US20030181794A1 - Implantable sensor housing, sensor unit and methods for forming and using the same - Google Patents

Abstract

An in vivo implantable sensor unit includes a glass sensor housing defining an elongated chamber. Sensor electronics are disposed in the chamber. The sensor electronics are adapted to wirelessly transmit data. The sensor unit is configured to wirelessly transmit data from an in vivo position to a remote receiver over a period of at least four weeks and the sensor housing is adapted to provide a hermetic seal about the sensor electronics for a period of at least four weeks. The hermetic seal is such that under a helium mass spectrometer leak detection test the sensor housing has a leak rate that is less than about 10⁻⁸atm-cc/s.

Description

RELATED APPLICATIONS
• The present application claims the benefit of and priority from U.S. Provisional Application Serial No. 60/352,912, filed Jan. 29, 2002, the disclosure of which is hereby incorporated herein by reference in its entirety.[0001]
FIELD OF THE INVENTION
• The present invention relates to sensors and, more particularly, to a sensor housing or a sensor unit which may be implanted in the body of a human or other animal, and methods for forming and using the same.[0002]
BACKGROUND OF THE INVENTION
• Sensors or markers may be implanted into the body of a human or other animal patient to facilitate diagnosis, treatment or identification. The sensor or marker may include various electronics and a surrounding housing. For example, a sensor may include electronics as needed to detect or measure parameters of the surrounding environment. The sensor or marker may also include electronics for wireless communication with a receiver unit located outside of the patient's body.[0003]
• It is often desirable to maintain the sensor or marker as described above in a particular location or region in the patient. Migration of the sensor or marker may diminish the effectiveness of the sensor or marker to accurately sense the desired parameters.[0004]
• The surrounding environment of the implanted sensor or marker can include physiological fluid, cells and tissue. The surrounding fluids or moisture from the surrounding cells and/or tissue may hydrate the sensor, and this intruding moisture may promote corrosion of or otherwise damage or interfere with the operation of the aforementioned electronics.[0005]
SUMMARY OF THE INVENTION
• According to embodiments of the present invention, an in vivo implantable sensor unit includes a glass sensor housing defining an elongated chamber. Sensor electronics are disposed in the chamber. The sensor electronics are adapted to wirelessly transmit data. The sensor unit is configured to wirelessly transmit data from an in vivo position to a remote receiver over a period of at least four weeks and the sensor housing is adapted to provide a hermetic seal about the sensor electronics for a period of at least four weeks. The hermetic seal is such that under a helium mass spectrometer leak detection test the sensor housing has a leak rate that is less than about 10[0006]⁻⁸atm-cc/s.
• According to further embodiments of the present invention, an implantable sensor unit includes a tube defining a chamber and an opening communicating with the chamber. Sensor electronics are disposed in the chamber. Epoxy is disposed in the chamber and surrounds the sensor electronics. The epoxy has an end surface adjacent the opening of the tube. An end plug is mounted in the opening of the tube. The end surface of the epoxy and the end plug define a gap therebetween configured to insulate the sensor electronics.[0007]
• According to still further embodiments of the present invention, an implantable sensor unit includes a tube defining an elongated chamber and an opening communicating with the chamber. Sensor electronics are disposed in the chamber. An end plug is mounted in the opening of the tube. The end plug is spherically shaped.[0008]
• According to further embodiments of the present invention, an implantable sensor unit includes a tube defining a chamber and an opening communicating with the chamber. Sensor electronics are disposed in the chamber. Epoxy is disposed in the chamber and surrounds the sensor electronics. The epoxy has an end surface adjacent the opening of the tube. The sensor unit further includes a retaining cap including at least one projection extending outwardly from the tube. The retaining cap is secured to the tube by the epoxy.[0009]
• According to embodiments of the present invention, an implantable sensor unit includes a sensor housing defining an elongated chamber. Sensor electronics are disposed in the chamber. A retention device is mounted on the sensor housing. The retention device includes a band surrounding a portion of the sensor housing and at least one projection secured to and extending from the band.[0010]
• According to further embodiments of the present invention, an implantable sensor unit includes a sensor housing having an outer surface and defining a chamber. Sensor electronics are disposed in the chamber. The sensor electronics are adapted to wirelessly transmit data. A bio-compatible anti-migration coating is disposed on the outer surface. The anti-migration coating is a Parylene C coating.[0011]
• According to still further embodiments of the present invention, an implantable sensor unit includes a sensor housing having an outer surface and defining a chamber. A bio-compatible anti-migration mesh layer is disposed on the outer surface.[0012]
• According to method embodiments of the present invention, a method for forming a sensor unit includes: inserting an uncured epoxy into a tube in a fluid state; inserting sensor electronics into the uncured epoxy in the tube; evacuating air bubbles from the epoxy and the sensor electronics in the tube; and then curing the epoxy.[0013]
• According to further method embodiments of the present invention, a method for forming a sensor unit includes: inserting an uncured epoxy in a fluid state into a tube through an opening in the tube; inserting sensor electronics into the uncured epoxy; curing the epoxy such that the epoxy stabilizes the sensor electronics; and sealing the opening in the tube to form a hermetically sealed tube.[0014]
• According to further method embodiments of the present invention, a method for forming a sensor unit includes: providing a sensor housing having an outer surface and defining a chamber; providing sensor electronics in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data; and applying a bio-compatible anti-migration coating to the outer surface of the sensor housing using a plasma polymerization thin film deposition technique.[0015]
• According to further method embodiments of the present invention, a method for forming a sensor unit includes: providing a sensor housing having an outer surface and defining a chamber; providing sensor electronics in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data; and applying a bio-compatible anti-migration coating to the outer surface of the sensor housing, wherein the anti-migration coating is a Parylene C coating.[0016]
• According to further method embodiments of the present invention, a method for forming a sensor unit includes: applying a bio-compatible anti-migration mesh layer to an outer surface of a sensor housing.[0017]
• According to further embodiments of the present invention, an implantable sensor unit includes a sensor housing having an outer surface. A bio-compatible anti-migration layer surrounds at least a portion of the outer surface of the sensor housing. The anti-migration layer is formed of a textile material.[0018]
• According to further method embodiments of the present invention, a method for forming an implantable sensor unit includes: providing a sensor housing; and placing a bio-compatible anti-migration layer over the outer surface of the sensor housing, the anti-migration layer being formed of a textile material.[0019]
• According to further embodiments of the present invention, an implantable sensor unit includes a sensor housing having an end and defining a chamber. Sensor electronics are disposed in the chamber. A holding tab extends from the end of the housing. The holding tab is adapted to facilitate handling of the housing.[0020]
• According to further method embodiments of the present invention, a method for implanting an implantable sensor unit in a body, the sensor unit including a sensor housing, includes handling the sensor housing in the body using a holding tab extending from an end of the housing.[0021]
• According to further method embodiments of the present invention, a method for using an implantable sensor unit in a body includes: implanting the sensor unit in the body; conducting an imaging procedure on the body such that the sensor unit in the body serves as a fiducial marker; detecting a parameter using the sensor unit in the body; and transmitting data associated with the detected parameter from the sensor unit to a remote receiver unit.[0022]
• According to still further embodiments of the present invention, an implantable sensor unit includes a sensor housing having an outer surface. A bio-compatible anti-migration layer surrounds at least a portion of the outer surface of the sensor housing. The anti-migration layer is formed of a heat shrinkable thermoplastic material.[0023]
• According to further method embodiments of the present invention, a method for forming a sensor unit includes: providing a sensor housing having an outer surface and defining a chamber; providing sensor electronics in the chamber, wherein the sensor electronics are adapted to wireless transmit data; placing a bio-compatible anti-migration layer about the sensor housing, wherein the anti-migration layer is formed of a heat shrinkable thermoplastic material; and heating the anti-migration layer to shrink the anti-migration layer about the sensor housing.[0024]
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain principles of the invention.[0025]
• FIG. 1 is a perspective view of a sensor unit according to embodiments of the present invention;[0026]
• FIG. 2 is a perspective view of a plug forming a part of the sensor unit of FIG. 1 according to embodiments of the present invention;[0027]
• FIG. 3 is an exploded, cross-sectional view of the sensor unit of FIG. 1 taken along the line[0028]4-4 of FIG. 1;
• FIG. 4 is a cross-sectional view of the assembled sensor unit of FIG. 1 taken along the line[0029]4-4 of FIG. 1;
• FIG. 5 is a cross-sectional view of a sensor unit according to further embodiments of the present invention;[0030]
• FIG. 6 is a perspective view of a plug forming a part of the sensor unit of FIG. 5;[0031]
• FIG. 7 is an exploded, cross-sectional view of a sensor unit according to further embodiments of the present invention;[0032]
• FIG. 8 is a perspective view of a plug forming a part of the sensor unit of FIG. 7;[0033]
• FIG. 9 is a cross-sectional view of the assembled sensor unit of FIG. 7;[0034]
• FIG. 10 is an exploded, cross-sectional view of a sensor unit according to further embodiments of the present invention;[0035]
• FIG. 11 is a perspective view of a cap forming a part of the sensor unit of FIG. 10;[0036]
• FIG. 12 is a cross-sectional view of the assembled sensor unit of FIG. 10;[0037]
• FIG. 13 is a cross-sectional view of a sensor unit according to further embodiments of the present invention;[0038]
• FIG. 14 is a cross-sectional view of a sensor unit according to still further embodiments of the present invention;[0039]
• FIG. 15 is a cross-sectional view of a sensor unit according to additional embodiments of the present invention;[0040]
• FIG. 16 is a perspective view of a sensor unit according to yet further embodiments of the present invention;[0041]
• FIG. 17 is a cross-sectional view of the sensor unit of FIG. 16 taken along the line[0042]17-17 of FIG. 16;
• FIG. 18 is a perspective view of a retention cap forming a part of the sensor unit of FIG. 16;[0043]
• FIG. 19 is a cross-sectional view of a sensor unit according to further embodiments of the present invention;[0044]
• FIG. 20 is an exploded, cross-sectional view of the sensor unit of FIG. 19;[0045]
• FIG. 21 is a perspective view of a spherical plug forming a part of the sensor unit of FIG. 19;[0046]
• FIG. 22 is a cross-sectional view of a sensor unit according to further embodiments of the present invention;[0047]
• FIG. 23 is a perspective view of a retention device forming a part of the sensor unit of FIG. 22;[0048]
• FIG. 24 is an exploded, side elevational view of the sensor unit of FIG. 22;[0049]
• FIG. 25 is a cross-sectional view of a sensor unit according to further embodiments of the present invention;[0050]
• FIG. 26 is a perspective view of a sensor unit according to further embodiments of the present invention;[0051]
• FIG. 27 is a side view of a sensor unit according to further embodiments of the present invention;[0052]
• FIG. 28 is a cross-sectional view of the sensor unit of FIG. 27 taken along the line[0053]28-28 of FIG. 27;
• FIG. 29 is a schematic view of an apparatus for forming the sensor unit of FIG. 27;[0054]
• FIG. 30 is a schematic view of a further apparatus for forming the sensor unit of FIG. 27;[0055]
• FIG. 31 is a partial, fragmentary, enlarged perspective view of the sensor unit of FIG. 27 being held by an instrument in a canula;[0056]
• FIG. 32 is a partial, fragmentary, schematic view of the sensor unit of FIG. 27 implanted in a body and secured to tissue of the body by a suture;[0057]
• FIG. 33 is a schematic view of an imaging system employing a sensor unit according to embodiments of the present invention;[0058]
• FIG. 34 is a flow chart representing operations for using an implantable sensor unit in an imaging procedure according to embodiments of the present invention; and[0059]
• FIG. 35 is a side view of a sensor unit according to further embodiments of the present invention.[0060]
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
• The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. In the figures, layers, components or regions may be exaggerated for clarity.[0061]
• As used herein, “textile material” means an article having structural integrity resulting from forced interassociation of a plurality of fibers, filaments, or strands, the forced interassociation resulting from processes such as weaving, knitting, braiding, needling hydroentangling, chemical coating or impregnation, autogenous bonding (i.e., heat- and/or pressure-promoted welding or solvent bonding) or felting.[0062]
• As used herein, “multi-filament textile material” means a textile material having structural integrity resulting from forced interassociation of a plurality of filaments.[0063]
• As used herein, “braided material” means a textile material in which one or more yams, filaments or strands pass alternately over or under one or more other strands; or in which one or more strands half-twist alternately about two or more adjacent strands.[0064]
• A desired function for an implantable sensor may be to sense a physical parameter and transmit this information for analysis. However, these parameters may only be interpreted with meaning if the sensor is in a specific location in the body. With this limitation, a design parameter for the device may be to keep the sensor in a desired location so that it is retained at the target implant site. The present invention may satisfy certain design parameters not only to ensure the safety of such a device, but also to produce reliable data from a specific implant location for a prolonged time period. The present invention may meet the more stringent regulations imposed on devices for use in humans. The present invention may also insure compatibility of tissue/blood contacting materials as well as device function compliance and approval. Embodiments of the invention include materials selection for bio-compatibility and function, moisture resistant design of components used for hermetic sealing, as well as novel means for retaining the implant in a desired location.[0065]
• In certain embodiments, the sensor units of the present invention may be implanted (e.g., injected) into various tissues of any animal subject, preferably mammalian subjects (e.g., humans, canines, felines, bovines, caprines, ovines, equines, rodents, porcines, and/or lagomorphs), and more preferably human subjects. The sensor units may be cost-effectively manufactured and implanted in or otherwise positioned at desired locations in or proximate to tissues or organs in the body and may be particularly suitable to position adjacent or in cancerous tumors.[0066]
• The sensor units described herein are particularly well-suited for use in monitoring systems, methods, and associated devices as disclosed in U.S. Pat. No. 6,402,689 issued Jun. 11, 2002, the disclosure of which is hereby incorporated herein by reference in its entirety. As described, the sensor unit can dynamically monitor multiple tumor physiological and biological parameters and/or changes associated with tumors to identify enhanced or favorable treatment conditions to thereby establish a patient-specific treatment delivery time or patient-specific treatment. The methods disclosed in U.S. Pat. No. 6,402,689 include methods of monitoring at least one physiological parameter associated with a tumor in a subject undergoing medical treatment with an in vivo sensor. Data associated with at least one monitored physiological parameter is wirelessly transmitted from an in vivo sensor to a receiver external of the subject. The transmitted data is analyzed and processed into meaningful parameters that may indicate how the tumor is responding to treatment. Additional data is transmitted and analyzed periodically at a plurality of sequential points in time, and a tumor treatment strategy is evaluated based on the analyzing step. The sensor units of the present invention can be used to monitor, in substantially real time and/or dynamically, specific indices associated with tumor physiology making monitored data available for immediate use in treatment decisions. Thus, the sensor units may be used to provide sufficient ongoing, and preferably substantially real-time, information pertaining to the physiological and/or biological condition of the tumor during a treatment period in a manner that provides the information to the physician to allow the physician to make informed therapeutic decisions.[0067]
• Moreover, the sensor units of the present invention may be used in the in vivo evaluation and monitoring of tumors prior to, during, and subsequent to an active treatment, and preferably over an entire treatment regime or period. That is, the sensor units are particularly suitable for monitoring the behavior of cancerous tumors such as sarcomas and carcinomas over a particular non-remission treatment period. As such, the sensor units of the present invention are preferably configured to be bio-compatible and provide at minimum a service life suitable for episodic treatment evaluation of at least about 4-6 weeks, and more preferably at least about 6-10 weeks, and still more preferably at least about 10-12 weeks, whether exposed to radiation, chemotherapy, heat or ionic electric fields (such as the treatment provided by a Thermotron® machine) directed to the tumor.[0068]
• With reference to FIGS.[0069]1-4, a sensor unit according to embodiments of the present invention is shown therein and generally designated by thenumber100. Thesensor unit100 includes generally a sensor housing101 (FIG. 1), andsensor electronics120 and epoxy130 disposed within thesensor housing101. Thesensor housing101 includes atube110, aplug140 and anoptional anti-migration coating150 disposed over a portion or all of the outer surface of thesensor unit100.
• In certain embodiments, the[0070]tube110 is cylindrically shaped and sized for injection through a trocar/cannula assembly, syringe or catheter, for example, into human tissue. Thetube110 defines aninterior chamber112. Thetube110 has a tapered or rounded, closed end114 (FIG. 3) to facilitate easier entry into the target tissue (e.g., the tumor). As shown in FIG. 3, thetube110 further has anopen end116 opposite theclosed end114. The rim at theopen end116 is preferably smooth and defines anopening118 which, in the absence of theplug140, fluidly communicates with thechamber112. Preferably, the length A (FIG.1) of thetube110 is between about 10 and 27 mm. In certain embodiments, the inner diameter E (FIG. 3) of thetube110 can be between about 1.5 and 2.5 mm. While the wall thickness of thetube110 can be between about 0.15 and 0.56 mm. Similarly, thechamber112 can have a volume of between about 16 and 127 mm³.
• The[0071]tube110 can be formed of a bio-compatible material. In certain embodiments, thetube110 is formed of a bio-compatible silicate, preferably a bio-compatible glass. Suitable bio-compatible glasses include, for example, glass as described in U.S. Pat. No. 5,121,748 to Ditz et al. (assigned to Schott Glaswerke of Germany). Preferably, theentire sensor unit100 is sterilized using a means that does not adversely affect the sensor's electronic components or housing materials before being injected or implanted.
• The[0072]sensor electronics120 are disposed in thechamber112. Thesensor electronics120 may include suitable components to measure temperature, level of oxygenation, cell proliferation, tumor or normal tissue pH, externally generated radiation and/or radiolabeled substances. Thesensor unit100 may include components suitable to provide a telemetry link to wirelessly communicate with an remotely or externally located receiver. Thesensor electronics120 may include various electronics such as those described in U.S. Pat. No. 6,402,689 and in PCT International Application No. PCT/US00/08310, filed Mar. 9, 2000, the disclosures of which are hereby incorporated herein in their entireties by reference. Accordingly, theelectronic components120 described herein are exemplary and are not exhaustive of the components which may be housed in thesensor unit100. As illustrated, thesensor electronics120 include a printed circuit board (PCB) or integrated circuit (IC)chip124 including circuitry operative to measure and process the desired environmental and physical parameter(s) (e.g., pH, gamma radiation, and fluorescence). The circuitry may include a power source such as a battery. Anantenna portion122 is positioned above theIC124. Theantenna portion122 may be formed to include a cylindrically wrapped antenna coil. Other antenna configurations can also be used as is known to those of skill in the art. Theantenna portion122 is joined to theIC124 at ajuncture121.
• As shown in FIG. 3, the[0073]sensor electronics120 can be substantially entirely surrounded by the epoxy130, which is cured to a non-flowable or solid state. Preferably, the epoxy130 fills a predominant portion, but less than all of thechamber112. More preferably, as shown in FIG. 4, theupper surface132 of the cured epoxy is disposed below the end116 a length D of between about 2 and 8 mm. The volume ofepoxy130 may surround all or portions of thecircuit board124 and/or theantenna portion122. Preferably, the epoxy130 surrounds or encapsulates at least a portion of theantenna portion122 and all of thejuncture121 in order to stabilize and secure theelectronic portions122 and124 to one another. The volume may be dependent on the method of sealing the housing.
• The epoxy[0074]130 can be USP Class VI epoxy material. Suitable epoxy materials include Product No. EPO-PEK301-2 available from Epoxy Technology Incorporated of Billerica, Mass.
• As shown in FIG. 2, the[0075]plug140 is substantially solid and cylindrical, and has blunt (i.e., flat) opposed end surfaces142 and144. Preferably, theplug140 is formed of the same glass material as thetube110. The length B (FIG. 3) of the plug can be between about 4 and 8 mm. The diameter C (FIG. 3) of theplug140 is preferably substantially the same as the inner diameter E of thetube110.
• The[0076]anti-migration coating150 is disposed on an exterior surface of thetube110. Theanti-migration coating150 is a selected coating adapted to inhibit significant migration of thesensor unit100 when thesensor unit100 is positioned in the targeted tissue. Preferably, thecoating150 is bio-compatible, and more preferably a Class VI medical grade coating. Preferably, thecoating150 promotes attachment of live tissue to thecoated tube110. Theanti-migration coating150 may be a polymer coating, preferably a Parylene C conformal coating, an epoxy coating or a polypropylene coating. In certain embodiments, theanti-migration coating150 has a higher coefficient of friction in an in vivo environment than theunderlying tube110. Thecoating150 may be hydrophobic. If desired, theanti-migration coating150 may be omitted from thesensor unit100 and from each of the sensor unit embodiments described below. Theanti-migration coating150 may cover all or a portion less than all of the outer surface of thetube110.
• The[0077]sensor unit100 may be assembled in the following manner. A volume ofuncured epoxy130 material is injected into thechamber112. Thesensor electronics120 are inserted into theuncured epoxy130. Theelectronics120 may settle to or adjacent the lower end of thetube110. Thetube110, the epoxy130 and theelectronics120 are subjected to a vacuum atmosphere to draw trapped air (e.g., air potentially trapped in the coil122) out of the epoxy. The epoxy may be subjected to a vacuum of between about 5 and 30 inches of mercury (in Hg) for a time of between about 15 and 60 minutes. The epoxy130 is then cured by time, chemical process, and/or exposure to heat or light. Theplug140 is then inserted into theopening118 of thetube110 as shown in FIG. 3 until theend face144 abuts theupper surface132 of the curedepoxy130. Theplug140 and thetube110 are then circumferentially laser welded (e.g., using an infrared laser) or flamed together to form aweld seal102, preferably at a distance away from the epoxy130 and thesensor electronics120. Other coupling or sealing means can also be used, such as brazing, adhesives, fusing the glass, O-rings and threaded attachment means. Theweld seal102 so formed may be a hermetic seal. Theanti-migration coating150 is applied to the outer surface of thetube110. Alternatively, the anti-migration coating may be applied to all or portions of thetube110 before the epoxy is injected into thetube110. Theentire sensor unit100 may then be sterilized.
• The[0078]anti-migration coating150 may be applied to the outer surface of thetube150 using a plasma polymerization thin film deposition or a vapor deposition polymerization (VDP) technique. For example, the coating may be a Parylene C coating applied by VDP and preferably having a thickness of between about 10,000 and 60,000 Angstroms. Alternatively, thecoating150 may be a plasma polymerized thin film coating (preferably a plasma polypropylene thin film) having a thickness of between about 4,000 and 60,000 Angstroms. Suitable plasma deposition techniques and equipment may be provided by Plasmatech, Inc. of Erlanger, Ky. Suitable VDP techniques and equipment may be provided by Specialty Coating Systems of Clear Lake, Wis.
• With reference to FIGS. 5 and 6, a[0079]sensor unit200 according to further embodiments of the present invention is shown therein. Thesensor unit200 includeselements210,220,230 and250 corresponding toelements110,120,130 and150, respectively, of thesensor unit100. Thesensor unit200 differs from thesensor unit100 in that theplug140 is replaced with aplug240 having a rounded or dome-shapedouter end242. Preferably, theplug240 has a length F (FIG. 5) of between about 4 and 8 mm. Theplug240 otherwise corresponds to theplug140. Thesensor unit200 may be formed in the same manner as described above with regard to thesensor unit100.
• With reference to FIGS.[0080]7-9, asensor unit300 according to further embodiments of the present invention is shown therein. Thesensor unit300 haselements310,320,330 and350 corresponding to theelements110,120,130 and150, respectively, of thesensor unit100. Thesensor unit300 has aplug340 in place of theplug140.
• The[0081]plug340 may be formed of the same materials as discussed above with regard to theplug140. As illustrated, theplug340 is formed as a solid member; however, thecap340 may be hollow with a closed outer surface. Theplug340 has an enlargedouter portion343 having a diameter I (FIG. 7) that is greater than the inner diameter E (FIG. 9) of thetube310 and, preferably, equal to or greater than the outside diameter of thetube310. Theplug340 also has aninner portion345 having the same relative diameter as the plug140 (i.e., substantially the same as the inner diameter E). In this way thebottom portion345 of the plug is received into thetube310. Preferably, the upper plugouter portion343 has a length G (FIG. 7) of between about 1 and 5 mm. A seal302 (FIG. 9) is formed between the rim of thetube310 and theplug portion343.
• As shown in FIG. 9, the length H (FIG. 7) of the[0082]inner portion345 is selected relative to the depth D (FIG. 9) of theupper surface332 of the epoxy330 such that agap304 is defined between theinner surface344 of theplug340 and theend surface332 of theepoxy330. Preferably, the length H is selected relative to the depth D such that thegap304 has a length J (FIG. 9) of between about 2 and 10 mm. Thegap304 may be filled with air or other suitable fluid or suitable solid material that may serve to insulate the electronics from heat. Thegap304 may serve to insulate theelectronics320 from heat, for example, during the laser welding or flaming procedure used to form theweld seal302. Preferably, the volume and height of thegap304 are sufficient to prevent the epoxy330 and theelectronics320 from being subjected to a prescribed temperature beyond which heat damage to theelectronics320 may occur. As before, other coupling means may also be employed.
• With reference to FIGS.[0083]10-12, asensor unit400 according to further embodiments of the present invention is shown therein. Thesensor unit400 includeselements410,420,430 and450 corresponding to theelements110,120,130 and150, respectively, of thesensor unit100. Thesensor unit400 differs from thesensor unit100 in that theplug140 is replaced with acap440.
• The[0084]cap440 has anend wall446 and acylindrical side wall447 together defining aninterior cavity448 and anopening449 communicating with thecavity448. Thecavity448 has an inner diameter K (FIG. 10) that is substantially the same as the outer diameter of thetube410 so as to snugly overlie the same when thecap440 is assembled to thetube410 as shown in FIG. 11. Thecavity448 can have a depth M (FIG. 10) of between about 2 and 10 mm.
• The[0085]sensor unit400 can be assembled in substantially the same manner as thesensor unit100 except that thecap440 is fitted over thetube410 and laser welded about theopening449. Thecap440 may be formed of the same materials as discussed above with regard to theplug140.
• With reference to FIG. 13, a[0086]sensor unit500 according to further embodiments of the present invention is shown therein. Thesensor unit500 corresponds to thesensor unit400 except that thecap440 is replaced with acap540. Thecap540 corresponds to thecap440 except that theouter end546 of thecap540 is dome-shaped and defines a correspondingly shapedcavity548.
• With reference to FIG. 14, a[0087]sensor unit600 according to further embodiments of the present invention is shown therein. Thesensor unit600 corresponds to thesensor unit100 except that thesolid plug140 is replaced with ahollow plug640. Theplug640 defines acavity648 and a communicatinginner opening649. Theplug640 otherwise corresponds to theplug140.
• With reference to FIG. 15, a[0088]sensor unit700 according to further embodiments of the present invention is shown therein. Thesensor unit700 corresponds to the sensor unit200 (FIG. 5) except that the rounded,solid plug240 is replaced with a rounded,hollow plug740. Theplug740 defines acavity748 and a communicatinginner opening749. Theplug740 otherwise corresponds to theplug240.
• With reference to FIGS.[0089]16-18, asensor unit800 according to further embodiments of the present invention is shown therein. Thesensor unit800 includeselements810,820,830 and850 corresponding toelements110,120,130 and150, respectively, except that the length of thetube810 may be reduced as compared to thetube110 as discussed below. Thesensor unit800 employs aretention cap860 in place of the plug140 (or to be attached over the plug140).
• As shown, the[0090]retention cap860 includes acylindrical wall862 defining aninterior passage864. In certain embodiments, thepassage864 can extend fully between and communicates with each of anouter opening864A and aninner opening864B. As also shown, ashoulder866 of enlarged diameter (as compared to the wall862) extends about an upper portion of thewall862. A plurality (shown as four) of fins orprojections865 extend outwardly and downwardly from theshoulder866. Theprojections865 can be equally spaced about the perimeter. Eachprojection865 preferably has a length N (FIG. 17) of between about 5 and 10 mm.
• The[0091]cap860 can be formed of a polymeric material. More preferably, thecap860 is formed of medical grade (i.e., Class VI) polypropylene or polyethylene.
• The[0092]sensor unit800 is preferably assembled in a different manner than that described above with regard to thesensor unit100. Theuncured epoxy830 is injected into thetube810. Theelectronics820 are inserted into theuncured epoxy830. The epoxy830 and theelectronics820 are subjected to a vacuum atmosphere to draw out trapped air bubbles. In order to further evacuate trapped air, additionaluncured epoxy830 may be injected prior to the curing step so that the uncured epoxy overflows thetube810. A suitable solvent may be used to clean the uncured epoxy from the outer surface of thetube810. Theretention cap860 is inserted into thetube810 and the epoxy830 as shown in FIG. 17 so that aconvex meniscus832 of epoxy is formed at theopening864A. The epoxy830 is then allowed to cure, thereby securely bonding theretention cap860 to thetube810. Theanti-migration coating850 is applied to the outer surface of thetube810, preferably after theuncured epoxy830 is cleaned from the outer surface of thetube810. Alternatively, theanti-migration coating850 may be applied to thetube810 before injecting the epoxy830 into thetube110.
• The[0093]retention cap860 provides a number of advantages. Theprojections865 serve to mechanically engage the tissue surrounding thesensor unit800 after the sensor unit has been injected or implanted. Thepassage864 allows for a substantial engagement between theretention cap860 and the epoxy to ensure strong retention of thecap860 on thetube810. Additionally, aportion820A (e.g., a portion of the antenna coil) of thesensor electronics820 may be received in thepassage864 so that the overall length of thesensor unit800 may be reduced.
• The procedures for removing trapped air bubbles reduce the risk of pooling of water vapor in retained air bubble voids. Such pooled water may cause corrosion of the[0094]electronics820.
• Alternatively, the[0095]retention cap860 may be modified to include a closure wall in place of theopening864A. More orfewer projections865 may be provided. Theprojections865 may be reversed such that the free ends thereof point away from rather than toward the end814 (FIG. 17) of the tube810 (i.e., upwardly rather than downwardly in the illustration of FIG. 17). Theprojections865 may be adapted to expand outwardly once implanted in tissues, for example, due to exposure to heat or moisture. For example, theprojections865 may be initially held in a first position by a dissolvable bio-compatible adhesive, which adhesive dissolves once the sensor unit is implanted to allow the projections to expand. In addition, sensor units can be configured as described for other embodiments with the cap positioned over a desired region of the perimeter/outer surface of the sensor housing. Suitable modifications to the methods of forming thesensor unit800 will be apparent to those of skill in the art.
• With reference to FIGS.[0096]19-21, asensor unit900 according to further embodiments of the present invention is shown therein. Thesensor unit900 includeselements910,920,930 and950 corresponding toelements110,120,130 and150, respectively, of thesensor device100. Thesensor unit900 has aplug940 in place of theplug140.
• As best seen in FIG. 21, the[0097]plug940 is a spherical bead. Preferably and as illustrated, theplug940 is solid. Theplug940 has a diameter Q that is preferably the same as or slightly greater than the inner diameter of theopening918 of thetube910. Theupper surface932 of the epoxy930 is positioned such that the lowermost portion of theplug940 and theepoxy surface932 define agap904 therebetween. Preferably, thegap904 has a height P (FIG. 19) of between about 2 and 6 mm.
• The[0098]plug940 may be a laser welded or flamed in place to form a seal902 (FIG. 19). Notably, the spherical shape of theplug940 facilitates convenient and accurate positioning of theplug940 thetube910.
• With reference to FIGS.[0099]22-24, asensor unit1000 according to further embodiments of the invention is shown therein. Thesensor unit1000 includeselements1010,1020,1030 and1050 corresponding toelements110,120,130 and150, respectively. As illustrated in FIG. 22, aglass cap1040 is welded (e.g., using a flame, laser or other suitable means) to the open end of thetube1010 to form a hermetic seal. However, any of the above-described caps, plugs and methods for closing the open end of the tube may be employed.
• The[0100]sensor unit1000 also includes aretention device1060 mounted on and surrounding a mid-portion (preferably at or near the center) of thetube1010. Theretention device1060 may be used in place of or in addition to theretention cap860. Theretention device1060 includes aband1066 defining anopening1064. Four substantiallyrigid projections1065 are secured to theband1066. In use, the projections may engage the surrounding tissue to prevent or inhibit migration in the manner discussed above with regard to theprojections865.
• Preferably, the[0101]band1066 is formed of an elastomeric material and has a relaxed diameter R (FIG. 23) that is less than the diameter of thetube1010 at the mounting location. Suitable elastomeric materials include silicone rubber. Theband1066 is elastically stretched, slid over thetube1010 and thecoating1050, and released so that elastic tension in theband1066 retains theretention device1060 on thetube1010. Optionally or alternatively, an adhesive or the like may be used to secure theretention device1060 in place.
• With reference to FIG. 25, a[0102]sensor unit1100 according to further embodiments of the invention is shown therein. Thesensor unit1100 includes atube1110 corresponding to thetube110 except that, in place of theopening118 and theplug140, thetube1110 has an integrally formed, hermeticallysealed end portion1117.Sensor electronics1120 corresponding to thesensor electronics120 are disposed in thetube chamber1112.Epoxy potting material1130 corresponding to the epoxy130 is also disposed in thechamber112 and surrounds theIC1124, a portion or all of theantenna portion1122 and thejuncture1121 between theportions1124 and1122. The cured epoxy1130 mechanically stabilizes theportions1124 and1122. A remaining portion of theantenna portion1122 is disposed in a gas-filledportion1104 of thechamber1112 between the epoxy1130 and an end of thetube1110. Ananti-migration coating1150 corresponding to thecoating150 coats (preferably, fully) the outer surface of thetube1110.
• The[0103]sensor unit1100 may be formed in the following manner. Thetube1110 is initially open on its upper end (i.e., has a shape corresponding to that of the tube110). A selected volume of the uncured epoxy is injected into the tube. Thesensor electronics1120 are placed into the epoxy in thetube1110. The amount of epoxy injected into the tube is sufficient to cover theIC1124 and at least thejunction1121. The epoxy is then cured. The open end of thetube1110 is flame or laser welded to form theclosed end portion1117. In this manner, thetube1110 is hermetically sealed. Theanti-migration coating1150 is applied to the outer surface of the hermetically sealedtube1110, preferably using a VDP technique as discussed above with regard to the formation of thesensor unit100.
• With reference to FIG. 26, a[0104]sensor unit1200 according to further embodiments of the invention is shown therein. Thesensor unit1200 corresponds to thesensor unit100 except that theanti-migration coating150 is replaced with ananti-migration mesh layer1250 surrounding a portion (as shown) or all of thetube1210. Themesh layer1250 is preferably a sleeve as shown. Themesh layer1250 may be secured to thetube1210 by a medical grade adhesive or by tying or fusing at one end or both ends. Themesh layer1250 may be used in place of any of the anti-migration coatings of the above-described embodiments.
• According to some embodiments, the[0105]mesh layer1250 is formed of a non-biodegradable polymer; however, a biodegradable polymer may be used. More preferably, themesh layer1250 is formed of non-biodegradable polypropylene. The mesh layer may be a textile material or fabric. Alternatively, the mesh layer may be extruded and stamped with the pores, molded with the pores, or molded and then stamped. Suitable polypropylene meshes include Prolene™ polypropylene mesh available from Ethicon, Inc. The pore size of themesh layer1250 should be selected to allow tissue in-growth. Preferably, the pore size is greater than 25 microns.
• With reference to FIGS. 27 and 28, an[0106]implantable sensor unit1300 according to further embodiments of the invention is shown therein. Thesensor unit1300 corresponds to thesensor unit1100 except that theanti-migration coating1150 is replaced with an anti-migration layer orsleeve1350 formed of a textile material surrounding a portion or all (as shown) of thetube1310. For clarity, only the tube1310 (which corresponds to the tube1110) and theanti-migration layer1350 are shown in FIG. 28.
• While a single piece housing including the[0107]tube1310 fused closed at one end is illustrated, housings including both a tube (e.g., the tube110) and a plug (e.g., the plug140) may be used instead. As in the other described embodiments, the housing is preferably a hermetically sealed glass housing or capsule.
• According to some embodiments, the[0108]anti-migration layer1350 shown in FIGS. 27 and 28 is a sleeve. The sleeve may substantially conform to and fit snugly against thetube1310. Theanti-migration layer1350 may include a pair of holdingtabs1352 extending from either end of thesensor unit1300 and beyond the adjacent ends1314,1316 of thetube1310. Alternatively, the sensor unit may have only oneholding tab1352. According to some embodiments, theanti-migration layer1350 substantially fully envelops the housing. The ends1354 of the sleeve-shapedanti-migration layer1350 can be fused or otherwise closed to reliably capture and maintain thetube1310 within theanti-migration layer1350. Alternatively, one or both of the ends of the sleeve (and, thus, the holding tabs where provided) may be left open.
• The[0109]anti-migration layer1350 may be formed of any suitable material. According to some embodiments, theanti-migration layer1350 is a multi-filament textile material. Theanti-migration layer1350 may be formed of a multi-filament suture material. Suitable suture materials may include, but are not limited to, silk, stainless steel, nylon, polyester, polypropylene, surgical gut,polyglactin 910, polyglycolic acid, poliglecaprone 25, polyglyconate, and polydioxanone. According to some embodiments, theanti-migration layer1350 is a braided material. According to some embodiments, theanti-migration layer1350 is preferably formed of polyester filaments.
• According to some embodiments, the[0110]anti-migration layer1350 is formed of filaments that are substantially non-absorbable and non-degradable in a human body. Alternatively, theanti-migration layer1350 may be formed of filaments that are absorbable in a human body, for example, after a period of 2 to 10 weeks.
• According to some embodiments, the[0111]anti-migration layer1350 is substantially free of pores having a size greater than 15 microns. Alternatively, theanti-migration layer1350 may be a mesh defining pores having a pore size of at least 25 microns.
• The holding[0112]tabs1352 preferably each have a length T (FIG. 27) of at least 2 mm. According to some embodiments, the length T of the holding tabs is between about 2 and 10 mm. Preferably, the thickness of eachtab1352 is between about 1 and 5 mm. Preferably, the width U of eachtab1352 is between about 50% and 100% of the outer diameter of thetube1310. According to some embodiments, the holdingtabs1352 are preferably flexible.
• The[0113]sensor unit1300 may be formed by any suitable method and apparatus. According to embodiments of the present invention and with reference to FIG. 29, thesensor unit1300 may be formed using anapparatus1370. Theapparatus1370 includes abraiding station1372 and a pair of spaced apart cutting/fusingstations1374. The sealedtube1310 with the desired electronics disposed therein, is fed through thebraiding station1372. As thetube1310 passes through thebraiding station1372, a plurality offilaments1351 are braided about thetube1310 to form a continuous, braidedsleeve1350A of textile material about thetube1310. Thebraiding station1372 may include a suitably modified braiding apparatus of the type used to form braided suture material.
• In operation, the[0114]sleeve1350A can be cut and fused closed on either side of thetube1310 by the cutting/fusingstations1374 after or as thetube1310 and thesleeve1350A exit the braiding station, thereby forming thesleeve1350 about thetube1310. An appropriate amount of thesleeve1350A is left on each end of thetube1310 to form the holdingtabs1352. As an alternative or in addition to fusing the ends of thesleeve1350 closed, the ends of thesleeve1350 may be tied, glued or otherwise closed. A single cutting/fusing station may also be used to serially cut and fuse the opposing ends of the sleeve as the tube is fed through the apparatus.
• According to further embodiments of the present invention and with reference to FIG. 30, the[0115]sensor unit1300 may be formed using anapparatus1380. Theapparatus1380 has abraiding station1382 and cutting/fusingstations1384 and corresponds to theapparatus1370 except for the further provision of amandrel1386. Thebraiding station1382 forms thecontinuous braided sleeve1350A of textile material on themandrel1386 rather than on thetube1310. As thesleeve1350A is generated as a continuous tubular sleeve from the braiding station, it passes downstream over thetube1310. Thesleeve1350A is then cut and fused closed on either side of thetube1310 by the cutting/fusingstations1384 in the same manner as discussed above.
• According to alternative method embodiments, the[0116]sleeve1350A may be cut to length and then pulled over thetube1310, rather than sliding the sleeve onto thetube1310 from themandrel1386 before cutting.
• The holding[0117]tabs1352 may be used to facilitate handling of thesensor unit1300. The holdingtabs1352 may be grasped, hooked, adhered to or otherwise held to allow transport, positioning and/or repositioning of the sensor unit. It is particularly contemplated that the holdingtabs1352 may be used to handle thesensor unit1300 while performing surgical procedures (i.e., intraoperatively). The holding tabs may be used to position thesensor unit1300 in the body during open surgery or using an instrument or insertion tool1390 (e.g., an endoscope) through acanula1392 as shown in FIG. 31. The holdingtabs1352 may be used to hold and manipulate thesensor unit1300 during laparoscopic surgery or similar surgeries using hollow canulas, for example.
• The holding[0118]tabs1352 may also be used to secure thesensor unit1300 to a desired substrate temporarily or indefinitely. For example, thesensor unit1300 may be secured to the substrate (such as tissue) using one or more sutures, staples or the like extending through the holding tab ortabs1352. FIG. 32 shows thesensor unit1300 implanted in a body Z and secured to tissue Z1 of the body Z by asuture1394 that extends through theholding tab1352 and the tissue Z1.
• One or both of the holding[0119]tabs1352 may be omitted. The holdingtabs1352 may be formed of a material other than a textile material. The holding tabs may be otherwise secured to the sensor housing. For example, the holding tabs may be fastened or adhered to the sensor housing, or may be integrally formed with or embedded in the sensor housing. The sensor units100-1200 described above may be modified to include one or more holding tabs as described herein.
• With reference to FIGS. 33 and 34, in accordance with method embodiments of the present invention, an[0120]implantable sensor unit1400 is used in animaging system1490 to facilitate an imaging procedure such as a radiographic scan. Non-X-ray imaging procedures may also be used such as ultrasound or MRI. The implantedsensor unit1400 is capable of emitting a signal (e.g., wirelessly or via wiring) for communication with areceiver unit1494 located outside of a body Z. At least a portion of thesensor unit1400 can be formed of a material that is highly detectable to asensing apparatus1492, such a planar film (X-ray) machine, a computer tomography machine or other radiographic sensing apparatus. For example, thesensor unit1400 may include a sufficient amount of a radiopaque material to be imaged during normal imaging procedures. Suitable radiopaque materials may include ferrite material or radiopaque epoxies, coatings, inks, thin-films, paints, tapes, strips, and the like. Thesensor unit1400 may be an implantable sensor unit as described above in accordance with various embodiments of the present invention.
• The[0121]sensor unit1400 can be inserted and positioned in the body Z by any suitable means (Block1401; FIG. 34). The body Z is then scanned, for example, in conventional manner, using the sensing apparatus1492 (Block1403). Thesensor unit1400 is highly visible on the scan results, thereby serving as a fiducial marker. For example, where thesensor unit1400 is radiopaque and thesensing apparatus1492 is a radiographic sensing apparatus, thesensor unit1400 blocks the transmission of X-rays to provide a contrasting image. The opacity, degree of contrast, and sharpness of the image may vary with the material and type of process used to create thesensor unit1400. Additionally, thesensor unit1400 serves to provide information as discussed above via communication with the receiver unit1494 (Block1403). One or moreadditional sensor units1400 may be implanted and used as fiducial markers and/or information providers.
• With reference to FIG. 35, an[0122]implantable sensor unit1500 according to further embodiments of the present invention is shown therein. Thesensor unit1500 corresponds to thesensor unit1100 except that theanti-migration coating1150 is replaced with a bio-compatible anti-migration layer ortube1550 formed of a heat shrinkable thermoplastic material surrounding a portion or all (as shown) of the tube1510 (which corresponds to the tube1110).
• The[0123]layer1550 is preferably formed of a heat shrinkable thermoplastic resin. According to some embodiments, thelayer1550 preferably has a thickness V of between about 1 and 3 mm. Thelayer1550 may be free of apertures or may have one or more holes punched or otherwise formed therein.
• The[0124]layer1550 may be installed on thetube1510 in the following manner. A tube of the heat shrinkable material is placed about the sealedtube1510. The tube of heat shrinkable material is then heated, using a suitable heating device, to a temperature sufficient to shrink the material. The tube of heat shrinkable material contracts to fit snugly and securely about thetube1510, thereby forming theanti-migration layer1550.
• If desired, one or both of the ends of the tube of heat shrinkable material may be closed (e.g., by fusing) or left open. The[0125]layer1550 may be formed so as to include one or more holding tabs corresponding to the holdingtabs1352.
• Following formation, each of the above-described sensor units is preferably subjected to a leak test to confirm that a proper hermetic seal has been achieved. The sensor units may be evaluated using a helium mass spectrometer leak detection test. Those sensor units which have leak rates exceeding a selected maximum leak rate may be discarded. Preferably, the hermetic seal provided by each hermetically sealed sensor unit is such that under a helium mass spectrometer leak detection test in accordance with Military Standard 202F, Test Condition C, the measured leak rate is less than about 1×10[0126]⁻⁸atm-cc/s.
• Each of the sensor units according to the present invention preferably has an overall length of no more than 27 mm and an overall maximum outer diameter of no more than 3.5 mm.[0127]
• The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.[0128]

Claims (75)

That which is claimed is:

1. An in vivo implantable sensor unit comprising:

a) a glass sensor housing defining an elongated chamber; and

b) sensor electronics disposed in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data;

c) wherein the sensor unit is configured to wirelessly transmit data from an in vivo position to a remote receiver over a period of at least four weeks and the sensor housing is adapted to provide a hermetic seal about the sensor electronics for a period of at least four weeks, wherein the hermetic seal is such that under a helium mass spectrometer leak detection test the sensor housing has a leak rate that is less than about 10⁻⁸atm-cc/s.

2. The sensor unit ofclaim 1 wherein the sensor electronics include a first portion and a second portion joined to the first portion at a junction, the sensor unit further including an epoxy disposed in the chamber and surrounding the junction, wherein the epoxy mechanically stabilizes the first and second portions.

3. The sensor unit ofclaim 2 wherein the sensor housing has a length of no more than 27 mm and an outer diameter of no more than 3.5 mm.

4. An implantable sensor unit comprising:

a) a tube defining a chamber and an opening communicating with the chamber;

b) sensor electronics disposed in the chamber;

c) epoxy disposed in the chamber and surrounding the sensor electronics, the epoxy having an end surface adjacent the opening of the tube; and

d) an end plug mounted in the opening of the tube;

e) wherein the end surface of the epoxy and the end plug define a gap therebetween configured to insulate the sensor electronics.

5. An implantable sensor unit comprising:

a) a tube defining an elongated chamber and an opening communicating with the chamber;

b) sensor electronics disposed in the chamber; and

c) an end plug mounted in the opening of the tube, wherein the end plug is spherically shaped.

6. The sensor ofclaim 5 including epoxy disposed in the chamber and surrounding the sensor electronics, the epoxy having an end surface adjacent the opening of the tube, and wherein the end surface of the epoxy and the end plug define a gap therebetween configured to insulate the sensor electronics.

7. An implantable sensor unit comprising:

a) a tube defining a chamber and an opening communicating with the chamber;

b) sensor electronics disposed in the chamber;

c) epoxy disposed in the chamber and surrounding the sensor electronics, the epoxy having an end surface adjacent the opening of the tube; and

d) a retaining cap including at least one projection extending outwardly from the tube;

e) wherein the retaining cap is secured to the tube by the epoxy.

8. The sensor unit ofclaim 7 configured such that the at least one projection will expand outwardly from the tube when exposed to at least one of heat and moisture.

9. The sensor unit ofclaim 7 including a bio-compatible anti-migration coating disposed on an outer surface of the tube.

10. The sensor unit ofclaim 7 including an anti-migration mesh layer disposed on an outer surface of the tube.

11. An implantable sensor unit comprising:

a) a sensor housing defining an elongated chamber;

b) sensor electronics disposed in the chamber; and

c) a retention device mounted on the sensor housing, the retention device including a band surrounding a portion of the sensor housing and at least one projection secured to and extending from the band.

12. The sensor unit ofclaim 11 wherein the band is formed of an elastomeric material.

13. An implantable sensor unit comprising:

a) a sensor housing having an outer surface and defining a chamber;

b) sensor electronics disposed in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data; and

c) a bio-compatible anti-migration coating disposed on the outer surface, wherein the anti-migration coating is a Parylene C coating.

14. The sensor unit ofclaim 13 wherein the sensor housing is formed of glass.

15. The sensor unit ofclaim 13 wherein the Parylene C coating has a thickness of between about 10,000 and 60,000 Angstroms.

16. An implantable sensor unit comprising:

a) a sensor housing having an outer surface and defining a chamber; and

b) a bio-compatible anti-migration mesh layer disposed on the outer surface.

17. The sensor unit ofclaim 16 wherein the sensor housing is formed of glass.

18. The sensor unit ofclaim 16 wherein the mesh layer is formed of polypropylene.

19. A method for forming a sensor unit, the method comprising the steps of:

a) inserting an uncured epoxy into a tube in a fluid state;

b) inserting sensor electronics into the uncured epoxy in the tube;

c) evacuating air bubbles from the epoxy and the sensor electronics in the tube; and then

d) curing the epoxy.

20. The method ofclaim 19 including the step of mounting and sealing a closure member onto the tube.

21. The method ofclaim 19 including the step of laser sealing an open end of the tube.

22. A method for forming a sensor unit, the method comprising the steps of:

a) inserting an uncured epoxy in a fluid state into a tube through an opening in the tube;

b) inserting sensor electronics into the uncured epoxy;

c) curing the epoxy such that the epoxy stabilizes the sensor electronics; and

d) sealing the opening in the tube to form a hermetically sealed tube.

23. The method ofclaim 22 wherein the step of sealing the opening in the tube includes at least one of flame sealing and laser sealing the tube.

24. The method ofclaim 22 including the step of applying a bio-compatible anti-migration coating to an outer surface of the tube using a plasma polymerization thin film deposition technique.

25. The method ofclaim 22 including the step of applying a bio-compatible anti-migration coating to an outer surface of the tube using vapor deposition polymerization.

26. The method ofclaim 22 including applying an anti-migration mesh layer to an outer surface of the tube.

27. A method for forming a sensor unit, the method comprising the steps of:

a) providing a sensor housing having an outer surface and defining a chamber;

b) providing sensor electronics in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data; and

c) applying a bio-compatible anti-migration coating to the outer surface of the sensor housing using a plasma polymerization thin film deposition technique.

28. The method ofclaim 27 wherein the sensor housing is formed of glass.

29. The method ofclaim 27 wherein the anti-migration coating has a thickness of between about 4,000 and 60,000 Angstroms.

30. The method ofclaim 27 wherein the anti-migration coating is a polypropylene thin film.

31. A method for forming a sensor unit, the method comprising the step of:

a) providing a sensor housing having an outer surface and defining a chamber;

b) providing sensor electronics in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data; and

c) applying a bio-compatible anti-migration coating to the outer surface of the sensor housing, wherein the anti-migration coating is a Parylene C coating.

32. The method ofclaim 31 wherein the Parylene C coating has a thickness of between about 10,000 and 60,000 Angstroms.

33. The method ofclaim 31 including using vapor deposition polymerization to apply the anti-migration coating to the outer surface of the sensor housing.

34. A method for forming a sensor unit, the method comprising the step of:

applying a bio-compatible anti-migration mesh layer to an outer surface of a sensor housing.

35. An implantable sensor unit comprising:

a) a sensor housing having an outer surface; and

b) a bio-compatible anti-migration layer surrounding at least a portion of the outer surface of the sensor housing;

c) wherein the anti-migration layer is formed of a textile material.

36. The sensor unit ofclaim 35 wherein the sensor housing is formed of glass.

37. The sensor unit ofclaim 35 wherein the anti-migration layer is a flexible sleeve.

38. The sensor unit ofclaim 37 wherein the sleeve substantially fully envelops the sensor housing.

39. The sensor unit ofclaim 35 wherein the anti-migration layer comprises a multi-filament textile material.

40. The sensor unit ofclaim 39 wherein the anti-migration layer comprises a multi-filament suture material.

41. The sensor unit ofclaim 39 wherein the anti-migration layer comprises a braided material.

42. The sensor unit ofclaim 39 wherein the anti-migration layer comprises polyester filaments.

43. The sensor unit ofclaim 35 wherein the textile material is substantially non-absorbable and non-degradable in a human body.

44. The sensor unit ofclaim 35 wherein the textile material is absorbable in a human body.

45. The sensor unit ofclaim 35 wherein the anti-migration layer is substantially free of pores having a size greater than 15 microns.

46. The sensor unit ofclaim 35 wherein the anti-migration layer is a mesh having a pore size of at least 25 microns.

47. The sensor unit ofclaim 35 wherein the anti-migration layer includes a holding tab extending beyond an end of the housing.

48. A method for forming an implantable sensor unit, the method comprising:

a) providing a sensor housing; and

b) placing a bio-compatible anti-migration layer over the outer surface of the sensor housing, the anti-migration layer being formed of a textile material.

49. The method ofclaim 48 including forming the anti-migration layer from a multi-filament textile material.

50. The method ofclaim 48 including forming the anti-migration layer from a multi-filament suture material.

51. The method ofclaim 48 including forming the anti-migration layer as a sleeve.

52. The method ofclaim 51 including closing an open end of the sleeve to secure the sleeve about the sensor housing.

53. The method ofclaim 51 including forming the sleeve directly on the outer surface of the sensor housing using a plurality of filaments.

54. The method ofclaim 53 wherein the step of forming the sleeve directly on the outer surface of the housing includes braiding the plurality of filaments about the sensor housing.

55. The method ofclaim 51 including:

a) forming the sleeve on a mandrel using a plurality of filaments; and thereafter

b) mounting the sleeve on the sensor housing.

56. The method ofclaim 55 wherein the step of mounting the sleeve on the sensor housing is executed directly after forming the sleeve on a mandrel.

57. The method ofclaim 55 wherein the step of forming the sleeve on the mandrel includes braiding the plurality of filaments about the mandrel.

58. The method ofclaim 48 including forming a holding tab on the anti-migration layer and mounting the anti-migration layer on the sensor housing such that the holding tab extends beyond an end of the sensor housing.

59. The method ofclaim 58 including:

a) forming the anti-migration layer as a sleeve; and

b) closing an end of the sleeve to form the holding tab.

60. An implantable sensor unit comprising:

a) a sensor housing having an end and defining a chamber;

b) sensor electronics disposed in the chamber; and

c) a holding tab extending from the end of the housing, the holding tab being adapted to facilitate handling of the housing.

61. The sensor unit ofclaim 60 wherein the sensor housing is formed of glass.

62. The sensor unit ofclaim 60 wherein the holding tab is flexible.

63. The sensor unit ofclaim 62 wherein the holding tab is formed of a textile material.

64. The sensor unit ofclaim 60 wherein the holding tab has a length of between about 2 and 10 mm.

65. The sensor unit ofclaim 60 including a sleeve surrounding at least a portion of the sensor housing, wherein the holding tab is integral with the sleeve.

66. The sensor unit ofclaim 65 wherein the sleeve and the holding tab are formed of a textile material.

67. A method for implanting an implantable sensor unit in a body, the sensor unit including a sensor housing, the method comprising:

handling the sensor housing in the body using a holding tab extending from an end of the housing.

68. The method ofclaim 67 wherein the step of handling the sensor housing includes moving the sensor unit within the body while performing a surgical procedure.

69. The method ofclaim 68 wherein the step of handling the sensor housing includes moving the sensor unit within the body using an insertion tool.

70. The method ofclaim 68 wherein the step of handling the sensor housing includes moving the sensor unit within the body during an open surgical procedure.

71. The method ofclaim 67 including securing the holding tab to tissue of the body to thereby secure the implantable sensor unit.

72. A method for using an implantable sensor unit in a body, the method comprising:

a) implanting the sensor unit in the body;

b) conducting an imaging procedure on the body such that the sensor unit in the body serves as a fiducial marker;

c) detecting a parameter using the sensor unit in the body; and

d) transmitting data associated with the detected parameter from the sensor unit to a remote receiver unit.

73. The method ofclaim 72 wherein the imaging procedure includes a radiographic imaging procedure and at least a portion of the sensor unit is radiopaque.

74. An implantable sensor unit comprising:

a) a sensor housing having an outer surface; and

b) a bio-compatible anti-migration layer surrounding at least a portion of the outer surface of the sensor housing;

c) wherein the anti-migration layer is formed of a heat shrinkable thermoplastic material.

75. A method for forming a sensor unit, the method comprising the step of:

a) providing a sensor housing having an outer surface and defining a chamber;

b) providing sensor electronics in the chamber, wherein the sensor electronics are adapted to wirelessly transmit data;

c) placing a bio-compatible anti-migration layer about the sensor housing, wherein the anti-migration layer is formed of a heat shrinkable thermoplastic material; and

d) heating the anti-migration layer to shrink the anti-migration layer about the sensor housing.

Images