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Claims  |
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We claim:
1. Apparatus for investigating the mechanical properties of a solid
material, including:
means for positioning the apparatus in proximity to a surface of a solid
material;
at least one emitting ultrasound transducer positioned for emitting an
ultrasound wave towards a surface of the material;
at least one receiving ultrasound transducer positioned for receiving an
ultrasound wave that has been emitted and has contacted the surface of the
material;
means for varying the angle of incidence of the emitted ultrasound wave
towards the surface of the material;
means responsive to the received ultrasound wave for determining the
alignment of the surface of the material with respect to the emitting and
receiving ultrasound transducers; and
signal analyzer means coupled to the at least one receiving ultrasound
transducer for determining at least one characteristic of the received
ultrasound wave which is indicative of a mechanical property of the
material.
2. The apparatus of claim 1, further comprising means for varying the
emitting plane which is defined by the emitted ultrasound wave and the
normal to the surface of the material at the location where the ultrasound
wave has contacted the surface of the material.
3. The apparatus of claim 2, where the means for varying the emitting plane
include a stepper mechanism coupled to the transducers, which stepper
mechanism comprises means for moving and positioning the transducers in
relation to the material.
4. The apparatus of claim 1, where the at least one receiving ultrasound
transducer is positioned to receive an ultrasound wave that has been
reflected from the surface of the material.
5. The apparatus of claim 4, where the signal analyzer means is operable to
determine the amplitude of the reflected ultrasound wave as a function of
the angle of incidence.
6. The apparatus of claim 5, where the signal analyzer means comprises
means for determining at least one edge in which the amplitude of the
reflected ultrasound wave decreases rapidly as a function of the angle of
incidence between two regions of slower variability.
7. The apparatus of claim 4, where the signal analyzer means comprises
means for determining the phase of the reflected ultrasound wave as a
function of angle of incidence.
8. The apparatus of claim 7, where the signal analyzer means is also
operable to determine at least one angle of incidence at which the phase
of the reflected ultrasound wave first appreciably deviates from zero as
that angle increases from 0.degree..
9. The apparatus of claim 1, where the at least one receiving ultrasound
transducer is positioned to receive an ultrasound wave that has been
transmitted through the material.
10. The apparatus of claim 9, where the signal analyzer means comprises
means for determining the amplitude of the transmitted ultrasound wave as
a function of the angle of incidence.
11. The apparatus of claim 10, where the signal analyzer means comprises
means for determining maxima and minima in the amplitude of the
transmitted ultrasound wave as a function of the angle of incidence.
12. The apparatus of claim 1, where the signal analyzer means comprises
means for determining at least one characteristic of the received
ultrasound wave selected from the group consisting of amplitude and phase.
13. The apparatus of claim 1, where the means for varying the angle of
incidence include a stepper mechanism coupled to the transducers, which
stepper mechanism comprises means for moving and positioning the
transducers in relation to the material.
14. The apparatus of claim 1, where the apparatus includes an array of
transducers, said array comprising the at least one emitting ultrasound
transducer and the at least one receiving ultrasound transducer.
15. The apparatus of claim 14, where the array of transducers is in the
form of a semicircular array.
16. The apparatus of claim 14, where the array of transducers is in the
form of a hemispherical array.
17. The apparatus of claim 14, where the means for varying the angle of
incidence include a switching circuit for selectably operating at least
one transducer in the array as an emitting transducer.
18. The apparatus of claim 14, where the means for varying the angle of
incidence include a switching circuit for selectably operating at least
one transducer in the array as a receiving transducer.
19. The apparatus of claim 1, where the material is bone.
20. The apparatus of claim 19, where the signal analyzer means comprises
means for approximating the velocity of a pressure wave in the bone based
on a first critical angle corresponding to a first maxima in amplitude
encountered as the angle of incidence increases in the range of
0.degree.-90.degree..
21. The apparatus of claim 20, where the signal analyzer means comprises
means for approximating the velocity of a shear wave in the bone based on
a second critical angle corresponding either to a second maxima in
amplitude followed by a deep minimum or to an inflection point in
amplitude following a deep minimum and encountered after the first maxima
as the angle of incidence increases in the range of 0.degree.-90.degree..
22. The apparatus of claim 19, where the apparatus includes a liquid-filled
bag which has at least one surface that is flexible and which can be
positioned on the surface of a patient's body in proximity to a bone, and
where the ultrasound transducers are in acoustic contact with the liquid
in the bag.
23. Apparatus for investigating the mechanical properties of bone,
including:
a liquid-filled bag which has at least one surface that is flexible;
an array of ultrasound transducers which are in acoustic contact with the
liquid in the bag, and which include switching means for selectably
operating at least one transducer in the array as an emitting ultrasound
transducer positioned for transmitting an ultrasound wave towards a
surface of the bone, and for selectably operating at least one ultrasound
transducer in the array as a receiving ultrasound transducer positioned
for receiving ultrasound waves reflected by the surface of the bone;
means for varying the angle of incidence of the emitted ultrasound wave
towards the surface of the bone;
means for varying the emitting plane which is defined by the emitted
ultrasound wave and the normal to the surface of the bone; and
signal analyzer means coupled to the array of ultrasound transducers, which
receive the reflected ultrasound wave and are operable to determine at
least one characteristic of the reflected ultrasound wave as a function of
the angle of incidence, and from that to estimate the strength of the
bone.
24. The apparatus of claim 23, where the signal analyzer means comprises
means for determining the phase of the reflected ultrasound wave as a
function of the angle of incidence.
25. A method of investigating the mechanical properties of a material,
including the steps of:
a. emitting an ultrasound wave to impinge a surface of a material at an
angle of incidence;
b. receiving the ultrasound wave after it has contacted the material;
c. determining the normal to the surface of the material by analyzing the
received ultrasound waves generated when the emitted ultrasound wave
impinges the material from each of a plurality of varying directions; and
d. determining a characteristic of the received ultrasound wave at each of
a plurality of varying angles of incidence in the range of
0.degree.-90.degree., and in a plurality of varying emitting planes
defined by the emitted ultrasound wave and the normal to the surface of
the material, and using that characteristic to estimate a mechanical
property of the material.
26. The method of claim 25, where the characteristic in step d is selected
from the group consisting of amplitude and phase of the received
ultrasound wave.
27. The method of claim 25, where the ultrasound wave is received after
reflecting from the surface of the material.
28. The method of claim 27, where step d includes determining the amplitude
of the reflected ultrasound wave as a function of the angle of incidence.
29. The method of claim 28, where step d also includes determining at least
one edge in which the amplitude of the reflected ultrasound wave decreases
rapidly as a function of the angle of incidence between two regions of
slower variability.
30. The method of claim 27, where step d includes determining the phase of
the reflected ultrasound wave as a function of angle of incidence.
31. The method of claim 30, where step d also includes determining at least
one angle of incidence at which the phase of the reflected ultrasound wave
first appreciable deviates from zero as the angle is increased from
0.degree..
32. The method of claim 25, where the ultrasound wave is received after
being transmitted through the material.
33. The method of claim 32, where step d includes determining the amplitude
of the transmitted ultrasound wave as a function of the angle of
incidence, and determining maxima and minima in the amplitude.
34. The method of claim 25, where the material is bone.
35. The method of claim 34, where step d includes approximating the
velocity of a pressure wave in the bone based on a first critical angle
corresponding to a first maxima in amplitude encountered as the angle of
incidence increases in the range of 0.degree.-90.degree..
36. The method of claim 35, where step also includes approximating the
velocity of a shear wave in the bone based on a second critical angle
corresponding either to a second maxima in amplitude followed by a deep
minimum or to an inflection point in amplitude following a deep minimum
and encountered after the first maxima as the angle of incidence increases
in the range of 0.degree.-90.degree..
37. The method of claim 36, where step d includes computing the shear wave
velocity (v.sub.s) using the relationship:
##EQU14##
where c is the velocity of the transmitted ultrasound wave (I) in the
medium adjacent the bone and .phi..sub.2 is the angle of incidence at the
second critical angle.
38. The method of claim 35, where step d includes computing the pressure
wave velocity (v.sub.p) using the relationship:
##EQU15##
where c is the velocity of the transmitted ultrasound wave in the medium
adjacent the bone and .phi..sub.1 is the angle of incidence at the first
critical angle. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for determining the
mechanical properties of a material, such as bone.
A number of situations arise where it is important to assess the mechanical
properties of a material without destroying or damaging the material. In
some cases, this can be done using simplified techniques as a result of
the homogeneity of the material. However, in other cases, the material is
not homogenous and therefore simplified techniques do not give accurate
results.
For instance, in medical applications, it is frequently desirable to
determine the mechanical properties of a material such as bone, but
destructive tests of course cannot be used in a living patient. Further,
invasive tests are undesirable, and the bone is nonhomogeneous and
nonisotropic. These complications present a particular problem in the case
of patients suffering from osteoporosis, who are more susceptible to
fractures as a result of decreased bone strength. Standard radiographic
properties of bone, such as bone mineral density, do not correlate well
with bone strength, and therefore are of relatively little use in
diagnosing osteoporosis or evaluating the results of treatment for that
condition.
Although some treatments for osteoporosis are available that can increase
the strength of a patient's bones, the utility of those treatments would
be enhanced by a noninvasive method of assessing their effect on the
patient's bones. In the past, various methods have been investigated for
this purpose, but have failed to solve the problem. For example,
radiologic methods such as quantitative computed tomography, single or
dual photon absorptiometry, and dual energy X-ray absorptiometry measure
the amount and distribution of minerals in bone, but do not directly
assess its mechanical qualities. These problems of the prior art are
minimized or solved by the method and apparatus of the present invention.
SUMMARY OF THE INVENTION
The present invention relates to apparatus for investigating the mechanical
properties of a solid material, such as bone. The apparatus can include
means for positioning the apparatus in proximity to a surface of a solid
material, at least one emitting ultrasound transducer positioned for
emitting an ultrasound wave towards the surface of the material, at least
one receiving ultrasound transducer positioned for receiving ultrasound
waves that have been emitted and have contacted the surface of the
material, means for varying the angle of incidence of the emitted
ultrasound wave towards the surface of the material, means responsive to
the received ultrasound wave for determining the alignment of the surface
of the material with respect to the emitting and receiving ultrasound
transducers, and signal analyzer means coupled to the receiving ultrasound
transducer for determining at least one characteristic of the received
ultrasound wave which is indicative of a mechanical property of the
material.
"Emitting" and "receiving" are intended to cover both embodiments in which
the ultrasound wave is reflected from the material, and embodiments in
which the ultrasound is transmitted through the material. In either case,
the receiving ultrasound transducer receives the wave after it has
contacted the material (i.e., reflected from the material or transmitted
through it).
The apparatus preferably also includes means for varying the emitting plane
which is defined by the emitted ultrasound wave and the normal to the
surface of the material. The means for varying the emitting plane, as well
as the means for varying the angle of incidence, can constitute a stepper
mechanism which is coupled to the transducers, or, if the apparatus
includes an array of transducers, can constitute a switching circuit for
selectably operating at least one transducer in the array as an emitting
transducer and at least one transducer in the array as a receiving
transducer.
The signal analyzer means is preferably operable to determine at least one
characteristic of the received ultrasound wave, selected from the group
consisting of amplitude and phase of the received ultrasound wave. With
respect to the amplitude of the received ultrasound wave, parameters such
as maxima, minima (collectively referred to as "extrema"), and edges can
be used to determine various velocities, and from that to estimate
mechanical properties of the material. With respect to phase, parameters
such as the angle of incidence at which phase first appreciably deviates
from zero can likewise be used to estimate mechanical properties of the
material.
The present invention also relates to a method of investigating the
mechanical properties of a material, such as bone. The method includes the
steps of emitting an ultrasound wave to impinge a surface of a material at
an angle of incidence, receiving ultrasound waves after they have
contacted the material, determining the normal to the surface of the
material by analyzing the received ultrasound waves generated when the
emitted ultrasound wave impinges the material from each of a plurality of
varying directions, and determining a characteristic of the received
ultrasound wave at each of a plurality of varying angles of incidence in
the range of 0.degree. to 90.degree., and in a plurality of varying
emitting planes defined by the emitted ultrasound wave and the normal to
the surface of the material, and using the characteristic to estimate a
mechanical property of the material. The characteristic of the received
ultrasound wave that is determined is preferably selected from the group
consisting of amplitude and phase. Again, the received ultrasound wave can
either be reflected from the material or transmitted through it.
The present invention provides the capability of determining the normal to
the surface of the bone, which permits the use of a rational set of
measurements to align the detectors and the bone. This is important
because the normal defines the zero angle as well as the emitting plane
(or plane of scattering), which must contain the normal and the incident
wave (I). If the plane and zero were chosen incorrectly, the measurements
obtained would be of little value as the angles would not be well
measured. No known prior art procedure has this same capability.
In determining the normal, measurements could be taken in scattering planes
some angle less than 90 degrees apart, such as 30 degrees apart; the
smaller the incremental angle, the higher the accuracy and the precision
of the method. Critical angles would be obtained for each plane. In an ex
vivo use of the present invention, the bone sample would be rotated, while
in clinical use with living patients, the applicator device (which would
include the transducers) would be rotated while the patient remains
stationary.
The advantages of the present invention are believed to be quite
significant in evaluating the results of treatment for osteoporosis.
Treatment of that condition can cause small variations in the material
properties of bone (e.g., 2-5 percent change as a consequence of treatment
over two years in representative experiments), and yet those small
variations can correlate to clinically significant improvements in the
resistance of the bone to fracture. Therefore, the present invention
provides a much more accurate and useful means of evaluating the effect of
osteoporosis treatment than any known prior art ultrasound apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the propagation patterns of the ultrasound
waves in the method of the present invention.
FIG. 2 is a schematic view of an apparatus in accordance with the present
invention.
FIG. 3 is a schematic view showing in block diagram the components of an
embodiment of the apparatus of the present invention.
FIG. 4 is a schematic view showing in block diagram an alternative
embodiment of the apparatus of the present invention.
FIG. 5 is a flow chart of the application software for the computer of
FIGS. 3 and 4, where:
FIG. 5A describes the "Distance to Bone" subroutine,
FIG. 5B describes the "Find Flat Spot" subroutine,
FIG. 5C shows the "Locate Surfaces" subroutine,
FIG. 5D illustrates the "Scan Bone" subroutine,
FIG. 5E describes the "Signal Analysis" subroutine, and
FIG. 5F illustrates the "Cross Comparison" subroutine.
FIG. 6 is a graph of the amplitude of a reflected ultrasound wave in the
method of the present invention as a function of angle of incidence of the
emitted wave.
FIG. 7 is a graph of the phase of a reflected ultrasound wave in the method
of the present invention as a function of the angle of incidence of the
emitted wave.
FIG. 8 is a simplified block diagram of the apparatus used in the tests of
Example 2.
FIG. 9 is a graph of reflected ultrasound wave amplitude vs. angle of
incidence in samples that are and are not saturated with MMA plastic.
FIG. 10 is a histogram of the distribution of ultrasound velocities in bone
biopsy specimens (A) before and (B) following two years of intermittent
slow-release fluoride therapy.
FIG. 11 is a comparison of pre- versus post-treatment ultrasound velocities
in bone biopsy specimens from 16 patients before and after two years of
intermittent slow-release fluoride therapy. Measurements for each angle of
specimen orientation are plotted. The solid line represents the line of
identity whereby points above and below the line represent negative and
positive responses respectively.
FIG. 12 is a histogram of the change in ultrasound velocity in bone biopsy
specimens following two years of intermittent slow-release fluoride
therapy.
FIG. 13 shows the mean and 95% confidence levels for ultrasound velocity in
cancellous bone in five groups of subjects.
FIG. 14 shows the mean values and standard errors of velocity (solid dots)
and vertebral bone mineral density (open dots) (BMD) in five patient
groups.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The method and apparatus of the present invention are useful in determining
the physical properties of a variety of materials. Because the present
invention relies on ultrasound waves, the only material requirements are
that the material under investigation reflect and/or transmit a
significant ultrasound component, and that the velocity of sound in it be
greater than that of the first medium (e.g. water or soft tissue).
FIGS. 1 and 2 illustrate the general critical angle of reflection method of
the present invention and are useful in understanding the specific
embodiments of FIGS. 3-5. FIG. 1 illustrates an ultrasound transducer 10
functioning as an emitter or transmitter and an ultrasound transducer 12
functioning as a receiver. An ultrasound wave (I) impinges upon a plane
separating the material under investigation 14 (such as bone) from a
separating medium 16 (such as soft tissue). For convenience, the plane
defined by the direction of propagation of the transmitted wave and the
normal to the surface of the material 14 is defined as the XY plane in
FIG. 1. The incoming or transmitted wave (I) upon arrival at the interface
of the material 14 and medium 16 (YZ plane with X=0) gives rise to a
reflected wave (R) redirected through the medium 16 to the receiving
transducer 12. For illustrative purposes, particle motion in FIG. 1 is
seen to be constrained to the XY plane, so that the transmitted wave (I)
gives rise to a pressure wave T.sub.p and shear wave T.sub.s. The angle of
refraction of the pressure wave T.sub.p is denoted as .beta., while the
angle of refraction of the shear wave T.sub.s is .gamma.. In FIG. 1, the
angle of incidence of the transmitted wave (I) is .phi., and in a
preferred embodiment the angle of reflection of the reflected wave (R) is
about equal to the angle of incidence .phi..
In an alternate embodiment, the transmitted wave (I) contacts the material
14 and is transmitted through the material, with the receiving transducer
12 located on the opposite side of the material.
The amplitudes of the displacement velocities corresponding to the pressure
wave T.sub.p and shear wave T.sub.s are determined by conservation laws,
which take into account the properties of material 14 and medium 16 as
follows:
(1) continuity of normal components of the displacement (displacements
along the normal are equal on each side of the interface);
(2) continuity of normal components of the stresses;
(3) continuity of the normal components of the intensity vector (absence of
energy absorption at the interface); and
(4) constant phase relationship between waves along the entire wave front.
Obeying such conservation laws, from FIG. 1 the angles are related by the
following condition:
##EQU1##
where c is the velocity of the transmitted wave (I) in the medium 16,
v.sub.p is the velocity of the pressure wave T.sub.p, and v.sub.s is the
velocity of the shear wave T.sub.s in the material 14.
At a certain angle of incidence .phi., T.sub.p =T.sub.s =0, and therefore
all the wave energy is reflected (reflection is a maxima, R=1). This angle
of incidence is referred to as the first critical angle .phi..sub.1, and
is useful in the method of the present invention.
A second critical angle (.phi..sub.2) occurs when the transmitted shear
wave vanishes (T.sub.s =0) and the absolute value of the reflected wave
(R) is at or near a maximum. This second critical angle is greater than
the first critical angle .phi..sub.1, but is still less than 90.degree..
At this angle, the amplitude T.sub.p represents a surface wave traveling
parallel to the surface of the medium 16. .phi..sub.2 occurs either at a
maximum (R.sub.2 positive) or at an inflection point (R.sub.2 negative).
In this latter case, .phi..sub.2 falls between a zero (minimum) and a
maximum.
Turning to FIG. 2 the schematic of an apparatus 20 in accordance with the
present invention is illustrated. Broadly speaking, the apparatus 20
includes a means for emitting or transmitting an ultrasound wave
(transducer 10) and a means for receiving the reflected ultrasound wave
(transducer 12). (In an embodiment where the system uses transmitted
ultrasound rather than reflected ultrasound waves, the receiving
transducer 12 would be positioned on the opposite side of the material 14
from the transmitting transducer 10.) A holding mechanism 22 positions the
material under examination, while the separating medium 16 is interposed
between the material 14 and transmitter and receivers 10 and 12. In FIG.
2, the material 14 under examination is a bone, while the separating
medium 16 includes water and soft tissue.
A stepping motor 24 is coupled to transmitter 10 and receiver 12
respectively, and is coupled to the holding mechanism 22 by a toothed
circular rail (not shown). The stepping motors are operable through motor
controls 30 to move the transmitter 10 and receiver 12 through an arc
about the material 14.
The signal analyzer 26 is preferably a microcomputer, which periodically
triggers the signal generator 28. Upon receiving the trigger, the signal
generator 28 generates a pulse which is amplified and passed to the
transmitter 10. The transmitter 10 upon receiving the pulse transmits the
ultrasound wave (I) through the medium 16 towards the material 14. The
receiver 12 receives the ultrasound wave (R) reflected by the material 14
(or transmitted through the material 14 in an alternate embodiment).
Preferably the transmitter 10 and receiver 12 are tuned to the same
frequency.
During examination, the transmitter 10 and receiver 12 are initially
positioned close to the normal to the material 14 (adjacent the Y axis as
shown in FIG. 1). The transmitter 10 and receiver 12 are simultaneously
stepped about the holding mechanism 22 so that the angle of incidence of
the transmitted wave (I) is equal to the angle of reflection of the
reflected wave (R). As shown in FIG. 1, this angle is denoted .phi. and
preferably increases in the range from 0.degree.-90.degree., but useful
investigations may be conducted using a more restricted range, e.g. to
include only the first critical angle. As can be appreciated from FIG. 2,
after each ultrasound transmitted wave (I), the motor controls 30
simultaneously step the transmitter 10 and receiver 12 to a new position.
Depending upon the number of measurements desired (i.e. resolution), the
transmitter 10 and receiver 12 are preferably stepped in increments of a
fraction of a degree. Thus, the receiver 12 generates a signal at each
increment which is recorded by the signal analyzer means 26 and represents
the amplitude of the reflected wave (R) for a corresponding angle .phi..
The result of this examination is a plot of reflected amplitude (ordinate)
versus the angle of incidence .phi. (abscissa).
Turning now to FIG. 3, an embodiment of the apparatus 20 of the present
invention is illustrated in more detail. In the embodiment of FIG. 3, the
transmitting transducer 10 is used as a signal transceiver, while the
receiving transducer 12 is used as a receiver only. The microcomputer 26
periodically generates a trigger signal through the timer and pulse
generator 32. The timer 32 generates a trigger to the signal generator 28
as shown in the drawing, and additionally generates a signal which is
simultaneously passed to the analog-to-digital converters 34. The signal
generator 28 generates a signal which is amplified by RF power amplifier
36, with the amplified signal passing through transmit switch 38 to the
impedance matching network 40.
As can be appreciated from FIG. 1, the ultrasonic wave pressure from the
transmitted wave (I) is reflected from the material surface 14 as
reflected wave (R) and received by the receiver 12. The receiver 12
transforms the reflected wave (R) into a return signal which is passed
through an impedance matching network 42, amplified at power amp 44, and
presented to the A to D converters 34 as a return (retarded) pulse. The A
to D converters 34 generate a digital signal which is representative of
the analog return signal from transducer 12. As can be appreciated, if the
transducer 10 is operated as a receiver, the switch 38 is toggled and the
return signal amplified by the power amp 46 and presented to the A to D
converters 34 in a similar fashion.
Digital oscilloscope 50 is used as needed and can be coupled as shown to
the various circuits to verify, quantify and test signals in these
circuits. Thus, the digital oscilloscope can monitor the amplified signal
from the power amplifier 36, the return signals from the amplifiers 44 and
46, as well as the timing pulse from the timer 32. The signals monitored
by the digital oscilloscope 50 may be graphically presented through the
IEEE-488 interface 52 on the graphic display of the computer 26. A
printer/plotter 54 is provided as an output option from the computer 26.
The stepper motor controls 30 receive inputs from the computer 26 as shown
to incrementally step the transducers 10 and 12 about the material 14. As
can be seen, the motor drivers 56 sense the input from the motor control
30 to synchronously, but independently, actuate the respective stepping
motors 24 to move the transducers 10 and 12. The transducers 10 and 12 are
preferably moved in incremental steps of fixed value and are at the
approximately identical angle of incidence .phi. for each increment.
The holding mechanism 22 is adaptable for different uses, primarily
dependent upon its size. For example, in the preferred embodiment of FIG.
3 a small, laboratory size system has been used for holding a single
sample of polished bone or other material 14 in the water medium 16. This
holding mechanism 22 has been found useful not only for experimental
verification, but also for ex vivo analysis of samples and biopsies.
Alternatively, a clinical system of the holding mechanism 22 has been
devised in which the holding mechanism 22 is sufficiently large to receive
portions of the human skeletal structure. This clinical system may be used
for in vivo or in situ analysis and diagnosis of the tendency of bone to
fracture, of bone healing, etc. Of course, different types of holding
mechanisms 22 may be devised for holding different types of materials 14
other than bone.
Turning to FIG. 4, a block diagram of an alternative embodiment is
illustrated in which the transducers are fixed and the transmission and
reception are controlled electronically rather than mechanically as
illustrated in FIG. 3. In FIG. 4, in situ analysis of a material 14 (bone)
is illustrated. A transceiver system 60 includes an applicator head 62
which is capable of three dimensional adjustment motion (as shown by the
direction arrows in FIG. 4). Although the applicator head 62 of FIG. 4 is
manually adjustable, computer adjustment control is a desirable
alternative. As can be seen, a pressurized, temperature controlled water
bag or water bolus 64 is interposed between the applicator head 62 and
patient, assuring good contact and match with the surface of the body of
the patient. The water bag 64 has at least one surface that is flexible
and can be positioned on the surface of a human body in proximity to a
bone. The ultrasound transducers are in acoustic contact with the water
bag. For example, the transducers can be immersed in the bag, or can be
external to the bag but contacting it such that the ultrasound is
conducted through the bag to or from the transducers. The applicator head
62 is positioned so that its focal point on the bone surface and its axis
is aligned with the axis of the normal to the bone surface 14 at the point
of interest as illustrated in FIG. 4.
The transceiver system 60 incorporates a circular transducer array
comprising eighty small (1/2 inch by 1/4 inch) transducers 66. As can be
appreciated, with the transceiver system 60 positioned in a desired
location adjacent the patient, the transducers 66 can be electronically
activated alternatively as transmitters or receivers as desired.
Preferably, the transducers 66 are sequentially activated one at a time as
a transmitter, or may be activated in a small group to give better
definition of sound wave as it intersects with the bone 14. After a
transducer 66 pulse, the transducers will be switched to act as receivers
for the reflected sound energy of the reflected wave (R).
Sequence and timing mechanism 70 is provided which upon receiving a trigger
signal from the computer 26 selects which transducer 66 (or group of
transducers) will be pulsed and the duration of the pulse. The timing
signal at the beginning of the pulse is also supplied to the A/D converter
section 34. The pulse generator and switcher 72 generates and amplifies
the signal which is directed through a specific lead line and switch 38
and impedance matching network 40, to a specific transducer 66 (or group
of transducers). As soon as the transmitted wave (I) is generated from the
activated transducer 66, the pulse generator and switcher 72 toggles the
switches 38 to convert the transducers 66 to receive operation. Thus, all
eighty transducers are acting as receivers for the reflected wave (R). The
return signals indicative of the reflected wave (R) will pass through the
A/D convertors 34, digitized, and presented to the computer 26 for
processing and presentation.
FIG. 5 represents the flow charts for the operating software of the
computer 26 of FIG. 3. FIG. 5 illustrates the main program or program
overview, while FIGS. 5A-5F illustrate the subroutines as indicated. As
can be seen from FIGS. 5 and 5A, the first subroutine is designed to
determine the distance from the transducer 10 (or transducer "A") to the
bone 14. This is easily accomplished using the apparatus 20 of FIG. 3, by
operating the transducer 10 alternately in the transmit and receive mode.
As can be seen from FIG. 5A, the patient or bone 14 is first manually
positioned in the holding mechanism 22 and the transducer 10 manually
positioned in a direct vertical orientation to the bone as viewed in FIG.
3. The transducer 10 is then pulsed and the echoes received with the
lapsed time determinative of the distance to the bone 14. Distance to the
bone can be calculated for each incremental increase in the angle of
incidence .phi. (transducer 10 positioned in the arc about bone 14 as in
FIG. 2 or by moving the applicator head 62 as in FIG. 4).
After the completion of subroutine 5A, the program proceeds to subroutine
"Find Flat Spot" as illustrated in FIG. 5B. The distance to the bone
calculated at various increments from the subroutine "Distance To Bone"
are graphically displayed as an image on the computer 26 and correlated to
find a relatively smooth, flat spot for evaluation. Once such a relatively
flat spot is located, patient movement is prohibited and the transducers
are positioned for evaluation of the flat spot, i.e. at a distance such
that this spot is at the center of rotation and taking the normal to the
flat spot as the axis of symmetry of transducer motion in a given plane
(direction). The direction of the plane can be varied.
The program's next step is the subroutine "Locate Surfaces" illustrated in
FIG. 5C, which is designed to locate the surfaces separating various media
(tissues) which intervene between the transducers and bone surface. The
transducer 10 is first positioned at a relatively small angle of incidence
.phi. and the transmitted signal (I) initiated (pulsed). The reflected
signal (R) is received, digitized, and stored on computer 26 before
stepping the transducer 10 in the arc about the bone 14. Note from FIG. 5C
that after the arc is completed and the digitized amplitude of the echo
return signals stored, the various patient tissues are identified. That
is, the patient surface, bone surface, and other intervening tissue
boundaries (muscle, fat) are located, attenuation and scatter coefficients
are assigned for each respective tissue, and the angle dependent
attenuation thicknesses and beam path calculated. Thus, the "Locate
Surfaces" subroutine primarily identifies the intervening tissue
boundaries so that tissue attenuation and the ray path followed by the
incident and reflected waves can be identified.
The next subroutine is illustrated in FIG. 5D and performs the "Scan Bone"
routine to generate the primary raw data. As can be seen in FIG. 5D, the
transmitted wave (I) is generated and the reflected wave (R) is received
for each increment in angle of incidence .phi.. The distance from
transducer 10 to the patient surface and bone surface is retrieved and the
time of flight calculated for both the transmitted wave (I) and reflected
wave (R). These are compared to the information obtained in the previous
routine to check for patient movements. If no movement occurred, the "Scan
Bone" subroutine then calculates bone echo amplitude corrected for
attenuation in the intervening tissues and stores the digitized echo
amplitude. The "Scan Bone" subroutine loops until the scan is complete. If
more scans at the same site but along different directions are desired,
the program loops back to "Locate Surfaces" until all desired scan
directions are completed. Once all selected scan sites and | | |
