Plane reconstruction ultrasound tomography device

An ultrasound tomography device for scanning an object under examination from a plurality of directions. Coronal slice images of the plane areas near or at the female breast wall are obtained. Ultrasound lobes from ultrasound transducers are electronically directed or mechanically positioned to obliquely strike the coronal slice located at or near the breast wall. A full image of the coronal slice plane is reconstructed through section by section combination of the images obtained from the several ultrasound lobes.

BACKGROUND OF THE INVENTION 
The invention relates to an ultrasound tomography device for producing 
coronal slice views of female breast tissue. 
Ultrasound tomography devices can be operated in accordance with the 
transmission as well as the reflection method. For example an ultrasound 
tomography device for transmission tomography (UCTT) is known through U.S. 
Pat. No. 4,105,018. Ultrasound tomography devices for reflection 
tomography (UCTR), on the other hand, are known through the essay 
"Resolution and Image Quality by Ultrasonic Echo Tomography: Experimental 
Approach" by E. Hundt, G. Maderlechner, E Kronmueller and E. Trautenberg 
from the "Fifth International Symposium on Ultrasonic Imaging and Tissue 
Characterization and Second International Symposium on Ultrasonic 
Materials Characterization", June 1-6, 1980, page 7 and through the essay 
"Ultrasonic Reflectivity Tomography: Reconstruction with Circular 
Transducer Arrays" by Stephen J. Norton and Melvin Linzer from "Ultrasonic 
Imaging 1", 1979, pages 154-184. 
However, these known ultrasound tomography devices do not allow scanning 
close to the breast wall in the sense of generating a coronal slice image 
of tissue situated close to the breast wall during an examination of a 
female breast. The dimensions of the ultrasound transmitting/receiving 
system are such that they interfere with required positioning of the 
equipment close to the breast wall. 
The breast wall is the area which lies generally parallel to and near the 
chest surface. Coronal slices are plane views of a female breast tissue 
where the planes are generally oriented parallel to the breast wall. 
SUMMARY OF THE INVENTION 
It is an objective of the present invention to disclose an ultrasound 
tomography device, which provides with a minimal of technical investment 
coronal slices close to the breast wall. 
The present invention enables a section by section reconstruction of a 
coronal slice situated close to the breast wall, by combining several 
individual coronal slices which are slightly tilted toward each other. 
This is accomplished by adjusting the tilting angle of several 
transmitting/receiving ultrasound lobes and through a section by section 
acquisition of signal data related to each of the step adjustments. The 
combination and filtering of the composite data yields the final product 
representing a coronal slice image of tissue situated close to the breast 
wall. 
The groups of ultrasound transducers may be of different designs. 
Ultrasound transducers can include converter elements, which are similar 
to linear arrays, arrays for electronically controlled sector scan, ring 
arrays or other comparable devices. The ultrasound transducer may also 
include a single ultrasound resonator (transducer), which may be part of a 
slowly rotating sector scanner. Preferred embodiments of this invention 
are described in the detailed description. In other preferred embodiments 
of this invention, the individual or groups of ultrasound transducers are 
provided with different apertures for focusing at different object depths. 
Other features and advantages of the present invention will become apparent 
from the following description of the preferred embodiments, and from the 
claims. 
For a full understanding of the present invention, reference should now be 
made to the following detailed description of the preferred embodiments of 
the invention and to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a FIG. 1 a female breast 1, the object to be examined, extends through 
the application opening 2 of a board 3 (i.e. part of a patient table, on 
which a patient has been placed). Arrow 4 indicates a slice plane close to 
the breast wall, from which an ultrasound transmitting/receiving system 5 
is to provide a coronal slice image of tissue situated close to the breast 
wall. In the present case the ultrasound transmitting/receiving system 5 
consists of three ultrasound transducers 6, 7 and 8, which have been 
installed in one housing. However, these converters can be also arranged 
in an offset fashion at the perimeter of a ring disk, as illustrated in 
FIG. 3. In the present case, the ultrasound transducers 6, 7 and 8 are 
mechanical sector scanners. They include ultrasound transmitting/receiving 
quartzes 9, 10 and/or 11, which have been arranged on the carrier 12, 13, 
14 (as schematically depicted). 
Configuration adjustment components for adjusting the direction of the 
ultrasound waves or lobes emanating from the ultrasound transducers are 
provided below. The first major characteristics of the ultrasound 
transducer configuration is found in the swivel capability of the 
individual ultrasound transducers 6, 7 and 8 provided by means of the 
horizontal rotating joints 15, 16, 17. By means of a motorized driving 
system 18, 19 and 20, the individual ultrasound transducers can be 
adjusted in relation to one another, so that different tilting angles 
result with respect to the indicated coronal scanning plane close to the 
breast wall of the object to be examined (in this case the female breast 
1). In FIG. 1, the tilting angle of one of the ultrasound transducers is 
0.degree. (1=0). Different tilting angles .alpha.2 and .alpha.3 as well as 
angles .alpha.4 and .alpha.5 and .alpha.6 have been allocated to the 
second ultrasound transducer 7 as well as to the third ultrasound 
transducer 8 respectively. In addition, the entire system 5 can be slowly 
rotated around axis of rotation 29 (symmetrical axis of breast 1) by means 
of rotation drive 20'. 
The second major characteristic of the ultrasound transducer configuration 
is found in the different apertures for each of the three ultrasound 
transducers. The aperture of the smallest ultrasound transducer 6 is such 
that its transmitting/receiving lobe is focused at surface tissue area T1 
of female breast 1. The aperture of the next largest ultrasound transducer 
7 is such that the transmitting/receiving lobe is focused at medium depth 
area T2 of female breast 1. On the other hand, the transmitting/receiving 
lobe of the ultrasound transducer 8 with the largest aperture is focused 
at the largest depth area T3 of female breast 1. 
Through step by step adjustment of the tilting angle of the respective 
converter heads and through simultaneous rotation of the system 5 around 
breast 1 as well as by simultaneous activation of a time gate circuit 
(according to FIG. 2), the signal data from the area sections 21, 22, 23, 
24, 25, and 26 can be acquired section by section in successive time 
intervals t1, t2, t3, t4, t5 and t6, as seen in FIG. 1. However, the 
sections 21 through 26 approximate very closely the coronal slice plane 
close to the breast as indicated by arrow 4. An appropriate computer 
conversion of the data results in a tomography image of a coronal plane 
close to the breast wall. Other slice planes parallel to the breast wall 
are provided by adjusting the height of the system 5 over motor drive 
system 27 in the direction of arrow 28. 
FIG. 2 provides a basic circuit diagram for controlling the ultrasound 
transmitting/receiving system 5 depicted in FIG. 1. The individual 
ultrasound transducers with different apertures are again identified as 6, 
7, and 8 in the basic circuit diagram. As is known, the ultrasound 
transducers are operated with a high frequency transmitter 30 including 
clock generator 31. Suitable time and position control of the ultrasound 
transducers is obtained via control switches 32, 33, and 34. The 
ultrasound echo signals received from the breast 1 during the rotation of 
the system are forwarded from a receiver amplifier 35 to a time gate 
circuit 45 including time gates 36 through 41. The time gates 36 through 
41 will only allow echo signals to be forwarded section by section to the 
computer during the times t1 through t6 as illustrated in FIG. 1. From the 
data selected in this manner, the computer 42 computes the approximated 
coronal slice image close to the breast wall, which will be displayed on a 
display device 43. The central system control configuration has been 
identified with reference No. 44. 
The central control circuit 44 preferably is a programmable computer having 
various output control lines. The computer program may be designed as 
follows. 
In order to start the operation, the height of the transducer 6 is defined 
and adjusted through the motor 27. The transducer 6 is positioned to take 
the emission and receiving angle .alpha.1. Simultaneously the beam 
direction of the second transducer 7 is adjusted to take the angle 
.alpha.2, and the beam direction of the transducer 8 is adjusted to take 
the angle .alpha.4. All transducers 6, 7, 8 have the same position (scan 
position) with respect to an axis going through 15, 16 and 17, 
respectively, which three axes are parallel to the double arrow 28 shown 
in FIG. 1. 
In a first step, the control circuit 44 will close switch 32. In a 
subsequent step the control circuit 44 will trigger the clock pulse 
generator 31 which is turn via high frequency transmitter 30 will cause 
transducer 6 to emit an ultrasound pulse. As a next step, the control 
circuit 44 will activate the time gate 36. The echo signal from the depth 
region 22 equivalent to the time period t.sub.1 will be received through 
transducer 6 and receiving amplifier 35. The echo signal is passed to the 
time gate 36 and subsequently stored in the computer 42 according to the 
coordinates within the scanning plane. In a next step the central control 
circuit 44 will open switch 32 and close switch 33. Now, the central 
control circuit 44 will trigger the clock pulse generator 32 again. As a 
result, the transducer 7 will emit an ultrasound pulse in .alpha.2 
direction. Next control circuit 44 will activate gate 37. Thus, the 
corresponding echo signal will pass the time gate 37 and will arrive at 
the computer 42. In other words, the echo signal from a depth region 22 
equivalent to the time period t.sub.2 is stored in the computer 42 
according to the coordinates within the scanning plane. 
In a next step the control circuit 44 will open switch 33 and close switch 
34. As a consequence, transducer 8 will issue an ultrasound pulse as soon 
as pulse generator 31 is triggered again. Now the control circuit 44 will 
activate time gate 39 which corresponds to the time interval T.sub.4. The 
echo signal resulting from the ultrasound pulse will be received by 
transducer 8 and subsequently passed through gate 39 to the computer 42. 
This echo signal is derived from a depth region which corresponds to the 
time period t.sub.4. The echo signal is also stored in the memory of the 
computer 42 according to the scanning coordinates. 
Next, the central control unit 44 will cause transducer 7 to assume the 
emission and receiving angle .alpha.3. It will also adjust the position of 
transducer 8 such that transducer 8 will emit and receive ultrasound in 
and from angle direction .alpha.5, respectively. Now switch 33 is closed, 
and the central control unit 44 will cause transducer 7 to emit an 
ultrasound pulse. The corresponding echo signal is received during time 
period t.sub.3 through time gate 38 which has been activated before hand. 
The echo signal which corresponds to the depth region 23 is passed to the 
computer 42 and stored therein. 
During the next data acquisition cycle, the switch 33 is opened and switch 
34 is closed. An ultrasound pulse is emitted through transducer 8, and the 
resulting echo signal is received during time period t.sub.5 via time gate 
40. This echo signal is also stored in computer 42. 
In the following cycle the transducer 8 takes the angle position .alpha.6. 
The pulse generator 31 is triggered, and the transducer 8 emits an 
ultrasound pulse into the object 1 under investigation. The control unit 
44 opens gate 41 in order that signals from a depth region 26 
corresponding to the time interval t.sub.6 may pass. This echo signal from 
the depth region 26 is received by the computer 42 and stored in a 
suitable location of its memory. 
Thus, a plurality of data have been assembled in the computer 42. In a next 
fundamental step, all three transducers 6, 7, 8 are rotated an increment 
about the afore-mentioned axes parallel to the double arrow 28. Each of 
these axes is perpendicular to the scanning plane. Thus, the three 
transducers 6, 7 and 8 take a second scanning position. Subsequently the 
whole procedure as discussed above is repeated step by step. The data 
received during these various operations are also stored in the computer 
42. 
It should be noted that typically between 50 and 200 different scanning 
positions can be assumed. In other words, there may be between 50 and 200 
different positions which vary by a predetermined increment with respect 
to the axes which are parallel to the double arrow 28. 
After data have been acquired from all these 50 to 200 scanning positions, 
the transducers 6, 7 and 8 including the scanning mechanism 15, 16, 17, 27 
are rotated by an incremental angle about the axis 29, and the whole 
scanning procedure as discussed above is repeated. In total, 20 to 200 
incremental angle positions with respect to axis 29 may be taken such that 
the object 1 is examined from all directions. In each of these incremental 
angle positions, the scanning procedures as discribed before are 
performed. The data received are also stored in the computer 42. Finally 
the computer 42 determines a reflection CT image from all these data in a 
conventional way, and the CT image will be displayed on the screen of the 
display device 43. 
As already mentioned, the three converters shown in FIG. 1, may be also 
arranged at the perimeter of a ring disk, as depicted in FIG. 3. In FIG. 3 
three mechanical sector scanners 51, 52, and 53 are arranged at the edge 
of a ring disk 50. The tilting angle of these sector scanners can be 
adjusted to change the directions of the transmitting/receiving lobes 54, 
55, and 56 in accordance with FIG. 1. Again these sector scanners are 
provided with different sized apertures for focusing at different object 
depths T1, T2 and T3. Furthermore, the ring disk 50 rotates together with 
the mechanical sectors scanners 51, 52, and 53 around rotation axis 29 
extending through breast 1. Sector scan fields can be generated through 
swivelling of the sector scanners, as displayed in FIG. 1 by the swivel 
arrows 57, 58, 59 which are bounded by limiting lines 60 to 65 (depicted 
as dotted lines) of the respective sector field. Similarly, the individual 
sector scanners may be rotatable scanners, as indicated by the dotted 
arrow line 66 for sector scanner 52 in FIG. 3. In both cases the ring disk 
50 rotation speed of angular frequency is much lower than the angular 
frequency with which the sector scanner is either swivelled or rotated. 
For example, the rotation speed of the ring disk which carries the sector 
scanner is approximately 0.1 Hz. However, the swivel or rotation frequency 
of the sector scanner ranges between 3 to 4 Hz. The direction of rotation 
of ring disk 50 is indicated by rotation arrow 67. 
FIG. 4 shows another possible sample embodiment for an ultrasound 
transmitting/receiving system designed in accordance with the present 
invention. In FIG. 4 the ultrasound transducer is an ultrasound array 70 
(or several of these arrays combined), such as a linear array or an array 
with electronically controlled beam sweep for sector scanning, which is 
rotated slowly in a circular path 71 around the axis 29 extending through 
breast 1. A second rotation position of the ultrasound array 70 has been 
depicted as a dotted line configuration in FIG. 4. Preferably, the array 
70 is a multi-line array, that is to say an array with matrix-like 
arranged converter elements. FIG. 5 illustrates for example such an array 
70 with converter elements 72 tiered at three lines. During the 
transmitting and/or receiving phase different apertures can be obtained 
through the usual electronic connection or disconnection of individual 
transmitting elements to/or from transmitters with different transmitting 
characteristics. Such an aperture configuration is indicated by the three 
different sized apertures 73, 74 and 75. 
Finally, FIG. 6 displays an ultrasound transmitting/receiving system 
designed as a ring array in which the elements 81 are laminarly arranged. 
The beam sweep and continuous beam switching along the ring array is 
performed in a purely electronic mode (e.g. in accordance with FIG. 5 of 
U.S. Pat. No. 4,105,018). Again, the setting of different apertures 82, 
83, and 84 is performed as usual by connecting or disconnecting several 
converter elements within one group. 
The ultrasound transducers of FIGS. 1 to 6 radiate directly into the object 
to be examined. Of course, the present invention also includes embodiments 
or configurations in which the ultrasound transducer or transducers 
radiate indirectly into the object to be examined via a mirror or other 
means. 
There has thus been shown and described novel apparatus for ultrasound 
tomography which fulfills all the objects and advantages sought therefor. 
Many changes, modifications, variations and other uses and applications of 
the subject invention will, however, become apparent to those skilled in 
the art after considering this specification and the accompanying drawings 
which disclose preferred embodiments thereof. All such changes, 
modifications, variations and other uses and applications which do not 
depart from the spirit and scope of the invention are deemed to be covered 
by the invention which is limited only by the claims which follow.