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

<bold>Purpose: </bold>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.<bold>Materials and methods: </bold>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).<bold>Results: </bold>The difference between eGFR (89.91 +/- 18.45 ml<middle dot>min(-1)<middle dot>1.73 m(-2)) as reference standard and CT-GFR(iodine) (90.06 +/- 20.89 ml<middle dot>min(-1)<middle dot>1.73 m(-2)) was not statistically significant, showing excellent correlation (r = 0.88, P < 0.001) and agreement (+/- 19.75 ml<middle dot>min(-1)<middle dot>1.73 m(-2), P = 0.866). The correlation between eGFR and CT-GFR(120kvp) (66.13 +/- 19.18 ml<middle dot>min(-1)<middle dot>1.73 m(-2)) was poor (r = 0.36, P < 0.001), and the agreement was poor (+/- 40.65 ml<middle dot>min(-1)<middle dot>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).<bold>Conclusion: </bold>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.