Abstract:
Systems and methods deliver ultrasound energy to an ultrasound transducer having an impedance subject to variations. The systems and methods electrically couple an ultrasound generator to the ultrasound transducer to deliver ultrasound energy. The systems and methods deliver ultrasound energy to the ultrasound transducer at a set output frequency and at an output power level that remains essentially constant, despite variations in the impedance, based upon preprogrammed rules.

Description:
RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/935,908, filed Aug. 23, 2001, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/645,662, filed Aug. 24, 2000, and entitled “Systems and Methods for Enhancing Blood Perfusion Using Ultrasound Energy,” which are both incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to systems and methods for increasing blood perfusion, e.g., in the treatment of myocardial infarction, strokes, and vascular diseases.  
         BACKGROUND OF THE INVENTION  
         [0003]    High frequency (5 MHz to 7 MHz) ultrasound has been widely used for diagnostic purposes. Potential therapeutic uses for ultrasound have also been more recently suggested. For example, it has been suggested that high power, lower frequency ultrasound can be focused upon a blood clot to cause it to break apart and dissolve. The interaction between lower frequency ultrasound in the presence of a thrombolytic agent has also been observed to assist in the breakdown or dissolution of thrombi. The effects of ultrasound upon enhanced blood perfusion have also been observed.  
           [0004]    While the therapeutic potential of these uses for ultrasound has been recognized, their clinical promise has yet to be fully realized. Treatment modalities that can apply ultrasound in a therapeutic way are designed with the premise that they will be operated by trained medical personnel in a conventional fixed-site medical setting. They assume the presence of trained medical personnel in a non-mobile environment, where electrical service is always available. Still, people typically experience the effects of impaired blood perfusion suddenly in public and private settings. These people in need must be transported from the public or private settings to the fixed-site medical facility before ultrasonic treatment modalities can begin. Treatment time (which is often critical in the early stages of impaired blood perfusion) is lost as transportation occurs. Even within the fixed-site medical facility, people undergoing treatment need to be moved from one care unit to another. Ultrasonic treatment modalities must be suspended while the person is moved.  
         SUMMARY OF THE INVENTION  
         [0005]    The invention provides systems and methods for delivering ultrasound energy to an ultrasound transducer having an impedance subject to variations. The systems and methods electrically couple an ultrasound generator to the ultrasound transducer to deliver ultrasound energy. The systems and methods deliver ultrasound energy to the ultrasound transducer at a set output frequency and at an output power level that remains essentially constant, despite variations in the impedance, based upon preprogrammed rules.  
           [0006]    In one embodiment, the systems and methods can interrupt delivery of ultrasound energy to the transducer, e.g., when the impedance is greater than a predetermined maximum level, or when the impedance is less than a predetermined minimum level.  
           [0007]    In one embodiment, the preprogrammed rules increase output voltage in response to an increase in impedance. The preprogrammed rules can also prevent increases in the output voltage to a level greater than a predetermined maximum level.  
           [0008]    In one embodiment, the preprogrammed rules increase output current in response to a decrease in impedance. The preprogrammed rules can also prevent increases to the output current to a level greater than a predetermined maximum level.  
           [0009]    In one embodiment, the preprogrammed rules vary the operating frequency of the ultrasound energy relative to the set operating frequency in response to variations in impedance.  
           [0010]    The systems and methods can locate the transducer to transcutaneously apply the ultrasound energy to a targeted tissue region.  
           [0011]    Other features and advantages of the inventions are set forth in the following specification and attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of a system for transcutaneously applying ultrasound energy to affect increased blood perfusion.  
         [0013]    [0013]FIG. 2 is an enlarged exploded perspective view of an ultrasound applicator that forms a part of the system shown in FIG. 1.  
         [0014]    [0014]FIG. 3 is an enlarged assembled perspective view of the ultrasound applicator shown in FIG. 2.  
         [0015]    [0015]FIG. 4 is a side section view of the acoustic contact area of the ultrasound applicator shown in FIG. 2.  
         [0016]    [0016]FIG. 5 is a view of the applicator shown in FIG. 2 held by a stabilization assembly in a secure position overlaying the sternum of a patient, to transcutaneously direct ultrasonic energy, e.g., toward the vasculature of the heart.  
         [0017]    [0017]FIG. 6 is a side elevation view, with portions broken away and in section, of an acoustic stack that can be incorporated into the applicator shown in FIG. 2.  
         [0018]    [0018]FIG. 7 is a side elevation view, with portions broken away and in section, of an acoustic stack that can be incorporated into the applicator shown in FIG. 2.  
         [0019]    [0019]FIG. 8 a  to  8   c  graphically depict the technical features of a frequency tuning function that the system shown in FIG. 1 can incorporate.  
         [0020]    [0020]FIG. 9 graphically depicts the technical features of a power ramping function that the system shown in FIG. 1 can incorporate.  
         [0021]    [0021]FIG. 10 is a schematic view of a controller that the system shown in FIG. 1 can incorporate, which includes a frequency tuning function, a power ramping function, an output power control function, and a use monitoring function.  
         [0022]    [0022]FIG. 11 is a diagrammatic view of a use register chip that forms a part of the use monitoring function shown in FIG. 10.  
         [0023]    [0023]FIG. 12 is a diagrammatic flow chart showing the technical features of the use monitoring function shown in FIG. 10. 
     
    
       [0024]    The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    The various aspects of the invention will be described in connection with the therapeutic indication of providing increased blood perfusion by the transcutaneous application of ultrasonic energy. That is because the features and advantages of the invention are well suited to this therapeutic indication. Still, it should be appreciated that many aspects of the invention can be applied to achieve other diagnostic or therapeutic objectives as well.  
         [0026]    Furthermore, in describing the various aspects of the invention in the context of the illustrated embodiment, the region targeted for an increase in blood perfusion is the thoracic cavity (i.e., the space where the heart and lungs are contained). It should be appreciated, however, that the features of invention have application in other regions of the body, too, for example, in the arms, legs, or brain.  
         [0027]    I. System for Providing Noninvasive Ultrasound-Assisted Blood Perfusion  
         [0028]    [0028]FIG. 1 schematically shows a compact, portable therapeutic system 10 that makes it possible to treat a person who needs or who is likely to need an increase in the flow rate or perfusion of circulating blood.  
         [0029]    The system  10  includes durable and disposable equipment and materials necessary to treat the person at a designated treatment location. In use, the system  10  affects increased blood perfusion by transcutaneously applying ultrasonic energy.  
         [0030]    As FIG. 1 shows, the system  10  includes at the treatment location an ultrasound generating machine  16 . The system  10  also includes at the treatment location at least one ultrasound applicator  18 , which is coupled to the machine  16  during use. As FIG. 5 shows, the system  10  also includes an assembly  12  for use with the applicator  18  to stabilize the position of the applicator  18  on a patient for hands-free use. In the illustrated embodiment (see FIG. 5), the applicator  18  is secured against movement on a person&#39;s thorax, overlaying the sternum, to direct ultrasonic energy toward the vasculature of the heart.  
         [0031]    The location where treatment occurs can vary. It can be a traditional clinical setting, where support and assistance by one or more medically trained care givers are immediately available to the person, such as inside a hospital, e.g., in an emergency room, catheter lab, operating room, or critical care unit. However, due to the purposeful design of the system  10 , the location need not be confined to a traditional clinical setting. The location can comprise a mobile setting, such as an ambulance, helicopter, airplane, or like vehicle used to convey the person to a hospital or another clinical treatment center. The location can even comprise an everyday, public setting, such as on a cruise ship, or at a sports stadium or airport, or a private setting, such as in a person&#39;s home, where the effects of low blood perfusion can arise.  
         [0032]    By purposeful design of durable and disposable equipment, the system  10  can make it possible to initiate treatment of a reduced blood perfusion incident in a non-clinical, even mobile location, outside a traditional medical setting. The system thereby makes effective use of the critical time period before the person enters a hospital or another traditional medical treatment center.  
         [0033]    The features and operation of the system  10  will now be described in greater detail.  
         [0034]    A. The Ultrasound Generator  
         [0035]    [0035]FIG. 1 shows a representative embodiment of the ultrasound generating machine  16 . The machine  16  can also be called an “ultrasound generator.” The machine  16  is intended to be a durable item capable of long term, maintenance free use.  
         [0036]    As shown in FIG. 1, the machine  16  can be variously sized and shaped to present a lightweight and portable unit, presenting a compact footprint suited for transport. The machine  16  can be sized and shaped to be mounted at bedside, or to be placed on a table top or otherwise occupy a relatively small surface area. This allows the machine  16  to travel with the patient within an ambulance, airplane, helicopter, or other transport vehicle where space is at a premium. This also makes possible the placement of the machine  16  in a non-obtrusive way within a private home setting, such as for the treatment of chronic angina.  
         [0037]    In the illustrated embodiment, the machine  16  includes a chassis  22 , which, for example, can be made of molded plastic or metal or both. The chassis  22  houses a module  24  for generating electric signals. The signals are conveyed to the applicator  18  by an interconnect  30  to be transformed into ultrasonic energy. A controller  26 , also housed within the chassis  22  (but which could be external of the chassis  22 , if desired), is coupled to the module  24  to govern the operation of the module  24 . Further desirable technical features of the controller  26  will be described later.  
         [0038]    The machine  16  also preferably includes an operator interface  28 . Using the interface  28 , the operator inputs information to the controller  26  to affect the operating mode of the module  24 . Through the interface  28 , the controller  26  also outputs status information for viewing by the operator. The interface  28  can provide a visual readout, printer output, or an electronic copy of selected information regarding the treatment. The interface  28  is shown as being carried on the chassis  22 , but it could be located external of the chassis  22  as well.  
         [0039]    The machine  16  includes a power cord  14  for coupling to a conventional electrical outlet, to provide operating power to the machine  16 . The machine  16  can also include a battery module (not shown) housed within the chassis  22 , which enables use of the machine  16  in the absence or interruption of electrical service. The battery module can comprise rechargeable batteries, that can be built in the chassis  22  or, alternatively, be removed from the chassis  22  for recharge. Likewise, the battery module (or the machine  16  itself) can include a built-in or removable battery recharger. Alternatively, the battery module can comprise disposable batteries, which can be removed for replacement.  
         [0040]    Power for the machine  16  can also be supplied by an external battery and/or line power module outside the chassis  22 . The battery and/or line power module is releasably coupled at time of use to the components within the chassis  22 , e.g., via a power distribution module within the chassis  22 .  
         [0041]    The provision of battery power for the machine  16  frees the machine  16  from the confines surrounding use of conventional ultrasound equipment, caused by their dependency upon electrical service. This feature makes it possible for the machine  16  to provide a treatment modality that continuously “follows the patient,” as the patient is being transported inside a patient transport vehicle, or as the patient is being shuttled between different locations within a treatment facility, e.g., from the emergency room to a holding area within or outside the emergency room.  
         [0042]    In a representative embodiment, the chassis  22  measures about 12 inches×about 8 inches×about 8 inches and weighs about 9 pounds.  
         [0043]    B. The Ultrasound Applicator  
         [0044]    As shown in FIG. 5, the applicator  18  can also be called the “patient interface.” The applicator  18  comprises the link between the machine  16  and the treatment site within the thoracic cavity of the person undergoing treatment. The applicator  18  converts electrical signals from the machine  16  to ultrasonic energy, and further directs the ultrasonic energy to the targeted treatment site.  
         [0045]    Desirably, the applicator  18  is intended to be a disposable item. At least one applicator  18  is coupled to the machine  16  via the interconnect  30  at the beginning a treatment session. The applicator  18  is preferably decoupled from the interconnect  30  (as FIG. 1 shows) and discarded upon the completing the treatment session. However, if desired, the applicator  18  can be designed to accommodate more than a single use.  
         [0046]    As FIGS. 2 and 3 show, the ultrasound applicator  18  includes a shaped metal or plastic body  38  ergonomically sized to be comfortably grasped and manipulated in one hand. The body  38  houses and supports at least one ultrasound transducer  40  (see FIG. 3).  
         [0047]    In the illustrated embodiment, the ultrasound transducer  40  comprises an acoustic stack  20 . The acoustic stack  20  comprises a front mass piece  32 , a back mass piece  34 , and one or more piezoelctric elements  36 , which are bolted together. The back mass piece  34  comprises an annular ring of material having relatively high acoustic impedance, e.g., steel or stainless steel. “Acoustic impedance” is defined as the product of the density of the material and the speed of sound.  
         [0048]    The front mass piece  32  comprises a cone-shaped piece of material having relatively low acoustic impedance, e.g., aluminum or magnesium. The piezoelectric elements  36  are annular rings made of piezoelectric material, e.g., PZT. An internally threaded hole or the like receives a bolt  42  that mechanically biases the acoustic stack  20 . A bolt  42  that can be used for this purpose is shown in U.S. Pat. No. 2,930,912. The bolt  42  can extend entirely through the front mass piece  32  or, the bolt  42  can extend through only a portion of the front mass piece  32  (see FIG. 7).  
         [0049]    In an alternative embodiment (see FIG. 6), the acoustic stack  20 ′ of a transducer  40 ′ can comprise a single piezoelectric element  36 ′ sandwiched between front and back mass pieces  32 ′ and  34 ′. In this arrangement, the back mass piece  34 ′ is electrically insulated from the front mass piece  32 ′ by, e.g., an insulating sleeve and washer  44 .  
         [0050]    The piezoelectric element(s)  36 / 36 ′ have electrodes  46  (see FIG. 2) on major positive and negative flat surfaces. The electrodes  46  electrically connect the accoustic stack  20  of the transducer  40  to the electrical signal generating module  24  of the machine  16 . When electrical energy at an appropriate frequency is applied to the electrodes  46 , the piezoelectric elements  36 / 36 ′ convert the electrical energy into mechanical (i.e., ultrasonic) energy in the form of mechanical vibration.  
         [0051]    The mechanical vibration created by the transducer  40 / 40 ′ is coupled to a patient through a transducer bladder  48 , which rests on a skin surface. The bladder  48  defines a bladder chamber  50  (see FIG. 4) between it and the front mass piece  32 . The bladder chamber  50  spaces the front mass piece  32  a set distance from the patient&#39;s skin. The bladder chamber  50  accommodates a volume of an acoustic coupling media liquid, e.g., liquid, gel, oil, or polymer, that is conductive to ultrasonic energy, to further cushion the contact between the applicator  18  and the skin. The presence of the acoustic coupling media also makes the acoustic contact area of the bladder  48  more conforming to the local skin topography.  
         [0052]    Desirably, an acoustic coupling medium is also applied between the bladder  48  and the skin surface. The coupling medium can comprise, e.g., a gel material (such as AQUASONIC® 100, by Parker Laboratories, Inc., Fairfield, N.J.). The external material can possess sticky or tacky properties, to further enhance the securement of the applicator  18  to the skin.  
         [0053]    In the illustrated embodiment, the bladder  48  and bladder chamber  50  together form an integrated part of the applicator  18 . Alternatively, the bladder  48  and bladder chamber  50  can be formed by a separate molded component, e.g., a gel or liquid filled pad, which is supplied separately. A molded gel filled pad adaptable to this purpose is the AQUAFLEX® Ultrasound Gel Pad sold by Parker Laboratories (Fairfield, N.J.).  
         [0054]    In a representative embodiment, the front mass piece  32  of the acoustic stack  20  measures about 2 inches in diameter, whereas the acoustic contact area formed by the bladder  48  measures about 4 inches in diameter. An applicator  18  that presents an acoustic contact area of larger diameter than the front mass piece  32  of the transducer  40  makes possible an ergonomic geometry that enables single-handed manipulation during set-up, even in confined quarters, and further provides(with the assembly  12 ) hands-free stability during use. In a representative embodiment, the applicator  18  measures about 4 inches in diameter about the bladder  48 , about 4 inches in height, and weighs about one pound.  
         [0055]    An O-ring  52  (see FIG. 4) is captured within a groove  54  in the body  38  of the applicator  18  and a groove  84  on the front mass piece  32  of the transducer  40 . The o-ring  52  seals the bladder chamber  50  and prevents liquid in the chamber  50  from contacting the sides of the front mass piece  32 . Thus, as FIG. 4 shows, only the outer surface of the front mass piece  32  is in contact with the acoustic coupling medium within the chamber  50 .  
         [0056]    Desirably, the material of the O-ring  52  is selected to possess elasticity sufficient to allow the acoustic stack  20  of the transducer  40  to vibrate freely in a piston-like fashion within the transducer body  38 . Still, the material of the O-ring  52  is selected to be sturdy enough to prevent the acoustic stack  20 , while vibrating, from popping out of the grooves  54  and  84 .  
         [0057]    In a representative embodiment, the O-ring  52  is formed from nitrile rubber (Buna-N) having a hardness of about 30 Shore A to about 100 Shore A. Preferably, the O-ring  52  has a hardness of about 65 Shore A to about 75 Shore A.  
         [0058]    The bladder  48  is stretched across the face of the bladder chamber  50  and is preferably also locked in place with another O-ring  56  (see FIG. 4). A membrane ring may also be used to prevent the O-ring  56  from popping loose. The membrane ring desirably has a layer or layers of soft material (e.g., foam) for contacting the skin.  
         [0059]    Localized skin surface heating effects may arise by the presence of air bubbles trapped between the acoustic contact area (i.e., the surface of the bladder  48 ) and the individual&#39;s skin. In the presence of ultrasonic energy, the air bubbles vibrate, and thereby may cause cavitation and attendant conductive heating effects at the skin surface. To minimize the collection of air bubbles along the acoustic contact area, the bladder  48  desirably presents a flexible, essentially flat radiating surface contour where it contacts the individual&#39;s skin (see FIG. 4), or a flexible, outwardly bowed or convex radiating surface contour(i.e., curved away from the front mass piece) where it contacts with or conducts acoustic energy to the individual&#39;s skin. Either a flexible flat or convex surface contour can “mold” evenly to the individual&#39;s skin topography, to thereby mediate against the collection and concentration of air bubbles in the contact area where skin contact occurs.  
         [0060]    To further mediate against cavitation-caused localized skin surface heating, the interior of the bladder chamber  50  can include a recessed well region  58  surrounding the front mass piece  32 . The well region  58  is located at a higher gravity position than the plane of the front mass piece  32 . Air bubbles that may form in fluid located in the bladder chamber  50  are led by gravity to collect in the well region  58  away from the ultrasonic energy beam path.  
         [0061]    The front mass piece  32  desirably possesses either a flat radiating surface (as FIG. 4 shows) or a convex radiating surface (as FIG. 7 shows). The convex radiation surface directs air bubbles off the radiating surface. The radiating surface of the front mass piece may also be coated with a hydrophilic material  60  (see FIG. 4) to prevent air bubbles from sticking.  
         [0062]    The transducer  40  may also include a reflux valve/liquid inlet port  62 .  
         [0063]    The interconnect  30  carries a distal connector  80  (see FIG. 2), designed to easily plug into a mating outlet in the applicator  18 . A proximal connector  82  on the interconnect  30  likewise easily plugs into a mating outlet on the chassis  22  (see FIG. 1), which is itself coupled to the controller  26 . In this way, the applicator  18  can be quickly connected to the machine  16  at time of use, and likewise quickly disconnected for discard once the treatment session is over. Other quick-connect coupling mechanisms can be used. It should also be appreciated that the interconnect  30  can be hard wired as an integrated component to the applicator  18  with a proximal quick-connector to plug into the chassis  22 , or, vice versa, the interconnect  30  can be hard wired as an integrated component to the chassis  22  with a distal quick-connector to plug into the applicator  18 .  
         [0064]    As FIG. 5 shows, the stabilization assembly  12  allows the operator to temporarily but securely mount the applicator  18  against an exterior skin surface for use. In the illustrated embodiment, since the treatment site exists in the thoracic cavity, the attachment assembly  54  is fashioned to secure the applicator  18  on the person&#39;s thorax, overlaying the sternum or breastbone, as FIG. 5 shows.  
         [0065]    The assembly  12  can be variously constructed. As shown in FIG. 5, the assembly  12  comprises straps  90  that pass through brackets  92  carried by the applicator  18 . The straps  90  encircle the patient&#39;s neck and abdomen.  
         [0066]    Just as the applicator  18  can be quickly coupled to the machine  16  at time of use, the stabilization assembly  12  also preferably makes the task of securing and removing the applicator  18  on the patient simple and intuitive. Thus, the stabilization assembly  12  makes it possible to secure the applicator  18  quickly and accurately in position on the patient in cramped quarters or while the person (and the system  10  itself) is in transit.  
         [0067]    Desirably, when used to apply ultrasonic energy transcutaneously in the thoracic cavity to the heart, the front mass piece  32  is sized to deliver ultrasonic energy in a desired range of fundamental frequencies to substantially the entire targeted region (e.g., the heart). Generally speaking, the fundamental frequencies of ultrasonic energy suited for transcutaneous delivery to the heart in the thoracic cavity to increase blood perfusion can lay in the range of about 500 kHz or less. Desirably, the fundamental frequencies for this indication lay in a frequency range of about 20 kHz to about 100 kHz, e.g., about 27 kHz.  
         [0068]    II. Controlling the Application of Ultrasound Energy  
         [0069]    To achieve the optimal application of ultrasound energy and the optimal therapeutic effect, the application of ultrasound energy should desirably incorporate one or more of the following features: (1) choice, or tuning, of the output frequency, (2) power ramping, (3) output power control, and (4) pulsed power.  
         [0070]    A. Tuning of Output Frequency  
         [0071]    Depending upon the treatment parameters and outcome desired, the controller 26 can operate a given transducer  40  at a fundamental frequency below about 50 kHz, or in a fundamental frequency range between about 50 kHz and about 1 MHz, or at fundamental frequencies above 1 MHz.  
         [0072]    A given transducer  40  can be operated in either a pulsed or a continuous mode, or in a hybrid mode where both pulsed and continuous operation occurs in a determined or random sequence at one or more fundamental frequencies.  
         [0073]    The applicator  18  can include multiple transducers  40  (or multiple applicators  18  can be employed simultaneously for the same effect), which can be individually conditioned by the controller  26  for operation in either pulsed or continuous mode, or both. For example, the multiple transducers  40  can all be conditioned by the controller  26  for pulsed mode operation, either individually or in overlapping synchrony. Alternatively, the multiple transducers  40  can all be conditioned by the controller  26  for continuous mode operation, either individually or in overlapping synchrony. Still alternatively, the multiple transducers  40  can be conditioned by the controller  26  for both pulsed and continuous mode operation, either individually or in overlapping synchrony.  
         [0074]    One or more transducers  40  within an array of transducers  40  can also be operated at different fundamental frequencies. For example, one or more transducers  40  can be operated at about 25 kHz, while another one or more transducers  40  can be operated at about 100 kHz. More than two different fundamental frequencies can be used, e.g., about 25 kHz, about 50 kHz, and about 100 kHz.  
         [0075]    Operation at different fundamental frequencies provides different effects. For example, given the same power level, at about 25 kHz, more cavitation effects are observed to dominate, while above 500 kHz, more heating effects are observed to dominate.  
         [0076]    The controller  26  can trigger the fundamental frequency output according to time or a physiological event (such as ECG or respiration).  
         [0077]    A given transducer  40  can be operated at a frequency within a certain range of frequencies suitable to the transducer  40 . The optimal frequency for a given treatment is dependent on a number of factors, e.g., the magnitude of the fill volume of the bladder chamber  50 ; the characteristics of the acoustic coupling between the acoustic contact area (i.e., bladder  48 ) and the patient&#39;s skin; the morphology of the patient (e.g., size, weight, girth) which affect the transmission of ultrasound energy through the skin and within the body; the acoustic load impedance seen by the transducer  40 .  
         [0078]    As FIG. 10 shows, the controller  26  desirably includes a tuning function  64 . The tuning function  64  selects an optimal frequency at the outset of each treatment session, taking into account at least some of the above-listed factors. In the illustrated embodiment (see FIGS. 8A to  8 C), the tuning function sweeps the output frequency within a predetermined range of frequencies (f-start to f-stop). The frequency sweep can be and desirably is done at an output power level that is lower than the output power level of treatment (see FIG. 9). The frequency sweep can also be done in either a pulsed or a continuous mode, or in a hybrid mode. An optimal frequency of operation is selected based upon one or more parameters sensed during the sweeping operation.  
         [0079]    As FIG. 8A shows, the frequency sweep can progress from a lower frequency (f-start) to a higher frequency (f-stop), or vice versa. The sweep can proceed on a linear basis (as FIG. 8A also shows), or it can proceed on a non-linear basis, e.g., logarithmically or exponentially or based upon another mathematical function. The range of the actual frequency sweep may be different from the range that is used to determine the frequency of operation. For instance, the frequency span used for the determination of the frequency of operation may be smaller than the range of the actual sweep range.  
         [0080]    In one frequency selection approach (see FIGS. 8A and 8C), while sweeping frequencies, the tuning function  64  adjusts the output voltage and/or current to maintain a constant output power level (p-constant). The function  64  also senses changes in transducer impedance (see FIG. 8B)—Z-min to Z-max—throughout the frequency sweep. In this approach (see FIG. 8B), the tuning function  64  selects as the frequency of operation the frequency (f-tune) where, during the sweep, the minimum magnitude of transducer impedance (Z-min) is sensed. Typically, this is about the same as the frequency of maximum output current (I), which in turn, is about the same as the frequency of minimum output voltage (V).  
         [0081]    In an alternative frequency selection approach, the tuning function  64  can select as the frequency of operation the frequency where, during the sweep, the maximum of real transducer impedance (Z) occurs, where: 
         | Z |={square root}{square root over (( R )} 2   +X   2 ) 
         [0082]    and where |Z| is the absolute value of the transducer impedance (Z), which derived according to the following expression: 
         
       Z=R+iX 
     
         [0083]    where R is the real part, and X is the imaginary part.  
         [0084]    In another alternative frequency selection approach, while sweeping the frequencies, the tuning function  64  can maintain a constant output voltage. In this approach, the tuning function  64  can select as the frequency of operation the frequency where, during the sweep, the maximum output power occurs. Alternatively, the tuning function  64  can select as the frequency of operation the frequency where, during the sweep, the maximum output current occurs.  
         [0085]    B. Power Ramping  
         [0086]    As before described, the tuning function  64  desirably operates an output power level lower than the output power level of treatment. In this arrangement, once the operating frequency has been selected, the output power level needs to be increased to the predetermined output level to have the desired therapeutic effect.  
         [0087]    In the illustrated embodiment (see FIG. 10), the controller  26  includes a ramping function  66 . The ramping function  66  (see FIG. 9) causes a gradual ramp up of the output power level from the power level at which the tuning function  64  is conducted (e.g., 5 W) to the power level at which treatment occurs (e.g., 25 W). The gradual ramp up decreases the possibility of unwanted patient reaction to the ultrasound exposure. Further, a gradual ramp up is likely to be more comfortable to the patient than a sudden onset of the full output power.  
         [0088]    In a desired embodiment, the ramping function  66  increases power at a rate of about 0.01 W/s to about 10 W/s. A particularly desired ramping rate is between about 0.1 W/s to about 5 W/s. The ramping function  66  desirably causes the ramp up in a linear fashion (as FIG. 9 shows). However, the ramping function can employ non-linear ramping schemes, e.g., logarithmic or according to another mathematical function.  
         [0089]    C. Output Power Control  
         [0090]    Also depending upon the treatment parameters and outcome desired, the controller  26  can operate a given transducer  40  at a prescribed power level, which can remain fixed or can be varied during the treatment session. The controller  26  can also operate one or more transducers  40  within an array of transducers  40  (or when using multiple applicators  18 ) at different power levels, which can remain fixed or themselves vary over time.  
         [0091]    The parameters affecting power output take into account the output of the signal generator module; the physical dimensions and construction of the applicator; and the physiology of the tissue region to which ultrasonic energy is being applied.  
         [0092]    During a given treatment session, the transducer impedance may vary due to a number of reasons, e.g., transducer heating, changes in acoustic coupling between the transducer and patient, and/or changes in the transducer bladder fill volume due to degassing and /or leaks. In the illustrated embodiment (see FIG. 10) , the controller  26  includes an output power control function  68 . The output power control function  68  holds the output power constant, despite changes in transducer impedance within a predetermined range. If the transducer falls out of the predetermined range, for instance, due to an open or a short circuit, the controller  26  shutdowns the generator ultrasound module  24  and desirably sounds an alarm.  
         [0093]    Governed by the output power control function  68 , as the transducer impedance increases, the output voltage is increased to hold the power output constant. Should the output voltage reach a preset maximum allowable value, the output power will decrease, provided the transducer impedance remains within its predetermined range. As the transducer impedance subsequently drops, the output power will recover, and the full output power level will be reached again.  
         [0094]    Governed by the output power control function  68 , as the transducer impedance decreases, the output current is increased to hold the power output constant. Should the output current reach a preset maximum allowable value, the output power will decrease until the impedance increases, again, and will allow full output power.  
         [0095]    In addition to the described changes in the output voltage and current to maintain a constant output power level, the output power control function  68  can vary the frequency of operation slightly upward or downward to maintain the full output power level within the allowable current and voltage limits.  
         [0096]    D. Pulsed Power Mode  
         [0097]    The application of ultrasonic energy in a pulsed power mode can serve to reduce the localized heating effects that can arise due to operation of the transducer  40 .  
         [0098]    During the pulsed power mode, ultrasonic energy is applied at a desired fundamental frequency or within a desired range of fundamental frequencies at the prescribed power level or range of power levels (as described above, to achieve the desired physiologic effect) in a prescribed duty cycle (DC) (or range of duty cycles) and a prescribed pulse repetition frequency (PRF) (or range of pulse repetition frequencies). Desirably, the pulse repetition frequency (PRF) is between about 20 Hz to about 50 Hz (i.e, between about 20 pulses a second to about 50 pulses a second).  
         [0099]    The duty cycle (DC) is equal to the pulse duration (PD) divided by one over the pulse repetition frequency (PRF). The pulse duration (PD) is the amount of time for one pulse. The pulse repetition frequency (PRF) represents the amount of time from the beginning of one pulse to the beginning of the next pulse. For example, given a pulse repetition frequency (PRF) of 30 Hz (30 pulses per second) and a duty cycle of 25% yields a pulse duration (PD) of approximately 8 msec. At these settings, the system outputs an 8 msec pulse followed by a 25 msec off period 30 times per second.  
         [0100]    Given a pulse repetition frequency (PRF) selected at 25 Hz and a desired fundamental frequency of 27 kHz delivered in a power range of between about 15 to 30 watts, a duty cycle of about 50% or less meets the desired physiologic objectives in the thoracic cavity, with less incidence of localized conductive heating effects compared to a continuous application of the same fundamental frequency and power levels over a comparable period of time. Given these operating conditions, the duty cycle desirably lays in a range of between about 10% and about 35%.  
         [0101]    III. Monitoring Use of the Transducer  
         [0102]    To protect patients from the potential adverse consequences occasioned by multiple use, which include disease transmission, or material stress and instability, or decreased or unpredictable performance, the controller  26  desirably includes a use monitoring function  70  (see FIG. 10) that monitors incidence of use of a given transducer  40 .  
         [0103]    In the illustrated embodiment, the transducer  40  carries a use register  72  (see FIG. 4). The use register  72  is configured to record information before, during, and after a given treatment session. The use register  72  can comprise a solid state micro-chip, ROM, EEROM, EPROM, or non volatile RAM (NVRAM) carried by the transducer  40 .  
         [0104]    The use register  72  is initially formatted and programmed by the manufacturer of the system to include memory fields. In the illustrated embodiment (see FIG. 11), the memory fields of the use register are of two general types: Write Many Memory Fields  74  and Write-Once Memory Fields  76 . The Write Many Memory Fields  74  record information that can be changed during use of the transducer  40 . The Write-Once Memory Fields  76  record information that, once recorded, cannot be altered.  
         [0105]    The specific information recorded by the Memory Fields  74  and  76  can vary. The following table exemplifies typical types of information that can be recorded in the Write Many Memory Fields  74 .  
                                                       Size       Field Name   Description   Location   (Byte)                   Treatment   If a transducer has been used for a   0    1       Complete   prescribed maximum treatment time           (e.g., 60 minutes), the treatment           complete flag is set to 1 otherwise           it is zero.       Prescribed   This is the allowable usage time of   1-2    2       Maximum   the transducer. This is set by the       Treatment   manufacturer and determines at what       Time   point the Treatment Complete flag is       (Minutes)   is set to 1.       Elapsed   Initialized to zero. This area is then   3-4    2       Usage Time   incremented every minute that the       (Minutes)   system is transmitting ultrasound           energy. This area keeps track of the           amount of time that the transducer           has been used. When this time           reaches the Prescribed Maximum           Treatment Time, the Treatment           Complete flag is set to 1.       Transducer   This is an area that could be used to   5-6    2       Frequency   prescribe the operational frequency of           the transducer, rather than tuning the           transducer to an optimal frequency,           as above described. In the latter           instance, this area shows the tuned           frequency once the transducer has           been tuned.       Average   The system reads and accumulates   7-8    2       Power   the delivered power throughout the       (Watts)   procedure. Every minute, the average           power number is updated in this area           from the system, at the same time the           Elapsed Usage Time is updated.           when the Usage time clock is           updated. This means that the average           power reading could be off by a           maximum of 59 seconds if the           treatment is stopped before the           Treatment Complete flag is set. This           average power can be used as a check           to make sure that the system was           running at full power during the           procedure.       Applicator   Use Register CRC. This desirably    9-10    2       CRC   uses the same CRC algorithm used to           protect the controller ROM.       Copyright   Desirably, the name of the   11-23   11       Notice   manufacturer is recorded in this area.           Other information can be recorded           here as well.                  
 
         [0106]    The on/off cycles of ultrasound transmission could affect the accuracy of the recorded power levels because of the variance of the power levels due to ramping function  66 . For this reason it may be advantageous to also record the number of on/off cycles of ultrasound transmission. This will help explain any discrepancies in the average power reading. It might also allow the identification of procedural problems with system use.  
         [0107]    Each use register  72  can be assigned a unique serial number that could be used to track transducers in the field. This number can be read by the use monitoring function  70  if desired.  
         [0108]    The following table exemplifies typical types of information that can be recorded in the Write-Once Memory Fields  76 .  
                                                         Size       Field Name   Description   (Bytes)                                Start Date Time   Once the system has tuned the transducer           and started to transmit ultrasound, the current           date and time are written to this area. This           area is then locked, which prevents the data           from ever-being changed.       Tuned Frequency   The tuned frequency is written to this           location when the Start Date and Time is set.           This prevents this information from being           written over on subsequent tunes (if           necessary).                  
 
         [0109]    As FIG. 12 shows, when a transducer  40  is first coupled to the machine  16 , and prior to enabling the conveyance of ultrasound energy to the transducer  40 , the use monitoring function  70  prompts the use register  72  to output resident information recorded in the memory fields.  
         [0110]    The use monitoring function  70  compares the contents of the Copyright Notice field to a prescribed content. In the illustrated embodiment, the prescribed content includes information contained in the Copyright Notice field of the Write Many Memory Fields  74 . The prescribed content therefore includes the name of the manufacturer, or other indicia uniquely associated with the manufacture. If the prescribed content is missing, the use monitoring function  70  does not enable use of the transducer  40 , regardless of the contents of any other memory field. The transducer  40  is deemed “invalid.” In this way, a manufacturer can assure that only transducers meeting its design and quality control standards are operated in association with the machine  16 .  
         [0111]    If the contents of the Copyright Notice field match, the use monitoring function  70  compares the digital value residing in the Treatment Complete field of the Write Many Memory Fields  74  to a set value that corresponds to a period of no prior use or a prior use less than the Prescribed Maximum Treatment Time—i.e., in the illustrated embodiment, a zero value. A different value (i.e., a 1 value) in this field indicates a period of prior use equal to or greater than the Prescribed Maximum Treatment Time. In this event, the use monitoring function  70  does not enable use of the transducer  40 . The transducer  40  is deemed “invalid.” 
         [0112]    If a value of zero resides in the Treatment Complete field, the use monitoring function  70  compares the date and time data residing in the Write-Once Start Date and Time field to the current date and time established by a Real Time Clock. If the Start Date and Time is more than a prescribed time before the Real Time (e.g., 4 hours), the controller does not enable use of the transducer  40 . The transducer  40  is deemed “invalid.” 
         [0113]    If the Start Date and Time field is empty, or if it is less than the prescribed time before the Real Time, the use monitoring function  70  deems the transducer  40  to be “valid” (providing the preceding other criteria have been met). The use monitoring function  70  reports a valid transducer to the controller  26 , which initiates the tuning function  64 . If the Start Date and Time field is empty, once the tuning function  64  is completed, the controller prompts the use monitoring function  70  to records the current date and time in the Start Date and Time Field, as well as the selected operating frequency in the Tuned Frequency field. The controller  26  then proceeds to execute the ramping function  66  and, then, execute the prescribed treatment protocol.  
         [0114]    If the Start Date and Time field is not empty (indicating a permitted prior use), once the tuning function  64  is completed, the controller  26  immediately proceeds with the ramping function  66  and, then, execute the treatment protocol.  
         [0115]    During use of the transducer  49  to accomplish the treatment protocol, the use monitoring function  70  periodically updates the Elapsed Usage Time field and Average Power field (along with other Many Write Memory Fields). Once the Treatment Complete flag is set to a 1 value (indicating use of the transducer beyond the Prescribed Maximum Treatment Time), the use monitoring function  70  interrupts the supply of ultrasound energy to the transducer. The transducer  40  is deemed “invalid” for subsequent use. The use monitoring function  70  can also generate an output that results in a visual or audible alarm, informing the operator that the transducer  40  cannot be used.  
         [0116]    The information recorded in the use register  72  can also be outputted to monitor use and performance of a given transducer  40 . Other sensors can be used, e.g., a temperature sensor  78  carried on the front mass piece  32  (see FIG. 4), in association with the use register.  
         [0117]    As described, the use register  72  allows specific pieces of information to be recorded before, during and after a treatment is complete. Information contained in the use register  72  is checked before allowing use of a given transducer  40 . The use register  72  ensures that only a transducer  40  having the desired design and performance criteria imparted by the manufacturer can be used. In addition, the use register  72  can be used to “lock out” a transducer  40  and prevent it from being used in the future. The only way the transducer  40  could be reused is to replace the use register  72  itself. However, copying the architecture of the use register  72  (including the contents of the Copyright Message field required for validation) itself constitutes a violation of the manufacturer&#39;s copyright in a direct and inescapable way.  
         [0118]    Various features of the invention are set forth in the following claims.