Imaging Modalities Overview

Modality	Core Utility	Key Pediatric Indications
Ultrasonography (US) / Doppler	First-line screening, hemodynamics.	Liver size, echotexture, gallstones, portal hypertension, biliary dilatation.
Computed Tomography (CT)	Cross-sectional vascular and mass detail.	Trauma, focal liver lesions, tumor staging, abscesses.
Magnetic Resonance (MRI / MRCP)	Biliary anatomy, detailed mass characterization.	Choledochal cysts, primary sclerosing cholangitis, avoiding radiation exposure.
Elastography	Fibrosis quantification.	Chronic liver disease, nonalcoholic fatty liver disease (NAFLD), biliary atresia.
Nuclear Scintigraphy (HIDA)	Biliary excretion assessment.	Differentiating biliary atresia from neonatal hepatitis.

Specific Modalities & Clinical Applications

Non-invasive, non-ionizing first-line diagnostic tool.
Evaluates liver span, parenchymal echotexture, nodularity, and ascites.
Identifies biliary dilatation, gallstones, inspissated bile, and thick-walled gallbladder.
Contrast-enhanced ultrasound (CEUS) differentiates benign from malignant focal liver lesions without utilizing ionizing radiation.

Doppler determines portal vein patency, flow direction, and flow velocity.
Detects hepatofugal (reversed) portal flow, correlating with severe portal hypertension and increased variceal bleeding risk.
Identifies cavernous transformation of portal vein in extrahepatic portal venous obstruction (EHPVO).
Diagnoses Budd-Chiari syndrome via absent hepatic vein flow or stagnant/turbulent flow patterns.

Utilizes multiphase imaging (arterial, portal venous, delayed) to characterize complex vascular anatomy and tumor extent.
Identifies calcifications, central hemorrhage, and necrosis in hepatoblastoma and hepatocellular carcinoma.
Gold standard for blunt abdominal trauma evaluation; detects active extravasation, lacerations, and contusions.
Major limitation: Significant ionizing radiation exposure.

Provides high-resolution anatomical delineation without radiation.
Gadoxetate disodium (Eovist) administration assists in characterizing focal liver lesions.
MR cholangiopancreatography (MRCP) accurately classifies choledochal malformations and pancreaticobiliary junction anomalies.
Demonstrates multifocal stricturing and dilation ("beading") characteristic of primary sclerosing cholangitis.
Detects "central dot sign" (enhancing portal vein branch protruding into dilated duct) pathognomonic for Caroli disease.

Vibration-controlled transient elastography (FibroScan) and magnetic resonance elastography (MRE) measure liver stiffness.
Replaces invasive liver biopsy for quantifying fibrosis progression and cirrhosis development.
Highly useful in monitoring nonalcoholic fatty liver disease (NAFLD) and post-Kasai biliary atresia outcomes.

Utilizes technetium-99m-labeled agents undergoing hepatocyte phagocytosis and biliary excretion.
Crucial for differentiating biliary atresia from idiopathic neonatal hepatitis.
Biliary atresia findings: Normal radiotracer hepatic uptake with complete failure of intestinal excretion at 24 hours.
Phenobarbital or ursodeoxycholic acid priming (3-5 days) significantly improves diagnostic predictive value.

Selective angiography maps extrahepatic vasculature, localizes microaneurysms in polyarteritis nodosa, and guides transarterial embolization.
Endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC) provide therapeutic interventions, including stone extraction and stricture dilatation.

US detects "triangular cord sign" (echogenic density >3 mm cranial to portal bifurcation) and small/absent gallbladder, highly suggestive of biliary atresia.
HIDA scan confirms absence of biliary excretion.

Infantile Hepatic Hemangioma: Demonstrates peripheral nodular enhancement with progressive centripetal filling on CEUS or multiphase MRI. High-flow lesions show aortic tapering and prominent draining veins.
Focal Nodular Hyperplasia (FNH): Exhibits centrifugal spoke-wheel arterial enhancement with hyperintense central scar on T2-weighted MRI.

Splenic length measurement aids non-invasive prediction of varices.
Cross-sectional imaging (CT/MRI) defines vascular anatomy prior to surgical shunting (meso-Rex bypass) or transjugular intrahepatic portosystemic shunt (TIPS) placement.