Abstract:
A system and method include a sensor overlying a target area of skin to aid in diagnosing subcutaneous fluid leakage. The sensor includes an absorbent that minimizes noise in detected electromagnetic radiation to make it easier to analyze a signal that is indicative of subcutaneous fluid leakage.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of U.S. Provisional Application No. 61/706,726, filed 27 Sep. 2012, 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 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]      FIGS. 4 and 4A  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). 
         [0004]    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. 
         [0005]    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. 
         [0006]    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  34 . Roller clamps and Dial-A-Flo®, manufactured by Hospira, Inc. (Lake Forest, Ill., USA), 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., USA), is an example of a typical leak-proof coupling. 
         [0007]    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. 
         [0008]    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., USA) and Flo-Gard® Volumetric Infusion Pumps manufactured by Baxter International Inc. (Deerfield, Ill., USA) are examples of typical infusion pumps. 
         [0009]    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. 
         [0010]    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 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.” 
         [0011]    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 such as 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 
       [0012]    Embodiments according to the present invention include a sensor for evaluating an anatomical change over time in perivascular tissue. The sensor includes an emitter face, a detector face, and an absorber. The emitter face is configured to emit a first electromagnetic radiation signal. The detector face is configured to detect a second electromagnetic radiation signal. The second electromagnetic radiation signal is at least one of a reflection, scattering and redirection of the first electromagnetic radiation signal by the perivascular tissue. The absorber is configured to absorb a third electromagnetic radiation signal. The third electromagnetic radiation signal is at least one of a reflection, scattering and redirection of the first electromagnetic radiation signal by an epidermis overlying the perivascular tissue. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    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. 
           [0014]      FIG. 1  is a schematic cross-section view illustrating an electromagnetic energy sensor. 
           [0015]      FIG. 2  is a schematic cross-section view illustrating separation of the electromagnetic energy sensor shown in  FIG. 1 . 
           [0016]      FIGS. 2A and 2B  are schematic cross-section views illustrating alternative details of area II shown in  FIG. 2 . 
           [0017]      FIG. 3  is a schematic cross-section view illustrating an embodiment of an electromagnetic energy sensor according to the present disclosure. 
           [0018]      FIG. 3A  is a plan view illustrating a superficies of the electromagnetic energy sensor shown in  FIG. 3 . 
           [0019]      FIG. 4  is a schematic view illustrating a typical set-up for infusion administration. 
           [0020]      FIG. 4A  is a schematic view illustrating a subcutaneous detail of area IVA shown in  FIG. 4 . 
       
    
    
       [0021]    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 
       [0022]    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. 
         [0023]    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 which may be exhibited by some embodiments and not by others. Similarly, various features are described which may be included in some embodiments but not other embodiments. 
         [0024]    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. 
         [0025]    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. 
         [0026]      FIG. 1  shows an electromagnetic energy sensor  1000  preferably coupled with the skin S. According to one embodiment, electromagnetic energy sensor  1000  preferably operates in portions of the electromagnetic spectrum that include wavelengths generally not harmful to tissue, e.g., wavelengths longer than at least approximately 400 nanometers. Preferably, electromagnetic energy sensor  1000  operates in the visible radiation (light) or infrared radiation portions of the electromagnetic spectrum. According to other embodiments, electromagnetic energy sensor  1000  may operate in shorter wavelength portions of the electromagnetic spectrum, e.g., ultraviolet light, X-ray or gamma ray portions of the electromagnetic spectrum, preferably when radiation intensity and/or radiation duration are such that tissue harm is minimized. 
         [0027]    Preferably, electromagnetic energy sensor  1000  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 and activities of an Animalia body, e.g., pulse, at a point in time. 
         [0028]    Electromagnetic energy sensor  1000  preferably 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. 
         [0029]    Electromagnetic energy sensor  1000  preferably uses electromagnetic radiation to aid in diagnosing infiltration or extravasation. Preferably, electromagnetic energy sensor  1000  includes an electromagnetic radiation signal transmitter  1002  and an electromagnetic radiation signal receiver  1004 . Electromagnetic radiation signal transmitter  1002  preferably includes an emitter face  1002   a  for emitting electromagnetic radiation  1002   b  and electromagnetic radiation signal receiver  1004  preferably includes a detector face  1004   a  for detecting electromagnetic radiation  1004   b . According to one embodiment, electromagnetic radiation signal transmitter  1002  preferably includes a set of first optical fibers and electromagnetic radiation signal receiver  1004  preferably includes a set of second optical fibers. Individual optical fibers in the first or second sets preferably each have end faces that form the emitter or detector faces, respectively. Preferably, emitted electromagnetic radiation  1002   b  from emitter face  1002   a  passes through the target area of the skin S toward the perivascular tissue P. Detected electromagnetic radiation  1004   b  preferably includes at least a portion of emitted electromagnetic radiation  1002   b  that is at least one of specularly reflected, diffusely reflected (e.g., due to 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 to detector face  1004   a . Preferably, an accumulation of fluid in the perivascular tissue P affects the absorption and/or scattering of emitted electromagnetic radiation  1002   b  and accordingly affects detected electromagnetic radiation  1004   b . Accordingly, electromagnetic energy sensor  1000  preferably senses changes in detected electromagnetic radiation  1004   b  that correspond with anatomic changes over time, such as infiltration or extravasation of the perivascular tissue P. 
         [0030]    Emitted and detected electromagnetic radiations  1002   b  and  1004   b  preferably are 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. Emitted and detected electromagnetic radiations  1002   b  and  1004   b  preferably are tuned to a common peak wavelength. According to one embodiment, emitted and detected electromagnetic radiations  1002   b  and  1004   b  each have a peak centered about a single wavelength, e.g., approximately 970 nanometers (approximately 309 terahertz). According to other embodiments, emitted electromagnetic radiation  1002   b  includes a set of wavelengths in a band between a relatively short wavelength and a relatively long wavelength, and detected electromagnetic radiation  1004   b  encompasses at least the band between the relatively short and long wavelengths. According to still other embodiments, detected electromagnetic radiation  1004   b  is tuned to a set of wavelengths in a band between a relatively short wavelength and a relatively long wavelength, and emitted electromagnetic radiation  1002   b  encompasses at least the band between the relatively short and long wavelengths. 
         [0031]    Electromagnetic energy sensor  1000  preferably includes a superficies  1000   a  that confronts the skin S. Preferably, superficies  1000   a  is generally smooth and includes emitter and detector faces  1002   a  and  1004   a . As the terminology is used herein, “smooth” preferably refers to being substantially free from perceptible projections or indentations. 
         [0032]    Electromagnetic energy sensor  1000  preferably is positioned in close proximity to the skin S. As the terminology is used herein, “close proximity” of electromagnetic energy sensor  1000  with respect to the skin S preferably refers to a relative arrangement that minimizes gaps between superficies  1000   a  and the epidermis of the skin S. Preferably, electromagnetic energy sensor  1000  contiguously engages the skin S as shown in  FIG. 1 . 
         [0033]    The inventors discovered a problem regarding accurately identifying the occurrence of infiltration or extravasation because of a relatively low signal-to-noise ratio of detected electromagnetic radiation  1004   b . In particular, the inventors discovered a problem regarding a relatively large amount of noise in detected electromagnetic radiation  1004   b  that obscures signals indicative of infiltration/extravasation events. Another discovery by the inventors is that the amount of noise in detected electromagnetic radiation  1004   b  tends to correspond with the degree of patient activity. In particular, the inventors discovered that detected electromagnetic radiation  1004   b  tends to have a relatively lower signal-to-noise ratio among patients that are more active, e.g., restless, fidgety, etc., and that detected electromagnetic radiation  1004   b  tends to have a relatively higher signal-to-noise ratio among patients that were less active, e.g., calm, sleeping, etc. 
         [0034]    The inventors also discovered that a source of the problem is an imperfect cavity that may unavoidably and/or intermittently occur between superficies  1000   a  and the skin S. As the terminology is used herein, “imperfect cavity” preferably refers to a generally confined space that at least partially reflects electromagnetic radiation. In particular, the inventors discovered that the source of the problem is the imperfect cavity reflects portions of emitted electromagnetic radiation  1002   b  and/or detected electromagnetic radiation  1004   b  that are detected by electromagnetic radiation signal receiver  1004 . Accordingly, detected electromagnetic radiation  1004   b  includes reflected extracorporeal electromagnetic radiation in addition to transcutaneous electromagnetic radiation. As the terminology is used herein, “extracorporeal electromagnetic radiation” generally refers to portions of emitted electromagnetic radiation  1002   b  and/or detected electromagnetic radiation  1004   b  that are reflected in the imperfect cavity, and “transcutaneous electromagnetic radiation” preferably refers to portions of emitted electromagnetic radiation  1002   b  that penetrate through the skin S and are reflected, scattered or otherwise redirected from the perivascular tissue P. Preferably, transcutaneous electromagnetic radiation includes a signal that indicates an infiltration/extravasation event whereas extracorporeal electromagnetic radiation predominately includes noise that tends to obscure the signal. Thus, the inventors discovered, inter alia, that a cavity between superficies  1000   a  and the skin S affects the signal-to-noise ratio of detected electromagnetic radiation  1004   b.    
         [0035]      FIG. 2  illustrates the source of the problem discovered by the inventors. Specifically,  FIG. 2  shows a cavity C disposed between electromagnetic energy sensor  1000  and the skin S. The size, shape, proportions, etc. of cavity C are generally overemphasized in  FIG. 2  to facilitate describing the source of the problem discovered by the inventors. Preferably, emitted electromagnetic radiation  1002   b  includes a transcutaneous portion  1002   b   1  that passes through the cavity C and passes through the target area of the skin S toward the perivascular tissue P. Emitted electromagnetic radiation  1002   b  also includes an extracorporeal portion  1002   b   2  that is reflected in the cavity C. Detected electromagnetic radiation  1004   b  preferably includes signal  1004   b   1  as well as noise  1004   b   2 . Preferably, signal  1004   b   1  includes at least a portion of transcutaneous portion  1002   b   1  that is at least one of reflected, scattered or otherwise redirected from the perivascular tissue P before passing through the target area of the skin S, passing through the cavity C, and being received by electromagnetic radiation signal receiver  1004 . Noise  1004   b   2  includes at least a portion of extracorporeal portion  1002   b   2  that is reflected in the cavity C before being received by electromagnetic radiation signal receiver  1004 . 
         [0036]      FIGS. 2A and 2B  illustrate that the cavity C preferably includes one or an aggregation of individual gaps.  FIG. 2A  shows individual gaps between superficies  1000   a  and the skin S that, taken in the aggregate, preferably make up the cavity C. Preferably, the individual gaps may range in size between approximately microscopic gaps G 1  (three are indicated in  FIG. 2A ) and approximately macroscopic gaps G 2  (two are indicated in  FIG. 2A ). It is believed that approximately microscopic gaps G 1  may be due at least in part to epidermal contours of the skin S and/or hair on the skin S, and approximately macroscopic gaps G 2  may be due at least in part to relative movement between superficies  1000   a  and the skin S. Patient activity is an example of an occurrence that may cause the relative movement that results in approximately macroscopic gaps G 2  between superficies  1000   a  and the skin S. 
         [0037]      FIG. 2B  shows electromagnetic energy sensor  1000  preferably isolated from the skin S by a foundation  1010 . Preferably, foundation  1010  contiguously engages superficies  1000   a  and contiguously engages the skin S. Accordingly, the cavity C between foundation  1010  and the skin S preferably includes an aggregation of (1) approximately microscopic gaps G 1  (two are indicated in  FIG. 2A ); and (2) approximately macroscopic gaps G 2  (two are indicated in  FIG. 2A ). Foundation  1010  preferably is coupled with respect to electromagnetic energy sensor  1000  and includes a panel  1012  and/or adhesive  1014 . Preferably, panel  1012  includes a layer disposed between electromagnetic energy sensor  1000  and the skin S. Panel  1012  preferably includes Tegaderm™, manufactured by 3M (St. Paul, Minn., USA), REACTIC™, manufactured by Smith &amp; Nephew (London, UK), or another polymer film, e.g., polyurethane film, that is substantially impervious to solids, liquids, microorganisms and/or viruses. Preferably, panel  1012  is transparent or translucent with respect to visible light, breathable, and/or biocompatible. As the terminology is used herein, “biocompatible” preferably refers to compliance with Standard 10993 promulgated by the International Organization for Standardization (ISO 10993) and/or Class VI promulgated by The United States Pharmacopeial Convention (USP Class VI). Other regulatory entities, e.g., National Institute of Standards and Technology, may also promulgate standards that may additionally or alternatively be applicable regarding biocompatibility. Panel  1012  preferably is generally transparent with respect to emitted and detected electromagnetic radiations  1002   b  and  1004   b . Preferably, adhesive  1014  bonds at least one of panel  1012  and electromagnetic energy sensor  1000  to the skin S. Adhesive  1014  preferably includes an acrylic adhesive, a synthetic rubber adhesive, or another biocompatible, medical grade adhesive. Preferably, adhesive  1014  minimally affects emitted and detected electromagnetic radiations  1002   b  and  1004   b . According to one embodiment, as shown in  FIG. 2B , adhesive  1014  preferably is omitted where emitted and detected electromagnetic radiations  1002   b  and  1004   b  penetrate foundation  1010 , e.g., underlying emitter and detector faces  1002   a  and  1004   a.    
         [0038]      FIG. 3  shows an electromagnetic energy sensor  1100  according to the present disclosure that preferably includes a housing  1110  with an electromagnetic radiation absorber  1130 . According to one embodiment, housing  1110  preferably includes a first housing portion  1112  coupled with a second housing portion  1114 . Preferably, electromagnetic radiation signal transmitter  1002  and electromagnetic radiation signal receiver  1004  extend through a space  1116  generally defined by housing  1110 . Housing  1110  preferably includes a biocompatible material, e.g., polycarbonate, polypropylene, polyethylene, acrylonitrile butadiene styrene, or another polymer material. A potting material  1120 , e.g., epoxy, preferably fills space  1116  around electromagnetic radiation signal transmitter  1002  and electromagnetic radiation signal receiver  1004 . According to one embodiment, potting material  1120  preferably cinctures transmitting and receiving optical fibers disposed in space  1116 . Preferably, housing  1110  includes a surface  1118  that confronts the skin S and cinctures emitter and detector faces  1002   a  and  1004   a . Accordingly, as shown in  FIG. 3A , a superficies  1102  of electromagnetic energy sensor  1100  preferably includes emitter face  1002   a , detector face  1004   a  and surface  1118 . 
         [0039]    Absorber  1130  preferably absorbs electromagnetic radiation that impinges on surface  1118 . As the terminology is used herein, “absorb” or “absorption” preferably refer to transforming electromagnetic radiation to another form of energy, such as heat, while propagating in a material. Preferably, absorber  1130  absorbs wavelengths of electromagnetic radiation that generally correspond to the wavelengths of emitted and detected electromagnetic radiations  1002   b  and  1004   b . According to one embodiment, absorber  1130  preferably absorbs electromagnetic radiation in the near-infrared portion of the electromagnetic spectrum. Absorber  1130  may additionally or alternatively absorb wavelengths in other parts of the electromagnetic radiation spectrum, e.g., visible light, short-wavelength infrared, mid-wavelength infrared, long-wavelength infrared, or far infrared. Preferably, absorber  1130  absorbs at least 50% to 90% or more of the electromagnetic radiation that impinges on surface  1118 . 
         [0040]    Absorber  1130  preferably includes a variety of form factors for inclusion with housing  1110 . Preferably, absorber  1130  includes at least one of a film, a powder, a pigment, a dye, or ink. Film or ink preferably are applied on surface  1118 , and powder, pigment or dye preferably are incorporated, e.g., dispersed, in the composition of housing  1110 .  FIG. 3  shows absorber  1130  preferably is included in first housing portion  1112 ; however, absorber  1130  or another electromagnetic radiation absorbing material may also be included in second housing portion  1114  and/or potting material  1120 . Examples of absorbers  1130  that are suitable for absorbing near-infrared electromagnetic radiation preferably include at least one of antimony-tin oxide, carbon black, copper phosphate, copper pyrophosphate, illite, indium-tin oxide, kaolin, lanthanum hexaboride, montmorillonite, nickel dithiolene dye, palladium dithiolene dye, platinum dithiolene dye, tungsten oxide, and tungsten trioxide. 
         [0041]    Absorber  1130  preferably improves the signal-to-noise ratio of received electromagnetic radiation  1004  by reducing noise  1004   b   2 . Compared to electromagnetic energy sensor  1000  ( FIG. 2 ), the propagation of extracorporeal portion  1002   b   2  preferably is substantially attenuated by absorber  1130  in electromagnetic energy sensor  1100 . Preferably, extracorporeal portion  1002   b   2  that impinges on surface  1118  is absorbed rather than being reflected in the cavity C and therefore does not propagate further, e.g., toward electromagnetic radiation signal receiver  1004 . Other electromagnetic radiation that impinges on surface  1118  preferably is also absorbed rather than being reflected in the cavity C. For example, absorber  130  may also absorb a portion of transcutaneous portion  1002   b   1  that is at least one of reflected, scattered or otherwise redirected from the perivascular tissue P, then passes through the target area of the skin S and through the cavity C, but impinges on surface  1118  rather than being received by electromagnetic radiation signal receiver  1004 . 
         [0042]    Electromagnetic energy sensor  1100  preferably may be used, for example, (1) as an aid in detecting at least one of infiltration and extravasation; (2) to identify an anatomical change in perivascular tissue; or (3) to analyze a transcutaneous electromagnetic signal. Preferably, electromagnetic radiation signal transmitter  1002  transmits emitted electromagnetic radiation  1002   b  via emitter face  1002   a . Emitted electromagnetic radiation  1002   b  preferably propagates through foundation  1010  and/or cavity C, if either of these is disposed in the path of emitted electromagnetic radiation  1002   b  toward the target area of the skin S. According to one embodiment, emitted electromagnetic radiation  1002   b  divides into transcutaneous portion  1002   b   1  and extracorporeal portion  1002   b   2  in the cavity C. 
         [0043]    Transcutaneous portion  1002   b   1  of emitted electromagnetic radiation  1002   b  preferably propagates through the skin S toward the perivascular tissue P. Preferably, at least a portion of transcutaneous portion  1002   b   1  is at least one of reflected, scattered or otherwise redirected from the perivascular tissue P toward the target area of the skin S as signal  1004   b   1 . After propagating through the target area of the skin S, signal  1004   b   1  preferably further propagates through the cavity C and foundation  1010 , if either of these is disposed in the path of signal  1004   b   1  toward electromagnetic radiation signal receiver  1004 . Preferably, electromagnetic radiation signal receiver  1004  receives signal  1004   b   1  via detector face  1004   a . Signal  1004   b   1  preferably includes a transcutaneous electromagnetic signal that may be analyzed to, for example, identify anatomical changes in perivascular tissue and/or aid in detecting an infiltration/extravasation event. 
         [0044]    Extracorporeal portion  1002   b   2  of emitted electromagnetic radiation  1002   b  is reflected in cavity C, but preferably is generally absorbed by absorber  1130 . Preferably, absorber  1130  absorbs at least 50% to 90% or more of extracorporeal portion  1002   b   2  that impinges on surface  1118 . Accordingly, a first portion of noise  1004   b   2  due to extracorporeal portion  1002   b   2  preferably is substantially eliminated or at least reduced by absorber  1130 . 
         [0045]    Absorber  1130  preferably also absorbs a second portion of noise  1004   b   2  due to electromagnetic radiation other than extracorporeal portion  1002   b   2  in cavity C. For example, absorber  1130  preferably also absorbs a portion of signal  1004   b   1  that impinges on surface  1118  rather than being received by electromagnetic radiation signal receiver  1004  via detector face  1004   a.    
         [0046]    Thus, absorber  1130  preferably improves the signal-to-noise ratio of detected electromagnetic radiation  1004   b  by absorbing noise  1004   b   2 . Preferably, reducing noise  1004   b   2  in detected electromagnetic radiation  1004   b  makes it easier to analyze signal  1004   b   1  in detected electromagnetic radiation  1004   b.    
         [0047]    Changes in the size and/or volume of cavity C preferably may also be used to monitor patient activity and/or verify inspections by caregivers. Preferably, information regarding the frequency and degree of patient motion may be detected by electromagnetic energy sensor  1100 . Accordingly, this information may aid a caregiver in evaluating if a patient is obsessed with or distracted by cannula  20  and therefore at greater risk of disrupting the patient&#39;s infusion therapy. Similarly, electromagnetic energy sensor  1100  preferably may be used to detect caregiver inspections of the target area of the skin and/or the insertion site N. Preferably, a caregiver periodically inspects the patient during infusion therapy for indications of infiltration/extravasation events. These inspections preferably include touching and/or palpitating the target area of the patient&#39;s skin; which tends to cause relative movement between electromagnetic energy sensor  1100  and the skin. Accordingly, a record of detected electromagnetic radiation  1004   b  preferably includes the occurrences over time of caregiver inspections. 
         [0048]    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. 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.