Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-06-17
2001-05-01
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S443000
Reexamination Certificate
active
06224552
ABSTRACT:
This invention relates to ultrasonic diagnostic imaging systems and, in particular, to ultrasonic diagnostic imaging systems which produce spatially compounded images with reduced seam artifacts.
Spatial compounding is an imaging technique in which a number of ultrasound images of a given target that have been obtained from multiple vantage points or angles are combined into a single compounded image by combining the data received from each point in the compound image target which has been received from each angle. Examples of spatial compounding may be found in U.S. Pat. Nos. 4,649,927; 4,319,489; and 4,159,462. Real time spatial compound imaging is performed by rapidly acquiring a series of partially overlapping component image frames from substantially independent spatial directions, utilizing an array transducer to implement electronic beam steering and/or electronic translation of the component frames. The component frames are combined into a compound image by summation, averaging, peak detection, or other combinational means. The acquisition sequence and formation of compound images are repeated continuously at a rate limited by the acquisition frame rate, that is, the time required to acquire the full complement of scanlines over the selected width and depth of imaging.
The compounded image typically shows lower speckle and better specular reflector delineation than conventional ultrasound images from a single viewpoint. Speckle is reduced (i.e. speckle signal to noise ratio is improved) by the square root of N in a compound image with N component frames, provided that the component frames used to create the compound image are substantially independent and are averaged. Several criteria can be used to determine the degree of independence of the component frames (see, e.g., O'Donnell et al. in IEEE Trans. UFFC v.35, no.4, pp 470-76 (1988)). In practice, for spatial compound imaging with a steered linear array, this implies a minimum steering angle between component frames. This minimum angle is typically on the order of several degrees.
The second way that spatial compound scanning improves image quality is by improving the acquisition of specular interfaces. For example, a curved bone-soft tissue interface produces a strong echo when the ultrasound beam is exactly perpendicular to the interface, and a very weak echo when the beam is only a few degrees off perpendicular. These interfaces are often curved, and with conventional scanning only a small portion of the interface is visible. Spatial compound scanning acquires views of the interface from many different angles, making the curved interface visible and continuous over a larger field of view. Greater angular diversity generally improves the continuity of specular targets. However, the angular diversity available is limited by the acceptance angle of the transducer array elements. The acceptance angle depends on the transducer array element pitch, frequency, and construction methods.
One of the problems that can arise when image lines from a plurality of look directions are acquired by a transducer is that all points in the ultimate compound image may not be insonified by the same number of differently steered beams. Consequently, different points or pixels in the compound image may be formed with different amounts of acquired data. Generally points in the central near field of the image will be formed from the greatest number of acquired echoes, while points at the lateral extremes and greater depths of the image are formed with fewer echoes, as fewer beams of different look directions are conveniently steered to those locations. While the processing of a compound image will usually take this uneven distribution of echoes into account when the echoes are summed by normalizing the sums as a function of the number of echoes or component pixels used to form the compound image pixel, the boundaries or seams between image regions of greater and lesser numbers of overlapping echoes can still be apparent in the image. Accordingly it is desirable to reduce these seam appearances in a spatially compounded image.
In accordance with the principles of the present invention, several techniques are described for reducing seam artifacts in a spatially compounded image. Transmit, receive or processing adjustments can be made to ensure that all regions in the compounded image have the same brightness. For example, compensation can be made for changes in echo amplitude due to beam steering or due to variable transmit or receive aperture size. Receive gain compensation, preferably automatic gain compensation, can be used to overcome conditions of varying attenuation of an echo signal. Seams due to motion effects can be reduced by resampling the echo data as a function of the sensing of motional effects. Seam blending, by which echo or pixel data in the vicinity of a seam is weighted, can be used to reduce seam artifacts in a compound image. Preferably, a number of these techniques are applied to the same image so that seam artifacts arising from a variety of causes can be reduced.
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Entrekin Robert R.
Jago James R.
Schmiesing Daniel C.
ATL Ultrasound
Lateef Marvin M.
Patel Maulin
Yorks, Jr. W. Brinton
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