Method for automatic measurement of the doppler angle and arrangement for carrying out the method
AssigneeU.S. Philips Corporation
InventorAntoine Goujon
Life of this patent
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Abstract
Automatic measurement is made of the angle DA enclosed by the direction of ultrasonic echographic excitation and the axis of a vessel in an echographic image on the basis of prior designation of an initial point P.sub.i in the vessel. A first isotropic tracing of rays starting from the initial point P.sub.i is used to produce a histogram of the grey levels of the points of the rays. An algorithm is then applied to the histogram in order to classify the grey levels of selected points. A second tracing of rays is made which is restricted to the walls of the vessel and results in a local mark with triangular sectors from which the slope (a) of a regression line is determined and the calculation of the Doppler angle DA is made as DA=Arc tg(a).
Claims11
A method for automatic determination of Doppler angle DA, enclosed by the direction of an echographic excitation and the axis of a relevant 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, comprising the following steps:
- a) first isotropic tracing of rays from said initial point which traverse the entire echographic image and forming a histogram of grey levels of selected points which are regularly distributed along said rays,
- b) applying an image processing algorithm to said histogram in order to classify the grey levels of said selected points into at least two classes 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 a lower threshold T.sub.i-1, being representative of walls of blood vessels in said image,
- c) second tracing of rays from said initial point, during which the grey 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 equal to or higher than T.sub.i-1, and producing a representation of said relevant blood vessel in the form of a first local mark which is composed of triangular sectors which have said starting point within said first local mark in common,
- d) determining a slope (a) of the regression line of said first local mark by applying a linear regression method to the N pixels, having the coordinates x(n) and y(n) of said first local mark, as:
- ##EQU14## e) and calculating a Doppler angle as:
- DA=Arc tg (a).
An arrangement for automatic determination of 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 a initial pixel situated in the vicinity of the axis of the relevant vessel, which arrangement comprises:
- a memory for storing the grey-level values of the echographic image in the form of a matrix of pixels,
- a screen for displaying the echographic image in the form of a two-dimensional matrix of pixels,
- pointer means for pointing out said initial pixel in the displayed image, and
- calculation means which can access said memory and said initial point,
- the calculation means being arranged to perform:
- first isotropic tracing of rays from said initial pixel which traverse the entire echographic image and formation of a histogram of grey levels of pixels which are selected so as to be regularly distributed along said rays,
- application of an image processing algorithm to said histogram in order to classify the grey levels of said selected pixels in at least two classes 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,
- second tracing of rays from said initial pixel, during which the grey level of each pixel of each ray is compared with the threshold T.sub.i-1 and each ray is restricted to the first end pixel Pl encountered whose grey level is equal to or higher than T.sub.i-1, and production of a representation of said blood vessel in the form of a first local mark which is composed of triangular sectors which have said starting pixel within said first local mark in common,
- determination of a slope (a) of the regression line of said first local mark by application of a linear regression method to the N pixels, having the coordinates x(n) and y(n) of said first local mark, as:
- ##EQU18## and calculation of a Doppler angle as:
- DA=Arc tg (a).
Dependencies are inferred from the claim text.