Magnetic resonance imaging of in vitro urine flow in single and tandem stented ureters subject to extrinsic ureteral obstruction

Abstract

Objective: To quantify the relative volumetric flows in stent and ureter lumina, as a function of stent size and configuration, in both unobstructed and externally obstructed stented ureters.

Methods: Magnetic resonance imaging was used to measure flow in stented ureters using a phantom kidney model. Volumetric flow in the stent and ureter lumina were determined along the stented ureters, for each of four single stent sizes (4.8F, 6F, 7F, and 8F), and for tandem (6F and 7F) configurations. Measurements were made in the presence of a fully encircling extrinsic ureteral obstruction as well as in benchmark cases with no extrinsic ureteral obstruction.

Results: Under no obstruction, the relative contribution of urine flow in single stents is 1-10%, while the relative contributions to flow are ~6 and ~28% for tandem 6F and 7F, respectively. In the presence of an extrinsic ureteral obstruction and single stents, all urine passes within the stent lumen near the extrinsic ureteral obstruction. For tandem 6F and 7F stents under extrinsic ureteral obstruction, relative volumetric flows in the two stent lumina are ~73% and ~81%, respectively, with the remainder passing through the ureter lumen.

Conclusions: Magnetic resonance imaging demonstrates that with no extrinsic ureteral obstruction, minimal urine flow occurs within a stent. Stent lumen flow is significant in the presence of extrinsic ureteral obstruction, in the vicinity of the extrinsic ureteral obstruction. For tandem stents subjected to extrinsic ureteral obstruction, urine flow also occurs in the ureter lumen between the stents, which can reduce the likelihood of kidney failure even in the case of both stent lumina being occluded.

Keywords: drainage; flow dynamics; noninvasive measurement; phantom kidney.

FIGURE 1

(a) 3D rendition of renal pelvis and calyxes based on human CT, and (b) phantom kidney model; ~5 cm wide, ~9.5 cm high, ~1.5 cm thick. [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Experimental setup showing the phantom renal pelvis (a) with single 6F stent, (b) with tandem 6F stent, and (c) with the full stented ureter and bladder system. Note the three injection tubes into the (three) major calyxes are visible. [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

Representative MRI stented ureter cross‐sections showing the stent(s) within the ureter lumen, without and with EUO. Colors: Black represents no flow regions (stent walls and border of ureter walls); white/gray represents fluid velocity, normalized within each image, with higher intensity of white representing higher velocity. (a) Single 6F, no EUO; (b) single 6F, with EUO; (c) single 6F, distal to the EUO; (d) tandem 6F, no EUO; (e) tandem 6F, with EUO; and (f) tandem 6F, proximal to the EUO. [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 4

Representative MRI cross‐sections showing flow through side holes proximal (1) and distal (4) to the EUO (2, 3). Images are for a single 6F stent. Images (1) and (4) show urine velocities in stent and ureter lumina, and as well within the connecting stent side hole; images (2) and (3) show relative urine velocities in the stent lumen, which in this region conduct 100% of the flow. *Indicates location of a stent side hole. [Colour figure can be viewed at wileyonlinelibrary.com]