System for the treatment of pathological tissue having a catheter with a pressure sensor

A therapy system for treating pathological tissue with heating radiation includes an ultrasound locating system and a catheter introducible into the body of a patient to be treated, the catheter having at least one pressure sensor in the region of its distal end. The catheter is used to apply the heating radiation to a specified site within the patient. The pressure sensor generates signals due to interaction with the diagnostic ultrasound waves of the ultrasound locating system, and these signals are supplied to an image generating unit within the ultrasound locating system. The image generating unit calculates the position of the pressure sensor in the ultrasound image on the basis of the signals from the pressure sensor, and mixes a mark into the displayed image at the appropriate location, so that the position of the catheter is thereby identifiable.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a system for treatment of pathological 
tissue in a patient by charging a region containing the pathological 
tissue with heating radiation by means of a catheter. 
2. Description of the Prior Art 
It is known to treat pathological tissue by heating the pathological 
tissue, for example, with microwaves or ultrasound waves that are 
generated with suitable sources. To the extent that the resulting tissue 
temperatures lie below 45.degree. C., the cell metabolism is disturbed 
with the consequence that growth is slowed in the case of tumors or a 
regression of the tumor even occurs. This type of treatment is known as 
local hyperthermia. When temperatures above 45.degree. C. are reached, the 
cell protein coagulates, with the consequence that the tissue is 
necrotized. The latter type of treatment is referred to as thermotherapy. 
In order to avoid the unintentional treatment of healthy tissue in the case 
of local hyperthermia and to avoid the unintentional necrotization of 
healthy tissue in the case of thermotherapy, suitable measures must be 
undertaken. In this context, U.S. Pat. No. 4,620,546 discloses that the 
region to be heated with a therapeutic ultrasound source be localized by 
detecting harmonics of the therapeutic ultrasound emitted by the 
therapeutic ultrasound source from the output signal of a diagnostic 
ultrasound transducer, and the position of the heated region identified on 
this basis is mixed into the ultrasound image. It is also known, for 
example from WO 91/13650, to bring a catheter into the region of the 
pathological tissue in a suitable way and to monitor the resulting 
temperatures with a temperature sensor integrated into the catheter. For 
protecting healthy tissue, moreover, the catheter can have a coolant 
flowing through it. Nonetheless, an unintentional treatment or 
necrotization of healthy tissue cannot be reliably precluded. In 
particular, the necrotization of healthy tissue can lead to a serious 
injury to the patient. In the treatment of benign prostate hyperplasia 
(BPH), for example, there is thus the risk of injury to one or both 
bladder sphincters. An injury to the outer sphincter (sphincter externus) 
leads to incontinence of the patient; injury to the inner sphincter 
(sphincter internus) deteriorates the procreative capability of the 
patient as a consequence of retrograde ejaculation. 
A catheter is disclosed in U.S. Pat. No. 5,161,536 which is provided with 
an ultrasound transducer at its distal end. The ultrasound transducer 
responds to ultrasound incident thereon from an ultrasound diagnostic 
system, and generates output signals which are processed so that the 
position of the ultrasound transducer is mixed into the ultrasound image. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a therapy system for 
the treatment of pathological tissue in a patient by charging a region of 
the pathological tissue with heating radiation employing a catheter, 
wherein the risk of unintentional tissue damage, particularly 
necrotization of tissue, is minimized. 
The above object is achieved in accordance with the principles of the 
present invention in a therapy apparatus for treating pathological tissue 
with heating radiation which includes a source of heating radiation having 
an effective therapeutic region, a catheter introducible into the body of 
a patient to be treated, the catheter having at least one pressure sensor 
in the region of its distal end, and an ultrasound locating system which 
generates an ultrasound image of a region to be treated, the ultrasound 
locating system including an ultrasound locating transducer and an 
image-generating unit to which the output signals of the pressure sensor 
are supplied. The output signals from the pressure sensor arise due to the 
charging of the pressure sensor with the diagnostic ultrasound waves 
emitted by the ultrasound locating transducer. The image-generating unit 
calculates the position of the pressure sensor in the ultrasound image on 
the basis of the output signals from the pressure sensor, and mixes a mark 
into the displayed image corresponding to and thus identifying, i.e. 
indicating, the position of the pressure sensor. The image-generating unit 
also identifies the position of the center of the region of therapeutic 
action, and mixes a further mark into the ultrasound image identifying, 
i.e. indicating, this center. 
Before beginning a treatment, the catheter is introduced into the patient 
under diagnostic ultrasound supervision, using the ultrasound locating 
system, so that the pressure sensor comes to be located in the region of 
the tissue to which damage is to be avoided. The placement of the catheter 
can take place either by natural paths or by punctation, or 
endoscopically. The mark mixed into the ultrasound image by the 
image-generating unit identifies the tissue region to which damage is to 
be avoided. By observing this mark as well as the mark which identifies 
the position of the active therapeutic region, it is thus easily possible 
to select an alignment of the source of heating radiation and the subject 
to be treated relative to each other so that charging of the tissue region 
neighboring the pressure sensor with heating radiation is avoided. The 
risk of unintentional tissue damage, particularly necrotization of tissue, 
is thereby significantly reduced by the therapy apparatus of the 
invention. 
In a preferred embodiment of the invention, displacement of the region to 
be treated can be undertaken dependent on the marks (or the signals 
generating the marks) which identify the position of the pressure sensor 
and/or the position of the region of therapeutic action. To this end, an 
adjustment unit can be provided for displacing the region to be treated 
and the region of therapeutic action of the heating radiation relative to 
each other, and a control unit for actuating this adjustment unit is also 
provided. The control unit is supplied with signals corresponding to the 
position of the pressure sensor from the image-generating unit, and the 
control unit actuates the adjustment unit so that charging of the tissue 
region neighboring the pressure sensor with heating radiation is 
suppressed. The therapy procedure is thus controlled by the control unit 
so that unintentional damage, particularly necrotization of the tissue 
region neighboring the pressure sensor, is virtually impossible. 
Additional reliability can be achieved in an embodiment wherein the source 
of heating radiation is a source of focused ultrasound waves, by supplying 
the control unit with the output signals of pressure sensor which arise 
due to the pressure sensor being charged with the focused ultrasound waves 
emanating from this source. The control unit can generate an alarm signal 
and/or suppress the output of ultrasound waves, or at least lower the 
intensity of the ultrasound waves, when the level of the output signal of 
the pressure sensor exceeds a limit value. 
A further object of specifying a catheter that is especially suited for 
treatment of prostate conditions, for example of benign prostate 
hyperplasia or of prostate carcinoma, is achieved in an embodiment wherein 
the catheter is adapted for introduction into the urethra and has pressure 
sensors that are arranged at a distance from one another along the 
catheter, this distance corresponding to the distance between the 
sphincter externus and sphincter internus of the patient to be treated. 
Injury to the sphincters can thus be easily avoided, since these are 
exactly marked. The distance between the two sphincters can be easily 
identified in a known way from the ultrasound image. 
In order to adapt the spacing of the pressure sensors to individual 
requirements, in a further version of the invention the distance between 
the pressure sensors is variable. There is also the possibility, however, 
of keeping a plurality of catheters on hand, each of which has a different 
spacing between the pressure sensors, whereby the spacing, for example, 
can be graduated in steps of 2 millimeters each. 
In order to facilitate the positioning of the catheter, an expandable 
balloon is provided at the distal end of the catheter in a further version 
of the invention. This expandable balloon is disposed a distance from the 
pressure sensor neighboring it which is equal to the average distance of 
the inside of the urinary bladder from the sphincter internus. One then 
proceeds in the catheterization by first introducing the catheter with the 
balloon to such an extent that it is situated within the urinary bladder. 
Subsequently, the balloon is expanded and the catheter is withdrawn to 
such an extent that that side of the balloon facing away from the distal 
end of the catheter comes to be placed against the inside wall of the 
urinary bladder. The pressure sensor neighboring the distal end of the 
catheter is then located inside the sphincter internus, whereas the other 
pressure sensor is located inside the sphincter externus when the spacing 
of the pressure sensors from one another is correctly selected or set. The 
positioning of the catheter can be easily monitored in the ultrasound 
image. 
In a further version of the invention, the catheter is provided with an 
acoustic marking member in the region of the pressure sensor (or in the 
region of at least one of the pressure sensors, in embodiments having more 
than one pressure sensor). The acoustic marking member has an acoustic 
impedance which deviates from the acoustic impedance of the surrounding 
tissue, so that it is easily identifiable in the ultrasound image. As a 
result, the positioning of the catheter under ultrasound supervision is 
further facilitated because the marking member is clearly perceptible in 
the ultrasound image, so that it is easily possible to determine the 
alignment of the catheter wherein the pressure sensor is located at the 
desired location. Additionally, by providing for further optical marking 
in the ultrasound image of the tissue region to be protected against 
damage, the risk of such damage is even further reduced. 
In another embodiment of the invention the catheter has a coolant flowing 
through it during operation, so that injury to healthy tissue adjoining 
the catheter is practically precluded in the case of benign prostate 
hyperplasia of the urethra. 
In a further embodiment of the invention the catheter has at least one 
temperature sensor in the region of its distal end, preferably between the 
pressure sensors, so that a qualitative acquisition of the temperature 
occurring in the region of the tissue to be treated is possible.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the invention in the embodiment of a therapy system for 
treating benign prostate hyperplasia, which has a source of heating 
radiation, namely a therapeutic ultrasound applicator 1. The ultrasound 
applicator 1 has a tubular housing 2 that is filled with a liquid acoustic 
propagation medium, for example water, and has an application end closed 
with a flexible coupling membrane 3. The membrane 3 serves the purpose of 
coupling the ultrasound applicator 1 to the body surface of a patient to 
be treated. In the example of FIG. 1, the applicator 1 is acoustically 
coupled in the region of the perineum, i.e. between scrotum 4 and rectum 5 
of the patient P. For acoustic coupling, the coupling membrane 3 of the 
ultrasound applicator 1 is pressed against the body surface of the patient 
P. 
An ultrasound resonator 6 having an emission surface of a concave, 
spherically curved shape, is located in the inside of the housing 2. The 
ultrasound resonator 6 is attached to a carrying member composed of 
several parts that is generally referenced 7. The ultrasound resonator 6 
is constructed in a known way, i.e. the ultrasound resonator 6 can be a 
single, appropriately shaped piezo ceramic member; the ultrasound 
transducer 6, however, can also be composed of a plurality of small piezo 
ceramic transducers arranged mosaically. In both instances, a backing 
(supporting member) having a suitable thickness can be provided in a known 
way that is not shown, this backing being formed of a material having a 
suitable acoustic impedance. 
The ultrasound resonator 6 has an acoustic axis A along which the generated 
ultrasound waves propagate. The ultrasound waves converge in a focus F, 
which is the center of the spherically curved emission surface of the 
ultrasound resonator 6. A focus zone FZ that is indicated with broken 
lines in FIG. 1 surrounds the focus F. The focus zone FZ, which 
corresponds to the effective therapeutic region of the ultrasound waves, 
is that zone within which the peak pressure of the ultrasound waves is no 
lower than half the peak pressure maximally occurring in the focus zone FZ 
(-6 dB zone). The drive of the ultrasound resonator 6 ensues with an 
electric generator contained in a control and imaging unit which is 
described below. 
An ultrasound locating transducer 9, preferably a B-scan applicator, is 
accepted in a bore of the carrying member 7, this ultrasound locating 
transducer 9 serving the purpose of locating the region to be treated, 
i.e. the prostate 8. In order to be able to align the ultrasound locating 
transducer 9 relative to the prostate 8 such that a good image is 
obtained, the ultrasound locating transducer 9 is accepted longitudinally 
displaceable and rotatable in the bore of the carrying member 7, this 
being indicated in FIG. 1 by corresponding arrows. During operation of the 
ultrasound locating transducer 9, it lies against the body surface of the 
patient P with the coupling membrane 3 therebetween for a good image 
quality. 
As may be seen from FIG. 1, the side of the carrying member 7 facing away 
from the ultrasound resonator has a spherically curved bearing surface 10 
that cooperates with a spherically cap-shaped bearing surface of a 
corresponding radius in a bearing member 11, that is accepted 
longitudinally displaceable but non-rotatably in the bore of a housing 
flange 12. The center of the bearing surface 10 is different from the 
focus F. It is thus possible to spatially modify the alignment of the 
ultrasound resonator 6 and of the ultrasound locating transducer 9 
relative to the body of the patient P without a relative motion occurring 
between the coupling membrane 3 and the body surface of the patient P. 
Adjustment units 13 and 14 are provided for adjusting the ultrasound 
locating transducer 9 relative to the carrying member 7 and for adjusting 
the carrying member 7 having the ultrasound resonator 6 relative to the 
housing 2 and relative to the coupling membrane 3. This latter adjustment 
possibility serves the purpose of displacing the focus zone FZ and the 
patient relative to one another. The adjustment unit 13 and 14 are 
schematically indicated in FIG. 1 and are preferably motor-driven 
adjustment units. A position sensor 15 schematically indicated in FIG. 1 
is allocated to the adjustment unit 13. This position sensor 15 provides 
signals corresponding to the momentary position of the ultrasound locating 
transducer 9 relative to the carrying member 7. Both the adjustment units 
13 and 14 and the position sensor 15 are connected to a control and 
imaging unit 16 to which a monitor 17 and a keyboard 18 are connected. The 
control and imaging unit 16 cooperates with the ultrasound locating 
transducer 9 in a known way as an imaging diagnostics installation for 
generating image information, namely ultrasound B-images, with the current 
ultrasound image being displayed on the monitor 17. The arrangement of the 
ultrasound locating transducer 9 relative to the ultrasound resonator 6 is 
selected such that the acoustic axis A of the ultrasound resonator 6 lies 
in the body slice of the patient P shown in the ultrasound B-image. Taking 
the output signal of the position sensor 15 into consideration, the 
control and imaging unit 16 mixes a mark F' into the ultrasound image, 
this mark F' identifying the current position of the center of the focus 
zone FZ (i.e., the center of the therapeutic action). 
In addition to containing the image-generating electronics required for 
producing ultrasound images, the control and imaging unit 16 contains all 
circuits that are required for driving the adjustment units 13 and 14 as 
well as for driving the ultrasound resonator 6. 
FIG. 1 also shows a catheter 19 that is introduced into the urethra 20 of 
the patient P for the implementation of a treatment, such that the distal 
end of the catheter 19 projects into the urinary bladder 21. The catheter 
19 has an expandable balloon 22 at its distal end. When the distal end of 
the catheter 19 is advanced into the urinary bladder 21, the balloon 22 is 
inflated. Subsequently, the catheter is retracted such that the balloon 22 
presses against the region of the inside wall of the urinary bladder 21 
surrounding the opening of the urethra 21. The region of the distal end of 
the catheter 19, namely between the balloon 22 and the proximal end, is 
provided with two pressure sensors D1 and D2. The pressure sensors D1 and 
D2 have a spacing from one another that essentially corresponds to the 
distance between the sphincter internus 23 and the sphincter externus 24 
of the patient P to be treated, whereby the distance between the pressure 
sensor D1 and the side of the balloon 22 facing it has a spacing that 
identically corresponds to the spacing of the inside of the urinary 
bladder 21 from the sphincter internus that is averaged over the patient 
population. The pressure sensors D1 and D2 are preferably annular and are 
constructed using piezoelectrically activated polymer foil, for example 
polyvinylidenefluoride (PVDF) foil, which is metallized in a known manner 
to form electrodes for the purpose of electrical contacting. 
The output signals of the pressure sensors D1 and D2 are supplied to the 
control and imaging unit 16 via lines 27a and 27b. The control and imaging 
unit 16 undertakes a comparison, against a limit value, of at least those 
output signals of the pressure sensors D1 and D2 which arise due to 
ultrasound waves, emanating from the ultrasound resonator 6 during 
treatment, being incident on the pressure sensors D1 and D2. The limit 
value is dimension so that injury to the bladder sphincters is precluded 
as long as the amplitude of the ultrasound waves which are present in the 
region of the pressure sensors D1 and D2 is not so high that the output 
signal of the pressure sensors exceeds the limit value. The reaction of 
the therapy apparatus to an upward transgression of the limit value is 
dependent on which of three possible operating modes is selected by a 
switch 37. 
In the operating mode corresponding to the switch position referenced I, 
the control and imaging unit 16 causes a humanly perceptible alarm to be 
generated, such as by driving a warning lamp 38 and/or an acoustic signal 
generator 39. Alternatively or additionally, an optical alarm signal may 
be generated on the monitor 17, for example by causing the monitor image 
to flash when the limit value is upwardly transgressed. 
In the operating mode corresponding to the switch position referenced II, 
the amplitude of the generated ultrasound waves is reduced, given an 
upward transgression of the limit value, to such an extent that the output 
signal of the pressure sensors D1 and D2 falls below the limit value. 
In the operating mode corresponding to switch position III, the control and 
imaging unit 16 entirely suppresses the emission of ultrasound waves given 
an upward transgression of the limit value. 
In operating mode II as well as in operating mode III, the generation of 
alarm signals can additionally ensue in the manner set forth in 
conjunction with operating mode I. 
A switch 40 is connected to the control and imaging unit 16 in addition to 
the switch 37, the switch 40 having two switch positions referenced A and 
B. When the switch 40 is in switch position A, the control and imaging 
unit 16 evaluates the output signals of the pressure sensors D1 and D2 not 
only during operation of the ultrasound resonator 6, but also during 
operation of the ultrasound locating transducer 9. The control and imaging 
unit 16 calculates the points in time at which those output signals of the 
pressure sensors D1 and D2 appear which arise by virtue of the diagnostic 
ultrasound generated by the ultrasound locating transducer 9 being 
incident on the pressure sensors D1 and D2. A defined picture element, or 
a defined image zone, in the current ultrasound image corresponds to each 
points in time. Marks referenced D1' and D2' in FIG. 1 are mixed into the 
image at the appropriate locations shown on the monitor 17. Further, the 
control and imaging unit 16, utilizing the signal of the path sensor 15, 
calculates the position of the pressure sensors D1 and D2 relative to the 
focus zone FZ. 
When the switch 40 assumes the position referenced B, the consideration of 
the output signals of the pressure sensors D1 and D2 ensues only during 
operation of the locating transducer 9, but not during operation of the 
ultrasound resonator 6. 
For implementing a treatment, one proceeds by applying the coupling 
membrane of the ultrasound applicator 1 to the perineum of the patient P 
to be respectively treated, who preferably assumes what is referred to as 
the lithotomy position (see Pschyrembel, "Klinisches Woerterbuch", Edition 
185-250, page 1156). The coupling ensues so that no air bubbles are 
enclosed between the body surface and the coupling membrane 3. Thereupon, 
the production of ultrasound images is started by appropriate actuation of 
the keyboard 18. Likewise by appropriate actuation of the keyboard, the 
adjustment units 13 and 14 are now actuated such that an alignment of the 
ultrasound locating transducer 9 relative to the body of the patient P is 
obtained wherein the prostate 8 is clearly imaged in the ultrasound image. 
The distance between the two sphincters is now identified and displayed on 
the monitor 17 by the control and imaging unit 16 in a known way, for 
example by marking the sphincter internus 23 and the sphincter externus 24 
in the ultrasound image with a light pen 25. Subsequently, a catheter 19 
whose pressure sensors D1 and D2 have a spacing from one another that 
essentially corresponds to the spacing between the two bladder sphincters 
of the patient to be treated, is selected from a stock of catheters 19 
whose respective pressure sensors D1 and D2 have different spacings from 
one another. This catheter 19 is now introduced into the urethra 20 of the 
patient P and is positioned with the assistance of the balloon 22 such 
that the pressure sensors D1 and D2 are located in the region of tissue 
that is not to be heated, i.e. inside the sphincter internus 23 and, 
respectively, the sphincter externus 24. 
A region of the prostate 8 to be treated can now be marked in the 
ultrasound image with the light pen 25 or with a similar input means. In 
response to an appropriate actuation of the keyboard 18, the control and 
imaging unit 16 now actuates the adjustment unit 14 such that the focus 
zone FZ is displaced into that region of the prostate 8 that corresponds 
to the region marked with the light pen 25. This is shown in the 
ultrasound image in that the mark F' comes into coincidence with the 
region marked with the light pen 25 after the actuation of the adjustment 
unit 14 has been carried out. When this is the case, the control and 
imaging unit 19 drives the ultrasound resonator 6 to generate ultrasound. 
Continuous sound is emitted over a time span that is selected such that 
the temperature required for the necrotization of tissue, which usually 
lies beyond 45.degree. C., is exceeded. 
Thereupon, a region of the prostate 8 to be treated can again be marked 
with the light pen 25 and can be treated in the described way. The risk 
that the sphincter internus 23 or, respectively, sphincter externus 24 
will be injured or destroyed in this procedure, with the consequence of a 
deterioration of the procreative ability or, respectively, of 
incontinence, is less than slight, since the two bladder sphincters have 
their position clearly identified in the ultrasound image by the clearly 
perceptible images D1' and D2' of the pressure sensors D1 and D2. 
It is thus substantially impossible to mistakenly mark a region to be 
treated with a light pen 25 that lies entirely or partially within one of 
the sphincters. When the switch 40 assumes the position referenced A, 
either the attending personnel are also alerted (operating mode I), the 
amplitude of the ultrasound waves is lowered to harmless values (operating 
mode II) or the emission of ultrasound waves is entirely suppressed 
(operating mode III) as soon as the intensity of the ultrasound waves in 
the region of the pressure sensors D1 and D2, and thus in the region of 
the bladder sphincters, upwardly exceeds the allowable limit value. 
Moreover, there is also the possibility of tracing the contours of a region 
of the prostate 8 to be treated with the light pen 25 in the ultrasound 
image. In response to an appropriate actuation of the keyboard 18, the 
focus zone FZ is then displaced step-by-step within the region traced with 
the light pen 25 upon activation of the ultrasound resonator 6 such that 
the entire traced region is charged with ultrasound waves and is 
necrotized. Here, too, the risk that a region of treatment marked with the 
light pen 25 that mistakenly contains one or both bladder sphincters is 
inconceivably slight. Even if this were to occur, injury would not be 
possible with the switch 40 in the position referenced A since, dependent 
on whether the switch 37 is in position I, II or III, either the attending 
personnel will be alerted, or the amplitude of the ultrasound waves will 
be lowered, or the emission of ultrasound waves will be completely 
suppressed. 
In any case, regardless of the operating mode selected by means of the 
switches 37 and 40, the control and imaging unit 16 calculates the 
positions of the pressure sensors D1 and D2 relative to the focus zone FZ 
in the manner described above, and drives the adjustment unit 14 so that 
displacement of the focus zone FZ into the current position of the 
pressure sensor D1 or D2 is precluded. Even under the worst conditions, it 
is assured with extremely high probability that injury to the bladder 
sphincters will be avoided. 
In order to preclude damage to the urethra 20, it is provided that a 
coolant flows through the catheter 19. The corresponding coolant 
circulator 26 is shown in FIG. 1, which also serves as a heat exchanger. 
In order to be able to monitor the therapy process, at least one 
temperature sensor is arranged in the region of the distal end of the 
catheter 19 between the pressure sensors D1 and D2. The output signals 
supplied by these sensors are supplied to the control and imaging unit 16, 
this being illustrated in FIG. 1 by schematically indicated line 27c. The 
evaluation of the output signals of the sensors is assumed by the control 
and imaging unit 16 which also mixes the measured pressure and temperature 
values into the ultrasound image. Further details regarding the cooling 
and the arrangement of the sensors shall be set forth in conjunction with 
FIG. 3. 
In FIG. 2, wherein only the urethra 20 and the prostate 8 are shaded for 
clarity, the distal end of the catheter 19 correctly placed in the urethra 
20 is shown. The catheter 19 optimally corresponds to the anatomy of the 
patient P to be treated, since the spacing of the pressure sensors D1 and 
D2 from each other is identical to the spacing between the sphincter 
internus 23 and sphincter externus 24. As also shown in FIG. 2, the 
annular pressure sensors D1 and D2 are accepted in respective channels 28a 
and 28b. 
The structure of the catheter 19 in the region of its distal end may be 
seen in detail in FIG. 3. The catheter 19 is biluminar, having a flexible, 
outer catheter tube 29 in which an inner catheter tube 30 that is likewise 
flexible is coaxially arranged. A closure part 31 formed by a rounded-off 
introduction end is provided at the distal end; this closure part 31 
closes the outer catheter tube 29 liquid-tight. The inner catheter tube 30 
is accepted liquid-tight in a bore of the closure part 31. Just before the 
closure part 31, the inner catheter tube 30 has a plurality of 
flow-through openings 32 that produce a connection between the inner lumen 
surrounded by the inner catheter tube 30 and the outer lumen situated 
between the outer catheter tube 29 and the inner catheter tube 30. A 
preferably liquid coolant can be caused to flow through the catheter 19 
with the coolant circulator 26 in the way indicated by the arrows in FIG. 
3. 
The catheter 19 shown in FIG. 3 differs from the embodiment shown in FIGS. 
1 and 2 by virtue of the pressure sensors D1 and D2 not being directly 
accepted into the channels 28a and 28b of the outer catheter tube 29, but 
instead being attached on annular, acoustic marking members M1 and M2. The 
acoustic marking members M1 and M2 are accepted in the channels 28a and 
28b of the outer catheter tube 29, together with the pressure sensors D1 
and D2. The marking members MI and M2 are composed of a material, for 
example, stainless steel, having an acoustic impedance which deviates from 
that of the surrounding tissue. The marking members M1 and M2 can thus be 
clearly perceived in the ultrasound images generated by the ultrasound 
locating transducer 9 and the control and imaging unit 16. Images M1' and 
M2' of the marking members M1 and M2 appear in the ultrasound image at the 
same location as the marks D1' and D2', as indicated by the additional 
entry of the references M1' and M2' in FIG. 1. When the acoustic marking 
members M1 and M2 are present according to the embodiment of FIG. 3, the 
monitoring of the output signals of the pressure sensors D1 and D2 during 
the operation of the ultrasound locating transducer 9 can be suppressed, 
since the positions of the pressure sensors D1 and D2 are indicated in the 
ultrasound image by the marks M1' and M2' of the marking members M1 and 
M2. The positions of the marking members M1 and M2 relative to the focus 
zone FZ can also be calculated by the control and imaging unit 16 on the 
basis of known image processing methods, and taking the output signals of 
the path sensor 15, proceeding from the positions of the images M1' and 
M2' in the ultrasound image, into consideration. 
A channel 33 that accepts a flexible balloon part 22' is introduced into 
the outer generated surface of the outer catheter tube 29 between the 
closure part 31 and the pressure sensor M1. This flexible balloon part 22' 
has the region of its two ends connected liquid-tight to the outer 
catheter tube 29, for example by gluing. As long as the pressure of the 
coolant flowing through the catheter 19 does not exceed a limit value, the 
balloon part 22' has the shape shown with solid lines in FIG. 3 wherein it 
presses against the channel 33. Since a plurality of openings 34 
penetrating the wall of the outer catheter tube 29 are provided in the 
region of the channel 33, however, there is the possibility of expanding 
the balloon part 22' into the balloon 22 by increasing the pressure of the 
coolant in the way indicated with broken lines in FIG. 3. 
A temperature sensor 36 is applied to the inside wall of the outer catheter 
tube 29 at that side of the marking member M1 facing away from the balloon 
22; this sensor is in communication with the control and imaging unit 16 
via the schematically indicated line 27c. 
Silicone rubber or polyethylene, for example, are suitable as materials for 
the inner catheter tube 29, for the outer catheter tube 30 and for the 
closure part 31. 
The above-described exemplar,/embodiment is directed to the treatment of 
benign prostate hyperplasia. However, other maladies can also be treated. 
If tumor conditions are to be treated, the regions to be treated are only 
heated to such an extent that a disturbance of the cell metabolism ensues 
but the coagulation of the cell protein is suppressed. 
As noted above, the output signals of the pressure sensors D1 and D2 can be 
monitored both during the operation of the ultrasound resonator 6 and the 
operation of the ultrasound locating transducer 9, thereby avoiding 
unintentional injury to the bladder sphincters with especially high 
reliability. Generally, however, it will be sufficient to undertake 
monitoring of the output signals of the pressure sensors D1 and/or D2 
either only during operation of the ultrasound resonator 6 or only during 
operation of the ultrasound locating transducer 9. It is clear that the 
desired therapeutic effect need not necessarily be achieved using 
ultrasound waves as the heating radiation if evaluation of the output 
signals of the pressure sensors D1 and D2 ensues only during operation of 
the ultrasound locating transducer 9. This permits the use of other types 
of heating radiation, for example, microwaves. 
The generation of the ultrasound waves need not necessarily ensue using a 
piezoelectric ultrasound resonator. It is also possible to employ 
ultrasound transducers operating according to other principles, for 
example magnetostrictively. The focusing of the ultrasound waves also need 
not necessarily ensue on the basis of an appropriate shaping of the 
emission face of the ultrasound resonator. Alternatively, acoustic lenses 
and/or reflectors can be employed for focusing. 
Instead of a mark F' which identifies the center of the region of 
therapeutic action, a mark can alternatively be employed which indicates 
the contour of the region of therapeutic action, and which may also 
indicate the center thereof. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventors to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of their contribution to the art.