Time-scale detection of microemboli in flowing blood with Doppler ultrasound

Brian S. Krongold, Akbar M. Sayeed, Mark A. Moehring, James A. Ritcey, Merrill P. Spencer, Douglas L. Jones

Research output: Contribution to journalArticlepeer-review

Abstract

Small formed elements and gas bubbles in flowing blood, called microemboli, can be detected using Doppler ultrasound. In this application, a pulsed constant-frequency ultrasound signal insonates a volume of blood in the middle cerebral artery, and microemboli moving through its sample volume produce a Doppler-shifted transient reflection. Current detection methods include searching for these transients in a short-time Fourier transform (STFT) of the reflected signal. However, since the embolus transit time through the Doppler sample volume is inversely proportional to the embolus velocity (Doppler-shift frequency), a matched-filter detector should in principle use a wavelet transform, rather than a short-time Fourier transform, for optimal results. Closer examination of the Doppler shift signals usually shows a chirping behavior apparently due to acceleration or deceleration of the emboli during their transit through the Doppler sample volume. These variations imply that a linear wavelet detector is not optimal. We apply linear and quadratic time-frequency and time-scale detectors to a set of noise-corrupted embolus data. Our results show improvements of about 1 dB using the time-scale detectors versus an STFT-based detector signifying that embolus detection is best approached as a time-scale problem. A time- scale-chirp detector is also applied and is found to have the overall best performance by about 0.5-0.7 dB while coming fairly close (about 0.75 dB) to a theoretical upper bound.

Original languageEnglish (US)
Pages (from-to)1081-1089
Number of pages9
JournalIEEE Transactions on Biomedical Engineering
Volume46
Issue number9
DOIs
StatePublished - 1999

Keywords

  • Doppler ultrasound
  • Microemboli
  • Time-frequency
  • Time-scale
  • Wavelet detection

ASJC Scopus subject areas

  • Biomedical Engineering

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