Source: https://patents.google.com/patent/US9849273
Timestamp: 2018-07-18 05:14:38
Document Index: 680708397

Matched Legal Cases: ['Application No. 61', 'Application No. 08705775', 'Application No. 08705775', 'Application No. 08705775', 'Application No. 10794791', 'Application No. 10794791']

US9849273B2 - Power parameters for ultrasonic catheter - Google Patents
Power parameters for ultrasonic catheter Download PDF
US9849273B2
US9849273B2 US13454983 US201213454983A US9849273B2 US 9849273 B2 US9849273 B2 US 9849273B2 US 13454983 US13454983 US 13454983 US 201213454983 A US201213454983 A US 201213454983A US 9849273 B2 US9849273 B2 US 9849273B2
US13454983
US20120271203A1 (en )
Kim R. Volz
An ultrasound catheter system and a method for operating an ultrasonic catheter at a treatment site within a patient's vasculature or tissue are disclosed. The ultrasound catheter system comprises a catheter having at least one ultrasonic element and a control system configured to generate power parameters that drive the at least one ultrasonic element to generate ultrasonic energy. The control system is configured to vary at least one of the power parameters and at least one physiological parameter by repeatedly cycling the power parameter and the physiological parameter through two set of values.
This application is a continuation of U.S. patent application Ser. No. 12/830,145, filed Jul. 2, 2010, now U.S. Pat. No. 8,192,391, which claims the priority benefit of U.S. Provisional Application No. 61/222,959, filed Jul. 3, 2009, the entirety of which are hereby incorporated by reference herein.
The present invention relates generally to ultrasound systems, and more specifically to ultrasound catheter systems.
While such ultrasound catheters systems have been proven to be successful, there is a general need to continue to improve the effectiveness and speed of such systems. In this manner, treatment and/or hospital time can be reduced.
Accordingly, one aspect of the present invention comprises an ultrasound catheter system comprising a catheter having at least ultrasonic element; a control system configured to generate power parameters to drive the ultrasonic element to generate ultrasonic energy. The control system is configured to vary at least one of the power parameters and at least one physiological parameter. In some embodiments, the power parameters include at least peak power. In some embodiments, the peak power is ramped repeatedly ramped between a first minimum value and a first maximum value, while the physiological parameter is repeatedly ramped between a second minimum value and a second maximum value during operation of the catheter.
Another aspect of the present invention comprises a method of operating an ultrasonic catheter. In the method, a catheter with at least one ultrasonic element is advanced to a treatment site in a patient's vascular system or tissue. The at least one ultrasonic element is driven to generate ultrasonic energy. A therapeutic compound is delivered to the treatment site through the catheter. A power parameter and a physiological parameter of the ultrasonic element is varied during the operation. In some embodiments, the power parameter includes at least peak power. The peak power and the physiological parameter was varied by repeatedly ramping the peak power between a first maximum value and a first minimum value and repeatedly ramping the physiological parameter between a second minimum value and a second maximum value. The driving parameters of the ultrasonic element can in some embodiments attain non-linear or pseudo-linear acoustic output, or in other embodiments attain linear acoustic output.
Another aspect of the present invention is a control system for an ultrasound catheter. The control system includes control unit configured to vary acoustic parameters of an ultrasonic element of an ultrasonic catheter.
Exemplary embodiments of the cavitation promoting systems and methods disclosed herein are illustrated in the accompanying drawings, which are for illustrative purposes only. The drawings comprise the following figures, in which like numerals indicate like parts.
FIG. 11 is a longitudinal cross-sectional view of selected components of an exemplary ultrasound catheter assembly that is particularly well-suited for treatment of cerebral vascular occlusions, and that includes a cavitation promoting surface.
FIG. 14 is a chart illustrating Peak Power (W) as a function of time according to one embodiment.
As will be described below, the ultrasound catheter can include one or more one or more ultrasound radiating members positioned therein. Such ultrasound radiating members can comprise a transducer (e.g., a PZT transducer), which is configured to convert electrically energy into ultrasonic energy. In such embodiments, the PZT transducer is excited by specific electrical parameters (herein “power parameters” that cause it to vibrate in a way that generates ultrasonic energy). As will be explained below, Applicants have discovered that by non-linearly (e.g., randomly or pseudo randomly) varying one or more of the power parameters the effectiveness of the ultrasound catheter (e.g., the effectiveness of enhancing the removal of a thrombus) can be significantly enhanced. While, for example, U.S. Pat. No. 5,720,710 taught that randomly changing the frequency of the ultrasonic frequency could significantly enhance the remedial effect of the ultrasonic energy, these results with respect to varying the other acoustic parameters were not expected. In addition, because PZT transducers are often configured to be driven and a particularly frequency, varying the other acoustic parameters may have significant advantages over varying the frequency. In addition, varying the electrical parameters may also be used in combination with varying the frequency (e.g., in a manner taught by U.S. Pat. No. 5,720,710).
The techniques disclosed herein are compatible with a wide variety of ultrasound catheters, several examples of which are disclosed in USA Patent Application Publication US 2004/0024347 A1 (published Feb. 5, 2004; discloses catheters especially well-suited for use in the peripheral vasculature) and USA Patent Application Publication 2005/0215942 A1 (published Sep. 29, 2005; discloses catheters especially well-suited for use in the cerebral vasculature). Certain of the techniques disclosed herein are compatible with ultrasound catheters that would be unable to generate cavitation at an intravascular treatment site but for the use of such techniques.
The catheter 100 is configured to have one or more ultrasound radiating members positioned therein. For example, in certain embodiments an ultrasound radiating member is fixed within the energy delivery section 18 of the tubular body, while in other embodiments a plurality of ultrasound radiating members are fixed to an assembly that is passed into the central lumen. In either case, the one or more ultrasound radiating members are electrically coupled to a control system 1100 via cable 1450. In one embodiment, the outer surface of the energy delivery 18 section can include an cavitation promoting surface configured to enhance/promote cavitation at the treatment site.
With reference to FIG. 2-10, an exemplary arrangement of the energy delivery section 18 and other portions of the catheter 10 described above. This arrangement is particularly well-suited for treatment of peripheral vascular occlusions.
The ultrasound radiating members are preferably operated in a pulsed mode. For example, in one embodiment, the time average electrical power supplied to the ultrasound radiating members is between about 0.001 watts and about 5 watts and can be between about 0.05 watts and about 3 watts. In certain embodiments, the time average electrical power over treatment time is approximately 0.45 watts or 1.2 watts. The duty cycle is between about 0.01% and about 90% and can be between about 0.1% and about 50%. In certain embodiments, the duty ratio is approximately 7.5%, 15% or a variation between 1% and 30%. The pulse averaged electrical power can be between about 0.01 watts and about 20 watts and can be between approximately 0.1 watts and 20 watts. In certain embodiments, the pulse averaged electrical power is approximately 4 watts, 8 watts, 16 watts, or a variation of 1 to 8 watts. As will be described above, the amplitude, pulse width, pulse repetition frequency, average acoustic pressure or any combination of these parameters can be constant or varied during each pulse or over a set of portions. In a non-linear application of acoustic parameters the above ranges can change significantly. Accordingly, the overall time average electrical power over treatment time may stay the same but not real-time average power.
In one embodiment, the pulse repetition rate is preferably between about 1 Hz and about 2 kHz and more can be between about 1 Hz and about 50 Hz. In certain preferred embodiments, the pulse repetition rate is approximately 30 Hz, or a variation of about 10 to about 40 Hz. The pulse duration or width is can be between about 0.5 millisecond and about 50 milliseconds and can be between about 0.1 millisecond and about 25 milliseconds. In certain embodiments, the pulse duration is approximately 2.5 milliseconds, 5 or a variation of 1 to 8 milliseconds. In addition, the average acoustic pressure can be between about 0.1 to about 2 MPa or in another embodiment between about 0.5 or about 0.74 to about 1.7 MPa.
In one particular embodiment, the transducers are operated at an average power of approximately 0.6 watts, a duty cycle of approximately 7.5%, a pulse repetition rate of about 30 Hz, a pulse average electrical power of approximately 8 watts and a pulse duration of approximately 2.5 milliseconds.
The ultrasound radiating member used with the electrical parameters described herein preferably has an acoustic efficiency than about 50% and can be greater than about 75%. The ultrasound radiating member can be formed a variety of shapes, such as, cylindrical (solid or hollow), flat, bar, triangular, and the like. The length of the ultrasound radiating member is preferably between about 0.1 cm and about 0.5 cm. The thickness or diameter of the ultrasound radiating members is preferably between about 0.02 cm and about 0.2 cm.
As will be described below, the ultrasound catheter includes one or more one or more ultrasound radiating members positioned therein. Such ultrasound radiating members can comprise a transducer (e.g., a PZT transducer), which is configured to convert electrically energy into ultrasonic energy. In such embodiments, the PZT transducer is excited by specific electrical parameters (herein “power parameters” or “acoustic parameters” that cause it to vibrate in a way that generates ultrasonic energy). As will be explained below, Applicants have discovered that non-linearly varying (e.g., randomly or pseudo randomly) one or more of the power parameters the effectiveness of the ultrasound catheter (e.g., the effectiveness of enhancing the removal of a thrombus) can be significantly enhanced. By non-linearly varying one or more of the power parameters the ultrasound radiating members create nonlinear acoustic pressure, which as described above can increase the effectiveness of the acoustic pressure in enhancing a therapeutic compound. In one application, the effect of nonlinearly varying acoustic pressure has been found by Applicant to enhance enzyme medicated thrombolysis by almost 1.9 times as compared to the application of substantially constant acoustic pressure. Examples of nonlinear variances include, but are not limited to, multi variable variations, variations as a function of a complex equation, sinusoidal variations, exponential variations, random variations, pseudo random variations and/or arbitrary variations. While nonlinear variance is preferred, in other arrangements it is anticipate that one or more of the parameters discussed can be varied in a linear manner either alone or combination with the nonlinear variance.
FIG. 12 will be used to explain certain power parameters which can used to drive the ultrasound radiating members. As shown, the members can be driven a series of pulses 2000 having peak power P or amplitude and duration τ. During these pulses 2000, the ultrasound radiating members as driven at a certain frequency f as described above by the electrical current. The pulses 2000 can be separated by “off” periods 2100. The cycle period T is defined as the time between pulse initiations, and thus the pulse repetition frequency (“PRF”) is given by T−1. The duty cycle is defined as the ratio of time of one pulse to the time between pulse initiations τT−1, and represents the fraction of time that ultrasonic energy is being delivered to the treatment site. The average power delivered in each cycle period is given by PτT−1. Accordingly, the illustrated embodiment, the ultrasound radiating members are operated using pulses, or modulated electrical drive power instead of continuous drive power
In another embodiment, the duty cycle is preferably between about 1% and about 50%, is more preferably between about 2% and about 28%. During operation of the catheter, the duty cycle can vary in a nonlinear fashion. For instance, in one such modified embodiment, the duty cycle that is randomly or pseudo randomly distributed between a maximum duty cycle and a minimum duty cycle. For example, in one embodiment, the values for the maximum duty cycle are between about 25% and about 30%, and typical values for the minimum duty cycle are between about 1.5% and about 3.5%. In yet another embodiment, the duty cycle is varied non-linearly from a minimum value of about 2.3% and a maximum value of about 27.3%. In one embodiment, other parameters of the waveform are manipulated such that each cycle period has the same average power, even though the duty cycle for each cycle period is varying in a nonlinear fashion.
In another embodiment, the peak power P delivered to the treatment site is preferably between about 0.1 watts and about 20 watts, is more preferably between about 5 watts and about 20 watts, and is most preferably between about 8 watts and about 16 watts. Within the ranges, during operation of the catheter, the peak power P can vary in a nonlinear fashion. For instance, in one such modified embodiment, each cycle period has a peak power quantity that is randomly or pseudo randomly distributed between a maximum peak power Pmax and a minimum peak power Pmin. Typical values for the maximum peak power Pmax are between about 6.8 watts and about 8.8 watts, and typical values for the minimum peak power Pmin are between about 0.1 watts and about 1.0 watts. In another embodiment, the peak power is varied non-linearly between a maximum peak power Pmax of about 7.8 watts and a minimum peak power Pmin of about 0.5 watts. In one embodiment, other parameters of the waveform are manipulated such that each cycle period has the same average power, even though the peak power P for each cycle period is varying in a nonlinear fashion.
In one example embodiment, the pulse duration τ is preferably between about 1 millisecond and about 50 milliseconds, is more preferably between about 1 millisecond and about 25 milliseconds, and is most preferably between about 2.5 milliseconds and about 5 milliseconds. In a modified embodiment, each cycle period has a different pulse duration τ, wherein the pulse duration values vary in a nonlinear fashion with the ranges described above. For instance, in one such modified embodiment, each cycle period has a pulse duration quantity that is randomly distributed between a maximum pulse duration τmax and a minimum pulse duration τmin. Typical values for the maximum pulse duration τmax are between about 6 milliseconds and about 10 milliseconds (and in one embodiment about 8 milliseconds), and typical values for the minimum pulse duration τmin are between about 0.1 milliseconds and about 2.0 milliseconds (and in one embodiment 1 millisecond), In one embodiment, other parameters of the waveform are manipulated such that each cycle period has the same average power, even though the pulse duration τ for each cycle period is varying in a nonlinear fashion. In other embodiments, the average power can be varied non-linearly.
In addition, the average acoustic pressure can also non-linearly varied as described above between about 0.1 to about 2 MPa or in another embodiment between about 0.5 or about 0.74 to about 1.7 MPa.
A study to investigate the effect of a variety of randomization protocols on clot lysis was conducted. The randomization protocols involved non-linearly varying peak power, pulse width, pulse repetition frequency, or combinations of the above. The randomization protocols were tested using a time average power of either about 0.45 W or about 0.90 W, and were compared to a standard Neurowave E11 protocol.
Description of acoustic protocols
Acoustic Protocol Power Peak Power PW PRF
L ⁢ ⁢ E ⁢ ⁢ F ⁢ ⁢ % = ( ( W c - W lus i W c - W l ) - 1 ) × 100
Wc [mg]: Average clot weight of the negative control samples (no treatment).
W1 [mg]: Average clot weight from positive control group (drug treatment only).
Wlus [mg]: Average clot weight from each individual ultrasound treatment group.
In some embodiments, it is desirable to deliver a particular time averaged power. Because the power parameters may be randomized, it may take the execution of a plurality of ultrasonic cycle profiles before the time averaged power approaches an asymptotic value. In some embodiments, the execution of about 40 to about 50 ultrasonic cycle profiles is required for the time averaged power to become asymptotic. In other embodiments, less than about 40 ultrasonic cycle profiles are required, while in yet other embodiments, more than about 50 ultrasonic cycle profiles are required. In some embodiments, ultrasonic cycle profiles are executed until the time average power approaches an asymptotic value. For example, if the profile execution time is 5 seconds and the overall execution time is 30 minutes, 360 ultrasonic cycle profiles will be executed, which in some embodiments is sufficient for the time average power to approach an asymptotic value.
I SPPA = p r 2 2 ⁢ ⁢ ρ ⁢ ⁢ c × 10 - 4
Another parameter is spatial peak time-average intensity, ISPTA, which is defined as the value of the temporal-average intensity at the point in the acoustic field where the pulse-average intensity is a maximum or is a local maximum within a specified region. Spatial peak time-average intensity can range from about 0.1 W/cm2 to about 50 W/cm2, or about 0.5 W/cm2 to about 40 W/cm2, or about 7 W/cm2. The spatial-peak temporal-average intensity can be calculated from the spatial-peak pulse-average intensity as:
I SPTA =I SPPA×DC÷100
In addition to the acoustic and electrical parameters described above, it can also be desirable to focus on non-linearly or randomly varying physiological parameters. For example, the mechanical index, MI is a relative indicator of the potential for mechanical bioeffects, particularly cavitation. Scientific evidence suggests that mechanical bioeffects, like cavitation, are a threshold phenomenon, occurring only when a certain level of output is exceeded. The potential for mechanical effects increases as peak rarefactional pressure increases, but decreases as ultrasound frequency increases. The mechanical index accounts for both rarefactional pressure and frequency. The higher the index reading, the larger the potential for mechanical bioeffects. In addition, the occurrence of cavitation is also highly dependent on properties of the medium such as viscosity, temperature, and dissolved gas content. The mechanical index can range from about 0.1 to about 3, or about 0.5 to about 2, or about 0.7 to about 1.6, or about 1.3. Mechanical index can be calculated by dividing the peak rarefactional pressure (in MPa) by the square root of the frequency (in MHz):
M ⁢ ⁢ I = p r f 1 / 2
In addition, although many embodiments have been described in the context of an intravascular catheter it should be appreciated that the non-linear application of one or more power parameters can also be applied to non-intravascular catheters or devices and/or non catheter applications. For example, the non-linear varying of one or more power parameters may also find utility in applications in which the ultrasound is applied through an external (with respect to the body or with respect to the vascular system). In particular, the discussion above can be applied to external ultrasound application in which the ultrasound source is external to the patient and/or treatment site. It is also anticipated that the methods and techniques described herein can be applied to non-vascular applications. In addition, in some embodiments, the therapeutic affects of the ultrasound can be utilized alone without a therapeutic compound.
Peak Power and Physiological Parameter Variation
FIG. 14 illustrates an embodiment in which peak power is varied in specific manner. Specifically, in this embodiment, peak power is repeatedly increased and decreased over time. As shown, the peak power can be increased and then decreased (e.g., ramped up to a peak value than ramped down to a minimum value) in a linear manner. However, in modified embodiments, the peak power can be increased to a specific value and then decreased to a specific value in a non-linear or pseudo-linear manner (e.g., a sinusoidal, curved, or non-linear or complex profile). In the illustrated embodiment, the peak power is ramped up and down by moving through discrete peak power values labeled A-D. However, more or less values can be used or a substantially continuous ramping can also be used. In some embodiments, the maximum and minimum peak values between which the peak power is ramped, can be changed and/or varied over time. In some embodiments, the each of the maximum and the minimum values remains constant.
In one embodiment, the peak power varies from about 0.1 Watts to about 30 Watts and in another embodiment from about 1.5 Watts to about 8 Watts. Within these ranges, in one embodiment, the peak power can have between about 1 to 5 discrete values and in another embodiment 2 specific values.
In some embodiments, while the peak power is ramped up and down, the other power parameters can remain constant, substantially constant and/or varied (e.g., as described above). For example, Table 2 shows the power parameters for one embodiment in which peak powers ramped between about 1.5 and about 7.88 W. During this ramping, pulse width (PW) and pulse repetition frequency (PRF) are varied. In this embodiment, pulse width and pulse repetition frequency were varied in a manner to maintain pulse repetition (PRF) is 20-40 Hz, in other embodiments the pulse repetition can be maintained within 15-45 Hz. These pulse repetition frequency ranges are presently preferred by Applicant. In one embodiment, the pulse length (pulse width, PW) can be adjusted to each selected pulse repetition frequency to ensure that temporal average power over treatment time and resulting thermal index (heat generation) remains within a clinically acceptable range.
Example Power Protocol
Peak Power PW PRF
(W) (mSec) (Hz)
5 6.86 26
2.5 5 24
1.5 8.06 21
2.5 5 27
5 6.86 21
7.88 4 24
Similarly, the physiological parameter described above can also be varied in the same manner as varying the peak power. In some embodiments, the physiological parameter can be ramped up- and down-wards between a minimum value and a maximum value. The maximum and the minimum values may not be the same as the maximum and the minimum values for the peak power ramping. In some embodiments, the ramping of the physiological parameter may also be done in a linear manner, and in other embodiments, the ramping can be done in a non-linear or pseudo-linear manner (e.g., a sinusoidal, curved, or non-linear or complex profile). As with the peak power, the physiological parameter can be ramped up and down by moving through discrete physiological parameter values. In some embodiments, the maximum and minimum values between which the physiological parameter is ramped can be changed and/or varied over time. In some embodiments, each of the maximum and the minimum values remains constant.
In some embodiments, both the peak power and at least one physiological parameter can be varied in any of the manner described above at the same time. For example, both the peak power and the physiological parameter may be ramped up and down in a linear manner or in a non-linear or pseudo-linear manner at the same time. However, in some embodiments, the peak power may be ramped in a non-linear manner while the physiological parameter is ramped in a linear manner. In other embodiments, the peak power may be ramped in a linear manner while the physiological parameter is ramped in a non-linear manner.
Varying peak power and/or physiological parameter as described above has particular advantages. For example, Applicants believe that ramping peak power and/or physiological parameter creates acoustic “momentum” that advantageously results in radiation force transfer to media such as effectively accelerating acoustic streaming, which can enhance the therapeutic effects (described above) of the ultrasound.
1. A method of operating an ultrasonic catheter which comprises at least one ultrasonic element, the method comprising the steps of:
advancing the ultrasonic catheter to a treatment site in a patient's vascular system or tissue;
driving the at least one ultrasonic element to generate ultrasonic energy;
delivering a therapeutic compound to the treatment site through the ultrasonic catheter; and
varying a peak power and a physiological parameter of the ultrasonic element, and wherein varying the peak power and the physiological parameter comprises:
repeatedly cycling the peak power through a first set of preset values between a preset minimum value and a preset maximum value; and
repeatedly cycling the physiological parameter through a second set of preset values.
2. The method of claim 1, wherein the peak power and the physiological parameter are cycled in a linear manner.
3. The method of claim 1, wherein the peak power and the physiological parameter are cycled in a non-linear or pseudo-linear manner.
4. The method of claim 1, wherein cycling the peak power comprises repeatedly moving through discrete peak power values, and cycling the physiological parameter comprises repeatedly moving through discrete physiological parameter values.
5. The method of claim 1, wherein cycling the peak power is independent of any temperature measurement.
6. The method of claim 1, wherein the first set of values include the minimum value, the maximum value, and 1 to 5 discrete values between the minimum value and the maximum value.
7. The method of claim 1, wherein the first set of values include the minimum value, the maximum value, and 2 discrete values between the minimum value and the maximum value.
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US22295909 true 2009-07-03 2009-07-03
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US13454983 US9849273B2 (en) 2009-07-03 2012-04-24 Power parameters for ultrasonic catheter
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US13454983 Active 2031-11-29 US9849273B2 (en) 2009-07-03 2012-04-24 Power parameters for ultrasonic catheter
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Prokop et al. 2007 Cavitational mechanisms in ultrasound-accelerated fibrinolysis