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184.108.40.206. INDIRECT RADIONUCLIDE CYSTOGRAPHY (IRC)
Indirect radionuclide cystography is obtained as a part of dynamic renal imaging study. IRC should be undertaken in any child who is toilet trained. The child is encouraged to drink before the dynamic study as well as following the study. The child is asked not to void until the bladder is maximally filled. When the bladder is as full as the child can tolerate, a prevoid image is obtained. Usually, after 30-60 min after i.v. injection of radiopharmaceutical (preferable 99mMAG3) the child is asked to void in front of the gamma camera. Boys prefer to stand erect, while the girls sit with their back to the gamma camera. Dynamic images are then recorded continuously during voiding. After voiding is complete, a postvoid image is obtained. Reflux is diagnosed by the presence of more activity in the ureter and renal pelvis during voiding or on the postvoid image than was present just before the initiation of voiding.
The clear advantages of IRC are that it avoids bladder catheterization, allows assessment of both renal reflux and bladder function under physiological conditions, the effect of micturition on upper tract drainage and the difference between a true post-micturition residue and a false residue due to a secondary filling from dilated upper tracts.
There is a increase in radiation exposure compare with the direct technique , but radiation burden is still low. There must be enough renal function to concentrate the urine to the point that it can be visualized above background. Enough of the activity in the renal pelvis and ureter must have drained that reflux activity can be distinguished from residual upper tract activity. The indirect method cannot detect those patients who reflux only during the I'illing phase of the study. Conway and Kruglick reported that 21% of refluxing units were only seen during the filling phase , but Willi and Traves showed VUR in only3% of all kidney with reflux in their study .Additionally, no urine specimen is available for culture.
Evaluating any technique for the detection of VUR will remain difficult since there is no absolute referent method . It is important to underline that there is tremendous variability of the results from one author to another: some authors, an one extreme find as much as 30-50% false negatives with the direct technique; on the other extreme there is almost no false negative direct cystography, while the rate of false negative indirect cystography can reach as mush as 60% . On the other hand, some authors showed that IRC is as sensitive and specific as MCU in detection of VUR . Piepsz et al reviewed 12 studies published in the literature and found 409 refluxing kidneys with both techniques. 294 with direct technique and 274 with indirect technique only. Part of this variability may be due to the fact that reflux is an intermittent phenomenon. However, it is is more likely, that the results are depending on the technique which is used and the personal interpretation of the results. More efforts should be put into standardization of both techniques.
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