Radiology

CT Imaging

This section covers the CT protocols used in urology and their genitourinary indications.

Specific CT Protocols

• Renal colic: no contrast, assess for stones, sensitivity 96-100%, specificity 92-100%
• CT w/ contrast: diagnose/evaluate cysts/masses
• CT urography: 3-phase imaging for hematuria, assess non-contrast, arterial phase, and excretory phase
• CT fluoroscopy: useful for real-time imaging, such as biopsy, drain placement, mass ablation
• Adrenal protocol: assesses post-contrast washout to differentiate adenoma from other masses

Genitourinary Indications

• Adrenal: masses, cyst
• Kidney: Bosniak class for cysts, masses, upper tract disease, stones, trauma, infection
• Bladder: infection, cancer, trauma
• Prostate: abscess/infection, cancer staging
• Scrotum: infection (Fournier)
• Testis: assess retroperitoneal disease

XR Imaging (Still Images + Fluoroscopy)

This section covers plain film and fluoroscopic studies of the urinary tract.

Kidney/Ureter/Bladder (KUB) Plain Film

• Indications: assess residual contrast from prior imaging, assess stone disease, assess stent/drain position, assess ileus
• Stones: may not be visible due to overlying gas or radiolucency, can be confused with pelvic vascular calcifications (phleboliths)

Retrograde Pyelogram

• Indications: ureteral obstruction (trauma, stone, neoplasm, hematuria), filling defects, allow for percutaneous access
• Option 1: cannulate ureteral orifice and inject to visualize entire upper tract
• Option 2: place catheter in renal pelvis, then inject while withdrawing to assess upper tract
• Tips: sterilize urine prior, avoid overinjection (can cause pyelovenous/lymphatic backflow), use open-ended or whistle-tip (prevents backflow) catheters, clear air before injecting
• May be difficult if hematuria or difficult angle of ureteral orifice with bladder neck

Loopogram/Pouchogram

• Indications: contrasted imaging of urinary diversions to assess for obstruction, infection, hematuria, pain, cancer recurrence after urinary diversion
• Technique: insert catheter into conduit/pouch past fascia, gently inject contrast until upper tracts opacify, may need oblique images to fully image loop/pouch, assess postdrainage imaging, reflux expected as long as patient has refluxing anastomosis

Retrograde Urethrogram

• Indications: evaluate length/location/severity of urethral stricture, extravasation/hematuria after trauma, assess for foreign bodies, diverticula/fistula
• Technique: position patient obliquely, place penis on stretch, gently inject contrast via meatus

Cystography

• Technique: fill bladder via gravity with 300+mL or until patient uncomfortable
• Views: take pre-fill, max fill, and post-fill images, take in two-views
• No difference between XR and CT cystography for assessing bladder trauma
• Static: assess diverticula, fistula, trauma, post-surgical extravasation
• Voiding: assess reflux, bladder outlet obstruction, urethral integrity

IV Urography

• Bowel prep: consider to provide better visualization
• Technique: give contrast bolus 50-100mL, take pre-contrast, nephrogenic phase, and then q5min images until GU tract completely visualized
• Kidney appearance: 3-4x height of L2, usually between T11 and L3, runs parallel to psoas shadow, smooth contour
• On-table IVU: give 2mL/kg bolus (max 150mL), image after 2-10min, confirms kidney location, function, and extravasation
• Indications: supine/upright to confirm renal ptosis, confirm contralateral kidney in emergent trauma, assess stone material layering

Angiography

• Can be diagnostic and therapeutic (perform embolization)
• Renal indications: renal artery stenosis, renal trauma, vascular imaging and embolization
• Adrenal indications: adrenal vein sampling

Nuclear Medicine

This section covers the radiotracers used in urologic nuclear imaging and the renal scintigraphy and PET protocols built on them.

Radiotracer	Indication	Notes
99Tc-DTPA	Renal obstruction, renal function, renovascular hypertension, ureteral reflux	Dependent on GFR; excreted through filtration
99Tc-DMSA	Cortical defects, ectopic kidneys	Not good for imaging collecting system; bound in renal tubules
99Tc-MAG3	Renal plasma flow, renal obstruction, renovascular hypertension, renal transplant function	Cannot evaluate GFR (bound to plasma proteins); cleared by tubular secretion
11C-choline	mPCa recurrence after treatment	Not useful for primary disease
18F-fluciclovine (Axumin)	—	—
99Tc	Bone scan for metastatic disease (PCa, RCC, BCa, UTUC)	Confirmatory imaging to differentiate cancer from benign lesions
Na18F	—	—
68Ga-PSMA (gozetotide)	mPCa in primary and recurrent cancer	—
Piflufolastat F-18	—	—
Flotufolastat F-18	—	—
68Ga DOTATATE	Neuroendocrine tumors	Useful for metastatic PCC or extraadrenal tumors, but not benign PCC
111In Pentetreotide	—	—
18F-DOPA (Fluorodopa)	Pheochromocytoma	Less sensitive for metastatic disease
18F-Dopamine (Fluorodopamine)	—	—
18F-FDG	Identify cancers using aerobic glycolysis	Locates areas of increased metabolic activity; assess for recurrence
123I MIBG	Identify pheochromocytoma	Preferred over 131I MIBG

Renal Scintigraphy

• Indications: assess renal split function, renal obstruction, cortical defects/scarring, renal vascular hypertension, renal transplant function, vesicoureteral reflux
• Optimization of the results: ensure pre-imaging hydration, stop any medications that may affect renal blood flow, focus on location of renal anatomy
• Flow phase: 2s images x2min then 1s images x1min, assess abnormal vascular lesions
• Renal phase: 1min images x30min, assess split renal function and cortical defects
• Excretory phase: 1min images x30min, assess renal obstruction
• T1/2: time it takes from administration of diuretic (at maximum activity) for the collecting system to reach 50% activity
• Catheter placement: consider to maximize antegrade flow and prevent iatrogenic obstruction

Renal Scintigraphy Findings

• Decreased renal perfusion: flow curve with normal aortic spike, but no visualized renal uptake
• Obstruction (based on T1/2): present if > 20min, absent if < 10min, equivocal if 10-20min
• Transplant kidney: acute rejection shows poor perfusion/uptake, otherwise normal curve with ATN, cyclosporine toxicity, interstitial nephritis

Non-Prostatic Oncologic Imaging (FDG-PET)

• Bladder cancer: indicated for possible metastasis if other imaging findings equivocal and unable to obtain biopsy
• Kidney cancer: indicated for possible metastasis
• Penile cancer: helpful to confirm presence of inguinal LN metastases if palpable LN to determine need for neoadjuvant chemotherapy
• Testis cancer: helpful to assess residual mass after chemotherapy in seminoma-only patients, sensitivity 78% and specificity 86%, no benefit in NSGCT

PSMA PET/CT

• Indications: initial workup of unfavorable intermediate or high risk localized prostate cancer, metastatic prostate cancer, evaluation for biochemical recurrence after local therapy
• Detection rates: 31-42% for PSA < 0.5, 45-57% for PSA 0.5-1, 57-84% for PSA 1-2, 77-86% for PSA 2-5, 90-97% for PSA > 5 ng/mL

Radiation Exposure

This section covers radiation dosimetry units and practical ways to limit exposure to patients and staff.

Radiation Dosage

• Radiation exposure: charge per unit mass (C/kg), also measured in roentgens (r)
• Absorbed dose: energy absorbed from exposure, measured in Gray (Gy), 100Gy = 1 rad
• Equivalent dose: absorbed dose with a conversion factor, measures amount of energy absorbed by different tissues, measured in Sieverts (Sv), 1 Sv = 100 rem
• Recommended annual dose limit: 50 mSv

Limiting Exposure

• Fluoroscopy tips: use single images, pulsed images, collimate images, increase kVp (rather than mA) if underpenetrated, keep image intensifier above table (and XR tube below table), radiation scattered from patient is source of highest radiation exposure to staff
• General tips: minimize time, maximize distance to source, shield other areas of the body

MR Imaging

This section covers MR sequences, their genitourinary indications, gadolinium safety, and the MR signal characteristics used to differentiate renal masses.

Phases

• T1: time to return to equilibrium in z-axis, water appears dark (low signal intensity)
• T2: time to return to equilibrium in xy-axis, water appears bright (high signal intensity)
• DWI: assess Brownian motion (water diffusion), more cellular/compact tissue limits water motion
• ADC: calculated from DWI, assess capillary perfusion and water diffusion
• DCE: T1 with gadolinium-based contrast, assess vascular permeability/perfusion

Genitourinary Indications

• Renal mass: differentiates benign/malignant, can use clear cell likelihood score to differentiate types of RCC, assess extent of IVC thrombus
• Prostate cancer: assess PIRADS lesions to determine biopsy targeting, extraprostatic extension, ability to perform nerve sparing, nodal metastases, post-prostatectomy recurrence, cancer surveillance
• Bladder cancer: assess VIRADS lesions to assess depth of wall invasion, extravesical invasion, nodal metastases
• Penile cancer: can assess degree of local invasion
• Testis cancer: helpful for evaluating small equivocal and bilateral masses
• Prolapse: assess location/severity with MR defecography
• Diverticulum: most accurate way to assess presence and severity of urethral diverticulum
• Pheochromocytoma: bright on T2 images (lightbulb sign)

Gadolinium Contrast Reactions

• Severe/fatal reactions extremely rare
• Nephrogenic systemic fibrosis: avoid contrast if eGFR < 30, can give to dialysis patients (perform dialysis afterwards)

Renal Mass Differentiation

T1	T2	Contrast enhancing?	Diagnosis
Dark	Bright	Yes	ccRCC
	Heterogenous		chromophobe RCC
			Oncocytoma
	Dark		pRCC
			fat-poor AML
			Capsule leiomyoma
Bright	Variable		AML
	Dark	No	Hemorrhagic cyst

US Imaging

This section covers Doppler principles and the transducers and indications for ultrasound across the genitourinary organs.

Doppler

• Pulse: measures direction/velocity of flow at specific point, displayed as continuous waveform
• Duplex: real-time imaging with pulse doppler
• Color: shows direction/velocity of flow as color scale over real-time imaging
• Power: evaluates flow in small vessels, does not provide info on velocity/direction

Renal US

• Transducer: curved transducer 3.5-5MHz, can use linear transducer 6-10MHz for intraoperative US
• Indications: assess hydronephrosis, masses, flank pain, hematuria (unable to undergo CTU/MRU), percutaneous access
• Biopsies: can be performed in-office and under local anesthesia with 6hr observation, 18% minor and 3% major complications, sufficient tissue obtained in 99%

Bladder US

• Transducer: curved transducer 3.5-5MHz
• Indications: post-void residual, prostate size/shape, bladder wall thickness, clot burden, ureteroceles/ureteral obstruction, confirm catheter position, SPT placement
• Ureteral jets: presence indicates unobstructed ureter, may need to wait 10-15min to confirm absence of jet

Transrectal Prostate US

• Transducer: end fire (biplane) or side fire (single plane) transducer 7.5-10MHz
• Perform rectal exam prior to inserting probe to ensure no difficulties
• Indications: prostate sizing, prostate biopsy, seminal vesicle cyst aspiration, infertility

Scrotal US

• Transducer: high-frequency linear transducer 7-18MHz
• Indications: scrotal/testis mass, scrotal/testis pain, scrotal trauma, infertility, torsion
• Resistive index: if elevated (> 0.6), concerning for impaired spermatogenesis
• Torsion: diagnosed with absence of testicular blood flow, but epididymis may maintain blood flow

Penile/Urethral US

• Transducer: linear transducer 12-18MHz
• Indications: localize foreign body, vascular dysfunction, urethral stricture, fracture, trauma, fibrosis, priapism
• Arterial insufficiency: peak systolic velocity < 25cm/s
• Venoocclusive dysfunction: end diastolic velocity > 5cm/s or resistive index < 0.75 in setting of adequate (> 25cm/s) inflow
• Peyronie: calcified plaques indicate poor candidate for intralesional therapy or incisional grafting

Contrast Reactions

This section covers the types of contrast reactions and their graded management from mild to severe.

Adverse Reactions

• Allergy-like reactions: do not occur from IgE mediated process, but result in histamine release, not dose dependent
• Physiologic reactions: due to specific reaction to contrast, dose dependent
• Many reactions appear to be fear/anxiety related
• Assess appearance, ability to speak, vitals
• Delayed reaction: can occur 3hr-7d after contrast, usually rash +/- itching
• Shellfish allergy: unrelated to iodine, therefore no increased risk of contrast reaction

Mild Contrast Reaction

• Treatment: usually need observation only, but wait 20-30min in case reaction worsens, may require benadryl PO/IV/IM (1-2mg/kg up to 50mg)
• Anxiety: can give chlorpheniramine 4-10mg PO/IV/IM or diazepam 5mg
• Bronchospasm: can give O2 6-10L/min and B-agonist inhaler 90mg/puff x2 puffs for x3 cycles total

Moderate Contrast Reaction

• Occur in 0.5-2%
• Treatment: hydrocortisone 100-500mg IM/IV, B-agonist inhaler 90mg/puff x2-3puffs repeat PRN
• Bronchospasm: O2 6-10L/min and B-agonist inhaler 90mg/puff x2 puffs for x3 cycles total

Severe Contrast Reaction

• Occur in 0.1%
• Treatment: give epinephrine for bronchospasms +/- laryngospasms, no benefit to antihistamines
• Epinephrine IV: 0.01mg/kg (0.1mL/kg of 1:10K dilution), repeat q5-15min, max single dose 1.0mL (0.1mg), max total dose 1mg
• Epinephrine IM: 0.01mg/kg (0.01mL/kg of 1:1K dilution), maximum 0.15mg < 30kg or 0.30mg > 30kg, inject into lateral thigh, repeat q5-15min, total dose 1mg
• Hypotension: give multiple liters IV fluids, dopamine 2-10ug/kg/min if IVF unsuccessful

Reaction Prevention and Nephropathy

This section covers premedication regimens for at-risk patients and the assessment and prevention of contrast-induced nephropathy.

Premedication Regimens

• Premedication lowers but does not eliminate contrast reaction risk
• Extravascular (GU imaging) contrast reactions are rare, consider premedication for patients with history severe reactions
• Option #1: prednisone 50mg PO 13hr, 7hr, and 1hr before contrast injection + diphenhydramine (benadryl) 50mg IV/IM/PO 1hr before contrast injection
• Option #2: methylprednisolone 32mg PO 12hr and 2hr before contrast injection + diphenhydramine (benadryl) 50mg IV/IM/PO 1hr before contrast injection
• Emergency: hydrocortisone 200mg IV or methylprednisolone 40mg IV q4hr until contrast administration + diphenhydramine (benadryl) 50mg IV/IM/PO 1hr before contrast administration

Contrast Nephropathy (CT Contrast)

• Per Davenport 2020, no contraindications to contrast unless GFR < 30 or 30-59 with risk factors (and even then probably safe)
• Risk factors: preexisting CKD, DM, dehydration, diuretic use, older age, multiple contrast doses
• Renal function: no clear cutoff, may be Cr > 1.5-2.0 or eGFR < 30-45
• Metformin: contrast administration can cause drug accumulation and lead to biguanide lactic acidosis (50% mortality), discontinue metformin for 48hr after contrast if patient has CKD (eGFR < 30)
• Potential prevention: avoid NSAIDs 2-3d prior, avoid ACEi and diuretics 24hr prior, consider hydration starting 6-12hr prior and continuing for 4-12hr afterwards, consider acetylcysteine 600mg BID day before and day of contrast