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REFERENCES TO COPENDING APPLICATIONS
This application contains matter disclosed and claimed in the following
copending applications filed on even date with the present application:
ULTRASOUND SCANNING SYSTEM FOR SKELETAL IMAGING, Ser. No. 415,042, by Paul
D. Sorenson, Dale A. Dickson, Larry A. McNichols, and John D. Badzinski;
ULTRASOUND SCANNER WITH MAPPED DATA STORAGE, Ser. No. 415,044, by Paul D.
Sorenson and John D. Badzinski;
SYSTEM WITH SEMI-INDEPENDENT TRANSDUCER ARRAY, Ser. No. 414,704, by Paul D.
Sorenson and Dale A. Dickson; and
ULTRASOUND IMAGING SYSTEM, Ser. No. 415,043, by Paul D. Sorenson and Larry
A. McNichols.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention in general relates to the field of ultrasound imaging, and
more particularly concerns a system and method for ultrasound imaging of
structures of the human back, such as the spinal column and ribs, which
lends itself to the diagnosis of scoliosis.
2. Description of the Prior Art
Scoliosis is a disease resulting in the deformity of the spine. The
disorder, which is a significant worldwide health problem, is
characterized by both lateral curvature and rotation of the vertebrae. The
cause of idiopathic scoliosis, which is the most common class of
scoliosis, is unknown, but the symptoms generally appear during the
developmental years. Failure to effectively treat the disorder in those
cases where the curvature progressively grows worse leads to deformity of
the torso and potentially, cardiopulmonary distress. Patients are often
treated by orthopedic surgeons during the adolescent years of childhood by
one or more methods which include external orthotic bracing, spinal fusion
surgery, and electrical stimulation (internal and/or external) of the
paraspinal muscles.
Presently, the most widely used clinical method employed to diagnose,
assess, and track the course of the disease is standard X-ray imaging.
Since there are no reliable methods yet available to predict the rate of
progression of the disease, the patient is examined on a regular basis.
Typically, a child will be subjected to a large number of X-rays over the
course of the disease regardless of the treatment modality implemented. In
many cases, no treatment is warranted, but the child is X-rayed
periodically to verify that the curve has not progressed significantly. It
therefore becomes highly desirable to develop a technique of detecting and
monitoring scoliosis which will minimize or eliminate X-ray exposure. In
recent years, great emphasis has been placed on the need to develop
effective, safe methods of screening children in public schools.
Aside from the issue of safety, the X-ray instrumentation currently used
does not lend itself optimally to the rapid assessment of scoliosis. For
example, just the right contrast must be obtained and then the equipment
must be run by a radiological specialist. Further, the orthopedic surgeon
must ponder the X-ray and then perform certain geometric operations on the
image in order to extract quantitative information regarding the nature of
the spinal curvature. Another parameter which is becoming increasingly
important to measure is the amount of vertebral rotation which accompanies
the lateral curvature of the spine. This is presently difficult to
accurately assess using X-ray.
Not many alternative means to X-ray for assessing scoliosis appear in the
literature. One method currently under limited evaluation is called the
Moire technique. This is an optical photographic technique which detects
bilateral nonsymmetry in the surface features of the back. The method
employs the principle of interference fringes. The patient's back is
photographed through an interference screen or defraction grating. This
results in a set of contour-line shadows on the photograph which is
indicative of the surface topology of the back. The main shortcomings of
this system are two-fold. First, there are no established scientific
correlative studies relating visual surface features to spinal curvature.
Secondly, the device is primarily aimed at screening rather than the
quantitative assessment of the magnitude of the spinal curvature. Thus a
system and method with which spinal curvature could be directly measured
which can be repeatedly used without damage to a child or other person
would be highly desirable.
The present invention employs an ultrasound imaging system for scanning the
back. A wide variety of ultrasound imaging systems for medical purposes
have been developed although none of them known to me appear to be
appropriate for scanning the back. U.S. Pat. Nos. 4,271,842 and 4,272,991
disclose typical ultrasound scanners in the prior art.
SUMMARY OF THE INVENTION
It is an object of the invention to provide apparatus for imaging of
skeletal structure that overcomes the disadvantages of the above prior
art.
It is another object of the invention to provide an ultrasound scanning
system including a means for scanning ultrasound transducers along the
back while providing a signal representative of the transducers' position
along the back.
It is a further object of the invention to provide an ultrasound system
which is particularly well-suited for imaging of the spinal column and the
rib structure adjacent the spinal column.
It is an additional object of the invention to provide an ultrasound
imaging system which provides one or more of the above objects in a system
that can provide a diagnostic image in a single scan.
It is a further object of the invention to provide an ultrasound imaging
system that provides one or more of the above objects in a system that
provides data quickly so that it is utilizable in real time by the
physician.
It is another object of the invention to provide a skeletal imaging system
that is safe and economical so that it can be utilized in regular periodic
treatment of children and other persons.
It is again a further object of the invention to provide an ultrasound
imaging system that provides skeletal representations that are accurate
and are easily correlated with established scientific norms.
The invention provides an ultrasound imaging system for scanning the human
back. There is at least one ultrasound transducer for generating an
ultrasound signal, for receiving an ultrasound signal, and for producing
an electrical signal representative of the received ultrasound signal and
a means for supporting the transducer and moving it along the human back.
There is a means responsive to the electrical signal for producing a range
signal representative of the distance from the transducer of objects
interacting with the ultrasound signal, and a means for producing a
position signal representative of the transducer position along the back.
There is a means responsive to the range signal, and the position signal
for producing an output signal representative of the structure of the
body.
Preferably, the means for producing a position signal includes a means for
referencing the position of the means for supporting the transducer to at
least one reference point on the back and a means for producing a position
signal representative of the position of the transducer in the means for
supporting.
Preferably there is a plurality of transducers and the means for supporting
and moving the transducers comprises a means for moving the transducers
along lines parallel to the line connecting the spinal cervix and sacrum
of the patient.
Numerous other features, objects and advantages of the invention which will
become apparent from the following detailed description when read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing
FIG. 1 shows an imaging system according to the invention with the
transducer transport portion of the system in position to image a portion
of a patient's ribs and spinal column;
FIG. 2 shows a perspective view of the transducer transport system of FIG.
1;
FIG. 3 shows a front view of the transport system of FIG. 2;
FIG. 4 shows a cross-sectional view of the transport system taken through
line 4--4 of FIG. 3;
FIG. 5a shows a cross section of the scanner head taken through line 5a--5a
of FIG. 3 and showing the transducers pressed against a section of the
patient's back;
FIG. 5b is a cross-sectional side view of an alternative embodiment of the
scanner head showing a linear position transducer;
FIG. 6a shows a side view of an alternative embodiment of a portion of a
transducer transport system according to the invention;
FIG. 6b shows a top view of the portion of the transport system of FIG. 6a;
FIG. 7 shows a block diagram of the preferred embodiment of the ultrasound
imaging system according to the invention;
FIG. 8a shows the motor control circuit utilized in the embodiment of FIG.
7;
FIG. 8b shows the electronic circuit of the A/D converter for scanner head
position utilized in the embodiment of FIG. 7;
FIG. 8c shows the electronic circuitry for the transducer drivers and
receivers including the 1 of 16 selector, the received signal multiplexer
and the linear preamp utilized in the embodiment of FIG. 7;
FIG. 8d shows the arrangement of FIGS. 8d.1 and 8d.2 which in turn show the
electronic circuitry for the non-linear time-gain amplifier, including the
echo discriminator (rf detector and comparator), utilized in FIG. 7;
FIG. 8e shows the electronic circuitry for a range counter utilized in the
embodiment of FIG. 7;
FIG. 8f shows the electronic circuitry for a second range counter utilized
in the embodiment of FIG. 7;
FIG. 8g (located after FIG. 6) shows the arrangement of FIGS. 8g.1 and 8g.2
which, in turn, show the electronic circuitry for the high-speed A/D
converter and memory buffer system utilized in the embodiment of FIG. 7;
FIG. 8h (located after FIG. 8g on the same sheet of drawings as FIG. 6)
shows the arrangement of FIGS. 8h.1 and 8h.2 which, in turn, show the
electronic circuitry for the control logic for data expansion which is
part of the high-speed A/D converter and memory buffer system utilized in
the embodiment of FIG. 7;
FIG. 8i shows the block diagram for the microprocessor system utilized in
the embodiment of FIG. 7; and
FIG. 9 shows a flow diagram for the preferred embodiment of the method
according to the invention indicating the progression of scanner startup,
data acquisition and data processing.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An exemplary embodiment of the preferred ultrasound imaging system,
according to the invention, for scanning of the human back is shown in
FIG. 1. The system includes several major subsystems, including a scanner
head 10, a transport system 30 for orienting and moving the scanner head
in a particular fashion, a microprocessor-based control and display
console 60, and keyboard terminal 80. The scanner head 10 provides a means
for acoustically coupling low-intensity ultrasound energy to the back of
the patient 11. The transport system 30 moves scanner head 10 in a
straight line between two anatomical landmarks--cervical reference means
31 and sacral reference means 32. Control for the scanning process, data
processing, record storage, and output of results is provided by
microprocessor-based system counsole unit 60 which iC which, in turn,
communicates with a Shugart SA-400 mini-floppy drive 75D, available from
Harold E. Shugart Company, Inc., 1415 Gardena Avenue, Glendale, CA 91204.
The display system includes three Matrox MSBC-512 graphic display boards,
such as 84A, a Matrox MSBC-2480 alpha display board, 84B, an Axiom EX-850
printer 84C, and a Ball TV-120 display 84D. The Matrox display boards can
be provides a means of inputing scanner control commands as well as
pertinent patient information.
In order to clearly illustrate the invention, the description will contain
three parts. First, a brief description of the mechanics of ultrasound
will be presented. Second, a detailed description of the structure and
electronic circuitry of the preferred embodiment will be given. Finally, a
description of the operation of the invention including the principle
features of the invention will be given.
ULTRASOUND MECHANICS
If a mechanical sound wave in an ultrasonic frequency range (typically 1
MHz to 10 MHz) is generated and acoustically coupled to biological tissue,
the wave will propagate through the tissue at a velocity determined by the
physical properties of the tissue. Reflections or "echoes" will occur
whenever the velocity of propagation of the sound wave is altered.
Interfaces between different tissue types within the overall biological
media, in general, present a change in propagation velocity and hence a
portion of the incident energy is reflected. The magnitude of an echo is
proportional to the magnitude of the incident energy and the change in
velocity at the interface. For example, when ultrasonic energy traveling
at 1580 m/s through a layer of muscle tissue encounters bone, the velocity
of propagation is increased to 4800 m/s and about 40% of the energy
incident on the bone will be reflected in the form of an echo.
Low power (typically less than 100 mW/cm.sup.2 average) ultrasound may be
easily generated by the application of a short pulse of voltage (200 V for
1 .mu.s typical) to an appropriately constructed piezoelectrical crystal
such as 12 (FIG. 5a). Momentary deformation of the crystal 12 ensues and
it vibrates for a short period of time at its natural resonant frequency
(2.25 MHz for the present embodiment). Consequently, a low intensity
mechanical pressure wave or sound wave is set up in the media 11 to which
the element is coupled.
Conversely, the presence of an incoming ultrasonic wave front in the form
of an echo may be detected because the resulting pressure on the crystal
12 produces a voltage across the crystal 12. Such crystals 12 are called
ultrasound transducers and the same transducer is typically employed to
both transmit and receive pulses of ultrasonic energy.
By aiming the transducer 12 at a target in a particular direction within a
defined coordinate system and measuring the time elapsed between the
transmission of a sound wave and the reception of an echo from the target
it is possible to calculate the distance or range to the target, and
subsequently to locate the position of the target within the coordinate
system. Further, it is possible to determine certain features of the
target (for example surface texture) by analyzing the resulting echo
waveform.
In the prior art, medical ultrasound has been employed to examine internal
soft tissue organ structures. Frequently, a "target" structure is treated
as a composite of many individual target components. The present
disclosure will disclose how the above principles of ultrasound may be
applied under the management of a microprocessing system to perform a
specific type of scan of the human back.
STRUCTURAL AND ELECTRICAL DESCRIPTION
We now proceed to the detailed structural description of the apparatus
according to the invention. A perspective view of the scanner 10 and the
transport system 30 for moving the scanner head 10 is shown in FIG. 2. A
frontal view of the same system is shown in FIG. 3 and a cross section
taken through lines 4--4 of FIG. 3 is shown in FIG. 4. FIG. 5a shows a
cross section of the scanner head taken through lines 5A--5A of FIG. 3.
The transducer shoes 14 of FIG. 3 are omitted in FIG. 5a for clarity. All
these figures will be discussed together.
Together the scanner head 10 and the transport system 30 provide a means
for supporting and moving the transducer 12 along the back. In the
embodiment shown there are sixteen transducers such as 12. Each
transducer, such as 12, is embedded in a transducer shoe, such as 14,
which is attached to the end of a movable plunger, such as 15. The scanner
head 10 comprises scanner body 16 having sixteen cylindrical bores, such
as 13. Each of the bores 13 is of a diameter just slightly larger than the
plungers such as 15, and each of the plungers 15 slide within one of the
bores such as 13. Within each of the bores, such as 13, there is a spring
such as 17, one end of which seats against the bottom 13A of its
respective bore 13 and the other end of which seats against the end 15B of
plunger 15 opposite transducer 12. A wire, such as 18, is electrically
connected to each of the transducers, such as 12, and extends through the
plunger 15 and bore 13 through scanner body 16 into scanner electrical box
19 where they are connected into the transducer electronics (see below)
and ultimately to flexible electrical cable 61.
Scanner transport system 30 includes a frame top plate 31 and a frame base
plate 32 separated and connected by a pair of scanner head rails 33A and
33B. Rails 33A and 33B pass through a cylindrical bore within scanner head
blocks 34A and 34B respectively. The bore of blocks 34A and 34B is just
slightly larger than the diameter of rails 33A and 33B respectively so
that blocks 34A and 34B slide easily on their respective rails. Scanner
body 16 is secured to the inner side of blocks 34A and 34B so that the
whole scanner head 10 moves as a unit on rails 33A and 33B. The major
portions of the drive system 40 for the scanner head 10 is mounted on top
plate 31. Drive means 40 includes motor 41 which drives a worm and wheel
gear (42 and 43 respectively). Wheel 43 is supported by and locked to axle
44 which is, in turn, supported on frame 46 and turns in bushings 46A and
46B (not shown) in frame 46. Frame 46 is mounted on plate 31 to support
the drive system. Groved drums 47A and 47B are connected to either end of
axle 44 and turn with the axle 44. A pair of cables 48A and 48B seat in
the grooves of drums 47A and 47B respectively, pass through holes 35A and
35B respectively in top plate 31 and are fastened to pins 36A and 36B set
in blocks 34A and 34B respectively. The other end of cables 48A and 48B
pass over guide pulleys 49A and 49B mounted in slots 37A and 37B in plate
31, then pass under pulleys 38A and 38B mounted on the base plate 32 and
return upward to fasten to pins 39A and 39B secured to blocks 34A and 34B
respectively.
FIGS. 6a and 6b show an alternative embodiment of the transport system
which may be used if it is desired that the transducer remains tangent to
the curvature of the surface of the back. We have found experimentally
that this is often advantageous in maximizing the reflected energy
received and thus maximizing the signal strength from the transducers. In
FIGS. 6a and 6b the motor and other elements for moving the head are not
shown for clarity and as these aspects would be similar to those shown in
FIGS. 1 through 4. This embodiment includes a scanner head 9 having a
rotational degree of freedom which permits the transducer element 149 to
be tangent to the surface of back 11. Scanner head 9 includes blocks 144A
and 144B which slide on rails 140A and 140B as described above. Probes
141A and 141B are attached to brackets on the lower and upper ends of
rails 140A and 140B also as described earlier. Blocks 144A and 144B are
connected to scanner body brackets 144C and 144D respectively by pivot
pins 145A and 145B respectively. Scanner body brackets 144C and 144D are
C-shaped brackets which fit about the sides of scanner body 142C holding
it securely in both the vertical direction and the direction into the
plane of the drawing (FIG. 6a), but permitting it to slide in the
horizontal direction of the drawing. Y-brackets 142A and 142B are secured
(by screws not shown) to scanner body 142C. Rollers 146A and 146B are
attached to the ends of the "Y" of brackets 142A and 142B by axles 146C
and 146D respectively. Axles 146C and 146D fit within a bore of rollers
146A and 146B so that the rollers may rotate freely on the axles. Plungers
147A and 147B slide within bores in scanner body brackets 144C and 144D
respectively and seat between Y-brackets 142A and 142B and springs 147D
and 147C respectively within the bores. Transducer plungers such as 143
are spring-loaded (springs not shown), ride in bores in scanner body 142C,
and have transducer shoes, such as 148 holding transducer elements, such
as 149, mounted on the distal ends of the plungers as in the embodiments
described with reference to FIGS. 2 through 5.
The apparatus described in the preceding three paragraphs comprises a means
for moving the transducers over a field so as to define a plane. The field
is the whole 3-dimensional space moved through by the transducers 12, 149
as they traverse the back while the plane may be any generalized plane
defined by the movement of the transducers such as 12 or 149. The plane is
generalized in the sense that it may or may not be a flat plane; that is,
it may either be the actual "plane" through which the transducer elements
12 or 149 move, or it may be a plane which is abstracted from the space
through which they move. For example, in the embodiment of FIGS. 6a and 6b
and using the linear position transducers of FIG. 5b, the plane may be a
curved surface such as the plane of the back, or if may be a flat plane
essentially parallel to the plane in which rails 33A and 33B lie. The
invention relates to a means for storing data in an array such that the
position of the data in an array corresponds to the position of the
transducer such as 12 or 149 in this generalized plane when the data is
produced.
Position transducer 50 is mounted on top plate 31 and is driven by
transducer drive belt 52 which rotates about position transducer drive
pulley 53 which is secured to axle 44 and pulley 54 which is fastened to
the drive shaft of position transducer 50. The position transducer 50 is a
potentiometer connected nominally across 0 to 12 volts d.c. (typical
operating range 2-8 volts d.c.). As pulley 59 turns, a wiper within the
potentiometer 50 moves and produces a voltage proportional to the distance
which the scanner head 10 has moved. Wires 55 which carry the output
signal of position transducer 50 and wires 56 which carry the input
current to motor 41 form flexible electrical cable 62 (FIG. 1).
Located on the transducer support system 30 are means 57 for referencing
the ultrasonic transducer position to a cervical reference point and a
means 58 for referencing the ultrasonic transducer position to a sacral
reference point. Each of these reference means includes a bracket such as
59A which supports a push rod, such as 59B which is mounted in a hole
through bracket 59A. A spring 59C seats between one side of bracket 59A
and a cap 59D mounted on the end of push rod 59C. Together the reference
means such as 57, scanner head 10, the cables such as 48A, drums 47A, axle
44, drive pulley 53, drivebelt 52 and position transducer 50 provide a
means for producing a position signal representative of the position of
transducer 12 along the back.
FIG. 5b is a cross-sectional side view of an alternative embodiment of the
scanner head. In the figure the transducer sleeve is again not shown. This
embodiment includes a linear position transducer 20 which produces a
signal proportional to the position of plunger 21. Linear position
transducer 20 includes a contact 22 secured on the bottom side of plunger
21 and extending a small distance beyond the side of the plunger 21, and a
resistance element 23 embedded in scanner body 24A with its surface
exposed along a section of bore 24B so that contact 22 moves along
resistance element 22 as plunger 21 moves in bore 24B. Wire 25A is
attached to contact 22 and wire 25B is attached to one end of resistance
element 23 and both wires 25A and 25B are input to an A/D converter 26 to
complete a circuit through resistance element 23. The voltage through the
linear transducer circuit 20 is proportional to the position of contact 22
on resistance element 23 and thus is a measure of the position of plunger
21 and ultimately of the position of transducer 28. The A/D converter
translates the voltage to a digital signal in a manner similar to that
described below with reference to FIG. 8b. The digital signal is input to
the central console 27 for use as will be discussed below.
Note that wires 18 (in FIG. 5a) and 24A (in FIG. 5b) are shown straight
only for clarity. In actuality they are coiled in the bore so that they
may extend and contract as plungers 15 and 21 move.
FIG. 7 shows a block diagram of the electronic system utilized in the
embodiment of the invention shown in FIG. 1. The electronics included in
scanner head 10 is enclosed in the dashed rectangle. In this diagram the
transducers are indicated as T.sub.0,T.sub.1,T.sub.2 . . . T.sub.I . . .
T.sub.N-2,T.sub.N-1 for purposes of the generalized discussion below. In
the preferred embodiment there are sixteen such transducers and thus, N is
equal to 16. The transducer driver and receiver circuitry 71 delivers
signals to and receives signals from the ultrasonic transducers 70. One of
sixteen selector circuitry 72 receives signals from the microprocessor
system 75 and in turn, applies signals to the transducer drivers and
receiver circuitry 71. Received signal multiplexer 73 receives the signals
derived from the reflected ultrasonic waves from the transducer driver and
receiver circuitry 71. A signal from the microprocessor system 75 is
applied to received signal multiplexer 73 to inform it which signal should
be recognized. The signals recognized by the received signal multiplexer
73 are passed to the linear preamp 74 and, after amplification, proceed on
to the nonlinear time-gain amplifier 76. The doubleline 77 indicates a
mechanical linkage between the motorized mechanical transport system 78
and the ultrasonic transducers 70. As discussed above, there is also a
mechanical linkage between motorized mechanical transport system 78 and
position transducer 79. The signal from position transducer 79 is applied
to position A/D converter 81 and the digital output from the position A/D
converter is applied to the microprocessor system 75. The microprocessor
system 75 applies a clock signal and a start signal to range counters 82.
The output of the nonlinear time gain amplifier 76 is applied to echo
discriminator 83 and when an echo is detected a signal is applied to the
stop input 83C of range counters 82. The signal from the range counters is
applied to the microprocessor system 75. In this embodiment the
microprocessor 75, the range counters 82, and the echo discriminator 83
together comprise a means for providing a range signal representative of
the distance of objects interacting with the ultrasound signal. The
microprocessor system 75 provides an output to the display system 84.
High-speed A/D converter and memory buffer system 85 is an optional part
of the system which will be discussed below. This system 85 receives
signals from nonlinear time-gain amplifier 76 and microprocessor system
75; these signals are indicated by dotted lines to indicate they are
optional. The signal from high-speed A/D converter and memory buffer
system 85 is applied to microprocessor system 75.
FIGS. 8a through 8h show details of the circuitry of each of the portions
of the circuitry shown in FIG. 7. With the exception of the time-gain
amplifiers, the particular elements of the subcircuits are for the most
part conventional and those skilled in the art will be able to develop
such circuits and alternatives to such circuits from the description given
and standard electronic literature. However, the various parts used and
sources for those parts will be presented in order to fully elucidate the
construction of the invention.
The motor control circuitry is shown in FIG. 8a. In this figure, and the
subsequent figures showing electronic circuitry, standard electronic
symbols for the various circuit elements are used. Each of these elements
will be pointed out in the first figure in which they are encountered. In
FIG. 8a, a resistor is shown at 78A, with the value of the resistor given
in ohms alongside the resistor. A transistor is shown at 78B, with the
standard trade designation for the transistor type given alongside the
transistor (MJ4032 for transistor 78B). A capacitor is shown at 78C with
the value of the capacitance, 0.01 .mu.f, given next to the capacitor. A
field effect transistor (FET) is shown at 78D, with the standard trade
designation of the FET type, 2N6660 given next to the FET. The symbol at
78E, shaped like the tail of an arrow, indicates a connector. The number
next to the connector symbol, such as J1-30 at 78E, indicates where the
connection is to be made. For example, the J1-24 at 72B in FIG. 8c is
connected to the J1-24 connection at 76A in FIG. 8d. Furthermore, | | |
