Abstract:
A catheter assembly for an intravascular ultrasound system includes a catheter with a lumen and an imaging core insertable into the lumen. The imaging core includes a rotatable driveshaft, at least one transducer, and at least one optical transport medium. The at least one transducer is mounted to the rotatable driveshaft and transforms applied electrical signals to acoustic signals and also transforms received acoustic signals to electrical signals. The at least one optical transport medium emits light and rotates with the driveshaft. The at least one transducer also receives acoustic signals generated by an object in response to illumination of the object by the light emitted from the distal end of the optical transport medium.

Description:
TECHNICAL FIELD 
       [0001]    The present invention is directed to the area of intravascular ultrasound imaging systems and methods of making and using the systems. The present invention is also directed to intravascular ultrasound systems that also include photo-acoustic imaging, as well as methods of making and using the intravascular ultrasound systems. 
       BACKGROUND 
       [0002]    Intravascular ultrasound (“IVUS”) imaging systems have proven diagnostic capabilities for a variety of diseases and disorders. For example, IVUS imaging systems have been used as an imaging modality for diagnosing blocked blood vessels and providing information to aid medical practitioners in selecting and placing stents and other devices to restore or increase blood flow. IVUS imaging systems have been used to diagnose atheromatous plaque build-up at particular locations within blood vessels. IVUS imaging systems can be used to determine the existence of an intravascular obstruction or stenosis, as well as the nature and degree of the obstruction or stenosis. IVUS imaging systems can be used to visualize segments of a vascular system that may be difficult to visualize using other intravascular imaging techniques, such as angiography, due to, for example, movement (e.g., a beating heart) or obstruction by one or more structures (e.g., one or more blood vessels not desired to be imaged). IVUS imaging systems can be used to monitor or assess ongoing intravascular treatments, such as angiography and stent placement in real (or almost real) time. Moreover, IVUS imaging systems can be used to monitor one or more heart chambers. 
         [0003]    IVUS imaging systems have been developed to provide a diagnostic tool for visualizing a variety is diseases or disorders. An IVUS imaging system can include a control module (with a pulse generator, an image processor, and a monitor), a catheter, and one or more transducers disposed in the catheter. The transducer-containing catheter can be positioned in a lumen or cavity within, or in proximity to, a region to be imaged, such as a blood vessel wall or patient tissue in proximity to a blood vessel wall. The pulse generator in the control module generates electrical pulses that are delivered to the one or more transducers and transformed to acoustic pulses that are transmitted through patient tissue. Reflected pulses of the transmitted acoustic pulses are absorbed by the one or more transducers and transformed to electric pulses. The transformed electric pulses are delivered to the image processor and converted to an image displayable on the monitor. 
         [0004]    Photo-acoustic imaging utilizes light and acoustic signals to form displayable images. In one exemplary photo-acoustic imaging technique, patient tissue is pulsed with light from a light source, such as a laser. Some of the emitted light is absorbed by the tissue and converted to heat. The heat causes a transient ultrasonic expansion of the illuminated tissue and a corresponding ultrasonic emission, which may be received by one or more transducers and processed into a displayable image. 
       BRIEF SUMMARY 
       [0005]    In one embodiment, a catheter assembly for an intravascular ultrasound system includes a catheter and an imaging core. The catheter has a distal end, a proximal end, and a longitudinal length. The catheter defines a lumen that extends along the longitudinal length of the catheter from the proximal end to the distal end. The imaging core is configured and arranged for inserting into the lumen. The imaging core includes a rotatable driveshaft, at least one transducer, at least one conductor, and at least one optical transport medium. The rotatable driveshaft has a distal end, a proximal end, and a longitudinal length. The at least one transducer is mounted to the distal end of the rotatable driveshaft and is configured and arranged for transforming applied electrical signals to acoustic signals and also for transforming received acoustic signals to electrical signals. The at least one conductor is coupled to the at least one transducer and extends along the longitudinal length of the driveshaft. The at least one optical transport medium has a proximal end, a distal end, and a longitudinal length. The distal end of the at least one optical transport medium is positioned in proximity to the at least one transducer. The at least one optical transport medium is configured and arranged to emit light from the distal end of the at least one optical transport medium and to rotate with the driveshaft. The at least one transducer is configured and arranged to receive acoustic signals generated by an object in response to illumination of the object by the light emitted from the distal end of the optical transport medium. 
         [0006]    In another embodiment, an intravascular ultrasound imaging system includes a catheter, an imaging core, and a drive unit. The catheter has a distal end, a proximal end, and a longitudinal length. The catheter defines a lumen that extends along the longitudinal length of the catheter from the proximal end to the distal end. The imaging core is configured and arranged for inserting into the lumen. The imaging core includes a rotatable driveshaft, at least one transducer, at least one conductor, and at least one optical transport medium. The rotatable driveshaft has a distal end, a proximal end, and a longitudinal length. The at least one transducer is mounted to the distal end of the rotatable driveshaft and is configured and arranged for transforming applied electrical signals to acoustic signals and also for transforming received acoustic signals to electrical signals. The at least one conductor is coupled to the at least one transducer and extends along the longitudinal length of the driveshaft. The at least one optical transport medium has a proximal end, a distal end, and a longitudinal length. The distal end of the at least one optical transport medium is positioned in proximity to the at least one transducer. The at least one optical transport medium is configured and arranged to emit light from the distal end of the at least one optical transport medium and to rotate with the driveshaft. The at least one transducer is configured and arranged to receive acoustic signals generated by an object in response to illumination of the object by the light emitted from the distal end of the optical transport medium. The drive unit is coupled to the proximal end of the catheter. The drive unit includes a rotatable transformer and a motor. The rotatable transformer includes a rotor and a stator. The rotor is coupled to the proximal end of the driveshaft and defines at least one hollow shaft into which at least one optical transport medium is disposed. The at least one optical transport medium is configured and arranged to couple to the proximal end of the at least one optical transport medium disposed in the imaging core. The motor is for driving rotation of the driveshaft and is coupled to the rotatable transformer by a rotary motion interchanger. 
         [0007]    In yet another embodiment, a method for photo-acoustic imaging of a patient using an intravascular ultrasound imaging system includes inserting a catheter into patient vasculature, illuminating patient tissue with light, receiving at least one emitted acoustic signal from the illuminated patient tissue, transmitting at least one acoustic signal to patient tissue from the at least one transducer, and receiving at least one reflected acoustic signal from the patient tissue. The catheter includes at least one optical transport medium coupled to a light source and at least one rotatable transducer electrically coupled to a control module by at least one conductor. The at least one optical transport medium rotates with the at least one transducer and maintains a constant position and direction relative to the at least one transducer. The light is emitted from the light source and is transmitted along the at least one optical transport medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
           [0009]    For a better understanding of the present invention, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a schematic view of one embodiment of an intravascular ultrasound imaging system, according to the invention; 
           [0011]      FIG. 2  is a schematic side view of one embodiment of a catheter of an intravascular ultrasound imaging system, according to the invention; 
           [0012]      FIG. 3  is a schematic perspective view of one embodiment of a distal end of the catheter shown in  FIG. 2  with an imaging core disposed in a lumen defined in the catheter, according to the invention; 
           [0013]      FIG. 4A  is a schematic perspective view of one embodiment of a distal end of a catheter for an IVUS imaging system, the catheter including a light director for directing light emissions from the catheter and at least one transducer for transmitting and receiving acoustic signals, according to the invention; 
           [0014]      FIG. 4B  is a schematic longitudinal cross-sectional view of the distal end of the catheter shown in  FIG. 4A , the catheter including an imaging core that includes an optical transport medium and a pair of conductors, according to the invention; 
           [0015]      FIG. 5  is a schematic perspective view of one embodiment of a connector at a proximal end of the catheter shown in  FIG. 4A , according to the invention; 
           [0016]      FIG. 6  is a schematic cross-sectional view of one embodiment of a proximal end of the catheter shown in  FIG. 4A  coupled to a drive unit, according to the invention; 
           [0017]      FIG. 7  is a schematic side view of one embodiment of the motor shown in  FIG. 6  coupled to the transformer shown in  FIG. 6  by a rotary motion interchanger, according to the invention; 
           [0018]      FIG. 8  is a schematic distal perspective view of one embodiment of the motor shown in  FIG. 6  coupled to the transformer shown in  FIG. 6  by a rotary motion interchanger, according to the invention; 
           [0019]      FIG. 9  is a schematic proximal perspective view of one embodiment of the motor shown in  FIG. 6  coupled to the transformer shown in  FIG. 6  by a rotary motion interchanger, according to the invention; and 
           [0020]      FIG. 10  is a schematic longitudinal cross-sectional view of one embodiment of a light source configured and arranged to provide light to one or more optical transport media disposed in a proximal end of the transformer shown in  FIG. 6  via one or more other optical transport media, according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The present invention is directed to the area of intravascular ultrasound imaging systems and methods of making and using the systems. The present invention is also directed to intravascular ultrasound systems that also include photo-acoustic imaging, as well as methods of making and using the intravascular ultrasound systems. 
         [0022]    Suitable intravascular ultrasound (“IVUS”) imaging systems include, but are not limited to, one or more transducers disposed on a distal end of a catheter configured and arranged for percutaneous insertion into a patient. Examples of IVUS imaging systems with catheters are found in, for example, U.S. Pat. Nos. 7,306,561; and 6,945,938; as well as U.S. Patent Application Publication Nos. 20060253028; 20070016054; 20070038111; 20060173350; and 20060100522, all of which are incorporated by reference. 
         [0023]      FIG. 1  illustrates schematically one embodiment of an IVUS imaging system  100 . The IVUS imaging system  100  includes a catheter  102  that is coupleable to a control module  104 . The control module  104  may include, for example, a processor  106 , a pulse generator  108 , a drive unit  110 , and one or more displays  112 . In at least some embodiments, the pulse generator  108  forms electric pulses that may be input to one or more transducers ( 312  in  FIG. 3 ) disposed in the catheter  102 . In at least some embodiments, mechanical energy from a motor disposed within the drive unit  110  may be used to drive an imaging core ( 306  in  FIG. 3 ) disposed in the catheter  102 . In at least some embodiments, the drive unit  110  additionally includes a transformer. 
         [0024]    In at least some embodiments, electric pulses transmitted from the one or more transducers ( 312  in  FIG. 3 ) may be input to the processor  106  for processing. In at least some embodiments, the processed electric pulses from the one or more transducers ( 312  in  FIG. 3 ) may be displayed as one or more images on the one or more displays  112 . In at least some embodiments, the processor  106  may also be used to control the functioning of one or more of the other components of the control module  104 . For example, the processor  106  may be used to control at least one of the frequency or duration of the electrical pulses transmitted from the pulse generator  108 , the rotation rate of the imaging core ( 306  in  FIG. 3 ) by the drive unit  110 , the velocity or length of the pullback of the imaging core ( 306  in  FIG. 3 ) by the drive unit  110 , or one or more properties of one or more images formed on the one or more displays  112 . As discussed in more detail below, a light source  114  is provided to generate light for illuminating patient tissue in proximity to a distal end of the catheter  102 . 
         [0025]      FIG. 2  is a schematic side view of one embodiment of the catheter  102  of the IVUS imaging system ( 100  in  FIG. 1 ). The catheter  102  includes an elongated member  202  and a hub  204 . The elongated member  202  includes a proximal end  206  and a distal end  208 . In  FIG. 2 , the proximal end  206  of the elongated member  202  is coupled to the catheter hub  204  and the distal end  208  of the elongated member is configured and arranged for percutaneous insertion into a patient. In at least some embodiments, the catheter  102  defines at least one flush port, such as flush port  210 . In at least some embodiments, the flush port  210  is defined in the hub  204 . In at least some embodiments, the hub  204  is configured and arranged to couple to the control module ( 104  in  FIG. 1 ). In some embodiments, the elongated member  202  and the hub  204  are formed as a unitary body. In other embodiments, the elongated member  202  and the catheter hub  204  are formed separately and subsequently assembled together. 
         [0026]      FIG. 3  is a schematic perspective view of one embodiment of the distal end  208  of the elongated member  202  of the catheter  102 . The elongated member  202  includes a sheath  302  and a lumen  304 . An imaging core  306  is disposed in the lumen  304 . The imaging core  306  includes an imaging device  308  coupled to a distal end of a rotatable driveshaft  310 . 
         [0027]    The sheath  302  may be formed from any flexible, biocompatible material suitable for insertion into a patient. Examples of suitable materials include, for example, polyethylene, polyurethane, plastic, spiral-cut stainless steel, nitinol hypotube, and the like or combinations thereof. 
         [0028]    One or more transducers  312  may be mounted to the imaging device  308  and employed to transmit and receive acoustic pulses. In a preferred embodiment (as shown in  FIG. 3 ), an array of transducers  312  are mounted to the imaging device  308 . In other embodiments, a single transducer may be employed. In yet other embodiments, multiple transducers in an irregular-array may be employed. Any number of transducers  312  can be used. For example, there can be two, three, four, five, six, seven, eight, nine, ten, twelve, fifteen, sixteen, twenty, twenty-five, fifty, one hundred, five hundred, one thousand, or more transducers. As will be recognized, other numbers of transducers may also be used. 
         [0029]    The one or more transducers  312  may be formed from one or more known materials or devices capable of transforming applied electrical pulses to pressure distortions on the surface of the one or more transducers  312 , and vice versa. Examples of suitable materials or devices include piezoelectric ceramic materials, piezocomposite materials, piezoelectric plastics, barium titanates, lead zirconate titanates, lead metaniobates, polyvinylidenefluorides, capacitive micromachined ultrasonic transducers, and the like. 
         [0030]    The pressure distortions on the surface of the one or more transducers  312  form acoustic pulses of a frequency based on the resonant frequencies of the one or more transducers  312 . The resonant frequencies of the one or more transducers  312  may be affected by the size, shape, and material used to form the one or more transducers  312 . The one or more transducers  312  may be formed in any shape suitable for positioning within the catheter  102  and for propagating acoustic pulses of a desired frequency in one or more selected directions. For example, transducers may be disc-shaped, block-shaped, rectangular-shaped, oval-shaped, and the like. The one or more transducers may be formed in the desired shape by any process including, for example, dicing, dice and fill, machining, microfabrication, and the like. 
         [0031]    As an example, each of the one or more transducers  312  may include a layer of piezoelectric material sandwiched between a conductive acoustic lens and a conductive backing material formed from an acoustically absorbent material (e.g., an epoxy substrate with tungsten particles). During operation, the piezoelectric layer may be electrically excited by both the backing material and the acoustic lens to cause the emission of acoustic pulses. 
         [0032]    In at least some embodiments, the one or more transducers  312  can be used to form a radial cross-sectional image of a surrounding space. Thus, for example, when the one or more transducers  312  are disposed in the catheter  102  and inserted into a blood vessel of a patient, the one more transducers  312  may be used to form an image of the walls of the blood vessel and tissue surrounding the blood vessel. 
         [0033]    The imaging core  306  is rotated about a longitudinal axis of the catheter  102 . As the imaging core  306  rotates, the one or more transducers  312  emit acoustic pulses in different radial directions. When an emitted acoustic pulse with sufficient energy encounters one or more medium boundaries, such as one or more tissue boundaries, a portion of the emitted acoustic pulse is reflected back to the emitting transducer as an echo pulse. Each echo pulse that reaches a transducer with sufficient energy to be detected is transformed to an electrical signal in the receiving transducer. The one or more transformed electrical signals are transmitted to the control module ( 104  in  FIG. 1 ) where the processor  106  processes the electrical-signal characteristics to form a displayable image of the imaged region based, at least in part, on a collection of information from each of the acoustic pulses transmitted and the echo pulses received. 
         [0034]    As the one or more transducers  312  rotate about the longitudinal axis of the catheter  102  emitting acoustic pulses, a plurality of images are formed that collectively form a radial cross-sectional image of a portion of the region surrounding the one or more transducers  312 , such as the walls of a blood vessel of interest and the tissue surrounding the blood vessel. In at least some embodiments, the radial cross-sectional image can be displayed on one or more displays  112 . 
         [0035]    In at least some embodiments, the imaging core  306  may move longitudinally within the lumen of the catheter  102  while the catheter  102  remains stationary. For example, the imaging core  306  may be advanced (moved towards the distal end of the catheter  102 ) or retracted/pulled back (moved towards the proximal end of the catheter  102 ) within the lumen  304  of the catheter  102  while the catheter  102  remains in a fixed location within patient vasculature (e.g., blood vessels, the heart, and the like). During longitudinal movement (e.g., pullback) of the imaging core  306 , an imaging procedure may be performed, wherein a plurality of cross-sectional images are formed along a longitudinal length of patient vasculature. 
         [0036]    In at least some embodiments, the catheter  102  includes at least one retractable section that can be retracted during an imaging procedure. In at least some embodiments, a motor disposed in the drive unit ( 110  in  FIG. 1 ) drives the pullback of the imaging core  306  within the catheter  102 . In at least some embodiments, the pullback distance of the imaging core is at least 5 cm. In at least some embodiments, the pullback distance of the imaging core is at least 10 cm. In at least some embodiments, the pullback distance of the imaging core is at least 15 cm. In at least some embodiments, the pullback distance of the imaging core is at least 20 cm. In at least some embodiments, the pullback distance of the imaging core is at least 25 cm. 
         [0037]    The quality of an image produced at different depths from the one or more transducers  312  may be affected by one or more factors including, for example, bandwidth, transducer focus, beam pattern, as well as the frequency of the acoustic pulse. The frequency of the acoustic pulse output from the one or more transducers  312  may also affect the penetration depth of the acoustic pulse output from the one or more transducers  312 . In general, as the frequency of an acoustic pulse is lowered, the depth of the penetration of the acoustic pulse within patient tissue increases. In at least some embodiments, the IVUS imaging system  100  operates within a frequency range of 5 MHz to 60 MHz. 
         [0038]    In at least some embodiments, one or more conductors  314  electrically couple the transducers  312  to the control module ( 104  in  FIG. 1 ). In at least some embodiments, the one or more conductors  314  extend along a longitudinal length of the imaging core  306 . In at least some embodiments, the one or more conductors  314  may extend along at least a portion of the longitudinal length of the catheter  102  as shielded electrical cables, such as a coaxial cable, or a twisted pair cable, or the like. 
         [0039]    In at least some embodiments, the catheter  102  with one or more transducers  312  mounted to the distal end  208  of the imaging core  306  may be inserted percutaneously into a patient via an accessible blood vessel, such as the femoral artery, at a site remote from the selected portion of the selected region, such as a blood vessel, to be imaged. The catheter  102  may then be advanced through the blood vessels of the patient to the selected imaging site, such as a portion of a selected blood vessel. 
         [0040]    Differentiating between two or more different tissue types displayed on an IVUS image is desirable, but can be difficult using the IVUS image. For example, it may be difficult to determine where a border between two or more tissue types is located, or even if a border exists. 
         [0041]    One technique for tissue differentiation is photo-acoustic imaging, wherein patient tissue is pulsed with light from a light source, such as a laser. When patient tissue is pulsed with light, some of the emitted light is absorbed by the tissue and converted to heat. The heat causes a transient ultrasonic expansion of the illuminated tissue and a corresponding ultrasonic emission, which may be received by one or more transducers and processed into a displayable image (or one or more audible tones). 
         [0042]    Photo-acoustic imaging capabilities may be incorporated into an IVUS imaging system. Such an arrangement includes a light source that provides light to an optical transport medium (such as an optical fiber) to transport light to a distal portion of the catheter. Light is emitted from the distal end of the optical transport medium in proximity to one or more transducers disposed on an imaging core in the catheter so that the subsequently-emitted acoustic pulses from the illuminated tissue may be received by the one or more transducers. 
         [0043]    The one or more transducers disposed on the imaging core rotate. Thus, it is desirable to have the light-emitting portion of the optical transport medium also be disposed on the imaging core so that the light-emitting portion of the optical transport medium also rotates, thereby maintaining a constant relative position with respect to the one or more transducers. However, the proximal portion of an imaging core is generally obstructed by the drive unit (which, as discussed above, includes the transformer and the motor). Thus, there is no convenient way to provide light from a light source to the optical transport medium. 
         [0044]    Previous systems have embedded optical fibers in a sheath of a catheter. However, embedding optical fibers in the sheath can make sheath manufacturing difficult. Moreover, the embedded optical fibers do not rotate with transducers. Additionally, embedding optical fibers in the sheath may hinder, or even eliminate, the pullback function of the imaging core during an imaging procedure. 
         [0045]    In at least some embodiments, an IVUS imaging system incorporates photo-acoustic imaging capabilities into the IVUS imaging system. In at least some embodiments, one or more optical transport media (e.g., optical fibers, light pipes, light guides, light tubes, or the like) are disposed in an imaging core of the IVUS imaging system. In at least some embodiments, the one or more optical transport media disposed in the imaging core couple to additional optical transport media disposed in a transformer of a drive unit of the IVUS imaging system. In at least some embodiments, a proximal end of the transformer provides access to the one or more optical transport media disposed in a rotor of the transformer, thereby allowing the light source to provide light to the optical transport medium. In at least some embodiments, the transformer is positioned side-by-side with the motor and is coupled to the motor via one or more rotary motion interchangers (e.g., a timing belt, one or more gears, and the like). 
         [0046]      FIG. 4A  is a schematic perspective view of one embodiment of a distal end of a catheter  402  for an IVUS imaging system ( 100  in  FIG. 1 ). The catheter  402  includes a light director  404  and one or more transducers  406 . The one or more transducers  406  are coupled to the processor ( 106  in  FIG. 1 ) via one or more conductors  408  disposed in an imaging core ( 410  in  FIG. 4B ). In at least some embodiments, the light director  404  may be used to direct light that is emitted from a light source ( 704  in  FIG. 7 ) and transported along a longitudinal length of the catheter  402  via one or more optical transport media ( 412  in  FIG. 4B ). 
         [0047]    In at least some embodiments, the light director  404  includes a mirror ( 414  in  FIG. 4B ) to redirect the light from an optical transport medium to a desired tissue. In at least some embodiments, the light director  404  includes a diffuser to diffuse light from a narrow point source (such as an optical transport medium). In at least some embodiments, the light director  404  includes a mirror ( 414  in  FIG. 4B ) and a diffuser. In at least some embodiments, the mirror ( 414  in  FIG. 4B ) and the diffuser are separate from one another. In at least some embodiments, the diffuser is on the emitting end of the optical transport medium. In at least some embodiments, the mirror ( 414  in  FIG. 4B ) has a light-diffusing reflective surface. The light director  404  may be fabricated from any material suitable for reflecting or orienting light including, for example, glass, plastic, and the like or combinations thereof. 
         [0048]      FIG. 4B  is a schematic longitudinal cross-sectional view of one embodiment of a distal end of the catheter  402 . The catheter  402  includes a lumen into which an imaging core  410  is disposed. In at least some embodiments, the imaging core  410  includes the one or more conductors  408  extending along at least a portion of the imaging core  410 . The imaging core  410  also includes one or more optical transport media, such as optical transport medium  412 , also extending along at least a portion of the imaging core  410 . In at least some embodiments, the one or more conductors  408  may extend along at least a portion of the longitudinal length of the catheter  402  as shielded electrical cables, such as a coaxial cable, or a twisted pair cable, or the like. In at least some embodiments, the one or more optical transport media  412  wrap at least one time around the one or more conductors  408 . In at least some embodiments, the one or more optical transport media  412  are coupled at a distal end to the light director  404 , through which light from the one or more optical transport media  412  is emitted. In at least some embodiments, the light director  404  and the one or more transducers  406  have the same rotational velocity. In at least some embodiments, the light director  404  maintains a constant relative position with respect to the one or more transducers  406 . In at least some embodiments, the light director  404  is fixed to the one or more transducers  406 . 
         [0049]    Light provided from a light source ( 704  in  FIG. 7 ) may be transported along one or more optical transport media  412 , passed through the light director  404 , and used to illuminate selected patient tissue for photo-acoustic imaging. In at least some embodiments, the light may be emitted in one or more timed patterns, such as pulses. In at least some embodiments, the light emission may be timed with respect to the transmission of one or more acoustic signals from the one or more transducers  406 . 
         [0050]    In at least some embodiments, the IVUS imaging system may be used to perform photo-acoustic imaging without performing ultrasound imaging. In at least some embodiments, the IVUS imaging system is configured to perform both photo-acoustic imaging and ultrasound imaging, either sequentially or independently. In at least some embodiment, the data from a photo-acoustic image and an ultrasound image may be combined to form a composite image. 
         [0051]    In at least some embodiments, a proximal end of the catheter  402  couples with a transformer ( 606  in  FIG. 6 ) disposed in a drive unit ( 602  in  FIG. 6 ).  FIG. 5  is a schematic perspective view of one embodiment of a connector  502  in a proximal end of the catheter  402 . In at least some embodiments, the connector  502  is configured and arranged to couple to a drive unit ( 602  in  FIG. 6 ). A proximal end of the one or more optical transport media  412  terminates in proximity to the connector  502 . In at least some embodiments, a coupler (not shown in  FIG. 5 ) may be disposed at the proximal end of the catheter  402  to facilitate coupling of the one or more optical transport media  412  to one or more optical transport media ( 806  in  FIG. 8 ) disposed in the transformer ( 606  in  FIG. 6 ). 
         [0052]      FIG. 6  is a schematic cross-sectional view of one embodiment of a proximal end of the catheter  402  coupled to a drive unit  602 . The drive unit  602  includes a drive sled  604  configured and arranged to slide along a length of the drive unit  602  during pullback of the imaging core ( 410  in  FIG. 4B ) in the direction shown by directional arrow  605 , thereby retracting the proximal end of the catheter  402 . The drive unit  602  also includes a rotary transformer  606  and a rotary motor  608 . In  FIG. 6 , the rotary transformer  606  and the rotary motor  608  are shown coupled to the drive sled  604 . 
         [0053]    The transformer  606  and the motor  608  are coupled to one another via a rotary motion interchanger  610 . In at least some embodiments, the motor  608  drives the rotation of the transformer  606  which, in turn, drives the rotation of the imaging core ( 410  in  FIG. 4B ). Thus, coupling the transformer  606  to the motor  608  via the rotary motion interchanger  610  permits the transformer  606  and the motor  608  to be coupled together without a proximal end of the transformer  606  being obstructed by the motor  608 , thereby providing an access point for light from a light source ( 704  in  FIG. 7 ) into the imaging core ( 410  in  FIG. 4B ). 
         [0054]    In at least some embodiments, positioning the transformer  606  and the motor  608  adjacent to one another and coupled via the rotary motion interchanger  610  may allow the size of the drive unit  602  to be reduced. In at least some embodiments, gearing may be added to the drive train to increase the torque delivered by the motor  608 . In at least some embodiments, positioning the transformer  606  and the motor  608  adjacent to one another may also allow the motor  608  to operate at a more efficient velocity range, thereby decreasing the temperature of the motor  608 . In at least some embodiments, the motor and the transformer have the same rotational velocity. In at least some embodiments, gearing may be added so that the transformer has a rotational velocity that is different from the rotational velocity of the motor. 
         [0055]    The transformer  606  is also coupled to the proximal end of the catheter  402 . In at least some embodiments, the catheter  402  is coupled to the transformer  606  via a drive unit connector  612  which couples to the connector ( 502  in  FIG. 5 ) disposed at the proximal end of the catheter  402 . In at least some embodiments, the one or more optical transport media ( 412  in  FIG. 4B ) disposed in the imaging core ( 410  in  FIG. 4B ) couple to one or more optical transport media ( 806  in  FIG. 8 ) disposed in the transformer  606 . 
         [0056]    In at least some embodiments, the transformer  606  and the motor  608  are positioned such that the one or more optical transport media disposed in the transformer  606  are accessible at both a proximal and a distal end of the transformer  606 .  FIG. 7  is a schematic side view of one embodiment of the transformer  606  and the motor  608  coupled to the drive sled  604  and to the rotary motion interchanger  610 . A distal end of the transformer  606  is configured and arranged to couple with the catheter ( 402  in  FIG. 6 ), as shown by directional arrow  702 . A proximal end of the transformer  606  is configured and arranged to provide access to one or more optical transport media disposed in the transformer  606  by a light source  114 . 
         [0057]    In at least some embodiments, the light source  114  is disposed in the control module ( 104  in  FIG. 1 ). In at least some embodiments, the light source  114  is a laser. In at least some embodiments, the light from the light source  114  may be emitted at various frequencies. Different types of tissues may respond differently to being illuminated by light of different frequencies. Thus, illuminating tissue with various frequencies of light and processing received acoustic signals from the illuminated tissue may be used as a way to differentiate between two or more types of tissues. 
         [0058]      FIG. 8  is a schematic proximal perspective view of one embodiment of a distal end of the transformer  606  being coupled to the motor  608  via the rotary motion interchanger  610 . The transformer includes a rotor  802  and a stator  804 . The one or more optical transport media  806  terminate in proximity to the distal end of the transformer  606 . In at least some embodiments, the one or more optical transport media  804  disposed in the transformer are configured and arranged to couple to the one or more optical transport media ( 412  in  FIG. 4B ) disposed in the catheter ( 402  in  FIG. 4A ). In at least some embodiments, a coupler (not shown in  FIG. 8 ) may be disposed at the distal end of the transformer  606  to facilitate coupling of one or more optical transport media  806  disposed in the transformer  606  to the one or more optical transport media ( 412  in  FIG. 4B ) disposed in the catheter ( 402  in  FIG. 4B ). 
         [0059]    In at least some embodiments, the one or more optical transport media disposed in the transformer  606  extend along one or more hollow shafts defined in the rotor  802  of the transformer  606 . In at least some embodiments, the one or more optical transport media  806  (e.g., optical fibers, light pipes, light guides, light tubes, and the like) are the same type of optical transport medium as the one or more optical transport media ( 412  in  FIG. 4B ). In at least some embodiments, the one or more optical transport media  806  are a different type of optical transport medium from the one or more optical transport media ( 412  in  FIG. 4B ). For example, in at least one embodiment, the one or more optical transport media ( 412  in  FIG. 4B ) may be one or more optical fibers and the one or more optical transport medium  806  may be one or more light pipes. In at least one other embodiment, the one or more optical transport media ( 412  in  FIG. 4B ) may be one or more light pipes and the one or more optical transport media  806  may be one or more optical fibers. In at least some embodiments, more than one type of optical transport medium may be used in combination. For example, the one or more optical transport media  806  may include one or more optical fibers and one or more light pipes. 
         [0060]      FIG. 9  is a schematic proximal perspective view of one embodiment of a distal end of the transformer  606  being coupled to the motor  608  via the rotary motion interchanger  610 . In  FIG. 9 , the one or more optical transport media  806  are shown terminating in proximity to the proximal end of the transformer  606 . In at least some embodiments, one or more additional materials may be employed to facilitate the emission of light at the interfaces between optical transport media (i.e., between the one or more optical transport media  412  disposed in the catheter  402  and the one or more optical transport media  806  disposed in the transformer  606 , and between the one or more optical transport media  806  disposed in the transformer  606  and the light source  114 ) including, for example, one or more types of optical grease. 
         [0061]    In at least some embodiments, the one or more optical transport media  806  are positioned in the center of the rotor such that there is little, if any, wobble as the one or more optical transport media  806  rotate with the rotor. In at least some embodiments, the one or more optical transport media  806  are positioned off center of the rotor. In at least some embodiments, the light source may be positioned in proximity to the proximal portion of the transformer. In at least some embodiments, the light source emits light directly into a proximal end of the one or more optical transport media  806 . In at least some other embodiments, the light source provides light to the one or more optical transport media  806  via one or more optical transport media. 
         [0062]      FIG. 10  is a schematic longitudinal cross-sectional view of one embodiment of the light source  114  configured and arranged to provide light to one or more optical transport media  806  disposed in a proximal end of the transformer  606  via one or more optical transport media  1002 . In  FIG. 10 , the transformer  606  includes the rotor  802  and the stator  804 . The one or more optical transport media  806  are disposed in a hollow shaft  1004  defined in the rotor  802 . In at least some embodiments, a coupler  1006  may be disposed at the proximal end of the transformer  606  and configured and arranged to hold the one or more optical transport media  1002  in a steady position in proximity to the proximal end of the one or more optical transport media  806 . In at least some embodiments, the coupler  1006  is an end cap with an aperture through which the one or more optical transport media  1002  extend. 
         [0063]    The above specification, examples and data provide a description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.