Digital Signal Processing 18 (2008) 669–676 www.elsevier.com/locate/dsp Spectral broadening of lower extremity venous Doppler signals using STFT and AR modeling Sadık Kara a,* , Semra ˙ Içer b , Nuri Erdogan c a Erciyes University, Department of Electronics Engineering, 38039 Kayseri, Turkey b Erciyes University, Department of Biomedical Devices Technology, 38039 Kayseri, Turkey c Erciyes University, Faculty of Medicine, Radiology, 38039 Kayseri, Turkey Available online 14 September 2007 Abstract This study researches the behaviour of spectral broadening index (SBI) obtained from spectra achived using short-time Fourier transform (STFT) analysis compared to that of SBI based on autoregressive (AR) modeling of clinical Doppler lower extremity vein signal. Doppler signals from 12 healthy subject with eight different physiologic situations were analysed. Sonograms obtained from Doppler signals were used to compare the applied methods in terms of their frequency resolution and their effectiveness for the determination of SBI. The AR based sonograms produced narrower spectra compared to STFT sonograms. Besides, the magnitude of the STFT based SBI was larger than that of the AR based SBI. Furthermore, standard deviations and coefficient of variations of STFT and AR based SBIs changed depending on each physiologic situation. The results of this research have also shown that despite the qualitative improvement in the individual frequency spectra, there was no quantitative advantage in using the AR approach over the STFT for the determination of SBI. Moreover there was also an additional computational complexity income connections with AR modeling.  2007 Elsevier Inc. All rights reserved. Keywords: Spectral broadening; Venous Doppler signals; STFT; AR modeling 1. Introduction Ultrasonic Doppler flow imaging has become a powerfull tool in clinical applications. The Doppler effect, resulting from interaction of the ultrasonic wave with moving red blood cells, has been extensively used to determine blood flow velocity [1]. Doppler systems are based on the principle that ultrasound, emitted by an ultrasonic transducer, is returned partially toward the transducer by the moving red blood cells, thereby inducing a shift in frequency propor- tional to the emitted frequency and the velocity along the ultrasound beam [2–4]. The Doppler shift is related to the flow velocity by f D = 2υ λ cos θ, (1) * Corresponding author. Fax: +90 352 4375784. E-mail address: kara@erciyes.edu.tr (S. Kara). 1051-2004/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.dsp.2007.09.002