Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-06-29
2003-04-29
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S443000, C128S916000
Reexamination Certificate
active
06554769
ABSTRACT:
RELATED APPLICATIONS
The present application is a U.S. national application of PCT/IL97/00442, filed Dec. 31, 1997.
FIELD OF THE INVENTION
The invention relates to the determination of the relative spatial position of two surfaces from values of functions on the two surfaces and especially to the determination of the relative position of the planes of two ultrasound tomography slices.
BACKGROUND OF THE INVENTION
In many ultrasonic imagers, a hand unit is used to scan an object and acquire data for images of tomograph slices of the object. The unit transmits ultrasound pulses into the object and receives reflections of these pulses from structures in the tomograph slices of the object. An operator holds the hand unit and moves it over that portion of the object that is being imaged. Data for an image of a complete slice of the object is acquired rapidly so that as the operator moves the hand unit over the object being imaged, imaging data for many closely spaced slices is acquired.
In order to construct an accurate three dimensional image of the portion of the object scanned, the location and orientation of the tomograph slices with respect to each other must be accurately known. The location of a tomograph slice with respect to the hand unit, and the locations of points, hereafter referred to as “data points”, in the tomograph slice at which data are acquired, are accurately known from the structure of the hand unit. However, the structure of the hand unit does not provide any information as to where the tomograph slices are located with respect to each other. In order to determine the relative locations of the tomograph slices, the location and orientation of the hand unit for each tomograph slice for which data is acquired is determined. This is generally done by monitoring the location and orientation of the hand unit with respect to a reference coordinate system fixed in the room in which the ultrasound equipment is operated. The location and orientation of the reference coordinate system is defined by an array of receivers appropriately positioned in the room. The hand unit is equipped with transmitters that transmit signals to these receivers. The location and orientation of the hand unit can be accurately determined from these signals at any time while the hand unit is scanning the object. This system for locating the hand unit and the tomograph slices for which data is acquired is expensive and cumbersome and precludes the possibility of easily moving the ultrasound equipment from place to place.
A mechanical system for locating the position and orientation of a source of ultrasound energy used to produce a three dimensional image an object is described in U.S. Pat. No. 5,487,388 to M. J. Rello et al. In this patent the source described emits a thin planar fan beam of ultrasound energy. The source is fixed to a mechanical stage which rotates the source about a fixed axis of rotation to accurately position the fan beam at different known angles around the fixed axis.
U.S. Pat. No. 5,503,152 to C. G. Oakley et al describes using two elongated arrays of transducers in fixed relation to each other to produce a three dimensional image of an object in a thick volume slice of the object. The slice of the object imaged is an “overlap” volume of the object which is illuminated by ultrasound energy from both arrays. The two arrays receive reflections of ultrasound pulses from the same structures in the overlap volume with different time delays. The time delays are translated into distances from the arrays and the structures are located in the overlap region using triangulation and the distance between the arrays. To produce an image of extended volumes, a transducer assembly is mounted to a mechanical device which moves a transducer assembly over a wide range of controllable positions.
It would be advantageous to have a system for locating the relative positions of ultrasound tomograph slices acquired with a mobile hand source of ultrasound energy that did not depend upon locating the position of the moving source with respect to a fixed reference coordinate system.
SUMMARY OF INVENTION
It is an object of some aspects of the present invention to provide a relatively simple and inexpensive method for accurately locating the relative positions of tomograph slices at which image data for an ultrasound image of an object are acquired.
In a preferred embodiment of the present invention, the relative locations and orientations of tomograph slices are determined by calculation based on the acquired image data. The method determines the location of the slices without the need to determine the location and orientation of the slices with respect to a fixed reference coordinate system.
For each of a plurality of tomograph slices, values for the image data and values for the first spatial derivative of the image data in the direction perpendicular to the plane of the slice are acquired for a plurality of data points in the slice. For each particular slice, the data points are located in the space of the slice by coordinate values measured relative to a coordinate system specific to the particular slice, which coordinate system is defined and known with respect to the plane of the slice. Preferably, the origin of the coordinate system is located at a point in the plane of the slice, the x and y axes are in the plane of the slice and the z axis is perpendicular to the plane of the slice. Spatial derivatives of the image data at data points in the plane of the slice along the x and y axes are calculated from differences between values of the image data at data points in the slice. The coordinate systems specific to different slices are not the same. They may be displaced one from the other and/or their coordinate axes may be rotated with respect to each other.
Since for each slice, the image data and its first spatial derivatives are known at data points in the slice, first order Taylor series can be expanded about these data points that provide estimates of the image data in volumes of space centered at the data points. As a result, for any given tomograph slice, the image data is known in a volume of space centered about the slice, hereafter referred to as the “Taylor volume”. The Taylor volume extends about the plane of the tomograph slice to points located at distances from the plane for which the Taylor series expanded about the data points provide substantially accurate estimates of the image data.
In accordance with a preferred embodiment of the present invention, adjacent tomograph slices are located sufficiently close together so that at least one of the adjacent slices, hereafter referred to as the “target slice” is located inside the Taylor volume of the other slice, hereafter referred to as the “Taylor slice”. For a point on the target slice, a measured value of the image data, and a value of the image data for the same point, calculated from a Taylor series expanded about a data point in the Taylor slice, must be the same. In accordance with a preferred embodiment of the present invention, the relative location and orientation of the two adjacent tomograph slices are determined from the requirement that Taylor series expansions of the image data from points in the Taylor slice must provide values for the image data, at points on the target slice, that are substantially the same as the measured values of the image data at the points on the target slice.
In accordance with a preferred embodiment of the present invention, the relative locations and orientations of the specific coordinate systems associated with a plurality of adjacent tomograph slices are determined. Once this is accomplished, image data acquired as functions of the coordinates of the various specific coordinate systems a preferably transformed to a single common coordinate system. The images of the object from the various tomograph slices are then be correlated with each other and an accurate image of the volume of the object containing the tomograph slices is constructed.
Let x,y,z, (in vector notation {right arro
Entis Allan
Friedman Zvi
Fenster & Company Patent Attorneys Ltd.
GE Ultrasound Israel Ltd.
Lateef Marvin M.
Patel Maulin
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