Fig. 7.

Mean transit time (MTT). a Using the two-compartment Annet model, we evaluated tubular function by calculating the MTT. In an unpublished study of 38 children with normal-appearing kidneys on MR urography (i.e. 76 kidneys), the MTT was 53.9 s with a standard deviation of 9.4 s. b The MTT is another potentially reversible parameter when evaluating hydronephrosis and obstruction. In a group of 37 people with unilateral decompensated ureteropelvic junction (UPJ) obstruction, the average preoperative MTT for the hydronephrotic kidney was 149 s with a standard deviation of 88 s. Following successful pyeloplasty, the average MTT fell to (mean ± standard deviation) 47.8±14 s (J. D. Grattan-Smith, unpublished data). The MTT for the normal contralateral kidneys were 48±14 s preoperatively and 59±9 s postoperatively