Hepatic Veins and Liver Enhancement, Analysis of Scan Delay Timing.

 

During the portal-venous phase of liver enhancement, it is desirable to achieve peak liver enhancement.  It is also desirable to set the scan delay long enough so that the hepatic veins are opacified.  Both  liver and hepatic veins enhancement are affected by the scan delay.  Un-opacified "hypodense" hepatic veins are a potential problem that could cause mis-diagnosis of hepatic veins as metastatic lesions, or could cause small metastatic lesions to be missed.  It is therefore important to set the scan delay optimally.  Each weight category requires different scan delays, with the heavier patients needing longer scan delays than lighter patients. (see below for justification).

If perfection could be achieved, a 0% incidence of hypodense hepatic veins would be the goal.  However if the delays were set long enough to achieve 0%, the liver enhancement would be past peak in some circumstances.  Therefore, a compromise goal is to achieve near-peak liver enhancement while keeping the hypodense hepatic veins incidence under 5%.

The time delay at which an incidence of  5% hypodense hepatic veins occurs, is at different delays for each weight category:
At approximately  65 seconds for the 78-97kg group,  at 62 seconds for the 64-77kg group, and at <58 seconds for the 48-63kg group. These delays should be considered as minimums.

78-97 kg group

Scans start at Abdomen

Scans start at Chest

120AbdHepV.gif (2801 bytes) 120ChestHepV2.gif (3330 bytes)

These graphs show the
percentage of patients
that had Hypodense
hepatic veins visible on
their CT scans.

These heavier patients show
a trend line that crosses 5%
at approx 64-65 seconds.

64-77 kg group

Scans start at Abdomen

Scans start at Chest

100AbdHepV.gif (2728 bytes) 100ChestHepV.gif (2919 bytes)

These medium sized
patients show a trend
line that crosses 5%
at approx 62-63 seconds.

48-63 kg group

Scans start at Abdomen

Scans start at Chest

80AbdHepV.gif (2640 bytes) 80ChestHepV.gif (2713 bytes)

These lighter patients show
a trend line that probably
crosses 5% at less than 58
seconds. There is a
significant difference between
the lighter patients and the
heavier patients.

 

The Enhancement of the liver should be the highest possible, in order to maximize the visual contrast between normal liver and metastases (which are usually hypodense).   The graphs below show that scan delay time has little effect on liver enhancement in the 78-97 kg group (heavier patients),  whereas there is a definite trend towards higher liver enhancement at earlier scan delays in lighter patients, particularly in the 48-63 kg group.

78-97 kg group

Scans start at Abdomen

Scans start at Chest

120AbdHouns.gif (2669 bytes) 120ChestHouns.gif (2701 bytes)

The graphs show fairly
flat trendlines,  indicating
that liver enhancement
isn't affected very much
by changing scan delay,
in this group of heavier
patients.

64-77 kg group

Scans start at Abdomen

Scans start at Chest

100AbdHouns.gif (2487 bytes) 100ChestHouns.gif (2654 bytes)

These medium sized
patients also show
fairly flat trendlines,
with mildly decreasing
liver enhancement as
scan delay increases.

48-63 kg group

Scans start at Abdomen

Scans start at Chest

80AbdHouns.gif (2452 bytes) 80ChestHouns2.gif (2625 bytes)

But these lighter patients
show a definite trend
towards higher liver
enhancement at earlier
scan delays. This is a
significant difference
compared to the
heavier patients.

 

The extreme lightest and heaviest patient groups are the 38-47 kg and the 98-117 kg groups.   These groups have too few patients in each group to allow an accurate trend analysis of their incidence of hypodense hepatic veins.  But the data for liver enhancement from these extreme groups, shows the same pattern as the above.  The heavier patients benefit from later scan delays, while lighter patients benefit from earlier scan delays.

38-47 kg group

Scans start at Chest

98-117 kg group

Scans start at chest
38ChestHouns.gif (2410 bytes) 98ChestHouns.gif (2445 bytes)

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