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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method and to an apparatus for this
method of displaying an image wherein the signals forming the image are
obtained by irradiating an examination subject with a radiation field,
such as ultrasound, and detecting the reflected (echo) signals.
2. Description of the Prior Art
A precautionary examination of the female mammary gland for early detection
of breast cancer with imaging methods is extremely desirable since this
illness, which represents the most common type of cancer in women in
industrialized countries, has a significant tendency to spread and an
early detection of the sickness usually means a cure.
By contrast to x-ray mammographic examinations, ultrasound examinations are
completely non-hazardous and even extremely dense gland tissue
(mastopathy) does not represent a problem since the tumors in dense gland
tissue can be visibly identified in a sonographic display. X-ray
mammography provides no diagnostic utility given patients with a
mastopathy or with endoprotheses in the breast region since the tumors can
then not be displayed or can only be poorly displayed.
By contrast thereto, however, many previous sonographic methods were
incapable of exceeding x-ray mammography in the early detection of
malignant tumors in the case of breast examination with respect to
sensitivity and specificity. It is precisely this capability, however,
that would be desirable since an ultrasound method would represent the
ideal examination method because of the completely risk-free nature
thereof.
An ultrasound examination is normally undertaken with an acoustic head
(applicator) that the physician places onto the organ to be examined in
order to thus acquire a tomogram which, as a so-called B-image,
corresponds to a slice presentation. Methods are also known that
superimpose a number of images registered from different directions on one
another in the fashion of a computer tomograph.
A method and an apparatus for producing an image from ultrasound echoes is
known from the article by K. Soetanto, "An in-vivo technique for
estimation of size and relative sound velocity of breast tumor using
distorted image in ultra-sonic tomogram", which appeared in Japanese
Journal of Applied Physics, Vol. 24, No. 24-1, 1985, Tokyo (JP), pp.84-86.
This describes a method for estimating the size and relative speed of
sound in a breast tumor wherein a distorted ultrasound image is evaluated.
The distortions arise because tumorous tissue has a different speed of
sound than healthy tissue. The article describes investigations of a
cylindrical member situated in a water tank, this member having a speed of
sound therein different from the surrounding water and a reflector plate
arranged therebehind. A linear distortion of the ultrasound image of the
reflector plate arises because of, the different speeds of sound and the
reflector plate in the ultrasound image has lateral tails because of, the
refraction of the ultrasound waves is visible in the ultrasound image. The
spacing of the tails from one another indicates the diameter of the
cylinder. This perception is then used in ultrasound echo tomography of
the female breast. The chest wall behind the tumor is used as the planar
reflector. The ultrasound examination itself is implemented with a normal
ultrasound apparatus, whereby the examining person can freely move the
ultrasound transducer without auxiliaries.
In an ultrasound tomography apparatus disclosed by U.S. Pat. No. 4,509,368,
transmitted and reflected signals are superimposed and correlated.
Although this arrangement enables a gain in information compared to
previously known solutions, systems operating according to this method
have not been used in practice in significant numbers. It is thereby an
impediment that the apparatus is relatively complicated in structure and
that a plurality of acoustic transmitters and acoustic receivers are
required, as a result of which the apparatus is expensive to acquire and
is also not simple in terms of manipulation.
Further, German OS 40 37 387 discloses a method wherein the echo values
obtained for coinciding spatial points from radiation directions opposite
one another are superimposed, so that signal parts ultimately remain only
for those spatial points that deviate from one another dependent on the
radiation direction. As a result, information with respect to the shape
and the surface structure of a recognized inhomogeneity can be derived
better, since acoustic occlusions and the like are eliminated. It is still
a disadvantage of this method, however, that the part of the body to be
examined must be irradiated from two opposite spatial directions, so that
the acoustic head must either be shifted correspondingly in location or
two acoustic heads are required.
Published PCT Application 83/02053 also discloses an ultrasound scanner
means for producing ultrasound tomograms of the female breast. The breast
is thereby situated in an examination position that corresponds to the
examination position in X-ray mammography, so that the ultrasound
mammogram can be easily correlated with the X-ray image. The ultrasound
scanner means includes an ultrasound-transmissive plate on which the
breast is seated. A movable ultrasound transducer or an ultrasound array
with which a complete scanning of the breast can be implemented is
situated under the plate. Similar to X-ray mammography, an external
compression with an air-filled or water-filled balloon or with sand bags
or vacuum means as well can ensue. The means needed for compression,
however, impede access in the upper breast region. It is noted with
respect thereto in the reference that this region should remain free so
that it can be brought into a shape wherein the visibility of details is
optimized.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and an
apparatus for producing an ultrasound image from received ultrasound echo
signals wherein the information derivable from the ultrasound image in
ultrasound examinations, particularly in serial examinations within the
framework of cancer prevention (screening), has particular diagnostic
capability.
The above object is achieved in a method and apparatus for producing an
image of a portion of the human body with echo signals of primary
radiation directed at the portion of the human body, wherein the body
portion is disposed between a primary radiation transmitter/echo signal
receiver and a reference surface which reflects the primary radiation as
an echo signal more strongly than other regions of the body portion
situated in the field view of the radiation transmitter. The average or
expected transit time and/or amplitude of an echo signal of the primary
radiation passing through the body portion, that is reflected from the
reference surface and received by the receiver, is calculated, or is set
to a predetermined value, as a reference echo signal. The actual transit
time and/or actual amplitude of an echo signal of the primary radiation
passing through the body portion and reflected from the surface and
received by the primary radiation receiver is calculated. The deviation of
the transit time and/or amplitude from the actual echo signal reflected
from the reference surface compared to the reference echo signal is
evaluated, and this deviation is used as a criterion for the probability
of a tumor in the region of the direction of propagation of the received
echo signal. The reference surface is aligned perpendicularly to the
primary propagation direction of the primary radiation, and the body
portion is clamped, so as to be spatially fixed in position, between a
plate-shaped clamping element and the reference surface, the plate-shaped
element and the reference surface being substantially parallel.
The invention is based on the perception that influence of a malignant
tumor on the transit time and/or amplitude of an ultrasound signal
reflected by the malignant tumor deviates from the influence on transit
time and/or, amplitude of a reference ultrasound signal transmitted by
healthy tissue. Thus a reference signal is generated by arranging an
object at the far side of the part of the body to be examined, the object
being highly ultrasound-reflective and spatially fixed at a predetermined
distance from the transmitter/receiver. The reference signal enables an
evaluation of the influencing of the transit time and/or of the amplitude
change. The deviation in transit time and/or amplitude of received echo
signals compared to the known or identifiable transit time of the
reference echo signal and intensity of the reference echo signal
registered as amplitude, is then, taking the registered amplitude curves
into consideration, used as a criterion for the tumor probability in the
area of the spatial direction of the propagation of the respective echo
signals. The change in transit time thereby results from the respectively
different, resultant propagation speed of the sound in different tissue
areas, whereas acoustic cancellation (or amplification) is produced by
diffraction and reflection phenomena.
The apparent position and displayed intensity of a reference surface that
is arranged at the other side of the part of the body to be examined and
is aligned perpendicularly to the spatial direction of the emitted
ultrasound signal is thereby distorted and shifted in the regions beyond a
tumor which causes the image of the reference surface to be displayed to
be modified from an expected position or appearance. Conclusions about the
probability of a tumor in the area of the part of the body above the shift
can be drawn on the basis of the arrangement, the nature of the edge
contour and the amount (or the direction) of the shift.
An important feature of the inventive method and apparatus is that a
linking or correlation of picture elements of the image containing only
two-dimensional information (and thus corresponding to pixels as are
required by shadowing as in fluoroscopy) with depth information obtained
from the echo signal, so as to obtain three-dimensional information. The
inventive ultrasound method and apparatus thereby enable depth locating of
findings that are emphasized or can only be initially localized with the
inventive, two-dimensionally imaging method steps.
For calculating the transit time of the echo signal, the echo signals that
have an amplitude upwardly exceeding a predetermined level within a
defined time window are registered by the ultrasound transmitter/receiver
in an embodiment of the inventive method. The level is dependent on the
nature of the reference surface employed and the time window is located in
the region of the echo signal in which one can count on a transit time
shift of the relative exultation of the amplitude level deriving from the
reference surface. Either the absolute or, on the other hand, only the
relative transit time deviation can thus be calculated in the region of
the time window. A calculation of the transit time deviation in the region
of the time window prevents other, acoustically reflective regions of the
body part under examination such as gland members, fatty tissue, etc.,
generating a similar amplitude from being erroneously confused with the
reference surface.
In general form, regions of the image presentation can thereby be generated
by common evaluation of echoes registered for points neighboring one
another, so that a complete display of the reference plane is enabled
given maximum utilization of the registered signal information.
The points or regions can be superimposed to form a two-dimensional or
three-dimensional graphic display, particularly a color display.
The inventive method can also be employed for a spatial image presentation
in the fashion of computer tomography by emitting primary radiation onto
the body part to be examined along a path covering the area of the body
part either continuously or in an essentially equidistant succession of
adjoining spatial directions (i.e., a number of slices).
An embodiment of an apparatus for the implementation of the inventive
method thus includes the corresponding radiation sources or and radiation
receivers forming signal transducers as well as a signal processor with a
program memory and signal connections to the signal transducers.
Since the wave radiation scans the relevant body part, i.e. the subject to
be examined, in chronological succession and a stable support of, in
particular, moving subjects is beneficial in this respect, the subject in
the preferred embodiment of the inventive apparatus is arranged between a
plate-shaped element that is essentially transparent for the wave
radiation and the reference surface that reflects the echo signals,
whereby the element and the reference surface are aligned parallel to one
another.
Because subjects to be examined can have different shapes, the element
transparent for the wave radiation and the reflective reference surface
are connected to one another with an axial adjustment means. The subject
to be examined and surrounded by a coupling medium is thus clamped in a
fixed fashion by actuating the adjustment means after introducing the
subject between the reference surface and the element, which are likewise
provided with the coupling medium, so that relatively large regions of the
subject directly touch the element and the reference surface and a good
coupling between subject and the element and the reference surface is thus
guaranteed in a simple way. Since the thicknesses of the regions to be
traversed by the ultrasound signal are thus defined, a
transmitter/receiver having suitable focusing can be selected, so that
losses in time due to mismeasurements are avoided.
The coupling medium surrounding the subject is preferably confined in a
flexible container whose shape can be adapted to the shape of the subject.
The container is made of a material transmissive for the wave radiation
and the coupling medium is such that the speed of sound and/or the
absorption of the wave radiation in the coupling medium is essentially the
same as that of the wave radiation in the body tissue of the subject to be
examined. As a result, those regions of the subject whose surface does not
reside in immediate contact with the transmissive element or the
reflective reference surface can also be examined.
In a preferred embodiment of the inventive apparatus, the ultrasound
transmitter/receiver can be locked in a carriage lying against the outside
surface of the plate-shaped element transmissive for the wave radiation
and arranged translationally movable such that the subject to be examined
together with the reflective reference surface behind it can be scanned
grid-like point-by-point in chronological succession in a simple way
either manually or under motor drive. In the case of a linear or
two-dimensional array, the required motion sequences are simplified or can
be entirely eliminated. In a two-dimensional array embodiment, this itself
can form the pressing surface. The drive thereby ensues in scanning
fashion with a corresponding electronic circuit.
In the examination of a human body part, the regions of the respective
surfaces of the element transmissive for the wave radiation and the
reflective reference surface are matched to the shape of the body part
adjacent thereto and, in particular, are provided with a connecting edge
having a concavely shaped recess. This is a preferred arrangement, in
particular, for examining the female mammary gland.
In a preferred embodiment for evaluating the obtained information, a
computer-calculated, three-dimensional display of the
ultrasound-reflective reference surface is produced on a monitor, so that
the size of the region of the subject to be examined wherein a tumor is
present with high probability can be simultaneously surveyed. The
simultaneous display of the characteristic information is thus possible in
a single image that can be aligned in different views by the
corresponding, graphic control means of the computer.
A closer diagnosis can then ensue by selecting the display of the tissue
regions associated with the conspicuous regions of the reference surface.
By enlargement (zoom) of an image excerpt, tissue zones of interest can
thereby be separately reproduced, so that a more exact evaluation is
possible.
DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the preferred embodiment of the inventive apparatus for
the implementation of the inventive method, shown in section.
FIG. 2 illustrates the apparatus of FIG. 1 in a perspective view.
FIGS. 3a-3d schematic views of tissue inhomogeneities shown in section, as
arise upon transirradiation of a subject in accordance with the principles
of the present invention.
FIGS. 4a-4d show the respective echo signal curves for the views according
to FIGS. 3a-3d.
FIGS. 5a-5e illustrate echo signal curves at various registration points of
a plane in a selected spatial direction.
FIG. 6 is a three-dimensional illustration of the ultrasound-reflective
support in the ultrasound image given an existing tumor in the subject
under examination obtained in accordance with the inventive method and
apparatus.
FIG. 7 is a block circuit diagram of a processor system for signal
processing in accordance with the inventive method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the preferred embodiment of the inventive apparatus shown in FIGS. 1 and
2, two plane-parallel elements, a plate 6 and an element 7, are provided
that limit the subject 1 to be examined in two directions in two planes
aligned essentially parallel to one another. The element 7 is transmissive
for ultrasound waves, whereas the plate 6 reflects ultrasound waves. Plate
6 and element 7 are connected to one another with an axial adjustment
mechanism 8. The spacing between the element 7 and the plate 6 can be
individually set with adjustment elements 9 and 10. The following spatial
directions shall be employed for the following description: x forms the
penetration direction of the ultrasound signals and, thus, the t-axis for
the ultrasound echoes received in chronological succession. The y-axis
forms a first "motion" axis in the signal pick-up and, thus, the second
coordinate for the illustration of a tomogram. The z-axis then forms the
secondary motion axis of the signal pick-up and thus enables the
generation of a three-dimensional image. The "motion", however, need not
ensue mechanically but can be undertaken by electronic scanning given the
employment of linear or planar transmitter/receiver arrays.
The primary wave transmitter/echo signal receiver 2 is arranged so as to be
movable and lockable in a carriage 12 along the longitudinal axis of the
carriage 12 that is likewise connected to cross-rods 11 of the adjustment
mechanism 8 in this preferred embodiment of the apparatus. The carriage 12
is in turn displaceable along the longitudinal axis of the cross-rods 11.
The primary wave transmitter/echo signal receiver 2, which lies against
the outside of the element 7, can move over the entire planar surface of
the element 7 with the carriage 12 for scanning the subject 1 to be
examined. The position, i.e. the spatial direction, of the primary wave
transmitter/echo signal receiver 2 can be set either manually or driven by
a stepping motor or with electronic scan means. Given manual setting, the
coordinates or the position of the primary wave transmitter/echo signal
determining the spatial direction are acquired.
The respective edges 13 and 14 of the plate 6 and of the element 7 lying
against the human body are anatomically rounded, in particular, concave.
This preferred exemplary embodiment is especially simple in mechanical
terms because an examination subject 1 having an arbitrary shape can be
surrounded at any time by a flexible, sealed container 15 that contains a
coupling medium 17 and is transmissive for the (wave) radiation employed.
The container 15 is filled and emptied via a filling nozzle 16. In
addition, the coupling medium must merely be applied to the plate 6 and to
the element 7 in order to assure that the wave radiations can be
well-transmitted.
In a further embodiment of the inventive apparatus that is not shown, the
reflective plate 6 simultaneously forms a reception means for a further
imaging signal effective in spatial direction.
Such a further examination may be an x-ray examination or a digital
radiography examination of the subject in the identical position. Further
information with respect to the detected inhomogeneity can thereby be
acquired with an advantageous reduction of the x-ray load by comparison
examinations conducted only by means of x-ray exposures from two different
spatial directions that are currently standard. The x-ray tube can thereby
temporarily take the place as warranted of the ultrasound transmission and
reception means.
Thereafter, the subject 1 to be examined is fixed with the adjustment
mechanism 8 employing the adjustment elements 9 and 10 and the primary
radiation signals 3 emitted by the primary wave transmitter/echo signal
receiver 2 are reflected by the plate 6, after passing through the subject
1, as echo signals 4, and are picked up by the primary wave
transmitter/echo signal receiver 2. The transit times and the amplitudes
of the echo signals 4 are thereby registered for the different spatial
directions 5 of the emitted primary radiations 3 by the evaluation means
connected to the primary wave transmitter/echo signal receiver 2.
The signal curves that arise for the various at boundaries of
inhomogeneities and the signal curves therefrom shall now be discussed in
greater detail with reference to FIGS. 3a-3d and 4a-4d.
The sectional views according to FIGS. 3a-3d show various inhomogeneities
in an examination subject which become apparent upon transirradiation with
ultrasound (in the x-direction) for explaining the inventive method. The
spatial direction of the primary radiation is in the direction of the
arrow, whereby the degree of shading of the illustration indicates the
number or the intensity of the echoes obtained.
FIG. 3a shows a tumor-free subject containing fatty tissue F and glandular
member DK. The fatty tissue F has a lower echo density than the glandular
member DK, and the ultrasound-reflective plate P has the highest echo
density.
FIG. 3b shows a subject having a malignant tumor T. The malignant tumor
appears nearly without echo and with a bilateral edge shadow behind the
tumor.
FIG. 3c shows a subject having a malignant tumor T. The malignant tumor
appears nearly without echo but, by contrast to FIG. 3b has a moderate
central shadow behind the tumor.
FIG. 3d shows a subject having a benign cyst Z. Like most cysts, the cyst Z
appears without echoes and with a central sound intensification behind the
cyst.
The various echo signal curves respectively arising from FIGS. 3a-3d are
shown in FIGS. 4a-4d (z-direction).
FIG. 4a shows the echo signal curve of the reference primary radiation 3'
that passes through the tumor-free subject containing fatty tissue F and
glandular member DK. The variations in the echo amplitude A with the time
t and, therefore, with increasing distance from the primary radiation
transmitter/echo signal receiver are thereby entered. The fatty tissue F
has a lower amplitude than the glandular member DK, whereby the region of
the highest amplitude values Pa indicates the position of the
ultrasound-reflective plate.
FIG. 4b shows the echo signal curve of a primary radiation 3 passing
through the malignant tumor T. The amplitude in the region of the tumor T
and of the bilateral edge shadow is substantially lower than that of the
surrounding fatty tissue F. It may also be seen that the transit time
L.sub.b up to the region of the increased amplitude values P.sub.b of the
plate has shortened in comparison to the transit time L.sub.a of the echo
signal according to FIG. 4a, but the increased amplitude values P.sub.b
are lower than the increased amplitude values P.sub.a of the echo signal
curve according to FIG. 4a. The shortening of transit time thereby
presents itself as an apparent plate deformation.
FIG. 4c shows the echo signal curve of a primary radiation 3 passing
through the malignant tumor T. The amplitude in the region of a tumor T is
significantly lower than that of the surrounding fatty tissue F and the
moderate central shadow has a reduced amplitude compared to the amplitude
in front of the tumor T. As can be seen in the same way as in FIG. 4b the
transit time L.sub.c up to the region of increased amplitude values
P.sub.c of the plate has shortened in comparison to the transit time
L.sub.a of the echo signal according to FIG. 4a and, but the increased
amplitude values P.sub.c are lower than the increased amplitude values
P.sub.a of the echo signal curve according to FIG. 4a.
FIG. 4d shows the echo signal curve of a primary radiation 3 that passes
through the benign cyst Z. The amplitude in the region of the cyst Z is
essentially equal to zero and the central sound intensification having an
amplitude following the cyst Z that is increased compared to the amplitude
preceding the cyst Z may be seen. As can also be seen the transit time
L.sub.d up to the region of the increased amplitude values P.sub.d of the
plate 6 has in fact shortened in comparison to the echo signal curve
according to FIG. 4a, but the increased amplitude values P.sub.d
essentially continue to exceed the increased amplitude values P.sub.a of
the echo signal curve according to FIG. 4a.
By repeated scanning of the subject in further planes directed
perpendicularly relative to the first plane, a three-dimensional image can
be produced in a further exemplary embodiment (not shown here) via a
linking of the identified echo signal curves by superimposition.
FIGS. 5a-5e show five echo signal curves identified at various points in a
plane in a selected spatial direction.
According to FIG. 5a, the echo signal passes through fatty tissue F up to
the plate 6, in the region whereof the amplitude of the echo signal is
substantially boosted relative to the basic level of the amplitude values.
The transit time L.sub.a of the echo signal can be calculated with
reference to the distance of this region of relatively low amplitude from
the zero point of the x-axis (time axis). A time window Z.sub.f can also
be defined on the basis of this echo signal wherein one can expect a
transit time shift of the relative increase of the amplitude level arising
from the plate 6.
In the graphic illustration of FIG. 5b, the echo signal passes through the
subject to be examined in a rastered spacing from the echo signal shown in
FIG. 5a and proceeds through two glandular members DK that may be
recognized on the basis of the amplitude ranges boosted in the same
direction. The transit time L.sub.b of this echo signal thereby
corresponds to the transit time L.sub.a of the echo signal of FIG. 5a, so
that the position of the relatively increased amplitude value P.sub.b in
the time window Z.sub.f corresponds to that of the relatively exalted
amplitude value P.sub.a in the time window Z.sub.f. The amplitude values
for P.sub.a and P.sub.b are thereby essentially alike.
In the illustration of FIG. 5c, the echo signal passes through a malignant
tumor T. An extremely low amplitude is registered in the region of the
malignant tumor, and the amplitude following the tumor T is lower than
preceding the tumor T because of a middle acoustic shadow. The transit
time L.sub.c of the echo signal has shortened somewhat by comparison to
the echo signals of FIGS. 5a and 5b since the speed of sound in the tumor
is higher than in the rest of the body tissue. The relative shortening of
transit time within the time window Z.sub.f is shown as L.sub.c'. The
relatively low amplitude value P.sub.c is again located in the time window
Z.sub.f, but it is now located close to the lower boundary of the time
window Z.sub.f because of the shortened transit time L.sub.c and now has a
substantially lower value than the relatively low amplitude values P.sub.a
and P.sub.b of FIGS. 5a and 5b.
The echo signal according to FIG. 5d also passes through the tumor T but
the path of this echo signal through the tumor T is different than that of
the echo signal of FIG. 5c, so that, given the same shortening of transit
time (L.sub.d corresponds to L.sub.c and the relative shortening of
transit time L.sub.d' corresponds to L.sub.c' within the time window
Z.sub.f) and position in the time window Z.sub.f, the relatively low
amplitude value different from the relatively low amplitude value P.sub.c
of FIG. 5c.
The echo signal shown in FIG. 5e, corresponding to FIG. 5a, again still
proceeds through the fatty tissue F, so that a determination can be made
on the basis of these five echo signals that a tumor is present in this
plane in the region between the points of the emitted primary rays
corresponding to FIGS. 5c and 5d, since both shortenings of transit time
L.sub.c and L.sub.d or, respectively, the relative transit time
shortenings L.sub.c', and L.sub.d ' as well as relatively exhausted
amplitude values P.sub.c and P.sub.d were found in the region of the
defined time window Z.sub.f.
In order to be able to distinguish a benign inhomogeneity that shortens the
transit time of the echo signals from a malignant inhomogeneity even
better, the resultant ultrasound image of the reflective plate 6 is
three-dimensionally shown in FIG. 6. The spatial contour of the region in
which an inhomogeneity is to be expected with high probability can thus be
graphically reproduced. The nature of the edge contour of the distorted
region of the reflective plate 6 can thus be seen, enabling a conclusion
about the nature of the edge contour of the inhomogeneity. Studies have
shown that malignant findings usually have irregular edge contours. By
retrieval of the primary image directed parallel to the direction of
acoustic propagation, further, the inhomogeneity causing a disturbance is
directly accessible for observation, so that more detailed
characterization is possible.
The three-dimensional illustration according to FIG. 6 shows the
ultrasound-reflective plate 6 given the presence of a malignant tumor in
the subject to be examined. The irregular nature of the contour of the
region of the plate 6 displayed distorted can be clearly recognized. It
can thus be seen with reference to the nature of the edge contour that
there is a high probability of a malignancy being present. Further, a
spatially limited region of the body part under examination wherein the
malignancy can be expected with high probability can be identified by the
projection of the region displayed distorted in the direction of the upper
wave-transmissive element.
Given the fundamental structure of an evaluation means for the inventive
method shown in the form of a block circuit diagram in FIG. 7, the
ultrasound echoes S.sub.1 picked up by an ultrasound reception unit 40 are
written into a memory 42 as digitized amplitude signals, for example, into
shift registers for the acceptance of the digitized signals. (A further
reception unit 41 serves the purpose of receiving another spatially
correlated, imaging signal derived from the organ under examination that
shall be set forth in greater detail below.) The signal present in the
shift register constitutes the digitized amplitude values of the received
echo, with reception being started after an output signal of a time delay
unit 44 activated by a timer 45 that defines the point in time of emission
of the ultrasound signals was activated. The returning signal is thus
retained in the memory 42 in response to every ultrasound signal pulse
that is emitted, whereby the digitized representation in x-direction
(penetration depth) corresponds to that of FIGS. 4 and 5.
The sound reception unit 40 is positioned in different positions with
reference to the organ under examination, such as with an apparatus for
line-by-line linear shift in the y-direction (see FIG. 3) that is
preferably automated. A line-by-line scanning for slice-by-slice
presentation of the organ to be examined or the body part to be examined
is thus possible. In a modification of the invention (not shown here), the
line-by-line scanning can also ensue by simultaneous pick-up of a
respective, entire line with a corresponding array of ultrasound
transmitters/receivers.
The exemplary embodiment shown in FIG. 7 represents the evaluation circuit
for the signals successively registered within a spatial plane, i.e. for a
two-dimensional region. An ultrasound transmitter/receiver that emits
signals for an entire slice is required for a simultaneous two-dimensional
acquisition, whereas such an arrangement would have to be correspondingly
multiplied for every further slice to be acquired given a
three-dimensional acquisition. This leads to a planar-like array
arrangement for the ultrasound transmitters/receivers.
Since, as a consequence of a scanning of the signals registered without
mechanical motion, however, the further-processing thereof is ultimately
again successively undertaken, the operating mode in the acquisition of
the individual, geometric planes is the same, so that processing
conforming to the following description ensues.
Upward transgressions of a predetermined threshold in the echo signal that
are received and retained in digitized form in the shift register 42 and
those that exceed the amplitudes of echoes of body tissue and form echoes
of the highly reflective plate are retained with a threshold detector 46.
This value is written into an average value or reference value memory 47
wherein the chronological averages of the amplitudes and/or echo delays,
or the delay times of the majority of the registered echo delay times of
the pulses exceeding the threshold are written. In another version of the
illustrated exemplary embodiment, the reference value can alternatively be
a permanently prescribed value that is obtained on the basis of empirical
values or values that were calculated from the known geometry of the
arrangement.
In a further processing stage 48, the difference of t | | |
