High-frequency subharmonic emission with chirp-coded excitation: implications for imaging

Himanshu Shekhar; Marvin M. Doyley

doi:10.1117/12.911952

24 February 2012 High-frequency subharmonic emission with chirp-coded excitation: implications for imaging

Himanshu Shekhar, Marvin M. Doyley

Proceedings Volume 8320, Medical Imaging 2012: Ultrasonic Imaging, Tomography, and Therapy; 83200V (2012) https://doi.org/10.1117/12.911952
Event: SPIE Medical Imaging, 2012, San Diego, California, United States

Abstract

There is growing interest in developing techniques to assess the structure and function of microvasculature, to enable clinical diagnosis and to gain insights into disease pathology. High-frequency subharmonic imaging is an emerging technique that can visualize the microvasculature with high specificity. However, the sensitivity of high-frequency subharmonic imaging is compromised because of the pressure threshold for subharmonic behavior, which may limit its potential for preclinical and clinical imaging. The goal of this work was to demonstrate that the sensitivity of subharmonic imaging could be improved by rectangular apodization and chirp-coding of the excitation pulse. We report an experimental study carried out at 20-MHz transmit frequency to compare the efficacy of narrowband sine bursts and coded-chirps towards generating subharmonics. It was demonstrated that chirp-coding of the excitation pulse could generate stable subharmonic signals for excitation bandwidths of 10-20%. The threshold for onset of subharmonic behavior was lowest when rectangularwindowed excitation pulses were employed. The subharmonic to fundamental ratio of RF spectra using coded chirps was up to 5.7 dB higher for sine bursts, and the axial resolution obtained with chirp-coded excitation was up to twofold better compared to that obtained using sine bursts. At 20-MHz transmit frequency, 20% bandwidth rectangular chirp-coded pulse appears to be a good tradeoff between sensitivity and axial resolution.

Citation Download Citation

Himanshu Shekhar and Marvin M. Doyley "High-frequency subharmonic emission with chirp-coded excitation: implications for imaging", Proc. SPIE 8320, Medical Imaging 2012: Ultrasonic Imaging, Tomography, and Therapy, 83200V (24 February 2012); https://doi.org/10.1117/12.911952

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