Surgery – Truss – Pad
Patent
1996-08-06
1997-11-25
Jaworski, Francis
Surgery
Truss
Pad
A61B 800
Patent
active
056901160
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for automatic measurement of the Doppler angle DA, enclosed by the direction of an echographic excitation and the axis of a blood vessel in an ultrasonic echographic grey-level image, on the basis of prior designation of an initial point situated in the vicinity of the axis of the relevant vessel.
The invention also relates to an arrangement for carrying out the method.
In order to provide a quantitative measure of the speed of blood in arteries, a method for the ultrasonic imaging of speeds by colour encoding is based on knowing the angle between the incident ultrasonic beam and the local axis of the vessel. This holds for all ultrasonic signal processing methods currently carried out to produce a colour-encoded representation of flows in any commercially available echograph. Moreover, reliable determination of this angle, referred to as the Doppler angle, is necessary to extract echographic data of parameters whose measurement is rather complex and to make further progress in the study of the behaviour of arteries.
Considering the foregoing, it would be justified to conceive and carry out an automatic process for the extraction of the value of the Doppler angle from a medical ultrasonic image with a high precision, for example of the order of 1 degree.
The Doppler angle still is a difficult aspect of all commercially available apparatus: the radiologist must determine the value thereof in a rather approximative manner by judging the alignment of a small line segment traced in the image with respect to the axis of the blood vessel analyzed.
From Japanese Patent No. 5-31110 it is known to detect automatically the angle enclosed by the direction of the blood flow with respect to the direction of an echographic beam. Via a transmission using an echographic probe comprising several transducers, followed by a separate analysis in respect of phase and frequency of the reflected beams received in two receiving sections of the probe, a given Doppler displacement is determined wherefrom a speed vector can be deduced at the point affected by the probe; this corresponds to the determination of a Doppler angle. However, it is very difficult to carry, out a direct measurement without an intermediate echographic image, because it is not ensured that the axis of the blood vessel probed is indeed present in the plane of the image of the artery as is necessary for the measurement of the Doppler angle. When the axes of the echographic excitation and that of the vessel are not situated in the same plane, the detection of the Doppler angle remains possible, but it is liable to be affected by substantial errors; this is not acceptable when the required precision is of the order of approximately 1 degree.
It is an object of the invention to provide a method for automatic measurement of the Doppler angle of a trace of a blood vessel in an echographic image, starting from a designated point in the direct vicinity of said trace.
It is another object of the invention to provide a method for automatic measurement of the Doppler angle which is exact and fast.
It is another object to provide an arrangement for carrying out the above measuring method.
These objects are achieved, and the drawbacks of the prior art are mitigated, in that the method of the kind set forth is characterized in that it includes the following steps: traversing the echographic image partly or entirely so as to provide a histogram of the grey levels of selected points which are regularly distributed along said rays, histogram in order to classify the grey levels of said selected points into at least two categories CL.sub.1, CL.sub.2, . . . , two adjacent classes being separated by thresholds T.sub.1, T.sub.2, . . . , expressed in grey levels, one of the classes CL.sub.i, bounded by the lower threshold T.sub.i-1, being representative of walls of blood vessels in said image, level of each point of each ray is compared with the threshold T.sub.i-1 and each ray is restricted to the first end point Pl encountered whose grey level is
REFERENCES:
patent: 5305753 (1994-04-01), Wilson
patent: 5465721 (1995-11-01), Kishimoto et al.
patent: 5495852 (1996-03-01), Stadler et al.
Jaworski Francis
Slobod Jack D.
U.S. Philips Corporation
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