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Evaluation of renal oxygen saturation using photoacoustic imaging for the early prediction of chronic renal function in a model of ischemia-induced acute kidney injury

Kenichiro Okumura, Junichi Matsumoto, Yasunori Iwata, Kotaro Yoshida, Norihide Yoneda, Takahiro Ogi, Azusa Kitao, Kazuto Kozaka, Wataru Koda, Satoshi Kobayashi, Dai Inoue, Norihiko Sakai, Kengo Furuichi, Takashi Wada, Toshifumi Gabata
PURPOSE: To evaluate the utility of photoacoustic imaging in measuring changes in renal oxygen saturation after ischemia-induced acute kidney injury, and to compare these measurements with histological findings and serum levels of kidney function. MATERIAL AND METHODS: Acute kidney injury was induced by clamping the left renal pedicle in C57Bl/6 mice, with a 35-min ischemic period used to induce mild renal injury (14 mice) and a 50-min period for severe injury (13 mice). The oxygen saturation was measured before induction, and at 5 time-points over the first 48 h after induction, starting at 4 h after induction. Oxygen saturation, histological score, kidney volume, and the 24 h creatinine clearance rate and serum blood urea nitrogen were also measured on day 28. Between-group differences were evaluated using a Mann-Whitney U-test and Dunn's multiple comparisons. The association between oxygen saturation and measured variables was evaluated using Spearman's correlation. A receiver operator characteristic curve was constructed from oxygen saturation values at 24 h after heminephrectomy to predict chronic renal function. RESULTS: The oxygen saturation was higher in the mild than severe renal injury group at 24 h after induction (73.7% and 66.9%, respectively, P<0.05). Between-group comparison on day 28 revealed a higher kidney volume (P = 0.007), lower tubular injury (P<0.001), lower serum level of blood urea nitrogen level (P = 0.016), and lower 24 h creatinine clearance rate (P = 0.042) in the mild compared with the severe injury group. The oxygen saturation at 24 h correlated with the 24 h creatinine clearance rate (P = 0.036) and serum blood urea nitrogen (P<0.001) on day 28, with an area under the receiver operating curve of 0.825. CONCLUSION: Oxygen saturation, measured by photoacoustic imaging at 24 h after acute kidney injury can predict the extent of subsequent histological alterations in the kidney early after injury.

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