When the urine passing down the ureter reaches the vesicoureteric junction (VUJ), it is forced out into the bladder via a strong contraction of the smooth muscle of the ureter.
Ureteric jets can be seen on most modalities, including grey-scale ultrasound, color Doppler ultrasound, CT, MRI, fluoroscopy and nuclear medicine studies.
In addition, ureteric jets can be visualized during direct cystoscopy by the observation of colored dye (historically it was indigo carmine) being expelled from the ureter into the bladder.
Grey-scale ultrasound of the bladder demonstrates a short burst of low-level echoes being emitted from the VUJ into the bladder.
The speed of expulsion of the urine from the VUJ is high enough that a frequency shift occurs. Therefore the jet can be appreciated on a color Doppler study as a sudden burst of color in the bladder lasting for a few seconds .
Physiologic ureteral jets in well-hydrated patients should usually occur twice or more per minute, course anteromedially from the trigone, and traverse the patient's midline. Ureteric obstruction, especially when severe, may obliterate or divert the orientation of the ipsilateral ureteric jet. Shortening of the jet duration (normal jet duration is 6 seconds or more) is thought to be suggestive of partial ureteric obstruction.
A large amount of work has been done showing that the distinct waveforms of the ureteric jets may itself have significance . The use of pulsed wave Doppler allows determination of the maximal jet velocity (Vmax), with values consistently below 19.5 cm/s suggestive of obstructive uropathy .
On CT and MRI, the visualization of ureteric jets is one of chance, rather than by design. On CT it is usually seen on a urographic phase study when the rapid expulsion of the urine bolus is accidentally captured as the study proceeds. On MRI the change in flow characteristics in the region of the UVJ might be observable.
History and etymology
The visualization of ureteric jets on Doppler ultrasound was first described by Dubbins et al. in 1981 .
- in simplistic terms, the complete absence of ureteric jets on one or both sides raises the possibility of renal tract obstruction