Liver Ultrasound

Basics

• Types of Ultrasound

  • Gray scale

  • Color doppler

  • Spectral Doppler

• Doppler angle

  • Angle formed between doppler waves and the structure of interest

  • Need to be <60 deg (bunch of physics shit for this)

• Terminology

  • Terms referring to anatomy

    • Antegrade flow

      • Blood flowing forward in normal circulatory flow pattern

      • i.e - IVC = toward the heart, aorta, away from heart, etc.

    • Retrograde flow

      • Blood flowing backward in opposite direction of normal flow pattern

  • Terms referring to probe/transducer location

    • Toward transducer —> red —> above line

    • Away from transducer —> blue —> below line

  • Key point

    • Ante-grade flow does not mean toward the transducer, you can have antegrade flow that is away from transducer and vice verse, same goes for retrograde flow

• Phasicity

  • Basically how many different shapes there are within a wave

  • You can get lost in the terms here which I doubt really matter much, beyond maybe aphasic which is just a flat line

• Spectral broadening

  • Area under the curve - how sharp a line is - something like this idk should relook at this

Hepatic Artery

• Pulsatile

• Antegrade throughout entire cycle —> therefore entire waveform should be above the line

• Peak = peak systolic velocity

• Trough = end diastolic velocity

• Low RI = 0.55-0.7

  • Reasons for increased RI —> postprandial, old age, peripheral microvascular disease, hepatic venous congestion, etc.

  • Reasons for decreased RI —> HHT, arcuate ligament syndrome, cirrhosis with portal HTN,

Portal Vein

• Normal Characteristics

  • Hepatopetal flow (toward the liver)

    • Should make sense because portal system is basically its own closed circuit of veins and exchanges at the liver so should not be hepatofugal because, well the portal vein does not go to the heart

  • Antegrade (above the line)

    • Can have gentile undulations (wavy appearance)

  • Normal velocity = 16-40

  • Normal size = <13 mm

TIPS Evaluation

• Normal portal vein flow is hepatopetal (to the liver)

  • SMV/splenic vein —> portal vein —> liver sinusoid —> hepatic vein —> IVC —> RA

• In cirrhosis there is increased pressure in liver so you get hepatofugal flow (flow away from the liver)

  • Goes to portal vein —> pressure in liver too high —> blood shunted away from liver into varicies and shit

• In TIPS we make a connection typically from right portal vein to hepatic vein

  • This completely bypasses the liver sinusoids so no blood is really going into liver

  • This creates a low pressure channel for blood to flow into —> decreases the pressure in the portal system

  • Because it is bypassing the liver it is technically flowing away from the liver therefore the normal flow in TIPS is hepatofugal

• Caudal (inferior) portion is in portal vein

  • Flow is red = toward probe = above line

• Cephalic (superior) portion is in hepatic vein

  • Flow is blue = away from probe (and to IVC/heart) = below line

• Raw info

  • Main portal vein - hepatopetal normally and in TIPS

  • Right and left portal vein —> hepatopetal normally, and should be hepatofugal after TIPS

  • Hepatic veins —> flow toward IVC normally and in TIPS

• Values

  • Normal TIPS velocity = 90-190

  • Target portal vein pressure <12 mmHg —> decreased risk of variceal bleeds

    • Some say decreased by 50% of original pressure

  • Change in velocity >50 mmHg between exams -> concern for stenosis

• Hepatic venous portal gradient

  • Normal = 1-5 mmHg

  • Clinically significant portal HTN occurs when HVPG is >10 mmHg

• Child Pugh

  • B & C = increased risk for variceal hemorrhage and should be a green light for TIPS

  • A = basically normal

  • D = contraindication =

• MELD score > 24 is a contraindication to TIPS —> 60% 30 day mortality if performed

Steatosis

• Increased liver echogenicity (brighter)

• Multiple stages - no body cares except body imagers

Cirrhosis

• Nodular contour

• Coarse and heterogenous echotexture

• Enlarged portal vein with decreased portal vein velocity