Dynamic Renal T2-mapping After Furosemide Administration for Measurement of Differential Renal Function in Pediatric MR Urography.

BACKGROUND

Functional imaging of the kidney in pediatric patients is typically performed using contrast-enhanced MR urography (MRU) or nuclear scintigraphy, both of which require either gadolinium-based contrast agents or ionizing radiation. Furosemide, a loop diuretic routinely used in both modalities to stimulate urinary flow, acutely increases tubular fluid volume. These changes in renal water content can be detected by MRI-based quantitative T2 mapping, which may provide a contrast- and radiation-free alternative for evaluating kidney function.

OBJECTIVE

To assess renal T2 relaxation time changes following intravenous furosemide administration as a surrogate marker for differential renal function (DRF) in pediatric MRU.

MATERIALS AND

METHODS

In this prospective single-center study (June 2024 to March 2025), pediatric patients undergoing clinically indicated MRU received additional dynamic T2 mapping during furosemide administration using a respiratory-triggered gradient-and-spin-echo (GraSE) sequence. Two readers independently assessed T2 relaxation time changes. DRF was derived from the slope of the T2 increase (SlopeDRF) as well as from pre-T2 to post-T2 differences, expressed as each kidney's relative contribution to total function. These measures were compared with contrast-enhanced, Patlak-derived DRF (pDRF) using Pearson correlation and Bland-Altman analysis. Interreader agreement was assessed with the intraclass correlation coefficient (ICC).

RESULTS

Thirty-two patients (16 males; median age: 7 y, IQR: 0 to 11) were included. Renal parenchymal T2 relaxation times increased significantly after furosemide administration (pre: 118.4 ms, IQR: 110.8 to 124.4; post: 134.8 ms, IQR: 126.9 to 141.3; P < 0.001). SlopeDRF correlated strongly with pDRF (r = 0.81), and T2-difference DRF also demonstrated strong correlation with pDRF (r = 0.80). Interreader agreement for DRF was excellent (ICC = 0.94).

CONCLUSION

Dynamic renal T2 mapping after intravenous furosemide administration shows strong correlation with Patlak-derived DRF from contrast-enhanced MRU and may provide a noninvasive, contrast- and radiation-free method for quantifying differential renal function in children.