Repository logo

Browsing by Issue Date, starting with "2011-11-16"

Filter results by year or month
Now showing 1 - 2 of 2
  • Solving practical issues of a portable Doppler ultrasound system for blood flow assessment during coronary graft surgery
    Publication . Zabihian, B.; Ruano, M. Graça; Gonzalez, J. S.; Nocetti, D. F. G.; Cruz, M. F.
    This paper presents some practical issues regarding the development of a dedicated Doppler Ultrasound system (DUS) for the assessment of blood flow signal on coronary grafts during heart surgery. The DUS is composed of several processing units. This paper concentrates on front-end units: the transducer and a particular issue of the software interface for clinical evaluation, the noise cancellation technique (NCTech). The experimental set-up implemented to evaluate the transducer response is presented. The procedure employed to eliminate the noise components embedded in the DUS data is described. Each of these units was primarily tested in laboratory. Results show their effectiveness in achieving their specific goals. Comments on the overall system's performance are presented denoting the usefulness of such dedicated DUS during bypass assessment at heart surgery. © 2011 IEEE.
    2011-11-16Conference object Restricted access Show more
  • Enhancing time-frequency parameters estimation for Doppler ultrasound blood-flow signals
    Publication . Zabihian, B.; Ruano, M. Graça
    Doppler Ultrasound (DU) blood flow signals, particularly when collected under intra-operative conditions are noisy; accurate extraction of clinical parameters from their spectra becomes a difficult task. The spectral center frequency and bandwidth were estimated using two estimators with alternative time-frequency resolutions: a fixed resolution method, the Short-Time Fourier Transform (STFT) and the multi-resolution Continuous Wavelet Transform (CWT). Their performance was also assessed when the DU signals were pre-processed by a recently proposed Noise Cancellation Technique (NCTech). The NCTech algorithm enables quantification of the magnitude of the canceled noise in the form of percentage, called Cancellation Level (CL). Quantitative comparisons have been performed in terms of bias of the estimators when four signal-to-noise (SNRs) on DU simulated signals are employed: infinity, 20 dB, 10 dB and 5 dB. Results prove that CWT produced spectral parameters estimates with less bias than STFT; however these estimates were less consistent than the STFT ones. When NCTech is primarily applied to the signal, the STFT is the method to benefit most from this pre-processing technique. The CWT combined with NCTech produced estimates of both spectral parameters with better accuracy over the majority of the cardiac cycle, except where the frequency varies within a small range of frequencies during a short period of time. © 2011 IEEE.
    2011-11-16Conference object Restricted access Show more