Experimental investigation of chirp coded excitation in ultrasound superharmonic imaging

Arif, Muhammad; Harput, Sevan; Freear, Steven

doi:10.1109/ultsym.2010.5935434

Cited by 2 publications

(2 citation statements)

References 11 publications

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“…Several recent studies have used chirps for superharmonic imaging and achieved results similar to those presented in this section [24]- [26].…”

Section: A Without Filtering In the Fcht Domainsupporting

confidence: 58%

“…To improve the SNR and penetration depth, chirp coded excitation techniques have been used for tissue harmonic imaging instead of conventional pulsed excitation [21]- [23]. Chirp excitation has already been employed for superharmonic imaging by [24]- [26]; however their results showed that linear frequency modulated (LFM) signals underperformed due to the high sidelobe levels caused by the spectral overlap between the harmonic components.…”

Section: Introductionmentioning

confidence: 99%

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Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics

Harput

McLaughlan

Cowell

et al. 2014

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Abstract-Superharmonic imaging improves the spatial resolution by using the higher-order harmonics generated in tissue. The superharmonic component is formed by combining the third, fourth and fifth harmonics, which has low energy content and therefore poor SNR. This study uses coded excitation to increase the excitation energy. The SNR improvement is achieved on the receiver side by performing pulse compression with harmonic matched filters.The use of coded signals also introduces new filtering capabilities that are not possible with pulsed excitation. This is especially important when using wideband signals. For narrowband signals the spectral boundaries of the harmonics are clearly separated and thus easy to filter, however the available imaging bandwidth is underused. Wideband excitation is preferable for harmonic imaging applications to preserve axial resolution, but it generates spectrally overlapping harmonics that are not possible to filter in time and frequency domains. After pulse compression this overlap increases the range sidelobes, which appear as imaging artifacts and reduce the B-mode image quality. In this study, the isolation of higher-order harmonics was achieved in another domain by using the Fan Chirp Transform (FChT).To show the effect of excitation bandwidth in superharmonic imaging, measurements were performed by using linear frequency modulated chirp excitation with varying bandwidths of 10 − 50%. Superharmonic imaging was performed on a wire phantom using a wideband chirp excitation. Results were presented with and without applying the FChT filtering technique by comparing the spatial resolution and sidelobe levels. Wideband excitation signals achieved a better resolution as expected, however range sidelobes as high as −23 dB were observed for the superharmonic component of chirp excitation with 50% fractional bandwidth. The proposed filtering technique achieved > 50 dB range sidelobe suppression and improved the image quality without affecting the axial resolution.

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“…Several recent studies have used chirps for superharmonic imaging and achieved results similar to those presented in this section [24]- [26].…”

Section: A Without Filtering In the Fcht Domainsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics

Harput

McLaughlan

Cowell

et al. 2014

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Accuracy of coded excitation methods for measuring the time of flight: Application to ultrasonic characterization of wood samples

et al. 2018

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Ultrasound computed tomography (USCT) using the transmission mode is a way to detect and assess the extent of decay in wood structures. The resolution of the ultrasonic image is closely related to the different anatomical features of wood. The complexity of the wave propagation process generates complex signals consisting of several wave packets with different signatures. Wave paths, depth dependencies, wave velocities or attenuations are often difficult to interpret. For this kind of assessment, the focus is generally on signal pre-processing. Several approaches have been used so far including filtering, spectrum analysis and a method involving deconvolution using a characteristic transfer function of the experimental device. However, all these approaches may be too sophisticated and/or unstable. The alternative methods proposed in this work are based on coded excitation, which makes it possible to process both local and general information available such as frequency and time parameters. Coded excitation is based on the filtering of the transmitted signal using a suitable electric input signal. The aim of the present study was to compare two coded-excitation methods, a chirp- and a wavelet-coded excitation method, to determine the time of flight of the ultrasonic wave, and to investigate the feasibility, the robustness and the precision of the measurement of geometrical and acoustical properties in laboratory conditions. To obtain control experimental data, the two methods were compared with the conventional ultrasonic pulse method. Experiments were conducted on a polyurethane resin sample and two samples of different wood species using two 500 kHz-transducers. The relative errors in the measurement of thickness compared with the results of caliper measurements ranged from 0.13% minimum for the wavelet-coded excitation method to 2.3% maximum for the chirp-coded excitation method. For the relative errors in the measurement of ultrasonic wave velocity, the coded excitation methods showed differences ranging from 0.24% minimum for the wavelet-coded excitation method to 2.62% maximum for the chirp-coded excitation method. Methods based on coded excitation algorithms thus enable accurate measurements of thickness and ultrasonic wave velocity in samples of wood species.

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Experimental investigation of chirp coded excitation in ultrasound superharmonic imaging

Cited by 2 publications

References 11 publications

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics

Accuracy of coded excitation methods for measuring the time of flight: Application to ultrasonic characterization of wood samples

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