explaining hepatic vasculature Doppler principles

1. Hepatic Doppler US [3]
Dr. Kamal Sayed MBBS MSc US UAA
Color parameters/normal.liverS/G/liver.failure/
HA.waveform/tardus.parvus/PVs/HVs/hepatopetal/
Hepatofugal/hellical.flow/
[57]

2. •
(C) Color-Specific Parameters
•
Several operator-adjustable parameters are specific for the
color Doppler component :
•
[color gain/color bar/color box/color velocity scale/color priority]
•
When color velocities are depicted, the beam-vessel angle is
assumed to be 0° throughout the image.
•
However, velocity determinations are highly dependent on the
[dopp angle]. Colors that are depicted on the image are thus
equally dependent on the [angle of insonation].

3. •
[1] Color Gain
•
Gain refers to amplification of the sampled information for
purposes of improving the depiction of acquired data (,,,,Fig
18). The computer is unable to amplify data that are not
present. For example, increasing the gain will not facilitate
depiction (or identification) of slow flow in the portal vein; it
will only improve the apparent intensity of flow on the
monitor.
•
If one is struggling to identify flow, the @ gain should not be
independently increased without @ optimizing other
parameters and ensuring that the gain is sufficiently high to
depict flow.

4. •
If flow is present and the gain is set too low, it is possible that
no flow will be depicted on the monitor. Both color and
spectral gain should be adjusted to alter sensitivity to Doppler
flow. Doppler sensitivity varies according to tissue interfaces
and composition. Increasing the gain amplifies the
appearance of the acquired signal; however, an overly high
color gain setting produces noise, obscuring the true Doppler
signal. Too low a setting also results in underestimation of
flow disturbances.
•
Color gain should be set as high as possible without
displaying random color speckles.

5. •
Figure 18 [slide 6] CFD color gain adustment :
•
(a, b) CFD US images [slide 6 & 7] obtained with a gain setting
of 44% (a) and 100% (b) show underadjustment and
overadjustment, respectively.
•
c) CFD US image [slide 8] obtained with an optimal gain
setting of 65% demonstrates normal-appearing wall-to-wall
flow in the main portal vein.
•
Note that, although the color gain changes, NO change occurs
in the color velocity scale (23 cm/sec) or sampling rate (PRF =
1,500 Hz).

6. Figure 18 a : CFD gain adjusted at 44% [under adjustment] = underestimation.

7. Figure 18 b : CFD gain adjusted 100% [overadjudtment] = overestimation.

8. Figure 18 c : CFD gain adjusted optimally [65%] = normal wall-to-wall flow.

9. •
[2] Color Bar
•
The color bar displayed on the monitor shows the color
assignment for mean Doppler shift frequencies (velocities) at
the selected gate location.
•
The scale or range of operator-selected velocities is thereby
displayed. By convention, positive Doppler shifts (ie, those
toward the transducer) appear red.
•
Many manufacturers place a horizontal black line across the
color bar; this line represents the baseline, and its position
will shift as the baseline is changed.

10. •
The width of this horizontal black line depicts the wall filter
setting.
•
Any increase or decrease in the color range will be depicted
on the color bar, both as @ a change in the color spectrum
@and as the actual velocity range that is shown (usually in
centimeters per second).
•
It is important to remember that the velocity shifts for a
given PRF.
•

11. •
[3] Color Box or Overlay
•
The color box is an operator-adjustable area within the US
image (displayed on the monitor) in which all color Doppler
information is displayed.
•
The size, shape, and location of the box are adjustable and
define the volume of tissue from which color data are
acquired.
•
All velocity information from this user-defined volume of
tissue is presented as color-encoded Doppler shifts in the
image field.

12. •
Because the frame rate decreases as box size & width
increase, and increase the required processing power and
time, resulting in inferior depiction of flow, thus :
•
resolution and quality are affected by box size and width.
•
Thus, the overlay should be as small and superficial as
possible while still providing the necessary information,
thereby maximizing the sampling or frame rate
•
A deep color box will result in a slower PRF, which may
produce aliasing of the depicted color flow.
•
fig 19 [slide 14/15].

13. •
fig 19 : Color box or overlay.
•
(a) CFD US image [slide 14] @ obtained with an oversized
color box results in : @ an increased frame rate @ and the
inclusion of extraneous data [unrelated or irrelevant].
•
(b) CFD US image [slide 15] @ obtained with the box size
reduced demonstrates @ a decreased frame rate ,
•
@ and improved image quality.

14. Fig 19 a : oversized color box = increased FR = irrelevant dada.

15. Fig 19 b : reduced box size = reduced FR = improved image quality.

16. •
The frame rate [FR] is the rate (per second) at which
complete images are produced.
•
FR is influenced by @ the number of scan lines @ and the
width & depth of the region being imaged.
•
The FR is an important specification of a scanner because it
affects the temporal detail that can be resolved.
•
With pulse-echo imaging alone, the FR can exceed 50 images
per second.
•
However, the time required to produce color flow images is
much longer, which significantly lowers the frame rate.

17. •
The FR in color imaging is dependent on several factors :
•
1- the size and position of the color box have a great effect
on the FR .
•
2- The width of the box is especially important:
•
@ The wider the box, the more scan lines are required AND
the longer it will take to acquire the data to produce the
image.
•
@ If box width is kept constant, adjusting the depth will not
make any noticeable difference in the image depicted on the
monitor.

18. •
3- Increasing the imaging depth also decreases the frame rate
because it results in a longer wait time or delay for returning
echoes.
•
4- The PRF also influences the frame rate :
•
Increasing PRF increases FR ; decreasing PRF decreases FR.
A compromise must be reached between @ the area over
which color information is acquired and @ the time needed
to acquire it.

19. •
[4] Color Velocity Scale
•
The color velocity scale can be changed separately from the
scale depicted on the spectral baseline and should be
adjusted for the anticipated range of velocities to be studied.
The color velocity range depicts the range of velocities that
are represented in the color overlay.
•
Too low a range will result in color aliasing, which may
complicate interpretation of flow direction.

20. •
[5] Color Priority
•
Because each pixel is displayed either as gray-scale or color,
increasing the color priority, will permit color information to
be displayed where low-intensity signals may be present, such
as at the periphery of vessels.
•
Alternatively, increasing the gray-scale priority will result in
gray-scale information being depicted and displacing color
data. Depending on the manufacturer, many US imagers
permit adjustment of the color priority on a scale that is often
depicted adjacent to the color bar.
•

21. LT hepatic artery arises from LT gastric artery.
RT hepatic artery arises from SMA.
•
Hepatic Artery
•
Identification and characterization of hepatic arterial flow is
essential after liver transplantation.
•
in healthy individuals, hepatic arterial flow velocity varies
from 30 to 60 cm/s.
•
Note should be made of accessory or replaced left or right
hepatic arteries, which arise from the left gastric and superior
mesenteric arteries, respectively.

22. •
Hepatic arterial flow typically has a characteristic :
•
1- pulsatile 2- low-resistance waveform with 3- a broad
systolic peak, 4- antegrade diastolic flow, 5- and spectral
broadening.
•
In normal patients, the hepatic artery is @ a low-resistance
systemic artery @ with low-resistance monophasic
waveforms.
•
@ Peak systolic velocities approximate 100 cm/sec.
@Normal RI for the hepatic artery is usually 0.6 to 0.9 (or
60% to 90% if using percent values).
•

23. •
hepatic artery can be identified adjacent to the main portal
vein with color flow US, which is used for localization of the
artery; flow within the artery is characterized with spectral
Doppler US.
•
Indications for stenosis of the hepatic artery that exceeds
50% include :
•
1- focal velocity increases (>200 cm/sec) associated with
•
2- turbulence, 3- a low resistive index [RI] (< 0.5),
•
4- and systolic acceleration times greater than 0.8 seconds.
(,Fig 21/slide 27).

24. •
Figure 20. Color duplex image [slide 25] Hepatic arterial
waveform : @ obtained with a small gate @placed over the
hepatic artery @ adjacent to the main portal vein & shows
•
@ a normal spectral waveform @ and a low-resistance profile
with @ systolic velocities ranging from 30 to 40 cm/sec.
•

25. Figure 20. Hepatic arterial waveform.

26. •
Hepatic artery occlusion may occur following cadaveric or
living donor liver transplantation.
•
This complication can be devastating because the biliary
endothelium is supplied by the hepatic artery.
•
In addition, hepatic artery stenosis may occur at or near the
anastomotic site.
•
Depending on the extent of stenosis, spectral waveforms
obtained at or distal to the stenosis may demonstrate :
@elevated peak systolic velocity, @ spectral broadening, or a
@ tardus parvus waveform (,Fig 21/slide 28).

27. •
Figure 21. Tardus parvus hepatic arterial waveform.
•
Color duplex US image [slide 27] obtained in a patient who
had undergone liver transplantation 24 hours earlier shows :
•
@ slow upslope, @ broadening of the spectral waveform, and
@ low-peak-velocity flow.
•
This waveform is commonly seen in liver transplant recipients
and resolves by 24-48 hours after surgery.
•
When this finding is seen more than 48 hours after the
procedure, @ hepatic artery stenosis or even @ dissection
should be excluded.

28. Figure 21. Tardus parvus hepatic arterial waveform post liver transplant.

29. •
Portal Vein
•
The portal vein confluence is best identified with a midline
transverse or oblique approach.
•
Intercostal scanning is frequently required to assess flow in
the intrahepatic branches of the right portal vein.
•
Flow in the portal vein is typically :
•
1- hepatopetal [towards the liver], 2- mildly undulating, 3-
and laminar,
•
4- displaying respiratory variation [Phasicity].

30. •
5- Normal portal venous flow velocity is 20–30 cm/sec (,fig
22/slide 41). 6- Pulsatility is typically absent, unless there is
right-sided heart failure with or without pericarditis, 7- but
the portal and hepatic veins can both demonstrate periodicity
(ie, normal variations in velocity resulting from cardiac
motion).
•
What is the portal confluence?
•
The portal vein (PV) is the main vessel of the PVS, resulting
from the confluence of the splenic and superior mesenteric
veins, and drains directly into the liver, contributing to
approximately 75% of its blood flow. Hepatic artery provides
the remaining hepatic blood flow.

31. •
The PV is formed by the @ union of the splenic vein and the
SMV, @ posterior to the neck of the pancreas, @ at the level
of L2. @ As it ascends towards the liver, @ the PV passes
posteriorly to the superior part of the duodenum and the bile
duct. @ PV drains blood from the spleen, pancreas, and
gastrointestinal tract to the liver The blood leaves the liver to
the heart in the hepatic veins.
•
## Cirrhosis slows liver blood flow and puts stress on
the portal vein. This causes high blood pressure known
as portal hypertension.

32. •
Normal main PV (MPV) peak systolic velocities range between
20 cm/sec and 40 cm/sec.
•
A low flow velocity of < 16 cm/sec in addition to a caliber
increase (diameter of greater than 13 or 15 mm) in the MPV
are diagnostic features of portal hypertension.
•
Which scanning plane is best to visualize hepatic veins?
•
An anterior sagittal approach usually provides the best view
to image the left portal vein, left and middle hepatic veins,
and ligamentum teres. It is important to image this anatomy
to rule out the presence of a paraumbilical vein. A transverse
image can also be used to display the paraumbilical vein.

33. Measurement of the portal vein diameter was taken :
•
@ in quiet respiration @ at the hilum of the liver @ just
before bifurcation into right and left. @ The diameter was
taken by putting the two cursors in the internal wall of
the PV;
•
the wall of the PV was excluded from the measurement.
•
The most common complication of portal hypertension is
•
Variceal hemorrhage which is associated with portal
hypertension. Almost 90% of patients with cirrhosis develop
varices, and approximately 30% of varices bleed.

34. •
The hepatic portal system is a series of veins that carry blood
•
from the capillaries of the stomach, intestine, spleen, and
pancreas to capillaries in the liver.
•
The portal vein is not a true vein, because it conducts blood
to capillary beds in the liver and not directly to the heart..
•
Blood flow to the liver is unique in that it receives both
oxygenated [hepatic artery 25%] and (partially) deoxygenated
blood [PV 75%]. As a result, the partial gas pressure of oxygen
(pO2) and perfusion pressure of portal blood are lower than in
other organs of the body.

35. Normal ultrasound findings of the liver
@ The liver parenchyma should be evaluated for focal and/or
diffuse abnormalities.
•
@ The normal liver appears as homogeneous & echogenic
texture.
•
@ In normal conditions, liver echogenicity equals or slightly
exceeds that of the renal cortex.
•
@ steatotic livers look brighter than normal livers, and
cirrhotic livers (advanced fibrosis) look lumpy and shrunken.

36. •
Stages of liver failure
•
1- Inflammation : the early stage, liver is enlarged or
inflamed.
•
2- Fibrosis : Scar tissue begins to replace healthy tissue in the
inflamed liver.
•
3- Cirrhosis : Severe scarring has built up, making it difficult
for the liver to function properly.
•
4- End-stage liver disease (ESLD). ...
•
5- Liver cancer.

37. •
What is the function of portal circulation?
•
The portal venous blood contains all of the products of
digestion absorbed from the GI tract, so all useful and non-
useful products are processed in the liver before being either
@ released back into the hepatic veins which join the inferior
vena cava just inferior to the diaphragm, in the way to RT
atrium @ or stored in the liver for later use.

38. •
What causes a split liver?
•
If the blood pressure rises to a certain level, it can become
too high for the varices to cope with, causing the walls of the
varices to split and bleed.
•
Portal hypertension develops when resistance
to portal blood flow increases. @ This resistance often occurs
within the liver, as in cirrhosis. It can @ be outside of the
liver, such as *prehepatic in PV thrombosis, * posthepatic in
the case of constrictive pericarditis or Budd-Chiari syndrome.

39. •
normal PV diameter (PVD) can vary normally b/w 7 to 15
mm while normal portal venous pressure lies b/w 5 and 10
mmHg (14 cm H2O).
•
If portal venous pressure is more than 15 mmHg (30 cm of
H2O), then it might indicate portal hypertension.
•
The most common cause of hepatofugal flow [nonforward
portal flow from periphery towars the porta hepatis] in the
portal venous system is @ portal hypertension, which in turn
is usually caused by @ cirrhosis, less commonly by hepatic
venous @ outflow obstruction or @ extrahepatic portal vein
thrombosis.
•

40. •
Helical portal venous flow is seen @ in 20% of patients with
severe liver disease @ or shunting @ and is an expected
observation following liver transplantation (,Fig 23/slide 43)
Intrahepatic helical flow may be seen in * patients with TIPS
or with * liver tumors that abut the portal vein.
•
CDF will show flow both toward and away from TXR because
normal laminar flow is replaced by flow with a spiral
appearance.
•
The spectral waveform may demonstrate hepatopetal, fugal,
or bidirectional flow (,Fig 23). In patients with well-functioning
TIPS, reversal of flow (ie, toward the stent) typically occurs in
the contralateral intrahepatic portal veins (,Fig 24).

41. •
Figures 22. Helical portal venous flow.
•
On a color duplex US image [slide 42] of the main portal vein,
the spectral waveform shows @ phasicity secondary to
patient respiration. @ The color Doppler component shows
flow as both blue (away from the transducer) and red (toward
the transducer), a finding that is consistent with helical flow.

42. Figures 22. Helical portal venous flow.

43. •
Figures 23. Helical portal venous flow in a liver transplant
recipient :
•
On a color duplex US image [slide 44], helical flow in the main
portal vein appears both red and blue and is depicted as
occurring both above and below the baseline.
•
If a gate is too small and is placed on a single component of
portal venous flow, the flow may inadvertently appear
reversed.

44. Figures 23. Helical portal venous flow in a liver transplant recipient.

45. •
Intrahepatic helical flow may be seen in patients with TIPS or
with liver tumors that abut the portal vein.
•
CFD US will show flow @ both toward and away from the
transducer because @ normal laminar flow is replaced by
flow with a spiral appearance.
•
The spectral waveform may demonstrate @ hepatopetal,
@fugal, or @ bidirectional flow (,Fig 23/slide 44]).
•
In patients with well-functioning TIPS, reversal of flow (ie,
toward the stent) typically occurs in the contralateral
intrahepatic portal veins (,Fig 24/slide 46]).

46. Figure 24. Reversal of left portal venous flow in a patient with a TIPS

47. •
Figure 24. Reversal of left portal venous flow in a patient with
a TIPS.
•
Color Doppler flow US image [slide 46] shows @ flow toward
the transducer (red) in the left hepatic artery (LHA),
•
@ and reversed flow (blue) in the left portal vein (LPV).
•
These findings are expected when a functioning TIPS bridges
the right portal and hepatic veins.

48. •
When thrombus is identified in the PV, identification of
pulsatile intrathrombus flow (typically low-resistance pulsatile
or nonpulsatile) is used to distinguish bland thrombus from
tumor thrombus.
•
The waveform morphology differs from that of the hepatic
artery and that of the nonthrombosed portions of the portal
vein.
•
Often, however, flow cannot be detected in tumor thrombus. Thus,
absence of flow should not be used to distinguish tumor thrombus from
bland thrombus. Given the importance of this observation and its
potential impact on patient care, Doppler parameters must be fully
optimized when characterizing flow within a thrombus.

49. •
Hepatic Veins
•
The hepatic veins possess @ a triphasic waveform, with both
@ respiratory variation @ and cardiac pulsatility (,Fig 25/ slide
52).
•
The waveform is altered in the presence of hepatic or cardiac
disease.
•
Hepatic veins are imaged with a transverse midline or
intercostal approach. Because liver disease may obscure or
dampen flow patterns, hepatic veins should initially be
sampled near their confluence with the vena cava.

50. •
Doppler US may show abnormalities in the hepatic veins, such
as absent flow or loss of the normal triphasic waveform in the
portal vein (where flow may be reversed) and vena cava.
Absent hepatic venous flow may be partial or complete,
depending on the extent of intrahepatic collateral vessels.
Reversed flow in adjacent hepatic vein branches may produce
a “hockey stick” appearance [slide 51].
•
Collateral vessels may be @ capsular or @ communicate with
the vena cava, or @ enhanced drainage via accessory hepatic
veins may occur.

51. hockey stick

52. •
Figure 25. Normal hepatic venous waveform.
•
On a color duplex US image [slide 53], @ the spectral
waveform for a normal hepatic vein shows triphasic flow
above and below the baseline.
•
@ The waveform shows periodicity @ and is triphasic due to
transmitted cardiac activity, @ similar to the waveform for
the jugular vein.
•
The component above the baseline corresponds to atrial
systole; the components below the baseline correspond to
ventricular systole and the filling phase during atrial diastole.

53. Figure 25. Normal hepatic venous waveform.

54. •
Optimization for Detection of Slow Flow in the Liver
•
To document & characterize portal flow in PHTN, liver tumors,
or post surgery, is crucial.
•
This flow may not only be @ hepatofugal (reversed), but may
@ be stagnant or slow, or @ the vein may be occluded.
•
when thrombus is present in the portal vein, it is important to
search for flow within the thrombus, because such a finding
may be used to distinguish tumor thrombus from bland
thrombus. When thrombus is identified, careful search should
be made for tumor within the liver.

55. •
Most commonly, flow is slow. To accurately identify slow flow
and not mistakenly consider flow to be absent, the Doppler
parameters must be optimized for detection of slow flow
•
1ST , one must be sure that the B-mode parameters are
optimized, including 1- depth of field, 2- location
•
and 3- number of focal zones, 4- output power, 5- and time-
compensated gain.
•
2ND , 1- Spectral or power Doppler US is more sensitive in the
detection of slow flow than is standard color Doppler flow US.
2- The wall filter setting should be as low as possible so that
low-frequency signals arising from the portal vein are not
eliminated.

56. •
2ND, The Doppler angle should be optimized, : not only
•
by @ correcting the angle with the computer,
•
but by @ positioning the patient so as to allow the TXR to be
placed in an appropriate superficial location.
•
This placement is often achieved by @ putting the patient on
the left side in the decubitus position @ and the TXR in a high
intercostal location @ in the region of the right midaxillary
line.

57. •
@ The strength of the color flow image decreases with the
Doppler angle; if the angle is too small, the transducer should
be moved to a more suitable position. In addition,
•
3RD, the color box should be as 1- small, 2- narrow,
•
and 3-superficial as possible, whereas 4- the gate used for
pulsed Doppler sampling should be wide.
•
A larger or wider box (ie, greater depth) 1- requires a longer
round-trip time for pulses, 2- reducing the PRF, 3- increasing
the signal processing time, 4- degrading the image , 5- and
diminishing the ability to depict slow portal venous flow.
•
4TH, The velocity range should be adjusted to a level
appropriate for flow within the portal vein.