kidneys were examined. To avoid inter-examiner variabili- ty, the author performed all examinations. A 3 8 MHz transducer with PFD function (Logiq 700, General Electric Medical Systems, Milwaukee, Wis., U.S.A.) was used, the patients being divided into two groups. Group A included 30 kidneys in 16 patients, in whom CCD was used first to locate a sample volume to measure RI, and RI was measured again using PFD (Fig. 1). Group B included the remaining 26 kidneys in 15 patients in whom the order of examinations was reversed in order to eliminate any bias due to ordering. After choosing an imaging plane optimal for Doppler study, a gray-scale image was obtained and the current time was noted. This image was used as the starting point, and the subsequent time in seconds required to obtain a spectral wave sufficient for RI measurement was recorded. In each kidney, RI was measured twice in the same man- ner. One report has emphasized that the correct diagnosis of segmental renal arterial stenosis depends on whether multiple sampling locations are chosen (6), but in this study, which focused on a comparison between PFD and CCD, RI was measured at a single location, without target- ing a specific portion of kidneys (e.g. upper, mid-, or lower pole) for such measurement. Instead, the same imaging plane was used as the starting point in both CCD and PFD examinations, and in both procedures all Doppler parame- ters were kept identical. In color Doppler, the wall filter was set to 27 and the velocity scale or pulse repetition fre- quency (PRF) was 630 Hz. In spectral Doppler, sample volume size was 3 mm, wall filter was 56, and PRF was 2700. This setting was most commonly used in this study, but some modification was applied according to the patient involved. Kim Spectral waveform quality was graded as 0, 1, or 2, ac- cording to the degree of spectral broadening encountered and the consistency of the waveform pattern. Grade 0 indi- cates ‘poor’, with difficulty in locating the cursor to mea- sure peak velocity due to spectral broadening, or the re- production of less than two waves with the same peak ve- locity and pattern. Grade 2 indicates ‘excellent’, with spec- trums clear enough to easily locate the measurement cur- sor, and the consistent reproduction of more than four waves. Grade 1 indicates an intermediate quality, between grade 0 and grade 2. In PFD there are two modes of coloring, three-color and two-color (Fig. 2). In the former, pulsatile flow is green and added to the coloring of CCD, which is red (forward) and blue (backward). In the two-color mode, all pulsatile flows Fig. 2. PFD color modes. In the two-color mode (left), all pulsatile flows are red, while nonpulsatile flows are blue. In the three-color mode (right), pulsatile flows are green, and are added to colors depicted by directional color Doppler (red / blue). A B Fig. 1. A. PFD image of a kidney. Interlobar arteries are colored green (arrows) and easily distinguished from other non-pulsatile flows. B. The Doppler cursor is located on a green-colored interlobar artery and clear spectral waveforms (grade 2) are obtained. 46 Korean J Radiol 3(1), March 2002