A pilot study using normalised residual activity: a technique to minimise the renogram scan time in infants and children

The aim of this study is to assess the diagnostic utility of Normalised residual activity (NORA) in reducing the total acquisition time, by estimating the renal emptying during the 99m-Tc EC (Ethylene dicysteine) renogram acquisition and interpreting their values with delayed images in obstructed and un-obstructed kidneys. A total of 42 cases, of which 34 male and 8 female children with mean age group of 1.38 ± 2.00 years, were included in this study between September, 2014 to March, 2015. These cases were referred to Department of nuclear medicine in view of clinical suspicion of obstruction and inconclusive findings on various conventional imaging modalities such as ultrasound (US) examination, intravenous urography (IVU) or computerized tomography (CT) of abdomen or magnetic resonance urography (MRU) and renal function tests including serum creatinine level in all cases. All 42 cases underwent renogram of 30 mins. acquisition after administration of 1.5 ± 0.3 mCi of 99m-Tc EC with F+0 protocol with initial perfusion images with 2 sec/Frame for 60 sec. followed by dynamic images of 15 sec/Frame for later 29 mins. with 128*128 matrix and zoom of 1.2 to 2.0 depending on age of child by using low energy high resolution all-purpose collimator. NORA was calculated by taking counts at 3^rd and 20^th mins. of acquisition for all cases and correlated with delayed images. We have considered NORA cut off value of ≤ 0.5 as normal un-obstructive drainage pattern. On correlation with delayed images of both left and right kidneys, NORA parameter showed concordance of 94% and discordance of 5% with delayed images in total of 84 kidneys with measure of agreement i.e. Cohen's kappa (κ) of 0.865 with p value <0.001, which is statistically significant. From this study, we can conclude that NORA is the parameter, which can be used in early assessment of obstructive drainage pattern, particularly in post Pyeloplasty cases in infants and children where total duration of imaging can be reduced by avoiding delayed image acquisition. (author)