A Comparative Study of Normalized Residual Activity and Standard Parameters in 99mTc-DTPA Diuretic Renography:

September 3, 2026 updated by: Mahytab Abdelhafez Ezzat Abdelhafez, Assiut University

Improving Obstruction Diagnosis in 99mTc-DTPA Diuretic Renography: A Comparative Study of Normalized Residual Activity and Standard Parameters

The present study aims to compare the diagnostic performance of Normalized Residual Activity (NORA) with conventional renographic parameters obtained from 99mTc-diethylenetriamine pentaacetic acid (99mTc-DTPA) diuretic renography in the evaluation of patients with suspected urinary tract obstruction. The study seeks to determine whether NORA provides superior diagnostic accuracy and specificity for differentiating true urinary tract obstruction from non-obstructive dilatation, thereby improving the interpretation of diuretic renography and supporting appropriate clinical decision-making.

Study Overview

Status

Not yet recruiting

Conditions

Urinary Tract Obstruction

Intervention / Treatment

Detailed Description

Urinary tract obstruction is a common clinical condition encountered in both pediatric and adult populations and represents a significant cause of potentially reversible renal impairment. Persistent obstruction to urinary outflow may result in progressive deterioration of renal function, recurrent urinary tract infections, nephrolithiasis, hypertension, and ultimately irreversible renal damage if diagnosis and appropriate intervention are delayed. Consequently, early identification of clinically significant obstruction is essential to preserve renal function and optimize patient outcomes. However, differentiating true functional obstruction from non-obstructive dilatation remains one of the major diagnostic challenges in daily clinical practice, particularly in patients presenting with hydronephrosis detected by ultrasonography or other anatomical imaging modalities. (1-3) Although ultrasonography, computed tomography (CT), and magnetic resonance urography provide excellent anatomical information regarding the urinary collecting system, they cannot always determine whether dilatation is associated with functionally significant obstruction. Hydronephrosis may occur in the absence of obstruction due to physiological or congenital causes, including an extrarenal pelvis, non-obstructive pelvicalyceal dilatation, vesicoureteral reflux, or postoperative changes. Therefore, anatomical imaging alone is frequently insufficient for determining the need for surgical intervention, emphasizing the importance of functional assessment of urinary drainage. (1-3)

Diuretic renography has become the established functional imaging technique for evaluating suspected urinary tract obstruction. It provides simultaneous assessment of renal perfusion, differential renal function, and urinary drainage after pharmacologically induced diuresis, thereby enabling distinction between obstructive and non-obstructive dilatation. Among the radiopharmaceuticals used in renal scintigraphy, 99mTc-diethylenetriamine pentaacetic acid (99mTc-DTPA) remains widely used because it is eliminated exclusively by glomerular filtration, allowing for the estimation of glomerular filtration rate (GFR) in addition to assessing urinary drainage within a single examination. (1,4)

Interpretation of diuretic renography has traditionally relied on several qualitative and quantitative parameters, including visual assessment of the renogram curve, time to peak activity (Tmax), half-time of tracer clearance (T½), post-diuretic washout, and differential renal function. Although these parameters remain fundamental components of routine clinical practice, each has recognized limitations. Factors such as impaired renal function, severe pelvicalyceal dilatation, inadequate hydration, bladder distension, patient motion, and variations in diuretic administration protocols may significantly influence tracer washout and reduce diagnostic accuracy. Consequently, equivocal or false-positive interpretations may occur, particularly in markedly dilated but non-obstructed collecting systems. (1,4,7)

To overcome these limitations, several alternative quantitative indices have been proposed to improve the assessment of urinary drainage. One of the most promising parameters is Normalized Residual Activity (NORA), which represents the proportion of residual renal tracer activity at a specified time relative to the initial renal uptake. Unlike conventional washout measurements, NORA is less dependent on renal function and collecting system compliance and provides a simple quantitative estimate of residual tracer retention. Previous investigations have demonstrated that NORA improves discrimination between true urinary tract obstruction and non-obstructive dilatation, particularly when measured on post-micturition images. (5-7)

Recent evidence has suggested that NORA demonstrates superior diagnostic specificity compared with conventional renographic interpretation, reducing the number of equivocal examinations and minimizing unnecessary surgical intervention. Beatović et al. reported that post-micturition NORA correctly reclassified the majority of indeterminate or false-positive renographic studies while maintaining excellent diagnostic accuracy for urinary outflow obstruction. Such findings support the incorporation of quantitative drainage parameters into routine renographic interpretation; however, the clinical utility of NORA has not yet been universally adopted and remains insufficiently evaluated across different patient populations and imaging protocols. (5,7)

Given the continuing reliance on conventional renographic parameters in many nuclear medicine departments and the increasing interest in quantitative assessment of renal drainage, further evaluation of NORA is warranted. Comparing NORA with established renographic indices may

provide additional evidence regarding its diagnostic value and its potential role in improving the accuracy of diuretic renography for patients with suspected urinary tract obstruction. Therefore, the present study aims to compare the diagnostic performance of Normalized Residual Activity with conventional renographic parameters in 99mTc-DTPA diuretic renography for the diagnosis of urinary tract obstruction.

Additionally, Cortical Transit Time (CTT) is an effective metric for distinguishing between obstructed and non-obstructed kidneys. A delayed CTT flags kidneys at risk of functional deterioration if surgery is delayed, whereas a normal CTT signals that the kidney is safe from decline, independent of T_(1/2) values or drainage curve patterns. Ultimately, a normal CTT rules out obstruction as effectively as a favorable diuretic renogram drainage pattern [1].

Study Type

Observational

Enrollment (Estimated)

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Name: Mahytab Abdelhafez Ezzat, Bachelor
Phone Number: 0201096549745
Email: mahytababdelhafezmaster@gmail.com

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

Child
Adult
Older Adult

Accepts Healthy Volunteers

N/A

Sampling Method

Non-Probability Sample

Study Population

Pediatric or adult patients referred for 99mTc-DTPA diuretic renography because of suspected urinary tract obstruction.

Description

Inclusion Criteria:

Patients fulfilling all of the following criteria will be eligible for inclusion:

Pediatric or adult patients referred for 99mTc-DTPA diuretic renography because of suspected urinary tract obstruction.
Availability of a clinical reference standard (e.g., confirmation of obstruction via surgical findings/pyeloplasty, or proven non-obstruction via stable long-term clinical and radiological follow-up of at least 6-12 months).

Exclusion Criteria:

Patients meeting any of the following criteria will be excluded:

Patients with severe renal impairment.
Patients with renal congenital anomalies e.g. horseshoe kidneys
Technical failure during the scan, including severe patient motion artifacts or failure to properly administer the diuretic

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Diagnostic performance of Normalized Residual Activity (NORA) Versus conventional renographic parameters in 99mTc-DTPA diuretic renography in the diagnosis of urinary tract obstruction. Time Frame: approximately 2 years	approximately 2 years

Secondary Outcome Measures

Outcome Measure	Time Frame
• The ability of NORA to differentiate true urinary tract obstruction from non-obstructive urinary tract dilatation. Time Frame: approximately 2 years	approximately 2 years
Clinical usefulness of incorporating NORA into the routine interpretation of 99mTc-DTPA diuretic renography. Time Frame: approximately 2 years	approximately 2 years
The Predictive value of cortical transit time "CTT" for the deterioration in the function of the hydronephrotic kidney. Time Frame: approximately 2 years	approximately 2 years

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Assiut University

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

August 26, 2026

Primary Completion (Estimated)

September 1, 2027

Study Completion (Estimated)

August 1, 2028

Study Registration Dates

First Submitted

August 30, 2026

First Submitted That Met QC Criteria

September 3, 2026

First Posted (Actual)

September 10, 2026

Study Record Updates

Last Update Posted (Actual)