Surgery – Truss – Pad
Patent
1992-10-29
1994-04-26
Kamm, William E.
Surgery
Truss
Pad
A61B 800
Patent
active
053057538
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the measurement of liquid flow. It provides a method and apparatus for the determination of both the direction and magnitude of the two-dimensional velocity of small samples of a flowing liquid. It is particularly, but not exclusively, useful in the investigation of blood flow through vessels or parts of vessels in the human body, for which purpose ultrasonic echoscopy has been used previously. Thus the present invention is an alternative to the conventional measurement of liquid flow using the Doppler frequency shift of ultrasonic signals which have been reflected by ultrasound scatterers in suspension in a flowing liquid.
BACKGROUND OF THE INVENTION
It is now well known that ultrasonic echoscopy techniques can be used to provide information about an object that is not visible to the eye. The basic technique of ultrasonic echoscopy involves directing a short pulse of ultrasonic energy, typically in the frequency range from 1 MHz to 30 MHz, into the region of the object that is being examined, and observing the energy that is reflected, as an echo, from each acoustic impedance discontinuity in that region. Each echo received is converted into an electrical signal and displayed as either a blip or an intensified spot on a single trace of a cathode ray tube or television screen. Such a display of the echoes is known as an "A-mode" echograph or echogram, and is useful in a number of diagnostic techniques to locate the boundaries of the object or to provide other information about the region into which the pulse of ultrasonic energy has been directed.
If a series of adjacent A-mode displays are obtained (for example, by physically or electrically moving the transmitting transducer which produces the pulses of ultrasonic energy, or by scanning the direction of transmission of the pulses of ultrasonic energy), a two-dimensional image of the object under examination may be displayed on the cathode ray tube or television screen. Such an image or display of acoustic discontinuities, which corresponds to the structure of the object, is known as a "B-mode" image or display.
The use of the Doppler frequency shift in the ultrasonic examination of flowing liquids and moving objects is also well known. Many echoscopes which perform the B-mode imaging examination described above can also perform Doppler frequency shift measurements in respect of echoes returned from moving objects within the region receiving ultrasonic energy from the echoscope. When the object under examination is a blood vessel, measurement of the Doppler shift of echoes from the blood cells within the vessel permits the velocity of those blood cells to be estimated. As pointed out by R W Gill, in his article entitled "Measurement of Blood Flow by Ultrasound: Accuracy and Sources of Error", which was published in Ultrasound in Medicine and Biology, Volume 11 (1985), pages 625 to 641, it is possible to measure the total volume of flow per unit time using an ultrasonic examination technique which includes the measurement of frequency changes due to the Doppler effect.
In ultrasonic examinations including Doppler frequency shift measurements, it is necessary to obtain echoes from a limited volume of the flowing liquid which is within the vessel being examined. This is achieved by fixing the line of sight of the ultrasonic transducer and, in the most commonly used version of Doppler measurement known as "pulsed Doppler", analyzing the echoes obtained from the sample volume for a limited range of time delays. The Doppler shift in the received echoes is averaged in order to calculate the average speed of scatterers in the flowing liquid.
In current implementations of the pulsed Doppler technique, the quantity measured as "velocity" is actually the component of velocity measured along the line of sight of a beam of ultrasound. Therefore the actual velocity (magnitude and direction) of the flowing liquid is not determined, although it can sometimes be inferred (for example, when the flow is along a vessel with clear
REFERENCES:
patent: 5050611 (1991-09-01), Takamizawa et al.
patent: 5105817 (1992-04-01), Uchibori et al.
patent: 5190044 (1993-03-01), Kawasaki et al.
Commonwealth Scientific and Industrial Research Organisation
Kamm William E.
Manuel George
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