The Usefulness of Pulsatile Flow Detection in Measuring Resistive Index in Renal Doppler US are red, while non-pulsatile flows are blue. In applying the PFD function, we only used the three-color mode. RESULTS RI examination times are shown in Table 1. In group A, the mean time was 70.3 secs with CCD and 39.8 secs with PFD, while in group B the respective times were 24.6 secs and 42.7 secs. In both groups A and B, the first examina- tion time was longer than the second (p = 0.022 in group A; p = 0.0014 in group B). In group B (with PFD first), the first examination took less time than in group A (mean 42.7 secs vs. mean 70.3 secs; p = 0.031). Furthermore, CCD showed a statistically Table 1. Examination Time Group A CCD time PFD time Group B PFD time CCD time First Examination Time Group A (CCD first) Group B (PFD first) CCD examination time When used first When used after PFD PFD examination time When used first When used after CCD N 30 30 26 26 30 26 30 26 26 30 Mean (secs) SD T = 2.37, p = 0.022* 70.3 39.8 T = 3.51, p = 0.0014* 42.7 24.6 T = 2.25, p = 0.031* 70.3 42.7 T = 3.98, p = 0.0004* 70.3 24.6 T = 0.37, p = 0.71* 42.7 39.8 Note. N = numbers of kidneys examined, secs = seconds, SD = standard deviation, * = t test was used, CCD = conventional color Doppler, PFD = pulsatile flow detection Table 2. Quality of Spectral Doppler Waveforms in Conven- tional Color Doppler (CCD) and Pulsatile Flow Detection (PFD) Gr 0 (N = 5) 3 1 1 PFD Gr 1 (N=29) 07 1 07 CCD Gr 0 (N = 12) Gr 1 (N = 31) Gr 2 (N = 13) Note. Gr = grade; N and other figures indicate the numbers of kidneys examined. Bold figures show the numbers of PFD exami- nations in which the grades obtained were the same or better than those obtained in CCD (47/56 = 83.9%) Korean J Radiol 3(1), March 2002 62.0 33.4 24.5 9.3 62.0 4.8 62.0 9.3 24.5 33.4 Gr 2 (N=22) 5 02 05 significant difference in examination time (p = 0.0004) when used after PFD (mean, 24.6 secs) than when used first (mean, 70.3 secs) whereas PFD did not (39.8 vs. 42.7 secs, respectively; p = 0.37). Waveform quality is summarized in Table 2. Grade 2 waveforms were more common in PFD examinations than in CCD examinations (39.3% vs. 23.2%, respectively), while grade 0 waveforms were less common in PFD than in CCD examinations (8.9% vs. 21.4%, respectively). In the same kidney, 83.9% of waveforms (47/56) showed the same or a better grade with PFD than with CCD, though this finding was not statistically significant. DISCUSSION PFD was developed by GE Medical Systems in 1999 and installed first in their Logiq500 series. It is a function of color Doppler, and can be activated only in that mode. Compared with CCD, it provides additional information (on flow pulsatility) and is more sensitive. To distinguish pulsatile flow, a ‘pulsatile flow detector’ was added to the color flow processor (Fig. 3). PFD, based on power Doppler imaging (PDI) or directional PDI, is highly sensitive in the detection of blood flow and also sup- presses random noise. To avoid the misinterpretation of non-arterial flows such as that of the portal vein or inferior vena cava, which show some pulsatility, this is determined not only by velocity difference but as a function of velocity difference, variance and power. In some flows, however, overlapping inevitably occurs. Degree of pulsatility may be influenced by pulse repeti- tion frequency (PRF). In a given flow, if PRF is set too high, the pulsatility of that flow appears to be low, and to avoid misinterpretation the optimal PRF setting is needed. As mentioned above, PFD has two color modes (Fig. 2), 1 5 Fig. 3. Principle of PFD. A ‘pulsatile flow detector’ is placed in a color flow processor and flow pulsatility is determined as a func- tion of velocity difference, variance, and power. 47