The Usefulness of Pulsatile Flow Detection in Measuring Resistive Index in Renal Doppler US Sun Ho Kim, MD1 Index terms : Kidney, US Ultrasound (US), technology Ultrasound (US), Doppler studies Korean J Radiol 2002; 3: 45-48 Received September 19, 2001; accepted after revision February 9, 2002. Department of 1Radiology, Seoul National University College of Medicine and the Institute of Radiation Medicine, SNUMRC, Seoul National University Hospital, Seoul, Korea Address reprint requests to: Sun Ho Kim, MD, Department of Radiology, Seoul National University Hospital, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea. Telephone: (822) 760-2584 Fax: (822) 743-6385 E-mail: pinksu77@korea.com Objective: To assess the usefulness of pulsatile flow detection (PFD), a newly developed function of color Doppler US, in measuring resistive index (RI) in renal Doppler US and to compare it with conventional color Doppler (CCD). Materials and Methods: Fifty-six kidneys in 31 patients were randomly select- ed and divided into two groups. In group A, RI was measured first with the aid of CCD, and then with PFD. In group B, data were obtained in the reverse order. The time required for each RI measurement was recorded in seconds. The quali- ty of the Doppler spectral waveform was subjectively graded as 0, 1, or 2 and examination time and waveform quality were compared between PFD and CCD. Results: The time required to measure RI with PFD (PFD time) was less than with CCD (CCD time) (mean 42.7 secs vs. mean 70.3 secs; p = 0.031). There was no significant difference in PFD time between group A and B, but CCD time was shorter in group B (70.3 secs vs. 24.6 secs; p = 0.0004). Spectral waveform quality was not significantly different between PFD and CCD. Conclusion: The time required to measure RI in kidneys can be shortened with the aid of the PFD function in color Doppler US without affecting the quality of the examination. R renal diseases including urinary tract obstruction, renal parenchymal dis- enal Doppler US provides valuable hemodynamic information in various ease, renal vascular disease, and renal tumor (1 3). Nowadays, Doppler US is an essential part of renal US. Among Doppler indices, resistive index (RI) is most commonly used. To measure this accurately, it is essential to demonstrate intrarenal arterial branches with sufficient Doppler signal (4, 5). Conventional color Doppler (CCD) or power Doppler US has been used for this pur- pose. CCD gives information about flow direction, but with limited sensitivity, while power Doppler has higher sensitivity to slow flow but does not give directional infor- mation. Pulsatile flow detection (PFD) is a newly developed function of color Doppler which displays pulsatile flows in distinct color and with high sensitivity (Fig. 1). The purpose of this article is to assess the usefulness of PFD in measuring RI and to compare PFD with CCD in renal Doppler US. MATERIALS AND METHODS Thirty-one patients (17 men and 14 women) who were referred for kidney US and were randomly selected were included in this study. Six patients had only a single functioning kidney due to previous nephrectomy or transplantation, and thus, fifty-six Korean J Radiol 3(1), March 2002 45