Enhanced method for reducing ultrasound speckle noise using wavelet transform
First Claim
1. An adaptive method for reducing signal-dependent noise mixed with a true signal in a coherent imaging system signal, comprising the steps of:
- for sampled amplitudes at each beam angle;
(a) dividing a sampled range amplitude signal into a number of first subinterval signals of equal length;
(b) transforming each of said first subinterval signals using discrete wavelet transformation to provide first wavelet transform coefficients for each of a plurality of first wavelet scales having different levels of resolution ranging from a first finest wavelet scale to a first coarsest wavelet scale;
(c) for each transformed beam subinterval, deleting all of the first wavelet transform coefficients representing said finest first wavelet scale;
(d) for each said first wavelet scale other than said finest first wavelet scale, identifying for each of said first subinterval signals which of said first wavelet transform coefficients are related to noise and which are related to a true signal through use of adaptive nonlinear thresholding;
(e) setting to zero those first wavelet transform coefficients which are identified as being related to noise;
(f) inverse transforming the so modified first wavelet transform coefficients using an inverse discrete wavelet transformation to provide a filtered range amplitude signal;
repeating steps (b)-(f) for each subinterval signal comprising said sampled range amplitude signal; and
for filtered amplitudes at each range;
(g) dividing a sampled beam angle amplitude signal into a number of second subinterval signals of equal length;
(h) transforming each of said second subinterval signals using discrete wavelet transformation to provide second wavelet transform coefficients for each of a plurality of second wavelet scales having different levels of resolution ranging from a finest second wavelet scale to a coarsest second wavelet scale;
(i) for each second wavelet scale, identifying for each of said second subinterval signals which of said second wavelet transform coefficients are related to noise and which are related to a true signal through the use of adaptive nonlinear thresholding;
(j) setting to zero those second wavelet transform coefficients which are identified as being related to noise;
(k) inverse transforming the so modified second wavelet transform coefficients using an inverse discrete wavelet transformation to provide a speckle-reduced beam angle amplitude signal; and
repeating steps (h)-(k) for each subinterval signal comprising said sampled beam angle amplitude signal to provide a speckle-reduced range-beam angle image.
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Abstract
Signal-dependent noise in a coherent imaging system signal, such as in medical ultrasound imaging, is reduced by filtering speckle noise using nonlinear adaptive thresholding of received echo wavelet transform coefficients, thereby enhancing the resultant image by improving the signal-to-noise ratio. The method includes the steps of dividing the imaging system signal into a number of subinterval signals of equal length; transforming each subinterval signal using discrete wavelet transformation to provide wavelet transform coefficients for each of a plurality of wavelet scales having different levels of resolution ranging from a finest wavelet scale to a coarsest wavelet scale: deleting all of the wavelet transform coefficients representing the finest wavelet scale: for each wavelet scale other than the finest wavelet scale, identifying for each subinterval signal which of the wavelet transform coefficients are related to noise and which are related to a true signal through the use of adaptive nonlinear thresholding; selecting those wavelet transform coefficients which are identified as being related to a true signal; and setting to zero those wavelet coefficients which are identified as being related to noise: inverse transforming the modified wavelet transform coefficients using an inverse discrete wavelet transformation to provide an enhanced true signal with reduced noise.
109 Citations
11 Claims
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1. An adaptive method for reducing signal-dependent noise mixed with a true signal in a coherent imaging system signal, comprising the steps of:
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for sampled amplitudes at each beam angle; (a) dividing a sampled range amplitude signal into a number of first subinterval signals of equal length; (b) transforming each of said first subinterval signals using discrete wavelet transformation to provide first wavelet transform coefficients for each of a plurality of first wavelet scales having different levels of resolution ranging from a first finest wavelet scale to a first coarsest wavelet scale; (c) for each transformed beam subinterval, deleting all of the first wavelet transform coefficients representing said finest first wavelet scale; (d) for each said first wavelet scale other than said finest first wavelet scale, identifying for each of said first subinterval signals which of said first wavelet transform coefficients are related to noise and which are related to a true signal through use of adaptive nonlinear thresholding; (e) setting to zero those first wavelet transform coefficients which are identified as being related to noise; (f) inverse transforming the so modified first wavelet transform coefficients using an inverse discrete wavelet transformation to provide a filtered range amplitude signal; repeating steps (b)-(f) for each subinterval signal comprising said sampled range amplitude signal; and for filtered amplitudes at each range; (g) dividing a sampled beam angle amplitude signal into a number of second subinterval signals of equal length; (h) transforming each of said second subinterval signals using discrete wavelet transformation to provide second wavelet transform coefficients for each of a plurality of second wavelet scales having different levels of resolution ranging from a finest second wavelet scale to a coarsest second wavelet scale; (i) for each second wavelet scale, identifying for each of said second subinterval signals which of said second wavelet transform coefficients are related to noise and which are related to a true signal through the use of adaptive nonlinear thresholding; (j) setting to zero those second wavelet transform coefficients which are identified as being related to noise; (k) inverse transforming the so modified second wavelet transform coefficients using an inverse discrete wavelet transformation to provide a speckle-reduced beam angle amplitude signal; and repeating steps (h)-(k) for each subinterval signal comprising said sampled beam angle amplitude signal to provide a speckle-reduced range-beam angle image. - View Dependent Claims (2, 3, 4, 5)
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6. A speckle noise filter for an ultrasound imaging system, comprising:
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means for dividing a sampled range signal into a number of subinterval signals of equal length for each beam; means for transforming each of said subinterval signals using discrete wavelet transformation to provide wavelet transform coefficients for each of a plurality of wavelet scales having different levels of resolution ranging from a finest wavelet scale to a coarsest wavelet scale; means for deleting all of the wavelet transform coefficients representing said finest wavelet scale for each transformed beam subinterval; adaptive nonlinear thresholding means for identifying which of said wavelet transform coefficients are related to noise and which are related to a true signal for those subinterval signals corresponding to wavelet scales other than said finest wavelet scale; means for selecting only those wavelet transform coefficients which are identified as being related to a true signal; and means for inverse transforming said selected wavelet transform coefficients using an inverse discrete wavelet transformation to provide an enhanced true signal with reduced noise. - View Dependent Claims (7, 8)
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9. An ultrasound imaging system comprising:
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an array of transducers; means for selectively operating said transducers in a transmission mode to produce propagating pulses from electrical signals, said electrical signals being timed to produce transmitted ultrasound beams focused at selected points; means for selectively operating said transducers in a reception mode to produce electrical detection signals from received ultrasound echoes, said electrical detection signals being delayed and summed to produce sampled range signals which are dominated by the received echoes reflected from respective focal points;
a speckle noise filter for filtering out speckle noise included in said sampled range signals;a scan converter for scan converting said filtered range signals into X-Y display coordinates; and a display monitor for displaying a series of data samples produced by said means for selectively operating said transducers in a reception mode and scan convened by said scan converter, wherein said speckle noise filter comprises; means for dividing the sampled range signal into a number of subinterval signals of equal length for each of said beams; means for transforming each of said subinterval signals using discrete wavelet transformation to provide wavelet transform coefficients for each of a plurality of wavelet scales having different levels of resolution ranging from a finest wavelet scale to a coarsest wavelet scale; means for deleting all of the wavelet transform coefficients representing said finest wavelet scale for each of the transformed beam subintervals; adaptive nonlinear thresholding means for identifying which of said wavelet transform coefficients are related to noise and which are related to a true signal for those of said subinterval signals corresponding to a wavelet scale other than said finest wavelet scale; means for setting to zero those wavelet transform coefficients which are identified as being related to noise; and means for inverse transforming the so modified wavelet transform coefficients using an inverse discrete wavelet transformation to provide an enhanced true signal with reduced noise. - View Dependent Claims (10, 11)
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Specification