The rotation method for correcting renal depth in the determination of glomerular filtration rate using Tc-99m diethylenetriamine pentaacetic acid (DTPA)-based renal dynamic imaging in patients with hydronephrosis.

Background: Kidney depth significantly affects the accuracy of glomerular filtration rate (GFR) measurement, and hydronephrosis-induced morphological changes further challenge its estimation through traditional formulas. This study evaluated the rotation method's efficacy in correcting kidney depth and depth difference during Tc-99m diethylenetriamine pentaacetic acid (DTPA) renal dynamic imaging for GFR assessment.

Methods: This study analyzed 66 individuals treated at First Hospital of Shanxi Medical University with unilateral hydronephrosis between January 2022 and June 2023. Abdominal computed tomography (CT) scans were used to classify hydronephrosis severity into mild (20 cases), moderate (23 cases), and severe hydronephrosis groups (23 cases). Depth and depth differences of the kidneys were measured using CT, the rotation method, the Tonnesen formula, and the Li-Qian formula to evaluate their impact on total and single-kidney GFR.

Results: (I) Regarding renal depth and GFR, compared to CT, the Tonnesen formula underestimated both the depth and GFR for normal and hydronephrotic kidneys (NKs and HKs). The mean depth of normal kidneys (NKs) measured by the Tonnesen formula was 6.14 cm, approximately 19% lower than the 7.59 cm measured by CT. Similarly, the GFR of NKs estimated by the Tonnesen formula was 37.13 mL/min/1.73 m, approximately 21% lower than the 47.24 mL/min/1.73 m measured by CT (P<0.05). The Li-Qian formula underestimated the renal depth and GFR for HKs. The mean depth of HKs measured by the Li-Qian formula was 7.62 cm, approximately 9% lower than the 8.41 cm measured by CT. Similarly, the GFR estimated by the Li-Qian formula was 25.50 mL/min/1.73 m, about 19% lower than the 31.51 mL/min/1.73 m measured by CT (P<0.05). There were no statistically significant differences in the GFR or renal depth measurements between the rotation method and CT for both NKs and HKs (P>0.05). In HKs, the depth and GFR measured by the rotation method were 8.17 cm and 30.41 mL/min/1.73 m, respectively, closely matching the CT measurements of 8.41 cm and 31.51 mL/min/1.73 m. (II) A comparison of the renal depth and GFR in the mild, moderate, and severe hydronephrosis groups was conducted. Compared with CT, the Tonnesen formula undervalued renal depth and GFR across all severity levels (P<0.05); meanwhile, the Li-Qian formula underestimated the renal depth and GFR of the moderate and severe hydronephrosis groups (P<0.05). The rotation method demonstrated no variance across the three groups compared to CT (P>0.05). (III) In terms of depth difference, the Tonnesen and the Li-Qian formulae produced a significantly lower value than did CT (P<0.05). Statistical analyses showed no difference between the rotation and CT methods (P>0.05).

Conclusions: In patients with hydronephrosis, the renal depth and depth difference measured by the rotation method are similar to those measured by CT, which can accurately correct the renal depth and depth difference without increasing the patient's additional radiation, enhancing the precision of total and separate renal GFR.