Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Patent
1996-11-04
1998-07-28
Jaworski, Francis
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
600468, A61B 806
Patent
active
057856575
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention pertains to medical technology. It relates to fluid flow measurement in the field of medicine, and in particular to a blood flow measurement device.
BACKGROUND AND PRIOR ART
Fluid flow measurement plays an important part in modern medicine. This applies both to pure diagnostic procedures as well as to direct control of disease treatment. The various fluids which are, in this sense, of interest in the human body are very different in properties and include blood, pus, urine, inhaled and exhaled air, drug infusions, etc. In all the cases there exists a possibility of measurement of the flow using the Doppler effect provided there exist a wave reflecting or transmitting entity within the said liquid. A basic property of the Doppler effect is that it takes place if there exists a velocity along the line connecting the wave transmitter and its receiver. For plane waves, the Doppler effect equals zero if the probing waves are at 90.degree. to the direction of movement of the said fluid. This means that only the velocity component projected to the line connecting the wave transmitter and its receiver is measured. This limitation applies strictly only to plane waves, while for bundled waves (beams) one can theoretically obtain a low frequency Doppler effect due to the fact that the wave fronts in a beam are not plane (Censor D., W. L. Newhouse, T. Wonz, H. V. Ortega: Theory of Ultrasound Doppler Spectra Velocimetry for Arbitrary Beam and Flow Configurations, IEEE Trans. on Biomedical Engineering, 35 (1988)740). This, however, is a part of frequency spectrum which is fully within the Doppler shift frequency spectrum of other movements in the body, such as the movement of the blood vessel walls, movement of the liver due to the heart beats, breathing movements, etc. This makes the cited phenomenon hard (and often impossible) to use, and in particular to use when the measurement process is unattended by interpreting humans (i.e. is used for some automatic regulation). Cross correlation techniques for velocity measurement exist in the form of wave transmitter-receiver array systems where the correlation among different lines-of-sight is used to obtain the velocity information. Due to the intrinsic physical impossibility to reduce the size of such a system the measurement is slowed down, thus correctly yielding only the low range of velocities encountered in the body. In addition, to the said velocity limitation the said cross correlation method is limited to pulsed wave mode in the case when velocities axial to the measurement device are measured. (Kasai, C., K. Namekawa: Real-time two-dimensional blood flow imaging using an autocorrelation technique, Proc. IEEE Ultrasonic Symposium 1985, IEEE, p. 953). While this approach yields Doppler equivalent results when used along the scanner line-of-sight and can even measure slow perpendicular velocities, it always requires full arrays of multiple transducers and is problematic in the measurement of the high velocities perpendicular to probing beams. In EP 228 070 assigned to Aloka Co.Ltd. the problem of the knowledge of the angle has been partially solved by using two probing beams under slightly different angles. The method requires fairly elaborate electronic systems and is usable only when the acoustic window is large enough to accommodate for the said two beams. In EP-144 968 and JP-228 330 the time domain calculation is adjusted for simplified calculation of the effects along the line-of-sight, yielding a Doppler-like result. The time domain calculation method has further been described in EP-92841, JP-070479 and U.S. Pat. No. 4,573,477 with the advantage of increasing and optimizing the sampling rate of the Doppler equivalent on-line measurement.
A larger number of prior inventors concern themselves with using the in-phase and quadrature detection components for further correlation calculations with improved results in Doppler-like procedures. This applies to EP-447597 which improves the measurable velocity by using multiple measur
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Breyer Branko
Ferek-Petric Bozidar
Jaworski Francis
Pacesetter AB
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