Lucille E Anzia1, Cody J Johnson1, Diego Hernando1, Wade A Bushman2, Shane A Wells1, and Alejandro Roldán-Alzate3
1Radiology, University of Wisconsin Madison, Madison, WI, United States, 2Urology, University of Wisconsin Madison, Madison, WI, United States, 3Mechanical Engineering, University of Wisconsin Madison, Madison, WI, United States
Synopsis
Previous anatomic studies of the lower urinary tract predominantly utilize ultrasound and computed tomography. We present a novel method for measuring bladder wall volume (BWV), bladder wall thickness (BWT) and prostate volume (PV) using 30 (14 male) patients aged 30-39. Through MRI segmentation of the bladder and prostate in Mimics software, 3D models were quantified for BWV and PV. 3-matic was used to measure BWT. There were no significant differences in BWV or BWT between males and females (p=0.52,0.25). Mean PV was 28.7cm3 (16.7-47.8cm3). Non-significant variations in BWT were observed regionally. Future directions will use this methodology across age groups.
Introduction
Prior studies have shown that anatomic changes
that occur with aging lead to lower urinary tract symptoms (LUTS) in men and
women.1,2 Studies using ultrasound (US) and computed tomography (CT)
show increased bladder wall thickness (BWT) correlates with overactive bladder
in women and benign prostatic hyperplasia (BPH)/LUTS in men.1-13 In previous
studies, BWT and bladder volume were quantified through localized measurements
on a 2D plane1,2,6-13 and mathematical estimation.1,8 The
use of MRI to examine lower urinary tract anatomy is more limited.14,15
We present a novel method for analyzing lower urinary tract anatomy using MRI and
report the normative values for BWT, bladder wall volume (BWV) and prostate
volume (PV) in young, asymptomatic men and women.Methods
With IRB approval and following a
HIPAA compliant protocol, 30 pelvic MRIs (14 male) of subjects age 30-39 [mean 35.2±3.21
years (males), 35.1±2.68 (females) and 35.2±2.89 years (entire population)]
were retrospectively analyzed. The MRIs were performed either on a 3T scanner
(Discovery MR 750, GE Healthcare, Waukesha, WI) using a 32-channel surface coil
(NeoCoil, Pewaukee, WI) or 1.5T scanner (MR450) with an 8-channel surface coil.
The fast-spin echo T2-weighted acquisitions were performed at the University of
Wisconsin Health system between June 1, 2017 and May 31, 2018 in subjects
without known LUTS/bladder outlet obstruction (BOO) and for indications
unrelated to the lower urinary tract. Patients below age 30, above age 39 or with an MRI without
complete coverage of the bladder/prostate were excluded.
MR images were uploaded into the
design software “Mimics” (Materialise, Belgium).
The bladder lumen, bladder wall and prostate (males) were reconstructed by
segmentation (Figure 1) to create an organ ‘mask’, and then converted into a 3D
model (Figure 2). BWV and PV were recorded from the 3D model. BWT was manually measured
at 1) the anterior bladder wall (Figure 3) and 2) the site of maximum
thickness. Each site was measured three times and averaged.
Each bladder and prostate 3D model
and the corresponding center of gravity of the bladder were exported into
3-matic (Materialise,
Belgium) for further manipulation and quantification. A thickness gradient was
applied to the bladder wall structure (Figure 4) and the computational median
BWT was recorded. The bladder was divided along a plane intersecting the center
of gravity into six pairwise halves: the
anterior, posterior, dome, base, left and right sidewalls (Figure 4). The
median BWT of each half was recorded. Then, each BWT parameter was analyzed for
mean, median and range values and the difference between male and female
cohorts was quantified (Table 1). Results
Mean BWV was similar for men and women (24.7cm3 vs
22.8cm3, p=0.52). The manually measured mean and maximum anterior BWT
were also similar for men and women (3.98mm vs 3.58mm, p=0.36 and 5.24mm
vs 4.76mm, respectively, p=0.31). From the 3D model, mean BWT was 2.46mm in
males and 2.14mm in females (p=0.25). Regional BWT values of anterior,
posterior, dome, base, left and right were similar for men and women (2.61mm vs
2.44mm, 2.22mm vs 1.81mm, 2.47mm vs 2.03mm, 2.40mm vs 2.12mm, 2.65mm vs 2.13mm
and 2.22mm vs 2.11mm, respectively, p=0.09-0.69). Mean prostate volume was
28.7cm3 (16.7-47.8cm3) for males.Discussion
We introduced a novel MR methodology
that can be used to quantify multiple anatomic parameters (BWV, BWT and PV) of
the lower urinary tract in men and women. We found that young, healthy subjects
without LUTS have similar bladder anatomy on both 2D images and 3D renderings.8,16
Importantly, changes to the these anatomic parameters are relevant in the
clinical setting and can be seen in over-active bladder17,
under-active bladder18 and BOO12,13,19. Our method has
several advantages, notably the ability to measure bladder and prostate anatomy
three dimensionally, allowing assessment of each organ regionally and as a
volume without ionizing radiation. While previous studies have focused on the
anterior wall, our methods provide an opportunity to observe fluctuations in thickness
of the entire bladder wall, which may have important clinical implications.
There
is potential for variability from manual segmentation and measurement, which we
mitigated by limiting measurements to a single investigator. Future studies
will assess intra- and inter-reader variability. Further, manual segmentation
is labor intensive and dependent on the anatomic expertise of the investigator.
An automated method may save time and improve consistency. Lastly, we did not
control for bladder volume which has been shown to correlate with BWT.12Conclusion
Pelvic MRI with segmentation and 3D anatomical renderings
provide a novel method for quantifying clinically relevant parameters of the
lower urinary tract including BWV, BWT and PV. Here, we demonstrate the ability
to collect these values in young, healthy subjects. Future studies will collect
and compare bladder wall thickness, bladder wall volume and prostate volume
values in male and female cohorts throughout the lifespan. Acknowledgements
The authors would like to thank the University of Wisconsin Summer Program for Undergraduate Urology Research (SPUUR) for their contributions to this study.References
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