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© 2021 The Authors. Société Internationale d'Urologie Journal, published by the Société Internationale d'Urologie, Canada.

Effect of Metallic Ureteric Stents on  
Magnetic Resonance Imaging: Implications  
for Malignant Ureteral Obstruction
Mahima Tellambura,1 Isaac Thangasamy,1,2 Kwang Chin,1 Declan Murphy1,3

1 Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne, Australia  2 Faculty of Medicine, University of Queensland, Australia   
3 The Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia

Abstract

Metallic ureteric stents are increasingly used for the management of malignant ureteric obstruction, a commonly 
encountered complication in urological and other malignancies. However, there has been limited evaluation of 
complications associated with these stents, including those that might arise from the use of magnetic resonance 
imaging (MRI). While most devices are deemed nominally “MRI-safe,” their implication on the quality of imaging 
produced has not been evaluated in clinical trials, and in our practice, significant artefact has been encountered with 
some ureteric stents—specifically, the Teleflex Rüsch DD tumour stent—compromising image quality and diagnostic 
certainty.

Key Words Competing Interests Article Information

Ureteric stents, metallic stents, magnetic 
resonance imaging, malignant ureteric 
obstruction

None declared. Received on March 20, 2021 
Accepted on May 14, 2021

Soc Int Urol J.2021;2(4):256-258

DOI: 10.48083/ WLVR1509

In managing malignant ureteric obstruction, metal or 
metal-incorporating stents are an increasingly popular 
option, owing to evidence suggesting improved patency 
compared with conventional polymeric stents[1]. In our 
practice, 44% of patients undergoing ureteral stenting 
between March 2017 and March 2018 (n = 77) had one or 
more metallic stents inserted.

Depending on t he ma ligna nc y, a signif ica nt 
proportion of patients undergoing stenting will require 
further pelvic magnetic resonance imaging (MRI) for 
staging or re-staging. This is particularly the case in the 
management of rectal cancer. While all the stents are 
certified MRI-safe, their effect on the quality of MRI 
images produced has not been fully elucidated. MRI 
compatibility has largely focused on energy absorption 
and safety within MRI systems; however, their effect on 
the quality of diagnostic imaging has received limited 
mention.

Metals produce aberrancy within MRI images through 
several mechanisms[2,3]:

• Inhomogeneities in the strong magnetic field, 
pr o d u c e d  b y  p a r a m a g n e t i c /f e r r o m a g n e t i c  
components.

• Frequency-encoding misregistration, due to changes 
in frequency of dephasing.

• Signal loss, due to increase in the rate of T2 phase 
decay.

• Failure of fat suppression, owing to the effect of 
metallic implants on the resonance frequency of 
nearby fat. 

The following factors contribute to the extent of artefact 
formed[3]:
• The size of metallic implant.
• Specific composition of the implant.

• Artefact worsens with ferromagnetic implants  
(steel, iron) compared with those of paramagnetic 
or diamagnetic metals (titanium, platinum, 
copper).

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• Most ureteral stents incorporate nitinol into their  
structure—a proven MRI-safe nickel-titanium 
alloy with limited ferromagnetism. Developed in 
1963, it is used widely in implantable biomedical 
devices across all specialties, including surgery, 
cardiology,and interventional radiology[4].

• The orientation of the implant relative to the strong  
magnetic field.

While ureteral stents produce markedly less artefact 
than larger metallic implants (such as joint prostheses), 
their location (particularly where MRI of the pelvis is 
concerned) can have impact on diagnosis and staging. In 
MRI of pelvic cancer, the posterior relation of the stented 
ureter may impact the diagnostic imaging produced[5] 
(Figure 1).

The Figures (using the Teleflex Rüsch DD Tumour 
Stent) highlight the potential for metallic stents to 
produce clinically significant artefact. The patient is 
a 39-year-old woman with metastatic squamous cell 
carcinoma of the cervix, with locally advanced pelvic 
disease, and retroperitoneal metastasis. She presented 
with malignant right ureteric obstruction and urosepsis. 
The ureteric stent was inserted to improve drainage 
while on chemotherapy, and management of malignant 
obstructive uropathy.

In patients such as the above, the role of MRI is multi-
faceted, in that it is used for treatment planning, local 
staging, and for consideration of radical salvage surgery 
(for example, anterior or total pelvic exenteration, which 
is offered at this centre). As seen on this re-staging 
study, the artefact produced by the stainless steel cross-
braiding component of the stent markedly compromises 
image quality, and with it, diagnostic certainty. A similar 
effect is not seen in CT imaging (Figure 2).

Limited high-quality studies exist in comparing 
the current array of metallic stents available, including 
evaluation of their impact on imaging; a 2018 systematic 
review by Khoo et al.[6] found high heterogeneity in 
21 studies evaluated, and an overall “low quality of 
evidence” in evaluating efficacy. This was echoed in 
the 2021 review by Corrales et al.[7]. Significantly, no 
randomized controlled trials exist to evaluate outcomes 
between devices, and none of the existing literature 
considers impact on imaging.

The MRI compatibility and safety information for 
the available stents (provided by the manufacturers, and 
regulatory bodies) also differs. For example, Resonance 
is a full-metallic stent (compared with alternatives, 
which are silicon polymer with metallic framework—for 
example, Rüsch Tumour Stents, used commonly at our 
institution). Manufacturer specification states that the 
device is “MR conditional,” stipulating the following:

• A spatial gradient field (SGF) ≤450 Gauss/cm.
• Whole-body averaged specif ic absorption rate 

(SAR) of 1.5W/kg for 20mins, with an associated  
temperature rise < 0.800C.

Within these constraints, however, the manufacturer 
nevertheless acknowledges that image quality may 
be compromised when the area of interest relatively 
close to the position of the stent, with an artefact 
radius approximately 16mm per manufacturer testing 
protocol[8].

Manufacturers of other metallic stents do not 
provide a similar level of detail with respect to their 
MRI compatibility; most are classified as MRI-safe  
(Table 1). The only exception is the Telef lex Rüsch 
DD stent: during post-marketing surveillance, the 
manufacturer has released new advice recommending 
that MRI not be performed. The manufacturer has 
reaffirmed, however, that the product is MRI-safe, and 
that further testing is currently being undertaken. For 
patients with Rüsch stents already implanted, however, 
the options are limited to stent exchange (if required); 
given the significant impact on imaging, most of these 
patients cannot be offered MRI with stents in situ.

While corrective techniques exist to account for these 
artefacts, there is limited research on the potential for 
clinically significant degradation in image quality.

Given the role that MRI plays in the diagnosis and 
staging of malignancy, particularly pelvic malignancy, 
the artefact produced by ureteral stents has the potential 
to compromise MRI as a diagnostic/staging tool. Of 
particular concern is the potential for under-staging of 
cancer because the extent of peri-ureteral invasion may 
not be fully apparent.

FIGURE 1. 

Gross stent-related artefact on coronal MRI of patient 
with Teleflex Rüsch DD Tumour Stent in situ

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Effect of Metallic Ureteric Stents on Magnetic Resonance Imaging: Implications for Malignant Ureteral Obstruction

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Further clarification is required on the part of 
manufacturers regarding the effect of metallic ureteral 
stents on MRI imaging. Clinicians in centres where 
such devices are implanted should be aware of these 
limitations before inserting these stents.

References

1. Asakawa J, Iguchi T, Tamada S, Ninomiya N, Kato M, Yamasaki T,  
et al. Treatment outcomes of ureteral stenting for malignant extrinsic 
ureteral obstruction: a comparison between polymeric and metallic 
stents. Cancer Manag Res.2018;10:2977-2982. doi: 10.2147/CMAR.
S172283.

2. Hargreaves B A , Wor ters P W, Pauly K B, Pauly JM, Koch 
K M, Gold GE. Metal-induced ar tifacts in MRI. AJR Am J 
Roentgenol.2011;197(3):547-555. doi: 10.2214/AJR.11.7364.

3. Fowler KJ, Maxwell J, Saad NE, Yano M, Raptis C, Menias C, et al. 
Magnetic resonance imaging of iatrogeny: understanding imaging 
artifacts related to medical devices. Abdom Imaging. 2014;39(2):411-
423. doi.org/10.1007/s00261-013-0065-x.

4. Szold A. Nitinol: shape-memory and super-elastic materials in surgery. 
Surg Endosc.2006;20(9):1493-1496. doi: 10.1007/s00464-005-0867-1.

5. Chin K. Coronal magnetic resonance image of patient with Teleflex 
Rüsch DD Tumour Stent in situ. In: 1.jpg F, editor. Melbourne, VIC, 
Australia: Peter MacCallum Cancer Centre; 2019.

6. Khoo CC, Abboudi H, Cartwright R, El-Husseiny T, Dasgupta R. Metallic 
ureteric stents in malignant ureteric obstruction: a systematic review. 
Urology.2018;118:12-20. doi: 10.1016/j.urology.2018.01.019.

7. Corrales M, Doizi S, Barghouthy Y, Kamkoum H, Somani B, Traxer O. A 
systematic review of long-duration stents for ureteral stricture: which 
one to choose? World J Urol.2021.Online ahead of print. doi: 10.1007/
s00345-020-03544-x.

8. Teleflex Rüsch Tumour Stents. Manufacturer specifications. Teleflex 
Medical Australia. 

TABLE 1. 

Sample of metallic stents available in Australia

Stent Design Material MRI Data

Resonance  
(Cook Medical)

Metallic coil stent
Nickel–cobalt- chromium-
molybdenum alloy

MRI-safe

Memokath 051  
(PNN Medical)

Thermo-expandable  
shape-memory alloy

Nitinol–nickel- titanium alloy MRI-safe

Allium  
(Allium Medical)

Polymer stent with nitinol mesh Nitinol–nickel- titanium alloy MRI-safe

Uventa  
(Taewoon Medical)

Layered polymer stent with  
nitinol mesh

Nitinol–nickel- titanium alloy MRI-safe

Rüsch DD Tumour Stent 
(Teleflex)

Polyurethane stent with metallic 
cross- braiding

Stainless steel braiding
MRI-safe 
Not recommended  
per manufacturer

FIGURE 2. 

CT of patient with Teleflex Rüsch DD Tumour Stent in situ

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