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

7.8.1 Radiopharmaceutical:

Na[^99mTc]TcO₄ ([^99mTc]Sodium pertechnetate)

7.8.2 Uptake mechanism / biology of the tracer

(Na[^99mTc]TcO₄) is introduced in the bladder mixed with sterile isotonic saline, warmed to body temperature. It is usually 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.

The bladder wall can absorb Na[^99mTc]TcO₄especially in the case of augmented bladder, and renal excretion of the absorbed pertechnetate can lead potentially to false positive studies. Therefore, it is recommended to use non-absorbable tracers ([^99mTc]Tc-DTPA, colloids) in these cases, even if this phenomenon is rarely observed in the clinical routine.

7.8.3 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 for the assessment of the results of endoscopic or surgical treatment or for the detection of VUR in renal transplant recipients.

7.8.4 Contra-indications

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

7.8.5 Clinical performances

Direct radionuclide cystography has a higher sensitivity for VUR than VCUG with the additional benefit of a lower radiation exposure, at least in the majority of cases (81,82).

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.

7.8.6 Activities to administer

The suggested activity to administer is:

Na[^99mTc]TcO₄: 20 MBq

In paediatric nuclear medicine, the activities should be modified according to the EANM paediatric dosage card (https://www.eanm.org/publications/dosage-calculator/). The minimum recommended activity to administer is 20 MBq, no adjustment to weight.

7.8.7 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 of age, 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.

Caveat:
“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but  it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."

7.8.8 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.

7.8.9 Patient preparation

No specific preparation is required.

7.8.10 Methods

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