Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-07-01
2001-07-17
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06261233
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus and methods for non-invasive measurement of parameters of the cardiovascular system, such as local blood flow volume, blood pressure and detection of gas bubbles in the blood.
BACKGROUND OF THE INVENTION
One of the important physiological systems in the human body is the cardiovascular system, which includes the heart, the arterial system and the venous system. Many imaging modalities can be used to investigate the structural properties of the cardio-vascular system, including, angiography, X-ray CT, MRI, SPECT and ultrasound. However, it is difficult to non-invasivly determine haemodynamic properties of the cardiovascular system. Determining the following haemodynamic properties is particularly useful:
(a) blood flow volume in a particular arterial/venous subsystem;
(b) local turbulence and pressure drops, which may indicate stenoses and/or aneurysms;
(c) pulse wave velocity;
(d) cardiac left ventricular stroke volume; and
(e) the reaction of arteries and veins to a pulse wave.
Doppler ultrasound imaging is widely used to determine local blood velocity flow in arteries. The frequency shift &Dgr;f of an ultrasonic wave of wavelength X, which impinges particles moving at a velocity v, is given by the following equation:
Δ
f
=
2
*
v
λ
[
cos
(
α
)
+
cos
(
β
)
]
(
1
)
In the case of blood, the ultrasonic wave is reflected mainly from red blood cells, which move in the same direction as the blood flow. It is relatively straightforward to transmit a wave of a known wavelength to a blood vessel, detect a reflected wave and determine the velocity of the blood based on equation (1). However, the magnitude of the frequency shift &Dgr;f is affected not only by the blood velocity v but also by an angle of incidence &agr; and a reflectance angle &bgr; of the wave from the blood. Typically in prior art measurements, these angles are not definitely determined, leading to an error of over 15% in velocity determination, as will be shown below with reference to FIG.
2
.
One known method of more precisely determining the angle of incidence &agr; and the reflectance angle &bgr; is to generate an ultrasonic image including the blood vessel. The angles &agr; and &bgr; are measured on the image along an imaging beam which is used for Doppler frequency shift determination. However, due to limitations of the ultrasonic imaging modality, the angle determination is not sufficiently precise and a significant error in velocity determination can be expected. In addition, the price and complexity of an ultrasonic imaging system are much higher than that of a simple Doppler-ultrasound system.
There also exist many invasive methods for determining haemodynamic properties. One method includes inserting a sensor carrying catheter into a vein or artery. Haemodynamic properties, such as pressure or velocity, are very precisely sensed by the sensor and are converted into a host of dependent properties, such as blood vessel impedance.
Another, less invasive, method is magnetic flow determination. In this method, a coil is placed around an intact blood vessel. A magnetic field is induced in the coil. Since blood is a conductor, the flow of blood in the magnetic filed induces a voltage across the blood vessel which is proportional to the flow.
There is however a need for a precise, non-invasive method for determining blood velocity and other haemodynamic properties.
Blood velocity determination and detection of small gas bubbles in the blood are related, since encapsulated gas bubbles are readily detectable using Doppler-ultrasound. Gas bubbles do not naturally occur in the vascular system. Certain medical procedures, such as CPB (cardiopulmonary bypass), and certain types of physical trauma, may infuse air bubbles into the vascular system. In addition, certain activities, most notably sea-diving, can cause the creation of air bubbles in the vascular system. In general, gas bubbles cause severe and lasting neurological effects, as well as other grievous bodily damage. However, it is relatively difficult to monitor the formation of gas bubbles in vivo. As a result, sea-divers use non-personalized diving tables which estimate the danger from gas bubbles in the divers blood.
As mentioned above, Doppler-ultrasound can be used to detect gas bubbles, however, the current state of the art does not provide means sensitive enough to detect small, yet damaging, gas bubbles in the blood. In addition, there is no commercially available simple apparatus for monitoring of gas bubbles in sea-divers.
Gas bubbles can also be detected, counted and monitored under a microscope., however, this type of monitoring is generally not practical even for medical situations, as well as being extremely invasive.
Blood pressure is usually determined using a pressure cuff on the brachial artery in the arm. This method has a relatively low precision and only measures the systolic and diastolic pressures. In “Ultrasonic System for Noninvasive Measurement of Hemodynamic Parameters of Human Arterial-Vascular System”, by Powalowski T.,
Archives Of Acoustics
, Vol. 13, Issue 1-2, p. 89-108 (1988) and in “A Noninvasive Ultrasonic Method for Vascular Input Impedance Determination Applied in Diagnosis of the Carotid Arteries”, by Powaiowski T.,
Archives Of Acoustics
, Vol. 14, Issue 3-4, p. 293-312 (1989), the disclosures of which are incorporated herein by reference, a method of estimating instantaneous blood pressure in a blood vessel is described. However, Powalowski's estimation method has at least two limitations. First, estimating the instantaneous blood pressure requires determining the diastolic and systolic blood pressures using a pressure cuff Second, the method used for determining the velocity of the blood flow in the blood vessel is not very precise.
U.S. Pat. No. 5,488,953 to Vilkomerson, the disclosure of which is incorporated herein by reference, describes a method and a device for measuring the flow velocity in a blood vessel using ultrasonic Doppler processing, independent of an orientation of the device. However, the method described in the '953 patent requires that the angles between a plurality of ultrasonic beams and the flow be determined.
An article titled “Vector Doppler: Accurate Measurement of Blood Velocity in Two Dimensions,” by John R. Overbeck. Kirk W. Beach and D. Eugene Strandness, Jr.,
Ultrasound in Medicine and Biology
, Vol. 13, No. 1, pp. 19-31, printed by Pergamon press, USA, 1992, and which is incorporated herein by reference describes several multi-transducer Doppler ultrasound devices, in which the angle of incidence is determined by analyzing the difference in Doppler spectra of different transducers.
U.S. Pat. No. 5,406,854, the disclosure of which is incorporated herein by reference, describes a Doppler flowmeter in which signals from several receivers, all of which are similarly oriented to the flow, are mixed to increase the system sensitivity.
U.S. Pat. No. 5,119,821, the disclosure of which is incorporated herein by reference, describes an ultrasonic probe having two probes oriented at about 45 degrees to each other. By comparing the signals received by the two probes from a blood flow, constrictions in the flow can be determined.
Woodcock, J. P., “The Transcutaneous Ultrasonic Flow-Velocity Meter in the Study of Arterial Blood Velocity,”
Proceedings of the Conference on Ultrasonics in Biology and Medicine
, UBIMED-70, Jablonna-Warsaw, Oct. 5-10, 1970, the disclosure of which is incorporated herein by reference, describes the use of two simultaneous measurements of flow parameters to ascertain the condition of corollary blood vessels.
SUMMARY OF THE INVENTION
It is an object of some embodiments of the present invention to provide apparatus and methods for precise determination of various haemodynamic parameters of the cardiovascular system, including at least one of:
(a) blood velocity;
(b) blood flow rate;
(c) pulse wave velocity;
(d) vessel dilation;
(e) dynamic vessel r
Jaworski Francis J.
Kenyon & Kenyon
Sunlight Medical Ltd.
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