Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-05-18
2003-01-07
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06503205
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a dual ultrasonic transducer probe for use in a Doppler based ultrasound system for blood flow measurement and determination of associated hemodynamic parameters, and a blood vessel diameter determination method.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,370,985 discloses a Doppler based ultrasound probe device for measuring a blood flow rate and a blood vessel diameter. This technique is based on the continuous transmission of ultrasonic waves.
EP 0150672 discloses a process and device for determining the velocity and rate of flow of a fluid in a pipe by using a Doppler echographic method. Here, two mutually attached wave-train transmitter-receiver units are used and oriented with respect to a pipe such that the axis of one of the units is perpendicular to the axis of the pipe. According to this technique, the transit time between the transmission of a wave train by this transmitter-receiver unit and the reception of the reflected train is measured for calculating the diameter and perpendicular cross-section of the pipe.
In U.S. Pat. No. 4,103,679 to Aronson, there is illustrated and described a Doppler based ultrasound system for blood flow measurement in a blood vessel which requires that an ultrasound transducer array be so disposed relative to the blood vessel's longitudinal axis that a Pulse Wave ultrasound beam emanating therefrom intercepts the blood vessel's longitudinal axis at a variable beam inclination angle &thgr;, whereby blood flow measurement can be quantitatively measured independent of the beam inclination angle.
An article entitled “
New, Angle-independent, Low-Cost Doppler System to Measure Blood Flow
” by M. Skladany et al., The American Journal of Surgery, Volume 176, August 1998, pgs. 179-182, illustrates and describes a similar Doppler based ultrasound system for blood flow measurement.
Another technique based on the transmission of pulses of two ultrasound waves aimed at determining the blood velocity is disclosed in WO 97/24986. This technique is based on the zero-crossing method for frequency measurement of Doppler shifts and the use of FM modulated or pulse signals with range clipping for localizing velocity measurements.
However, the aforementioned references neither address the practical difficulties involved with ensuring that an ultrasound beam is correctly positioned with respect to a blood vessel's longitudinal axis, nor the accurate measurement of a blood vessel's diameter, both factors playing a major role in an accurate blood flow measurement determination.
SUMMARY OF THE INVENTION
There is accordingly a need in the art to facilitate measurements of a blood vessel diameter, as well as a blood flow and velocity profile at the blood vessel axis, by providing a novel dual ultrasonic transducer probe and a method of blood vessel diameter measurement utilizing a pair of ultrasound beams.
The main idea of the present invention consists of the following. Two transducers in the probe should be oriented with respect to each other such that ultrasound beams generated by the transducers define beam propagation axes intercepting at a certain acute angle. The transducers should be desirably positioned with respect to the blood vessel under measurements, namely such that each of the beam propagation axes intercept the longitudinal axis of the blood vessel. This can be implemented by displacing the transducers with respect to the blood vessel (either manually or by means of a specifically designed support assembly) and performing preliminary measurements of the blood vessel diameter.
According to the invented method, once the probe is desirably positioned, measurements are carried out consisting of insonating the blood vessel with two pulse-wave ultrasound beams, in a manner to substantially simultaneously (in comparison to the physiological time scale) obtain multiple sample volumes at successive coordinates (gates) all along each of the beam propagation axis. In other words, for each of the beams an amplitude vector of the reflections with Doppler shifted frequencies is obtained as an n-element vector. By applying the complex demodulation technique, which utilizes the synchronous multiplication of the input real vector of reflection amplitudes on two periodic functions with 90°-shift in phase, and a low pass filtering, the n-element vector of complex values (I & Q) for each of the beam is obtained. By this, the central frequency of the complex vector is shifted from that of the ultrasound pulse towards zero frequency. By repeating the ultrasound pulses transmission/receiving procedure m times, an n×m two-dimensional matrix E
ij
of reflection amplitude values is obtained for each of the beams. Here, i is the gate coordinate index (i=1, . . . , n) and j is the time coordinate index (j=1, . . . , m). It should be understood that each of the reflection amplitude values is complex and is indicative of the amplitude and the phase of the reflection at the respective gate at a certain time. By processing and analyzing these matrices (for two beams), the diameter of the blood vessel can be calculated, as well as dynamic characteristics of the blood flow, such as Doppler shifts, inclination angles, velocity, and velocity profile along the ultrasound beam.
The present invention actually enables for automatic location of the central axis of the blood vessel. Therefore, by measuring the time variations of the detected reflection at this location, and calculating blood flow velocity values, the velocity profile at the central cross section of the blood vessel along the ultrasound beam can be determined.
Thus, in accordance with a first aspect of the present invention, there is provided a dual ultrasonic transducer probe for use in a Doppler based ultrasound system for blood flow measurement, the probe comprising: a housing containing first and second ultrasound transducers each operable in transmitting and receiving modes, the transducers producing first and second ultrasound beams propagating along first and second beam propagation axes, the first and second transducers being oriented with respect to each other such that the first and second beam propagation axes intersect at a certain acute angle, and being displaceable with respect to a patient's blood vessel to enable desired positioning of the probe such that each of the first and second beam propagation axes intersect a longitudinal axis of the blood vessel, which is determined by performing a preliminary measurement of a diameter of the blood vessel.
The housing may be of an elongated shape, the first and second transducers being mounted at a distal end of the housing. By the manual displacement of the housing with real-time analysis of the preliminary measurements, the desired positioning of the probe can be provided.
Alternatively, a specific support assembly may be used for the probe positioning. The support assembly is rotatable about the first beam propagation axis, whereby the second ultrasound transducer rotates about the first beam propagation axis. The support assembly is displaceably mounted in the housing for displacing the first and second ultrasound transducers in tandem. The arrangement is such that both the first and second beam propagation axes intercept the blood vessel's longitudinal axis and correspondingly subtend acute beam inclination angles &thgr;
1
and &thgr;
2
therewith for enabling the measurement of Doppler shift frequencies along said first and second beam propagation axes. Such a probe facilitates manipulation of its ultrasonic transducers relative to a blood vessel such that both their ultrasonic beam axes intercept the blood vessel's longitudinal axis, and subtend acute beam inclination angles therewith. Typically, such positioning is a two step process including a first step for intercepting the blood vessel's longitudinal axis with the first ultrasonic beam; and a second step for intercepting the blood vessel's longitudinal axis with the second ultrasonic beam
Bibi Roni
Levy Eli
Lukaschuk Sergei
Manor Dan
Browdy and Neimark
Cardiosonix Ltd.
Jaworski Francis J.
Patel Maulin
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