Abstract:
The present invention provides an imaging probe for imaging mammalian tissues and structures using high resolution imaging, including ultrasound and optical coherence tomography. The imaging probe uses electrostatic discharge for actuating a metalized cantilever which holds the end portion of imaging assembly which emits energy in the imaging probe device by holding the cantilever at a potential such that it is neither grounded or charged such that the only electrical path to ground is through a dissipative polymer forming part of the device which is enveloped by a wire or coil held at ground potential. A high voltage electrode attracts the metalized cantilever and the dissipative polymer is used to connect to the cantilever to ground causing the cantilever to move about thereby scanning the region in front of the probe.

Description:
CROSS REFERENCE TO RELATED U.S. APPLICATION 
     This patent application relates to, and claims the priority benefit from, U.S. Provisional Patent Application Ser. No. 60/881,169 filed on Jan. 19, 2007, in English, entitled IMAGING PROBE, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of imaging mammalian tissues and structures using high resolution imaging, including high frequency ultrasound and optical coherence tomography using electrostatic forces to generate motion of a scanning mechanism which is coupled to ground through a dissipative polymer to thereby scan regions of interest. 
     BACKGROUND OF THE INVENTION 
     Forward looking imaging devices for viewing small (1-20 mm) lumens, orifices, and cavities of the body remain a difficult engineering challenge. In many instances, the forward looking imaging geometry is, however, more amenable to providing interventional guidance than convention side-viewing probes. In order to address this challenge we present the use of an electrostatic probe that uses a dissipative polymer to indirectly couple a cantilever to a ground potential. 
     Boppart et al. (U.S. Pat. No. 6,485,413) describes the use of an electrostatic-based actuator for forward-viewing optical coherence tomography. The Boppart patent discloses a device in which the cantilever is directly connected to ground or enabled with an electrostatic slide. This direct connection to ground of the cantilever is problematic resulting in significant electrostatic discharge given the high voltage necessary to oscillate a rigid fiber. 
     Other forward-viewing catheter patents of note are Park et al. (U.S. Pat. No. 7,115,092) which describes a forward looking device scanned using shape memory alloys. Liang and Hu (U.S. Pat. Nos. 5,651,366 and 5,606,975 respectively) describe various forward looking ultrasound imaging devices in which ultrasound energy is directed in a forward direction by mechanically moved mirrors. 
     Couvillon et al. (U.S. Pat. No. 7,077,808) also describe forward viewing ultrasound imaging devices where in the scanning mechanism is an electroactively driven polymer. 
     It would be very advantageous to provide an imaging device having a scanning mechanism which avoids significant electrostatic discharge. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel imaging probe for ultrasound or optical coherence tomography (OCT) which uses an electrostatic means for actuating a metalized cantilever (which holds the end portion of imaging system which emits energy) in an imaging probe device by holding the metalized cantilever at a potential such that it is neither grounded or charged such that the only electrical path to ground is through a dissipative polymer forming part of the device which is enveloped by a wire or coil held at ground potential. A high voltage electrode attracts the metalized cantilever and the dissipative polymer is used to connect to the cantilever to ground. 
     The scanning cantilever coupled to an imaging system coupled to the scanning cantilever may be configured for optical coherence tomography, ultrasonic imaging, or confocal imaging. 
     Tuning the oscillation frequency of the cantilever may be provided by varying the degree to which the dissipative polymer is coupled to ground potential. The oscillation frequency of the cantilever may be varied by increasing or decreasing the driving voltage used to attract the cantilever. 
     An electrostatic peak voltage obtained by measuring the voltage in the grounding wire wrapped around the dissipative polymer catheter may be used as a triggering means. 
     Thus, in one embodiment of the present invention there is provided an electrostatically driven imaging probe, comprising:
         a) an elongate hollow catheter sheath having distal front and back sections and an elongate proximal section and having a diameter suitable to permit insertion of the elongate hollow catheter sheath into bodily lumens and cavities, the distal back section containing an electrically dissipative polymer sealed therein which is wrapped by a metal coil for connection to ground potential and a timing circuit;   b) imaging means located in said distal front section for emitting energy and receiving energy reflected back from interior surfaces of said bodily lumens and cavities, said distal front section containing one of a medium and vacuum sealed therein which allows transmission of imaging energy emitted by the imaging means, said imaging means being connected to an imaging conduit which extends through a proximal end of the elongate hollow catheter sheath for connection to an image processing and display system, said imaging conduit being enveloped by metal and a portion of the metal enveloped imaging conduit in the distal front section forming a cantilever; and   c) an elongate electrode located in the elongate hollow catheter sheath having an elongate uninsulated electrode section located in said front distal section, the elongate electrode being connected to a high voltage power supply, wherein in operation when a high voltage is applied to the elongate electrode the cantilever is electrically attracted to the elongate uninsulated electrode section and undergoes deflection towards the elongate uninsulated electrode section and upon contacting the elongate uninsulated electrode section the portion of the metal enveloped imaging conduit in the distal front section acquires an electrical charge from the elongate uninsulated electrode section thereby causing the metal enveloped imaging conduit in the distal front section to be repelled therefrom thereby causing the imaging means to scan the field of view.       

     Another embodiment of the present invention provides an electrostatically driven imaging probe, comprising: 
     a) an elongate hollow catheter sheath having distal front and back sections and an elongate proximal section and having a diameter suitable to permit insertion of the elongate hollow catheter sheath into bodily lumens and cavities, the distal back section containing an electrically dissipative polymer sealed therein which is wrapped by a metal coil which is connected to ground potential and a timing circuit; 
     b) imaging means located in said distal front section for emitting energy and receiving energy reflected back from interior surfaces of said bodily lumens and cavities, said distal front section containing one of a medium and vacuum sealed therein which is transparent to said energy emitted by the imaging means, said imaging means being connected to an imaging conduit which extends through a proximal end of the elongate hollow catheter sheath for connection to an image processing and display system; 
     c) a conductive, reflective disc pivotally mounted about a pivot axis in said front distal section and electrically coupled to said electrically dissipative polymer, said reflective member being positioned to receive and reflect said energy from said imaging means, and to receive and reflect said energy reflected back from interior surfaces of said bodily lumens and cavities back to said imaging means; 
     d) a ground electrode having an uninsulated section located in said distal front section connected to said electrical ground potential; and 
     e) an elongate electrode located in the elongate hollow catheter sheath having an elongate uninsulated electrode section located in said front distal section, the elongate electrode being connected to a high voltage power supply, wherein in operation when a high voltage is applied to the elongate electrode the conductive, reflective disc is electrically attracted to the elongate uninsulated electrode section causing said conductive, reflective disc to pivot about said pivot axis in one direction causing an outer edge off said conductive, reflective disc to tilt towards said elongate electrode and upon contact with said elongate electrode said conductive, reflective disc acquires charge from said elongate electrode causing it to be repelled thereby resulting in the conductive, reflective disc to pivot towards said ground electrode, and upon contact of said conductive, reflective disk with said ground electrode the conductive, reflective disk loses its charge resulting in its ability to once again be attracted to said electrode. 
     A further understanding of the functional and advantageous aspects of the invention can be realized by reference to the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which: 
         FIG. 1A  is a schematic of an imaging system including ultrasound and optical imaging components; 
         FIG. 1B  is a cross sectional view of an embodiment of a forward looking ultrasound or OCT imaging probe using an electrode and a dissipative polymer catheter; 
         FIG. 2  is a cross sectional view of the probe of  FIG. 1B  taken along line  2 - 2 ; 
         FIGS. 3 to 6  are cross sectional views similar to  FIG. 1B  illustrating a time sequence during operation in which an optical or acoustic signal emitter is displaced; 
         FIG. 7  is a cross sectional view of another embodiment of an imaging probe configured for use as an optical probe in which the focusing element includes a GRIN lens; 
         FIG. 8  is a cross sectional view of another embodiment of an imaging probe configured for use as an optical probe in which the focusing element is a ball lens on the optical fiber; 
         FIG. 9  is a cross sectional view of another embodiment of an imaging probe configured for use as an ultrasound probe having an ultrasound transducer mounted on the end of a microcoaxial cable; 
         FIG. 10  is a cross sectional view of another embodiment of an imaging probe in which two wires are used with one wire connected to the inside of the sheath and grounded and the second wire acts as an electrode; 
         FIG. 11  is a is a cross sectional view of another embodiment of an imaging probe in which two wires are used and each wire may be connected to a time varying voltage source or each wire may be alternatively activated and deactivated; 
         FIG. 12  is a sectional view through the diameter of an alternative embodiment of an imaging probe in which four wires arranged at ninety degrees to each other are used to actuate the cantilever; 
         FIG. 13  is a cross sectional view of another embodiment of an imaging probe in which a three lumen dissipative polymer catheter is used in conjunction with a fiber optic with an affixed ball lens; 
         FIG. 14  is a cross sectional view of another embodiment of an imaging probe in which a three lumen catheter is combined with a fiber optic that is scanned proximally to a GRIN lens; 
         FIG. 15  shows a similar embodiment to  FIG. 14  with the exception that the coupling to ground is instead provided by an exposed wire within one of the lumens; 
         FIG. 16  is a cross-section view of the probe shown in  FIG. 15  taken along the line  16 - 16 ; 
         FIG. 17  is a cross sectional view of another embodiment of an imaging probe in which an electrode with a ring element is fitted over the dissipative polymer catheter to provide a ground; 
         FIG. 18  is a cross section view of the probe shown in  FIG. 17  along the line  18 - 18 ; 
         FIG. 19  is a cross section view of the probe shown in  FIG. 17  along the line  19 - 19 ; 
         FIG. 20  is a cross sectional view of another embodiment of an imaging probe in which a three lumen dissipative polymer catheter is employed with a forward directed ultrasound transducer; 
         FIG. 21  is a cross sectional view of another embodiment of an imaging probe in which a three lumen dissipative polymer catheter is employed with a side directed ultrasound transducer that is coupled to a prism or mirror to redirect the ultrasound energy towards the front of the probe; 
         FIG. 22  is a photograph of an embodiment of the scanning probe in motion; 
         FIG. 23  is a graph of the frequency of oscillation of the cantilever as a function of driving voltage applied for motion in two different media: oil (shown with diamonds) and air (shown with circles); 
         FIGS. 24A-24C  show examples of optical coherence tomography images acquired using an embodiment of the probe with a ball lens; 
         FIG. 24A  shows an optical coherence tomography image of a nearly occluded piece of tubing; 
         FIG. 24B  shows a white light photograph of the nearly occluded piece of tubing; 
         FIG. 24C  shows an optical coherence tomography image of a piece of excised rabbit colon; 
         FIG. 24D  shows a white light image of a piece of excised rabbit colon; 
         FIGS. 25A and 25  B show an in vivo optical coherence tomography of a tadpole heart taken with an embodiment of the imaging probe in which a fiber was scanned proximal to a GRIN lens; 
         FIG. 25A  shows a structural image of the tadpole heart; 
         FIG. 25B  shows a Doppler flow map of the tadpole heart; 
         FIG. 26  shows a plot of the vertical displacement of the tip of cantilever as function of time for a driving voltage of 2100 V in oil; 
         FIGS. 27A and 27B  compare optical coherence tomography images taken using two different embodiments of the probe of an IR detection card; 
         FIG. 27A  shows a sector image taken with an embodiment that scans a ball lens; 
         FIG. 27B  shows a sector image taken with an embodiment of the probe in which a cleaved fiber is scanned proximal to a GRIN lens; 
         FIG. 28  is an alternative embodiment that shows the ground conductor withdrawn inside a three lumen catheter; 
         FIG. 29  is an embodiment of the imaging probe in which a mirror is scanned inside the catheter; 
         FIG. 30  is a cross section of  FIG. 29  along the line  30 - 30 ; 
         FIG. 31  is a cross section of  FIG. 29  along the line  31 - 31 ; and 
         FIG. 32  is a cross section of  FIG. 29  along the line  32 - 32 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Generally speaking, the systems described herein are directed to an imaging probe using either optical or ultrasonic (or both) imaging. As required, embodiments of the present invention are disclosed herein. However, the disclosed embodiments are merely exemplary, and it should be understood that the invention may be embodied in many various and alternative forms. The Figures are not to scale and some features may be exaggerated or minimized to show details of particular elements while related elements may have been eliminated to prevent obscuring novel aspects. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention. For purposes of teaching and not limitation, the illustrated embodiments are directed to an imaging probe. 
     As used herein, the terms “about”, and “approximately” when used in conjunction with ranges of dimensions, temperatures or other physical properties or characteristics is meant to cover slight variations that may exist in the upper and lower limits of the ranges of dimensions so as to not exclude embodiments where on average most of the dimensions are satisfied but where statistically dimensions may exist outside this region. For example, in embodiments of the present invention dimensions of components of the imaging probe are given but it will be understood that these are not meant to be limiting. 
     Generally, in the several embodiments of the present invention that enable forward looking imaging with a cantilever based imaging assembly; the principal of electrostatic dissipative polymers is used advantageously in order to create an oscillatory motion and/or to prevent electrostatic discharge. While direct connection of the cantilever to an electrical field such that the cantilever is held at ground/potential and an electrode within the catheter is held at a potential/ground, will cause motion of the cantilever as described in prior art, the present invention describes herein a configuration which includes coupling of the cantilever to a dissipative polymer. As discussed hereinafter, it is possible to cause the cantilever to move continuously in an oscillatory motion with the application of a high constant voltage, low current field when coupling a dissipative polymer between a metalized cantilever and the ground potential. The use of the probe with two electrodes in which motion is driven by turning individual electrodes either on or off or driven by providing different driving signals to each electrode is also described. In these cases the use of a dissipative polymer eliminates the direct connection to ground potential and hence limits the chance of electrical discharge. 
     The embodiments shown in  FIGS. 1B to 21  and  28  use electrostatic actuation in order to move a cantilever.  FIG. 29 to 32  describe an embodiment in which electrostatic actuation is used to move a reflecting disk. In all the drawings the source of the field is marked as “HV”. A high voltage power source with a low current (3 to 100 microamperes) has been used in the embodiments described hereinafter. However, those skilled in the art will understand that a high voltage amplifier may be used with a function generator as well as high voltage, high current sources. 
       FIG. 1A  represents an overview of an exemplary imaging system constructed in accordance with the present invention shown generally at  10 . It comprises an electrostatically driven imaging probe  200 , which connects via an adapter  14  to an image processing and display system  16 . The image processing and display system  16  comprises the necessary hardware to support one or more of the following imaging modalities: 1) ultrasound, 2) optical coherence tomography, 3) angioscopy, 4) infrared imaging, 5) near infrared imaging, 6) Raman spectroscopy-based imaging and 7) fluorescence imaging. 
     The system herein described further typically comprises a controller and processing unit  18  to facilitate the coordinated activity of the many functional units of the system, and may further comprise a display and/or user interface and may further comprise electrode sensors to acquire electrocardiogram signals from the body of the patient being imaged. The electrocardiogram signals may be used to time the acquisition of imaging data in situations where cardiac motion may have an impact on image quality. 
     The optical circuits and electronics forming image processing and display system  16 , if included in a particular implementation of the present invention, may include any or all of the following components: interferometer components, one or more optical reference arms, optical multiplexors, optical demultiplexors, light sources, photodetectors, spectrometers, polarization filters, polarization controllers, timing circuitry, analog to digital converters and other components known to facilitate any of the optical imaging techniques described in the background and prior art sections. The ultrasound circuitry  20  may include any or all of the following components: pulse generators, electronic filters, analog to digital converters, parallel processing arrays, envelope detection, amplifiers including time gain compensation amplifiers and other components known to facilitate any of the acoustic imaging techniques described in the background and prior art sections. 
     The controller and processing units  18 , if included in a particular implementation of the present invention, serve multiple purposes and the components would be markedly adapted based on the needs of a particular imaging system. It could include one or a combination of motor drive controller, data storage components (such as memory, hard drives, removable storage devices, readers and recorders for portable storage media such as CDs and DVDs), position sensing circuitry, timing circuitry, cardiac gating functionality, volumetric imaging processors, scan converters and others. A display and user interface  20  is also optionally provided for either real time display or display of data at a time later than the time at which imaging data is acquired. 
     The imaging probe  200  comprises an imaging means  206  in the distal front section, an imaging conduit  204  and a connector  36  at the back of the sheath  202 . The imaging means  206  is located at the distal end of a catheter for the purpose of scanning optical or ultrasonic energy in front of the catheter to examine tissue located either inside or on the surface of the human body. The imaging conduit  204  serves to transfer the information obtained from the scanned beam to either optical circuits and electronics or ultrasound electronics  20  outside of the imaging probe  200 . The imaging probe  200  will be discussed in more detail below, but it may comprise an optical fiber or an ultrasound transducer with associated coaxial cable in the imaging conduit  204 . 
     The adapter  14  facilitates transmission of signals within any fibers and/or wires to the appropriate image processing units. The adapter  14  may also incorporate a pullback mechanism or a reciprocating push-pull mechanism to facilitate longitudinal translation of the imaging assembly. Such longitudinal translation of the imaging assembly may occur in conjunction with the longitudinal translation of an external shaft that surrounds the imaging conduit  204 , or may occur within a relatively stationary external shaft. Additional sensors may be incorporated as part of the adapter  14 , such as position sensing circuitry, for example to sense the angle of rotation of a rotary component within the imaging probe  200 . 
     The imaging probe  200  may also include a memory component such as an EEPROM or other programmable memory device that includes information regarding the imaging probe  200  to the rest of the imaging system. For example, it may include specifications regarding the identification of specifications of the imaging probe  200  and may also include calibration information regarding the probe  200 . 
     Also included in the adaptor  14  is the possibility of a coupling means such as a fiber optic rotary joint and/or an electrical slip ring (not shown) to allow the imaging conduit  204  to be rotated while maintaining structural fidelity. This adaptor  14  may also provide a coupling means to the connector  36  such that a rotational torque may be applied to the imaging probe causing the probe to rotate. 
       FIG. 1B  shows a cross sectional view of an embodiment of the front portion of probe  200  in a forward looking ultrasound or OCT imaging catheter probe using an electrode and a dissipative polymer catheter shown generally at  200 .  FIG. 2  is a cross sectional view of the probe of  FIG. 1B  taken along line  2 - 2  of  FIG. 1B . Referring to  FIGS. 1B and 2 , probe  200  includes an outer sheath  202  which defines a distal front section which contains an imaging means, and a proximal back section. When the probe is configured for OCT, an imaging means  206  comprises an optical fiber (which forms the imaging conduit  204 ) which emits optical radiation from the front end of the optical fiber in the distal front section and the optical fiber is connected to a source of light through the proximal back section. This same optical fiber is capable of collecting the reflection of the emitted optical radiation from the tissue under examination and transfers this radiation to the optical circuits and electronics for detection. In the case where the probe is configured as an ultrasound probe the imaging means is an acoustic transducer located in the distal front section and the imaging conduit is an electrical wire connecting the transducer to a power supply through the proximal back section with a metal coil  205  disposed around the proximal end of the fiber/cable imaging conduit  204 . The proximal back section of the probe  200  includes a volume  210  containing a dissipative polymer which is wrapped by a metal wire or coil  212 . 
     The outer sheath  202  may be any plastic material of dimensions from about 300 to about 100,000 micrometers in diameter with wall thickness on the order of about 30 to about 1000 micrometers. Possible materials include, but are not limited to, PTFE (Teflon), polyethylene, nylon, polyetheretherketone (PEEK), nylon, acrylic (PMMA), polycarbonate (Lexan), polyimide, Latex, polyvinylchloride (PVC), silicone rubber, polyurethane and polyesters. 
     The distal front section of probe  200  includes a media  208 . The media  208  in is transparent or semitransparent to the imaging ultrasound or optical energy. This media may be a gas, vacuum or fluid, such as for example air, as well as where in the media was air with a drop of water on the proximal end of the GRIN lens, and also with low density oils such as olive oil and mineral oil. Additional possibilities include the use of carbon dioxide or helium gas within the catheter sheath which is advantageous due to their high solubility in blood. The media, in the case of fluids, may serve to dampen the oscillatory motion of the cantilever such that slower scanning speeds may be obtained. Potential fluids for use as the media include, but are not limited to, olive oil, mineral oil, silicone oil (of viscosity between about 0.1 to about 400 centipoises) also possible are glycerol, ethanol and distilled water. 
     An adapter ring  214  is located at the front end of the proximal back section containing dissipative polymer in volume  210  between the dissipative polymer and the outer sheath  202  and a high voltage electrode  218  is located beside the section of the imaging conduit  204  wrapped in the coil  205  in the distal front section of probe  200 . The purpose of the adapter ring  214  is to contain the media  208  located in the proximal compartment of the imaging probe. A high voltage power supply  222  is connected to the electrode  218 . A circuit  221  parallel to the grounded metal wire or coil  212  forms a trigger signal monitor  224 . This circuit  221  may possess a resistor to limit the current delivered to the trigger signal monitor  224 . This trigger signal monitor  224  may be connected to an oscilloscope or a data acquisition system for image segmentation. This circuit provides a peak for each time that the cantilever (combined imaging conduit  204 , coil  205  and fiber  204 ) touches the electrode  218  to be discussed hereinafter with the voltage being measured by the oscilloscope or the data acquisition card. 
     The functional purpose of the dissipative polymer in volume  210  of the catheter probe  200  is to allow an indirect electrical connection between ground potential and the cantilever (formed by combined coil  205  and the portion of the optical fiber  204  and/or ultrasound transducer located in the distal front section of probe  200 ). The dissipative polymer in volume  210  provides a finite migration time for the electrical charge to travel from the cantilever  204 / 205 / 206  to ground potential. It is this finite migration time that is used advantageously to provide an oscillatory motion and as well to limit electrostatic discharge within the catheter. 
     Generally, the dissipative polymer is made by either blending an antistatic agent (molecule) with another polymer or it may be made by adding conductive particles to a substantially insulating polymer. 
     A non-limiting example of a dissipative polymer that may be used in volume  210  is Pebax (trade name of Arkema group&#39;s polyether block amide (PEBA) compounds). This compound is also referred to as polyamide/polyether block copolymer. This polymer is a hydrophilic static dissipative polymer and a permanent antistatic polymer that is thermally stable. Its dissipative properties are independent of humidity. This polymer may be blended at 5% to 30% levels with Acrylonitrile butadience styrene (ABS), polycarbonate (PC), ABS/PC, polystyrene (PS), high impact polystyrene (HIPS), polybutylene terephtalate (PBT), acetal, polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene terephtalate glycol (PETG), or polyolefins. 
     Dissipative polymers may also be produced using other antistatic molecules combined with insulating polymers. Examples of additional antistatic agents include: PEDOT:PSS or Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), Glyceryl monostearate, Octadecylbis(2-hydroxyethyl)amine, N,N-Bis(2-hydroxyethyl)dodecanamide, Tallow bis(2-hydroxyethyl)amine, Sodium sec-alkanesulfonate, Cocobis(2-hydroxyethyl)amine, Alkyl(C14-C18)bis(2-hydroxyethyl)amine, Oleylbis(2-hydroxyethyl)amine, Ethoquad T/13-50 Acetate, Ciba® IRGASTAT® P. These antistatic agents may be blended with low density polyethylene (LDPE), high density polyethylene (HDPE), polymethyl methacrylate (PMMA), Polyethylene terephthalate (PET), SAN, polypropylene (PP), polystyrene (PS), polycarbonate (PC) acrylonitrile-butadiene-styrene terpolymer (ABS), styrene acrylonitrile copolymer (SAN) Teflon (PTFE), polyvinyl chloride (PVC), polyethylene terephthalate glycol (PETG) and Nylon (polyamide) to form polymer mixtures. 
     Alternatively, examples of conductive particles that may be potentially added to the above list of insulating polymers include: carbon black, carbon fiber, indium tin oxide (ITO), indium tin oxide doped with an additional metal such as antimony. Stainless steel, copper, gold, silver, tin, and lead may also be added to the above list of polymers in either particulate or fiber form to create a static dissipative effect. 
     The metallic coil  205  around the fiber/cable  204  forming the imaging conduit provides the function of metallizing the imaging conduit  204  as well as shielding the conduit itself from high voltage field. The metallic coil  205  may be a platinum coil of 300 micrometers in diameter. The coil  205  may be of dimensions between about 50 to about 1000 micrometers in diameter. The coil  205  may be comprised of any conductive metal such as, but not limited to, platinum, gold, copper, silver, steel, lead, aluminum and any of their alloys. The metallic coil  205  may also be replaced by a metal coating on the imaging conduit where the metal is comprised of, but not limited to, gold, chrome, brass, copper, or platinum. 
     The metal wire or coil  212  wrapped around the dissipative polymer in volume  210  provides a connection to ground potential through circuit  221 . Wire  212  may be any conductive metallic wire such as, but not limited to, copper, gold, lead, steel, platinum or any of their alloys. Wire  212  may also be fashioned in counter woven strands as described by Crowley et al. (U.S. Pat. No. 5,372,138) such that it would enable a torque applied at the proximal end of the catheter to be transmitted to the end. This cable would, therefore allow an angular rotation produced at one end to be transmitted to the other. Combining this rotation with the scanning of the cantilever would allow the cantilever to scan the two dimensional plane in front of it. Employing optical coherence tomography or ultrasound imaging with this complete two dimensional scan would allow for a three dimensional imaging volume to be obtained. 
     The electrode  218  shown in  FIG. 1B  may be an insulated wire and may be a copper beryllium alloy wire that includes four insulating layers. Additional possibilities include wires of dimensions from about 50 to about 1000 micrometers in diameter comprised of, but not limited to, steel, copper, gold, platinum, silver, iron or any of their alloys. The wire forming electrode  218  may or may not possess a single or a plurality of insulating layers. 
     A seal  220  for the probe located at the most distal end of the distal front section of the probe  200  would be required for use inside in a living organism. This seal  220  acts to seal the media  208  so that it remains within the front section of the probe  200  without being contaminated by fluid from the imaging field inside the patients body being imaged with the probe. The seal  220  would be anywhere from about 10 to about 4000 micrometers thick depending on the intending imaging field of the probe  200 . This seal  220  is preferably made of a material that is transparent to either optical and/or acoustic energy. Potential materials include a wide range of plastics such as but not limited to PTFE (Teflon), polyethylene terephthalate (PET), nylon, polyetheretherketone (PEEK), nylon, Poly(methyl methacrylate) (PMMA), polycarbonate (Lexan), polyimide, Latex, polyvinylchloride (PVC), silicone rubber, polyurethane and polyesters. A glass window may also be possible in some embodiments as may the use of a precisely fitted GRIN lens. Liquid sealants may also be employed in conjunction with the materials described above. 
     The imaging conduit  205  may be either an optical fiber for optical imaging, or a micro coaxial cable with an ultrasound transducer affixed to its end for ultrasound imaging. More particularly, imaging conduit  205  may either be a fiber optic cable capable of transmitting and receiving optical energy of wavelengths between about 250 to about 2000 nm. The fiber optic may be between about 15 to about 400 micrometers in diameter. The probe  240  shown in  FIG. 7  has a fiber optic forming the imaging conduit  204  to which there is coupled to a GRIN lens  228 , while  FIG. 8  shows a probe  250  having a ball lens  230  fused to the distal end of fiber optic  204 .  FIG. 9  shows a probe  256  configured with an ultrasound transducer  258  affixed to the distal end of a micro coaxial cable  207  for ultrasound imaging. The microcoaxial cable  207  may be between about 50 to about 400 microns in diameter. 
     The catheter used for initial experiments was a three lumen catheter to allow for separate lumens for the cantilever and two electrodes—a ground and a high voltage electrode. Also claimed are applications in which the dissipative polymer catheter possesses only a single lumen or multiple lumens such as 2-10 separate lumens within the dissipative polymer. 
       FIGS. 3 to 6  illustrate a time sequence during operation of probe  200  in which an optical or acoustic signal emitter is displaced.  FIG. 3  shows the probe immediately after the potential has been applied; the cantilever at this point is electrically neutral and therefore is attracted to the electrode.  FIG. 4  shows the cantilever undergoing some deflection towards the electrode  218 .  FIG. 5  shows the cantilever in contact with the electrode  218 , this results in the coil  205  acquiring a similar charge from the electrode  218 . This charge causes the coil  205  and hence fiber  204  to be repelled from the electrode  218  as like charges repel. This acquisition of charge is observed in the parallel circuit  221  as shown in the Figures as a spike on the trace in circuit  224 . Thus the coil  205  and hence fiber  204  (and/or ultrasound transducer) returns to its original position allowing the cycle to begin again as shown in  FIG. 6 . 
       FIGS. 10 ,  11  and  12  illustrate different embodiments of the catheter probe whereupon two wires are used in the imaging component. 
     In probe  260  shown in  FIG. 10  electrode  218  is connected to the high voltage source  222  as in  FIG. 1B , while the other wire  238  is connected to ground potential through ground circuit  221  and therefore acts as a ground electrode. This ground wire (ground electrode)  238  allows the cantilever to quickly dissipate all of its acquired charge upon contact and immediately be attracted to the high voltage electrode  218  once again. Thus, this ground wire  238  allows for more rapid oscillation than was observed in embodiments without this ground wire  238  that the coil  205  could take several seconds after repelling from the electrode  218  before it was once again attracted. When the ground wire  238  was added, this delay was eliminated. The presence of this ground wire  238  in close vicinity to the electrode  218  also insures that any electrostatic discharges will be delivered to the ground electrode  238  rather than the tissue under examination. In this probe  260  as before the imaging conduit  204  may be an optical fiber or a microcoaxial cable with a transducer. 
     In probe  270  shown in  FIG. 11  two electrodes,  218   a  and  218   b  are both connected to the high voltage source  222 . Time varying electrical potentials may be applied independently to either electrode  218   a  and  218   b  to allow for a desired scanning motion of the cantilever. Coupling to ground is provided by the wire  212  wrapped around the dissipative polymer in the proximal back section of probe  270 . In addition, or alternatively, in this embodiment either one of the electrodes  218   a  and  218   b , may be grounded at one time. 
       FIG. 12  shows a cross section of an embodiment of a catheter imaging probe  290  using four (4) electrodes  218   a ,  218   b ,  218   c  and  218   d  arranged as illustrated in order to provide actuation of the cantilever. In this embodiment, the four wires may possess different individual electrical potentials. In this embodiment each of the electrodes  218   a  to  218   d  may be driven individually at different voltages in order to adjust the angle by which the metallic coil and the imaging conduit move thereby to provide two dimensional control of the cantilever. Used in conjunction with an imaging conduit containing an ultrasound, or an optical coherence tomography probe, this embodiment may be used to form three dimensional images. 
       FIG. 13  shows a three lumen embodiment of a catheter probe  300  in which the distal front section of the outer sheath  202  is flared out to accommodate a rigid tube  225 . This rigid tube  225  is used to facilitate alignment of the distal portion of the catheter. This rigid tube  225  may be composed of, but not limited to, polymide, polycarbonate, glass, nylon or urethane. This embodiment of the probe  300  shows the imaging conduit  204  as a fiber optic with a ball lens  302  attached to it. The ball lens  302  serves to focus the light a distance of 10 to 3000 microns in front of the lens  302 . It will be appreciated by those skilled in the art that the ball lens  302  may be replaced with a multimode graded index fiber of a specified length such that the fiber length serves to focus the light a pre-selected distance in front of the distal end of the probe  300 . Alternatively one could use a miniaturized axicon (conical) lens at the end of the fiber  206  to create a “Bessel beam” that would not diverge as it propagates. 
       FIG. 14  shows another embodiment of a three lumen catheter probe  310  with the imaging conduit including a fiber optic  204  that is scanned proximal to GRIN lens  228 . By scanning the fiber proximal to a GRIN lens  228  the lateral displacement of the fiber  204  is translated into both a lateral displacement of the exiting beam as well as an angular offset of the exiting beam. It will be understood that the GRIN lens  228  may be replaced with a ball-lens or “fish eye” style lens or combination of lenses. Also possible would be to replace the GRIN lens  228  with a circular array of micro lenses. In these examples the fiber optic  204  would be scanned proximal to the imaging optics. 
       FIG. 15  illustrates another three lumen embodiment of a probe  320  in which an exposed portion of grounded electrode  322  is located within the proximal back portion of probe  320  in volume  210  containing the electrically dissipative polymer such that the exposed conductive portion of the grounded electrode  322  is in contact with the dissipative polymer material. This portion of electrode  322  thus provides a coupling to ground for the charge. This electrode  322  may be used to replace, or be used in conjunction with, grounding materials on the outside of the dissipative polymer. By varying the amount of conductive surface of the ground electrode  322  touching the inside of the polymer, it is possible to increase or decrease the coupling strength of the cantilever to ground. An increased coupling to ground will result in a larger force of attraction towards the applied voltage.  FIG. 16  shows a cross-section of  FIG. 15  along the  16 - 16  line as shown. 
       FIG. 17  shows an embodiment of a probe  330  in which a two lumen catheter is used with the grounding electrode comprised of a ring electrode  332  that fits inside sheath  202  in the proximal back section adjacent to the distal front section. This ring electrode  332  may be composed of, but not limited to: metals such as stainless steel, brass, or copper. It may also be machined from plastics such as polymethylmethylacrylate (PMMA), polyetheretherketone (PEEK), polymide, or polycarbonate that may be machined and then subsequently coated with a metal such as gold, chrome, or silver. This ring electrode  332  is connected to ground by ground electrode  238  that is insulated over a portion of its length. In this embodiment, the grounding wire  238  is placed underneath the ring electrode such that the ring electrode  332  allows both electrical coupling and precise positioning of the grounding electrode  238 . The ring electrode  332  may also be machined such that it contains a rigid extension that serves as the grounding electrode.  FIG. 18  is a cross section of the  FIG. 17  along the line  18 - 18 .  FIG. 19  is a cross section of the  FIG. 17  along the line  19 - 19 . 
       FIG. 20  shows an embodiment of a probe  350  in which the imaging means  206  includes forward-facing ultrasound transducer  352  that is affixed to the distal end of a micro-coaxial cable  353  which is connected to the ultrasound imaging system electronics This transducer  352  is capable of transmitting and receiving ultrasound energy. Thus, when combined with the electrostatic scanning mechanism described herein, two dimensional ultrasonic imaging is possible. It will be appreciated that shaping the end face of the transducer  352  may be employed for optimal ultrasound focusing. 
       FIG. 21  shows an embodiment of a probe  360  in which a more conventional side-directed ultrasound transducer  362  is coupled to a reflective prism or mirror like object  364  to direct the ultrasound energy forward. This prism or mirror  364  may be composed of, but not limited to, steel, brass, or glass. 
     A three lumen catheter that was used in the optical coherence tomography imaging experiments with the results shown in  FIGS. 24 ,  25  and  26  discussed hereinafter. The catheter was 1.8 mm in diameter with a 400 micron central lumen to house the cantilever and 300 micron peripheral lumens to contain the electrodes. The catheter was extruded using Arkema Pebax 7233 SA01. 
     An image of the cantilever probe in motion was taken using a low magnification stereomicroscope and is shown in  FIG. 22 . In this case, an electrical potential of 1700 Volts with 5 micro ampere current was applied as a driving voltage using a power supply that was current limited at 20 micro amperes. A thirteen (13) degree angle of oscillation was measured in software and is labeled in  FIG. 22  as θ. The probe used two electrodes in one electrode was grounded while the other electrode was held at a constant voltage of 1700 V. The electrodes both possess exposed regions which allow for electrical contact with the cantilever. A 60 micron optical fiber was contained within the oscillating metallic coil. The 60 micron diameter optical fiber was obtained by etching a stand 125 micron fiber in an acid. In this case the coil was composed of platinum. This design used to oscillate the cantilever is very similar to the embodiment shown in  FIG. 13 . 
       FIG. 23  shows a calibration plot for the frequency of oscillation of the cantilever in a configuration similar to that shown in  FIG. 13  and  FIG. 22 . We plot the frequency of oscillation when the cantilever is placed in either mineral oil (diamonds) or air (circles). The oscillation rate was measured using the frequency of the trigger signals that were measured on an oscilloscope. Note that a certain driving voltage is required to commence motion of the cantilever. This voltage is marked with arrows on the graph. Once motion is started, however, the voltage can be decreased and the cantilever will oscillate at a slower rate corresponding to the decreased driving voltage. 
       FIG. 24  shows OCT images taken with a probe similar to that shown in  FIG. 13 . In the embodiment of the imaging probe used to acquire the optical coherence tomography images a ball lens was affixed to a 60 micron optical fiber. The fiber was attached to the sample arm of a commercially available OCT system and scanning of the cantilever was initiated by activating the high voltage power source. An OCT image of an arterial phantom mimicking a nearly occluded vessel is shown in  FIG. 24A  with the corresponding photograph in  FIG. 24B . Walls of the phantom are labeled “W” and the channel is identified with an arrow in both  FIG. 24A  and  FIG. 24B . 
     The arterial occlusion phantom was created by mixing titanium dioxide powder into a poly(dimethylsiloxane) (PDMS) polymer prior to curing; this mixture was then allowed to cure inside a piece of tygon tubing; a wire was also placed in the tygon tubing to form a small channel that is seen on the OCT image. An OCT image of a formalin-fixed rabbit colon is shown in  FIG. 24C  with a corresponding white light picture shown in  FIG. 24D . A dashed circle identifies a crypt-like object seen in the OCT image while the letter “F” is used to denote fissures. Scale bars represent 1 mm. 
       FIGS. 25A and 25B  demonstrate the use of an electrostatic imaging probe similar to that shown in  FIG. 14  to image a stage  45   Xenopus Laevus  (African frog) embryo in vivo.  FIG. 25A  shows a structural image while  FIG. 25B  shows a processed Doppler image of the blood flow in the heart of the  Xenopus Laevus . In these images the probe was driven with 1700 V at an oscillation frequency of 5 Hz. This imaging speed allowed for sufficient signal to noise to allow for Doppler imaging. Scale bars in the image represent 1 mm. 
       FIG. 26  illustrates motion characterization of the vertical displacement of the cantilever tip as a function of time when driven at 2100 V in mineral oil. The design used to perform this calibration is very similar to the embodiment shown in  FIG. 13  and the oscillating probe shown in  FIG. 22 . The position of the end tip of the cantilever was imaged using a high speed camera with a frame rate of 454 frames per second; commercially available motion tracking software was used to track the position of the end tip of the cantilever. 
       FIGS. 27A and 27B  show a comparison of OCT images taken with two different probe designs. The image in  FIG. 27A  shows an OCT image of an IR card taken with a design similar to that shown in  FIG. 13  while the image in  FIG. 27B  shows was taken with a design similar to  FIG. 14 . Of importance to note is the increase in the angular field of view in the right hand image by scanning the fiber proximal to the GRIN lens. The left image has an angular field of view of 13 degrees while the right image has an angular field of view of 33 degrees. Scanning the optical fiber in front of the GRIN lens does however does introduce more image artifacts in the image. Scale bars represent 1 mm. 
       FIG. 28  illustrates an embodiment of an electrostatically driven imaging probe in which the grounding electrode  322  is located only inside the lumen of the dissipative polymer catheter  210  in the proximal back section of the probe. The grounding electrode  322  possesses an uninsulated length which is conductive that only contacts the dissipative polymer in the distal back section of the catheter. This grounding electrode  322  thus serves to indirectly couple the coil  205  to ground through the dissipative polymer. This conductor may or may not be sealed off from the media  208 . By being short enough so that it is not in direct conduct with the media  208  located in the distal front section of the probe, more conductive or polar media may be used in the distal front section of the probe without resulting in electrolysis of the media. It was observed that when a polar media was used in the probe design and the ground electrode was contained within the media as in  FIG. 15 , that bubbles were produced. Withdrawing the grounding electrode inside the proximal back section of the probe resulted in a slower oscillation rate, but without the production of bubbles inside the media  208 . 
       FIG. 29  illustrates an embodiment of an electrostatically driven imaging probe in which the cantilever is replaced by a reflecting disk  380 . This reflecting disk  380 , may be reflective to both ultrasound and/or optical energy. The reflecting disk  380  is pivotally mounted on a pivoting pin  384 , that allows the disk  380  to rotate and thus alter its angle. The disk  380  is electrically connected to the pivoting pin  384 , by producing both the disk  380  and the pin  384  using metal conductors. The pivoting pin  384  in turn, is connected to a wire  386  that connects to a conductive segment  390  contained within a lumen of the dissipative polymer in volume  210 . Thus the reflecting disk  380  is electrically connected to the conductive segment  390 . This conductive segment  390  is coupled to the ground electrode  322  through the dissipative polymer in section volume  210 . 
     Thus the reflecting disk  380  is indirectly coupled to ground through the dissipative polymer in volume  210 . Upon activation of the high voltage from the high voltage source  222  the reflecting disk  380  is attracted to the high voltage electrode  218 . This attraction results in the disk  380  pivoting about the pivoting pin  384  such that the proximal edge touches the electrode,  218 . Upon contact, the reflecting disk  380  acquires charge of the same polarity as the high voltage electrode  218  and thus repels. This repulsion results in the disk  380  pivoting about the pin  384  such that the proximal edge touches the ground electrode  322 . 
     Upon contract with the ground electrode  322  the disk  380  loses its acquired charge and may once again be attracted towards the high voltage electrode  218 . The imaging conduit  204  in this embodiment, is placed above the grounding electrode  322 . A beam directing element  366  causes the energy emitted from the imaging conduit  204  to be reflected towards the disk  380 . Finally an end cap  390  capable of transmitting optical and ultrasonic energy is located on the distal end of the probe that serves to seal the distal front section of the catheter. 
     The different embodiments of the imaging probe disclosed herein and the various components they are made from may span several different dimensions and properties depending on the anatomic location and application of the imaging probe. For example, for use in the cardiovascular system, including the cardiac chambers, the imaging probe would be elongate and flexible, with a length ranging from about 5 to about 2000 mm, preferably with a length ranging from about 300 mm to about 1500 mm. The imaging conduit and imaging assembly may have a maximum cross-sectional dimension ranging from about 200 microns to about 10 mm, preferably ranging from about 500 microns to 5 about mm. The imaging conduit and imaging assembly are surrounded by an external sheath. This enables the imaging conduit  204  ( FIG. 1B ) and imaging assembly to rotate within the external sheath while mechanically isolating the rotational motion of these two components from the surrounding tissues. 
     In yet another example, the use of the imaging probe in the gastrointestinal system would typically have the imaging probe being elongate and flexible, with a length ranging from about 100 mm to about 2000 mm and preferably in the range of about 300 mm to about 1500 mm. The maximum cross-sectional dimension would typically range from about 3 mm to about 20 mm. 
     In yet another example, the use of the imaging probe to image soft tissue via percutaneous means would require the imaging probe include a rigid shaft, rather than flexible as for the aforementioned applications. Thus the external sheath would be replaced by a rigid hollow shaft, such as a stainless steel tube. The length of the shaft would be from about 1 to about 12 cm. 
     As mentioned previously, Boppart et al. (U.S. Pat. No. 6,485,413) discloses an electrostatic-based actuator for forward-viewing optical coherence tomography in which the cantilever is directly connected to ground or enabled with an electrostatic slide. The direct connection to ground results in significant electrostatic discharge given the high voltage necessary to oscillate a rigid fiber. By coupling the cantilever to ground through a dissipative polymer such as disclosed in the present application circumvents this problem. Furthermore the Boppart et al. discloses the use of a time varying electrical field in order to produce an oscillatory motion. By using a dissipative polymer to couple the cantilever to ground in the present application allows production of oscillatory motion with both constant voltage as well as time varying driving voltages. 
     The electrostatic scanning motion described in this work can be used in conjunction with a torque cable as described by Crowley et al. in U.S. Pat. No. 5,372,138 (which is incorporated herein by reference in its entirety) to extend the scanning motion to cover a two dimensional scanning field by rotating the probe while the cantilever is scanning. In such an embodiment a torque cable may be placed over the dissipative polymer in volume  210  causing the cantilever, and the electrode(s)  218  to rotate inside the sheath  202  ( FIG. 1A ). 
     Alternatively the torque cable may be placed over the outer sheath  202  such that the entire imaging probe rotates at the same time as the cantilever scans. This rotational driving torque would be provided by a motor external to the catheter. This rotational torque would be coupled into the catheter through an element generally labeled as an adaptor  14  in  FIG. 1A . This adaptor  14  would include an electrical slip ring to allow electrical connections be preserved in the rotating catheter. It may also include a fiber optic rotary joint to allow optical connections to be maintained while the probe rotates. The goal of this rotation is to allow multiple different angles for the cantilever to scan. 
     It will be appreciated by those skilled in the art that the scanning cantilever disclosed herein may be used as a switching means in non-medical applications such as, but not limited to, optical networks, electrical switching, optical switching, and mechanical switches. 
     As used herein, the terms “comprises”, “comprising”, “includes” and “including” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in this specification including claims, the terms “comprises”, “comprising”, “includes” and “including” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components. 
     The foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.