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involved kidney. Pediatric kidneys, in particular, have a remarkable propensity to recover function when obstruction is relieved (Fig. 13).

By provoking maximal urine flow with furosemide, the patency of the urinary outflow tract can be assessed with a technique known as diuretic renography. This is useful to determine the significance of a dilated pelvicalyceal system. Prompt washout of tracer from the collecting system and renal pelvis effectively rules out functionally significant obstruction.

Procedure

Adequate hydration of the patient is critical for diuretic renography. When the patient is dehydrated, excretion of tracer is impaired as is the response to furosemide. Adults and older children can be hydrated orally with water (5-10 ml/kg) before the study. Younger children should receive oral hydration ad libitum beginning two hours before the study, and intravenous hydration of 15 ml/kg over a 30-minute period beginning 15 minutes before tracer injection.

The patient should void before the study. A urine specific gravity greater than 1.015 indicates inadequate hydration. A full bladder can prevent proper drainage of

Figure 10. Renal infarct. 99mTc-DTPA flow and early static images (A) show absent flow and function in the lower pole of the left kidney (black arrows) in this patient with recent onset of flank pain. The CT scan (B) shows lack of contrast enhancement in the left kidney cortex (white arrowhead). A selective left renal angiogram (C, shown in the same orientation as the renal scan) shows an aneurysm arising from the left renal artery which is occluded distally (white arrow).

Figure 10. Renal infarct. 99mTc-DTPA flow and early static images (A) show absent flow and function in the lower pole of the left kidney (black arrows) in this patient with recent onset of flank pain. The CT scan (B) shows lack of contrast enhancement in the left kidney cortex (white arrowhead). A selective left renal angiogram (C, shown in the same orientation as the renal scan) shows an aneurysm arising from the left renal artery which is occluded distally (white arrow).

Figure 11. Non-obstructive hydronephrosis. Sequential 1 mintue images (A) show relatively diminished function on the left with hold-up of tracer in both renal collecting systems. Furosemide was given at 12 minutes with rapid emptying of the renal pelves. Time activity curves (B) were generated from regions of interest placed over the renal pelves and exponential curves fitted to the excretion portion of the curves. The half times are normal (<5 minutes) bilaterally.

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