MRI in Reconstructive Urology

MRI is the pre-eminent soft tissue imaging modality for pelvic reconstructive surgery. Its multiplanar capability, superior soft tissue contrast, functional protocol flexibility, and absence of ionizing radiation make it indispensable across a wide spectrum of clinical problems — from pelvic fracture urethral injury gap measurement to carcinoma detection within a urethral diverticulum. This page provides protocol-level, clinically actionable MRI guidance for reconstructive urologists, urogynecologists, and pelvic surgeons.

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1. Overview: Why MRI Is Uniquely Valuable in Reconstruction

Unmatched Soft Tissue Resolution

Conventional fluoroscopic studies (RUG, VCUG, cystogram) delineate only the contrast-filled lumen. MRI visualizes the surrounding tissue — the fibrotic bridge in a urethral obliteration, the levator ani avulsion behind a prolapsed vault, the horseshoe neck of a urethral diverticulum, or the inflammatory halo of a VVF tract. This tissue-level information is what determines surgical approach, graft sizing, and dissection planes.

No Ionizing Radiation

Pelvic reconstructive patients are frequently young women who will undergo serial imaging. Eliminating cumulative radiation exposure is clinically and ethically significant — especially for pediatric cases (ureteral reimplantation, posterior urethral valves) and for patients requiring multiple pre- and post-operative studies.

Multiplanar Acquisition

Unlike CT (retrospective reconstruction from axial source data), MRI acquires true 3-plane images. Coronal imaging of the urethral diverticulum shows circumferential extent; sagittal dynamic imaging shows compartment descent in real time; oblique imaging aligns precisely with the urethral axis for stricture length measurement.

Functional Protocols

MRI is not purely anatomical. Dynamic defecation MRI captures real-time compartment motion. Dynamic contrast-enhanced (DCE) sequences characterize bladder wall enhancement kinetics for VI-RADS staging. DWI sequences detect cellular-dense tumors and fibrotic tissue based on water diffusion restriction. These functional dimensions are unavailable with any other pelvic imaging modality.

:::info Key Point MRI complements — rather than replaces — fluoroscopic urethrography and urodynamics. The goal is integrating structural, functional, and tissue-level information to plan the correct operation. :::

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2. Pelvic Fracture Urethral Injury (PFUI)

Background

Posterior urethral disruption complicates 5–10% of pelvic fractures. The essential pre-operative question is not whether injury is present (that is established by combined RUG/VCUG), but the precise anatomy of the obliteration: gap length, bladder neck integrity, stump angulation, degree of prostatic displacement, and the presence or absence of a fibrotic bridge. MRI answers these questions with a precision that fluoroscopy cannot match.

Full MRI Protocol for PFUI

Parameter	Specification
Magnet strength	1.5T minimum; 3T preferred for resolution
Coil	Phased-array pelvic coil; endorectal coil contraindicated (deforms anatomy)
Bladder status	Moderately full (150–200 mL) — provides bladder neck landmark
Suprapubic catheter	Leave clamped; fills posterior urethra retrograde
Timing	Optimally 3–6 months post-injury (scar maturation)

Core Sequences

Sequence	Plane	Slice Thickness	TR/TE	Clinical Target
T2 FSE (fast spin echo)	Sagittal	3 mm, no gap	3500/90	Gap length, bladder neck position, pubic arch
T2 FSE	Axial	3 mm, no gap	3500/90	Stump angulation, urethral remnant diameter, pelvic hematoma
T2 FSE	Coronal	3 mm, no gap	3500/90	Lateral displacement, symphysis diastasis
T1 post-contrast (gadolinium)	Axial + sagittal	3 mm	500/10	Fibrotic bridge enhancement, active inflammation
DWI (b = 0, 400, 800 s/mm²)	Axial	4 mm	EPI	Fibrosis vs. healthy tissue; carcinoma exclusion
STIR	Coronal	4 mm	4000/60	Bone marrow edema, pubic symphysis injury

What to Measure on MRI

1. Gap Length Measure along the urethral axis on sagittal T2 from the distal aspect of the prostatic stump to the proximal edge of the bulbar urethral stump. This is the single most important surgical planning parameter. Measure in two planes and report the larger value.

2. Stump Position The prostatic apex may be displaced superiorly and posteriorly by hematoma or fibrosis. Report the vertical height of the prostatic apex above the perineal skin in the sagittal plane and the degree of posterior displacement relative to the pubic symphysis.

3. Stump Angulation Report the angle between the bladder neck axis and the urethral axis on sagittal T2. Significant angulation (>30°) predicts difficulty achieving a tension-free anastomosis by the standard perineal approach alone.

4. Fibrotic Bridge A low-signal-intensity T2 band connecting the two stumps may represent a fibrotic bridge rather than a true luminal gap. Post-contrast T1 and DWI help distinguish fibrosis (restricted diffusion, late enhancement) from residual patent lumen.

5. Pubic Symphysis Integrity STIR imaging identifies pubic symphysis diastasis, osteitis pubis, and bone marrow edema. Diastasis >10 mm is associated with a longer gap and more difficult reconstruction. Transcoccygeal or transperineal approach decisions are informed by symphyseal anatomy.

6. Bladder Neck Integrity Sagittal T2 at the bladder neck identifies sphincteric damage, posterior bladder neck descent, and bladder neck contracture. Bladder neck incompetence significantly worsens post-operative continence outcomes and should be documented pre-operatively.

:::warning Pitfall Gap length on MRI consistently exceeds RUG/VCUG measurement by 3–8 mm because MRI measures tissue gap while fluoroscopy measures the contrast column gap. Use MRI measurements for approach planning — not fluoroscopy measurements alone. :::

MRI vs. RUG: Comparative Table

Feature	RUG + VCUG	MRI
Gap length accuracy	Moderate (underestimates)	High (true tissue gap)
Bladder neck evaluation	Limited (filling dependent)	Excellent
Prostatic stump position	Poor	Excellent
Fibrosis characterization	None	Excellent (T2/DWI)
Pubic symphysis	None	Excellent (STIR)
Pelvic floor muscles	None	Good
Radiation exposure	Yes	No
Dynamic filling	Yes	Limited
Availability	Universal	Center-dependent
Cost	Low	High

Surgical Approach Decision Thresholds

Gap Length (MRI)	Approach
<1 cm	Standard perineal bulbo-prostatic anastomosis
1–3 cm	Extended perineal approach ± inferior pubectomy
>3 cm	Abdominoperineal approach; consider staged repair
>3 cm + BN incompetence	Abdominoperineal + simultaneous BN reconstruction or AUS staging

:::tip Clinical Pearl The decision to perform inferior pubectomy is best made pre-operatively using MRI, not intraoperatively. Patients with gap >2 cm and high prostatic displacement benefit from pre-operative surgical planning that includes pubectomy. :::

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3. Dynamic (Defecation) MRI for Pelvic Organ Prolapse

Indications

Indication	Rationale
Discordant clinical exam and symptoms	Physical exam underestimates posterior compartment prolapse
Multicompartment prolapse	Define which compartments are dominant before surgery
Pre-surgical mapping (mesh or native tissue)	Identify enterocele, sigmoidocele, levator defects
Post-operative recurrence	Identify failed compartment and residual defects
Unexplained obstructed defecation	Rectocele vs. anismus vs. intussusception
Failed pelvic floor PT	Quantify defect severity before escalating treatment

Protocol

Equipment and Setup

Parameter	Specification
Magnet strength	1.5T or 3T; open MRI acceptable for patient comfort
Coil	Phased-array pelvic coil
Patient prep	Cleansing enema 2 hours pre-scan; empty bladder immediately pre-scan
Rectal contrast	200–250 mL ultrasound gel or gadolinium-saline suspension instilled rectally via rectal tube immediately before imaging
Vaginal contrast	Thin gauge instillation of ultrasound gel (optional but improves anterior rectocele delineation)
Patient positioning	Supine with knees slightly flexed over a bolster

Imaging Phases

Phase	Instruction	Sequences
Rest	Quiet breathing	T2 FSE sagittal (3 mm), T2 axial
Kegel/squeeze	Maximum pelvic floor contraction	T2 sagittal
Valsalva	Sustained strain (at least 5–10 sec)	T2 sagittal — 1 to 2 sec per acquisition
Defecation	Patient expels rectal gel onto absorbent pad	Fast T2 sagittal — 1 sec per frame, 20–30 frames
Post-void	Immediate post-defecation	T2 sagittal

:::info Protocol Note Dynamic acquisitions during defecation require rapid single-shot T2 or HASTE sequences with frame rates of 1–2 images/sec. Gradient echo sequences can be used but have inferior tissue contrast. Ensure the image FOV captures the entire pubococcygeal line and the perineal body. :::

Pubo-Coccygeal Line (PCL) Reference

The PCL is drawn from the inferior aspect of the pubic symphysis to the last coccygeal joint on the sagittal T2 image. All organ descent is measured perpendicular to or as vertical drop below this line. This is the internationally accepted reference for dynamic pelvic MRI.

Normal positions (relative to PCL):

• Bladder base: at or above the PCL
• Cervix/vaginal vault: within 1 cm below the PCL
• Anorectal junction: within 3 cm below the PCL

Compartment Descent Grading Table

Compartment	Structure	Mild	Moderate	Severe
Anterior	Bladder base (cystocele)	1–3 cm below PCL	3–6 cm below PCL	>6 cm below PCL
Middle	Cervix or vaginal vault	1–3 cm below PCL	3–6 cm below PCL	>6 cm below PCL
Posterior	Anorectal junction (rectocele)	1–3 cm below PCL	3–6 cm below PCL	>6 cm below PCL
Posterior	Rectocele depth	<2 cm (normal)	2–4 cm	>4 cm
Posterior	Peritoneocele/enterocele	Bowel loops to PCL	Bowel loops >3 cm below PCL	Bowel contents to perineum

Dietz Levator Ani Grading (Avulsion Scale)

Levator ani avulsion from the inferior pubic ramus is best visualized on axial T2 through the mid-levator plate.

Grade	Description	Clinical Significance
0	Normal insertion — symmetric	No structural defect
1	Increased signal at insertion without morphologic change	Partial or healing avulsion
2	Morphologic change with partial detachment	Partial avulsion — moderate POP risk
3	Complete detachment from inferior pubic ramus	Full avulsion — highest POP/recurrence risk

:::warning Surgical Implication Grade 3 bilateral levator avulsion is associated with significantly higher rates of anterior compartment prolapse recurrence after colporrhaphy (native tissue repair). Surgeons planning posterior compartment repair should identify levator grade pre-operatively to counsel patients regarding mesh augmentation vs. native tissue repair recurrence rates. :::

Clinical Utility Summary

Dynamic MRI prolapse imaging changes the surgical plan in 30–40% of cases compared to office examination alone, primarily by identifying occult posterior compartment pathology (enterocele, sigmoidocele) and levator avulsion not detected clinically. It is the only modality that simultaneously images all three compartments under physiologic strain.

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4. Urethral Diverticulum

Why MRI Is the Gold Standard

Urethral diverticulum (UD) is a cystic outpouching of the periurethral glands communicating with the urethral lumen. It is frequently missed or incompletely characterized by VCUG, urethroscopy, or ultrasound. MRI provides:

• Precise neck location (anterior/posterior, proximal/mid/distal urethra)
• Circumferential extent (horseshoe vs. unilateral)
• Internal complexity (fluid, debris, calculus, solid nodule)
• Sphincter proximity (critical for surgical planning)
• Fistula identification

Key Sequence and Findings

Protocol:

Sequence	Plane	Purpose
T2 FSE	Axial (3 mm, no gap)	Horseshoe morphology, neck location, sphincter relationship
T2 FSE	Sagittal	Length, posterior wall involvement
T2 FSE	Coronal	Lateral extent, vaginal fistula
T1 post-contrast	Axial + sagittal	Solid enhancement = carcinoma in UD
DWI (b800)	Axial	Restricted diffusion in malignancy

Horseshoe Sign The pathognomonic finding of UD is the horseshoe-shaped hyperintense (T2) fluid-filled sac wrapping around the urethra on axial imaging. The sac neck (ostium) is typically posterior and at the level of the mid urethra. The relationship of the neck to the external urethral sphincter (EUS) must be explicitly described.

Internal Complexity and Carcinoma Risk

Internal Content	T2 Signal	T1 Signal	Post-contrast	Clinical Action
Simple fluid	Bright	Dark	No enhancement	Standard diverticulectomy
Proteinaceous debris	Intermediate T2	Bright T1	No/rim enhancement	Drain + diverticulectomy
Calculus	Signal void	Signal void	No enhancement	Pre-operative lithotripsy vs. en-bloc excision
Solid nodule	Intermediate/low T2	Variable	Avid enhancement	Biopsy — carcinoma in UD until proven otherwise

:::warning Carcinoma Alert Adenocarcinoma arising within a urethral diverticulum is rare but well described. Any solid enhancing component on MRI mandates biopsy before surgical planning. The most common histology is adenocarcinoma (clear cell or mucinous), followed by transitional cell carcinoma. Do not proceed to diverticulectomy without excluding malignancy. :::

Surgical Planning Checklist from MRI

Parameter	What to Report	Surgical Relevance
Neck location (clock position)	3, 6, 9, 12 o'clock	Determines vaginal incision approach
Neck position on urethral axis	Proximal / mid / distal	Proximal neck = higher continence risk
Sphincter proximity	Distance from EUS to neck (mm)	<5 mm = high incontinence risk, consider staged SUI repair
Circumferential extent	Unilateral vs. horseshoe vs. circumferential	Circumferential = complex dissection, higher fistula risk
Fistula	Tract to vaginal wall or skin	Pre-operative counseling
Carcinoma	Solid enhancing component	Oncologic referral

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5. Vesicovaginal Fistula (VVF)

Role of MRI

Cystoscopy and EUA remain the primary tools for VVF diagnosis. MRI is indicated when:

• Fistula is not visualized endoscopically but symptoms are present
• Radiation-related fistula is suspected (tissue quality assessment)
• Ureteral proximity needs evaluation
• Planning transvaginal vs. transabdominal repair
• Multiple fistulae or complex anatomy is suspected

Sequences for VVF

Sequence	Plane	Finding
T2 FSE	Sagittal	Fistula tract (high signal), bladder wall thickness, vaginal anatomy
T2 FSE	Axial	Lateral position, proximity to ureters, vaginal cuff involvement
T2 FSE	Coronal	Ureteral proximity, bladder dome integrity
T1 post-contrast	Sagittal + axial	Tract enhancement, inflammatory margins, radiation changes
DWI	Axial	Radiation-induced fibrosis (restricted diffusion in fibrotic walls)

Fistula Tract Characteristics

Simple VVF: A linear T2 hyperintense tract connecting the posterior bladder wall to the anterior vaginal wall, typically at the level of the trigone or supratrigonal position. Tract length 5–15 mm. Bladder wall is otherwise normal thickness and signal.

Radiation-Related VVF: Diffuse T2 hypointensity and thickening of the bladder wall, rectum, and vaginal walls (fibrotic replacement). The fistula tract is often larger, more irregular, and surrounded by a hypovascular fibrous margin on post-contrast imaging. This pattern identifies poor tissue quality, predicting higher closure failure rates with transvaginal repair.

Surgical Approach Determination

MRI Finding	Preferred Approach
Simple VVF, tract <10 mm, posterior wall, no radiation	Transvaginal with Martius flap
Trigonal VVF, ureteral proximity <5 mm	Transabdominal (O'Connor) with ureteral stenting
Supratrigonal / dome fistula	Transabdominal
Post-radiation VVF, fibrotic walls	Transabdominal ± omentoplasty; vaginal route high failure
Multiple fistulae / complex	Abdominal approach with full urinary diversion staging

:::tip Ureteral Safety On T2 coronal imaging, identify both ureteral orifices relative to the fistula margin. Fistulae within 10 mm of a ureteral orifice mandate pre-operative ureteral stent placement regardless of surgical approach. Report ureteral proximity in the MRI interpretation. :::

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6. MRI Urethrogram

Indications

MRI urethrography (MRU — not to be confused with MR urography) refers to dedicated high-resolution T2 sequences of the male or female urethra for stricture assessment. Indications include:

• Male anterior urethral stricture when SUG is unavailable or suboptimal
• Spongiofibrosis characterization (depth, circumferential extent)
• Posterior urethral anatomy (membranous/prostatic urethra) after radical prostatectomy or radiation
• Female urethral stricture (rare, but fibrosis extent determines surgical approach)
• Failed urethroplasty evaluation

Spongiofibrosis Visualization

The corpus spongiosum is T2 hyperintense (vascular, water-rich tissue). Fibrosis replaces this signal with T2 hypointensity. The key advantage of MRI over fluoroscopic RUG:

Feature	RUG	SUG	MRI
Luminal narrowing	Yes	Yes	Yes
Spongiofibrosis depth	No	Yes (partial)	Yes
Periurethral fibrosis	No	Partial	Yes
Bulbospongiosus muscle	No	No	Yes
Posterior urethra	VCUG needed	Partial	Yes
Urethral carcinoma exclusion	No	No	Yes (DWI/DCE)

Fibrosis Grading on MRI (Buckley-McAninch adaptation):

Grade	MRI Appearance	Surgical Implication
Mild	Partial T2 signal loss, mucosa intact	Shorter resection margin needed
Moderate	Full-thickness spongiosum signal loss, <50% circumference	EPA feasible
Severe	Circumferential signal loss, periurethral extension	Staged augmented anastomosis or flap urethroplasty

Posterior Urethra

Membranous and prostatic urethral anatomy is well seen on sagittal T2. After radical prostatectomy, the anastomotic scar is visible as a T2 hypointense band. Dynamic contrast may show stricture enhancement vs. recurrent tumor — critical distinction before planning anastomotic revision vs. oncologic re-staging.

Female Urethral Stricture

Female urethral stricture is underdiagnosed. MRI shows circumferential periurethral fibrosis on axial T2 as a low-signal ring around the urethral lumen. Proximal strictures near the bladder neck suggest iatrogenic cause; distal strictures suggest trauma or lichen sclerosus. Pre-operative MRI guides the decision between urethral dilation, meatotomy, and formal urethroplasty.

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7. Peyronie's Disease

Role of MRI

Peyronie's disease is a fibromatosis of the tunica albuginea presenting as penile curvature, indentation (hourglass deformity), and sometimes pain. MRI is not the first-line investigation — clinical examination and erect photographs remain primary — but MRI is the most accurate tool for:

• Plaque mapping (location, dimensions, calcification)
• Hourglass deformity characterization (waist circumference, residual lumen)
• Vascular assessment (dynamic contrast for associated erectile dysfunction)
• Surgical planning (plication site, graft dimensions for grafting procedures)

:::info Erect Photography Protocol For documentation of curvature, a standardized erect photograph protocol should accompany MRI referral: three images (straight, left lateral, right lateral) taken by the patient using pharmacological erection (trimix 0.2 mL intraurethral or physician-supervised ICI), uploaded to patient portal. MRI is performed in the flaccid state. :::

Peyronie's MRI Protocol

Sequence	Plane	Purpose
T2 FSE	Axial (2–3 mm, no gap)	Plaque signal, tunica integrity, urethral displacement
T2 FSE	Sagittal	Plaque length along shaft axis
T1 FS (fat-saturated)	Axial	Distinguishes calcification (signal void) from fibrosis
T2* GRE	Axial	Calcification blooming artifact — most sensitive for calcification
DCE (dynamic contrast)	Axial	Cavernosal artery inflow — erectile function assessment
Post-contrast T1 FS	Axial + sagittal	Plaque enhancement = active phase (inflammatory)

Plaque Characteristics on MRI

Active Phase (acute): T2 intermediate signal plaque with post-contrast enhancement. Surrounding edema. Patient typically has pain. Medical therapy (colchicine, pentoxifylline, vitamin E) may still be effective. Surgery is not indicated in active phase.

Stable Phase (chronic): T2 hypointense plaque, no enhancement. Calcification appears as signal void on T2/T1 and blooms on T2* GRE. Surgery is appropriate when plaque is stable for >6 months.

Surgical Relevance

MRI Finding	Surgical Implication
Dorsal plaque only	Plication vs. dorsal graft
Ventral plaque	Ventral plication (higher ED risk); ventral graft for curvature >45°
Hourglass deformity (waist <60% shaft diameter)	Graft plaque excision; sizing from MRI measurement
Calcified plaque	Limited graft take; penile prosthesis as primary option in ED patients
Lateral curvature	Bilateral plication vs. opposite-side graft
Plaque length >4 cm	Grafting preferred over plication

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8. VI-RADS for Bladder Cancer

Overview

The Vesical Imaging Reporting and Data System (VI-RADS) is a standardized 5-point scoring system for multiparametric MRI (mpMRI) of the bladder, developed to assess the probability of muscle-invasive bladder cancer (MIBC). Published by Panebianco et al. in 2018, VI-RADS is increasingly adopted before transurethral resection of bladder tumor (TURBT) to reduce the rate of understaging.

mpMRI Sequences Used in VI-RADS

Sequence	Role
T2 FSE (axial, 3 mm)	Structural bladder wall layers, tumor morphology
DWI (b0/b800/ADC map)	Tumor cellularity, muscle layer disruption
DCE (dynamic contrast)	Early arterial enhancement of muscle-invasive tumors

VI-RADS Scoring System

Score	Description	Probability of MIBC
1	No mass OR small papillary lesion, intact low-signal muscle on T2 and DWI	Very low (<5%)
2	Superficial mass, intact muscle layer on T2 and DWI, no early DCE in muscle	Low (<10%)
3	Equivocal — disruption of inner muscle layer uncertain on at least one sequence	Intermediate (30–40%)
4	Disruption of inner muscle layer on T2 and/or DWI	High (65–75%)
5	Clear muscle invasion, extravesical extension on T2 and DWI	Very high (>90%)

:::tip Threshold for Decision-Making A VI-RADS score of 3 or higher should prompt re-evaluation for primary muscle-invasive disease before TURBT. VI-RADS 4–5 strongly favors radical cystectomy planning over repeat TURBT alone. :::

Relevance to Reconstructive Urologists

Reconstructive urologists encounter VI-RADS in several specific clinical contexts:

Clinical Scenario	VI-RADS Role
Pre-augmentation cystoplasty	Exclude urothelial malignancy in radiation-damaged or contracted bladders before augmentation
Post-radiation bladder evaluation	Distinguish radiation-induced fibrosis (VI-RADS 1–2) from occult muscle-invasive recurrence (VI-RADS 4–5)
Neurogenic bladder with hematuria	Screen for malignant transformation before major reconstruction
Bladder outlet reconstruction	Identify trigonal or bladder neck lesions before reconstructive procedures
Orthotopic neobladder surveillance	Detect recurrence at anastomotic site or in neobladder mucosa

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9. Upper Tract / MR Urography (MRU)

Indications for MRU Over CT or MAG3

Clinical Situation	Preferred Modality	Why
Pediatric UPJ obstruction	MRU	No radiation; anatomical + functional in single session
Contrast allergy or renal insufficiency	MRU	Gadolinium at reduced dose (0.05 mmol/kg) with caution
Complex duplicated system anatomy	MRU	Superior spatial delineation of crossing vessels, ectopic insertions
Pregnancy (non-first trimester)	MRU	No radiation; avoids iodinated contrast
Ureteral anatomy before reconstruction	MRU	3D ureteral course in relation to pelvic vasculature
Inconclusive MAG3 (equivocal T½)	MRU	Dynamic contrast corroborates functional data

:::warning MRU Limitations vs. MAG3 MRU provides inferior quantitative split renal function data compared to Tc-99m MAG3 nuclear scintigraphy. MAG3 remains the gold standard for split function. MRU gadolinium-enhanced functional data is semiquantitative and scanner/protocol dependent. Use MRU primarily for anatomy and use MAG3 for quantitative function. :::

MRU Protocol

Static MRU (anatomical):

Sequence	Purpose
Heavily T2-weighted 3D RARE/HASTE	Urothelial filling defects, ureteral course, hydronephrosis
T2 FSE axial/coronal (thin slice)	Periureteral anatomy, vessel crossing
STIR coronal	Perirenal inflammation, retroperitoneal fibrosis

Dynamic Gadolinium-Enhanced MRU (functional):

Phase	Sequence	Information
Pre-contrast	T1 3D GRE	Baseline signal
Corticomedullary (30 sec)	T1 3D GRE	Cortical perfusion
Nephrographic (90 sec)	T1 3D GRE	Parenchymal transit
Excretory (5–10 min)	T1 3D GRE	Collecting system filling, ureteral drainage
Post-furosemide (20–40 mg IV at 15 min)	T1 3D GRE	Diuresis challenge — obstruction vs. dilated non-obstructed

Furosemide Administration in MRU: Administer furosemide 15 minutes after gadolinium injection (F+15 protocol). This is equivalent to the F-15 protocol in MAG3 scintigraphy and provokes ureteral washout. Absent or sluggish washout post-furosemide on MRU indicates functional obstruction.

Pediatric Advantage

MRU is particularly valuable in children because:

• No ionizing radiation (cumulative dose concern over multiple VCUG/CT studies)
• Single-session anatomy and function (one anesthetic event)
• Superior soft tissue contrast for duplicated systems, ectopic ureters, and ureteroceles
• 3D reconstruction for pre-operative planning (robotic pyeloplasty templating)

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10. MRI Sequence Quick Reference Table

Indication	T2 FSE	STIR	T1 (plain)	DWI	DCE	T2* GRE
PFUI gap measurement	Primary sequence (sagittal)	Pubic symphysis edema	—	Fibrosis vs. lumen	Fibrotic bridge enhancement	—
Dynamic prolapse MRI	Primary (sagittal cine)	—	—	—	—	—
Urethral diverticulum	Primary (axial horseshoe)	—	—	Malignancy screen	Solid nodule characterization	—
VVF	Tract visualization	—	—	Radiation fibrosis	Tract/inflammatory margins	—
MRI urethrogram	Spongiofibrosis (axial)	—	—	Fibrosis characterization	Stricture enhancement	—
Peyronie's disease	Plaque signal	—	Calcification FS	—	Active phase	Calcification (blooming)
VI-RADS (bladder Ca)	Muscle layer integrity	—	—	Primary staging sequence	Kinetic enhancement	—
MR urography	Collecting system (static)	Retroperitoneal	Pre-contrast baseline	—	Dynamic functional	—

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11. Practical Protocol Tips

Magnet Strength: 1.5T vs. 3T

Parameter	1.5T	3T
Signal-to-noise ratio	Baseline	~2× higher
Spatial resolution achievable	Good	Superior
Susceptibility artifacts (DWI, bowel)	Lower	Higher
T2* artifact (bowel gas, implants)	Lower	Higher
Cost/availability	More accessible	Less accessible
Preferred use	Dynamic prolapse MRI, routine VVF	PFUI gap measurement, VI-RADS, UD carcinoma

For PFUI gap measurement and VI-RADS staging, 3T is preferred when available. For dynamic prolapse MRI, 1.5T is sufficient and produces fewer motion artifacts. Open-bore 3T systems are preferred for claustrophobic patients requiring dynamic protocols.

Coil Selection

Coil Type	Best Used For	Avoid For
Phased-array pelvic coil (surface)	All pelvic indications as default	—
Endorectal coil	Prostate MRI only	PFUI (deforms anatomy), UD, prolapse
Cardiac coil (small surface)	Penile MRI (Peyronie's)	Pelvic applications
Body coil (built-in)	Large FOV survey	High-resolution applications

Patient Preparation

Condition	Preparation	Rationale
All pelvic MRI	Antispasmodic (e.g., hyoscine butylbromide 20 mg IV or glucagon 1 mg IV 5 min pre-scan)	Reduces bowel motion artifact
Bladder tumour (VI-RADS)	Moderate bladder filling (150–200 mL)	Optimizes wall thickness and lesion conspicuity
PFUI	Suprapubic tube clamped; moderate bladder distension	Bladder neck visualization
Dynamic prolapse	Cleansing enema + rectal gel immediately pre-scan	Posterior compartment opacification
Peyronie's	No special preparation; cardiac coil positioned at bedside	Penile immobilization during acquisition
VVF	Moderate bladder filling; tampon in vagina (optional)	Vaginal wall delineation

:::tip Antispasmodic Use Hyoscine butylbromide (Buscopan, 20 mg IV) is effective and inexpensive. It is contraindicated in glaucoma and tachyarrhythmia. In these patients, glucagon 1 mg IV is an acceptable alternative. Antispasmodics are not needed for PFUI or Peyronie's protocols. :::

Bladder Filling Protocol

For PFUI and VI-RADS, optimal bladder filling is 150–200 mL. Overfilled bladder thins the wall and reduces VI-RADS sequence sensitivity. Underfilled bladder collapses the bladder neck and obscures PFUI landmarks. Have the patient void 1 hour before the scan and drink 200 mL of water. Aim to scan within 30–60 minutes.

Rectal Contrast for Prolapse MRI

Commercial ultrasound gel (not barium, not water-soluble contrast) provides excellent T2 bright rectal opacification. Instill 200–250 mL rectally with the patient on the scanner table 5 minutes before imaging. Gadolinium-saline mix (1:50) can be used if T1 sequences are planned but is unnecessary for routine T2 dynamic protocols.

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