodiment shown in  FIG. 8 , a superficies  1100  includes emitter face  112  clustered about geometric centroid  116  and an annular detector face  122  that preferably is concentrically disposed about geometric centroid  116 . Preferably, annular detector face  122  collects electromagnetic radiation from all directions surrounding emitter face  112 . According to other embodiments, detector face  122  preferably includes an incomplete annulus spanning an angular range less than 360 degrees. Preferably, detector face  122  spans an angular range between approximately 25 degrees and approximately 30 degrees. 
       FIG. 9  shows a superficies  1200  illustrating several combinations of geometric variables for emitter face  112  and detector face  122 . Preferably, superficies  1200  includes a line of symmetry L that extends through clustered emitter face  112  and arcuate detector face  122 . According to one embodiment, emitter face  112  preferably has any shape, e.g., a circle, that is suitable to be disposed inside a boundary  1210 , which is similar to boundary  1010  ( FIG. 7 ). According to other embodiments, there may be various nominal spacing distances along the line of symmetry L between detector face  122  and emitter face  112 ,  112 ′ or  112 ″. Accordingly, the radius of curvature R of detector face  122  preferably may be greater than the nominal spacing distance of emitter face  112 ′ from detector face  122 , the radius of curvature R of detector face  122  preferably may be substantially equal to the nominal spacing distance of emitter face  112  from detector face  122 , or the radius of curvature R of detector face  122  preferably may be less than the nominal spacing distance of emitter face  112 ″ from detector face  122 . 
       FIG. 10  shows a superficies  1300  that illustrates two geometric variables of emitter face  112  from detector face  122 . First, the line of symmetry L preferably is angularly oriented with respect to the edges of superficies  1300 . In contrast,  FIG. 9  shows the line of symmetry L perpendicularly oriented with respect to an edge of superficies  1200 . Preferably, a diagonal orientation of the line of symmetry L enlarges the range of the spacing distance available between emission and detection waveguides  110  and  120 . Second, the shapes of emitter face  112  and/or detector face  122  preferably include polygons. For example, the shape of emitter face  112  is a trapezoid and the shape of detector face  122  is a chevron. 
       FIG. 11  shows a superficies  1400  including emitter and detector faces  112  and  122  that preferably are non-specifically shaped. According to one embodiment, non-specifically shaped emitter and detector faces  112  and  122  preferably are caused by a generally happenstance dispersion of emission and detection optical fibers  114  and  124  in housing  130 . According to other embodiments, non-specifically shaped emitter and detector faces  112  and  122  preferably occur because broken fibers are unable to transmit emitted or collected electromagnetic radiation  102  or  106 . Preferably, the range of spacing distances between emitter face  112  and detector face  122  for superficies  1400  is generally similar to superficies  1000 - 1300 . 
       FIG. 12  shows a superficies  1500  according to another embodiment including preferably parallel emitter and detector faces  112  and  122 . Superficies  1500  preferably includes a line of symmetry L that extends perpendicular to emitter and detector faces  112  and  122 . Preferably, the nominal spacing distance D between emission and detection waveguides  110  and  120  is largest when emitter and detector faces  112  and  122  are individually disposed near opposite edges of superficies  1500 . According to one embodiment, emitter and detector faces  112  and  122  include bands disposed in parallel straight lines. Accordingly, the perpendicular and diagonal lengths between emitter and detector faces  112  and  122  preferably approximate the minimum and maximum values, respectively, of the spacing distance range between individual points of emitter and detector faces  112  and  122 . According to other embodiments, emitter and detector faces  112  and  122  preferably are disposed in parallel arcs. According to other embodiments, emitter and detector faces  112  and  122  preferably are substantially congruent. 
       FIG. 13  shows a superficies  1600  illustrating several combinations of geometric variables for emitter face  112  from detector face  122 . According to one embodiment, superficies  1600  includes a line of symmetry L that preferably extends through clustered emitter face  112  and straight-line detector face  122 . According to other embodiments, a clustered emitter face  112 ′ preferably is offset from the line of symmetry L. Preferably, the line of symmetry L extends generally perpendicular to a longitudinal axis of straight-line detector  122 , and emitter face  112 ′ includes geometric centroid  116  that is laterally displaced with respect to the symmetry L. 
     Individual superficies geometries preferably are suitable for observing anatomical changes over time in the perivascular tissue P at various depths below the stratum corneum. As discussed above, the depth below the stratum corneum of the perivascular tissue P at which signals indicative of anatomical changes over time preferably are expected to be observed is at least partially related to the range of spacing distances between emission and detection waveguides  110  and  120 .  FIGS. 14A-14D  illustrate distributions of the spacing distance ranges for examples of superficies geometries. 
       FIG. 14A  shows a distribution of the spacing distance range between individual points of emitter and detector faces  112  and  122  for superficies  1000  ( FIG. 4 ) when the radius of curvature R preferably is approximately 4 millimeters. The spacing distances preferably are in a range spanning approximately 1 millimeter, e.g., between approximately 3.5 millimeters and approximately 4.5 millimeters. Preferably, the distribution has a generally symmetrical profile with a mode that is approximately 4 millimeters. As the terminology is used herein, “mode” preferably refers to the most frequently occurring value in a data set, e.g., a set of spacing distances. 
       FIG. 14B  shows a distribution of the spacing distance range between individual points of emitter and detector faces  112  and  122  for superficies  1500  ( FIG. 12 ) when the nominal spacing distance D preferably is approximately 4 millimeters. Generally all of the spacing distances preferably are in an approximately 2 millimeter range that is between approximately 3.5 millimeters and approximately 5.5 millimeters. Preferably, the distribution overall has an asymmetrical profile; however, a portion of the profile in an approximately 0.3 millimeter range between approximately 3.6 millimeters and approximately 3.9 millimeters is generally symmetrical with a mode that is approximately 3.75 millimeters. 
     A comparison of the spacing distance distributions shown in  FIGS. 14A and 14B  preferably suggests certain relative characteristics of superficies  1000  and  1500  for observing anatomical changes over time in the perivascular tissue P. Comparing  FIGS. 14A and 14B , the magnitude of the spacing distance distribution at the mode for superficies  1500  is greater than for superficies  1000 , the range overall is smaller for superficies  1000  than for superficies  1500 , and the generally symmetrical portion is smaller for superficies  1500  than for superficies  1000 . Accordingly, superficies  1000  and  1500  preferably have certain relative characteristics for observing anatomical changes over time in the perivascular tissue P including: (1) the peak sensitivity of superficies  1000  covers a broader range of depths below the stratum corneum of the skin S than superficies  1500 ; (2) the peak sensitivity of superficies  1500  is greater in a narrower range of depths below the stratum corneum of the skin S than superficies  1000 ; and (3) the sensitivity to signals from deeper depths below the stratum corneum of the skin S is greater for superficies  1500  than for superficies  1000 . As the terminology is used herein, “peak sensitivity” preferably refers to an interval of spacing distances including the mode of the spacing distances. The interval preferably includes spacing distances having magnitudes that are at least half of the magnitude of the mode. 
       FIG. 14C  shows a distribution of the spacing distance range between individual points of emitter and detector faces  112  and  122  for a superficies geometry  1700 . Emitter face  112  is generally arcuate with a radius of curvature R 1 , detector face  122  is generally arcuate with a radius of curvature R 2 , and emitter and detector faces  112  and  122  are generally concentric with a separation R 2 -R 1  that preferably is approximately 4 millimeters. Preferably, emitter face  112  includes sets of detection optical fiber end faces arranged in individual generally concentric curves, e.g., similar to curve  126 . Generally all of the spacing distances preferably are in an approximately 2 millimeter range that is between approximately 3.7 millimeters and approximately 5.7 millimeters. Preferably, the spacing distance distribution has an asymmetrical profile and a mode that is approximately 4.1 millimeters. 
     A comparison of the spacing distance distributions shown in  FIGS. 14A-14C  preferably suggests certain relative characteristics of superficies  1000 ,  1500  and  1700  for observing anatomical changes over time in the perivascular tissue P. Comparing  FIGS. 14C and 14A , superficies  1700  includes a generally arcuate emitter face  112  whereas superficies  1000  includes a generally clustered emitter face  112 , the magnitude of the spacing distance distribution at the mode for superficies  1700  is greater than for superficies  1000 , and superficies  1700  includes a larger overall range of spacing distances than superficies  1000 . Accordingly, superficies  1700  and  1000  preferably have certain relative characteristics for observing anatomical changes over time in the perivascular tissue P including: (1) the peak sensitivity of superficies  1000  covers a broader range of depths below the stratum corneum of the skin S than superficies  1700 ; (2) the peak sensitivity of superficies  1700  is greater in a narrower range of depths below the stratum corneum of the skin S than superficies  1000 ; and (3) the sensitivity to signals from deeper depths below the stratum corneum of the skin S is greater for superficies  1700  than for superficies  1000 . Comparing  FIGS. 14C and 14B , superficies  1700  includes emitter and detector faces  112  and  122  disposed in concentric arcs whereas superficies  1500  includes emitter and detector faces  112  and  122  disposed in parallel straight lines, the magnitude of the spacing distance distribution at the mode for superficies  1700  is less than for superficies  1500 , and the mode and the range overall of superficies  1700  are shifted toward greater spacing distances than superficies  1000 . Accordingly, superficies  1700  and  1500  preferably have certain relative characteristics for observing anatomical changes over time in the perivascular tissue P including, for example, the peak sensitivity is at a greater depth below the stratum corneum of the skin S for superficies  1700  than for superficies  1500 . 
       FIG. 14D  shows a distribution of the spacing distance range between individual points of emitter and detector faces  112  and  122  for a superficies geometry  1800 . Preferably, emitter and detector faces  112  and  122  include parallel arcs with generally equal radii of curvature and a spacing distance D that is approximately 4 millimeters. Generally all of the spacing distances preferably are in an approximately 2.7 millimeter range that is between approximately 3.3 millimeters and approximately 6 millimeters. Preferably, the spacing distance distribution has an asymmetrical profile and a mode that is approximately 4 millimeters. 
     A comparison of the spacing distance distributions shown in  FIGS. 14A-14D  preferably suggests certain relative characteristics of superficies  1000 ,  1500 ,  1700  and  1800  for observing anatomical changes over time in the perivascular tissue P. Comparing  FIGS. 14D and 14A , superficies  1800  includes a generally arcuate emitter face  112  whereas superficies  1000  includes a generally clustered emitter face  112 . Preferably, superficies  1800  and  1000  share a number of common characteristics including (1) the modes of the spacing distance distributions are approximately equal; (2) the magnitudes of the modes are approximately equal; and (3) the spacing distance distribution profiles between the range minimums and the modes are generally similar. Individual characteristics of superficies  1800  and  1000  preferably include, for example, distinctive spacing distance distribution profiles between the mode and range maximum. According to one embodiment, the spacing distance distribution of superficies  1800  is larger than superficies  1000  at least partially because for the area of arcuate emitter face  112  (superficies  1800 ) is larger than the area of clustered emitter face  112  (superficies  1000 ). Superficies  1800  and  1000  preferably have certain relative characteristics for observing anatomical changes over time in the perivascular tissue P including, for example, superficies  1800  is more sensitivity to signals from deeper depths below the stratum corneum of the skin S than superficies  1000 . Comparing  FIGS. 14D and 14B , superficies  1800  includes emitter and detector faces  112  and  122  disposed in parallel arcs whereas superficies  1500  includes emitter and detector faces  112  and  122  disposed in parallel straight lines, the magnitude of the spacing distance distribution at the mode is less for superficies  1800  than for superficies  1500  and superficies  1800  includes a larger overall range of spacing distances than superficies  1500 . Accordingly, superficies  1800  and  1500  preferably have certain relative characteristics for observing anatomical changes over time in the perivascular tissue P including: (1) the peak sensitivity of superficies  1800  covers a broader range of depths below the stratum corneum of the skin S than superficies  1500 ; (2) the peak sensitivity of superficies  1500  is greater in a narrower range of depths below the stratum corneum of the skin S than superficies  1800 ; and (3) the sensitivity to signals from deeper depths below the stratum corneum of the skin S is greater for superficies  1800  than for superficies  1500 . Comparing  FIGS. 14D and 14C , superficies  1800  includes emitter and detector faces  112  and  122  disposed in parallel arcs whereas superficies  1700  includes emitter and detector faces  112  and  122  disposed in concentric arcs. Preferably, superficies  1800  and  1700  share a number of common characteristics including (1) the modes of the spacing distance distributions are similar; and (2) the magnitudes of the modes are similar. Individual characteristics of superficies  1800  and  1700  preferably include, for example, distinctive spacing distance distribution profiles on both sides of the mode. According to one embodiment, superficies  1800  includes a larger overall range of spacing distances than superficies  1700 . Superficies  1800  and  1700  preferably have certain relative characteristics for observing anatomical changes over time in the perivascular tissue P including, for example, superficies  1800  is more sensitivity to signals from both shallower and deeper depths below the stratum corneum of the skin S than superficies  1700 . 
     Thus, electromagnetic radiation sensor  100  preferably includes a superficies geometry that improves the signal-to-noise ratio of collected electromagnetic radiation  106 . Preferably, superficies geometries include suitable relative shapes and spacing distances between emitter and detector faces  112  and  122 . Examples of suitable shapes preferably include clusters, arcs, and straight lines. Suitable spacing distances generally correspond with the expected depth below the stratum corneum for the perivascular tissue P at which anatomical changes over time preferably are readily observed. An example of a suitable spacing distance is approximately 4 millimeters for observing anatomical changes at approximately 2.75 millimeters below the stratum corneum. 
     The inventors also discovered that the topography of superficies  1 X 00  preferably impacts the signal-to-noise ratio of electromagnetic radiation sensor  100 . As the terminology is used herein, “topography” preferably refers to a three-dimensional surface contour and “superficies  1 X 00 ” preferably is a generic reference to any suitable superficies of electromagnetic radiation sensor  100 . Preferably, superficies  1 X 00  includes, for example, superficies  1000  ( FIG. 4  et al.), superficies  1100  ( FIG. 8 ), superficies  1200  ( FIG. 9 ), superficies  1300  ( FIG. 10 ), superficies  1400  ( FIG. 11 ), superficies  1500  ( FIG. 12  et al.), superficies  1600  ( FIG. 13 ), superficies  1700  ( FIG. 14C ), and superficies  1800  ( FIG. 14D ). The inventors discovered, inter alio, that the signal-to-noise ratio of electromagnetic radiation sensor  100  preferably improves when the topography of superficies  1 X 00  minimizes gaps or movement with respect to the epidermis of the skin S. 
     The topography of superficies  1 X 00  preferably is substantially flat, convex, concave, or a combination thereof. According to one embodiment, superficies  1 X 00  preferably is substantially flat. For example, superficies  1000  ( FIG. 4 ) preferably is a substantially flat plane that overlies the epidermis of the skin S. According to other embodiments, superficies  1 X 00  preferably includes at least one of a convex superficies  1 X 00  ( FIG. 15 ) and a concave superficies  1 X 00  ( FIG. 16 ) to stretch the epidermis of the skin S. Preferably, the epidermis is stretched when (1) convex superficies  1 X 00  preferably presses emitter and detector faces  112  and  122  toward the skin S; or (2) the skin S bulges into concave superficies  1 X 00  toward emitter and detector faces  112  and  122 . Pressure along a peripheral edge of concave superficies  1 X 00  preferably causes the skin S to bulge into concave superficies 1×00. Preferably, stretching the epidermis with respect to superficies  1 X 00  minimizes relative movement and gaps between electromagnetic radiation sensor  100  and emitter and detector faces  112  and  122 . 
       FIGS. 17 and 18  show additional examples of superficies  1 X 00  that also have suitable topographies to stretch the epidermis of the skin S.  FIG. 17  shows a projection  150  extending from superficies 1×00. According to one embodiment, projection  150  preferably cinctures emitter and detector faces  112  and  122 . According to other embodiments, separate projections  150  preferably cincture individual emitter and detector faces  112  and  122 .  FIG. 18  shows separate recesses  160  preferably cincturing individual emitter and detector faces  112  and  122 . According to other embodiments, a single recess  160  preferably cinctures both emitter and detector faces  112  and  122 . Preferably, projection(s)  150  and recess(es)  160  stretch the epidermis with respect to superficies  1 X 00  to minimize relative movement and gaps between electromagnetic radiation sensor  100  and emitter and detector faces  112  and  122 . 
     Thus, superficies  1 X 00  preferably include topographies to improve the signal-to-noise ratio of electromagnetic radiation sensor  100 . Preferably, suitable topographies that minimize relative movement and gaps between the skin S and emitter and detector faces  112  and  122  include, e.g., flat planes, convex surfaces, concave surfaces, projections and/or recesses. 
     The inventors also discovered, inter alio, that angles of intersection between superficies  1 X 00  and emission and detection waveguides  110  and  120  preferably impact emitted and collected electromagnetic radiation  102  and  106 .  FIG. 19  shows a first embodiment of the angles of intersection, and  FIGS. 20A and 20B  show a second embodiment of the angles of intersection. Regardless of the embodiment, emission waveguide  110  transmits electromagnetic radiation generally along a first path  110   a  to emitter face  112 , and detection waveguide  120  transmits electromagnetic radiation generally along a second path  120   a  from detector face  122 . Superficies  1 X 00  preferably includes surface  130   a  and emitter and detector faces  112  and  122 . Preferably, first path  110   a  intersects with superficies  1 X 00  at a first angle α 1  and second path  120   a  intersects with superficies  1 X 00  at a second angle α 2 . In the case of concave or convex superficies  1 X 00 , or superficies  1 X 00  that include projections  150  or recesses  160 , first and second angles α 1  and α 2  preferably are measured with respect to the tangent to superficies  1 X 00 . Emitted electromagnetic radiation  102  preferably includes at least a part of the electromagnetic radiation that is transmitted along first path  110   a , and the electromagnetic radiation transmitted along second path  120   a  preferably includes at least a part of collected electromagnetic radiation  106 . Preferably, emitted electromagnetic radiation  102  exits emitter face  112  within an emission cone  104 , and collected electromagnetic radiation  106  enters detector face  122  within an acceptance cone  108 . Emission and acceptance cones  104  and  108  preferably include ranges of angles over which electromagnetic radiation is, respectively, emitted by emission waveguide  110  and accepted by detection waveguide  120 . Typically, each range has a maximum half-angle θ max  that is related to a numerical aperture NA of the corresponding waveguide as follows: NA=η sin θ max , where n is the refractive index of the material that the electromagnetic radiation is entering (e.g., from emission waveguide  110 ) or exiting (e.g., to detection waveguide  120 ). The numerical aperture NA of emission or detection optical fibers  114  or  124  typically is calculated based on the refractive indices of the optical fiber core (η core ) and optical fiber cladding (η clad ) as follows: NA=√{square root over (η core   2 −η clad   2 )}. Thus, the ability of a waveguide to emit or accept rays from various angles generally is related to material properties of the waveguide. Ranges of suitable numerical apertures NA for emission or detection waveguides  110  or  120  may vary considerably, e.g., between approximately 0.20 and approximately 0.60. According to one embodiment, individual emission or detection optical fibers  114  or  124  preferably have a numerical apertures NA of approximately 0.55. The maximum half-angle θ max  of a cone typically is a measure of an angle between the cone&#39;s central axis and conical surface. Accordingly, the maximum half-angle θ max  of emission waveguide  110  preferably is a measure of the angle formed between a central axis  104   a  and the conical surface of emission cone  104 , and the maximum half-angle θ max  of detection waveguide  120  preferably is a measure of the angle formed between a central axis  108   a  and the conical surface of acceptance cone  108 . The direction of central axis  104   a  preferably is at a first angle β 1  with respect to superficies  1 X 00  and the direction of central axis  108   a  preferably is at a second angle β 2  with respect to superficies  1 X 00 . Therefore, first angle β 1  preferably indicates the direction of emission cone  104  and thus also describes the angle of intersection between emitted electromagnetic radiation  102  and superficies  1 X 00 , and second angle β 2  preferably indicates the direction of acceptance cone  108  and thus also describes the angle of intersection between collected electromagnetic radiation  106  and superficies  1 X 00 . In the case of concave or convex superficies  1 X 00 , or superficies  1 X 00  that include projections  150  or recesses  160 , first and second angles β 1  and β 2  preferably are measured with respect to the tangent to superficies  1 X 00 . 
       FIG. 19  shows a generally perpendicular relationship between superficies  1 X 00  and emission and detection waveguides  110  and  120 . The inventors discovered, inter alio, if first and second angles α 1  and α 2  preferably are approximately 90 degrees with respect to superficies  1 X 00  then (1) first and second angles β 1  and β 2  preferably also tend to be approximately 90 degrees with respect to superficies  1 X 00 ; (2) emitted electromagnetic radiation  102  preferably is minimally attenuated at the interface between the skin S and emitter face  112 ; and (3) collected electromagnetic radiation  106  preferably has an improved signal-to-noise ratio. An advantage of having emission waveguide  110  disposed at an approximately 90 degree angle with respect to superficies  1 X 00  preferably is maximizing the electromagnetic energy that is transferred from along the first path  110   a  to emitted electromagnetic radiation  102  at the interface between sensor  100  and the skin S. Preferably, this transfer of electromagnetic energy may be improved when internal reflection in waveguide  110  due to emitter face  112  is minimized. Orienting emitter face  112  approximately perpendicular to first path  110   a , e.g., cleaving and/or polishing emission optical fiber(s)  114  at approximately 90 degrees with respect to first path  110   a , preferably minimizes internal reflection in waveguide  110 . Specifically, less of the electromagnetic radiation transmitted along first path  110   a  is reflected at emitter face  112  and more of the electromagnetic radiation transmitted along first path  110   a  exits emitter face  112  as emitted electromagnetic radiation  102 . Another advantage of having emission waveguide  110  disposed at an approximately 90 degree angle with respect to superficies  1 X 00  preferably is increasing the depth below the stratum corneum that emitted electromagnetic radiation  102  propagates into the skin S because first angle β 1  also tends to be approximately 90 degrees when first angle α 1  is approximately 90 degrees. Preferably, as discussed above with respect to  FIGS. 2A-2C  and  5 A- 5 C, the predominant electromagnetic radiation paths through the skin S are crescent-shaped and the increased propagation depth of emitted electromagnetic radiation  102  may improve the signal-to-noise ratio of collected electromagnetic radiation  106 . Thus, according to the first embodiment shown in  FIG. 19 , emission and detection waveguides  110  and  120  preferably are disposed in housing  130  such that first and second paths  110   a  and  120   a  are approximately perpendicular to superficies  1 X 00  for increasing the optical power of emitted electromagnetic radiation  102  and for improving the signal-to-noise ratio of collected electromagnetic radiation  106 . 
       FIGS. 20A and 20B  show an oblique angular relationship between superficies  1 X 00  and emission and detection waveguides  110  and  120 . Preferably, at least one of first and second angles α 1  and α 2  are oblique with respect to superficies  1 X 00 . First and second angles α 1  and α 2  preferably are both oblique and inclined in generally similar directions with respect to superficies  1 X 00 . According to one embodiment, the difference between the first and second angles α 1  and α 2  preferably is between approximately 15 degrees and approximately 45 degrees. Preferably, the first angle α 1  is approximately 30 degrees less than the second angle α 2 . According to other embodiments, first angle α 1  ranges between approximately 50 degrees and approximately 70 degrees, and second angle α 2  ranges between approximately 75 degrees and approximately 95 degrees. Preferably, first angle α 1  is approximately 60 degrees and second angle α 2  ranges between approximately 80 degrees and approximately 90 degrees. A consequence of first angle α 1  being oblique with respect to superficies  1 X 00  is that a portion  102   a  of the electromagnetic radiation transmitted along first path  110   a  may be reflected at emitter face  112  rather than exiting emitter face  112  as emitted electromagnetic radiation  102 . Another consequence is that refraction may occur at the interface between sensor  100  and the skin S because the skin S and the emission and detection waveguides  110  and  120  typically have different refractive indices. Accordingly, first angles α 1  and β 1  would likely be unequal and second angles α 2  and β 2  would also likely be unequal. 
       FIG. 20B  illustrates a technique for geometrically interpreting the interplay between emitted electromagnetic radiation  102  and collected electromagnetic radiation  106  when emission and detection waveguides  110  and  120  are obliquely disposed with respect to superficies  1 X 00 . Preferably, emission cone  104  represents the range of angles over which emitted electromagnetic radiation  102  exits emitter face  112 , and acceptance cone  108  represents the range of angles over which collected electromagnetic radiation  106  enters detection face  122 . Projecting emission and acceptance cones  104  and  108  to a common depth below the stratum corneum of the skin S preferably maps out first and second patterns  104   b  and  108   b , respectively, which are shown with different hatching in  FIG. 20B . Preferably, the projections of emission and acceptance cones  104  and  108  include a locus of common points where first and second patterns  104   b  and  108   b  overlap, which accordingly is illustrated with cross-hatching in  FIG. 20B . In principle, the locus of common points shared by the projections of emission and acceptance cones  104  and  108  includes tissue that preferably is a focus of electromagnetic radiation sensor  100  for monitoring anatomical changes over time. Accordingly, an advantage of having emission waveguide  110  and/or detection waveguide  120  disposed at an oblique angle with respect to superficies  1 X 00  preferably is focusing electromagnetic radiation sensor  100  at a particular range of depths below the stratum corneum of the skin S and/or steering sensor  100  in a particular relative direction. In practice, electromagnetic radiation propagating through the skin S is reflected, scattered and otherwise redirected such that there is a low probability of generally straight-line propagation that is contained within the projections of emission and detection cones  104  and  108 . Accordingly,  FIG. 20B  preferably is a geometric interpretation of the potential for electromagnetic radiation to propagate to a particular range of depths or in a particular relative direction. 
     Thus, the angles of intersection between superficies  1 X 00  and emission and detection waveguides  110  and  120  preferably impact emitted and collected electromagnetic radiation  102  and  106  of electromagnetic radiation sensor  100 . Preferably, suitable angles of intersection that improve the optical power of emitted electromagnetic radiation  102 , improve the signal-to-noise ratio of collected electromagnetic radiation  106 , and/or focus electromagnetic radiation sensor  100  at particular depths/directions include, e.g., approximately perpendicular angles and oblique angles. 
     The discoveries made by the inventors include, inter alio, configurations of an electromagnetic radiation sensor that preferably increase the power of emitted electromagnetic radiation and/or improve the signal-to-noise ratio of collected electromagnetic radiation. Examples of suitable configurations are discussed above including certain superficies geometries, certain superficies topographies, and certain angular orientations of emission and detection waveguides. Preferably, suitable configurations include combinations of superficies geometries, superficies topographies, and/or angular orientations of the waveguides. According to one embodiment, an electromagnetic radiation sensor has a configuration that includes approximately 4 millimeters between waveguides, a convex superficies, and waveguides that intersect the superficies at approximately 90 degrees. 
     An electromagnetic radiation sensor according to the present disclosure preferably may be used, for example, (1) as an aid in detecting at least one of infiltration and extravasation; (2) to monitor anatomical changes in perivascular tissue; or (3) to emit and collect transcutaneous electromagnetic signals. The discoveries made by the inventors include, inter alio, that sensor configuration including geometry (e.g., shape and spacing), topography, and angles of transcutaneous electromagnetic signal emission and detection affect the accurate indications anatomical changes in perivascular tissue, including infiltration/extravasation events. For example, the discoveries made by the inventors include that the configuration of an electromagnetic radiation sensor is related to the accuracy of the sensor for aiding in diagnosing at least one of infiltration and extravasation in Animalia tissue. 
     Sensors according to the present disclosure preferably are manufactured by certain methods that may vary. Preferably, operations included in the manufacturing method may be performed in certain sequences that also may vary. Examples of a sensor manufacturing method preferably include molding first and second housing portions  130   a  and  130   b . Preferably, superficies  1 X 00  is molded with first housing portion  130   a . At least one emission optical fiber  114  preferably is fed through at least one emission passage  136 , which includes emission aperture  136   a  penetrating superficies  1 X 00 . Preferably, at least one detection optical fiber  124  is fed through at least one detection passage  138 , which includes detection aperture  138   a  also penetrating superficies  1 X 00 . First and second housing portions  130   a  and  130   b  preferably are coupled to define interior volume  132 . Preferably, emission and detection optical fibers  114  and  124  extend through interior volume  132 . Internal portions of emission and detection optical fibers  114  and  124  preferably are fixed with respect to first housing portion  130   a . Preferably, internal volume  132  is occluded when filler  140 , e.g., epoxy, is injected via fill hole  142 . Filler  140  preferably cinctures the internal portions of emission and detection optical fibers  114  and  124  in internal volume  132 . Preferably, external portions of emission and detection optical fibers  114  and  124  are cleaved generally proximate superficies  1 X 00 . Cleaving preferably occurs after fixing emission and detection optical fibers  114  and  124  with respect to first housing portion  130   a . Preferably, end faces of emission and detection optical fibers  114  and  124  are polished substantially smooth with superficies  1 X 00 . According to one embodiment, each individual point on the end faces of emission optical fibers  114  preferably is disposed a distance not less than 3 millimeters and not more than 5 millimeters from each individual point on the end faces detection optical fibers  124 . According to other embodiments, first housing portion  130   a  preferably is supported with superficies  1 X 00  disposed orthogonal with respect to gravity when internal portions of emission and detection optical fibers  114  and  124  are fixed with respect to first housing portion  130   a . The first and second angles of intersection α 1  and α 2  between superficies  1 X 00  and emission and detection optical fibers  114  and  124  therefore preferably are approximately 90 degrees. According to other embodiments, at least one of emission and detection optical fibers  114  and  124  is fixed relative to first housing portion  130  at an oblique angle of intersection with respect to superficies  1 X 00 . According to other embodiments, occluding internal volume  132  preferably includes heating at least one of first housing portion  130   a , emission optical fiber  114 , and detection optical fiber  124 . Preferably, heating facilitates flowing filler  140 . 
     While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. For example, operation of the sensor may be reversed, e.g., collecting electromagnetic radiation with a waveguide that is otherwise configured for emission as discussed above and emitting electromagnetic radiation with a waveguide that is otherwise configured for detection as discussed above. For another example, relative sizes of the emission and detection waveguides may be reversed, e.g., the emission waveguide may include more optical fibers than the detection waveguide and visa-versa. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE A 
               
               
                   
               
               
                   
                   
                   
                   
                 Absorption 
               
               
                 Skin Tissue 
                 Thickness 
                 Refractive 
                 Scattering 
                 Coefficient 
               
               
                 Layer 
                 (mm) 
                 Index 
                 Coefficient (mm −1 ) 
                 (mm −1 ) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 epidermis 
                 0.0875 
                 1.5 
                 3.10-7.76 
                 0.24-0.88 
               
               
                 dermis 
                 1 
                 1.4 
                 0.93-2.24 
                 0.01-0.05 
               
               
                 hypodermis 
                 4 
                 1.4 
                 1.22-1.60 
                 0.01-0.04