CT liver volumetry (protocol)

CT liver volumetry is an essential imaging study in preoperative assessment for living donor liver transplantation.

NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on CT hardware and software, radiologists' and referrers' preferences, institutional protocols, patient factors (e.g. allergy), and time constraints. 

Indications

• preoperative assessment for living donor liver transplantation
• before the liver, resection to determine the remnant liver volume

Contraindications 

• previous severe reactions to iodinated contrast medium
• pregnancy
• non-compliance

Technique

Bolus tracking

• patient position
  • supine with their arms above their head
• scout 
  • from domes of the diaphragm to the pubic symphysis
• scan extent 
  • from the right dome of diaphragm down to the lower pole of kidneys
• scan direction
  • caudocranial
• contrast injection considerations
  • monitoring slice (region of interest)
    • descending aorta at the level of the carina
  • threshold
    • 100 HU
  • volume
    • 120-150 mL according to the donor’s weight (1.5–2 mL/kg) of non-ionic contrast medium using an automatic pump at a flow rate of 4–5 mL/sec
• scan delay
  • minimal scan delay
• ​respiration phase
  • ​inspiration 

Dynamic phases

• arterial phase
  • achieved by contrast agent bolus tracking usually at 15-25 seconds post-injection
• portal phase
  • starts about 40 seconds post-injection
• 3rd and 4th venous phases
  • start after a delay of 10 seconds from the end of the 2nd phase to the end of the whole examination

Post-processing

• the hepatic venous phase is used for CT volumetry, where hepatic veins appear opacified, using 6 or 8 mm slice thickness
• the liver boundary is traced to exclude the surrounding structures/organs as well as vessels and hepatic fissures, then we summate the liver area on every single cut
• virtual hepatectomy plane is drawn on each cut on axial images, to the right of the middle hepatic vein in right hemihepatectomy and along falciform ligament in left lateral segmentectomy
• the volume of all cuts is summed to get the total and lobar volume of the liver
• we assume that the mean liver density equals 1 gm/ml i.e the calculated volumes equal their respective weights

Practical points

• changing the scan direction to caudocranial can be used at the 3^rd and 4^th venous phases
• use of the 3^rd or 4^th hepatic venous phase for volumetric assessment depends upon the degree of hepatic veins opacification allowing better delineation of the virtual hepatectomy plane