A noncontrast renal MRA is a very useful and safe diagnostic tool for screening of renal artery stenosis and for following up of renal transplantation. Because a substantial population of these patients who require the examination is renal insufficiency was existed. Noncontrast renal 3D MRA using time-spatial labeling inversion pulse (Time-SLIP) with respiratory triggering (Time-SLIP renal MRA) was applied to visualize dedicated renal arteries without contrast medium (1-3). To our knowledge, there are no studies demonstrating the reproducibility of Time-SLIP renal MRA. Thus, the purpose of this study is to ascertain the reproducibility of Time-SLIP renal MRA in clinical setting on health checkup screenings. All studies were performed using a commercial 1.5-T scanner (Toshiba Medical Systems Corp., Tochigi, Japan) with parallel imaging ATLAS body coil. The coronal imaging parameters were: TR/TE/FA=4.3ms/2.2ms/120°, spatial resolution=0.7×0.7×1.25mm³ (after interpolation), respiratory triggering, STIR with TI= 190 ms, parallel imaging reduction factor=2.0, Time-SLIP tag slice thickness=240 mm, and 2 segmentations. Image quality was evaluated by using source and MIP images for renal arteries. A total of 36 cases of renal artery screening was performed twice with a mean interval of 2.3 years; we compared the image quality, motion degradation and visible number of branches of each renal artery. The image was evaluated in image quality, motion degradation, contrast ratio and countable number of each renal arterial branches by an experienced observer using randomized image pairs. The image quality was rated on a 4-point scale (0 = poor, 1 = fair, 2 = good, and 3 = excellent), and scores 2 and 3 were defined as an acceptable image quality. The motion degradation was also assessed on a 4-point scale at renal arteries and branches: 1 indicates no visible motion degradation, 2 minimal motion degradation, 3 moderate motion degradation with blurring of the vessel border but diagnostic, and 4 severe motion degradation and non-diagnostic. Relative signal contrast ratio between artery (S_A) and background (S_B, renal cortex and renal medulla) signals was measured from the source images using CR_A-B = (S_A-S _B)/S_A. Wilcoxon signed rank test was used on the image quality, motion degradation and countable number of each renal arterial branches and paired-t test was used contrast ratio. A p value of less than <0.05 was considered to indicate a significant difference. Reproducibility of the contrast ratio was analyzed using Bland-Altman analysis. All 36 cases were successfully scanned and reproduced in the original and the repeated Time-SLIP renal MRA scans. Table 1 shows the visual evaluation of source and MIP image of renal arteries. Excluding the image quality of right renal artery MIP (1st: 2.97±0.17, 2nd: 2.79±0.41, p =0.03) and visible number of branches of right renal artery MIP (1st: 4.00±0.85, 2nd: 4.32±0.98, p =0.04), the image quality score, the score of motion degradation, and visible number of branches were not significantly difference between the two scans. The image quality score of all was more than 2, the number of difference score between the original and the repeated scans was 7 in right renal artery MIP. The contrast ratio between the original and the repeated scans was also similar, and the inter-scan agreement for both arteries was reliable using Bland -Altman analysis. The reproducibility of the original and the repeated scans was consistent and some cases had a slight difference in image score, which may be caused by respiratory condition difference between the original and repeated scans as well as setting difference of the Time-SLIP tag position by different operators. The reason for the difference of the image quality between the right and left renal arteries in MIP was the anatomical location of right kidney, which was located near the infra vena cava and it is easy to be affected by breathing condition. The reproducibility of Time-SLIP renal MRA was acceptable over all.Time-SLIP renal MRA allows acceptable visualization of renal arteries in repeated scans and appears to be highly reproducible for assessment of renal arteries.Thus, Time-SLIP renal MRA is a safe and useful technique for renal artery screening.