U.S. patent application number 11/066102 was filed with the patent office on 2005-09-15 for ultrasound therapeutic device.
This patent application is currently assigned to Compex Medical S.A.. Invention is credited to Buhlmann, Felix, Muller, Pierre-Yves, Rigaux, Pierre, Schonenberger, Klaus.
Application Number | 20050203444 11/066102 |
Document ID | / |
Family ID | 32107100 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050203444 |
Kind Code |
A1 |
Schonenberger, Klaus ; et
al. |
September 15, 2005 |
Ultrasound therapeutic device
Abstract
The ultrasound therapeutic system of the present invention
generally includes a generator unit, at least one transducer
treatment head, and a programmable controller. The generator is in
operable communication with the at least one transducer treatment
head such that electric power outputted from the generator to the
head is converted into acoustic power by the head. Re-programmable
software at the controller generally controls all features and
functions for the system. In particular, the controller calculates
an initial optimal treatment dose, maintains effective acoustic
power transmitted to the patient through the at least one treatment
head, performs calibration procedures for the at least one
treatment head, controls outputting for each supported treatment
mode, and provides for various other features and functions.
Inventors: |
Schonenberger, Klaus;
(Ecublens, CH) ; Buhlmann, Felix; (Lausanne,
CH) ; Muller, Pierre-Yves; (Collonge-Bellerive,
CH) ; Rigaux, Pierre; (Verlaine, BE) |
Correspondence
Address: |
Patterson, Thuente, Skaar & Christensen, P.A.
4800 IDS Center
80 South 8th Street
Minneapolis
MN
55402-2100
US
|
Assignee: |
Compex Medical S.A.
|
Family ID: |
32107100 |
Appl. No.: |
11/066102 |
Filed: |
February 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11066102 |
Feb 25, 2005 |
|
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10281090 |
Oct 25, 2002 |
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6860852 |
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Current U.S.
Class: |
601/2 |
Current CPC
Class: |
A61N 7/00 20130101; A61B
8/4438 20130101; A61N 2007/0008 20130101; A61B 2017/00199
20130101 |
Class at
Publication: |
601/002 |
International
Class: |
A61H 001/00; A61B
008/00 |
Claims
What is claimed is:
1. A method of calibration for an ultrasound therapeutic treatment
head, comprising the steps of: determining the presence of a
treatment head in an ultrasound system; obtaining identification
information for the treatment head; performing a frequency scan
around a theoretical resonant frequency using stepped intervals to
determine a maximum unloaded conductance value of the treatment
head and a corresponding resonant frequency; storing the maximum
unloaded conductance value and the resonant frequency value;
calculating a maximum series conductance under load of the
treatment head; calculating a real-time acoustic coupling
efficiency of the treatment head from the maximum unloaded
conductance value and the maximum series conductance under load;
and compensating for real and complex changes in the electrical
characteristics of the treatment head according to the calculated
real-time acoustic coupling efficiency.
2. The method of claim 1, wherein the step of obtaining
identification information for a treatment head further comprises
retrieving stored identification information from the
controller.
3. The method of claim 1, wherein the step of determining the
presence of a treatment head further comprises introducing a new
treatment head to the ultrasound system.
4. The method of claim 1, wherein the step of determining the
presence of a treatment head further comprises reintroducing a
previously calibrated treatment head to the ultrasound system.
5. The method of claim 1, wherein the step of obtaining
identification information further comprises reading data stored
electronically for the treatment head by a controller in operable
communication with the treatment head.
6. An automatic calibration system for use in an ultrasound system
for physical therapy comprising: a generator for generating an
ultrasound output signal; at least one ultrasonic transducer
capable of receiving the ultrasound output signal to generate an
acoustic output; an input device for receiving histological tissue
data from a user including target treatment tissue type; and a
controller running treatment software and calibration software,
wherein the inputted histological tissue data is processed to
generate an acoustic intensity value and a treatment duration
value.
7. The system of claim 6, wherein the calibration software operably
calculates an acoustic coupling efficiency from an actual loaded
conductance and an unloaded series conductance to compensate for
changes in the electrical characteristics of the ultrasonic
transducer.
8. The system of claim 6, wherein the calibration software operably
considers both impedance amplitude and phase to account for complex
changes in the ultrasonic transducer and the ultrasound system.
9. The system of claim 6, wherein the at least one ultrasonic
transducer is new to the ultrasound system.
10. The system of claim 6, wherein the at least one ultrasonic
transducer is an ultrasonic transducer that has been previously
calibrated by the ultrasound system.
11. An automatic calibration system for use in an ultrasound system
for physical therapy comprising: means for generating an ultrasound
output signal; at least one ultrasonic transducer capable of
receiving the ultrasound output signal to generate an acoustic
treatment output; an input device for receiving histological tissue
data from a user including target treatment tissue type, and
intermediate tissue structure; means for running treatment
software, wherein the inputted histological tissue data is
processed to calculate an ultrasound dosage including an acoustic
intensity value and a treatment duration value; and means for
making a calibration adjustment to the ultrasound system that
considers impedance amplitude and phase and accounts for complex
changes in the electrical characteristics of the ultrasonic
transducer.
12. A method of monitoring and controlling the acoustic power
delivered to a treatment head of a therapeutic treatment system
using a feedback loop, comprising the steps of: applying electric
power from a generator to a treatment head to generate an acoustic
power output; measuring, at a controller in operable communication
with the generator, treatment head voltage values at stepped
intervals; calculating at the controller a coupling efficiency of
the treatment head and an applied electric power from the measured
treatment head voltage values at stepped intervals; calculating at
the controller an effective transmitted acoustic power; and
adjusting the electric power from the generator in response to the
calculated coupling efficiency in order to maintain a constant
level of effective acoustic power transmitted.
13. The method of claim 12, wherein the step of calculating at the
controller a coupling efficiency of the treatment head further
comprises: measuring a vector voltage output of a multiplier in the
feedback loop; and calculating the coupling efficiency of the
treatment head and the applied electric power using the vector
voltage output.
14. The method of claim 12, wherein the step of adjusting the
electric power includes performing the adjustment every 20
milliseconds.
15. The method of claim 12, further comprising the step of
notifying a user of the therapeutic treatment system if a feedback
loop failure occurs.
16. The method of claim 15, further comprising: suspending the
transmission of electric power from the generator; commencing a
resonance search and output calculation mode; monitoring the output
for a minimum tolerance; and restarting the feedback loop and
resuming normal operation when the output surpasses the minimum
tolerance.
17. A feedback loop for monitoring and controlling the acoustic
power delivered to a treatment head of a therapeutic treatment
system comprising: at least one ultrasonic transducer capable of
receiving an ultrasound output signal to generate an acoustic
treatment output; a generator unit in operable communication with
the ultrasonic transducer for generating the ultrasound output
signal; a voltage converter in operable communication with the
generator unit to supply a voltage control signal; a controller
running treatment software, wherein inputted histological tissue
data is processed to calculate an ultrasound dosage including an
acoustic intensity value and a treatment duration value, and
wherein the controller is in operable communication with the
voltage converter; an analog multiplier in operable communication
with the generator to receive measured voltage and current signals
and the controller adapted to supply a vector output signal; a
quadrature signal generator in operable communication with the
analog multiplier to provide reference signals; and a digital
sine-wave generator in operable communication with the controller,
the generator unit to provide a reference wave, and the quadrature
signal generator to provide a reference wave.
18. The feedback loop of claim 17, wherein a coupling efficiency is
calculated in the controller and the voltage control signal
supplied to the generator unit is adjusted to operably maintain a
constant level of effective acoustic power transmitted from the
ultrasonic transducer to a user.
19. The feedback loop of claim 18, wherein the constant level of
acoustic power transmitted to the user is maintained by adjusting
an electric power in response to the coupling efficiency calculated
by the controller.
20. The feedback loop of claim 19, wherein the electric power is
adjusted every 20 milliseconds.
21. The feedback loop of claim 18, wherein the controller scans a
maximum conductance value of the ultrasonic transducer to detect a
shift in a resonant frequency and readjust the electric power in
response.
22. A method of ultrasound therapy with a system having a
generator, a treatment head, and a programmable controller in
operable communication with the generator and the treatment head,
comprising the steps of: inputting histological tissue data by a
user, the histological tissue data representing at least tissue
type and tissue depth data; inputting a treatment mode from a
selection of thermal, biological, and phonophoresis; automatically
configuring treatment dosage parameters at the controller based on
the inputted histological tissue data and treatment mode;
monitoring the operation of the system during treatment of a user;
and maintaining a constant acoustic power transmitted to the user
during online use according to values received at the controller
from the treatment head.
23. The method of claim 22, wherein the step of monitoring the
operation of the system during treatment of a user further
comprises: monitoring a feedback loop within the system for
failure; monitoring a resonant frequency search and centering;
monitoring a presence of the treatment head; and monitoring a
temperature of the treatment head.
24. The method of claim 22, wherein the step of maintaining a
constant acoustic power further comprises the steps of: applying
electric power from a generator to the treatment head to generate
an acoustic power output; measuring, at a controller in operable
communication with the generator, treatment head voltage values at
stepped intervals; calculating at the controller a coupling
efficiency of the treatment head; and adjusting the electric power
from the generator in response to the calculated coupling
efficiency in order to maintain a constant level of effective
acoustic power transmitted.
25. The method of claim 24, wherein the step of calculating at the
controller a coupling efficiency of the treatment head further
comprises: measuring a maximum conductance of the treatment head in
an unloaded state; measuring a maximum conductance of the treatment
head in a loaded state; and calculating the coupling efficiency of
the treatment head using the measured maximum conductance of the
treatment head in an unloaded state and the measured maximum
conductance of the treatment head in a loaded state.
26. The method of claim 24, wherein the step of adjusting the
electric power is performed every 20 milliseconds
27. The method of claim 24, further comprising the step of
notifying an operator of the system if a feedback loop failure
occurs.
28. The method of claim 27, further comprising the steps of:
suspending the transmission of electric power from the generator;
commencing a resonance search and an output calculation mode;
monitoring the output for a minimum tolerance; and restarting the
feedback loop and resuming normal operation when the output
surpasses the minimum tolerance.
29. An ultrasound therapeutic treatment system, comprising: an
ultrasound treatment device having a generator capable of
generating an ultrasound output; an input device adapted to receive
histological tissue data from a user including treatment tissue
type and tissue depth; a controller running treatment software to
calculate an ultrasound dosage including a treatment duration
value, an acoustic intensity value, and an output frequency value;
a plurality of ultrasonic transducer heads capable of receiving the
ultrasound output from the generator to generate acoustic output;
and a cable having a first end connector adapted to attach to the
ultrasound treatment device; and a second end connector adapted to
selectively attach to each of the plurality of ultrasonic
transducer heads.
30. The system of claim 29, wherein each of the plurality of
ultrasonic transducer heads includes at least one memory device
capable of operable communication with the controller.
31. The system of claim 30, wherein the at least one memory device
is adapted to operably communicate with the controller to
communicate stored data to the controller for each of the plurality
of ultrasonic transducer heads.
32. The system of claim 31, wherein the data stored at the at least
one memory device is selectable from a group consisting of:
temperature data, transducer head serial number, and calibration
data.
33. The system of claim 29, wherein the attachment of the second
end connector of the cable to each of the plurality of ultrasonic
transducer heads results in a substantially watertight
attachment.
34. The system of claim 29, wherein each of the plurality of
ultrasonic transducer heads are configured to have different
acoustic output capabilities.
35. An ultrasound therapeutic treatment system, comprising: an
ultrasound treatment device having generator means for generating
an ultrasound output; input means for receiving histological tissue
data from a user including treatment tissue type and tissue depth;
control means for running treatment software to calculate an
ultrasound dosage including a treatment duration value, and an
acoustic intensity value; a plurality of delivery means for
receiving the generated ultrasound output from the generator means
to deliver acoustic output; and means for communicating the
generated ultrasound output to the delivery means, having first
connector means for attachment to the ultrasound treatment device;
and second connector means for selective attachment to each of the
plurality of delivery means.
36. The system of claim 35, wherein each of the plurality of
delivery means includes storage means for storing data at the
delivery means for communication with the control means.
37. The system of claim 35, wherein the plurality of delivery means
are substantially watertight when attached to the second connector
means.
38. The system of claim 35, wherein each of the plurality of
delivery means are capable of having different acoustic output
capabilities.
39. A method of interchangeably connecting a plurality of
transducer treatment heads for use with an ultrasound therapeutic
treatment device, the method comprising the steps of: connecting a
first transducer treatment head to a head connector at one end of a
cable in operable communication with a generator of the ultrasound
therapeutic treatment device; disconnecting the first transducer
treatment head from the head connector; and connecting a second
transducer treatment head to the head connector.
40. The method of claim 39, further including the step of reading,
at a controller in operable communication with the cable, data
stored at a memory device of the first transducer treatment
head.
41. The method of claim 39, further including the step of reading,
at a controller in operable communication with the cable, data
stored at a memory device of the second transducer treatment
head.
42. The method of claim 39, wherein the connecting of the second
transducer head includes connecting the second transducer head
having a different acoustic output capability than the first
transducer treatment head.
43. A feedback loop for monitoring and controlling the acoustic
power delivered at a treatment head of a therapeutic treatment
system comprising: at least one ultrasonic transducer capable of
receiving an ultrasound output signal to generate an acoustic
treatment output; means for generating the ultrasound output signal
in operable communication with the ultrasonic transducer; means to
supply a voltage control signal in operable communication with the
means for generating the ultrasound output signal; control means
for running treatment software, wherein inputted histological
tissue data is processed to calculate an ultrasound dosage
including an acoustic intensity value and a treatment duration
value, and wherein the controller is in operable communication with
the means to supply a voltage control signal; means to receive
measured voltage and current signals and to supply a vector output
signal in operable communication with the means for generating the
ultrasound output signal and the control means; means to provide
reference signals in operable communication with the means to
receive measured voltage and current signals and to supply a vector
output signal; and means to provide a reference wave in operable
communication with the control means, with the means for generating
the ultrasound electric output signal to provide a reference wave,
and with the means to provide reference signals.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional application of co-pending
U.S. application Ser. No. 10/281,090, entitled "Ultrasound
Theropeutic Device," filed on Oct. 25, 2002, which will issue as
U.S. Pat. No. 6,860,852, Mar. 1, 2005.
FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
ultrasound treatment. More specifically, the present invention
relates to an ultrasound therapeutic device capable of
automatically determining a considerate treatment dose, controlling
acoustic power output efficiency, and performing adjustable
calibration functions.
BACKGROUND OF THE INVENTION
[0003] Therapeutic ultrasound devices have long been utilized in
the treatment of musculoskeletal and tissue injuries. Greater
understanding of ultrasound, and the application of ultrasound to
human skin and tissue, have expanded the scope of possible uses for
these devices. For instance, in addition to the thermal or
vibratory focus of more traditional devices, developments have been
made in which ultrasound devices can be directed toward introducing
various drugs into the human body through the skin. However, the
increase in potential uses and advantages for these therapeutic
ultrasound devices has come at a price. Namely, advancements in the
technology and the understanding of the potential applications, has
correspondingly led to the complication of setup procedures,
inefficient power adjustments, and the need for more precise
calibration procedures.
[0004] Initial Parameter Inputs
[0005] Ultrasonic therapy devices impose mechanical vibrations on
tissue and skin to cause various thermal and non-thermal effects.
An ultrasound generator outputs electric power to a treatment head.
The treatment head includes a transducer which converts the power
from the generator into ultrasonic energy or acoustic power. It is
this acoustic power that is transmitted for therapeutic treatment
through the patient's tissue. The requisite acoustic power can vary
greatly depending on the treatment goals, the target tissue type,
the target tissue depth, and other like factors. In addition, the
duration of the ultrasonic treatment dosage to the patient is
important. Treatment goals, the unique characteristics of the
target tissue, and like considerations dictate the treatment
duration.
[0006] Conventional ultrasound treatment devices generate a
treatment dose based on manually inputted values or parameters.
Parameters such as treatment time/duration, frequency, and
treatment intensity are inputted by the end user. Generally, with
such devices, calculations and determinations are made by the user.
Consequently, it is up to the device user to come up with the ideal
treatment parameters required for a specific patient, assuming
specific treatment goals for that patient.
[0007] There are many drawbacks with manually operated devices.
Specifically, it is problematic that these manual systems are
reliant upon the skills and knowledge of the individual user. This
problem manifests itself in at least two respects. First, there is
no way to know or control exactly what factors are being considered
by the user in calculating the proper treatment parameters. For
example, there are no guarantees that the end user will properly
consider the target tissue characteristics, the target tissue type,
or the existence and depth of any intermediate tissue between the
treatment head and the target tissue. These are all highly relevant
factors that should play a primary role in determining the proper
treatment outputs and durations for any effective ultrasound
therapeutic treatment. In addition, accidental parameter entries,
and the varying level of user training introduce still more
uncertainty into the likelihood of providing optimized ultrasound
treatment for the patient.
[0008] As indicated, the unique and specific characteristics of the
target tissue, and the nature and thickness of intermediate tissue
and/or the target tissue, are requisite factors to be considered in
determining a proper ultrasound treatment dose. This is true since
both the thermal and non-thermal effects of ultrasound are
dependent upon these factors. Despite the fundamental importance of
these considerations, conventional ultrasound therapeutic devices
simply have not advanced methods and apparatus that properly
consider and process known histological tissue characteristics in
generating a treatment dose.
[0009] U.S. Pat. No. 5,413,550 ("the '550 Patent") discloses an
attempt to provide for considerate dose control. The '550 Patent is
directed to an ultrasound device including a controller programmed
to calculate a treatment dose. The treatment dose consists of
treatment frequency, output intensity, and treatment time. The
programmed controller determines and generates the dosage
parameters based on the inputting of numerous treatment parameters
by the end user. Specifically, the device requires values for the
following primary treatment parameters in order to calculate a
dosage: depth of tissue to be treated, the desired tissue
temperature rise, the tissue area to be treated, and the selection
of an ultrasound couplant. In addition the user may input the
tissue type, and a duty factor value as secondary parameters. The
device of the '550 patent performs routine checks to determine if
treatment parameters have been entered. If the controller
determines that specific primary treatment parameters have not been
inputted, the controller circuitry inserts a default value in place
of the missing parameter(s). As a result, it is possible to enter
only one of the primary treatment parameters, with each of the
remaining parameters being substituted for default values. Such a
default-driven device and process is problematic and fails to
properly focus the ultrasound treatment on ultrasound effects and
histological tissue data.
[0010] The use of default parameters to calculate dosage, by
definition, fails to take into account the unique circumstances and
characteristics of the patient, the treatment goals for the
specific target tissue of the patient, and like goals and
considerations that are essential in providing highly efficient and
effective ultrasound treatment. As indicated herein, knowledge and
specific consideration of the unique target treatment tissue, and
the depth of that tissue or the thickness of intermediate tissue,
are essential in generating an optimal treatment dose. Generating a
dose, regardless of the automated nature of the calculation, is
deficient if it fails to account for the true tissue structure,
such as the energy losses produced as a result of tissue heating,
and the losses caused by adjacent tissue structure. Ignoring such
essential characteristics of treatment on complex tissue structures
dilutes the efficacy of the dosage calculation. Proper acoustic
power outputs and treatment durations must be specified, monitored,
and updated in a manner most beneficial for the treatment goals for
the unique individual patient, after fully understanding and
processing data pertaining to the target tissue, intermediate
tissue, and tissue depths.
[0011] Treatment Dose Adjustments
[0012] Conventional ultrasonic therapeutic devices and systems are
generally deficient when it comes to the continuous and efficient
monitoring and controlling of the power being outputted from the
generator to the transducer. The typical approach to controlling
acoustic power from the transducer head is to merely provide alarm
and display notices to the user. For example, U.S. Pat. No.
4,791,915 is directed to a device wherein the coupling efficiency
between the transducer and the patient is displayed in the form of
a readable bar graph for the user to observe and monitor. However,
such systems and devices merely focus on preventing overheating and
electrical shorting. Threshold comparisons are merely made in order
to prevent catastrophic failures which could cause device
malfunction and/or injury to the patient.
[0013] Other conventional ultrasound treatment systems implement
adjustment techniques and controls directed to providing for a
relatively constant electric power output level to the patient. For
instance, U.S. Pat. No. 4,368,410 discloses an ultrasound therapy
device wherein an optimal electric output power level is inputted
into the device. Feedback signals from a driver circuit
proportional to the transducer voltage and current are returned to
an analog servo circuit and a voltage representing true electric
power is calculated. If the output power represented by the voltage
level increases then it is an indication that there is a reduction
in the load on the transducer, and the drive signal is decreased.
Similarly, if the instant voltage decreases, an increase in the
signal is initiated to compensate for an increase in the load on
the transducer. The innate problem with such a system is that while
it does acknowledge the effects varying treatment techniques,
treatment zones, and an individuals body can have on ultrasound
treatment, it does not properly use this information in providing
for a truly responsive individualized treatment dosage. Focus is on
maintaining a constant electric power output and not on performing
acoustic analysis. Events and circumstances effecting the
ultrasound treatment are not properly considered--i.e, the
introduction of intermediate tissue, the natural changes across a
patient's body "zones", and the like.
[0014] Treatment Head Calibration
[0015] Each treatment head of an ultrasound therapeutic device
requires calibration. Primarily, this calibration is needed in
order to accommodate and adjust for various innate properties and
characteristics unique to particular heads. The head must be
properly calibrated in order to correctly match the specific
resonance frequencies of its constituent ceramic. For instance,
each ceramic treatment head varies in its material properties. As a
result, proper operation and acoustic output for each and every
head mandates at least an initial head calibration. Typically, this
calibration is done in the factory prior to receipt of the device
by the end user. In many cases, this is the only calibration
allowed for, and any later re-calibration must again occur at the
factory. However, these factory calibrations are problematic since
untimely degeneration can adversely affect treatment quality and
effectiveness.
[0016] Even those conventional devices that permit for
user-initiated calibration require the initiation of complicated or
time-consuming procedures. Specifically, it is common to allow for
user calibration by immersing the head in water and making a series
of adjustments based on calibration readings displayed by the
device. For obvious reasons, such techniques are undesirable and
inconvenient. Additionally, conventional devices do not consider
complex changes introduced by slight imaginary components in the
acoustic impedance of the tissues being treated. Conventional
devices are thus unable to transmit an accurate amount of power to
the tissue or fully self-calibrate.
[0017] As a result, there is a need for an ultrasonic therapeutic
device, and method for operating and controlling thereof, that
substantially solves the problems and deficiencies described in the
prior art.
SUMMARY OF THE INVENTION
[0018] The ultrasound therapeutic system and methods in accordance
with the present invention substantially solve the problems and
weaknesses present in the prior art devices and methods. The
present invention is generally directed to an ultrasound treatment
system wherein it is preferred that each of the described prior art
deficiencies are addressed in one device. In general, the
ultrasound device and methods of the present invention are directed
to providing an optimal initial treatment dose based on complete
processing of user-inputted histological tissue data, employing an
automatic regulatory feedback loop to maintain optimal acoustic
power output to the patient during operation, and providing a
simple yet efficient user-initiated treatment head calibration
technique. Further, the treatment system of the present invention
includes multi-mode treatment techniques/effects, and user-specific
memorization functions.
[0019] The ultrasound therapeutic system of the present invention
generally includes a generator unit, at least one transducer
treatment head, and a programmable controller. The generator is in
operable communication with the at least one transducer treatment
head such that electric power outputted from the generator to the
head is converted into acoustic power by the head. Re-programmable
software at the controller generally controls all features and
functions for the system. In particular, the controller calculates
an initial optimal treatment dose, maintains effective acoustic
power transmitted to the patient through the at least one treatment
head, performs calibration procedures for the at least one
treatment head, controls outputting for each supported treatment
mode, and provides for various other features and functions as will
be discussed in further detail herein.
[0020] Unlike the prior art, the present invention is directed to
intelligent and simplified automatic dosage determination.
Specifically, the output dose is calculated by processing values
inputted by the user for target tissue type, intermediate tissue
type, and tissue depth/thickness. The present invention does not
import or process arbitrary default values for treatment couplant,
tissue configuration, and the like. Instead, dosage is based on the
fundamental tissue data inputted, wherein the controller performs
simulation comparisons to derive the smallest dosage needed to
optimally achieve the therapeutic treatment effect. Further, the
dosage determination of the present invention, through processing
of the inputted histological tissue data, takes into account the
relevant tissue layer structure to adjust for the effects caused by
innate losses through tissue absorption and reflections caused by
impedance discontinuities between different tissue layers. Wave
reflection and absorption characteristics are dynamically
considered in order to properly understand the resulting output
that will be delivered to the target tissue of the patient in light
of the relevant tissue structure.
[0021] The feedback loop of the present invention is also
considerate in its function. Rather than seeking to maintain a
constant electrical output, as is often practiced in conventional
devices, the ultrasound device of the present invention controls
and monitors the effects of the treatment on the transducer head to
maintain a constant ideal acoustic power. As a result, changes that
may occur naturally during treatment, such as changes caused by the
innate acoustic properties of the tissues proximate the treatment
head, are properly considered.
[0022] To ensure that the ultrasound device of the present
invention is operating safely and effectively, the present
invention includes an automatic calibration feature. This feature
enables new and replacement treatment heads to be introduced
without having to send the entire device away for calibration. The
ultrasound device of the present invention automatically determines
the complex impedance of the transducer head, after calibration,
and maintains acoustic power even in the presence of changes in the
real or imaginary portion of the acoustic impedance of the relevant
tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a front view of an embodiment of an ultrasound
therapeutic device in accordance with the present invention.
[0024] FIG. 2a is a diagram demonstrating ultrasonic beam
absorption and reflection losses resulting from a specific human
tissue structure.
[0025] FIG. 2b is a block diagram of the operation of thermal
dosage control in accordance with an embodiment of the present
invention.
[0026] FIG. 3 is a diagram plotting the frequency versus
conductance of a transducer in accordance with an embodiment of the
present invention.
[0027] FIG. 4a is a diagram of transducer circuitry in accordance
with an embodiment of the present invention.
[0028] FIG. 4b is a diagram of transducer circuitry in accordance
with an embodiment of the present invention.
[0029] FIG. 5 is a block diagram of the ultrasound system in
accordance with an embodiment of the present invention.
[0030] FIG. 6 is a diagram depicting the real and imaginary
components of measured voltage and current in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Referring primarily to FIGS. 1 and 5 , an ultrasound
therapeutic system 10 in accordance with the present invention is
shown. Specifically, the ultrasound system 10 generally includes a
device housing 12 , a generator/output stage high frequency
amplifier 14 , at least one transducer treatment head 16 , and a
programmable controller 18 . The generator 14 and controller 18 are
housed within the device housing 12 , and are both in operable
communication with the transducer 6 via a frequency cable 20 .
[0032] The generator 14 , as shown in FIG. 5, is an electric power
source commonly understood by one skilled in the art. For instance,
a 48 Volt dc, 0.85 Amp main power source can be utilized in one
embodiment, while others could implement similar compatible units.
First and second working frequencies of the generator 14 are
preferably approximately 1.017 MHz and 3.2 MHz, respectively. It is
possible to have a measurable tolerance/deviation of +/-30 KHz on
the first frequency and +/-50 KHz on the second frequency. Other
output frequencies and permissible frequency tolerances understood
to one skilled in the art are also envisioned. The electric power
frequency outputs are outputted from the generator 14 to the
transducer head 16 through the frequency cable 20.
[0033] The at least one transducer treatment head 16 is a
transducer head of a predetermined size, with the head 16 generally
including a handling portion 26, a transducer element 28, and a
treatment surface 30 . Each treatment head 16 utilized for the
present invention is preferably watertight for optimal use even if
completely submerged. Various embodiments can employ different
sized treatment heads 16. For instance, ultrasound treatment needs
and human body structure and size for a specific focus treatment
region on an individual can influence the size of the treatment
head. Generally, a large and small head will be interchangeable
using the same frequency cable 20. The ultrasonic transducer
element 28 of the treatment head 16 is typically constructed of a
ceramic (piezo) material. As such, the element 28 will have a
maximum output of acoustic power substantially at its resonance
frequency. As will be further discussed herein, the treatment head
16 will require initial and, perhaps, periodic self-calibration to
guarantee that this optimal resonance frequency for the respective
transmission element 28 is obtained and maintained. While various
treatment heads 16 can be exchanged to meet specific ultrasonic
treatment requirements, there is no need to switch out the cable
20. Conventional devices utilize a unique cable for each treatment
head, a practice that can be quite costly, and that can make
transportation and storage cumbersome and inconvenient. As
discussed herein in describing the cable 20, the present invention
eliminates this innate drawback found in conventional devices.
[0034] In one embodiment of the present invention, the treatment
head 16 further includes a configuration monitoring chip to
measure, observe and store data. For instance, operation
temperature at the head 16, head 16 serial numbers, head size,
calibration data, and a myriad of other information can be stored
such that the controller 18 in operable communication with the head
16 can store data to, and retrieve data from, the head 16. This
storage and reprogramming can be accomplished with the use of
EEPROM, or other non-volatile memory and storage technologies. For
instance, a Dallas DS-1820 chip (manufactured and sold by Dallas
Semiconductor of Dallas Texas), or other chips capable of
performing these storage and monitoring functions can be utilized
without deviating from the spirit and scope of the present
invention.
[0035] The frequency cable 20 shown in FIG. 1 generally includes at
least one set of end connectors 34 and 35 sized and shaped for
connecting to respective system 10 components. In particular, at
least one end connector 35 can be removably connected to the
generator 14 at the housing 12 and the distal end connector 34 of
the same cable 20 can be removably connected to the transducer
treatment head 16. As such, various treatment heads 16 can be
exchanged for operable use with the one common cable 20. This
unique swap/exchange feature is possible due to the selectively
engageable distal end connector 34. Unlike conventional practice, a
fixed and head-specific cable is avoided such that the present
invention promotes interchangeability and treatment flexibility,
while at the same time promoting storage and transportation. Each
of the end connectors 34 and 35 is generally combined or connected
to a system component via a socket or plug connection to facilitate
maintenance, selective replacement, and adjustable configuration,
with each connection preferably being watertight.
[0036] Referring primarily to FIG. 5, the controller 18 includes a
microprocessor 36 and control circuitry for providing
re-programmable software and hardware control of the present
invention. The microprocessor 36 is programmed to receive input and
execute control software/algorithms in accordance with
predetermined and inputted data. The microprocessor 36 is housed
within the housing 12 and is in operable communication with the
generator/output stage high frequency amplifier 14, treatment head
16, and each of the other components directly and/or through the
controller 18. In various embodiments, flash ROM, EEPROM,
non-voltaile memory, and RAM can be employed in conjunction with
the microprocessor 36 at the controller 18 for data storage and
retrieval.
[0037] Referring again to FIG. 1, the housing 12 generally includes
a data input portion 38 and a display portion 40. The input portion
38 can comprise input keys or other known input devices for
receiving data inputted by an end user in response to prompting
from the display portion 40 or from volitional decisions to pursue
known treatment goals and program routines. The data input portion
38 and display portion 40 are in operable communication with the
controller 18.
[0038] In operation, the system 10 of the present invention can
prompt the end user to input specific individualized treatment
data, wherein the controller 18 can utilize the data to calculate
and initiate ultrasound treatment, and provide responsive output
and interface adjustments during treatment. In one embodiment, a
treatment session or use of the system 10 will involve the
following series of inputs, outputs, and automatic adjustments.
[0039] First, a treatment "type" must be inputted into the system
10 via prompting on the display portion 40 . Generally, there are
at least three treatment types: thermal, biological, and
phonophoresis. Thermal allows the end user or patient to receive a
thermal energy effect from the treatment head 16 at the treatment
surface 30. Specifically, such a treatment selection initiates a
specific device configuration at the controller 18 wherein the
ultrasound energy transmission is converted into thermal energy.
Such a conversion leads to a local temperature elevation which
particularly effects deeper dense tissue of the patient. As further
discussed herein, the proper ultrasound transmission is highly
dependent upon inputted histological data from the patient/end
user.
[0040] The selection of a biological treatment type is directed to
a pulsed ultrasound output mode wherein the pulse causes the
oscillation of molecules accompanied by marked pressure variations.
In turn, this oscillation can lead to the formation of
micro-bubbles by cavitation, which in turn can produce a beneficial
micro-traumatic stress in indurated tissues, inflammatory foci,
local calcified accumulations, and the like.
[0041] The selection of a phonophoresis treatment type permits the
patient to take advantage of the increased skin permeability that
accompanies ultrasound waves. Radiation pressure at the skin due to
the inherent permeability increase promotes penetration of
medicines through the epidermis layer of the patient. With this
treatment selection, there is generally no need for the patient to
input histological data or treatment parameters since ideal
penetration of the substance is predetermined to facilitate
performance and efficiency. In one embodiment, the selection of the
phonophoresis treatment mode will cause the microprocessor 36 to
set the treatment parameters to the following values: intensity=1.5
W/cm.sup.2; duration=8 minutes; frequency=3.2 MHz; emission
mode=pulsed; duty cycle=1/2. Other variations on these values are
envisioned and can be employed and pre-programmed into the
microprocessor 36 software without deviating from the spirit and
scope of the present invention.
[0042] In addition, a manual setting is selectable so that the
patient can control each of the relevant microprocessor-controlled
treatment parameters--intensity, duration, frequency, and emission
mode. However, in preferred embodiments, these treatment parameters
are calculated and adjusted automatically by the controller 18
implementing software algorithms running on the microprocessor
36.
[0043] Specifically, in thermal and biological treatment modes,
histological structure data for the individual patient is needed.
This histological data generally comprises the target tissue type
(tissue to be treated), and the intermediate tissue type and depth
(subcutaneous tissue, if any, between the device and the target
tissue). Accurate calculation and inputting of this limited
histological data will provide the microprocessor 36 with enough
information to provide for a highly controlled and efficient
treatment of the patient. The necessary treatment parameters and
treatment dosage can be selectively and effectively controlled
having only this histological data from the patient/user.
[0044] The target tissue is generally selected at the input 38
panel of the system 10 from a programmable list. This list can
comprise bone, muscle, fat, aponeurosis, tendon, or other targets
known to one skilled in the art. In some circumstances, the target
tissue will be the only inputted/selected histological data. For
instance, if the target tissue is fat, there may not be an
intermediate tissue to take into account in controlling the
ultrasound treatment to the patient. As such, only the depth of the
fat target tissue will need to be inputted.
[0045] In other circumstances, the effect of relevant intermediate
tissue must be accounted for in determining a treatment dosage. For
example, in one operating scenario the target tissue selection may
be muscle. As such, it may be necessary to input the thickness or
depth of the intermediate tissue between the treatment head 16 and
the target muscle tissue. The intermediate tissue depth can be
measured with the use of skinfold pinch calipers, estimated on the
basis of the physician's or therapist's knowledge of human anatomy
(i.e., palpatory anatomy), and the like. The microprocessor 36 can
take the inputted histological data alone and determine the proper
intensity, duration, frequency, and emission mode. The software
will generally select the individual treatment parameters from the
following range list: intensity=0 to 2.3 W/cm.sup.2; duration 0 to
30 minutes (1800 seconds); frequency=approximately 1 or 3 MHz;
emission mode=continuous (1/1) or pulse (1/2, 1/4, or 1/8).
[0046] Upon the inputting of user selections and the computed
parameter settings and feedback controls, the treatment session
will begin by applying the treatment head to the target location on
the patient. The treatment head 16 output dosage is controlled by
the controller 18. If at any time the head 16 is removed from the
patient during the designated treatment period, for a predefined
period of time, the controller 18 will initiate a shut down
procedure to stop output from the generator 14 to the treatment
head 16.
[0047] Thermal Treatment Mode
[0048] In thermal mode, the algorithmic simulation functions of the
microprocessor 36 automatically calculate and control the treatment
dosage to create a tissue temperature elevation based on the
relevant histological data. Preferably, the intensity and duration
parameters are fully correlated. A change, either manually or
automatically, will cause the microprocessor 36 software to
automatically change the remaining value correspondingly such that
the product of the at least two values remains substantially
unchanged. The product of intensity and duration is generally used
to produce a target tissue temperature elevation of 7 degrees
Celsius. A continuous transmission (1/1), rather than pulsed, is
typically initiated by the software in thermal mode since such a
transmission promotes the desired tissue temperature elevation.
[0049] This product of acoustic intensity and treatment duration is
the treatment dosage. As shown in FIG. 2a, the dosage is a function
of the losses from absorption of the ultrasound beam as it travels
through relevant tissues and the losses from reflections at the
interfaces between adjacent tissues having different acoustic
impedances. The quantity of ultrasound which ultimately reaches the
target tissue is the therapeutically effective energy which
participates in the local elevation of tissue temperature. Since
the temperature elevation depends on dosage, the user can change
the remaining treatment duration or the intensity at anytime.
[0050] The software selects the frequency of the output signal
based on the histological data inputted. Specifically, the target
depth and intermediate tissue dictate the level of penetration
required to provide an effective therapeutic dose. In one
embodiment, a frequency of approximately 1 MHz is utilized to
penetrate relatively deep tissue since such a signal will be less
absorbed by the tissue. Conversely, a frequency of approximately 3
MHz is utilized to penetrate relatively shallow tissue. Preferably,
the microprocessor 36 software performs simulations at both the 1
MHz and 3 MHz levels to determine which signal will require the
smallest dosage while still obtaining the requisite therapeutic
effect. Other predetermined or variable frequency determinations
can be made as well without deviating from the spirit and scope of
the present invention.
[0051] Referring to FIG. 2b, one embodiment of the automatic mode
dosage determination software is shown. First, the user is required
to enter specific data at an initial input stage 50. At this data
input stage 50, the user is first prompted to enter a target tissue
type. Generally, fat, muscle, tendon, and bone are the tissue types
available for selection or input. Once the tissue selection has
been made, the user is prompted to input the depth of the tissue
between the target and the treatment head 16. It is preferred that
this depth be entered in centimeters, but other measurements are
also envisioned. For instance, if the target tissue inputted is
tendon, it is possible that there is muscle and/or fat intermediate
the tendon. As discussed, this tissue intermediate the target
tissue must be considered before calculating a truly effective
treatment dosage. Tissue depth and thickness calculations can be
performed using techniques known to one skilled in the art. For
instance, pinch calipers and the physician's or therapist's
knowledge of the human anatomy can be employed. Depending on the
presence of intermediate fat or muscle, and the corresponding depth
for the intermediate tissue, the microprocessor 36 software will
process the data at an intensity transmission stage 52.
[0052] At the intensity transmission stage 52, the actual
transmission effects of the tissue layer structure are considered
in calculating a transmission coefficient .tau.. Variable .tau.
represents reflection losses caused as a result of the layers and
tissue interfaces to assist in providing for needed adjustment in
the dosage, wherein .tau. is represented in equation form as:
.tau.=1-R.sub.ij
[0053] where R.sub.ij is the tissue intensity reflection
coefficient between layer i and j. This reflection coefficient
depends on the acoustic impedance of layer i (Z.sub.i) and layer j
(Z.sub.j): 1 R i j = ( z i - z j ) 2 ( z i + z j ) 2
[0054] Defined tissue impedance levels for bone, skin, tendon,
muscle, and fat are known and processed depending on the referenced
tissue inputs such that each impedance value corresponds to a wave
reflection at the interface of adjacent tissues. For instance, a
.tau. value representing the influence of the reflection
characteristics of interfacing fat and tendon tissue (.tau..sub.ft
) will equate to a coefficient of 0.934, which represents a 93.4%
transmission intensity and a 6.6% loss due to reflections at the
interface. Assuming m=muscle, t=tendon, f=fat, and b=bone, other
possible transmission loss characteristics can be accounted for as
.tau..sub.mt=0.974, .tau..sub.st=0.968, .tau..sub.sb=0.748,
.tau..sub.fb=0.685, .tau..sub.mb=0.761, .tau..sub.fm=0.990,
.tau..sub.fs=0.990, .tau..sub.sm=0. 890, .tau..sub.tb=0. 870, and
other transmission coefficients known to one skilled in the
art.
[0055] Additionally, reduction of the available energy at the
target tissue is caused by a beam attenuation (a) phenomenon.
First, this attenuation is due to absorption (.alpha.), which is a
transformation of a fraction of the acoustic beam into heat.
Second, beam diffusion or scattering (d) also contributes to the
beam attenuation. As such, a=.alpha.+d. For scenarios involving
soft tissues and at frequencies in the MHz range, scattering may be
neglected so that a=.alpha., for a unit measurement of Np/cm.sup.2
(Nepers per square centimeters).
[0056] At the thermal simulation stage 54, the appropriate
ultrasound frequency intensity (I.sub.0) and treatment duration (T)
are calculated such that the product of the intensity and the
treatment duration equals the treatment radiation dosage D. In
obtaining the correct variables for this dosage formula, an ideal
frequency must be calculated. This ideal frequency for the
ultrasound intensity I.sub.0 is based on a simulation run for at
least two frequencies--1 MHz and 3 MHz. It should be noted that
these frequencies, while preferred, are not in any way exhaustive
in nature. For instance, other frequency ranges and values can be
utilized depending on the particular desired therapeutic effect. In
addition, values such as 1 MHz and 3 MHz are obviously rounded for
ease of explanation an9d calculation. In one embodiment, the
frequency intensities can be assigned as 1.017 MHz.+-.30 KHz, and
3.2 MHz.+-.50 KHz. Other values and corresponding ranges are also
envisioned.
[0057] In an embodiment performing an individual simulation run for
both 1 MHz and 3 MHz levels, the following equation is implemented:
2 D = ( I 0 t ) = T C v 2 f 2 f ( a1e1 + a2e2 + a3e3 )
[0058] wherein the frequency value .function.is inserted by the
microprocessor 36 program as either 1 or 3 depending on the
particular simulation run, T is the treatment duration (i.e.,
seconds), C.sub.v is a thermal coefficient (heat capacity per unit
volume), a is the attenuation coefficient, and .tau. again
represents consideration of the effects of the actual tissue layer
structure in an intensity transmission coefficient. As the
appropriate .tau. value has already been processed in the intensity
transmission stage 52, that value is automatically inserted to
promote evaluation of true tissue effects during the treatment
simulation. The attenuation coefficient a represents absorption
within the tissue layer of a level of energy lost in the form of
heat. Variable attenuation coefficient values known to one skilled
in the art as being representative of these tissue-specific heat
absorption effects can be employed without deviating from the
spirit and scope of the present invention.
[0059] With calculation and insertion of the appropriate values
into the simulation equation, a product A is assigned the resulting
dosage product for 1 MHz, and B is assigned the dosage product for
3 MHz. The products A and B are compared and analyzed to determine
the smallest dose D that can be employed while still reaching the
desired therapeutic effect based on known histological data from
the user. Preferably, if A.gtoreq.B then a value of 3 MHz is
assigned as the output frequency, else a value of 1 MHz is
assigned. Next, intensity and treatment duration end points are
examined based on the simulation results to determine optimum
values for generating the product dosage, wherein the resulting
product dosage is processed to determine whether it falls within an
acceptable range defined by predetermined minimum and maximum
product dosage values. These values, in one embodiment, can be a
minimum dosage value of 6 Ws/cm .sup.2 (Watt seconds per square
centimeter) and a maximum value of 5400 Ws/cm.sup.2. For instance,
if a maximum product dosage of 5400 is calculated based on the
above simulation equations, then a set intensity I.sub.0, is
assigned to approximately 3 W/cm.sup.2, with a corresponding
treatment duration of approximately 1800 seconds. Further, the
microprocessor 36 can downsize the dosage if it exceeds the
maximum, up the dosage if it equates to a value below the
acceptable minimum level, and can process variable levels between
these end point values. At the completion of the comparison and
simulation, the duration T, and intensity I.sub.0 are known values
that can be linked at a product dosage stage 56, wherein the
product dosage P=I.sub.0.multidot.T. This equation links the
variables such that a change in one variable can cause the
microprocessor 36 program to correspondingly change the other
variables to produce a constant dosage.
[0060] Biological Treatment Mode
[0061] In biological mode, the algorithmic simulation functions of
the microprocessor 36 take tissue configuration into account and
automatically select the treatment parameters that will produce the
required mechanical effect and minimize tissue temperature
elevation. Whereas a tissue temperature elevation is the desired
effect in the thermal treatment mode, a thermal effect is not
beneficial and must be minimized in biological mode in favor of a
mechanical effect.
[0062] The software automatically determines the intensity,
frequency, emission mode and duration of treatment needed in
biological mode. In one embodiment, these values are obtained from
a look-up table. The desired mechanical effects of biological mode
are typically induced using a pulsed emission mode with different
duty cycles. The ultrasonic pressure waves produce an oscillation
of molecules in the target tissue. This oscillation creates
microscopic bubbles called cavitation bubbles that generate small
shockwaves in the tissue when they collapse. These small shockwaves
induce microscopic mechanical effects in the tissues that enhance
the healing process by causing the tissues to grow stronger in
reaction to the micro-traumatic stress effect. Biological mode is
typically beneficial to indurated tissues, inflamed areas, local
calcifications, accumulations of blood such as hematomas, bruises
and blood clots, and areas of fibrosis.
[0063] Phonophoresis Treatment Mode
[0064] In phonophoresis mode, ultrasound is employed to aid in the
penetration of drugs through the skin and into target tissue.
Phonophroesis mode enhances local application of a drug by
increasing the permeability of the skin and exerting a radiation
pressure that promotes the penetration of drugs deep into
tissues.
[0065] In one embodiment, all software parameters in phonophoresis
mode are fixed and the dose is held constant. While the intensity
and treatment duration may be adjusted, the microprocessor 36
software links the two conditions inversely such that an increase
inputted in either will cause the software to decrease the other.
Again, phonophoresis treatment mode will generally cause the
microprocessor 36 to set the treatment parameters to the following
values: intensity=1.5 W/cm.sup.2; duration=8 minutes (480 seconds);
frequency=3.2 MHz; emission mode=pulsed; duty cycle=1/2.
[0066] Automatic Feedback Loop
[0067] Ultrasound treatment is more effective when constant
acoustic power is delivered to the tissue. The ultrasound generator
14 includes a novel feedback loop feature that operates to maintain
the delivery of acoustic power at a constant level. A simplified
block diagram 100 of the feedback loop in accordance with the
present invention is shown in FIG. 5.
[0068] The feedback loop operates to measure a coupling efficiency
between the transducer treatment head 16 and the biological tissue
of the patient. The coupling efficiency is a ratio of the acoustic
power effectively transmitted into the patient to the electric
power delivered to the transducer treatment head 16 from the
generator 14 . Thus, the coupling efficiency can be expressed as: 3
= P a P e
[0069] where .eta. is the coupling efficiency, P.sub.a is the
effective transmitted acoustic power and P.sub.e is the delivered
electric power. The coupling efficiency is dependent on patient
tissue configuration as tissue impedance varies with tissue type.
For example, if the tissue in contact with the transducer treatment
head 16 is soft, i.e., skin with a thick layer of fat, the acoustic
impedance will be low and the coupling efficiency will be low. If
the tissue is instead skin with a thin layer of fat and a large
bone near the skin surface, the coupling efficiency will be
higher.
[0070] The microprocessor 36 adjusts the electric power, P.sub.e ,
such that the effective acoustic power transmitted to the patient
is maintained constant regardless of the tissue type encountered.
While the coupling efficiency, .eta., can be expressed by the above
equation, the microprocessor 36 uses a modified equation to
calculate .eta. and determine the transducer efficiency for the
purpose of adjusting the electric power to maintain the acoustic
power.
[0071] FIG. 4a depicts an equivalent circuit 88 of the piezo
transducer close to its resonant frequency in accordance with the
present invention. In the equivalent circuit 88, internal
mechanical losses are represented by R.sub.i 92, and R.sub.r 90
represents the radiation resistance. The acoustic power emitted can
be viewed as the power dissipated across the radiation resistance,
R.sub.r 90. Where R.sub.s represents the sum of R.sub.i 92 and
R.sub.r 90, the value of R.sub.s can be obtained by measuring the
overall admittance (the reciprocal of the overall impedance) of the
equivalent circuit at resonant frequency. At resonant frequency,
C.sub.s 74 and L.sub.s 76 resonate together and further reduce the
equivalent circuit 88 to the circuit 78 depicted in FIG. 4b. The
overall (complex) admittance, Y 80, of the circuit 78 (and the
equivalent circuit 88 of FIG. 4a) is the sum of the admittance of
the resistance R.sub.s (where R.sub.s=R.sub.r+R.sub.i) and the
admittance of the capacitor C.sub.0 82, such that: 4 Y _ = Y R + Y
C = G + j B = 1 R s + 1 j C 0
[0072] where G, the conductance, is the real portion of the
admittance and B, the susceptance, is the imaginary portion. Thus,
the conductance, G, of the equivalent circuit 88 of the transducer
at resonant frequency is 1/R.sub.s, which results in the value of
R.sub.s itself.
[0073] FIG. 3 is a diagram plotting the frequency 72 versus
conductance 70 of a transducer 16 in accordance with the present
invention. To measure the value of R.sub.s, it is necessary to find
the maximum value of the real portion of the admittance, G.sub.max
84, where 5 G max = 1 R s
[0074] This will also provide the series resonant frequency,
f.sub.s 86. The equation for Y 80, above holds true only at the
resonant frequency f.sub.s 86, of the piezo transducer 16, defined
by the maximum of the real portion of Y 80, G.sub.max 84. FIG. 4
depicts the shape of a curve of the conductance, G 70, plotted
against frequency, f 72, and demonstrates the relationship between
G.sub.max 84 and f.sub.s 86. Note that the series resonant
frequency f.sub.s 86 will vary for each transducer treatment head
16 used. Calibration of a particular transducer treatment head 16
consists of the microprocessor scanning the frequency of the signal
and simultaneously monitoring the conductance, G 70, in order to
detect a maximum (see FIG. 3). The locus of the maximum, G.sub.max
84, defines the resonant frequency, f.sub.s 86. This calibration
procedure is initiated by a user while the transducer 16 is
unloaded (e.g., not in contact with any tissue) and is discussed in
greater detail in the following section.
[0075] Referring again to FIGS. 4a and 4b, the effective radiation
resistance R.sub.r 90 actually represents the transmission of
ultrasonic energy out of the transducer. When measuring the
transducer radiating into a tissue load, the maximum conductance,
G.sub.max 84 of FIG. 3 as discussed above, actually provides: 6 G
max = G tissue = 1 R tissue + R i
[0076] When the maximum admittance is measured without any load,
the maximum conductance, G.sub.max 84 (the real portion of the
admittance), is almost exclusively the internal losses: 7 G max = G
0 = 1 R i
[0077] where G.sub.0 is the series conductance of the unloaded
transducer treatment head 16. Thus, if the dielectric losses are
neglected, the transducer 16 efficiency can be approximated by: 8
ea = G 0 - G tissue G 0
[0078] FIG. 5 represents a block diagram of the ultrasound system
in accordance with an embodiment of the present invention. In
operation, the analog multiplier 94 receives a measured voltage
signal 96 and a measured current signal 98 from the
generator/output stage high frequency amplifier 14. The analog
multiplier 94 is also connected to a 90-degree quadrature signal
generator 104. The 90-degree quadrature signal generator 104
receives a reference sine wave 110 from the digital sine wave
generator 112 and in turn provides the analog multiplier 94 with
sine 106 and cosine 108 reference signals. Vector voltage V.sub.i
114, the output of the analog multiplier 94 , represents V.sub.1
116, V.sub.2 118, V.sub.3 120 and V.sub.4 122, which are generated
by switching the inputs of the analog multiplier 94 circuit as
shown in FIG. 6.
[0079] The electrical power P.sub.e, can then be calculated from
V.sub.i 114, where:
P.sub.e=.vertline.{right arrow over
(V)}.vertline..multidot..vertline.{rig- ht arrow over
(I)}.vertline.cos .phi.
[0080] The complex transducer 16 impedance Z can be calculated by
dividing V by I, and the conductance G is the real portion of the
inverse of Z, or the real portion of I over V. After the efficiency
.eta. and the electric power P.sub.e are calculated from the input
voltage, the effective transmitted acoustic power P.sub.a can be
calculated. The voltage control signal V.sub.c 124 can then be
adjusted and readjusted accordingly to maintain the delivery of
acoustic power at a constant level.
[0081] In sum, the procedure used by the microprocessor 36 for
determining the efficiency of the transducer is as follows: (1)
determine vector voltage V.sub.i 114 , having components V.sub.1
116 , V.sub.2 118, V.sub.3 120 and V.sub.4 122, by measurement; (2)
calculate the coupling efficiency and the electric power from the
vector voltage 114; (3) calculate the effective transmitted
acoustic power; and (4) readjust the voltage control signal 124
accordingly. In operation, the microprocessor 36 is thus able to
maintain a constant level of effective acoustic power transmitted
to the patient by adjusting the electric power approximately every
20 milliseconds in response to the coupling efficiency calculated
in the feedback loop. Additionally, during emission, the
microprocessor 36 regularly scans the G.sub.max 84 value in order
to detect if f.sub.s 86 has shifted and readjusts accordingly.
[0082] Further, during transmission the microprocessor 36 monitors
the feedback loop, with notification provided if the feedback loop
fails. A failure of the feedback loop may occur, for example, when
the user removes the treatment head 16 from the patient, which
results in insufficient acoustic coupling. In the event of such a
failure, transmission is stopped and the ultrasound therapeutic
system 10 puts itself into resonance search and output calculation
mode. Once the acoustic coupling returns to an acceptable level (by
the user having placed the treatment head 16 back in contact with a
patient's skin), the feedback loop is restarted and normal
operation resumes. The microprocessor 36 also monitors the resonant
frequency 86 search and centering, and the presence of the
treatment head 16 . Throughout, the system 10 continuously scans
the frequency over a range around the nominal resonant frequency
f.sub.s 86 to ensure that the frequency of the excitation signal
remains centered on the maximum conductance G.sub.max 84 .
[0083] Automatic Calibration
[0084] For safe and effective ultrasound treatment, properly
calibrated equipment is required. The ultrasound therapeutic system
10 in accordance with the present invention generally includes a
calibration procedure that enables a user to calibrate the
transducer treatment heads 16 whenever necessary without having to
send the entire ultrasound therapeutic system 10 back to the
factory. In addition, the calibration procedure enables the user to
calibrate an entirely new transducer treatment head 16 as soon as
it is received, facilitating easy and efficient replacement of worn
or dysfunctional parts.
[0085] The calibration procedure of the present invention
automatically determines the impedance of the transducer treatment
heads 16. The procedure is based upon the measurement of the series
conductance G.sub.0 of the transducer treatment head when it is
unloaded. The series conductance is the real portion of the
admittance and the reciprocal of the impedance and represents the
losses of the transducer treatment head 16 itself. Referring
primarily to FIG. 5, the microprocessor 36 calibration software
scans the generator frequency to determine the maximum value of
G.sub.0 that also yields the resonant frequency f.sub.s 86 of the
transducer treatment head 16. The measurement of G.sub.0 is done by
a demodulation method in which the current 98 and voltage signals
96 from the treatment head are multiplied by quadrature reference
signals 106 and 108. This method considers the complex impedance
and thus accounts for the corresponding phase shifts between
current and voltage (.theta.): 9 Z _ = V _ I _ = Z - j
[0086] where .theta. is the phase of the complex impedance. The
complex admittance Y can then be determined, the real part of which
is the series conductance G.sub.0 :
G.sub.0=Re{Y}=(R.sup.-1)
[0087] where R=R.sub.s=R.sub.i as R.sub.r=0 with no acoustic
loading (see FIGS. 4a and 4b ). During the emission of ultrasound
energy into a patient's tissue, the ultrasound therapeutic system
10 constantly measures the maximum series conductance under load,
G.sub.tissue , using the same method: 10 G tissue = 1 R s = 1 R r +
R i
[0088] The system 10 then determines the real-time electro-acoustic
coupling efficiency .eta.: 11 = G 0 - G tissue G 0
[0089] In operation, the user initiates the calibration procedure.
Ideally the procedure is run annually, but other periodic
calibrations are envisioned as well. With the transducer 16
unloaded, the microprocessor 36 scans the excitation frequency in a
predefined range around the resonant frequency 86 and looks for the
maximum conductance G.sub.0. G.sub.0 is representative of the
transducer 16 losses as it is the real portion of the impedance
when no acoustic energy is produced by the piezo transducer 16. The
microprocessor 36 records the value of G.sub.0 and the resonant
frequency 86 for later use.
[0090] During normal use, the electro-acoustic coupling efficiency
.eta. is calculated from the actual loaded conductance
G.sub.tissue, where G.sub.max=G.sub.tissue, and from the recorded
value of G.sub.0 adjusted according to the equation above. In one
embodiment, this calibration procedure allows the system 10 to
compensate for any changes in the electrical characteristics of the
transducer 16, including the acoustic load, changes in the
capacitance C.sub.0 due to aging, temperature driven changes, and
like characteristics.
[0091] In this automatic calibration procedure, the system 10
considers both impedance amplitude and phase, allowing for
consideration of complex changes. Thus, the power transmitted to
the tissue remains accurate despite shifts in the resonant
frequency 86 due to slight imaginary components in the acoustic
impedance of the target tissues being treated.
[0092] Those skilled in the art will appreciate that other
embodiments in addition to the ones described herein are indicated
to be within the scope and breadth of the present application.
Accordingly, the applicant intends to be limited only by the claims
appended hereto.
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