Gapped sampled spectrum Doppler estimation.

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Signal Processing

Background:

• Conventional ultrasound transmit schemes with uniform sampling have limitations in flexibly increasing pulse repetition frequency (PRF) and frame rates.
• Duplex and triplex transmit patterns with spectral Doppler sample gaps offer potential for improved PRF and frame rate.
• Nonparametric gapped sampled spectrum estimators have not been fully explored for these advanced transmit patterns.

Purpose of the Study:

• To assess the technical feasibility of nonparametric gapped sampled spectrum estimators for duplex and triplex ultrasound transmit patterns.
• To compare the signal-to-noise ratio (SNR) of coherent versus incoherent gapped sampled spectrum estimators.
• To evaluate the performance of these estimators using quantitative metrics in phantom and in vivo experiments.

Main Methods:

• Implementation and testing of nonparametric gapped sampled spectrum estimators with duplex and triplex transmit patterns.
• Coherent and incoherent averaging techniques applied within an axial/temporal 2-D window.
• Validation using steady-state flow phantom experiments and in vivo imaging of the left clavicular artery and ascending aorta.
• Quantitative evaluation using SNR, root mean square error, and zero frequency peak full-width at half-maximum.

Main Results:

• Periodically gapped estimators can achieve results comparable to fully sampled counterparts with appropriate parameter selection.
• Coherent averaging within a 2-D window significantly improves SNR compared to incoherent averaging for gapped estimators.
• This SNR improvement also applies to previously reported fully sampled incoherent estimators when their coherent versions are used.
• Fourier synthesis enables the creation of fully sampled time-domain audio signals from spectral estimates.

Conclusions:

• Nonparametric gapped sampled spectrum estimators are technically feasible and advantageous for duplex and triplex ultrasound transmit patterns.
• Coherent averaging is crucial for enhancing SNR in gapped sampled spectrum estimation, outperforming incoherent methods.
• These advanced estimators offer a pathway to improved ultrasound imaging performance, with potential applications demonstrated in vascular imaging and audio synthesis.