Preliminary assessment of interand intraobserver reproducibility, and normative values of renal mean transit time (MTT) and parenchymal transit time (PTT) for 99mTc-etylenodicysteine

Abstract

BACKGROUND: The clinical significance of MTT and PTT, determined by deconvolution of renographic curves, is arguable. Their usefulness in diagnosis of obstructive uro- and nephropathy, renovascular hypertension and monitoring of transplanted kidneys is pointed out, but susceptibility of deconvolution methods to errors resulting from “statistical noise” is also stressed. So far there are no reports on normative MTT values for ^99mTc-EC, although such values were already determined for ¹³¹I-OIH, ^99mTc-DTPA and ^99mTc-MAG3. The aim of this study is an assessment of inter- and intraobserver reproducibility of MTT and PTT for ^99mTc-EC, and determination of normative values for these parameters.

MATERIALS AND METHODS: 31 patients (17 women and 14 men aged 19–75, average 44 years) referred for dynamic renal scintigraphy with: unilateral flow impairment (11), unilateral nephrolithiasis (2), control after unilateral lithotripsy (4), moderate hypertension (demographically with > 99% probability of primary hypertension) (4), suspected cirrhosis of one kidney (3), future kidney donors (3), control after abdominal injuries (3), incontinence (1). 42 functionally efficient kidneys were included in the study. Criteria for recognition of a kidney as functionally efficient were: — no earlier history of renal disease, signs of renal damage in basic blood and urine tests, or abnormalities in ultrasonography; — normal result of dynamic renal scintigraphy (in terms of sequential images and renographic curve). MTT and PTT values were determined independently by two operators, using a matrix method for deconvolution of renographic curves.

RESULTS: Differences between mean MTT and PTT from two studies by one operator were insignificant and those values were closely correlated (r = 0.99 and r = 0.97, respectively). Differences of values obtained by both operators were practically insignificant for MTT (r = 0.93), and significant for PTT (r = 0.81 and p < 0.001). These differences do not disqualify that processing method. The upper limits of normative values of MTT and PTT were based on the results from first study performed by more experienced operator — 200 s and 170 s, respectively.

CONCLUSIONS: The procedure of processing dynamic renal scintigraphy used in this study is reproducible. Normative values of MTT and PTT for ^99mTc-EC were established as 200 s and 170 s, respectively. An attempt to optimize and standardize the technique of determining parenchymal ROI in a matrix deconvolution method, followed by an evaluation of clinical usefulness of these parameters in the diagnosis of chosen renal function impairments would be a logical continuation of this initial research.