Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-11-17
2001-07-24
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S438000
Reexamination Certificate
active
06264607
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a system for the acoustic analysis of bone, and more particularly to a test object for calibrating such a system for accuracy and uniformity.
BACKGROUND ART
Various methods are known for measuring bone characteristics using acoustic techniques to identify patients in need of treatment for bone conditions and diseases. Many acoustic techniques utilize a first transmitting transducer to provide an acoustic signal, typically at ultrasonic frequencies, to the subject from a first external location and a second receiving transducer at a second external location disposed on the opposite side of the bone of interest to receive the signal transmitted by the first transducer through the bone and intervening soft tissue. Typically, such transducers are coupled to the subject through a suitable fluid, such as water or through ultrasound transmission gel.
One acoustic measure of bone often used is the so-called Broadband Ultrasound Attenuation (BUA), typically quoted for the frequency range of approximately 200 to 600 kHz. The BUA is defined as the slope of a linear logarithmic-amplitude versus frequency plot of the energy transmitted through the heel. BUA measures are typically performed by Fourier transforming the signal produced in the receiving transducer due to transmission of a broadband acoustic pulse through the bone undergoing measurement. The Fourier components of the received signal are typically ratioed to the corresponding components measured through a medium of known spectral attenuation characteristics so that the slope of the bone attenuation versus frequency may be derived.
Trabecular bone is known to have the effect of preferentially attenuating higher frequencies—the extent of the preferential attenuation is known to decrease as the bone becomes increasingly porous. Thus, the BUA similarly decreases for more porous bone. BUA measurements are complicated by a variety of factors. For example, the BUA computed may depend not only on the apparatus used, but on the length and portion of the time domain record that is used, the type, if any, of window function used with the data, the frequency range and method used for estimation of the slope, and the methods used for calibration. Further difficulties may result from the presence of received signals that result from transmission through the bone via multiple paths.
The early portion of the received waveform may be more representative of the measured body part. It is desirable, moreover, to express the results of measurements made with respect to early or other transient portions of the received signal in terms of BUA, since it has been common practice to relate BUA values to bone condition empirically.
For clinical utility, measured and quoted characteristics must be highly reproducible from measurement to measurement for a given subject, whether the measurements are made with one, or more than one, measurement unit. In order to monitor the reliability and repeatability of the measurements, standards of various sorts have been provided to simulate the attenuation properties of bone, namely preferential attenuation of higher frequencies. One type of standard requires fabrication of a model heel structure, or phantom, such as an epoxy-resin matrix filled with a fluid, or an epoxy resin filled with particles of another material such as tungsten powder or glass beads. Another type of standard known in the art is an electronic standard that simulates the spectral effect of an attenuating bone.
SUMMARY OF THE INVENTION
One embodiment of the present invention includes a calibration device for a bone density analyzer having substantially opposing ultrasonic transducers with spherical section ends. The calibration device includes a test object having opposing ends, the test object being made of material having known acoustic characteristics; and a transducer seat in each opposing end that receives the transducers, each transducer seat having a spherical section shape corresponding to the spherical section ends of the transducers that allows free translational and rotational coupling of the seat with a transducer.
A further embodiment may include a test object holder having a cradle that supports the test object. An elastomeric o-ring may be around the outer surface to stabilize the test object when laying at rest in the cradle. In such an embodiment, a lanyard assembly may connect the test object and the test object holder without affecting the acoustic characteristics of the test object.
The test object may have a cylindrical shape and/or be made of ABS plastic. The bone density analyzer may be of the mechanical scanning type. Each transducer seat may have an inner radius of curvature that creates an area of the transducer seat that matches the shape of a transducer end, and an outer radius of curvature that extends the area of direct acoustic contact between the transducer end and the transducer seat, and that limits any suction force between the transducer and the transducer seat.
Any of the above embodiments may also be used in a calibration device for a bone density analyzer that includes a test object having opposing ends connected by walls that define a fluid filled cavity, the fluid having known acoustic characteristics; and a transducer seat in each opposing end that receives the spherical section ends of the transducers. Each transducer seat may have an opening having a radius of curvature approximating the cross-sectional curvature of the transducer sidewall, and an inner elastomeric sheet that seals the fluid cavity and that may deform to accommodate the shape of a transducer end. The inner elastomeric sheet may be made of latex rubber or silicone rubber. Each transducer seat may have a shape such that when a spherical section end of a transducer contacts the seat for a calibration measurement, the contact area is substantially equivalent to the contact area when a spherical section end of a transducer contacts a human foot during normal use of the bone density analyzer. The fluid may be water or a mixture of fluids such as a solution of water and alcohol.
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McCarthy, K., “Quality Assurance in Medical Imaging” from a meetin gof the Instrument Science and Technology Group of the Institute of Physics on ‘Quality Assurance Aspects of Medical Imaging’,IOP Short Meeting Series No. 2 Institute of Physics, London, pp. 77-80, Jun., 1986.
Goll Jeffrey
Pratt David
Wood Donald
Bromberg & Sunstein LLP
Lateef Marvin M.
Metra Biosystems, Inc.
Patel Maulin
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