BACKGROUND OF THE INVENTION
Field of the invention
[0001] The present invention concerns an ultra-high-speed extracorporeal ultrasound hyuperthermia
method and treatment device.
Description of the prior art
[0002] It is known, in particular from RE 33,590, to use a focussed ultrasound beam to cause
extremely localized heating of biological tissue in order to destroy tumors. The beam
is transmitted in the form of periodic wave trains having a predetermined frequency
peak power and duration.
[0003] In the device described in the patent referred to above, the beam high frequency
is comprised between 0.5 and 5 MHz, for example, the lower frequencies being used
to destroy the deeper structures within the body and the electric peak power which
excites the transducer is comparatively low (10 to 100 watts, the higher powers being
used to destroy the deeper structures).
[0004] These wave trains, the duration of each of which is about 1 second, are separated
by intervals of about 1/10 second during which it is possible to carry out real time
(usually type B) ultrasound scanning to relocate the focus relative to the target
(which is affected by natural movements of the tissues caused by breathing) or to
examine the damage sustained by the tissues in the treated area.
[0005] With the power level and frequencies employed - which depend on the depth of the
target area - the target temperature is increased to approximately 45°C, a temperature
which is sufficiently high in principle to destroy malignant cells. It has been thought
previously that an excessive increase in the temperature of the target area could
cause serious burns in the surrounding area as the result of thermal diffusion.
[0006] As a result, treatment times are relatively long, possible several tens of minutes
or even several hours.
[0007] The invention is based on the discovery that increasing the peak power of the waves
used by a factor of 10 to 200 or more, depending on the depth and the absorbing power
of the target area, makes it possible, by causing an ultra-high-speed temperature
rise, to significantly reduce the effects of thermal diffusion and to destroy the
target area in time periods in the order of one second or less.
SUMMARY OF THE INVENTION
[0008] It is an object of the invention to provide a method of effecting an ultra-high-speed
treatment of a region of a subject located at a known depth within the body with compressional
wave energy derived from ultrasonic transducer means for applying to said region a
focussed beam transmitted in the form of periodic bursts of oscillations having a
predetermined frequency and a predetermined peak power, each burst having a predetermined
duration and the successive burst being separated by time intervals, said method comprising
the steps of :
- effecting tests with said ultrasonic transducer means on a target located at said
depth within the body for determining the curve of temperature increase of said target
as a function of the time of application of said compressional wave energy, said time
curve having a quasi-linear portion which starts at time zero and ends at a time to ;
- determining the particular peak power of said burst of oscillations which will provide
at least a substantial destruction of said region of the subject in a single burst
of oscillations having a duration equal to the time to and selecting a peak power of treatment at least equal to said particular peak power
and a duration of the treatment burst at most equal to the time to.
[0009] It is another object of the invention to provide a method of the type above referred
to, in which the frequency as well as the diameter of the transmitting surface of
the ultrasonic transducer means and the diameter of the focal spot are advantageously
determined and selected according to the nature and depth of the target so that the
concentration of the beam is maximized and the power is then determined for a selected
value of the frequency and of the selected diameters so that the target is destroyed
at a temperature much larger than that which was generally used in prior art and in
a time period much shorter.
[0010] Tests effected by the applicant have shown that the construction of the device which
implements this method, requiring the implementation of means for quasi-continuous
transmission of compressional wave energy at very high peak powers, can minmize the
destruction of healthy cells whilst enhancing the effectiveness with which the target
is destroyed, in particular as the result of an additional mechanical destructive
effect on the cells of the target, so providing a new localized ultrasound hyperthermia
treatment technique justifying subsequent use in this description of the term "ultra-high-speed
hyperthermia treatment".
[0011] According to another aspect of the invention, the ultra-high-speed hyperthermia treatment
method provides significantly improved echographic examination of changes to the target
during treatment.
[0012] Therefore, it is a further object of the invention to provide a method of ultra-high-speed
hyperthermia treatment in which the examination of the target is carried out by type
A or B echography during interruptions in the treatment beam at a given rate such
that the A echogram or the B image has time to undergo detectable modifications (which
could mean a few tenths of a second in ultra-high-speed hyperthermia treatment) which
are not masked by spurious modifications caused by movements of the wave trains (as
is the case in practice with prior art hyperthermia treatment techniques).
[0013] The invention also has for its object specific type A or B echographic methods which
facilitate the ultra-high-speed detection of change sustained by the target so that
treatment can be terminated as soon as the target is destroyed.
[0014] Other features and the advantages of the invention will be more clearly apparent
from the following description in which the ultra-high-speed echographic detection
methods are described first, to facilitate the subsequent description of the treatment
method and of the construction of the specific features of the ultra-high-speed hyperthermia
treatment device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
Figure 1 is a block diagram showing an ultra-high-speed hyperthermia treatment device
provided with means for ultra-high-speed detection of change to the target during
treatment ;
Figure 2 is a timing diagram showing the operation of said detection means ;
Figures 3a and 3b illustrate tables indicating the global concentration k and the
rate dT/sec of temperature rise as a function of frequency F, for given characteristic
parameters of the transducer means.
Figure 4 shows curves representing the temperature increase of a biological tissue
as a function of heating time ; and
Figure 5 is a graph illustrating the time of destruction of a biological tissue as
a function of the heating temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Figure 1 is a block diagram of a known type echography device comprising a real time
probe 1 including a piezoelectric transducer element 12 which is oscillated by an
electric motor 13 through a mechanical transmission system represented by the chain-dotted
line.
[0017] For example, this probe may be as described in US patent No. 4,418,698 granted December
6, 1983 in respect of : "Mechanical sector scanned echographic probe".
[0018] The piezo-electric element 12 is excited by a pulse generator 2 and the motor is
controlled by a sawtooth scanning signal generator (producing the waveform (A) shown
in figure 2) to scan a sector of the region to be treated, the scan passing through
the focus of the treatment beam emitter.
[0019] The echo pulses reflected from biological structures are amplified by a receiver
4 whose output is connected to an analog-to-digital converter 5.
[0020] An electronic switch 6 connects the output of the converter 5 to one or other of
two memories 61 and 62. Switching occurs on each scan, the switch 6 being connected
to an appropriate output of the sawtoolth generator 3 for this purpose.
[0021] In each memory, addressing of the writing operation is effected in a known manner
according to the angular position of the beam emitted by the probe and the time elapsed
since the start of each pulse transmission, so that a complete image of the treated
area is written into one of the two memories on each scan.
The memories are also read in a known way and the resulting signals are fed to a digital
subtractor through a switch 71 which reverses the connection between its inputs E1
and E2 and its outputs S1 and S2 on each scan (being connected to the appropriate
output of the generator 3 to this end).
[0022] If no inversion were applied, the subtractor, which computes the difference between
the serial digits which define the successive points of the two images, would subtract
the current image from the previous image and then the previous image from the current
image, and so on, the inversion being required so that the previous image is always
subtracted from the current image in each scan.
[0023] The output of the subtractor 7 is connected to a digital-to-analog converter 72 which
supplies a voltage for modulating the brightness of the cathode ray tube of a display
device 8.
[0024] The output S2 is connected to a second digital-to-analog converter 73. A potentiometer
74 provides a variable mix of the output voltage of the converter 72, representing
the differential image, and the output voltage of the converter 73, representing the
latest image stored.
[0025] The operator can then observe either the conventional image of the treated area,
enabling a preliminary identification of the strucutres concerned, or the differential
image, enabling him to observe how the structures change during the treatment.
[0026] As the treatment uses extremely high peak powers, the images cannot be formed during
emission of the treatment beam, the energy of which, reflected from the structures
concerned, is sufficient to "dazzle" the echographic transducer. The effect of this
can continue for one or more microseconds after the end of emission. It is therefore
necessary to emit wave trains separated by gaps (waveform (B) in figure 20) slightly
longer than the duration of an echographic scan, which might be 1/20 s, for example,
and to synchronize the latter with the emission.
[0027] It is obviously also necessary for the images to be formed at a sufficiently high
rate for natural movement of the tissue as a result of breathing not to introduce
excessive differences between two successive images, which would mask the differential
effect resulting from the modification of the structures due to the treatment. To
give an example, the emission time could be chosen to obtain an image every 0.5 s
at least. This implies that the peak power of the treatment emission be sufficient
for significant destruction of the target area cells to occur in a few tenths of a
second.
[0028] Figure 2 shows at (C) the intervals in which the memory 61 is written,at (D) the
intervals in which the memory 62 is written, at (E) the intervals in which the memory
61 is read, at (F) the intervals in which the memory 2 is read and at (G) and (H)
the resulting states of the outputs S1 and S2. The numbers of the images in memory
are shown. This shows that the previous image is always subtracted from the current
image.
[0029] Referring again to figure 1, the power transducer T, symbolically represented as
a spherical cup on which piezo-electric elements are placed, is energized by the treatment
beam emitter 10. The transducer is advantageously as described in RE 35,590 and the
probe 1, although shown separately, would in practice be attached to the cup, disposed
at its center and oriented along its axis, as explained in the aforementioned patent.
[0030] Figure 1 also shows units that are not used in the embodiment of the invention described
thus far, but only in a modified embodiment now to be described.
[0031] These units are a variable ratio frequency divider 9, an AND gate 11, a memory 12,
a display device 13 and a switch 14.
[0032] When the switch 14 is in position a, the divider 9 is connected to the sawtooth generator
3, which is adapted to provide a synchronization signal when the axis of the probe
passes through the focus of the treatment beam emitter ( the center of the sphere
of which the cup T constitutes a portion). The division ratio of the divider is then
set to a value between 1 and 5, for example.
[0033] It therefore provides every N scans a short signal applied to the power emitter 10
and which disables it for its duration of approximately 1 ms.
[0034] The short signal is also applied to the gate 11 which is therefore enabled for 1/1
000 s and passes to the memory 12 the digital signal from the converter 5.
[0035] The memory 12 has the time to acquire information representing a scanning line, the
duration of which is in the order of only 0.2 ms (as compared with 0.2 to 0.02 s to
acquire a complete image).
[0036] Thus in this modified embodiment the treatment beam will be interrupted for one ms
during the duration of the treatment beam pulses, and this will occur every 1/20 s,
for example, resulting in only a very slight reduction (2% for example) of the mean
power as compared with an uninterrupted treatment beam.
[0037] The line acquired "on the fly" in this way, every 1 to 5 scans, passes through the
focus. This method finally uses a type A echograpy, and the information collected
in one direction only is sufficient. An equivalent result could be obtained by immobilizing
the probe in a particular direction through the target.
[0038] The echo signals stored in the memory 12 are read out at a rate of 50 Hz, for example,
and displayed continuously on the screen of the device 13.
[0039] This reading frequency promotes visual comfort.
[0040] In this modified method, the eye of the operator performs the equivalent of the digital
subtraction of the information collected during treatment, at a rate such that it
can perceive changes in the amplitude of the ultrasound scan.
[0041] It should be understood that using a type B ultrasound probe to obtain type A echograms
has the advantage of enabling the same probe to be used for type B ultrasound scanning
before a target is treated (here the term "target" refers to a part of the tumor which
is exactly the same size as the focal spot, and complete treatment of the tumor will
entail focussing the beam onto the various target areas constituting it in succession),
to locate said target area as described in the previously mentioned RE 33,590. A relocation
can even be carried out by the same probe for type B ultrasound scanning during the
treatment of a target, by interrupting the treatment beam for a sufficient time to
obtain an image (1/20 s).
[0042] The ultra-high-speed hyperthermia treatment method will now be explained with reference
to figures 3a, 3b, 4 and 5.
[0043] The table illustrated in figure 3a corresponds to a power transducer T having a spherical
transmitting surface, with a focal distance of 10 cm and an aperture angle of 60°
of the beam.
[0044] The values of the global concentration factor
have been calculated by the applicant for a power transducer shaped as a spherical
cup having a given first diameter D and producing a focal spot having a given second
diameter d, from which the geometrical concentration factor
is known by calculating the attenuation factor k
a, starting from known experimental data which show that attenuation of acoustic waves
in a biological tissue other than a bone of a tissue which contains air, is about
1dB per MHz and per cm of propagation path within the tissue.
[0045] The rate dT/sec. of a temperature rise as a function of frequency F has been calculated,
for a given diameter d of the focal spot and a given entry diameter of the beam into
the body, for an aperture constant angle of the beam and a transmitted acoustic peak
power of 1 Kw, by making the assumption that the energy losses in the tissue which
are due to absorption amount to 1% of the transmitted power, other losses, amounting
to 9% of the transmitted power, being bound to multiple reflection upon the cell surfaces.
Thus, one has been able to calculate the fraction of the power losses which is absorbed
and is converted into heat within the tissue and therefore, the rate of temperature
rise.
[0046] It should be noted that available prior art data generally indicate absorption losses
higher than 1% (for instance between 2-3%). It therefore results from the assumption
made by the applicants that the calculated ratio of temperature rise is most probably
lower than that which will actually be obtained. This may lead to an overevaluation
of the calculated peak power required, but overevaluation is better than underevaluation,
which would lead to an increased risk of thermal diffusion in the tissues environing
the target.
[0047] Figure 3a corresponds to a focal length of 10 cm and an entry diameter of 10 cm,
whereas figure 3b corresponds to a focal length of 1.5 cm and an entry diameter of
1.5 cm.
[0048] The operating frequency F will be selected as follows : First, the focal length which
is nearer from the depth of the target within the body (i.e. the distance along the
beam path between skin and tumor) will be selected.
[0049] As an example; for a target depth of about 10 cm, a focal length of 10 cm will be
selected and therefore, the table of figure 3a will be used for frequency calculation.
[0050] The selected frequency will be that which both corresponds to the maximum value of
k and to the maximum rate of temperature rise. Figure 3a shows that
[0051] For a focal length of 1.5 cm (which will be selected for tumors of small depth),
the table of figure 3b shows that the selected frequency will be 6 MHz.
[0052] It should be noted that the above method of selecting the optimal operating frequency
is based on the hypothesis that thermal diffusion and cooling of the tissue, due to
blood circulation, are negligibly small, these phenomena not having been taken into
account in the applicant's calculations.
[0053] In fact, these phenomena could have - if the applicants's method were not used -
a very important effect when a heat source of small volume, as a focal spot of 1.5
mm of diameter is used. However, as the applicant's method effects heating only during
the quasi-linear part of the curve of temperature increase as a function of the heating
time, it finally results that nearly the whole of the energy which is absorbed by
the target is used for heating it and therefore, the losses due to the above mentioned
phenomena are actually negligibly small with respect to the absorbed power.
[0054] The curves of figure 4 show, for a small heat source (in this example a small diameter
focal spot), the experimentally determined increase in the temperature T of the area
acted on by an ultrasound beam as a function of the application time, for two different
applied power levels (curves II and II).
[0055] The temperature rise is seen to be quasi-linear over a time t
o which is substantially the same for both curves, but corresponds to different temperatures,
respectivly T
o1 and T
o2. After a ceiling which corresponds to an equality between the thermal losses and
the supply of heat, and which is reached after a time of 5 t
o and corresponds to a temperature of about 3 T
o1 for curve I and 2.6 T
o2 for curve II, the temperature T then rapidly decreases.
[0056] Note that t
o is independent of the applied power and is in direct proprotion to the focal spot
diameter. In the experiments yielding the curves shown in figure 4, the frequency
is 1 MHz, the focal spot diameter is 1.5 mm and t
o = 0.5 s. The applicant has determined similar curves from tests carried out for various
values of the operating frequency and of the focal spot diameter, in particular for
the values which are indicated in the tables.
[0057] The applicant's method, consisting in selecting a peak power such that a total or
at least a substantial destruction of the target cells will be obtained after a time
of t
o at most, it will result, according to the applicant's discovery, that minimal damage
will be caused to tissues in the area surrounding the target.
[0058] It further results that the total quantity of heat energy required by the method
for destroying the target is much smaller than in prior art methods.
[0059] These experimental results can be explained by the fact that, in the linear region
of the curve, losses by diffusion are negligible in comparison with the heat input.
Beyond this point, the losses are proportional to the temperature gradient between
the target and the surrounding tissue, and so increase rapidly until they are equal
to the heat input (at the ceiling temperature). When the input of heat is terminated,
the temperature of the target decreases exponentially to a value at which there is
substantially no more destruction after a time in the order of 3 to 6 x t
o in these experiments. This time (in the order of 1.5 to 3 s in this case) will substantially
define the minimum gap between two successive wave trains of the treatment wave, so
that all wave trains are subject to minimal losses by diffusion.
[0060] However, in practice, it has been found that a preferred value of the gap is at least
ten times the wave train duration.
[0061] In figure 2, where the wave train duration is sligthly less than 0.5 s, a value chosen
because it corresponds to t
o, the successive wave trains, separated by only 0.05 s, will be applied to different
targets in the tumor, a single wave train being sufficient to compare the reflective
state of each target before and after it is applied.
[0062] It is known that the time t to destroy tumor cells is inversely proportional to the
temperature T to which they are subjected from a threshold value T
i of the latter which is 40°C, for example. For
the graph of figure 5 shows that the value of t is in the order of 0.5 s. The application
time t is substantially halved for each increase in temperature of 10°C above 43°C,
so that it is divided by 4096 on increasing from 58°C to 70°C, for example.
[0063] It should be noted that, as the tissues will be destroyed in 0.5 seconds only if
the temperature of 58° has been reached in a time substantially lower than 0.5 s,
a value of t
o equalling half of the time indicated by the graph of figure 5 will preferably be
selected. Therefore, a value of
will be selected. A temperature of 70°C will then be reached at the end of the power
burst, i.e. in 0.25 s.
[0064] The table of figure 3a shows that
for an acoustic peak of 1 Kw. Therefore, to raise the target temperature approximately
32°C above normal in 0.25 s, representing a rate of temperature increase of 138°C/s,
the power should be multiplied by the ratio 138/33.97 = 4, it being obvious that the
rate of temperature rise is substantially proportional to the heating power when one
operates in the quasi-linear part of the curve.
[0065] The factor of power conversion of the transducer T being about 1/4, and account being
taken of the transmission losses along the path of the beam, an electric peak power
of about 20 Kw shall finally be used.
[0066] With the view of avoiding too large a power density on the piezoelectric transducer
element which comprises transducer T, the latter will consist of a spherical cap having
for instance a diameter of 300 mm and a focal length of 300 mm with an aperture angle
of 60°.
[0067] Selection of such a focal length results from a compromise between the required condition
that the aperture angle should be as large as possible so as to concentrate acoustic
energy at the focus and the requirement that the entry surface of the beam within
the body should be comparatively small, for avoiding an interference of the beam with
bones, air pockets or other obstacles to the propagation of ultrasounds.
[0068] In a practical embodiment, as the focal length of the apparatus will not be variable,
the operator will displace the transducer for bringing it to a distance from the skin
equalling the target depth, thus obtaining coincidence between the target and the
focal spot.
[0069] The attenuation of ultrasounds in the coupling water medium being negligibly small,
the tables of figures 1a and 1b remmain valid.
[0070] A single apparatus, having a maximum electric peak power of 20 Kw, and the power
of which is controllable, and having a wave train duration which may be varied between
0.01 and 1 s for instance, will enable the practician to treat targets of any depth
ranging from a few cm to 10-12 cm. A graph will be provided by the manufacturer to
indicate the optimal duration of the wave train for each tumor, as a function of its
depth.
[0071] The power may be adjusted, it being understood that the deeper tumors will require
the maximum power.
[0072] However, it might be preferred to manufacture three different devices for treating
three respective ranges of target depths.
[0073] For example, for an emitted power of 1 Kw, respective focal lengths of 10 and 12
cm and respective tissue entry diameters of 10 and 12 cm, the optimum frequency determined
from the tables is 1 Mhz, yielding temperature increase rates of 33.97°C/s and 21.43°
C/s respectively. An electric power of 20 Kw will then be used as explained hereinabove.
[0074] For focal lengths of 3 and 5 cm and respective entry diameters of 3 and 5 cm, the
respective optimal frequencies will be 3 and 1.5 MHz and the respective rates of temperature
increase will be 384.89°C/s and 135.91 C/s. Powers of between 2 and 5 Kw will then
for instance be used.
[0075] For a focal length of 1.5 cm, the optimum frequency will be 6 MHz and the temperature
increase 1 539.57°C, requiring in practice a power level in the order of 1 Kw.
[0076] Generally speaking, the peak powers used in ultra-high-speed hyperthermia treatment,
especially to treat deep tumors, require that special provisions are embodied in the
construction of the device. In particular, it is necessary to use piezo-electric ceramic
materials capable of supporting such high peak powers and of cooling quickly. Forced
cooling arrangements may be needed. The supply of power to the electrical generator
may require the use of auxiliary power supplies.
[0077] Note that the optimum power values specified should not be significantly exceeded,
to avoid the risk of lesions affecting the surrounding tissue. It has been shown that
the diameter of the area within which the temperature rise resulting from the diffusion
of heat energy accumulated in the focal region at the moment when appliction of power
is terminated remains sufficiently high to destroy the cells relatively quickly increases
in proportion to the square root of the temperature increase in the focal region,
which increase is in turn proportional to the power.
[0078] Finally, note that at the powers indicated the ultrasound beam is progressively transformed
to a significant degree during its propatation, the result being the appearance of
thermic components at higher frequencies than those of the original beam.
[0079] These high frequency components are more strongly absorbed by the tissue and therefore
have greater thermal effect. Moreover, experiments made by the applicant have shown
that the risk of burning the skin is decreased.
[0080] The frequencies and powers chosen enable the beam to pass with little damage through
the outer layers of tissue and to produce a thermal effect at the focal spot.
[0081] The beam additionally has a mechanical effect which complements its thermal effect
for increased treatment efficiency.
1. A method of effecting an ultra-high-speed hyperthermia treatment of a region of a
subject located at a known depth within the body, with compressional wave energy derived
from ultrasonic transducer means for applying to said region a focussed beam transmitted
in the form of periodic bursts of oscillations having a predetermined frequency and
a predetermined peak power, each burst having a predetermined duration and the successive
bursts being separated by time intervals, said method comprising the steps of :
a) effecting tests with said ultrasonic transducer means on a target located at said
depth within the body for determining the curve of temperature increase of said target
as a function of the time of application of said compressional wave energy, said curve
having a quasi-linear portion which starts at time zero and ends at a time to;
b) determining the particular peak power of said burst of oscillations which will
provide at least a substantial destruction of said region of the subject in a single
burst of oscillations having a duration equal to the time to and
c) selecting a peak power of treatment at least equal to said particular peak power
and a duration of the treatment bursts at most equal to the time to.
2. The method of claim 1, wherein said frequency is substantially equal to 1 Mhz and
an electric peak power of at least 10 Kw is applied to said ultrasonic transducer
means.
3. The method of claim 1, wherein said frequency is comprised between 1.5 and 3 MHz and
an electric peak power comprised between 5 Kw and 2 Kw is applied to said ultrasonic
transducer means.
4. The method of claim 1, wherein said frequency is substantially equal to 6 MHz and
an electric peak power of a few hundred watts is applied to said ultrasonic transducer
means.
5. The method of claim 1, wherein said frequency is substantially equal to 1 MHz and
an electric peak power ranging from 10 to 20 Kw is applied to said ultrasonic transducer
means.
6. The method of claim 1, wherein said duration is comprised between 0.5 and 3 seconds.
7. The method of claim 1, wherein said duration is comprised between 0.01 and 1 second.
8. The method of claim 1, wherein said time intervals each equal at least ten times said
duration.
9. The method of claim 1, wherein said duration substantially equals half of the the
time to.
10. The method of claim 1, wherein said transducer means has a predetermined focal length,
a circular transmitting surface and a circular focal spot having first and second
predetermined respective diameters, said method comprising the further steps of :
d) calculating, as a function of said frequencies and for a plurality of different
focal lengths and a peak power of said compressional wave energy equalling 1 Kw, tables
of the global concentration factor
of the focussed beam, ka being the attenuation factor of the compressional wave energy along the beam path
between said transmitting surface and said focal spot and kg being the ratio between said first and second diameters ;
e) selecting from said plurality of different focal lengths the focal length value
which is nearer from the depth of said region and, for said nearer value, selecting
from the table the maximum value of said global concentration factor, said maximum
value corresponding in the table to a particular frequency ;
f) selecting a frequency of treatment substantially equalling said particular frequency.
11. The method of claim 10, wherein said tables further comprise calculated values of
the temperature rise per unit of time of a region of a subject to which said compressional
wave energy is applied and said method comprises the further step of
g) calculating, from datas available in medical litterature and which provide different
values of the time of lethal exposure of animal or human living tissues to heat, as
a function of the temperature which said tissues are brought to, the value of the
temperature rise per unit of time to which the tissues should be subjected for destroying
them in the duration of the treatment burst which has been selected in step c). and
h) calculating the ratio between the value of the temperature rise per unit of time
which has been calculated in step g) and the value of the temperature rise per unit
of time which is given by the table for the focal lenght selected in step e). and
the particular frequency selected in step f) and wherein the determination of the
particular peak power in step b) is carried out by multiplying 1 Kw by the ratio calculated
in step h).
12. The method of claim 10, wherein said transmission surface has a diameter of 300 mm,
said focal spot a diameter of 1.5 mm, said focal distance is 300mm and said path has
an aperture angle of 60°.
13. Apparatus for ultrasonically effecting an ultra-high-speed hyperthermia treatment
of a subject volume, said apparatus comprising piezoelectric power transducer means
having a focussing surface and electric power generator means connected to said transducer
means and applying to said generator means periodic wave trains having an adjustable
peak power the maximum value of which is substantially comprised between 10 and 20
Kw and an adjustable duration comprised between 0.5 and 3 sec.
14. The apparatus of claim 13, wherein said adjustable duration is comprised between 0.01
and 1 sec.
15. The apparatus of claim 13, further comprising image forming means for echographic
examination of damage to the subject volume during treatment and means for comparing
two consecutive images of the subject volume respectively formed before and after
application of at least one of said wave trains.
16. The apparatus of claim 15, wherein said comparing means comprise means for storing
the consecutive images in the form of digital information and means for forming a
differential image by subtracting the stored information point by point.
17. The apparatus of claim 16, wherein said means for storing the consecutive images comprise
first and second digital memories, each having an output, sai means for forming a
differential image comprise subtractor means having first and second inputs, and the
apparatus further comprises switch means for successively connecting the output of
the first memory to the first input of the subtractor means and the output of the
second memory to the second input of the subtractor means during the formation of
a first image and the output of the first memory to the second input and the output
of the second memory to the first input during the formation of a second consecutive
image.
18. The apparatus of claim 16, further comprising means for superposing a stored image
on the differential image.
19. The apparatus of claim 13, further comprising echographic means, including a B-scan
probe, for effecting an angular sector scan of the target with a scanning beam and
receiving echoes from the target, means receiving said echoes and displaying A echograms
of the successive scanning lines and means for producing a pulse signal larger than
the duration of scanning of a line and smaller than the duration of a full scan of
the target, at each time when the scanning line passes through the focus of said power
tranducer means, a memory unit and divider means, responsive to 1/N of the pulse signals,
N being an integer, for disabling said electric power generator means and writing
said echogram in said memory.