Surgery – Truss – Pad
Patent
1992-09-16
1994-01-25
Jaworski, Francis
Surgery
Truss
Pad
12866005, A61B 800, A61B 806
Patent
active
052807878
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the measurement of the size and orientation of hidden vessels, such as the vessels in the human body through which blood flows, using ultrasonic echoscopy. It has particular application to the measurement of the flow of blood in blood vessels using the Doppler frequency shift in conjunction with ultrasonic measurement techniques, but it is not limited to blood flow measurement. The present invention provides a method for improving the current ultrasonic techniques for measuring the size and orientation of vessels, and hence for obtaining measurements of the flow through such vessels.
BACKGROUND
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 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", analysing 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 applications of the pulsed Doppler technique, a small sample volume within the vessel is selected by the operator of the echoscope, who moves a graphical representation of the sample volume over a B-mode image of the vessel. In this way, the B-mode imaging equipment is used to steer the ultrasonic beam and adjust the sample volume delay so that the actual sample volume position corresponds to that part of the vessel which is to be the subject of the Doppler shift measurement. T
REFERENCES:
patent: 4873985 (1989-10-01), Nakajima
patent: 4913159 (1990-04-01), Gardin et al.
patent: 5078148 (1992-01-01), Nassi et al.
patent: 5195521 (1993-03-01), Melton, Jr. et al.
Dadd Michael J.
Gill Robert W.
Wilson Laurence S.
Commonwealth Scientific and Industrial Research Organisation
Jaworski Francis
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