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MR Imaging

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

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 resiual, 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

Transperineal/translabial US

• Transducer: curved transducer 5MHz between the labia
• Indications: evaluate urethral anatomy, sling positioning