AUTOMATIC TIME-OF-FLIGHT SELECTION FOR ULTRASOUND TOMOGRAPHY
Ultrasound sound-speed tomography requires accurate picks of time-of-flights (TOFs) of transmitted ultrasound signals, however, manual picking on large datasets is time-consuming. An improved automatic TOF picker is taught based on the Akaike Information Criterion (AIC) and multi-model inference (model averaging), based on the calculated AIC values, to improve the accuracy of TOF picks. The automatic TOF picker of the present invention can accurately pick TOFs in the presence of random noise with average absolute amplitude of up to 80% of the maximum absolute synthetic signal amplitude. The inventive method is applied to clinical ultrasound breast data, and compared with manual picks and amplitude threshold picking. Test results indicate that the inventive TOF picker is much less sensitive to data signal-to-noise ratios (SNRs), and performs more consistently for different datasets in relation to manual picking. The technique provides noticeably improved image reconstruction accuracy.
1 . A method of selecting time-of-flight (TOF) for ultrasound tomography waveforms generated by a given ultrasound tomography transmitter-receiver device directed on a tissue sample, comprising:
receiving a plurality of ultrasound waveforms from an ultrasound tomography transmitter-receiver device;
determining Akaike Information Criterion (AIC) values within a predetermined time window; and
selecting TOF for each said ultrasound waveform in response to the application of wavelet transforms searching said time window.
2 . A method as recited in claim 1 , wherein said AIC is determined as a best-model in which the AIC value is minimized.
3 . A method as recited in claim 1 :
wherein said AIC value is determined in response to multi-model averaging in which a weighted average of models is generated; and
wherein said weights for each model are assigned in response to the relative accuracy of each candidate model within the multiple models being considered.
4 . A method as recited in claim 1 , wherein said predetermined time window comprises a timing window determined in response to transmitter-receiver geometry and the sound speed in water.
5 . A method as recited in claim 1 , further comprising filtering to eliminate outliers in the TOF picks.
6 . A method as recited in claim 5 , wherein said filtering comprises median filtering.
7 . A method as recited in claim 5 , wherein said median filter has a length customized to the time differences between picked TOFs and the corresponding calculated TOFs in water based on the ring array geometry.
8 . A method as recited in claim 7 , further comprising replacing filtered out values with median values.
9 . A method as recited in claim 1 , further comprising comparing TOFs of reciprocal transmitter-receiver pairs and adjusting the associated TOF picks if they exceed a threshold.
10 . A method as recited in claim 9 , wherein said threshold is selectable by a user based on individual requirements and data quality needs.
11 . A method as recited in claim 9 , wherein said adjusting of TOF picks comprises replacing the TOF and its reciprocal TOF with an average of both TOF values.
12 . A method as recited in claim 1 , wherein determining said AIC value comprises comparing AIC values to a series of models which are previously specified.
13 . A method as recited in claim 1 :
wherein said AIC value is determined from, AIC(k)=k log (var(S(1, k)))+(N−k−1) log (var(S(k+1, N))), where S(1, k) and S(k+1, N) are the two segments in the selected time window; and
the variance function “var(.)” is determined from,
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where S is the mean value of S(i,j).
14 . A method as recited in claim 1 , further comprising generating ultrasound tomograph imaging in response to said TOF selections.
15 . A method as recited in claim 1 , wherein said ultrasound tomograph comprises ultrasonic breast tomography.
16 . A method as recited in claim 1 , wherein said method is configured to provide operator-independent, automatic, determination of TOFs for a set of ultrasonic signals.
17 . A method as recited in claim 1 , wherein said method selects TOFs without necessitating manual picking of TOF timing points in each of said plurality of ultrasonic waveforms.
18 . A method of selecting time-of-flight (TOF) for ultrasound tomography waveforms generated by a given ultrasound tomography transmitter-receiver device directed on a tissue sample, comprising:
receiving a plurality of ultrasound waveforms from an ultrasound tomography transmitter-receiver device;
determining a predetermined time window using the sound speed of water for the given transmitter-receiver device;
determining Akaike Information Criterion (AIC) values for the received data within said predetermined time window;
calculating a weighted average model for the signal segment;
selecting a TOF for each said ultrasound waveform in response to the application of wavelet transforms searching said time window;
applying a median filter to the TOF selections; and
correcting each TOF associated with said plurality of ultrasound waveforms in response to the difference between reciprocals.
19 . An apparatus for processing for ultrasound tomography waveforms, comprising:
means for receiving a plurality of ultrasound waveforms from an ultrasound tomography transmitter-receiver device directed through a tissue sample;
a computer processor and memory coupled to said means;
programming executable on said processor for,
determining a predetermined time window,
determining Akaike Information Criterion (AIC) values within said predetermined time window, and
selecting TOF for each said ultrasound waveform in response to the application of wavelet transforms searching said time window.
20 . A computer-readable media executable on a computer apparatus configured for processing ultrasound tomography waveforms, comprising:
a computer readable media containing programming executable on a computer processor configured for processing ultrasound tomography waveforms in response to receiving a plurality of ultrasound waveforms from an ultrasound tomography transmitter-receiver device directed through a tissue sample;
said programming executable on said processor configured for,
determining a predetermined time window,
determining Akaike Information Criterion (AIC) values within said predetermined time window, and
selecting TOF for each said ultrasound waveform in response to the application of wavelet transforms searching said time window.