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home - Liver - Liver Imaging - Liver Imaging USS Written by Dr Sebastian Zeki

Liver Imaging USS

Color flow Doppler ultrasoundUses: Tumour-induced occlusion of major hepatic vesselsDuplex Doppler ultrasonographyCalculates frequency, amplitude, and flow direction.These features is important in the following circumstances:-Flow rate important post TIPS insertion.-Flow characteristics, eg inc flow resistance in rejecting livers (systolic wave peaking and no antegrade diastolic flow), or Tardus-Parvus waveform pattern assoc.with hepatic artery stenosis to evaluate the newly transplanted liver.-The duplex to-and-fro waveform has a characteristic diagnostic pattern in suspected arteriovenous fistulae following liver biopsies.Contrast agents3 contrast phases:-Arterial phase (hepatic artery) starts 10-20s post ivi; lasts for 10-15s.-Venous phase (portal vein) extends from 30-35s to 120s.-Late phase starts at 120s; lasts up to 5m post-ivi with the disappearance of bubbles.CO2 microbubbles injected into the hepatic art of patients with small (<3 cm) HCCs enhance most tumors, with a greater sensitivity for hypervascular lesions than conven-tional USS, angiography, or CT.Normally phagocytosed by the reticuloendothelial system and remain in the spleen and liver for a least two days, resulting in a rim-like region of increased echogenicity around tumors.Patterns seen with common hepatic lesions include the following:-Hemangiomas: peripheral globular contrast pooling in the early phase (cotton wool appearance);globules get larger and more numerous (centripetal fill-in).-Focal nodular hyperplasia: centrifugal stellate branching in early arterial phase then intense homogenous uptake (spoke wheel pattern). Rapid washout occurs thereafter with iso-/hyperechoic lesion is seen in portal venous phase.-HCC: Strong enhancement in arterial phase with +1 feeding arteries at periph; Intense global pooling in late arterial phase is followed by a rapid washout in the portal venous phase.Contrast US detects more liver mets than conventional US esp <1 cm lesions/ subcapsular or ventral locations/around ligamentum teres.Utility of contrast US reduced in severe steatosis/deep lesions 6. Screening for HCC7. Evaluation before and after liver transplantationPortal vein patencyDetects portosystemic shunts- can affect transplant outcome +predicts hepatic artery thrombosis based upon Doppler wave form.8. Follow-up of TIPSDoppler USS v. se and sp for blood flow velocity in stent+predicting stent stenosisSonographic criteria for stent stenosis include :-Low velocity flow (< 60 cm/sec) within any portion of the stent-Low flow velocity with focal velocity increase, usually at hepatic v. end of stent-Flow gradient inc >100 % from portal to hepatic v. ends-A temporal change in peak flow velocity of >50 cm/sec from the post TIPS baseline sonogramIdentification of new hepatopedal flow in the left portal vein or a newly recanalized periumbilical vein are indirect evidence for stent malfunction since left portal venous flow usually reverses towards the stent The gallbladder wall should be < or equal to 2 mm (in a distended or fasting gallbladder). Collapsed gallbladders, seen when the subject has eaten, typically appear The maximum dimension of the gallbladder is 5 X 10 cm. Common hepatic duct (inner wall to inner wall) is usually measured at the level of hepatic artery.In the normal fasting state it should be <7 mm in patients <60 years, and <10 mm in patients older than 60. CBD up to10 mm post cholecystectomy. 1. Differentiate cystic from solid lesions 2. Delineating septa-tions within cystic lesions such as biliary cystadenomas. 3. Can identify certain solid lesions eg fatty infiltration or haemangiomas 4. Evaluation of right upper quadrant painSe for gallstones >95 % (better than CT)Se for cholecystitis (gallbladder wall thickening and localized tenderness over the gallblad-der (Murphy's sign)).Se for CBD stone= CT (75 % if dilated ducts, 50 % for nondi-lated) so if inconclusive, MRCP preferred5. Evaluation of obstructive jaundiceSe for dilated bile ducts and biliary obstruction up to 91 %. (length of bilirubin and concen-tration increase sensitivity) Liver Imaging- USS Clinical Use 9. Liver tumor staging and treatmentAssess portal vein patency and whether is tumour ingrowth (has an arterial signal) or a thrombusAssess size, number, and exact location and extracapsular spread of liver tumors.The sensitivity for mets to liver is 85 %.10. Diagnosis of ascitesCan be used to guide paracentesis11. Intraoperative and laparoscopic ultrasoundGood for small (2 to 5 mm) mets in segmental liver resections.It is particularly well suited for imaging the biliary system. Written by Dr Sebastian Zeki USS Types

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