Estimation of renal function using iodine maps in dual-energy spectral computed tomography urography: a feasibility and accuracy study

To explore the feasibility of measuring glomerular filtration rate (GFR) using iodine maps in dual-energy spectral computed tomography urography (DEsCTU) and correlate them with the estimated GFR (eGFR) based on the equation of creatinine-cystatin C.

One hundred and twenty-eight patients referred for DEsCTU were retrospectively enrolled. The DEsCTU protocol included non-contrast, nephrographic, and excretory phase imaging. The CT-derived GFR was calculated using the above 3-phase iodine maps (CT-GFR_iodine) and 120 kVp-like images (CT-GFR_120kvp) separately. CT-GFR_iodine and CT-GFR_120kvp were compared with eGFR using paired t-test, correlation analysis, and Bland–Altman plots. The receiver operating characteristic curves were used to test the renal function diagnostic performance with CT-GFR_120kvp and CT-GFR_iodine.

The difference between eGFR (89.91 ± 18.45 ml·min⁻¹·1.73 m⁻²) as reference standard and CT-GFR_iodine (90.06 ± 20.89 ml·min⁻¹·1.73 m⁻²) was not statistically significant, showing excellent correlation (r = 0.88, P < 0.001) and agreement (± 19.75 ml·min⁻¹·1.73 m⁻², P = 0.866). The correlation between eGFR and CT-GFR_120kvp (66.13 ± 19.18 ml·min⁻¹·1.73 m⁻²) was poor (r = 0.36, P < 0.001), and the agreement was poor (± 40.65 ml·min⁻¹·1.73 m⁻², P < 0.001). There were 62 patients with normal renal function and 66 patients with decreased renal function based on eGFR. The CT-GFR_iodine had the largest area under the curve (AUC) for distinguishing between normal and decreased renal function (AUC = 0.951).

The GFR can be calculated accurately using iodine maps in DEsCTU. DEsCTU could be a non-invasive and reliable one-stop-shop imaging technique for evaluating both the urinary tract morphology and renal function.