Abstract:
An intravascular ultrasound probe is disclosed, incorporating features for utilizing an advanced transducer technology on a rotating transducer shaft. In particular, the probe accommodates the transmission of the multitude of signals across the boundary between the rotary and stationary components of the probe required to support an advanced transducer technology. These advanced transducer technologies offer the potential for increased bandwidth, improved beam profiles, better signal to noise ratio, reduced manufacturing costs, advanced tissue characterization algorithms, and other desirable features. Furthermore, the inclusion of electronic components on the spinning side of the probe can be highly advantageous in terms of preserving maximum signal to noise ratio and signal fidelity, along with other performance benefits.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 12/402,278 filed on Mar. 11, 2009, now U.S. Pat. No. 8,403,856, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Intravascular Ultrasound (IVUS) has become an important interventional diagnostic procedure for imaging atherosclerosis and other vessel diseases and defects. In the procedure, an IVUS catheter is threaded over a guidewire into a blood vessel of interest, and images are acquired of the atherosclerotic plaque and surrounding area using ultrasonic echoes. This information is much more descriptive than the traditional standard of angiography, which shows only a two-dimensional shadow of the vessel lumen. Some of the key applications of IVUS include: determining a correct diameter and length of a stent to choose for dilating an arterial stenosis, verifying that a post-stenting diameter and luminal cross-section area are adequate, verifying that a stent is well apposed against a vessel wall to minimize thrombosis and optimize drug delivery (in the case of a drug eluting stent) and identifying an exact location of side-branch vessels. In addition, new techniques such as virtual histology (RF signal-based tissue characterization) show promise of aiding identification of vulnerable plaque (i.e., plaque which is prone to rupture and lead to onset of a heart attack). 
     There are two types of IVUS catheters commonly in use: mechanical/rotational IVUS catheters and solid state catheters. In a rotational IVUS catheter, a single transducer consisting of a piezoelectric crystal is rotated at approximately 1800 revolutions per minute while the element is intermittently excited with an electrical pulse. This excitation causes the element to vibrate at a frequency dependent upon the particulars of the transducer design. Depending on the dimensions and characteristics of the transducer, this operating frequency is typically in the range of 8 to 50 MHz. In general terms, a higher frequency of operation provides better resolution and a smaller catheter, but at the expense of reduced depth of penetration and increased echoes from the blood (making the image more difficult to interpret). A lower frequency of operation is more suitable for IVUS imaging in larger vessels or within the chambers of the heart. 
     The rotational IVUS catheter has a drive shaft disposed within the catheter body. The transducer is attached to the distal end of the drive shaft. The typical single element piezoelectric transducer requires only two electrical leads, with this pair of leads serving two separate purposes: (1) delivering the intermittent electrical transmit pulses to the transducer, and (2) delivering the received electrical echo signals from the transducer to the receiver amplifier (during the intervals between transmit pulses). The IVUS catheter is removably coupled to an interface module, which controls the rotation of the drive shaft within the catheter body and contains the transmitter and receiver circuitry for the transducer. Because the transducer is on a rotating drive shaft and the transmitter and receiver circuitry is stationary, a device must be utilized to carry the transmit pulse and received echo across a rotating interface. This can be accomplished via a rotary transformer, which comprises two halves, separated by a narrow air gap that permits electrical coupling between the primary and secondary windings of the transformer while allowing relative motion (rotation) between the two halves. The spinning element (transducer, electrical leads, and driveshaft) is attached to the spinning portion of the rotary transformer, while the stationary transmitter and receiver circuitry contained in the interface module are attached to the stationary portion of the rotary transformer. 
     The other type of IVUS catheter is a solid state (or phased array) catheter. This catheter has no rotating parts, but instead includes an array of transducer elements (for example 64 elements), arrayed in a cylinder around the circumference of the catheter body. The individual elements are fired in a specific sequence under the control of several small integrated circuits mounted in the tip of the catheter, adjacent to the transducer array. The sequence of transmit pulses interspersed with receipt of the echo signals provides the ultrasound data required to reconstruct a complete cross-sectional image of the vessel, similar in nature to that provided by a rotational IVUS device. 
     Currently, most IVUS systems rely on conventional piezoelectric transducers, built from piezoelectric ceramic (commonly referred to as the crystal) and covered by one or more matching layers (typically thin layers of epoxy composites or polymers). Two advanced transducer technologies that have shown promise for replacing conventional piezoelectric devices are the PMUT (Piezoelectric Micromachined Ultrasonic Transducer) and CMUT (Capacitive Micromachined Ultrasonic Transducer). PMUT and CMUT transducers may provide improved image quality over that provided by the conventional piezoelectric transducer, but these technologies have not been adopted for rotational IVUS applications due to the larger number of electrical leads they require, among other factors. 
     There are many potential advantages of these advanced transducer technologies, some of which are enumerated here. Both PMUT and CMUT technologies promise reduced manufacturing costs by virtue of the fact that these transducers are built using wafer fabrication techniques to mass produce thousands of devices on a single silicon wafer. This is an important factor for a disposable medical device such as an IVUS catheter. These advanced transducer technologies provide broad bandwidth (&gt;100%) in many cases compared to the 30-50% bandwidth available from the typical piezoelectric transducer. This broader bandwidth translates into improved depth resolution in the IVUS image, and it may also facilitate multi-frequency operation or harmonic imaging, either of which can help to improve image quality and/or enable improved algorithms for tissue characterization, blood speckle reduction, and border detection. Advanced transducer technologies also offer the potential for improved beam characteristics, either by providing a focused transducer aperture (instead of the planar, unfocused aperture commonly used), or by implementing dynamically variable focus with an array of transducer elements (in place of the traditional single transducer element). 
     BRIEF SUMMARY 
     The present invention provides the enabling technology allowing advanced transducer technology to be introduced into a rotational IVUS catheter. This in turn will provide improved image quality and support advanced signal processing to facilitate more accurate diagnosis of the medical condition within the vessel. All of this can be achieved in a cost-effective way, possibly at a lower cost than the conventional technology. 
     Embodiments of an intravascular ultrasound probe are disclosed herein. The probe has features for utilizing an advanced transducer technology on a rotating transducer shaft. In particular, the probe accommodates the transmission of the multitude of signals across the boundary between the rotary and stationary components of the probe required to support an advanced transducer technology. These advanced transducer technologies offer the potential for increased bandwidth, improved beam profiles, better signal to noise ratio, reduced manufacturing costs, advanced tissue characterization algorithms, and other desirable features. Furthermore, the inclusion of electronic components on the spinning side of the probe can be highly advantageous in terms of preserving maximum signal to noise ratio and signal fidelity, along with other performance benefits. 
     In a disclosed embodiment, a rotational intravascular ultrasound probe for insertion into a vasculature is described. The rotational intravascular ultrasound probe can comprise an elongate catheter, an elongate transducer shaft, a spinning element, and a motor. The elongate catheter can have a flexible body. The elongate transducer shaft can be disposed within the flexible body and can have a drive cable and a transducer coupled to the drive cable. The spinning element can be coupled to the transducer shaft and can have an electronic component coupled thereto that is in electrical contact with the transducer. A motor may be coupled to the spinning element for rotating the spinning element and the transducer shaft. 
     In another disclosed embodiment, an interface module for a rotational intravascular ultrasound probe for insertion into a vasculature is described. The interface module can comprise a connector, a spinning element, and a motor. The connector can be used for attachment to a catheter having a transducer shaft with a transducer. The spinning element can be coupled to the connector and can have an electronic component coupled thereto that is in electrical contact with the connector. A motor may be coupled to the spinning element for rotating the spinning element. 
     In yet another disclosed embodiment, an interface module for a rotational intravascular ultrasound probe for insertion into a vasculature is described. The interface module can comprise a printed circuit board, a connector, a spinning element, and a motor. The connector can be used for attachment to a catheter having a transducer shaft with a transducer. The spinning element can be coupled to the connector. The spinning element has more than two signal pathways electrically connecting the spinning element to the connector. A motor may be coupled to the spinning element for rotating the spinning element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified fragmentary diagrammatic view of a rotational IVUS probe; 
         FIG. 2  is a simplified fragmentary diagrammatic view of an interface module and catheter for the rotational IVUS probe of  FIG. 1  incorporating basic ultrasound transducer technology; 
         FIG. 3  is a simplified fragmentary diagrammatic view of an embodiment of an interface module and catheter for the rotational IVUS probe of  FIG. 1  incorporating an advanced ultrasound transducer technology; 
         FIG. 4  is a simplified fragmentary diagrammatic view of another embodiment of an interface module and catheter for the rotational IVUS probe of  FIG. 1  incorporating an advanced ultrasound transducer technology; 
         FIG. 5  is a simplified fragmentary diagrammatic view of another embodiment of an interface module and catheter for the rotational IVUS probe of  FIG. 1  incorporating an advanced ultrasound transducer technology; and 
         FIG. 6  is a simplified fragmentary diagrammatic view of another embodiment of an interface module and catheter for the rotational IVUS probe of  FIG. 1  incorporating an advanced ultrasound transducer technology. 
     
    
    
     DETAILED DESCRIPTION 
     Turning to the figures, representative illustrations of rotational intravascular ultrasound (IVUS) probes, some of which include active spinning elements, are shown therein. An active spinning element can increase the number of signal paths available for the operation of the transducer so that advanced transducer technologies, such as PMUT (Piezoelectric Micromachined Ultrasonic Transducer) and CMUT (Capacitive Micromachined Ultrasonic Transducer), can be utilized with a rotational IVUS probe. In addition, an active spinning element can include active electronics on the rotary side of the probe. 
     Referring specifically to  FIG. 1 , a rotational intravascular ultrasound probe  100  for insertion into a patient for diagnostic imaging is shown. The probe  100  comprises a catheter  101  having a catheter body  102  and a transducer shaft  104 . The catheter body  102  is flexible and has both a proximal end portion  106  and a distal end portion  108 . The catheter body  102  is a sheath surrounding the transducer shaft  104 . For explanatory purposes, the catheter body  102  in  FIG. 1  is illustrated as visually transparent such that the transducer shaft  104  disposed therein can be seen, although it will be appreciated that the catheter body  102  may or may not be visually transparent. The transducer shaft  104  is flushed with a sterile fluid, such as saline, within the catheter body  102 . The fluid serves to eliminate the presence of air pockets around the transducer shaft  104  that adversely affect image quality. The fluid can also act as a lubricant. The transducer shaft  104  has a proximal end portion  110  disposed within the proximal end portion  106  of the catheter body  102  and a distal end portion  112  disposed within the distal end portion  108  of the catheter body  102 . 
     The distal end portion  108  of the catheter body  102  and the distal end portion  112  of the transducer shaft  104  are inserted into a patient during the operation of the probe  100 . The usable length of the probe  100  (the portion that can be inserted into a patient) can be any suitable length and can be varied depending upon the application. The distal end portion  112  of the transducer shaft  104  includes a transducer subassembly  118 . 
     The proximal end portion  106  of the catheter body  102  and the proximal end portion  110  of the transducer shaft  104  are connected to an interface module  114  (sometimes referred to as a patient interface module or PIM). The proximal end portions  106 ,  110  are fitted with a catheter hub  116  that is removably connected to the interface module  114 . 
     The rotation of the transducer shaft  104  within the catheter body  102  is controlled by the interface module  114 , which provides a plurality of user interface controls that can be manipulated by a user. The interface module  114  also communicates with the transducer subassembly  118  by sending and receiving electrical signals to and from the transducer subassembly  118  via wires within the transducer shaft  104 . The interface module  114  can receive, analyze, and/or display information received through the transducer shaft  104 . It will be appreciated that any suitable functionality, controls, information processing and analysis, and display can be incorporated into the interface module  114 . 
     The transducer shaft  104  includes a transducer subassembly  118 , a transducer housing  120 , and a drive cable  122 . The transducer subassembly  118  is coupled to the transducer housing  120 . The transducer housing  120  is attached to the drive cable  122  at the distal end portion  112  of the transducer shaft  104 . The drive cable  122  is rotated within the catheter body  102  via the interface module  114  to rotate the transducer housing  120  and the transducer subassembly  118 . The transducer subassembly  118  can be of any suitable type, including but not limited to one or more advanced transducer technologies such as PMUT or CMUT. The transducer subassembly  118  can include either a single transducer or an array. 
       FIG. 2  shows a rotational IVUS probe  200  utilizing a common spinning element  232 . The probe  200  has a catheter  201  with a catheter body  202  and a transducer shaft  204 . As shown, the catheter hub  216  is near the proximal end portion  206  of the catheter body  202  and the proximal end portion  210  of the transducer shaft  204 . The catheter hub  216  includes a stationary hub housing  224 , a dog  226 , a connector  228 , and bearings  230 . The dog  226  mates with a spinning element  232  for alignment of the hub  216  with the interface module  214  and torque transmission to the transducer shaft  204 . The dog  226  rotates within the hub housing  224  utilizing the bearings  230 . The connector  228  in this figure is coaxial. The connector  228  rotates with the spinning element  232 , described further herein. 
     As shown, the interior of the interface module  214  includes a motor  236 , a motor shaft  238 , a printed circuit board (PCB)  240 , the spinning element  232 , and any other suitable components for the operation of the IVUS probe  200 . The motor  236  is connected to the motor shaft  238  to rotate the spinning element  232 . The printed circuit board  240  can have any suitable number and type of electronic components  242 , including but not limited to the transmitter and the receiver for the transducer. 
     The spinning element  232  has a complimentary connector  244  for mating with the connector  228  on the catheter hub  216 . As shown, the spinning element  232  is coupled to a rotary portion  248  of a rotary transformer  246 . The rotary portion  248  of the transformer  246  passes the signals to and from a stationary portion  250  of the transformer  246 . The stationary portion  250  of the transformer  246  is wired to the transmitter and receiver circuitry on the printed circuit board  240 . 
     The transformer includes an insulating wire that is layered into an annular groove to form a two- or three-turn winding. Each of the rotary portion  250  and the stationary portion  248  has a set of windings, such as  251  and  252  respectively. Transformer performance can be improved through both minimizing the gap between the stationary portion  250  and the rotary portion  248  of the transformer  246  and also by placing the windings  251 ,  252  as close as possible to each other. 
     Advanced transducer technologies can require more than the two conductive signal lines that a single piezoelectric transducer utilizes on a conventional rotational IVUS probe. For example, in addition to signal pathways for ultrasound information communicated with the transducer, certain advanced transducer technologies also require a power supply in order to operate. In order to pass the necessary multiple of signals between the advanced transducer technology and the interface module, a suitable structure may be needed to transmit ultrasound signals, power, and any other suitable signals across the boundary between the rotating and stationary mechanical components. Particularly for ultrasound signals, the mode of transmission must also maintain reliable signal quality, without excess noise, sufficient for the interface module to form a reliable image of the target tissue from the sensitive ultrasound signals. It will be appreciated that any suitable signals can be communicated across the boundary between the rotating and stationary mechanical components including, but not limited to, A-scan RF data, power transmit pulses, low amplitude receive signals, DC power and/or bias, AC power, and/or various control signals. The signal transfer across the boundary between the rotating and stationary mechanical components can have high frequency capability and broadband response. 
     Multiple signal transfer pathways are presented herein for communicating signals across the boundary of the rotating and stationary parts. Each of these pathways are explained in further detail herein, and for purposes of discussion and explanation, certain pathways may be shown in combination with one another. It will be appreciated, however, that any of these pathways may be utilized in any suitable combination with one another to permit any suitable number of total signal pathways. Furthermore, as will be explained in further detail below, certain signal transfer pathways can be more conducive to transmitting either power or other signals, such as ultrasound signals. 
     Referring to  FIG. 3 , an embodiment of a rotational IVUS probe  300  having an interface module  314  and catheter  301  suitable for use with an advanced transducer technology is represented. As shown, the probe  300  has a catheter body  302 , a transducer shaft  304 , and a catheter hub  316 . The catheter body  302  has a proximal end  306  and the transducer shaft  304  has a proximal end  310 . The catheter hub  316  includes a stationary exterior housing  324 , a dog  326 , and a connector  328 . The connector  328  is represented with six conductive lines  354  shown in this embodiment. It will be appreciated, however, that any suitable number of conductive lines can be utilized. 
     As shown, the interior of the interface module  314  can include a motor  336 , a motor shaft  338 , a main printed circuit board (PCB)  340 , a spinning element  332 , and any other suitable components for the operation of the IVUS probe  300 . The motor  336  is connected to the motor shaft  338  to rotate the spinning element  332 . The printed circuit board  340  can have any suitable number and type of electronic components  342 . 
     The spinning element  332  has a complimentary connector  344  for mating with the connector  328  on the catheter hub  316 . The connector  344  can have conductive lines, such as  355 , that contact the conductive lines, such as  354 , on the connector  328 . As shown, the spinning element  332  is coupled to a rotary portion  348  of a rotary transformer  346 . The rotary portion  348  of the transformer  346  passes the signals to and from a stationary portion  350  of the transformer  346 . The stationary portion  350  of the transformer  346  is electrically connected to the printed circuit board  340 . 
     In this embodiment, the transformer  346  has multiple sets of windings for transmitting multiple signals across the transformer  346 . Specifically, as shown, the rotary portion  348  and the stationary portion  350  of the transformer  346  each have two sets of windings, such as windings  352 ,  353  on the stationary portion  350  and windings  351 ,  357  on the rotary portion  348 , to transmit two signals across the transformer  346 . In this way, more signal pathways are available for a probe  300  utilizing an advanced transducer technology. It will be appreciated that any suitable number of windings may be used to transmit any suitable number of signals across the transformer  346 . In alternative embodiments, planar flex circuits can be used in place of the windings in the transformer. The planar flex circuits can be placed very close to one another to enhance signal quality. 
     Another consideration for advanced transducer technologies is that the probe  300  can benefit from the utilization of certain active electronic components and circuitry in order to facilitate and/or complement the operation of the transducer. Through active electronic components and circuitry on the spinning element  332 , more complex electrical communication can take place between the interface module  314  and the transducer. Furthermore, by handling certain signal processing functions on the spinning element  332 , the number of signals that need to pass across the spinning element  332  can, in some embodiments, be reduced. 
     As shown, a printed circuit board  356  can be coupled to the spinning element  332 . The printed circuit board  356  can have any suitable number of electronic components  358  coupled thereto. Any suitable number of printed circuit boards  356  having any suitable number and type of electronic components  358  can be utilized on the spinning element  332 . The electronic components on the spinning element  332  allow for signal processing to take place on the spinning side of the probe  300  before the signal is communicated across the rotary/stationary boundary. 
     Typically, advanced transducer technologies require a DC power source. To provide DC power to the transducer, the spinning element  332  can be fitted with contacts, such as slip ring contacts  360 ,  361 , which are respectively engaged by stationary brushes  362 ,  363  within the interface module  314 . Each of the slip rings  360 ,  361  is coupled to a respective conductive line, such as  355 , in the connector  344 . 
     In other embodiments, the transducer can be powered by an AC power source. For example, instead of using brushes and contacts, AC power can be transmitted through a set of windings in the transformer  346 . Once the power has passed across from the stationary portion  350  of the transformer  346  to the rotary portion  348  of the transformer  346 , it can be passed to a power supply circuit, such as a diode rectifier, on the spinning element  332  that rectifies the AC power into DC power. The rectifier can be coupled to the printed circuit board  356  on the spinning element  332  as one of the electronic components  358 . After the AC power is converted to DC power, the DC power can be used to power the transducer, as well as the other electronic components  358  included on printed circuit board  356 . 
     Turning to  FIG. 4 , an embodiment of a rotational IVUS probe  400  having an interface module  414  and catheter  401  suitable for use with an advanced transducer technology is represented. As shown, the probe  400  has a catheter body  402 , a transducer shaft  404 , and a catheter hub  416 . The catheter body  402  has a proximal end portion  406 , and the transducer shaft  404  has a proximal end portion  410 . The catheter hub  416  includes a stationary exterior housing  424 , a dog  426 , and a connector  428 . The connector  428  is represented with four conductive lines  454  shown in this embodiment. It will be appreciated, however, that any suitable number of conductive lines can be utilized. 
     As shown, the interior of the interface module  414  can include a motor  436 , a motor shaft  438 , a main printed circuit board (PCB)  440 , a spinning element  432 , and any other suitable components for the operation of the IVUS probe  400 . The motor  436  is connected to the motor shaft  438  to rotate the spinning element  432 . The printed circuit board  440  can have any suitable number and type of electronic components  442 . 
     The spinning element  432  has a complimentary connector  444  for mating with the connector  428  on the catheter hub  416 . The connector  444  can have conductive lines, such as  455 , that contact the conductive lines, such as  454 , on the connector  428 . As shown, the spinning element  432  is coupled to a rotary portion  448  of a rotary transformer  446 . The rotary portion  448  of the transformer  446  passes the signals to and from a stationary portion  450  of the transformer. The stationary portion  450  of the transformer  446  is electrically connected to the printed circuit board  440 . 
     As shown, the rotary portion  448  and the stationary portion  450  of the transformer  446  each have a set of windings  451 ,  452  to transmit a signal across the transformer  446 . It will be appreciated that any suitable number of windings may be used to transmit any suitable number of signals across the transformer  446 . In this embodiment, the transformer  446  can be used to transfer the ultrasound signal. It will also be appreciated that a planar flex circuit may be used in place of one or more of the sets of windings as previously described. 
     The probe  400  can benefit from the utilization of certain electronic components and circuitry in order to facilitate and/or complement the operation of the transducer. As shown, one or more printed circuit boards  456 ,  457  can be coupled to the spinning element  432 . The printed circuit boards  456 ,  457  can have any suitable number of electronic components, such as  458  and  459 , coupled thereto. It will be appreciated that any suitable number of printed circuit boards  456 ,  457  having any suitable number and type of electronic components  458 ,  459  can be utilized on the spinning element  432 . Electronic components on the spinning element  432  allow for signal processing to take place on the spinning side of the probe  400  before the signal is communicated across the rotary/stationary boundary. 
     In this embodiment, power is provided to the transducer using a generator mechanism  464  to generate power locally. As illustrated in the figure, the generator mechanism  464  includes a generator coil  466  and a plurality of stator magnets  468 ,  469 . The generator coil  466  can be attached to the spinning element  432  to rotate with the spinning element  432  and generate power. The power generated is AC power, so a power supply circuit, such as a diode rectifier, can be used to convert the AC power into DC power. The rectifier can be coupled to the printed circuit boards  456 ,  457  on the spinning element  432 . After rectification, the DC power can be used to power the transducer as well as the other electronic components  458 ,  459  included on the printed circuit boards  456 ,  457 . It will be appreciated that any suitable generator can be utilized to provide power to the transducer. 
     Another embodiment of a rotational IVUS probe  500  having an interface module  514  and catheter  501  suitable for use with an advanced transducer technology is represented in  FIG. 5 . As shown, the probe has a catheter body  502 , a transducer shaft  504 , and a catheter hub  516 . The catheter body  502  has a proximal end portion  506 , and the transducer shaft  504  has a proximal end portion  510 . The catheter hub  516  includes a stationary exterior housing  524 , a dog  526 , and a connector  528 . The connector  528  is represented with four conductive lines  554  shown in this embodiment. It will be appreciated, however, that any suitable number of conductive lines can be utilized. 
     As shown, the interior of the interface module  514  can include a motor  536 , a motor shaft  538 , a main printed circuit board (PCB)  540 , a spinning element  532 , and any other suitable components for the operation of the IVUS probe  500 . The motor  536  is connected to the motor shaft  538  to rotate the spinning element  532 . The printed circuit board  540  can have any suitable number and type of electronic components  542 . 
     The spinning element  532  has a complimentary connector  544  for mating with the connector on the catheter hub  516 . The connector  544  can have conductive lines, such as  555 , that contact the conductive lines, such as  554 , on the connector  528 . As shown, the spinning element  532  is coupled to a rotary portion  548  of a rotary transformer  546 . The rotary portion  548  of the transformer  546  passes the signals to and from the stationary portion  550  of the transformer  546 . The stationary portion  550  of the transformer  546  is electrically connected to the printed circuit board  540 . 
     As shown, the rotary portion  548  and the stationary portion  550  of the transformer  546  each have one set of windings  551 ,  552  to transmit a signal across the transformer  546 . It will be appreciated that any suitable number of windings  551 ,  552  may be used to transmit any suitable number of signals across the transformer  546 . In this embodiment, the transformer  546  is used to transfer AC power. Once the power has passed across from the stationary portion  550  of the transformer  546  to the rotary portion  548  of the transformer  546 , it can be passed to a power supply circuit, such as a diode rectifier, on the spinning element  532  that rectifies the AC power into DC power. The rectifier can be coupled to the printed circuit boards  556 ,  557  on the spinning element  532 . After the AC power is converted to DC power, the DC power can be used to power the transducer as well as the other electronic components  558 ,  559  included on the printed circuit boards  556 ,  557 . It will also be appreciated that a planar flex circuit may be used in place of one or more of the sets of windings as previously described. 
     As previously mentioned, the probe  500  can benefit from the utilization of certain electronic components and circuitry in order to facilitate and/or complement the operation of the transducer. As shown, one or more printed circuit boards  556 ,  557  can be coupled to the spinning element  532 . The printed circuit boards  556 ,  557  can have any suitable number of electronic components, such as  558  and  559 , coupled thereto. It will be appreciated that any suitable number of printed circuit boards  556 ,  557  having any suitable number and type of electronic components  558 ,  559  can be utilized on the spinning element  532 . Electronic components  558 ,  559  on the spinning element  532  allow for signal processing to take place on the spinning side of the probe  500  before the signal is communicated across the rotary/stationary boundary. 
     In this embodiment, an optical coupler  570  is used to transmit the ultrasound signal. It will be appreciated that any suitable optical coupler may be used. The optical coupler can have a first end  572  and a second end  574 . The first end  572  can be stationary and receive optical signals from the second end  574 , which can be coupled directly or indirectly to the spinning element  532 . The ultrasound signal can be transmitted to circuitry on the printed circuit board  540  or can be carried external to the interface module  514 . 
     One illustrative example of how the ultrasound signal could be communicated over this optical path is that the printed circuit boards  556 ,  557  could include a high speed analog to digital converter (ADC) among electronic components  558 ,  559 . This ADC would be used to digitize the ultrasound echo signal and convert the resultant digital data into a serial bit stream. This serial data would then be provided to an optical transmitter, such as a laser diode circuit, also included on printed circuit boards  558 ,  559  to transmit the high-speed serial bit stream over the rotating optical coupler  570  to an optical receiver circuit included on printed circuit board  540  or located remotely from the interface module  514 . 
     As shown, a structure may be provided that can provide feedback as to the angular position of the transducer. For example, an optical device  576  may be provided that includes a stationary encoder wheel  578  and an optical detector  580 . The optical detector  580  can be attached to a printed circuit board  557  on the spinning element  532 . 
     Another embodiment of a rotational IVUS probe  600  having an interface module  614  and catheter  601  suitable for use with an advanced transducer technology is represented in  FIG. 6 . As shown, the probe  600  has a catheter body  602 , a transducer shaft  604 , and a catheter hub  616 . The catheter body  602  has a proximal end portion  606 , and the transducer shaft  604  has a proximal end portion  610 . The catheter hub  616  includes a stationary exterior housing  624 , a dog  626 , and a connector  628 . The connector is represented with four conductive lines, such as  654 , shown in this embodiment. It will be appreciated, however, that any suitable number of conductive lines  654  can be utilized. 
     As shown, the interior of the interface module  614  can include a motor  636 , a motor shaft  638 , a main printed circuit board (PCB)  640 , a spinning element  632 , and any other suitable components for the operation of the IVUS probe  600 . The motor  636  is connected to the motor shaft  638  to rotate the spinning element  632 . The main printed circuit board  640  can have any suitable number and type of electronic components  642  including but not limited to the transmitter and the receiver for the transducer. 
     The spinning element  632  has a complimentary connector  644  for mating with the connector  628  on the catheter hub  616 . The connector  644  can have conductive lines, such as  655 , that contact the conductive lines, such as  654 , on the connector  628 . As shown, the spinning element  632  is coupled to a rotary portion  648  of a rotary transformer  646 . The rotary portion  648  of the transformer  646  passes the signals to and from the stationary portion  650  of the transformer  646 . The stationary portion  650  of the transformer  646  is electrically connected to the printed circuit board  640 . 
     As shown, the rotary portion  648  and the stationary portion  650  of the transformer  646  each have a set of windings  651 ,  652  to transmit a signal across the transformer  646 . It will be appreciated that any suitable number of windings may be used to transmit any suitable number of signals across the transformer  646 . In this embodiment, the transformer  646  is used to transfer AC power. Once the power has passed across from the stationary portion  650  of the transformer  646  to the rotary portion  648  of the transformer  646 , it can be passed to a power supply circuit, such as a diode rectifier, on the spinning element  632  that rectifies the AC power into DC power. The rectifier can be coupled to printed circuit boards  656 ,  657  on the spinning element  632 . After the AC power is converted to DC power, the DC power can be used to power the transducer as well as the other electronic components  658 ,  659  included on the printed circuit boards  656 ,  657 . It will also be appreciated that a planar flex circuit may be used in place of one or more of the sets of windings as previously described. 
     As previously mentioned, the probe can benefit from the utilization of certain electronic components and circuitry in order to facilitate and/or complement the operation of the transducer. As shown, one or more printed circuit boards  656 ,  657  can be coupled to the spinning element  632 . The printed circuit boards  656 ,  657  can have any suitable number of electronic components, such as  658  and  659 , coupled thereto. It will be appreciated that any suitable number of printed circuit boards  656 ,  657  having any suitable number and type of electronic components  658 ,  659  can be utilized on the spinning element  632 . Electronic components  658 ,  659  on the spinning element  632  allow for signal processing to take place on the spinning side of the probe  600  before the signal is communicated across the rotary/stationary boundary. 
     In this embodiment, a wireless communication mechanism is used to transmit the ultrasound signal. Any suitable wireless communication mechanism may be used including, but not limited to, wireless mechanisms utilizing radio frequency or infrared. As shown, the wireless communication mechanism includes transmitter and/or receiver components  682  and  684 . The transmitter and/or receiver component  682  can be attached to any suitable location such as the printed circuit board  657  on the spinning element  632 . The transmitter and/or receiver component  684  can likewise be placed in any suitable location including the main printed circuit board  640  in the interface module  614 . 
     Therefore, it will be appreciated that signals can be carried across the rotating and stationary mechanical components via any suitable mechanism including, but not limited to, a transformer, an optical coupler, a wireless communication mechanism, a generator, and/or brushes/contacts. In certain embodiments, a transformer, an optical coupler, and/or a wireless communication mechanism can be utilized to carry signals such as an ultrasound signal. In certain embodiments, a transformer, a power generator, and/or brushes/contacts can be utilized to convey power to the transducer. 
     Furthermore, the spinning element can have one or more printed circuit boards with a suitable number and type of active electronic components and circuitry, thus making the spinning element an active spinning element. Examples of electronic components that can be utilized with the active spinning element include, but are not limited to, power supply circuits (such as a generator, rectifier, regulator, high voltage step-up converter, etc.), transmitters (including tripolar transmitters), time-gain-control (TGC) amplifiers, amplitude and/or phase detectors, ADC converters, optical transceivers, encoder circuits, wireless communication components, microcontrollers, and any other suitable components. In addition, the spinning element can include encoder and timing logic such that it can internally generate the transmit triggers, and thus, eliminate the need to communicate a timing signal across the spinning element. Through the embodiments described herein, excellent image quality is possible including wide bandwidth, frequency-agility, low ringdown, focused beam (including dynamically focused beam), and harmonic capability. 
     As mentioned, any suitable advanced transducer technology may be used, including but not limited to PMUT and CMUT transducers, either as single transducers or arrays. As an example, a PMUT transducer can be formed by depositing a piezoelectric polymer (such as polyvinylidene fluoride—PVDF) onto a micromachined silicon substrate. The silicon substrate can include an amplifier and protection circuit to buffer the signal from the PVDF transducer. It can be important to include the amplifier immediately adjacent to the PVDF element because the capacitance of the electrical cables can dampen the signal from the high impedance PVDF transducer. The amplifier typically requires DC power, transmit input(s), and amplifier output connections. The PVDF transducer can be a focused transducer to provide excellent resolution. 
     As mentioned above, having an active spinning element, such as is described herein, permits the utilization of an advanced transducer technology on a rotational IVUS probe. In addition, having an active spinning element can facilitate certain advanced operations of the probe. The enhanced bandwidth of the probe utilizing the active spinner permits the probe to obtain information at a plurality of different frequencies. By way of example and not limitation, the probe can be utilized to obtain ultrasound information taken at two diverse frequencies, such as 20 MHz and 40 MHz. It will be appreciated that any suitable frequency and any suitable quantity of frequencies may be used. 
     Generally, lower frequency information facilitates a tissue versus blood classification scheme due to the strong frequency dependence of the backscatter coefficient of the blood. Higher frequency information generally provides better resolution at the expense of poor differentiation between blood speckle and tissue, which can make it difficult to identify the lumen border. Thus, if information is obtained at a lower frequency and a higher frequency, then an algorithm can be utilized to interleave and display the two data sets to obtain frequency-diverse information that is closely aligned in time and space. In result, a high resolution ultrasound image can be produced with clear differentiation between blood and tissue and accurate delineation of vessel borders. 
     The typical 512 A-lines that compose a single frame of an image can be interspersed into alternating high and low frequency A-lines. As an example, a 20 MHz image can show the blood as black and the tissue as gray, while the 40 MHz image can show the blood and tissue as gray and barely, if at all, distinguishable from one another. It can be recognized through a provided algorithm that black in 20 MHz and gray at 40 MHz is blood, gray at both frequencies is tissue, and black at both frequencies is clear fluid. The broadband capability of advanced transducer technologies, such as PMUT, facilitated by the active spinning element, can allow for closely interleaved A-lines of two or more different center frequencies, possibly including pulse-inversion A-line pairs to generate harmonic as well as fundamental information, which is then combined to provide a robust classification scheme for tissue versus blood. 
     The dual frequency blood classification scheme can be further enhanced by other blood speckle reduction algorithms such as motion algorithms (such as ChromaFlo, Q-Flow, etc.), temporal algorithms, harmonic signal processing, etc. It will be appreciated that any suitable algorithm can be used. 
     Besides intravascular ultrasound, other types of ultrasound catheters can be made using the teachings provided herein. By way of example and not limitation, other suitable types of catheters include non-intravascular intraluminal ultrasound catheters, intracardiac echo catheters, laparoscopic, and interstitial catheters. In addition, the probe may be used in any suitable anatomy, including, but not limited to, coronary, carotid, neuro, peripheral, or venous. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. 
     It will be appreciated that like reference numbers and/or like shown features in the figures can represent like features. It will be appreciated that discussions of like reference numbers and/or like shown features in any embodiment may be applicable to any other embodiment. 
     Any references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein (including any references contained therein). 
     Illustrative embodiments of a rotational IVUS probe incorporating an advanced ultrasound transducer technology are described herein. Variations of the disclosed embodiments will be apparent to those of ordinary skill in the art in view of the foregoing illustrative examples. Those skilled in the relevant art will employ such variations as appropriate, and such variations, embodied in alternative embodiments, are contemplated within the scope of the disclosed invention. The invention is therefore not intended to be limited to the examples described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.