Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-12-08
2001-11-27
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S449000
Reexamination Certificate
active
06322507
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to ultrasonic tissue imaging techniques and, in particular, it concerns a method and apparatus for the ultrasonic evaluation of bone tissue.
It is known that ultrasonography is often used for diagnostic tissue imaging in human beings. As soft or fluid filled tissues possess favorable acoustic properties, ultrasonography is able to provide excellent imagine of these tissues. The ultrasonic evaluation of bone tissue, however (for example, for estimating the degree of osteoporosis, and thus bone fracture risk) is problematic, due to the difficulty in achieving adequate ultrasound penetration in complex solid biological structures Such as bone. To date, therefore, the reliable ultrasonic imaging of bone structure and density and has not been possible.
Ultrasonic evaluation of bone tissue, as with any biological tissue, is achieved by transmitting an ultrasonic pulse or pulses into the bone tissue, and then analyzing the acoustic qualities of the received reflected ultrasonic signals. Properties of bone tissue can then be determined by analyzing the amplitude and/or travel time of the received signals. The amplitude of the received pulses, which indicates the degree of attenuation of the transmitted ultrasound signals, correlates with bone mineral density. The travel time of the signal transmitted through the bone tissue is used for calculating the velocity of the ultrasound signal within the bone tissue, the so-called “speed of sound” (SOS), which also correlates with the degree of osteoporosis and/or risk of bone fracture.
Several techniques for the ultrasonic evaluation of bone tissue are known in the art.
FIG. 1
depicts a conventional ultrasonic apparatus for evaluation of bone tissue, generally designated
10
. Ultrasonic apparatus
10
for the evaluation of bone tissue includes an ultrasonic probe
12
for transmitting ultrasonic pulses towards a bone
14
via soft tissue
16
, and for receiving signals reflected from or transmitted through, bone
14
. Ultrasonic probe
12
is typically a hand-held implement for manipulation by an operator. The operator grips ultrasonic probe
12
and applies it to soft tissue
16
. As the surface of bone
14
is inaccessible for direct coupling with ultrasonic probe
12
, the operator is required to adjust the position and apposition of ultrasonic probe
12
on soft tissue
16
, in order to optimize the transmission into, and reception from, bone
14
of ultrasound signals. When ultrasonic probe
12
is optimally oriented, the amplitude of the received signals is maximal while the time of flight is minimal.
Ultrasonic apparatus
10
for evaluation of bone tissue further includes a digital computing device
18
for analyzing the received ultrasound signal and generating an image of bone
14
from the measured amplitude and/or time delay of the received signal. Ultrasonic apparatus
10
for evaluation of bone tissue also includes a display
20
for displaying the image generated by computing device
18
.
Turning now to
FIG. 2
, a part of ultrasonic apparatus
10
is depicted, including ultrasonic probe
12
. As the internal structure of bone
14
is inhomogeneous, the ultrasound signal received by probe
12
typically has a low signal to noise ratio. As such, the through transmission technique is typically employed, in which one transducer (that is, a scanning crystal) transmits signals while a second transducer receives the signals after they have traveled through the substance under investigation.
Ultrasonic probe
12
typically includes two resonant scanning crystals
22
and
24
, which work at a fixed frequency, and which are connected to digital computing device
18
. Scanning crystal
22
is operative to transmit ultrasonic pulses toward bone
14
via soft tissue
16
, while scanning crystal
24
is operative to receive ultrasonic signals which have passed through, or been reflected by, bone
14
and soft tissue
16
. Each of scanning crystals
22
and
24
have inclined delay lines
26
and
28
respectively. In other words, the part of the transducer in front of the scanning crystal, through which the longitudinal waves generated by the scanning crystal pass prior to entering the tissue to which the transducer has been applied, is inclined at an acute angle to the surface of that tissue. The velocity of ultrasound within delay lines
26
and
28
is approximately equal to the velocity of ultrasound in soft tissue
16
. Delay line
26
typically directs scanning crystal
22
at an angle &agr; with regard to the surface of soft tissue
16
, so as to cause propagation of longitudinal leaky waves along the surface of bone
14
. Delay line
28
directs scanning crystal
24
by the same angle &agr; with regard to the surface of soft tissue
16
, so as to facilitate optimal reception of the ultrasound signal passed along bone
14
.
The net travel time for ultrasound signals that have passed through bone
14
is described by the formula:
T
14
=T
&Sgr;
−T
26
−T
28
−T
16
,
where T
14
is the net travel time for a signal passed through bone
14
; T
&Sgr;
is the time delay between transmission of an ultrasonic pulse by scanning crystal
22
and reception of the pulse by scanning crystal
24
; T
26
and T
28
are the propagation times for ultrasonic pulses in delay lines
26
and
28
respectively; and T
16
is the propagation time for ultrasonic pulses in soft tissue
16
.
Two auxiliary crystals
30
and
32
are located in ultrasonic probe
12
, and are connected to digital computing device
18
. Auxiliary crystals
30
and
32
are typically used to determine the propagation time for ultrasonic pulses in soft tissue
16
. This is achieved by crystal
30
transmitting an ultrasonic pulse into soft tissue
16
while crystal
32
receives the reflected echo pulse from the surface of bone
14
. The measured delay between transmission and reception of this echo pulse determines the value of T
16
.
The velocity of ultrasound (SOS) in bone
14
is described by the formula:
SOS
=
BTD
T
14
Per the following reason:
It is well known that
V
[
m
/
sec
]
=
D
[
m
]
T
[
sec
]
SOS is defined as velocity; BTD is defined as distance and T is defined as time.
where BTD is the bone travel distance, which is determined by the distance between scanning crystals
22
and
24
and the value of angle &agr;.
Ultrasonic travel time and/or amplitude measurements for an ultrasonic pulse which has passed through bone
14
are heavily influenced by the proficiency with which the operator applies ultrasonic probe
12
to soft tissue
16
. Several techniques for maximizing operator proficiency have been described in the art. A typical technique is illustrated in
FIG. 3
, in which a part of ultrasonic apparatus
10
is depicted, including ultrasonic probe
12
. As shown in the figure, additional auxiliary crystals
34
and
36
are located within probe
12
, and are connected to digital computing device
18
. Crystal
34
is operative to transmit ultrasonic pulses into soft tissue
16
, while crystal
36
is operative to receive the reflected echo pulse from the surface of bone
14
. The measured delay between transmission and reception of said echo pulse is T
16a
. When I
16
=T
16a
, probe
12
is oriented in such a way that the BTD will be the shortest possible for that probe. A smaller value for BTD minimizes the impact of inevitable inaccuracies in the calculation of SOS. Thus, when digital computing device
18
determines that T
16
=T
16a
, probe
12
is deemed to be oriented appropriately with regard to soft tissue
16
, and the received echo signals are analyzed so as to image bone
14
. When the condition T
16
T
16a
is not met, received ultrasound signals are ignored by digital computing device
18
.
In an alternative method for minimizing operator unreliability, the operator applies ultrasonic probe
12
to a reference block made from material with known acoustical properties prior to applying probe
12
to soft tissue
Buksphan Shmuel
Golden Arcady
Halavee Uriel
Keren Gadi
Moshkovich Vladimir
Imam Ali M.
Lateef Marvin M.
Medson Ltd.
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