Type:
Educational Exhibit
Keywords:
Education and training, Cirrhosis, Technology assessment, Technical aspects, Education, Ultrasound, Elastography, Spleen, Liver, Abdomen
Authors:
P. Zoumpoulis1, E. Panteleakou1, K. Ng2, A. Soultatos1, I. Theotokas1, A. Dell'Era2; 1Athens/GR, 2Shenzhen/CN
DOI:
10.26044/ecr2019/C-0175
Findings and procedure details
The scanning protocol consists of recommended steps that any clinician should perform in order to achieve reliable and reproducible STE examinations,
avoid pitfalls,
and recognize artefacts.
This includes fasting,
intercostal approach,
ROI placement,
stability-immobility tips,
STE activation,
reliability indicators interpretation,
measurements,
and cut-off values.
As recommended by EFSUMB and WFUMB guidelines on liver Shear Wave Elastography [2,4],
proper training in the acquisition of real time 2D with simultaneous Shear Wave Elastography is required to obtain better accuracy and intra-observer and inter-observer reproducibility of liver stiffness measurement.
The protocol below includes “STE clinical tips” which are the outcome of a daily practice experience,
based on EFSUMB and WFUMB guidelines.
- Place the probe using intercostal approach on patient in supine position with the right arm raised above the head to increase the width of the intercostal space and scan the liver.
Probe and patient’s skin should form an 90° angle.
(Fig.
1)
- Obtain the best possible B-mode image quality in real time,
clearly visualizing the liver capsule as a white line without the rib’s or lung’s shadowing within the liver parenchyma.
- Place the STE ROI box in the central line of the B-mode image,
at a minimum of 1-2 cm and a maximum of 6 cm beneath the liver capsule,
in a homogeneous area of the liver parenchyma,
avoiding ligaments,
vessels,
and bile ducts.
- Perform a “stability test” on the B-mode image without excessive pressure,
since this may cause the appearance of artefacts within the ROI when the STE will be activated.
- Hold the probe steadily,
while asking the patient to take a normal breath and hold it for few seconds at mid expiration.
- When the patient holds his breath,
activate the STE function in dual mode to observe both B-mode and STE real-time images.
- When the STE acquisition starts,
the best possible frame is indicated by both the 5 green stars (in at least 3-5 consecutive frames) of the Motion Stability index and the full green coloured RLB Map.
Using both reliability and stability indicators ensures great reproducibility and high inter-/intra-observer consistency of the obtained measurements.
(Fig.
2)
- It is possible to use the trackball to select the most appropriate frame in which to perform the STE measurements in accordance with the stability level consistency and reliability index.
- Use the measurement button to place the circular area within the ROI box,
where the color is homogeneous,
avoiding artefacts.
To identify a good quality area of the Shear Wave elastogram,
the 30 kPa scale is recommended.
(Fig.
3)
- Set the circular ROI diameter up to 1-1.5 cm to reach better sensitivity and specificity to assess the stiffness of the target liver’s parenchyma.
To ensure high accuracy,
it is recommended to perform one measurement only within the ROI per each acquisition.
- Save an image per each acquisition.
Five acquisitions are recommended to better evaluate the variability between measurements by means of the IQR/M (interquartile range/median) ratio.
IQR/M is recommended as a quality factor [6] and it should be ≤ 30% when the median value is given in kPa and ≤ 15% if the median value is in m/s.
- The report page provides detailed information per each acquisition (depth,
ROI diameter,
mean value,
reliability) and overall statistics (median,
IQR,
average,
STD,
and ratios).
(Fig.
4)
In difficult-to-scan patients a good alternative may be to perform the evaluation with STQ,
which is less operator-dependent since the measurements are taken automatically by the system.
It is also required to hold the probe steadily,
while asking the patient to take a normal breath and hold it for 10 seconds at mid expiration.
The protocol below includes “STQ clinical tips” which replace the points from 6 to 12 of the protocol above,
with the following steps:
- When the patient holds his breath,
activate the STQ function.
- When the STQ acquisition starts,
keep the probe steady and allow the system to collect the measurements while the patient holds his breath.
It is recommended to record 10 measurements.
(Fig.
5)
- Save the image and go to the report in order to evaluate the measurement and decide which one should be discarded.
IQR/M is recommended as a quality factor [6] and it should be ≤ 30% when the median value is given in kPa and ≤ 15% if the median value is in m/s.
- The report page provides detailed information per each acquisition (depth,
ROI diameter,
mean value,
reliability) and overall statistics (median,
IQR,
average,
STD,
and ratios).
(Fig.
6)
Case Studies
Case 1: Normal Liver (Fig.
7)
- Patient: male,
35 years old,
epigastric pain.
- Pathology: none,
history of infectious mononucleosis.
- Fibroscan: 4.3 kPa (IQR 0.5).
- Ultrasound: normal liver echo-structure.
- Color Doppler: Normal hepatopetal and PW flow in the portal vein.
- STE: 4.01 kPa.
Clinical Comment: The 10mm circular ROI box should be placed within the homogeneous blue color mapping,
avoiding the red STE artefacts near the liver vessels.
Case 2: Pathological Liver (Fig.
8)
- Patient: female,
48 years old,
obesity,
chronic alcohol abuse (ALD).
- Pathology: F2 Metavir,
Steatosis grading 2,
necro-inflammatory process grading 9.
- Fibroscan: 10.6 kPa (IQR 1.7) .
- Ultrasound: hepatomegaly and hypertrophy of the left and caudate lobe.
- Color Doppler: no portal hypertension.
- STE: 11.54 kPa.
Clinical Comment: augmented volume of left lobe of the liver (LLL) offers an alternative acoustical window.
Immobility of LLL (no heart movement’s influence) is a pre requisite of reliable STE measurements.
Possible necro-inflammatory process may increase STE measurements.