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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic wave medical treatment
apparatus for treating treatment targets such as tumors, calculi, etc.
inside a living body by applying intense ultrasonic waves from an outside
of the living body or a body cavity of the living body, under the guidance
of the magnetic resonance imaging (MRI).
2. Description of the Background Art
In recent years, for a treatment of the calculosis, much attention has been
attracted to a lithotriptor for destroying calculi inside a living body
non-invasively by externally applying intense ultrasonic waves focused on
the calculi.
Also, for a treatment of the tumors, much attention has been attracted to a
hyperthermia for heating the tumor tissues at the temperature over
42.5.degree. C., and a thermal treatment for causing a thermal
degeneration by heating at the high temperature over 60.degree. C.
In order to carry out these treatments, there are many propositions for an
apparatus for focusing the intense ultrasonic waves generated outside of
the living body onto a treatment target portion within the living body,
and thermally treating a cancer by the heat generation of the cancer
tissue due to the absorption of the ultrasonic energy, such as those
disclosed in U.S. Pat. No. 4,620,546, and Japanese Patent Application Laid
Open No. 5-137733 (1993). This latter reference proposes a unified
configuration of the lithotritor and a thermal treatment apparatus, noting
that these tow apparatuses have similar structures.
On the other hand, the researches are also carried out for a treatment
method to kill the cancer tissue by the mechanical force of the pulse
shaped shock waves having sufficient intensity to destroy the calculi
which are irradiated onto the cancer, as disclosed in Hoshi, S. et al.:
"High Energy Underwater Shock Wave Treatment on Implanted Urinary Bladder
Cancer in Rabbits", Journal of Urology, Vol. 146, pp. 439-443, August,
1991.
Now, in positioning the focus in such a cancer treatment apparatus, the two
dimensional ultrasound topographic images are usually utilized, but this
use of the two dimensional tomographic images makes it very difficult to
carry out a thorough treatment of the entire tumor as the actual tumor
often has a complicated three dimensional shape. For this reason, there
has been a proposition to employ the three dimensional ultrasound images
instead of the ultrasound topographic images as disclosed in European
Patent No. 0 194 897.
However, in the ultrasound images, the region behind the pneumatic organs
such as the bones and the lung becomes invisible, so that the accurate
three-dimensional information cannot be obtained even when the three
dimensional ultrasound images are utilized.
Furthermore, in the conventional ultrasonic wave medical treatment
apparatus, only the relative position of the focal point and the treatment
target portion can be ascertained at best, and there has been no means for
judging the effect of the treatment, so that the decision for the
continuation or termination of the treatment cannot be made until several
weeks to several months after the treatment. For these reasons, there has
been a proposition for an ultrasonic wave medical treatment apparatus
incorporating the MRI or the X-ray CT (computed tomography) as disclosed
in Japanese Patent Application Laid Open No. 5-300910 (1993).
In this regard, it is known that the tissue degeneration due to the heat
can be confirmed by taking the T2 weighted images using the MRI, as
reported in Jolesz, F. A. et al.: "Laser Surgery Benefits from Guidance by
MR", Diagnostic Imaging, pp. 103-108, September 1990. Consequently, by
observing the difference between the T2 weighted images taken before and
after the treatment, it becomes possible to Judge the effect of the
treatment, so that the treatment can be carried out while checking the
untreated portion and the sufficient treatment effect can be secured by a
minimum amount of the shock wave irradiation.
It is also possible to set up a treatment plan concerning the scanning
method and range for the shock wave focal point, and the intensity,
period, and interval for the shock wave irradiation, according to the
frozen image obtained by the MRI. Here, however, even when such a
treatment plan is prepared, the accurate treatment cannot be expected
unless the accurate positioning of the shock wave focal point is
guaranteed.
In the conventional ultrasonic wave medical treatment apparatus, it has
been necessary to remove the ultrasonic wave applicator from the patient
at a time of moving the patient in and out of the MRI gantry, due to the
mechanism for moving the ultrasonic wave applicator and the structural
properties of the treatment bed and the MRI gantry.
For example, at the beginning of the treatment, after the MR images is
taken before the treatment In order to set up the treatment plan, the
patient is moved out of the MRI gantry once in order to attach the
ultrasonic wave applicator, and then after the positioning of the intense
ultrasonic wave focal point with respect to the treatment target portion
is made by using the MR images and the ultrasound images, the actual
treatment is started. In addition, in a case of carrying out the treatment
while judging the treatment effect and checking the untreated portion by
the MR images, it is necessary to repeat the operation in which the
ultrasonic wave applicator is removed from the patient once and the
patient is moved into the MRI gantry in order to take the MR images, and
after the treatment effect is judged, the patient is moved out of the MRI
gantry again in order to attach the ultrasonic wave applicator, and then
after the positioning of the ultrasonic wave focal point is
re-established, the treatment is resumed.
In re-establishing the positioning of the ultrasonic wave focal point, even
when the relative position of the ultrasonic transducer and the treatment
target portion is memorized accurately at a time of the initial
positioning, the focal point position can be displaced by a slight
movement of the patient. In particular, when it is necessary to repeat the
attaching and removing of the ultrasonic wave applicator for a number of
times, the probability for the focal point position to be displaced from a
desired position becomes large.
Moreover, when the ultrasonic wave applicator is simply pressed against the
body surface of the patient, there is a danger for the body surface to
move with respect to the ultrasonic wave applicator due to the respiration
movement.
Now, there is a recent proposition for mounting the ultrasonic transducer
on a catheter, and inserting this catheter into the patient's body under
the guidance of the MRI to establish the positioning of the ultrasonic
transducer and the treatment target portion, so as to treat the treatment
target portion by irradiating intense ultrasonic waves from the ultrasonic
transducer mounted on the catheter, as disclosed in Japanese Patent
Application Laid Open No. 4-53533 (1993).
In this proposition, when the receiving system of the MRI is for the entire
body, the S/N ratio becomes insufficient for the treatment plan set up,
the accurate treatment effect judgement, and the real time treatment
monitoring, so that it is necessary to use a surface coil to be placed on
the body surface in order to obtain the MR images at a sufficiently high
S/N ratio. However, because of the presence of the ultrasonic wave
applicator on the body surface near the treatment target portion, it is
impossible to place this surface coil on the body surface near the
treatment target portion during the ultrasonic wave medical treatment.
Also, when a surface coil is used for the receiving system of the MRI, the
positioning of the receiving system to image the desired treatment target
portion at a high S/N ratio becomes difficult as the surface coil has a
relatively large sensitivity fluctuation. Moreover, when the ultrasonic
transducer is mounted on the catheter and the ultrasonic waves are
irradiated from a body cavity, the surface coil cannot be position near
the treatment target portion, so that the sufficient MR images of the
treatment target portion cannot be obtained.
On the other hand, in the conventional piezoelectric type ultrasonic wave
medical treatment apparatus, the focal point is extremely small, so that
in the treatment method such as that for causing the thermal degeneration
on the tissues by heating the localized region at a high temperature over
80.degree. C. or that for destroying the tissues mechanically by the shock
waves, the displacement of the focal point position can lead to the
destroying of the normal tissues, unlike the treatment method such as the
hyperthermia which carries out the treatment by utilizing the difference
in the thermal sensitivity of the tissues. For this reason, it has been
necessary to make a highly accurate positioning in the conventional
piezoelectric type ultrasonic wave medical treatment apparatus, but there
has been a danger that the treatment target portion can be moved due to
the respiration or the body movement of the patient, or that the focal
point position can be shifted due to the reflection of the ultrasonic
waves at the body surface.
In addition, as the focal point is de-focused by the reflection of the
ultrasonic waves, there has been a possibility that the temperature at the
focal point does not reach to an expected level or that the treatment
becomes insufficient as the intensity of the shock waves becomes
insufficient. As a consequence, the burden on the patient as well as the
physician can be increased by the re-treatment required by the recurrence
of the cancer due to the insufficient treatment. Furthermore, there is a
danger than the treatment in an accurate range cannot be made as the focal
point size becomes larger due to the de-focusing of the focal point.
There is also a need to take an impedance matching between the driving
circuit and the ultrasonic transducer in the ultrasonic wave medical
treatment apparatus. However, because the piezoelectric element used as
the ultrasonic transducer has a high Q at the mechanical resonance point,
the impedance matching between the piezoelectric element and the amplifier
can be displaced during the treatment due to the change of the
characteristic caused by the heat generation of the piezoelectric element,
such that there is a danger for failing to obtain the expected acoustic
output.
Also, due to the displacement of the impedance matching, the reflected
electric power of the ultrasonic transducer can be increased such that
there is a possibility for the electro-acoustic conversion efficiency to
be deteriorated.
Moreover, in a treatment method in which the malignant tumor tissue located
at the focal point is killed by heat, the negative pressure at the focal
point becomes large as the focal point input power is large, such that the
stable cavitations can be generated and grown as the intense ultrasonic
waves are applied continuously, and there is a possibility that the
sufficient power cannot reach to the intended focal point due to the
scattering of the ultrasonic waves by the cavitations. In addition, there
has been a possibility for the appearance of a hot spot at an unexpected
location due to the heat generation by the scattered ultrasonic waves.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ultrasonic
wave medical treatment apparatus capable of preventing the displacement of
the focal point of the ultrasonic waves from the treatment target portion
within the patient during the treatment.
It is another object of the present invention to provide an ultrasonic wave
medical treatment apparatus capable of eliminating a need for
re-positioning of the ultrasonic wave applicator with respect to the
patient during the treatment.
It is another object of the present invention to provide an ultrasonic wave
medical treatment apparatus capable of carrying out the ultrasonic wave
medical treatment while taking MR images to be utilized during the
treatment at a high resolution.
It is another object of the present invention to provide an ultrasonic wave
medical treatment apparatus capable of compensating the deviation of the
impedance matching between the ultrasonic transducer and the driving
circuit during the treatment.
According to one aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: MRI means for
taking MR images of a patient in an MRI gantry; and ultrasonic wave
treatment means for treating a treatment target portion within the patient
by irradiating ultrasonic waves thereon in accordance with the MR images
taken by the MRI means, including ultrasonic wave applicator for
generating ultrasonic waves focused onto the treatment target portion
which is integrally incorporated within a treatment table for carrying the
patient into the MRI gantry.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: MRI means for
taking MR images of a patient, including a surface coil for receiving MR
signals in taking the MR images; and ultrasonic wave treatment means for
treating a treatment target portion within the patient by irradiating
ultrasonic waves thereon in accordance with the MR images taken by the MRI
means, including ultrasonic wave applicator for generating ultrasonic
waves focused onto the treatment target portion having an ultrasonic
transducer for generating the ultrasonic waves and a water bag for
containing a coupling fluid for leading the ultrasonic waves generated by
the ultrasonic transducer to a body surface of the patient by making a
contact with the body surface, wherein the surface coil of the MRI means
is attached on a surface film of the water bag which makes the contact
with the body surface.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: MRI means for
taking MR images of a patient; and ultrasonic wave treatment means for
treating a treatment target portion within the patient by irradiating
ultrasonic waves thereon in accordance with the MR images taken by the MRI
means, including ultrasonic wave applicator for generating ultrasonic
waves focused onto the treatment target portion having spike shaped
pointers for pointing a focal point of the ultrasonic waves.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: MRI means for
taking MR images of a patient, including a surface coil for receiving MR
signals in taking the MR images; and ultrasonic wave treatment means for
treating a treatment target portion within the patient by irradiating
ultrasonic waves thereon in accordance with the MR images taken by the MRI
means, including body cavity probe to be inserted into a body cavity of
the patient near the treatment target portion having an ultrasonic
transducer for generating ultrasonic waves focused onto the treatment
target portion, wherein the surface coil of the MRI means is provided on
the body cavity probe.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: ultrasonic wave
applicator for treating a treatment target portion within the patient by
irradiating ultrasonic waves focused onto the treatment target portion;
and support means for fixedly supporting the ultrasonic wave applicator
with respect to the treatment target portion of the patient.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: ultrasonic wave
applicator for treating a treatment target portion within the patient by
irradiating ultrasonic waves focused onto the treatment target portion,
including an ultrasonic transducer for generating the ultrasonic waves and
a water bag for containing a coupling fluid for leading the ultrasonic
waves generated by the ultrasonic transducer to a body surface of the
patient by making a contact with the body surface; and coupling fluid
adjustment means for adjusting a mixing rate of a water and a coupling
adjustment agent forming the coupling fluid contained in the water bag
according to a temperature of the coupling fluid in the water bag.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: ultrasonic wave
applicator for treating a treatment target portion within the patient by
irradiating ultrasonic waves focused onto the treatment target portion,
including an ultrasonic transducer for generating the ultrasonic waves;
and driving circuit means for driving the ultrasonic transducer to
generate the ultrasonic waves; impedance matching circuit means for making
an impedance matching between the ultrasonic transducer and the driving
circuit means; and control means for controlling one of the driving
circuit means and the impedance matching circuit means to make a reflected
electric power from the ultrasonic transducer minimum.
According to another aspect of the present invention there is provided an
ultrasonic wave medical treatment apparatus, comprising: ultrasonic wave
applicator for treating a treatment target portion within the patient by
irradiating ultrasonic waves focused onto the treatment target portion,
including an ultrasonic transducer for generating the ultrasonic waves;
and driving circuit means for driving the ultrasonic transducer to
generate the ultrasonic waves; and control means for changing a driving
frequency of the driving circuit means while the ultrasonic wave
applicator irradiates the ultrasonic waves onto the treatment target
portion.
Other features and advantages of the present invention will become apparent
from the following description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of of the first embodiment of an ultrasonic wave
medical treatment apparatus according to the present invention.
FIG. 2 is a perspective view of a phased array type ultrasonic transducer
used in the apparatus of FIG. 1.
FIGS. 3A and 3B are perspective and side views, respectively, of a
treatment table incorporating the ultrasonic wave applicator in the
apparatus of FIG. 1.
FIG. 4 is a cross sectional view of an ultrasonic wave applicator in the
second embodiment of the present invention.
FIG. 5 is a plan view of an electrode to be used for the ultrasonic
transducer in the ultrasonic wave applicator of FIG. 4.
FIG. 6 is an illustration of an MR tomographic image taken while using the
the ultrasonic wave applicator of FIG. 4.
FIG. 7 is an alternative configuration of spike shaped pointers that can be
used in the ultrasonic wave applicator of FIG. 4.
FIG. 8A is a plan view of a phased array type ultrasonic transducer that
can be used in the ultrasonic wave applicator of FIG. 4.
FIG. 8B is a plan view of an electrode to be used for the ultrasonic
transducer of FIG. 8A.
FIG. 9 is a perspective view of a body cavity probe in the third embodiment
of the present invention.
FIG. 10 is a cross sectional view of one modified configuration for the
body cavity probe in the third embodiment of the present invention.
FIG. 11 is a perspective view of another modified configuration for the
body cavity probe in the third embodiment of the present invention.
FIGS. 12A and 12B are cross sectional and plan views, respectively, of
another modified configuration for the body cavity probe in the third
embodiment of the present invention.
FIGS. 13A-B are perspective views of another modified configuration for the
body cavity probe in the third embodiment of the present invention.
FIG. 14 is a perspective view of another modified configuration for the
body cavity probe in the third embodiment of the present invention.
FIG. 15 is a diagrammatic illustration showing a possible operation
procedure for the body cavity probe in the third embodiment of the present
invention.
FIG. 16 is a partially cross sectional block diagram of a fourth embodiment
of an ultrasonic wave medical treatment apparatus according to the present
invention.
FIG. 17 is a cross sectional view of an alternative configuration for the
ultrasonic wave applicator that can be used in the apparatus of FIG. 16.
FIG. 18 is a partially cross sectional block diagram of one modified
configuration for the apparatus of FIG. 16.
FIG. 19 is a partially cross sectional block diagram of another modified
configuration for the apparatus of FIG. 16.
FIGS. 20A, 20B, and 20C are illustrations showing one scheme for measuring
sonic speeds in the apparatus of FIG. 19.
FIGS. 21A, 21B, 21C, 21D, and 21E are illustrations showing another scheme
for measuring sonic speeds in the apparatus of FIG. 19.
FIG. 22 is a partially cross sectional block diagram of a fifth embodiment
of an ultrasonic wave medical treatment apparatus according to the present
invention.
FIGS. 23A and 23B are graphs showing impedance and reflected electric power
characteristics as a function of frequency, respectively, in the apparatus
of FIG. 22.
FIG. 24 is an equivalent circuit diagram for an alternative configuration
of an impedance matching circuit in the apparatus of FIG. 22.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, the first embodiment of the ultrasonic wave
medical treatment apparatus according to the present invention will be
described in detail. This first embodiment concerns with an overall
configuration of the apparatus which is suitable for use in conjunction
with the MRI.
In this ultrasonic wave medical treatment apparatus of FIG. 1, an
ultrasonic wave applicator 1 is integrally incorporated by being fixedly
attached below a treatment hole 24 formed on the treatment table 22, with
its orientation made to be finely adjustable by a mechanical arm 17. This
ultrasonic wave applicator I comprises an ultrasonic transducer 2 for
generating intense ultrasonic waves for treatment, a water bag S
containing a coupling fluid 4 for leading the intense ultrasonic waves to
the patient 3 through the treatment hole 24, and an ultrasonic probe 6 for
ultrasound imaging provided at a center of the ultrasonic transducer 2,
where the ultrasonic transducer 2 has a detailed configuration as shown in
FIG. 2 in which a planar disk shaped ultrasonic transducer 2 is divided
into a number of channels in radial and circumferential directions while
the ultrasonic probe 6 is made to be movable forward and backward as well
as rotatable.
In this first embodiment, this ultrasonic wave applicator 1 and the
mechanical arm 17 are integrally incorporated within the treatment bed 22
as shown in FIGS. 3A and 3B such that the ultrasonic wave applicator 1
moves along with the treatment bed 22 when the treatment bed 22 is
controlled to carry the patient 3 in and out of an MRI gantry 25. Here, an
upper opening of the treatment hole 24 is covered by a film 26, and in
addition, an RF coil 20 for transmitting RF pulses and receiving MR
signals in the MRI is provided at a circumference of the treatment hole 24
in advance.
In short, in the treatment, the patient 3 is placed on the treatment table
22 such that the tumor 8 to be treated is located above the treatment hole
24, and the focal point 7 of the intense ultrasonic waves from the
ultrasonic transducer 2 is adjusted to be focused onto the tumor 8. Then,
the ultrasonic transducer 2 is driven by a driving circuit 12 to actually
irradiate the intense ultrasonic waves onto the tumor 8 so as to treat the
tumor 8 by maintaining the treatment target portion at a high temperature.
In this first embodiment, the ultrasonic transducer 2 is made to be a
phased array type in which the focal point position, the acoustic field,
and the heating region can be controlled without moving the ultrasonic
wave applicator 1 itself, by controlling the driving timings of the
driving circuit 12 by a phase control circuit 11. The driving circuit 12
is divided into a number of channels in correspondence to divided channels
of the ultrasonic transducer 2, and each channel is driven by an
independent timing signal obtained by appropriately delaying the control
signal from a controller 9 at the phase control circuit 11. In this
manner, the focal point of the intense ultrasonic waves can be positioned
at any desired three dimensional position such as 7 and 7' shown in FIG.
2. The detail concerning the shifting of the focal point position by the
delayed timing control is disclosed in U.S. Pat. No. 4,526,168.
Also, the size of the treatment hole 24 can be changed by changing the
treatment table 22 according to the size and the shape of the treatment
target portion.
Now, after the patient 3 is placed on the treatment table 22 with the
treatment target portion located above the treatment hole 24, the position
of the tumor 8 is checked by the ultrasound images taken by the ultrasonic
probe 6 attached to the ultrasonic wave applicator 1, and an ultrasonic
imaging device 10 supplies the data on the relative position of the tumor
8 and the ultrasonic probe 6 at that point to the controller 9. Also, the
relative position of the ultrasonic probe 6 and the ultrasonic transducer
2 at that time is determined by a probe position detector 26 and supplied
to the controller 9, while the positions of the ultrasonic transducer 2
and the ultrasonic wave applicator 1 with respect to the treatment table
22 at that time is determined by an applicator position detector 15
connected with the mechanical arm 17 and supplied to the controller 9. The
controller 9 calculates the relative position of the tumor 8 and the
ultrasonic transducer 2 from these position data, and determines and
memorizes the focal point position set by the phased array.
This focal point position set by the phased array is supplied from the
controller 9 to the ultrasound imaging device 10, such that the ultrasound
imaging device 10 can display the state of the tumor 8 at the treatment
target portion and the position of the focal point 7 in real time even
during the treatment.
Next, the patient 3 is carried into the MRI gantry 25 in which a static
field coil 18 and gradient field coils 19 for the MRI are provided, by
moving the treatment table 22 by a table control device 21 under the
control by the controller 9. At this point, there is no need to remove the
ultrasonic wave applicator 1 from the patient 3 as it moves along with the
treatment table 22 in a state of being fixedly attached below the
treatment hole 24, and consequently there is no need to adjust the
positioning of the ultrasonic wave applicator 1 every time the treatment
table 22 is moved in and out of the MRI gantry 25.
Here, in order to prevent the disturbance of the magnetic fields used in
the MRI due to the ultrasonic wave applicator 1 and the treatment table
22, there is a need to form the ultrasonic wave applicator 1 and the
treatment table 22 by non-magnetic materials as much as possible. For
example, the treatment table 22 can be made of wood or reinforced plastic,
while the ultrasonic wave applicator 1 and the mechanical arm 17 can be
made of materials such as reinforced plastic and the austenitic cast iron
which has nearly the same mechanical property as the usual cast iron while
being non-magnetic, except for wirings connecting the ultrasonic
transducer 2 and the driving circuit 12 which must be electrically
conductive. It is also possible to make the mechanical arm 17 to be a
hydraulic type rather than an electrical type using an electric motor, to
further reduce the amount of magnetic material.
When the patient 3 is moved into the MRI gantry 25, the controller 9
activates the gradient field power source 13 for driving the gradient
field coils 19 and the transceiver circuit 14 for driving the RF coil 20
according to the pulse sequence specified from a console 16 such as that
of the T2 weighted imaging, so as to obtain and store the three
dimensional MR images of the patient 3 in a memory.
At this point, it is possible to set up the treatment plan according to the
obtained MR images. To this end, the manner of displaying the MR images on
a CRT 23, the combined use of the ultrasound images, and a method of
setting up the treatment plan are described in detail in Japanese Patent
Application Laid Open No. 5-300910 (1993).
When the MR images are obtained, while the patient 3 is still in the MRI
gantry 25, the coincidence of the position of the focal point 7 memorized
in the controller 9 and the position of the tumor 8 is checked, and the
treatment is started as the controller 9 commands the start of the
ultrasonic wave irradiation to the driving circuit 12. In this case, there
is no need to move the patient 3 out of the MRI gantry for the purpose of
carrying out the treatment, so that the time lag between the treatment and
the MR image taking can be reduced and the chance for the patient 3 to
move during this time lag period can also be reduced.
At a middle or an end of the original treatment plan, the irradiation of
the ultrasonic waves is stopped to observe the progress state of the
treatment by the procedure similar to that described above. In this case,
the MR images in a vicinity of the tumor 8 are taken to examine the change
in the living body. During this observation, the ultrasonic wave
applicator 1 remains to be attached on the patient 3. Here, by subtracting
the T2 weighted MR image taken before the treatment and stored in the
memory from the T2 weighted MR image taken after the treatment, the
thermally degenerated region can be confirmed very clearly, such that it
becomes possible to judge whether the sufficient treatment has been done
or more treatment is necessary. This procedure for making the observation
may be incorporated into the treatment plan in advance, such that the MR
imaging is carried out at predetermined intervals automatically.
When the completion of the sufficient treatment is confirmed by this
observation using the MR images, the operator finishes the treatment
operation, and the controller 9 can call up the history of the treatment
condition from the memory and display it as a treatment record on the CRT
28.
It is to be noted that instead of the RF coil 20 provided on the treatment
hole 24, a body cavity probe may be used for the MRI if desired. Moreover,
instead of the phased array type ultrasonic transducer, the annular array
type or any other suitable type of the ultrasonic transducer may be used
if desired. Furthermore, instead of the MRI, the X-ray CT may be used if
desired.
As described, according to this first embodiment, it becomes possible to
fix the relative position of the ultrasonic wave applicator and the
treatment target portion throughout the treatment, so that the danger for
the erroneous irradiation of the intense ultrasonic waves or the
unexpected oversight due to the displacement of the focal point from the
intended treatment target portion can be reduced. Moreover, the
re-positioning after each treatment and treatment effect observation can
be avoided, so that the entire treatment period can be shortened
considerably.
Referring now to FIG. 4, the second embodiment of the ultrasonic wave
medical treatment apparatus according to the present invention will be
described in detail. This second embodiment concerns with the
configuration of the ultrasonic wave applicator that can be used in the
ultrasonic wave medical treatment apparatus suitable for use in
conjunction with the MRI. Consequently, the ultrasonic wave applicator of
this second embodiment described below can be used in the overall
configuration similar to that of FIG. 1 instead of the ultrasonic wave
applicator 1 of the first embodiment described above.
In this second embodiment, an ultrasonic wave applicator 31 is formed to
have a configuration as shown in FIG. 4, which comprises an ultrasonic
transducer 32 having a concave surface for generating intense ultrasonic
waves for treatment, a housing 34 made of resin for supporting the
ultrasonic transducer 32, a water bag 36 containing a coupling fluid 35
for leading the intense ultrasonic waves to the patient, a water pipe 37
provided on the housing 34 for supplying and withdrawing the coupling
fluid 35 to and from the water bag 36, and a surface coil 38 for the MRI
attached on a surface film of the water bag 36 on an upper side which
makes contact with the body surface of the patient.
Here, the ultrasonic transducer 32 has the concave surface such that the
generated ultrasonic waves will be propagated within a conical passing
route 39 indicated by a dashed line and focused on a focal point 33
located at a center of a curvature of the concave surface. The surface
coil 38 is provided on the upper side of the surface film of the water bag
36 such that the passing route 39 of the ultrasonic waves is contained
within its opening. This surface coil 38 can be attached on either an
inner side or an outer side of the surface film forming the water bag 36.
Thus, when this ultrasonic wave applicator 31 is attached to the patient
with the upper side of the surface film of the water bag 36 making a
contact with the body surface through ultrasonic jelly, the surface coil
38 can be brought into a tight contact with the body surface as the
surface film of the water bag 36 is deformed along the shape of the body
surface.
Now, in general, the ultrasonic transducer 32 is made of a piezoelectric
ceramic which is non-magnetic and non-conductive, but on front and back
sides of this ultrasonic transducer 32, electrodes for applying driving
voltages to the ultrasonic transducer 32 are provided. Consequently, when
the radio frequency magnetic field for the MRI is applied on the
ultrasonic wave applicator 31, the eddy currents can be induced on these
electrodes, and these eddy currents in turn can disturb the magnetic
fields for the MRI to cause the degradation of the image quality in the
obtained MR images. In order to avoid this adverse effect of the eddy
currents, each electrode 50 attached to the ultrasonic transducer 32 of
this second embodiment has a number of slits 52 formed thereon as shown in
FIG. 5, so as to reduce the electrical conductivity of the electrode 50
with respect to the eddy currents.
In addition, as shown in FIG. 4, the ultrasonic wave applicator 31 of this
second embodiment is further equipped with a needle or rod like spike
shaped pointer 41 located along a central axis 40 joining the focal point
33 and a center of the concave surface of the ultrasonic transducer 32,
and a plurality of needle or rod like spike shaped pointers 42 located
along the circumference of the concave surface of the ultrasonic
transducer 32 and pointing along the conical passing route 39 of the
generated ultrasonic waves for the purpose of indicating the focal point
33. These pointers 41 and 42 are made of material such as rubber which can
be imaged by the MRI but which are flexible enough not to hurt the
patient's body even when they touch the body surface of the patient.
Furthermore, there is also provided a protrusion 43 on the housing 34 at a
position of the central axis 40 as shown in FIG. 4.
When the MR topographic image is taken in a state in which this ultrasonic
wave applicator 31 is attached on the body surface of the patient, the
obtained MR tomographic image appears as shown in FIG. 6. In this case,
the tomographic image of the whole body of the patient 61 as well as the
high resolution image in a vicinity of the treatment target portion are
taken together by using the surface coil 38 provided on the ultrasonic
wave applicator 31 in conjunction with a whole body coil not shown in the
figure. As a result, the tumor 62 which is the treatment target portion
appears within the high resolution image region 63 taken by the surface
coil 38, while the tomographic image of the patient 61 and the ultrasonic
wave applicator 31 also appear in the MR topographic image taken by the
whole body coil.
By observing this MR tomographic image, it is possible to recognize that
the tomographic plane of this MR tomographic image contains the central
axis 40 of the ultrasonic waves when the pointer 41 and the protrusion 43
are visible on the MR topographic image, and the focal point 33 of the
ultrasonic waves can be determined as an intersection of two lines
extended from the pointers 42 on sides of the ultrasonic transducer 32.
In a case the tumor 62 is appearing clearly, but the pointer 41 and the
protrusion 43 are not, it is either that the central axis 40 of the
ultrasonic waves is on the tumor 62 but angled with respect to the
tomographic plane, or that the central axis of the ultrasonic waves is off
the tumor 62. Consequently, the operator aligns the tomographic plane of
the MRI with the central axis 40 of the ultrasonic waves, and detects the
deviation of the tumor 62 in a direction perpendicular to the tomographic
plane, and compensate the detected deviation by adjusting the positioning
of the ultrasonic wave applicator 31. In this manner, without mechanically
measuring the absolute position of the ultrasonic wave applicator 31 in
the spatial coordinate of the MRI, the positioning of the ultrasonic wave
applicator 31 can be achieved by utilizing the visual inspection of the
operator.
It is to be noted that instead of providing the pointers 41 and 42 as
described above, only a number of pointers 42 along the circumference of
the ultrasonic transducer 32 can be provided In a form shown in FIG. 7 to
indicate the position of the focal point 33.
Also, instead of the concave shaped si | | |
