Retrograde (Ascending or Direct) Radionuclide Cystogram (99mTc-DTPA)

7.7.1 Radiopharmaceutical

[^99mTc]Tc-diethylenetriaminepentaacetic acid, also known as

• [^99mTc]Tc-DTPA
• [^99mTc]Tc-Pentetate

7.7.2 Uptake mechanism / biology of the tracer

[^99mTc]Tc-DTPA is introduced in the bladder mixed with sterile isotonic saline, warmed to body temperature. It is retained in the bladder and excreted during micturition.

VUR is diagnosed when activity appears in the ureter(s) during the filling phase or during micturition.

[^99mTc]Tc-DTPA is not absorbed through the bladder wall, even after surgical augmentation (i.e., ileum).

7.7.3 Indications

• Direct radionuclide cystography is used for the detection and follow-up of VUR.
• The most relevant indications are detection of VUR in children after urinary tract infection or follow-up of children with known VUR during prophylactic antibiotic/bacteriostatic treatment.
• Many clinicians recommend a radiological VCUG as first exam in boys to visualize the urethra.
• DRC can be also used to assess the results of endoscopic or surgical treatment or for the detection of VUR in renal transplant recipients.

7.7.4 Contra-indications

• There are no contraindications, but bladder catheterization should be avoided during the active phase of urinary tract infection.

7.7.5 Clinical performances

Direct radionuclide cystography has a higher sensitivity for VUR than VCUG with the additional benefit of a lower radiation exposure in the majority of cases [121,122].

The lack of anatomical detail limits its use at the first diagnosis, particularly in boys, whereas it is the ideal technique for monitoring and follow-up.

7.7.6 Activities to administer

The suggested activities to be applied:

• [^99mTc]Tc-DTPA is 20 MBq

No recommendations are given for paediatric nuclear medicine.

7.7.7 Dosimetry

Effective dose is very low (0.048 mSv per 20 MBq), and the estimated dose to the bladder lies between 0.09 and 0.14 mSv per 20 MBq in children between 1 and 10 years, and the ovarian dose lies between 0.005-0.01 mGy [123].  Radiation exposure is further reduced by completely emptying the bladder after the examination.

7.7.8 Interpretation criteria/major pitfalls

VUR is diagnosed when the radiotracer is detected in the ureter and/or the renal collecting system. The number and duration of reflux episodes can be described, and a rough grading is possible. Standard five-degree grading is possible only in radiological VCUG.

VUR can be difficult to assess in ectopic pelvic kidneys and in transplanted kidneys, if the kidney is very close to the bladder and the ureter is very short.

7.7.9 Patient preparation

No specific preparation is required

7.7.10 Methods

The detailed recommendations study are available in Guidelines for Direct Radionuclide Cystography in Children [124].