NON-INVASIVE TECHNIQUE FOR BONE MASS MEASUREMENT

TECHNIQUE NON INVASIVE DE MESURE DU VOLUME OSSEUX

English Abstract

The present invention provides an apparatus for non-invasive determination of bone mass, said apparatus having a platform for supporting a bone to be measured, a spring having a selected stiffness which connects the platform to a sensor capable of measuring vibration velocity and force, and a vibrating means connected to the sensor, wherein the vibrating means exposes the sensor, the spring and the platform to vibration so that vibration velocity and force can be measured by the sensor and the mass of the bone determined. A second apparatus for non-invasive determination of bone mass having a gripping means, a spring having a selected stiffness which connects the gripping means to a platform for positioning of a bone, a sensor capable of measuring vibration velocity and force which connects the platform to a vibrating means, and a vibrating means which vibrates the sensor, the platform, the spring, and the gripping means so the vibration velocity and force can be measured by the sensor is also provided. In addition, a method of non-invasively determining mass of a bone with these apparatuses is provided.

French Abstract

La présente invention décrit un appareil destiné à mesurer grâce à une technique non invasive la masse osseuse, ledit appareil étant doté d'une plate-forme destinée à soutenir l'os à mesurer, d'un ressort d'une rigidité donnée, qui relie la plate-forme à un capteur capable de mesurer la vitesse et la force de vibration, et d'un vibreur relié au capteur. Ledit vibreur fait subir des vibrations au capteur, au ressort et à la plate-forme. Le capteur peut ainsi mesurer la vitesse et la force de ces vibrations, ce qui permet de déterminer la masse osseuse. La présente invention décrit également un deuxième appareil permettant de déterminer par technique non invasive la masse osseuse. Cet appareil est doté d'une pince, d'un ressort d'une rigidité donnée, qui relie la pince à une plate-forme destinée à positionner l'os à mesurer, d'un capteur capable de mesurer la vitesse et la force des vibrations, qui relie la plate-forme à un vibreur et d'un vibreur qui fait vibrer le capteur, la plate-forme, le ressort et la pince de façon à permettre au capteur de mesurer la vitesse et la force de vibration. La présente invention décrit en outre un procédé visant à déterminer de façon non invasive la masse d'un os à l'aide des appareils ci-dessus.

Claims

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What is claimed is:
1. A noninvasive apparatus for determining mass of a
bone comprising:
(a) a platform for supporting a bone;
(b) a sensor capable of measuring vibration
velocity and force;
(c) a spring having a selected stiffness which
connects the platform to the sensor; and
(d) a vibrating means connected to the sensor,
wherein the vibrating means exposes the sensor, the spring
and the platform to vibration so that vibration velocity and
force can be measured by the sensor and mass of the bone
supported by the platform determined.
2. The apparatus of claim 1 further comprising an
FTT analyzer which converts the vibration velocity and force
measured by the sensor into impedance.
3. A noninvasive apparatus for determining mass of a
bone comprising:
(a) a gripping means;
(b) a platform for supporting a bone;
(c) a spring having a selected stiffness which
connects the gripping means to the platform;
(c) a sensor capable of measuring vibration
velocity and force which connects the platform to a vibrating
means; and
(d) a vibrating means which vibrates the sensor,
the platform, the spring, and the gripping means so that the
vibration velocity and force can be measured by the sensor
and mass of the bone suported by the platform determined.
4. A method of noninvasively determining mass of a
bone comprising:
(a) positioning a bone to be measured on a
platform, wherein the platform is attached to a spring having
a selected stiffness;

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(b) exposing the platform to vibration, wherein
the vibration is generated by a vibrating means; and
(c) measuring vibration velocity and force to
determine mass of the bone.

Description

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NON-INVASIVE ~ QUE FOR BONE MASS MEASU~EMENT
Field of the Invention
This invention relates generally to bone quality
as~ m~nt, and, more particularly, relates to bone mass
5 measurement and monitoring in a patient which can be used for
the diagnosis of osteoporosis.
RA.I~:.J.~,U~,d of the Invention
Existing techniques for bone quality assessment are
based on photon and X-ray a~sorptiometry and X-ray
10 quantitative computed tomography. Gramp et al. The
Radfological Clinics o~ North America 1993 31(5):1133-1141;
Faulkner et al. Am. J. Roentgenology 1991 157:1229-1237. Each
of these methods are routinely used in clinical practice.
However, these t~-hn~ques have limited applicability because
15 of expensive and bulky equipment and potential risk of
radiation during the procedure.
The application of acoustic energy for non-invasive
skeletal diagnosis has also been shown to be feasible and has
advantages for bone mass and strength measurement. Jurist,
20 J. PAys. Med. ~iol. 1970 15:417-426; Orne, D. Biomechanics
1974 7:249-257; Thomson et al. Med. Biol. ~ng. 197~ 14:253-
262; Saha, S. and Lakes, R.S., J. Biomechan. ~ 977 10:393-401;
Doherty et al. J. Biomechan. 1974 7:559-561; Waud et al.
Calcif. Tissue Int. 1992 51:415-418; Selle, W.A. and Jurist,
25 J.M. J. Am. Geriat. Soc. 1966b 14:930. Unlike conventional
radiological techniques, acoustic techniques emit no
radiation, are cost effective, and utilize equipment which is
portable and easy to operate. Subsonic techniques for
detel ; n; ng the fn vivo properties of bone, known as
30 impedance and resonance methods are based on measurement of
the response of a bone to a flexural wave excitation in the
frequency range 200 to 1000 Hz. A correlation between the
resonance frequency of the human ulna and osteoporosis has
been reported. However, while a significant number of
35 acoustic tests have been performed, these techniques have not

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been used as a bone diagnostic tool for clinical application
because of difficulties in the interpretation of the
measurements. Ultrasound velocity and attenuation depend on
density as well as on certain other properties of bone. A
5 recent report showed that only 53% of broadband ultrasound
attenuation (BUA) value and 44~ of velocity of sound (VOS)
value can be accounted for by bone density. Waud et al.
Calci~. Tissue Int. 1992 5~:415-418. Interpretation of
subsonic measurement of flexural vibration of bone is also a
10 difficult task and to a great extent, depends upon a
corresponding mathematical model of the test object. The
effect of soft tissues creates additional difficulties in the
interpretation and use of these techniques.
A non-invasive, nonhazardous and cost effective
15 infrasound resonance method for the quantitative measurement
and monitoring of bone quality has now been developed
involving the measurement of the rigid body longit~ n~ 1
re~on~nc~ of a bone. Instrumentation for making these
measurements is also provided.
20 S -~y of the Invention
An object of the present invention is to provide a
noninvasive apparatus for measuring force and vibration
velocity to determine the mass of a bone which comprises a
platform for supporting a bone to be measured, a spring
25 having a selected stiffness which connects the platform to a
sensor capable of measuring vibration velocity and force, and
a vibrating means ~onn~ted to the sensor, wherein the
vibrating means exposes the sensor, the spring and the
platform to vibration so that vibration velocity and force
30 can be measured by the sensor and the mass of the bone
determined.
Another object of the present invention is to provide
a method of noninvasively measuring vibration velocity and
force to determine the mass of a bone which comprises
35 positioning a bone to be measured on a platform wherein the
platform is att~he~ to a spring having a selected stiffness,

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exposing the platform to vibration wherein the vibration is
generated by a vibrating means, and measuring vibration
velocity and force to determine bone mass.
Brief Description of the Figures
F~gure 1 provides a block diagram of a subsonic
anism for quantitative measurement of bone quality.
Figure 2 provides equivalent -chAnical ~Figure 2a)
and electrical (Figure 2b) diagrams of the driver-spring-
tibia/ulna system. F is an external vibromotive force, ka
10 and Ra are stiffness and damping coefficients of the
artificial spring, respectively, Kt and Rt are stiffness and
damping coefficients of the overlying soft tissue and mb is
the mass of the bone and the fixing platform.
Figure 3 represent the results o~ calculations of the
15 driving point imp~n~-~- vs. driving frequency. The dashed
curve corresponds with 80~ variation of soft tissue mass.
The dotted curve corresponds with 10~ variation of bone mass.
This figure shows that the deviation of resonance peak is
sensitive to mass of bone variation and is not susceptible to
20 overlying soft tissue.
Detailed Description of the Invention
With the increasing age of the population, there is a
great interest in the diagnosis, treatment and health care
costs relating to osteoporosis. Available data indicates
25 that 56.7~ of women 45 years of age and older have
osteoporosis. Praemer et al. American Academy o~ Ort~opaedic
Surgeons 1992 46-52. Current methods for monitoring bone
quality and diagnosing osteoporosis have limited
applicability because of expensive and bulky equipment and
30 procedures and the potential risk of radiation.
A cost effective subsonic technique and compact, low
cost instruments have now been developed for the quantitative
measurement of bone quality and the diagnosis of
osteoporosis. This technique can be used by general
35 practitioners, physicians and rehabilitation specialist,

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requiring no specific tr~ining and expertise for use. In the
present invention, the rigid body longit~ resonance of a
bone, preferably the tibia or ulna, is measured with the use
of an artificial spring having a known stiffness. This
5 procedure simplifies the interpretation of the measurements
and is much more accurate than existing acoustic methods
which measure flexural reson~ involving both the mass and
flexibility of a bone and the surrounding soft tissue.
In contrast to more conventional approaches which
lO measure the response of a bone to flexural mode excitation,
the present invention measures the response of a bone to
longit~ n~- excitation through an artificial spring. With
this method, the mechAn~cal model of the body is greatly
simplified by selection of an appropriate artificial spring.
In one embodiment, bone mass is determined by
measuring vibration velocity and force with an apparatus
which comprises a platform for supporting a bone to be
measured, a spring having a selected stiffness which connects
the platform to a sensor capable of measuring vibration
20 velocity and force, and a vibrating means cn~nected to the
sensor, whereîn the vibrating means exposes the sensor, the
spring and the platform to vibration so that vibration
velocity and force can be measured by the sensor. The ratio
of the vibration force versus the velocity is the mechanical
25 impedance which provides information concerning the mass of
the bone. In a preferred embodiment, the apparatus further
comprises an FTT analyzer which converts the vibration
velocity and force measured by the sensor into impe~n~.
This impedance is very sensitive to a variation of bone mass
30 and is not sensitive to soft tissue mass variation.
Therefore, the mass of the bone can be measured independently
of variations in bone flexibility and soft tissue parameters.
In another embodiment, bone mass is measured with an
apparatus which comprises a gripping means, a spring having a
35 selected stiffness which connects the gripping means to a
platform for positioning of a bone, a sensor capable o~
measuring vibration velocity and force which connects the

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platform to a vibrating means, and a vibrating means which
vibrates the sensor, the platform, the spring, and the
gripping means so the vibration velocity and force can be
measured by the sensor. The ratio of the vibration force
5 versus velocity is the mech~nical imp~A~n~e which provides
information ~-o~c~rning the mass of the bone.
For the purposes of the present invention, by a
"spring having a selected stiffness" it meant that the spring
may have stiffness ka much less than the stiffness of the
10 bone kb and the joints k~, but stiffer than the stiffness of
soft tissues k~, i.e. kt<<ka<~k~,k~. According to Orne
(Bin~Ch~nics 1974 7:249-257), kt=103 104 dyn/cm, kb,
~=108 101~ dyn/cm. Therefore, if the stiffness of the
artificial spring, k~, is in the range of 105 107 dyn/cm, the
flexibility of the bone and joints are negligible and the
?ch~n;cal and equivalent electrical model of a bone in the
correspondent frequency range can be represented as shown in
Figure 2, wherein F is an external vibromotive force, ~a and
Ra are stiffness and damping coefficients of the artificial
20 spring, respectively, k~ and Rt are stiffness and damping
coefficients of the soft tissue and mb is the mass of the
bone and a fixing platform. This system has a resonance. In
the vicinity of the resonance the driving point ;mpe~c~ is
very sensitive to a variation of bone mass, does not depend
25 on flexibility of bone, and is not sensitive to soft tissue
mass and damping effect.
Using this apparatus bone mass is measured
noninvasively by positioning a bone to be measured on the
platform for support wherein the platform is attached to a
30 spring having a selected stiffness. The platform and spring
are then exposed to vibration resulting from the vibration
means and vibration velocity and force are measured by an
impedance sensor att~ch~ to the spring. Based upon the
ratio of vibration force versus velocity, a m~.h~n; cal
impedance is calculated and mass of the bone is determined.
This determination is independent of variations in bone
flexibility and soft tissue parameters.

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The present invention provides a light weight, ~. act
and relatively inexpensive instrument which can be used for
~uantitative measurements as well as monitoring of bone mass
and bone quality. The present invention is especially useful
5 in the diagnosis and detection of osteoporosis. In addition,
the present invention offers a non-hazardous method as
compared with general X-ray techniques for general
practitioners, physicians and rehabilitation specialist to
monitor bone quality with the requirement for radiation
10 certification.

Representative Drawing