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Description  |
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TECHNICAL FIELD
This invention relates generally to catheters, systems, and methods for the
hyperthermia treatment of tissue, and particularly to the use of a
transurethral ablation catheter, system, and method for the hyperthermia
treatment of the prostate.
BACKGROUND OF THE INVENTION
Present modalities for treatment of malignant tumors include surgery,
radiation therapy, chemotherapy, and immunotherapy which apply a physical
or chemical force to alter the biological function of a tumor in order to
affect its viability. Despite the medical advances that these modalities
represent, most solid cancerous tumors carry with them a very poor
prognosis for survival. Quality of life during and after treatment for
survivors is often poor. The dismal prognosis for malignant solid tumors
has led to continuing research for more effective treatment modalities
with a lesser degree of disability and fewer side effects. In vitro and in
vivo evidence indicates hyperthermia produces a significant anti-cancer
activity through alteration of the physical environment of the tumor
caused by increasing the temperature. Hyperthermia is more cytotoxic to
tumor cells than normal cells because cancer cells are oxygen deprived,
nutritionally deficient, and low in pH making them incapable of tolerating
the stress imposed by elevated temperature. Tumor vasculature is immature,
lacking the smooth muscle and vasoactivity which allows mature vessels to
dilate, increasing blood flow to carry away heat, therefore intratumor
temperatures exceed those in normal tissue. The mechanisms of selective
cancer cell eradication by hyperthermia is not completely understood.
However, four cellular effects of hyperthermia on cancerous tissue have
been proposed: 1) changes in cell or nuclear membrane permeability or
fluidity, 2) cytoplasmic lysomal disintegration, causing release of
digestive enzymes, 3) protein thermal damage affecting cell respiration
and the synthesis of DNA and RNA, and 4) potential excitation of
immunologic systems.
The major forms of energy for generating hyperthermia to date include
microwaves, radio frequency induction, radio frequency localized current,
and ultrasound. Most of the techniques used to dispense these are
non-invasive, i.e., the heat generating source is external to the body and
does not invade the body. Consequently, the energy must pass through the
skin surface and substantial power absorption by normal peripheral body
tissue is unavoidable. Currently available external heating sources result
in nonuniform temperature profiles throughout the tumor and increased
temperature in normal tissue. It is desirable to selectively heat tissue
deep in a patient's body, i.e., to heat the tumor mass without heating
cutaneous and normal tissue.
Others have attempted the use of interstitial techniques to obtain local
hyperthermia, with limited success. Interstitial heating of brain tumors
through an implantable microwave antenna has been investigated. However,
microwave probes are ineffective in producing precisely controlled heating
of tumors. Temperatures may deviate as much as 10.degree. C from the
desired target temperature. Besides, microwave activity adversely affects
cellular structures and their integration, regardless of other thermal
effects. The result is nonuniform temperatures throughout the tumor.
Studies indicate that tumor mass reduction by hyperthermia is related to
the thermal dose. Thermal dose is the minimum effective temperature
applied throughout the tumor mass for a defined period of time. Hot spots
and cold spots which occur with microwave hyperthermia may cause increased
cell death at the hot spot, but ineffective treatment at cold spots
resulting in future tumor growth. Such variations are a result of the
microwave antenna's inability to evenly deposit energy throughout the
tissue.
Since efferent blood flow is the major mechanism of heat loss for tumors
being heated and blood flow varies throughout the tumor, more even heating
of tumor issue is needed to ensure more effective treatment.
To be effective, the application and deposition of thermal energy to the
tumor must be precisely controlled to compensate for the variations in
blood flow. In addition, the therapy itself will perturb the tumor's
vascular system during treatment causing variations in local perfusion
around the probe. Thus, heat loss from a tumor will be time dependent and
affected by the hyperthermia treatment. This demonstrates the need to both
monitor and control the temperature of the tumor throughout treatment.
Benign Prostatic Hyperplasia (BPH) is a disease that is traditionally
treatable by transurethral resection of the prostate (TURP). Patients who
undergo a TURP are typically hospitalized for two to five days and
convalesce afterward for another one to six weeks. Serious complications
following TURP include failure to void or urinary retention in 10-15
percent of patients; bleeding that requires a transfusion in 5-10 percent
of patients; urinary tract infection in 15-20 percent of patients;
retrograde ejaculation in 60-75 percent of patients; and impotence in 5-10
percent of patients. As a result of the recovery time, medical costs, and
likelihood of serious complications following a TURP, alternative methods
for treating BPH have been attempted.
BPH has been treated by applying hyperthermia temperatures to the prostate
of a patient. A hyperthermia device is inserted into the urethra so that
the heat generating portion of the device is positioned in the prostatic
urethra. To prevent damage to the internal and external sphincters, the
heat generating portion of the device must not be in contact with or
directed toward the sphincters. Damage to the internal sphincter results
in retrograde ejaculation. Damage to the external sphincter results in
incontinence. Damage to the nerves about the prostatic urethra results in
impotence. Therefore, positively securing the proper position of the heat
generating element is imperative for preserving these sphincters and their
functions.
Several known catheters for use in the hyperthermia treatment of the
prostate of a patient rely on microwave or radio frequency energy
deposition for generating heat. One known catheter has a distally
positioned bladder retention balloon, an inflatable prostate balloon, and
a microwave antenna positioned in a longitudinal lumen of the catheter.
The prostate balloon centers the antenna and compresses tissue while it is
being irradiated for mitigating the problem of the microwave field
intensity varying unevenly over the heated tissue.
Another known catheter has a distally positioned bladder retention balloon
for limiting the proximal migration of the catheter. The bladder retention
balloon also provides for maintaining the position of a diode centrally in
the prostate for directing the peak of electromagnetic energy applied
thereto by a microwave antenna toward the central area of the prostate.
Yet another known catheter has a distally positioned bladder retention
balloon and a helical coil antenna for receiving electromagnetic energy
from a microwave generator and heating tissue to hyperthermia temperatures
in the range of 41.degree. to 47.degree. C.
One problem with each of these devices is that they use microwave or radio
frequency energy deposition to effect heating. Radio frequency energy
deposition resulting in heat generation is unpredictable due to the
nonhomogeneous tissue between the applicator and grounding plate.
Similarly, microwave energy deposition is unpredictable due to the
different dielectric properties inherent in various types of tissue, such
as muscle, fascia, and viscera. As a result, there can be uneven heating
of anatomical regions with areas of overheated tissue and underheated
tissue. The energy deposition heating technology can undesirably heat and
damage the internal and external urethral sphincters. In addition, the use
of energy deposition technology limits the size of the heat-emitting
element. As a result, only limited modifications can be made to the
catheter for tailoring the catheter to variations in individual patient
anatomy.
Another problem with catheters using a distally positioned bladder
retention balloon for limiting the proximal migration of the catheter is
that the bladder retention balloon does not prevent a catheter from
migrating distally. Since the longitudinal position of the catheter is not
positively secured, the internal sphincter can be exposed to heat and
damaged or destroyed.
An alternative to energy deposition technology for heating tissue is the
application of thermally conducted heat. Several devices for applying heat
directly to the rectum and gastrointestinal tract are known. For example,
a thermoelectrical heat exchange capsule probe includes a plurality of
thermocouples that get hot on one end and cold on the other when
electrical current is passed therethrough. The probe can have a flexible,
expandable sheath affixed to the outside thereof for containing a heat
conducting fluid. The sheath is expandable for bringing a heated surface
in contact with the tissue to be treated.
Another known device is a suppository appliance for the therapeutic
treatment of hemorrhoids that is surrounded by a rigid, cylindrical jacket
sized for intimately fitting in the anal canal of a patient. When
electrical energy is applied to the appliance, a cylindrical electrical
resistor generates heat inside the jacket to a predetermined maximum
temperature of about 45.degree. C.
Yet another known device is a heatable dilation catheter for treating body
tissue and including an elastic, expandable heat-emitting element, such as
a braided stainless steel tube coated with silicone and mounted on a
dilation balloon, for increasing the proximity of the heat-emitting
element to tissue.
One problem with the use of any of these devices for treating BPH is that
none of these devices can be affixed in a particular longitudinal position
in a body passageway. As a result, anatomical structures that are
preferably preserved can be exposed to high temperatures and damaged or
destroyed. These devices are inappropriate for use in the urethra of a
patient, wherein the internal and external urethral sphincters can be
undesirably heated and damaged.
SUMMARY OF THE INVENTION
The present invention teaches the details of a method for cancer treatment
by means of interstitial conductive hyperthermia. The present invention
also teaches the construction and operation of hyperthermia apparatus
comprising a means for effectively achieving therapeutic heating of tumors
deep in a patient's body by generation of heat within the tumor that has
all of the desirable characteristics mentioned above. An embodiment of
this invention provides for monitoring and control of tumor temperature to
achieve a controlled pattern of energy deposition.
The method includes measurement and location of the tumor mass,
implantation of an array of treatment probes in the tumor, and generation
of volumetric hyperthermia through the implanted probes. Apparatus
invented to facilitate this procedure includes an array of probes, a heat
generating means for converting electrical energy into thermal energy, and
a temperature sensing means. According to one embodiment of the invention,
a template having an array of parallel apertures is affixed to a
supporting structure on an imaging system for registration of probe
position on an image generated by the imaging system.
It is accordingly an object of this invention to provide a safer and more
effective means for treating cancerous tumors using a system for
interstitial application of hyperthermia to the tumor with a multitude of
implantable probes which conductively heat the tumor with precisely
controlled temperature.
Another object is to locate a heater element at a location within the tumor
to be treated so that heat generated thereby emanates outwardly into the
surrounding tumor.
Another object is to minimize the surgical procedures necessary in the
treatment of cancerous tumors.
Another object is to teach the construction and operation of a novel probe
assembly capable of being implanted through tissues extending into a
cancerous tumor with the least of a surgical procedure and damage to the
patient.
Another object is to minimize the surgical procedures necessary to implant
and maintain a heat generating device in a tumor.
A further object of this invention is to provide controlled therapeutic
temperature fields in malignant structures using an array of interstitial,
surgically implanted, heater/temperature sensitive probes to maintain
tissue above a minimum cell death temperature throughout the tumor mass
for a defined time.
These and other objects of the invention will become more readily apparent
after considering the following detailed specification covering preferred
embodiments thereof in conjunction with the accompanying drawings.
The foregoing problems are solved and a technical advance is achieved by an
illustrative transurethral ablation catheter for ablating prostatic tissue
about the prostatic urethra positioned between the internal and external
sphincters. The catheter comprises an elongated member with an
intermediate portion shaped and sized for intimate contact with the
prostatic urethra. The elongated member also includes fixation means such
as an inflatable balloon positionable about at least one of the internal
and external sphincters for maintaining longitudinally the intermediate
portion in the prostatic urethra. A thermally conductive, heat-emitting
element is positioned in the intermediate portion and is responsive to
energy supplied thereto for producing a predetermined, thermally
conductive heat distribution in the tissue to ablate the tissue.
When inflated, the fixation balloon includes an annular recess for
positioning one of the internal and external sphincters therein. The
elongated member also includes supply means, such as a passageway
extending longitudinally in the elongated member, which communicates with
the fixation balloon for inflating it. The supply means further includes
means for circulating a coolant such as a second passageway extending
longitudinally in the elongated member and communicating with the fixation
balloon. One of the passageways includes a plurality of ports having
different cross-sectional areas for maintaining a uniform flow of the
coolant from the passageway into the interior of the balloon. The catheter
further advantageously includes a second inflatable balloon positionable
about the other one of the sphincters for further positioning the
intermediate portion of the catheter as well as cooling the other
sphincter. The same two passageways may be utilized to supply the second
inflatable balloon or preferably another set of longitudinally extending
passageways are used to inflate the balloon and supply coolant thereto.
This second fixation and cooling balloon further includes when inflated an
annular recess thereabout for positioning therein and cooling the other
sphincter.
To advantageously maintain the thermally conductive heat distribution in
the prostatic tissue, the catheter includes a temperature sensor
positioned about the intermediate portion such as a thermistor for
measuring the temperature thereabout. This temperature information is
advantageously provided to the controller of an ablation system of the
present invention. The controller is responsive to the temperature
measured about the sensor and the energy supplied to the heat-emitting
element for controlling the energy supplied thereto to produce and
maintain a minimum ablative temperature or thermally conductive heat
distribution in the prostatic tissue. The catheter further includes a
temperature sensor for measuring the temperature of the coolant. The
system controller is responsive to this coolant temperature for
advantageously maintaining the temperature of the sphincter below an
ablative temperature. This advantageously prevents chronic injury to the
sphincter and resulting incontinence and impotence.
To accommodate different length prostatic urethras among patients, the
catheter also advantageously includes telescopic, coaxial elongated
members for varying the spacing between the fixation and cooling balloons
for positioning the sphincters in the annular recesses thereof. The
heat-emitting element comprises a helically wound coil of electrically
semiconductive material positioned longitudinally in the intermediate
portion. So as not to ablate prostatic tissue about the ejaculatory duct,
the heat-emitting element is semicylindrically, serpentine shaped. The
supply means are advantageously positioned within the semicylindrical
interior of the heat-emitting element to further cool and maintain the
prostatic tissue about the ejaculatory duct below an ablative temperature.
The ablative system comprises the transurethral heat-emitting catheter for
producing the thermally conductive heat distribution to ablate prostatic
tissue. The heat-emitting catheter also includes sensor means for
measuring the temperature thereabout. The system also includes a
controller responsive to a temperature about the sensor and the energy
supplied to the heat-emitting catheter for controlling the energy supplied
to the catheter to produce the ablative heat distribution in the prostatic
tissue. The heat-emitting catheter of the system also includes cooling
and/or fixation balloons positioned about the sphincters for maintaining
the sphincters below an ablative temperature. Temperature sensors are
advantageously positioned within the interior of the cooling balloons for
providing coolant temperature information to the controller. The
controller is responsive to this coolant temperature information for
controlling the supply of coolant to the balloons. Furthermore, the
ablative system includes a pump responsive to the controller for
circulating coolant through the balloons.
The method of treating prostatic hyperplasia includes inserting the
heat-emitting catheter transurethrally and selectively applying a heat
distribution between the internal and external sphincters to produce
ablative temperatures in the prostatic urethra. As a result, the ablated
tissue subsequently sloughs and enlarges the lumen through the prostate
for increased fluid flow therethrough. The method further includes
positioning at least one of the sphincters about a fixation and cooling
balloon of the heat-emitting catheter and cooling the sphincter below a
predetermined maximum temperature. The method also includes producing
coagulation of blood perfusing through the prostate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of the head and upper body portion of a person
equipped with an implanted hyperthermia system constructed according to
the one embodiment of the present invention.
FIGS. 2A and 2B together are a schematic diagram of a control circuit for
an implantable hyperthermia system including an internal or implanted
system portion and the external portion for coupling to the internal
portion.
FIG. 3 is an enlarged cross-sectional view through a single element probe
with a portion of cable attached thereto for use with the present device.
FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 3.
FIG. 5 is an enlarged cross-sectional view through a multiple element probe
with a portion of cable attached thereto for use with the present device.
FIG. 6 is a side view of the probe and cable portion of FIG. 5 but shown in
a non-linear configuration.
FIGS. 7A and 7B together are a flowchart for the systems shown in FIGS. 2A
and 2B.
FIG. 8 is a block diagram of another embodiment of a hyperthermia system
according to the present invention.
FIG. 9 illustrates temperature distributions in planes perpendicular to
probes implanted according to the preferred embodiment of the present
invention.
FIG. 10 depicts an enlarged view of the connection of FIG. 8.
FIGS. 11-15 illustrate templates according to the preferred embodiment of
the present invention.
FIG. 16A and 16B together form a block diagram of an external control
system according to the preferred embodiment of the present invention.
FIGS. 17-19 are electrical schematics of the optoisolator shown in FIG. 16A
and 16B.
FIG. 20 is an electrical schematic of the status buffer shown in FIG. 16A
and 16B.
FIG. 21 is an electrical schematic of the control decoder shown in FIGS.
16A and 16B.
FIG. 22 is an electrical schematic of the multiplexer shown in FIGS. 16A
and 16B.
FIGS. 23A-23D are electrical schematics of circuits 473-476 shown in FIG.
16A and 16B.
FIG. 24 is an electrical schematic of the master control circuit shown in
FIGS. 16A and 16B.
FIG. 25 is an electrical schematic of the heater overtemperature circuit
shown in FIGS. 16A and 16B.
FIG. 26 is an electrical schematic of the manifold sense circuit shown in
FIGS. 16A and 16B.
FIG. 27 is an electrical schematic of the master relay circuit shown in
FIGS. 16A and 16B.
FIG. 28 is an electrical schematic of the power monitor shown in FIGS. 16A
and 16B.
FIGS. 29A and 29B are flowcharts of the exercise and treatment routines
executed by the system according to the preferred embodiment of the
present invention.
FIGS. 30 and 31 depict a partial, longitudinal view of the opposite ends of
a transurethral ablation catheter of the present invention.
FIG. 32 is a cross-sectional view of the ablation catheter of FIG. 31 taken
along the line 37--37.
FIG. 33 is a partial, longitudinally sectioned view of the distal and
intermediate portions of the ablation catheter of FIG. 31 taken along the
line 38--38.
FIG. 34 is a partial, longitudinally sectioned view of the proximal and
intermediate portions of the ablation catheter of FIG. 30 taken along the
line 39--39.
FIG. 35A is a partial, longitudinal view of the transurethrally positioned
ablation catheter of FIG. 30 for producing a non-cooled thermally
conductive heat distribution in the prostate.
FIG. 35B is a partial, longitudinal view of the transurethrally positioned
ablation catheter of FIG. 35A for producing a thermally conductive heat
distribution in the prostate and cooling the sphincters at the ends of the
prostatic urethra.
FIG. 36 depicts an ablation system of the present invention for ablating
tissue about the prostatic urethra.
FIG. 37 depicts a longitudinal view of another aspect of a transurethrally
positioned ablation catheter of the present invention for ablating only
prostatic tissue opposite the ejaculatory duct.
FIG. 38 depicts a cross-sectional view of the transurethral ablation
catheter of FIG. 37 taken along the line 43--43.
FIGS. 39 and 40 depict portions of an alternative embodiment of the
transurethral ablation catheter of the present invention having coaxial,
telescopic members to position the catheter in the internal and external
sphincters.
FIGS. 41-45 depict alternative configurations for the distal fixation and
cooling means of the transurethral ablation catheter of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings more particularly by reference numbers, number 10
in FIG. 1 refers to the head and upper body portion of a patient equipped
with an implantable system constructed according to one embodiment of the
present invention. The system includes a probe 12 which is shown embedded
in the head of the patient in position to extend from the surface of
cranium of the head inwardly into a tumor T to be treated. A cable 14 is
connected between the probe 12 and the internal control unit 16. The probe
12, the cable 14, and the internal control unit 16 are all surgically
implanted in the body of the patient beneath the surface of the skin so
that there is no protruding portion of the system which extends through or
pierces the skin surface. This is useful in that it substantially reduces
or eliminates the chances for infection and it is therefore expected that
the internal system can remain in place for an extended period of time
without any further surgical procedure being required. The details of the
probe 12 and the internal control unit 16 will be described more in detail
in connection with FIGS. 2A and 3.
In FIGS. 2A and 2B, the skin 18 of the patient is shown positioned between
the internal control unit 16 and an external control unit 22. The internal
control unit 16 is shown coupled by leads 24, 26, 28 and 30 which are in
the cable 14 to control elements located in the probe 12 including one or
more heater elements 34 and one or more heat sensitive elements or
thermistors 36. The probe 12, including the elements 34 and 36, and the
internal control unit 16, are all surgically implanted under the skin of
the patient so that nothing pierces or extends through the skin to cause
infection or other problems. As stated, this is an important advantage of
the present system. The internal control unit 16 includes means for
controlling the application of electrical energy to the heater element or
elements 34 according to some predetermined program or instructions
established in the internal control unit and changed from time to time by
the external unit 22 as will be described. The internal control unit 16
also has connections with the thermistor or thermistors 36 located on or
adjacent to the probe at locations such that the thermistors are able to
sense the temperature in the treatment area or tumor and provide outputs
which can be used to evaluate and assess the effect of the treatment to
enable modifying the treatment including the amount of heat generated by
the heater element 34 as required to maintain some internal temperature
condition for treatment purposes. For example, if the temperature of the
tumor as sensed decreases, then additional energy may need to be applied
to the heater element 34 to maintain the temperature in the tumor at some
desired level and for some desired time period or periods.
The heater elements 34 are preferably selected to be non-inductive, to have
relatively low temperature coefficients and to be resistive type elements.
The heaters should be able to increase the temperature of the surrounding
tissue from normal body temperature of about 37.degree. C. to a maximum
temperature adjacent thereto of about 45.degree. C. The heaters 34 should
also be able to withstand repeated exposure to radiation without any
degradation in performance characteristics such as degradation in
resistance, temperature coefficient, heat capacity and/or heat dissipation
constant. For a typical probe construction, the heater elements should
also be as small as practical, and a typical size is in the order of 2
millimeters in diameter and 6 millimeters in length. Such devices are
available commercially.
Referring to FIG. 2A, the internal control unit 16 includes a power supply
38, grounded at 40 and shown connected to a power pick-up trickle charge
circuit 42 which in turn is connected to a power inductor coil 44. The
inductor coil 44 is preferably located on the unit 16 as near as possible
to the surface of the skin 18 so that external means can be closely
coupled thereto when it is necessary to recharge or trickle charge the
power supply 38. The power supply 38 may include a rechargeable battery or
some other similar rechargeable energy source. The power supply 38 has an
output connection 46 which is the main power lead used to supply energy
for the internal control unit including for operating the heater and
thermistor elements 34 and 36.
The internal control unit (ICU) 16 is the portion of the system that
controls the temperature generated by the heater element 34 as programmed
internally by means of the external control unit (ECU) 22. The internal
control unit 16 also includes ultrasonic transmit/receive means
(transceiver) 50 which include transmitting portion 52 used to transmit
information for receipt by the external control unit 22, and a receiver
portion 54 which receives information transmitted by the external control
unit 22 for various purposes including programming and reprogramming the
internal control unit and controlling the transmissions of information
between the units. The internal control unit includes a digital to
analogue converter (DAC) circuit 56 which converts 8-bit binary parallel
words from the output of an internal microprocessor (.mu.P) 58 to current
outputs which are used to energize the heater 34 to produce the amount of
heat that is desired. The output of the 8-bit DAC 56 is applied through a
current driver circuit 60 which may be an emitter follower circuit that
receives power from the power supply 38 by way of emergency power-off
circuit 62 connected thereto, as shown. The output of the current driver
circuit 60 is a voltage that is applied to the non-grounded side of the
heater element 34 by leads 64 and 24. The same output applied to the
heater 34 is also applied as an input to an analogue multiplexer (MUX)
circuit 68. The analogue multiplexer 68, under control of the
microprocessor 58, is constructed and connected so as to be able to select
and monitor various conditions throughout the internal control unit
including the voltage on the heater element 34, the voltage on the
thermistor or heat sensor 36, as well as other circuit conditions, and it
converts the signals or responses being monitored to a digital format by
means of an 8-bit analogue to digital converter (ADC) 70 by way of
amplifier circuit 72. The signals thus converted are applied to the data
bus 73 for entry into the microprocessor 58 and other circuit components.
The analogue multiplexer 68 has other input connections from various
locations in the circuit including an input connection from the output of
the 8-bit digital to analogue converter 56 on lead 74, an input from the
output of the current driver 60 on leads 64 and 76, an input from the
output of the emergency power-off component 62 on lead 78, an input from
the non-grounded side of the thermistor 36 on lead 30 and 80, and inputs
from a precision voltage source 82 on leads 84, 86 and 80. The precision
voltage source 82 is used in connection with the calibration of the
thermistor 36. The lead 86 from the source 82 includes a biasing resistor
88. The analogue multiplexer 68 also has a power input connection on lead
90 which is connected to output lead 92 on the power supply 38. The
analogue multiplexer 68 is controlled from the microprocessor 58 and from
other circuit connections by signals present on address bus 93 whereby the
analogue multiplexer 68 can, among other things, maintain accuracy of the
system even if some of the circuit parameters drift out of specification
by automatically compensating for such errors. As a result, the need for
further surgery to manually adjust or replace implanted components is
substantially reduced.
The microprocessor 58, as indicated, is the portion of the internal control
unit 16 that controls all of the various functions thereof including also
the functions of communicating with the external control unit 22. The
microprocessor 58 has control and other connections including data and
address connections to a 1024 bit random access memory (RAM) 94 which
memory is programmable from the external control unit 22. When programmed,
the RAM 94 will enable a patient equipped with the subject internal
control unit 16 to be able to undergo hyperthermia treatment while away
from or out of communication with the external control unit 22. This is an
important feature of the present device because it means that therapy can
proceed continuously, reliably, safely, and in a precisely controllable
manner for extended periods of time without constant attention thereby
enabling the patient to maintain a fairly normal lifestyle even while
undergoing treatment. The RAM 94 also converts data from the MUX 68 for
subsequent transmittal to the external control unit.
Other portions of the internal control unit include a 2-K read only memory
(ROM) 96 which is shown as part of the microprocessor 58 itself, an
universal synchronous receive/transmit circuit (UART) 98 which is provided
to couple the microprocessor 58 as well as other portions of the internal
control unit 16 to the ultrasonic transmit/receive circuit 50 which
converts signals between the internal and external control units. The
internal control unit 16 may include an emergency digital to analogue
converter (DAC) 100 which can be connected to the ultrasonic transceiver
50 by lead 102 and connected to the power supply by way of the emergency
power-off circuit 62. In addition, the internal control circuit 16
includes various circuit connections including the data bus 73 described
above which has connections between the 8-bit DAC 56, the microprocessor
58, the 8-bit analogue to digital converter (ADC) 70, the RAM 94, and the
UART 98. A second group of interconnections identified as the address bus
93 which provides other connections between the microprocessor 58, the
analogue multiplexer (MUX) 68, the 8-bit (ADC) 70, the RAM 94, the UART 8,
the 8-bit (DAC) 56, the emergency power-off circuit 62 and the trickle
charge circuit 42. The circuit elements included in the internal control
unit 16 may be constructed using conventional technology, and their
operations will be described more in detail in connection wi | | |
