MRI quantitative T1 and T2 mapping of the renal cortex: Assessment of normal values and potential usefulness for renal masses at 3 T

Purpose: The purpose of this monocentric retrospective study consisted in exploring the potential improvement of the assessment of renal masses on MRI by using the T1 (T1m) and T2 (T2m) mapping relaxation times.

Materials and methods: We recorded the renal cortex values of 125 patients with normal kidneys (reference group) and 75 patients with renal masses on a clinical 3 T MR unit using T1m and T2m sequences. For the quantitative evaluation, measurements were performed by delineating ROIs on T1m and T2m sequences in renal cortex of the reference group and in renal masses. Interobserver agreement for the qualitative analysis of image quality was assessed using quadratic Cohen's weighted kappa statistics (k). Student's paired t-test and non-parametric Kruskal-Wallis test were used to compare our datasets in terms of T1m and T2m values.

Results: For the cohort of reference group, mean renal cortex T1m and T2m values were 1,529 ± 83 ms and 98 ± 7 ms, respectively. No statistically significant differences were found for T1m and T2m in the reference group regardless of age, gender or eGRF categories. For the group with renal masses, mean T1m and T2m values were 1,667 ± 87 ms and 105 ± 8 ms; 1,621 ± 96 ms and 117 ± 6 ms, and 1,530 ± 62 ms and 85 ± 4 ms for renal cell carcinomas, angiomyolipomas, and oncocytomas, respectively. For T1m values, there was no significant difference (p = 0.37) among the three types of renal masses. Among histological subtypes we have found: RCC versus angiomyolipoma (p = 0.25), RCC versus oncocytoma (p = 0.15), and oncocytoma versus angiomyolipoma (p = 0.47). However, we have found a statistically significant difference for the T2m value (p = 0.0005). Among histological subtypes, only T2m values were statistically significant for each combination: RCC versus angiomyolipoma (p = 0.012), RCC versus oncocytoma (p = 0.0002), and oncocytoma versus angiomyolipoma (p = 0.003).

Conclusion: As this is the largest normal patient cohort, the T1m and T2m values recorded could be proposed as reference values and can play a role in the differential diagnosis between benign and malignant renal tumoral masses.