Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-11-24
2003-02-25
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06524252
ABSTRACT:
FIELD
This patent specification relates to the field of ultrasound information processing systems. In particular, it relates to a method and system for generating ultrasound frames having decorrelated speckle patterns and generating compound ultrasound images therefrom.
BACKGROUND
Ultrasound imaging systems have become increasingly popular for use in medical diagnosis because they are non-invasive, easy to use, capable of real-time operation, and do not subject patients to the dangers of electromagnetic radiation. Instead of electromagnetic radiation, an ultrasound imaging system transmits sound waves of very high frequency (e.g., 1 MHz to 15 MHz) into the patient and processes echoes scattered from structures in the patient's body to derive and display information relating to these strictures.
One factor that currently limits the output quality of ultrasound imaging systems is the phenomenon of speckle. Speckle arises from the use of coherent signals to acoustically interrogate a target. Complex interference patterns arise from phase variations in the coherent signals as they propagate through, and reflect from, the many large and small acoustic reflectivity boundaries in the target. These phase variations may be caused by diffuse scatterers, by multiple scattering, by a non-homogeneous propagation medium which distorts the phase of the received wave, or by other factors.
Speckle appears to the viewer like random noise superimposed on the output image, and degrades the contrast resolution of the image (i.e., the accurate portrayal of the acoustic reflectivity of respective target locations). A speckle pattern will change in a visually recognizable (although complex) way upon a small displacement or rotation of the ultrasound transducer relative to the target, or upon small movements of the target tissue.
One common approach to reducing speckle involves image compounding, i.e., the combining of multiple component frames into an output image, the component frames having decorrelated, or at least partially decorrelated, speckle patterns. Most generally, decorrelation of the speckle patterns relates to how similar they are, or the degree to which their grainy structures appear to be derived from one another. As applied to image compounding, decorrelation of the speckle patterns relates to the degree to which compounding would reduce the speckle effects. Thus, for example, the compounding of two entirely correlated speckle patterns would cause little reduction in the amount of speckle. However, as the decorrelation of the speckle patterns is increased, compounding the patterns would result in speckle reduction, up to a maximum value when the two patterns became entirely decorrelated. It can be shown that, where direct frame averaging is used, this maximum value for speckle reduction is 2, or more generally N for N component frames. Mathematically, decorrelation of the two speckle patterns can be expressed by a measure such as a correlation coefficient, wherein a correlation coefficient of 1.0 corresponds to entirely correlated speckle patterns and a correlation coefficient of 0.0 corresponds to entirely decorrelated, speckle patterns.
Spatial compounding refers to the compounding of frame data from different sub-apertures and/or angular viewpoints for a given target location. Examples of spatial compounding from different angular viewpoints (“look angles”) can be found in U.S. Pat. No. 6,117,081 (Jago et. al.), U.S. Pat. No. 6,126,598 (Entrekin et. al.), U.S. Pat. No. 6,126,599 (Jago et. al.), and U.S. Pat. No. 6,135,956 (Schmiesing et. al.), which are incorporated by reference herein. There is a trade-off between speckle reduction and spatial resolution in such systems. For example, when using different sub-apertures, it is generally required that the relative translation of the sub-apertures be more than one-half the size of the sub-apertures to yield decorrelated speckle patterns. However, if more sub-apertures were formed to achieve this spacing, there would be a corresponding decrease in the spatial resolution of each component frame as the size of each aperture is decreased. Alternatively, if panoramic or extended view imaging is used to achieve a speckle reduction effect, image registration errors substantially reduce the spatial resolution.
Similar disadvantages are incurred in angular compounding systems such as those listed above, in which frames are taken from different “look angles” and compounded. As described therein, it is required that the “look angles” of the component frames be at least several degrees apart to achieve sufficiently decorrelated speckle patterns. However, as the angular separation of the “look angles” increases, there are beam steering and registration errors that reduce spatial resolution, as well as effective aperture reductions that reduce spatial resolution. Moreover, these errors get worse as the angles deviate further from the normal to the transducer, because small beam steering errors take on increased significance at these angles. Finally, these angular compounding systems suffer from grating lobes due to aliasing effects.
Frequency compounding is accomplished by dividing the bandwidth of the imaging system into multiple bands, and then processing and compounding signals from the different frequency bands. There is a trade-off between axial resolution and speckle reduction in these systems. For increased speckle reduction, it is desirable that the frequency bands of the interrogating pulses have lesser overlap in the frequency domain. However, to achieve this lesser overlap, the bandwidth of the interrogating pulses needs to be narrower, which corresponds to increased pulse length in the time domain and therefore reduced axial resolution. Frequency compounding also causes lateral resolution degradation due to contributions from the lower frequency component, thereby further decreasing spatial resolution.
Temporal compounding involves averaging successive frames together into a compound image. Because only one acoustic pulse can be sent into the target at a time, the above spatial compounding and frequency compounding techniques inherently involve temporal compounding as well. In theory, “pure” temporal compounding—in which no locations, angles, or frequencies are changed between frames—may not reduce speckle at all because the speckle pattern should not change between frames. In practice, however, many tissues and scattering structures incur a small amount of movement between component frames (e.g., through respiratory movements, gastric movements, small muscle movements, etc.) such that speckle patterns can change continually between component frames. Because no transducer movement, angle changes, or frequency changes are incurred between component frames, “pure” temporal compounding involves little or no loss of spatial resolution.
However, spatial compounding, frequency compounding, and temporal compounding each involve an additional trade-off between speckle reduction and temporal resolution, i e., the ability to “keep up” with moving tissue and/or a moving transducer. As more frames “N” are compounded to reduce speckle, the output image becomes increasingly blurry for locations of relative movement between the transducer and the target tissue, and/or the output frame rate is decreased.
Proposals have been made for dealing with the undesirable tradeoffs between speckle reduction and spatial and/or temporal resolution. For example, the '598 patent supra proposes a dynamic trade off between the blurring effect and the speckle effect, wherein the number of spatially compounded frames “N” is automatically reduced during fast tissue or transducer motion. The '081 patent supra proposes a substitute tradeoff, one between the blurring effect and the frame rate, wherein the “N” frames being compounded are first corrected for misregistration prior to compounding, albeit causing a concomitant reduction in output frame rate, and calling for a substantial increase in processing power and system complexity.
However, it is believed t
Lin Shengtz
Yin Feng
Yu Zengpin
Zhao Danhua
Cooper & Dunham LLP
Imam Ali M.
Lateef Marvin M.
U-Systems Inc.
LandOfFree
Method and system for generating ultrasound frames with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for generating ultrasound frames with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for generating ultrasound frames with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3171047