Ultrasonic diagnostic apparatus

An ultrasonic diagnostic apparatus comprises at least one piezoelectric transducer which is moved in a scanning process. A first transmission signal and a second transmission signal are different from each other. One of the first and second transmission signals is selectively applied to the transducer. The transducer converts the applied one of the first and second transmission signals into a beam of corresponding ultrasonic wave. The transducer emits the ultrasonic wave beam toward an examined body and receives an echo of the ultrasonic wave beam from the examined body. The transducer converts the received echo into a corresponding received signal. A first signal processor and a second signal processor have different characteristics. The received signal is selectively applied to one of the first and second signal processors to be processed thereby. A sectional image of the examined body is generated on the basis of an output signal from one of the first and second signal processors.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an ultrasonic diagnostic apparatus of a 
mechanical-scan type. 
2. Description of the Prior Art 
Some ultrasonic diagnostic apparatuses of a mechanical-scan type produce a 
sector sectional image of an examined body. In these prior art 
apparatuses, during the production of an image of an examined body, a 
support carrying a set of piezoelectric transducers is moved while a beam 
of ultrasonic wave is emitted from the transducers toward the examined 
body and echo signals are received via the transducers. 
Japanese published unexamined patent application 61-58648 discloses such a 
mechanical-scan type ultrasonic diagnostic apparatus. In the apparatus of 
Japanese patent application 61-58648, when a plurality of images of an 
examined body for respective different frequencies of ultrasonic waves are 
required, it is necessary to replace a set of piezoelectric transducers by 
another set upon each change of the ultrasonic wave frequency from one to 
another. Thus, it is necessary to previously prepare plurality of sets of 
piezoelectric transducers having resonance frequencies matching to the 
respective different frequencies of ultrasonic waves. In addition, the 
replacement of the transducer set necessitates a portion of a casing 
accommodating the transducer set to be opened. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a convenient ultrasonic 
diagnostic apparatus. 
A first ultrasonic diagnostic apparatus of this invention comprises at 
least one piezoelectric transducer; means for moving the transducer in a 
scanning process; means for generating a first transmission signal; means 
for generating a second transmission signal different from the first 
transmission signal; means for selectively applying one of the first and 
second transmission signals to the transducer, wherein the transducer 
converts the applied one of the first and second transmission signals into 
a beam of corresponding ultrasonic wave, wherein the transducer emits the 
ultrasonic wave beam toward an examined body and receives an echo of the 
ultrasonic wave beam from the examined body, wherein the transducer 
converts the received echo into a corresponding received signal; a first 
signal processor having a characteristic; a second signal processor having 
a characteristic different from the characteristic of the first signal 
processor; means for selectively applying the received signal to one of 
the first and second signal processors to allow said one of the first and 
second signal processors to process the received signal; and means for 
generating a sectional image of the examined body on the basis of an 
output signal from said one of the first and second signal processors. 
A second ultrasonic diagnostic apparatus of this invention comprises a 
piezoelectric transducer; means for moving the transducer in a mechanical 
scanning process; means for generating a first transmission signal; means 
for generating a second transmission signal different from the first 
transmission signal; means for selectively applying one of the first and 
second transmission signals to the transducer, wherein the transducer 
converts the applied one of the first and second transmission signals into 
a beam of corresponding ultrasonic wave, wherein the transducer emits the 
ultrasonic wave beam toward an examined body and receives an echo of the 
ultrasonic wave beam from the examined body, and wherein the transducer 
converts the received echo into a corresponding received signal; and means 
for generating a sectional image of the examined body on the basis of the 
received signal. 
A third ultrasonic diagnostic apparatus of this invention comprises means 
for generating a transmission signal; a first piezoelectric transducer 
converting the transmission signal into a first beam of corresponding 
ultrasonic wave, the first transducer emitting the first beam toward an 
examined body and receiving an echo of the first beam from the examined 
body, the first transducer converting the echo of the first beam into a 
first received signal, the first transducer having a characteristic; a 
second piezoelectric transducer converting the transmission signal into a 
second beam of corresponding ultrasonic wave, the second transducer 
emitting the second beam toward the examined body and receiving an echo of 
the second beam from the examined body, the second transducer converting 
the echo of the second beam into a second received signal, the second 
transducer having a characteristic different from the characteristic of 
the first transducer; means for moving the first and second transducers in 
a mechanical scanning process; means for selectively applying the 
transmission signal to one of the first and second transducers; means for 
generating a sectional image of the examined body on the basis of the 
first received signal; and means for generating a sectional image of the 
examined body on the basis of the second received signal. 
A fourth ultrasonic diagnostic apparatus of this invention comprises means 
for generating a first transmission signal having a frequency band; means 
for generating a second transmission signal having a frequency band 
different from the frequency band of the first transmission signal; a 
first piezoelectric transducer having a frequency characteristic matching 
to the frequency band of the first transmission signal, the first 
transducer converting the first transmission signal into a first beam of 
corresponding ultrasonic wave, the first transducer emitting the first 
beam toward an examined body and receiving an echo of the first beam from 
the examined body, the first transducer converting the echo of the first 
beam into a first received signal; a second piezoelectric transducer 
having a frequency characteristic matching to the frequency band of the 
second transmission signal, the second transducer converting the second 
transmission signal into a second beam of corresponding ultrasonic wave, 
the second transducer emitting the second beam toward the examined body 
and receiving an echo of the second beam from the examined body, the 
second transducer converting the echo of the second beam into a second 
received signal; means for moving the first and second transducers in a 
mechanical scanning process; means for generating a sectional image of the 
examined body on the basis of the first received signal; means for 
generating a sectional image of the examined body on the basis of the 
second received signal; and a casing accommodating the first and second 
transducers.

DESCRIPTION OF THE FIRST PREFERRED EMBODIMENT 
With reference to FIG. 1, an ultrasonic diagnostic apparatus includes an 
ultrasonic probe 1 and a main body 2. The ultrasonic probe 1 is of a 
mechanical-scan type. As will be described hereinafter, the ultrasonic 
probe 1 is electrically connected to the main body 2. 
For example, the ultrasonic probe 1 is designed for use in a colon of an 
examined body. The ultrasonic probe 1 includes first and second 
piezoelectric transducers 1a and 1b mounted on opposite surfaces of a 
rotor 90 respectively. The transducers 1a and 1b have different resonance 
frequency bands respectively. For example, the centers of the resonance 
frequency bands of the transducers 1a and 1b are 5 MHz and 7.5 MHz 
respectively. 
The ultrasonic probe 1 has a casing 3 provided with a hemispherical front 
end which is made of synthetic resin and which forms an acoustic window 4. 
The rotor 90 is rotatably supported within the acoustic window 4 by a 
rotary shaft 5. As the rotor 90 rotates, the transducers 1a and 1b are 
sequentially opposed to the examined body. 
The rotor 90 is mechanically coupled via a drive shaft 7 to a motor 6 
supported within a rear part of the casing 3. The rotor 90 is driven by 
the motor 6. An encoder 8 is connected to the motor 6. 
A partition wall provided with an oil seal 9 divides the interior of the 
casing 3 into a front portion and a rear portion accommodating the rotor 
90 and the motor 6 respectively. The front portion of the casing 3 is 
sealingly filled with ultrasonic wave propagation liquid 10 such as water 
or oil. 
The main body 2 feeds and receives transmission signals and reception 
signals to and from the transducers 1a and 1b via a rotary transformer 11 
and signal lines 12. The rotary transformer 11 is supported on the rotor 
90 and surrounds the rotary shaft 5. The signal lines 12 extend between 
the rotary transformer 11 and the main body 2. 
The encoder 8 is directly coupled to the drive shaft 7 and generates a 
signal representing conditions of rotation of the motor 6 and thus 
representing the positions of the rotor 90 and the transducers 1a and 1b. 
The output signal from the encoder 8 is transmitted to the main body 2. 
The main body 2 uses the encoder signal in various controls including 
control of timings of the transmission and reception of ultrasonic wave. 
It should be noted that a drive line to the motor 6, an output line from 
the encoder 8, and a power supply line to the encoder 8 are omitted from 
FIG. 1 for clarity. 
The main body 2 includes a transmitter 13 having first and second signal 
generators 13a and 13b. The first generator 13a outputs a first 
transmission signal having a frequency band whose center equals 5 MHz. The 
second generator 13b outputs a second transmission signal having a 
frequency band whose center equals 7.5 MHz. A switch 15 selects one of the 
first and second transmission signals and passes the selected transmission 
signal to a switch 16. The switch 16 passes the incoming signal to either 
the first transducer 1a or the second transducer 1b via the signal lines 
12. In other words, the switch 15 functions to select one of the 
generators 13a and 13b while the switch 16 selects one of the transducers 
1a and 1b. The selected generator and the selected transducer are used in 
the operation of the ultrasonic diagnostic apparatus. The switches 15 and 
16 are changed in response to a control signal outputted from a controller 
14. 
It should be noted that the selection of one of the first and second 
transmission signals may be responsive to turning on and off of the power 
supply. 
The main body 2 also includes a receiver 17 having first and second signal 
processors 17a and 17b. The first processor 17a is able to process an echo 
or reception signal having a frequency band whose center equals 5 MHz. In 
other words, the first processor 17a has frequency characterisitics 
matching to a frequency band whose center equals 5 MHz. The second 
processor 17b is able to process an echo or reception signal having a 
frequency band whose center equals 7.5 MHz. In other words, the second 
processor 17b has frequency characteristics matching to a frequency band 
whose center equals 7.5 MHz. Each of the processors 17a and 17b includes 
amplifiers, a detector, and various filters in a known way. 
It should be noted that the filters in the processors 17a and 17b may 
include dynamic filters whose center frequencies are subjected to 
time-dependent variations. 
The transducers 1a and 1b convert the first or second transmission signal 
into a beam of corresponding ultrasonic wave emitted into the examined 
body. Portions of the emitted ultrasonic beam are reflected within the 
examined body and return to the transducers 1a and 1b as ultrasonic 
echoes. The transducers 1a and 1b convert the ultrasonic echoes into first 
and second received signals which are transmitted to the switch 16 via the 
rotary transformer 11 and the signal lines 12. 
The switch 16 selects one of the first and second received signals and 
passes the selected received signal to a switch 18. The switch 18 passes 
the incoming received signal to either the first processor 17a or the 
second processor 17b. In other words, the switch 18 functions to select 
one of the processors 17a and 17b. The selected processor is used in the 
operation of the ultrasonic wave diagnostic apparatus. The switches 16 and 
18 are changed in response to the control signal outputted from the 
controller 14. 
Output signals from the processors 17a and 17b are converted by a scan 
converter 19 into a video signal having a television format. A display 20 
generates a sectional image of the examined body in accordance with the 
video signal outputted from the scan converter 19. 
As described previously, the controller 14 controls the switches 15,16, and 
18. The controller 14 may change the switches 15,16, and 18 at timings 
determined by the output signal from the encoder 8. 
The ultrasonic diagnostic apparatus operates as follows. The motor 6 drives 
the rotor 90 via the drive shaft 7. Specifically, the rotor 90 with the 
transducers 1a and 1b are rotated in one direction at a predetermined 
speed, for example, 600 rpm. One of the first and second transmission 
signals from the first and second generators 13a and 13b is selected by 
the switch 15 in response to the control signal from the controller 14. 
The switch 16 feeds the selected transmission signal to one of the 
transducers 1a and 1b via the signal line 12 and the rotary transformer 11 
in response to the control signal from the controller 14. One of the 
transducers 1a and 1b converts the fed transmission signal into a beam of 
corresponding ultrasonic wave and emits the beam toward an examined body. 
Echoes of the ultrasonic wave beam are generated at organs of the examined 
body. The echoes which return to the transducer 1a or 1b are converted 
into an echo signal or a received signal. The received signal is 
transmitted to the switch 18 via the rotary transformer 11, the signal 
line 12, and the switch 16. The switch 18 feeds the received signal to one 
of the processors 17a and 17b in response to the control signal from the 
controller 14. One of the processors 17a and 17b processes the received 
signal. The output signal from one of the processors 17a and 17b is 
converted by the scan converter 19 into a video signal having a television 
format. The display 20 generates a sectional image of the examined body in 
accordance with the video signal outputted from the scan converter 19. 
A manual switch (not shown) movable among a predetermined number of 
different positions is connected to the controller 14. The controller 14 
determines the positions of the switches 15, 16, and 18 in accordance with 
the position of the manual switch. Therefore, the selection of the 
generators 13a and 13b, the selection of the transducers 1a and 1b, and 
the selection of the processors 17a and 17b are controlled in accordance 
with the position of the manual switch. The selections are divided into 
the following eight different combinations. 
When the manual switch assumes a first position, the first generator 13a, 
the first transducer 1a, and the first processor 17a are selected. When 
the manual switch assumes a second position, the first generator 13a, the 
first transducer 1a, and the second processor 17b are selected. When the 
manual switch assumes a third position, the first generator 13a, the 
second transducer 1b, and the first processor 17a are selected. When the 
manual switch assumes a fourth position, the first generator 13a, the 
second transducer 1b, and the second processor 17b are selected. When the 
manual switch assumes a fifth position, the second generator 13b, the 
first transducer 1a, and the first processor 17a are selected. When the 
manual switch assumes a sixth position, the second generator 13b, the 
first transducer 1a, and the second processor 17b are selected. When the 
manual switch assumes a seventh position, the second generator 13b, the 
second transducer 1b, and the first processor 17a are selected. When the 
manual switch assumes an eight position, the second generator 13b, the 
second transducer 1b, and the second processor 17b are selected. 
It is preferable that the frequency characteristics of the selected signal 
processor match to the center frequency of the selected transducer. 
Accordingly, only the following four combinations among the 
previously-mentioned eight combinations are preferably used. In a first 
combination, the first generator 13a, the first transducer 1a, and the 
first processor 17a are selected. In a second combination, the first 
generator 13a, the second transducer 1b, and the second processor 17b are 
selected. In a third combination, the second generator 13b, the first 
transducer 1a, and the first processor 17a are selected. In a fourth 
combination, the second generator 13b, the second transducer 1b, and the 
second processor 17b are selected. 
FIG. 2 shows frequency characteristics of the second combination where the 
first generator 13a, the second transducer 1b, and the second processor 
17b are selected. As shown in FIG. 2, the first transmission signal 
generated by the first generator 13a has a frequency band whose center 
equals a frequency f1 (5 MHz). The second transducer 1b has a resonance 
frequency band whose center equals a frequency f2 (7.5 MHz) higher than 
the frequency f1. The frequency band of the first transmission signal and 
the resonance frequency band of the second transducer 1b partially overlap 
each other. In the second combination, an available sectional image of the 
examined body is derived from the received signals having a frequency band 
whose center equals a frequency f3 (6 MHz) between the frequencies f1 (5 
MHz) and f2 (7.5 MHz). 
Similarly, in the third combination where the second generator 13b, the 
first transducer 1a, and the first processor 17a are selected, an 
available sectional image of the examined body is derived from the 
received signals having a frequency band whose center equals a frequency 
(6.5 MHz) between the center (7.5 MHz) of the frequency band of the second 
transmission signal and the center (5 MHz) of the resonance frequency band 
of the first transducer 1a. 
In the first combination where the first generator 13a, the first 
transducer 1a, and the first processor 17a are selected, an available 
sectional image of the examined body is derived from the received signals 
having a frequency band whose center equals the center (5 MHz) of the 
frequency band of the first transmission signal and the center (5 MHz) of 
the resonance frequency band of the first transducer 1a. 
In the fourth combination where the second generator 13b, the second 
transducer 1b, and the second processor 17b are selected, an available 
sectional image of the examined body is derived from the received signals 
having a frequency band whose center equals the center (7.5 MHz) of the 
frequency band of the second transmission signal and the center (7.5 MHz) 
of the resonance frequency band of the second transducer 1b. 
In this way, four sectional images of the examined body are obtained from 
the ultrasonic waves having four different frequency bands respectively by 
changing the combination of the used generator, the used transducer, and 
the used processor. The second and third combinations derive sectional 
images of the examined body from the ultrasonic waves in the frequency 
band whose center resides between the centers of the frequency bands of 
the first and second transmission signals. In view of the 
frequency-dependent attenuation of ultrasonic waves in the examined body, 
the second combination is more preferable than the third combination. 
As understood from the previous description, a plurality of sectional 
images of the examined body are obtained respectively from ultrasonic 
waves having different frequency bands without opening a portion of the 
ultrasonic probe casing 3 to replace the piezoelectric transducers 1a and 
1b. 
This embodiment may be modified in various ways as follows. In a first 
modification, the rotor 90 is swung during the generation of a sectional 
image of an examined body. In a second modification, the transducers 1a 
and 1b are moved linearly during the generation of a sectional image of an 
examined body. In a third modification, the transducers 1a and 1b are 
moved along a predetermined curved line during the generation of a 
sectional image of an examined body. In a fourth modification, the number 
of the transducers, the number of the generators, and the number of the 
processors are three or more. A fifth modification has a single 
transducer. 
DESCRIPTION OF THE SECOND PREFERRED EMBODIMENT 
With reference to FIG. 3, an ultrasonic diagnostic apparatus includes an 
ultrasonic probe 21 and a main body 22. The ultrasonic probe 21 is of a 
mechanical-scan type. As will be described hereinafter, the ultrasonic 
probe 21 is electrically connected to the main body 22. 
For example, the ultrasonic probe 21 is designed for use in a colon of an 
examined body. The ultrasonic probe 21 includes first and second 
piezoelectric transducers 23a and 23b mounted on opposite surfaces of a 
rotor 24 respectively. The transducers 23a and 23b have different 
resonance frequency bands respectively. For example, the centers of the 
resonance frequency bands of the transducers 23a and 23b are 5 MHz and 7.5 
MHz respectively. 
The ultrasonic probe 21 has a casing 25 provided with a hemispherical front 
end which is made of synthetic resin and which forms an acoustic window 
26. The rotor 24 is rotatably supported within the acoustic window 26 by a 
rotary shaft 27. As the rotor 24 rotates, the transducers 23a and 23b are 
sequentially opposed to the examined body. 
The rotor 24 is mechanically coupled via a drive shaft 29 to a motor 28 
supported within a rear part of the casing 25. The rotor 24 is driven by 
the motor 28. The motor 28 includes an encoder. 
A partition wall provided with an oil seal 32 divides the interior of the 
casing 25 into a front portion and a rear portion accommodating the rotor 
24 and the motor 28 respectively. The front portion of the casing 25 is 
sealing filled with ultrasonic wave propagation liquid 33 such as water or 
oil. 
The main body 22 feeds and receives a transmission signal and a reception 
signal to and from the transducers 23a and 23b via a rotary transformer 30 
and signal lines 31. The rotary transformer 30 is supported on the rotor 
24 and surrounds the rotary shaft 27. The signal lines 31 extend between 
the rotary transformer 30 and the main body 22. 
The encoder within the motor 28 is directly coupled to the drive shaft 29 
and generates a signal representing conditions of rotation of the motor 28 
and thus representing the positions of the rotor 24 and the transducers 
23a and 23b. The output signal from the encoder is transmitted to the main 
body 22. The main body 22 uses the encoder signal in various controls 
including control of timings of the transmission and reception of 
ultrasonic wave. 
It should be noted that a drive line to the motor 28, an output line from 
the encoder within the motor 28, and a power supply line to the encoder 
are omitted from FIG. 3 for clarity. 
The main body 22 includes a transmitter having first and second signal 
generators 34a and 34b. The first generator 34a outputs a first 
transmission signal having a frequency band whose center equals 5 MHz. The 
second generator 13b outputs a second transmission signal having a 
frequency band whose center equals 7.5 MHz. The first and second 
transmission signals are fed from the generators 34a and 34b to the 
transducers 23a and 23b respectively via the signal lines 31 and the 
rotary transformer 30. 
The main body 22 also includes a receiver having first and second signal 
processors 35a and 35b. The first processor 35a is able to process an echo 
or reception signal having a frequency band whose center equals 5 MHz. In 
other words, the first processor 35a has frequency characteristics 
matching to a frequency band whose center equals 5 MHz. The second 
processor 35b is able to process an echo or reception signal having a 
frequency band whose center equals 7.5 MHz. In other words, the second 
processor 35b has frequency characteristics matching to a frequency band 
whose center equals 7.5 MHz. Each of the processors 35a and 35b includes 
amplifiers, a detector, and various filters in a known way. Echo signals 
or received signals are transmitted from the transducers 23a and 23b to 
the processors 35a and 35b respectively via the rotary transformer 30 and 
the signal lines 31. 
The transducers 23a and 23b convert the first and second transmission 
signals into beams of corresponding ultrasonic waves emitted into the 
examined body. Portions of the emitted ultrasonic beams are reflected 
within the examined body and return to the transducers 23a and 23b as 
ultrasonic echoes. The transducers 23a and 23b convert the ultrasonic 
echoes into received signals which are transmitted to the respective 
processors 35a and 35b via the rotary transformer 30 and the signal lines 
31. 
Output signals from the processors 35a and 35b are converted by a scan 
converter 36 into corresponding digital signals. The scan converter 36 
includes a frame memory into which the digital signals are stored. 
Specifically, the digital signals are stored into storage locations of the 
frame memory which are designated by a write address signal outputted from 
an address generator 38. In the scan converter 36, the digital signals are 
sequentially read out from the storage locations of the frame memory and 
are then converted into a video signal having a television format. The 
storage locations of the frame memory from which the digital signals are 
read out are designated by a read address signal outputted from the 
address generator 38. A display 37 generates a sectional image of the 
examined body in accordance with the video signal outputted from the scan 
converter 36. 
One of the generators 34a and 34b is selected by a control signal outputted 
from a controller 39. Specifically, one of the generators 34a and 34b is 
activated and the other is deactivated by the control signal. Similarly, 
one of the processors 35a and 35b is selected by the control signal 
outputted from the controller 39. Specifically, one of the processors 35a 
and 35b is activated and the other is deactivated by the control signal. 
The selection of the generators 34a and 34b has the following relationship 
with the selection of the processors 35a and 35b. When the first generator 
34a is selected, the first processor 35a is selected. In this case, the 
first transducer 23a is used in the operation of the ultrasonic diagnostic 
apparatus. When the second generator 34b is selected, the second processor 
35b is selected. In this case, the second transducer 23b is used in the 
operation of the ultrasonic diagnostic apparatus. The address signals 
outputted from the address generator 38 are generated in accordance with a 
control signal outputted from the controller 39. 
The ultrasonic diagnostic apparatus operates as follows. The motor 28 
drives the rotor 24 via the drive shaft 29. Specifically, the rotor 24 
with the transducers 23a and 23b are rotated in one direction at a 
predetermined speed, for example, 1200 rpm. 
During a first period, the controller 39 selects the first generator 34a 
and the first processor 35a so that the first devices 34a and 35a and the 
first transducer 23a are used in the operation of the ultrasonic 
diagnostic apparatus. During the first period, the first transducer 23a 
emits an ultrasonic wave beam into an examined body and receives echoes of 
the ultrasonic wave beam while the first transducer 23a is rotated through 
an angular range from a predetermined position P to a predetermined 
position Q. In this case, the ultrasonic wave beam has a frequency band 
whose center equals 5 MHz. The first transducer 23a converts the received 
echoes of the ultrasonic wave beam into a received signal which is 
processed by the first processor 35a. The scan converter 36 converts the 
output signal from the first processor 35a into a corresponding digital 
signal. The digital signal is stored into a storage location of the frame 
memory within the scan converter 36 in accordance with the write address 
signal from the address generator 38. The digital signal is read out from 
the frame memory in accordance with the read address signal from the 
address generator 38 and is converted by the scan converter 36 into a 
corresponding video signal. The display 37 indicates a sectional image of 
the examined body in accordance with the video signal. In this case, the 
sectional image of the examined body is derived from the echoes of the 
ultrasonic wave beam having a frequency band whose center equals 5 MHz. 
During a second period between the moment of the movement of the first 
transducer 23a out of the position Q and the moment of the movement of the 
second transducer 23b into the position P, the controller 39 changes the 
selection of the generators 34a and 34b and the selection of the 
processors 35a and 35b so that the second devices 34b and 35b are moved 
into operable states. The controller 39 is informed of the positions of 
the rotor 24 and the transducers 23a and 23b by the output signal from the 
encoder within the motor 28. The controller 39 determines the timings of 
the changes of the generators 34a and 34b and the processors 35a and 35b 
in accordance with the output signal from the encoder. 
During a third period following the second period, the controller 39 
selects the second generator 34b and the second processor 35b so that the 
second devices 34b and 35b and the second transducer 23b are used in the 
operation of the ultrasonic diagnostic apparatus. During the third period, 
the second transducer 23b emits an ultrasonic wave beam into the examined 
body and receives echoes of the ultrasonic wave beam while the second 
transducer 23b is rotated through the angular range from the position P to 
the position Q. In this case, the ultrasonic wave beam has a frequency 
band whose center equals 7.5 MHz. The second transducer 23b converts the 
received echoes of the ultrasonic wave beam into a received signal which 
is processed by the second processor 35b. The scan converter 36 converts 
the output signal from the second processor 35b into a corresponding 
digital signal. The digital signal is stored into a storage location of 
the frame memory within the scan converter 36 in accordance with the write 
address signal from the address generator 38. The digital signal is read 
out from the frame memory in accordance with the read address signal from 
the address generator 38 and is converted by the scan converter 36 into a 
corresponding video signal. The display 37 indicates a sectional image of 
the examined body in accordance with the video signal. In this case, the 
sectional image of the examined body is derived from the echoes of the 
ultrasonic wave beam having a frequency band whose center equals 7.5 MHz. 
During a fourth period between the moment of the movement of the second 
transducer 23b out of the position Q and the movement of the movement of 
the first transducer 23a into the position P, the controller 39 changes 
the selection of the generators 34a and 34b and the selection of the 
processors 35a and 35b so that the first devices 34a and 35a are moved 
into operable states. The controller 39 determines the timings of the 
changes of the generators 34a and 34b and the processors 35a and 35b in 
accordance with the output signal from the encoder within the motor 28 as 
in the second period. 
It should be noted that the digital signals corresponding to the echo 
signals received via the transducers 23a and 23b are stored into different 
regions of the frame memory within the scan converter 36 respectively. 
As the rotor 24 rotates through 360.degree. , the previously-mentioned 
operations during the first period to the fourth period are sequentially 
performed and one operation cycle is completed. One operation cycle is 
performed for every one revolution of the rotor 24. 
In FIG. 4, the character A1 denotes a scanning period where the first 
transducer 23a moves from the position P to the position Q. The character 
B1 denotes a scanning period where the second transducer 23b moves from 
the position P to the position Q. As shown in FIG. 4, the scanning periods 
A1 and B1 alternate with each other. A frame period A2 includes a pair of 
adjacent scanning periods A1 and B1. A frame period B2 includes a pair of 
adjacent scanning periods B1 and A1. Each of the frame periods A2 and B2 
corresponds to a period of updating of one frame having a pair of 5-MHz 
and 7.5-MHz sectional images. Each of the frame periods A2 and B2 
corresponds to one revolution of the rotor 24. Since the rotor 24 rotates 
at a speed of 1200 rpm, the frame frequency equals 20 Hz. 
As shown in FIG. 5, the display 37 indicates sector sectional images 40A 
and 40B of the examined body in separate parallel regions respectively. 
The sector sectional images 40A and 40B are obtained via the transducers 
23a and 23b respectively. The sector sectional images 40A and 40B have a 
frame frequency of 20 Hz and are indicated in real time. It should be 
noted that only one of the sector sectional images 40A and 40B may be 
indicated over an entire region of the display 37. 
As understood from the previous description, a plurality of sectional 
images of the examined body are obtained respectively from ultrasonic 
waves having different frequency bands without opening a portion of the 
ultrasonic probe casing 25 to replace the piezoelectric transducers 23a 
and 23b. 
This embodiment may be modified in various ways as follows. In a first 
modification, the number of different frequency transducers is other than 
two. In a second modification, transducers have a common resonance 
frequency characteristics. In a third modification, transducers have 
different opening diameters or different opening shapes. In a fourth 
modification, transducers have different focal distances. 
DESCRIPTION OF THE THIRD PREFERRED EMBODIMENT 
FIG. 6 shows a third embodiment of this invention which is similar to the 
embodiment of FIGS. 3-5 except for the following design changes. In the 
embodiment of FIG. 6, the display 37 indicates 5-MHz and 7.5 sectional 
images 40A and 40B in a sector region. Specifically, the 5-MHz sectional 
image 40A occupies an inner portion of the sector region while the 7.5-MHz 
sectional image 40B occupies an outer portion of the sector region. 
In respect of the scan converter 36 (see FIG. 3), the locations of the 
segments of the frame memory into which the digital signals are written 
are chosen so as to realize the image display manner of FIG. 6. 
DESCRIPTION OF THE FOURTH PREFERRED EMBODIMENT 
FIG. 7 shows a fourth embodiment of this invention which is similar to the 
embodiment of FIGS. 3-5 except for the following design changes. In the 
embodiment of FIG. 7, the display 37 indicates 5-MHz and 7.5-MHz sectional 
images 40A and 40B in respective adjoining regions. 
In respect of the scan converter 36 (see FIG. 3), the locations of the 
segments of the frame memory into which the digital signals are written 
are chosen so as to realize the image display manner of FIG. 7.