The Ultrasonography of the Liver – 2 CE Credits


Ultrasonography of the Liver

Ultrasonography of the Liver

CE Credits
2 Category A
FREE Course Content
Post-Test Price: $5.00
Expiry date: November 1, 2022
Course content
Accessible for free
No credit card required, no registration
Post-Test purchase

Approved by the ASRT (American Society of Radiologic Technologists) for 2 Category A CE Credits
Access to the accredited interactive course
License duration: 180 days from purchase date
Meets the CE requirements of the following states: California, Texas, Florida, Kentucky, Massachusetts, and New Mexico
Meets ARRT® CE reporting requirements
Refund Policy: Non-Refundable

Objectives

  • Describe liver anatomy
  • Understand the concepts of the different ultrasonography imaging modes and know how to apply them
  • List all the steps to perform the liver examination technique
  • Identify common liver pathologies

Description

The purpose of this module is to introduce users to ultrasonography of the liver and the modes used for the diagnosis of different types of tumors. It also helps technologists to determine the steps of the examination techniques and shows the strengths of ultrasound as compared to MRI and CT. This module also presents the indications of liver ultrasonography and highlights all the liver pathologies requiring imaging and the characteristics of these pathologies in order to allow technologists to differentiate between them. This article is accredited by the ASRT for 2 Category A CE Credits.

Discipline Major content category & subcategories CE Credits provided
BS-2016 Image Production
Image Formation 0.50
SON-2016 Image Production
Image Formation 0.50
SON-2019 Image Production
Image Formation 0.50
VS-2016 Image Production
Image Formation 0.50
VS-2021 Image Production
Image Formation 0.50
CT-2016 Procedures
Body 1.00
CT-2017 Procedures
Abdomen and Pelvis 1.00
MRI-2016 Procedures
Body 1.00
MRI-2020 Procedures
Body 1.00
NMT-2017 Procedures
Gastrointestinal and Genitourinary Procedures 1.00
PTH-2019 Procedures
Treatment Sites 1.00
RA-2017 Procedures
Abdominal Section 1.00
RA-2018 Procedures
Abdominal Section 1.00
SON-2016 Procedures
Abdominal and Transplant Vasculature 1.50
SON-2019 Procedures
Abdomen 1.50
THR-2017 Procedures
Treatment Sites and Tumors 1.00
VI-2016 Procedures
Abdominal Angiography and Intervention, GU and GI Nonvascular Procedures 1.00
VI-2017 Procedures
Vascular Diagnostic Procedures 1.00
VS-2016 Procedures
Abdominal/Pelvic Vasculature 1.50
VS-2021 Procedures
Abdominal/Pelvic Vasculature 1.50
BS-2021 Image Production
Image Formation 0.50

Post-Test & CE Certificate:

Post-Test Price: $5.00

Chapter selection

CHAPTER 1
Introduction

Since the discovery of ultrasonography, this imaging technique has been used for diagnosis and for guidance in the biopsy of an identified cancer. More recently, many new techniques have been presented using a contrast agent to identify and diagnose lesions, as well as to plan for transplantation and to detect metastasis. For example, the detection percentage of metastatic spread of cancer from other organs to the liver with conventional B-mode ultrasound is only about 70%, compared with approximately 98% detection with magnetic resonance imaging (MRI) and computed tomography (CT).

The Ultrasound Machine

How do ultrasound machines work?

Ultrasound uses the reflection of waves from different tissues where waves propagate to create images.

Technologists give the command to the transducer to send the high-frequency wave using piezoelectric crystals. The transducer pulse controls allow the operator to define the amplitude, frequency, and duration of the pulses emitted from the transducer probe. The propagated wave is consequently attenuated by the tissues and reflected back towards the transducer which absorbs it and sends it to the CPU. The CPU analyzes it by transforming the signal into an image, which appears directly on the screen. This image can be printed or stored in disk storage.

As we know, there is relation between the frequency, penetration, and image quality: higher-frequency ultrasound waves produce higher image resolution, but they are less able to penetrate to deeper structures and vice versa.

Ultrasonography is a safe, painless technique that uses waves to produce images of the different organs of the body. A gel is placed on the skin to allow the high-frequency sound waves to travel into the patient, and a transducer that emits ultrasound is moved over the gel on the specific zone of interest. The gel is used to create a bond between the skin and the transducer. It increases homogeneity and removes the air bubbles between the two mediums.

The reflected wave is received by the probe then analyzed to create the image. As these images are captured in real-time, this technique is used to show the structures as well as the movement of internal organs. Doppler ultrasound is used to show blood flow through the veins and arteries.

Ultrasound Techniques

Several modes of ultrasound are used in medical imaging. These are:

  • A-Mode: A-mode (amplitude mode) is a very simple type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth
  • B-Mode: In B-mode (brightness mode) ultrasound, also known as 2D mode, a linear array of transducers simultaneously scans a plane through the body, rendering a two-dimensional image on the screen
  • B-Flow is a mode that digitally highlights moving reflectors, such as red blood cells, while suppressing the signals from the surrounding stationary tissue. It can visualize flowing blood and surrounding stationary tissues simultaneously
  • C-Mode: During C-mode, a specific depth is determined from an A-mode; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. This mode displays the anatomic structure and the pathological changes on the biological tissue
  • M-Mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession to capture an image. These images are then used to produce a video in ultrasound. This mode is used to determine the velocity of the specific organ structures that produce reflections during the movement relative to the probe

Doppler Mode: This mode uses the Doppler effect to measure and visualize blood flow inside the vessels of any structure. Different techniques use the Doppler effect. We will mention them briefly:

  • Color Doppler: With this technique, velocity information is presented as a color-coded overlay on top of a B-mode image
  • Continuous Wave (CW) Doppler: With this technique, Doppler information is sampled along a line through the body, and all velocities detected at each time point are presented on a timeline
  • Pulsed Wave (PW) Doppler: Here, Doppler information is sampled from only a small sample volume defined in a 2D image and presented on a timeline
  • Duplex: This is a common name for the simultaneous presentation of 2D and, usually, PW Doppler information. In modern ultrasound machines, color Doppler is also used; in this case, the technique is termed Triplex

Pulse Inversion Mode: In this mode, two successive pulses with opposite signs are emitted and then subtracted from each other. This implies that any linearly responding constituent will disappear while gases with non-linear compressibility stand out.

Harmonic Mode: In this mode, a deep penetrating fundamental frequency is emitted into the body and a harmonic overtone is detected. With tissue harmonic imaging, side-lobe artifacts are substantially reduced and lateral resolution is increased.

Ultrasound is also used in more advanced techniques to increase the efficiency and quality of the images:

  • As mentioned before, Doppler ultrasonography is used to calculate the blood flow, its speed and direction, inside the organ vessels. Doppler ultrasonography has many specific modes, such as echocardiography, transcranial Doppler, and liver Doppler
  • Contrast enhanced ultrasonography is a formulation of encapsulated gaseous microbubbles that increase echogenicity of blood. Microbubbles-based contrast media is administered intravenously during examination to detect a hypervascular metastatic tumor, in which the circulation is faster than in the healthy biological tissue surrounding the tumor
  • Molecular ultrasonography: The future of contrast ultrasonography is in molecular imaging, with potential clinical applications in cancer screening expected to detect malignant tumors at their earliest stage of appearance. Molecular ultrasonography uses targeted microbubbles originally designed to accumulate in the malignant tumor, facilitating its localization in a unique ultrasound contrast image
  • Elastography is a relatively new imaging modality that maps the elastic properties of soft tissue. Elastography is useful in discerning healthy from unhealthy tissue for specific organs. Cancerous tumors will often be harder than the surrounding tissue, and diseased livers are stiffer than healthy ones
  • Interventional ultrasonography: Interventional ultrasonography involves biopsy, emptying fluids, and intrauterine blood transfusion using high frequency ultrasound (HFUS). It is often used to treat several gland conditions or to mark a cancer node one hour prior to surgery to help locate the node cluster at the time of surgery
  • Compression ultrasonography: In compression ultrasonography, the probe is pressed against the skin. This can bring the target structure closer to the probe, increasing spatial resolution. It is used in ultrasonography of deep venous thrombosis, wherein absence of vein compressibility is a strong indicator of thrombosis
  • Panoramic ultrasonography: Panoramic ultrasonography is the digital assembling of multiple ultrasound images into one larger image. It can display an entire abnormality and show its relationship to nearby structures in a single image

Advantages of Ultrasound Technique

Ultrasonography presents multiple points of strength. It is particularly useful in delineating the interfaces between solid and fluid-filled spaces. It images soft tissues, and muscles, as well as bone surfaces, with some limitations. It is capable of detecting local changes in and movement of soft tissue using widely available and comparatively flexible equipment. An ultrasound machine is a small and portable, making ultrasonography an examination technique that can be performed at the bedside, unlike MRI or CT scan. Moreover, ultrasonography is an inexpensive technique and it has better spatial resolution than CT scan and MRI. But ultrasonography’s greatest strength is that it has no long-term side effects, since there is no ionizing radiation used to reconstruct images.

Limitations of Ultrasound Technique

While ultrasonography has many strengths, it also has some weaknesses. These weaknesses can be avoided using the different advanced techniques that will be covered during this course.

  • Artifacts: The difference in the velocity of the waves between different mediums creates an artifact known in sonography as the double aorta artifact. This artifact can limit different types of sonography, specifically:
    • Brain sonography: bone is a dense medium that the wave cannot penetrate, resulting in a poor quality image
    • Pancreas sonography: the gas in the gastrointestinal tract limits ultrasonography performance due to the difference in acoustic impedance
    • Obese patients: In some cases, the frequency used can limit the wave’s depth penetration, even in the absence of bone or air. Fat also attenuates the sound beam. A lower frequency transducer is required to avoid this issue
    • Repetitive Strain Injuries (RSI) caused by the bad ergonomic positions
  • Technical limitations:
    • Ultrasonography requires a high level of skill: ultrasonography is an operator-dependent technique that requires an experienced user to acquire the best image quality for diagnoses
    • It is a challenge to manipulate and position the probe during examination to capture a quality image

CHAPTER 2
Liver Anatomy

To diagnose the liver, ultrasonographers must know the location, the characteristics, and the anatomy of the liver. This section will present the different parts of the liver, including the hepatic arteries and veins, the falciform ligament, the portal venous supply, and the different liver segments.

The liver is located in the lower part of the rib cage in the upper right quadrant of the abdomen. It typically measures about 15 cm in length, noting that liver size varies from one person to another. In the case of an enlarged liver, known as hepatomegaly, the length of the liver may be greater than 20 cm.

The entire liver is surrounded by a fibrous layer of connective tissue called Glisson’s capsule.

The classification system for liver segments uses the vascular supply to differentiate the functional segments. Segments are numbered from I to VIII.

  • Segment I: Has a more variable blood vessel anatomy that differs from the rest of the liver. It may have arterial and portal venous supply from both the right and the left branches of the portal vein. It contains one or more hepatic veins which drain directly into the inferior vena cava

The other segments (II to VIII) are numbered clockwise:

  • Segments II and III lie lateral to the falciform ligament with II superior to the portal venous supply and III inferior
  • Segment IV lies medial to the falciform ligament and is subdivided into IVa (superior) and IVb (inferior)
  • Segments V to VIII make up the right part of the liver:
    • Segment V is the most medial and inferior
    • Segment VI is located most posteriorly
    • Segment VII is located above segment VI
    • Segment VIII sits above segment V in the superio-medial position

The liver is divided according to the network of hepatic arteries and veins, portal veins, and bile ducts, which provides landmarks that define the different liver segments. The below image shows that:

  • The liver is divided into upper (II, IVa, VIII, VII) and lower (III, IVb, V, VI) segments by the branches of the portal veins
  • The left hepatic vein divides the left lobe into lateral (II and III) and medial (IVa and IVb) segments
  • The right hepatic vein divides the right lobe into anterior (V and VIII) and posterior (VI and VII) segments

CHAPTER 3
Ultrasonography Imaging Methods

Different ultrasonography imaging methods are used for liver imaging. This section will review the various diagnostic ultrasound methods used in liver ultrasonography, including color Doppler and power Doppler, contrast-enhanced ultrasound, elastography, and endoscopic ultrasonography.

Doppler Ultrasonography

Let’s review the specific modes often used for liver imaging.

As mentioned before, Doppler ultrasound is a special ultrasound technique that evaluates movement of materials in the body. It allows the doctor to see and evaluate blood flow through the arteries and veins.

There are three main types of Doppler ultrasound:

  • Color Doppler uses a computer to convert Doppler measurements into an array of colors to show the speed and direction of blood flow through a blood vessel
  • Power Doppler is a newer technique that is more sensitive than color Doppler and capable of providing greater detail of blood flow
  • Spectral Doppler displays blood flow measurements graphically in terms of the distance traveled per unit of time, rather than as a color picture. It can also convert blood flow information into a distinctive sound that can be heard with every heartbeat

Color Doppler

Power Doppler

Spectral Doppler

A Doppler ultrasound is a non-invasive technique that can be used to evaluate blood flow in arteries and veins. It can also be used to provide information regarding the perfusion of blood flow in the liver or within an area of interest.

The Doppler effect in diagnostic imaging can be used to study blood flow and provides information regarding:

  • The absence or presence of flow
  • The direction and the velocity of blood flow

The same transducer acts as a transmitter and receiver in Doppler ultrasound applications. When using the Doppler ultrasound technique to examine the blood flow in a vessel, the returning backscattered echoes from blood are detected by the transducer. These returning signals (Fr) are then processed to detect any frequency shifts by comparing these signals to the transmitted Doppler signals (Ft). The frequency shift detected will depend on two factors: the magnitude and the direction of the blood flow.

Let’s consider an example of a simple blood vessel. The transducer will first transmit a signal with frequency ft. Then this transmitted signal will reach a blood vessel. The transducer will receive the backscattered signals coming from the red blood cells at a frequency fr.

The Doppler frequency shift (δf) is calculated by subtracting the transmitted signal (ft) from the received signal (fr).

As mentioned previously, this effect is used to study blood flow by measuring the frequency shift of echoes scattered by moving red blood cells.

Blood flow moving towards the probe produces positive Doppler shifted signals. Conversely, blood flow moving away from the probe produces negative Doppler shifted signals.

When the blood is moving towards the transducer, the relative direction of the blood flow with respect to the Doppler beam is towards the transducer. Blood flow moving towards the transducer produces received signals (fr) which have a higher frequency than the transmitted beam (ft). The Doppler-shifted signal (δf) can be calculated by subtracting ft from fr. Here, the result is a positive Doppler-shifted signal.

When the blood flow moving away from the probe, the transducer produces received signals (fr) of lower frequency than the transmitted beam (ft). This time, the Doppler-shifted frequencies (fr − ft) produce a negative Doppler-shifted signal.

It is important to note that when no flow or movement is detected, the transmitted frequency (ft) is equal to the received frequency (fr). Therefore fr = ft and the Doppler-shifted signal (δf) = fr − ft = 0, resulting in no Doppler-shifted signals.

What is Color Doppler?

Color Doppler converts Doppler measurements into an array of colors. It is possible to obtain 2D or 3D velocity mapping by repeating the measurement at different depths.

In other words, the color Doppler technique estimates the average velocity of flow within a vessel by color-coding the information. The direction of blood flow is assigned the color red or blue, indicating flow toward or away from the ultrasound transducer respectively, and is superimposed on B-mode data from stationary structures within the beam width.

By convention, blood flow traveling toward the transducer is encoded in red, and blood flow moving away from the transducer is color-coded in blue.

Aliasing occurs when the Doppler shift of the moving blood is higher than half of the pulse repetition frequency. Aliased signals are presented in the wrong direction (blue instead of red and vice versa). In this example, the measured speed (2.3 m/s) is greater than half of the Nyquist limit (0.64 m/s), and so, instead of being coded in red, it will be presented in blue, as if the red blood cells are moving away from the transducer.

Coding of a speed of 2.3 m/s with a scale of 0.64 m/s
2.3 m / s coded in blue

This image obtained by color Doppler shows the direction of the blood flow as well as the velocity of the blood in the hepatic veins and arteries to identify liver pathologies. These pathologies will be discussed later in the course.

What is the difference between color Doppler and power Doppler?

Power Doppler is a newer type of color Doppler. Power Doppler is based on the same physics concept, but the color-coded image of blood flow is based on intensity rather than on the direction of the flow, with a paler color representing higher intensity.

Power Doppler is more precise for determining the velocity in the vessels and provides detailed information when blood flow is minimal. However, it does not show the direction of blood flow.

Both color and power Doppler techniques are essential for detecting diseases, whether they are benign tumors, malignant tumors, or inflammatory pseudotumors.

Hepatic Veins Power Doppler

Contrast-Enhanced Ultrasonography

The low degree of contrast between liver lesions and normal liver parenchyma presents a major limitation in ultrasound liver imaging. When evaluating liver metastases that arise from distant primary tumors such as metastatic colorectal cancer, it is difficult for the ultrasound operator to detect them, because their acoustic properties are similar to the surrounding normal liver tissue.

Some metastases are hyperechoic, though it might be difficult to differentiate them from certain nonmalignant lesions, such as hemangiomas. Therefore, in some cases where focal liver lesions are identified by unenhanced ultrasound examinations, further investigations are required to determine whether these lesions are malignant or benign.

Other techniques, such as CT and MRI, can provide additional information to detect these pathologies and differentiate between them. But these techniques have their own disadvantages, such as longer acquisition time and the use of ionizing radiation (in case of the CT scan).

For all these reasons, contrast-enhanced ultrasound (CEUS) was implemented for differentiating focal liver lesions (FLLs) without the risks of potential nephrotoxicity or ionizing radiation. The Food and Drug Administration (FDA) approved the first ultrasound contrast agent in April 2016.

How to detect these pathologies and avoid time waste and ionizing radiation?

In general, B-mode or color Doppler imaging is required first. Then a contrast-enhanced ultrasound (CEUS) examination is performed to obtain a better assessment.

CEUS is a technique that produces high-intensity ultrasound reflections, which are detected using a contrast-specific ultrasound mode that displays only the signal returned from the microbubbles, while cancelling ultrasound signals from tissues.

What are microbubbles?

Microbubbles are stabilized by a shell consisting of albumin, surfactants, or phospholipids. They can be administered during the same appointment as unenhanced ultrasound. Only a small amount of contrast agent is required (typically 1 to 2 mL). They vary in size between 1 and 4 micrometers and travel easily through the blood vessels, making it possible to perform real-time visualization and assessment of vascular structures in different phases.

Ultrasound contrast agents produce 3 distinct phases of liver contrast enhancement. These are:

  • The arterial phase, which occurs when the contrast arrives at the hepatic artery (10-35 seconds after injection)
  • The portal venous phase, which occurs after 35 to 120 seconds
  • And the late phase, which occurs after 120 seconds

Ultrasound contrast agents are administered intravenously in small volumes (e.g., 0.1-4.8 mL) using a sufficiently large needle to avoid causing bubble rupture.

Injected microbubbles are eliminated from the body partly by metabolism of the stabilizing shells within the liver and partly by the exhalation of the gas from the lungs over a period of approximately 15 to 20 minutes.

Using these microbubbles, CEUS has been shown to produce diagnostic accuracy similar to contrast-enhanced MRI or CT. Additionally, it is used to guide other procedures, such as liver biopsies or the radiofrequency ablation of liver lesions used to destroy tumors.

Elastography

Elastography is an ultrasound technique that measures tissue stiffness and compressibility. This technique is very effective for the assessment of liver fibrosis for chronic diseases, as well as for estimating the risk of liver cirrhosis progressing to hepatocellular carcinoma.

Elastography has also been used to distinguish between benign and malignant liver tumors. As we know, diseases affect the properties of liver tissues: benign lesions are usually more compressible than the surrounding healthy tissues, while tumors tend to be stiffer and less compressible.

Tissue fibrosis is common in several liver conditions, including liver injury, cirrhosis, and viral infections, and is also associated with significant alterations in tissue elasticity.

Liver ultrasound elastography techniques are based on the principle that the speed of a wave that propagates through the liver is influenced by the stiffness of the tissue. Basically, the stiffer the liver, the faster the wave passes through it. Different ultrasound elastographic techniques have been developed, such as:

  • Static elastography: compares ultrasonic signals before and following a manual compression, thus identifying areas of increased relative stiffness
  • Acoustic radiation force imaging (ARFI): uses an acoustic radiation force to produce an effective compression of the tissue
  • Shear wave imaging: utilizes acoustic radiation force imaging to generate shear waves in the tissue. The velocities of the resultant shear waves are used to calculate the elasticity map of the tissue which can then be overlaid on conventional ultrasound images
  • Transient elastography (TE): uses a low-frequency pulsed excitation to produce shear waves in the liver tissue. The response of the tissue is used to calculate the elasticity with an ultrasound pulse-echo technique

All elastography methods, including static loads, external vibrators, and acoustic radiation forces, have been applied to generate diverse responses in a soft tissue. These methods have the same steps of analysis shown in this diagram.

First, an external stimulus is applied to a biological tissue. Next, the mechanical responses of the target soft tissues must be accurately tracked, a critical step in any elastography method. Then, these responses are analyzed in order to infer the mechanical properties of the tissue.

In addition to linear elastic parameters of the tissue, it has been demonstrated that hyperelastic, viscoelastic, and anisotropic elastic parameters may be inferred using different inverse methods reported in recent years. These properties may provide valuable information for the diagnosis and treatment of some diseases.

To summarize:

In elastography, the ultrasound probe sends a stimulus and the response indicates the properties of the tissue (i.e., if it is a hard or a soft lesion). The color map indicates hard lesions with red points and soft lesions with blue points. Compared with the B-mode image on the left, the elastography method may provide more accurate information with respect to the size and the position of a lesion.

Endoscopic Ultrasonography

The last technique used for liver ultrasonography is endoscopic ultrasonography.

Endoscopic ultrasound (EUS) has been used to visualize the upper gastrointestinal tract and pancreas and has increasingly been studied for its use in diagnosing liver diseases and guiding liver biopsies.

An endoscope may be inserted into the upper or lower digestive tract. An ultrasound transducer is attached to the tip of the endoscope so it may be positioned closer to the organ of interest and thereby obtain better ultrasound images.

Many studies have demonstrated that EUS can detect focal lesions of less than 5mm for fine needle aspiration biopsy that are not visible on CT imaging.

EUS combined with elastography helps to detect malignant tumors and guide drainage of hepatic cysts.

CHAPTER 4
Liver Ultrasonography Examination Technique

Technologists shall be able to image the patient and identify different pathologies of the liver.

This section will cover examination techniques including, the indications of the liver, the position of the patient, the measurements to cover the entire liver, the obstacles that limit the efficiency of the image, and the different parts of the liver that should be included in the image to allow for the best possible diagnosis.

Indications for Liver Ultrasonography

When is liver ultrasonography required?

According to the clinical guidelines from the World Health Organization (WHO) and the American College of Radiology (ACR), potential indications for ultrasound of the liver include:

  • Enlarged liver (hepatomegaly)
  • Suspected liver abscess
  • Jaundice
  • Abdominal trauma
  • Suspected metastases in the liver
  • Palpable or suspected liver mass
  • Right upper abdominal pain
  • Follow-up of known or suspected abnormalities
  • Evaluation before and after liver transplant
  • Planning for or guiding invasive procedures

Scanning Technique

Liver Ultrasonography Examination Technique

The patient must avoid eating or drinking for 8 hours before the examination. The equipment should be adjusted for preadolescent pediatric patients using frequencies greater than 5 MHz. For adults, the typical frequency ranges used are between 2 and 5 MHz.

Real-time imaging is usually performed in the sagittal, transverse, and oblique planes and should include scans through the intercostal and subcostal, which are the most important for the detection of liver lesions in the supine position.

According to the individual case, the patient can be shifted from supine to decubitus position to move the liver into a better field of vision.

When performing a subcostal scan, firmly pressing the transducer under the thoracic wall generally produces better scanning results, but the patients may spontaneously exert pressure against the transducer by contracting the muscles of the abdominal wall. This tension may move the transducer from the subcostal area, resulting in poorer visualization. Asking the patient to take a deep breath may press the liver downward and help to relax these muscles.

While scanning the patient, the technician must look for:

  • Homogeneous or attenuative liver
  • Smooth or coarse echotexture
  • Rounded borders, which indicate if the liver is enlarged
  • Size of the liver using the sagittal approach in the midclavicular line
  • The lower edge of the liver to be situated halfway down the kidney

Normal Liver Measurements

  • You must be able to identify some pathologies, such as splenomegaly, renal impairment, and abdominal aortic aneurysm
  • Make sure that measurement is consistent so that you can compare sizes over time
  • The upper border lies in the right midclavicular line at the 5th intercostal
  • If the liver is measured in the midhepatic line with a large field of view, it should measure less than 16 cm from the posterior diaphragm to the lower anterior edge. However, it is important to note that liver size increases with gender, age, height, weight, and body surface area
  • If the measurement is made from the anterior diaphragm to the lower edge of the liver in the midclavicular line, it should be no greater than 13 cm

Guidelines from the ACR

How to perform the examination

Imaging should include the following, when possible:

  • The inferior vena cava (IVC), the hepatic veins, the main portal vein, and, if possible, the right and left branches of the portal vein
  • The hepatic lobes (right, left, and caudate) and, if possible, the right hemidiaphragm and the adjacent pleural space
  • Doppler mode should be used to evaluate the blood flow velocity and direction
  • The main and intrahepatic arteries, main and intrahepatic portal veins, intrahepatic portion of the IVC, collateral venous pathways, and transjugular intrahepatic portosystemic shunt (TIPS) stents

CHAPTER 5
Ultrasonography Findings

This section provides an overview of the characteristics of a healthy liver and describes liver diseases, including hepatitis, liver cirrhosis, infectious diseases, as well as all types of benign and malignant tumors.

Healthy Liver and Imaging Difficulties

A healthy liver contains a high quantity of water and has a homogenous parenchyma. In this medium, the waves propagate easily. A healthy liver is characterized by:

  • Smoothness, with no irregularities
  • Anechoic hepatic veins that frequently lack a clear vessel wall
  • Having a thin, bright wall

The lower parts of the rib cage, the vertebral column, and the muscles of the back are obstacles to sonographic imaging. The access to the liver is typically limited to the right subcostal space, the right intercostal spaces, and the middle and left part of the epigastrium. In fact, the quality of the liver parenchymal image is not equal throughout the entire liver. The portions of the liver that are closer to the transducer can be imaged using higher frequencies and at greater resolution, while the parts that are farther from the transducer have reduced spatial resolution.

Portions of the liver may also be concealed by other internal structures, including:

  • The heart
  • The right flexure of the colon
  • A gallstone-filled gallbladder
  • Large amounts of subcutaneous or intra-abdominal fat

Hepatitis

Hepatitis is an inflammation of the liver that can be caused by infectious or noninfectious agents. It can be acute or chronic.

How to differentiate between acute and chronic hepatitis:

  • Acute hepatitis is described by a decreased echogenicity accompanied by brightness of the portal triads
  • With chronic hepatitis, the liver appears normal, but presents with a coarsened liver parenchyma and a decreased brightness of the portal triads

The liver can be affected by different stages of hepatitis, from acute hepatitis to liver cancer. Each has different symptoms, including:

  • Flu-like symptoms
  • Gastrointestinal symptoms, including loss of appetite, nausea, vomiting, and fatigue

Liver Cirrhosis

Cirrhosis is a developed disease of the liver characterized by the death of liver cells accompanied by the regeneration of the fibrous bands interspersed with the remaining liver tissue.

What are the different causes of cirrhosis?

In general, alcohol is the leading cause of liver cirrhosis. Other potential causes include: viral hepatitis, drug toxicity, autoimmune diseases, and disorders of the bile ducts.

Sonographic diagnosis of cirrhosis can be difficult: fibrosis and nodularity cause a coarse pattern that limits the efficiency of ultrasound. In addition, the increased attenuation and decreased vascular markings reduce the quality of the images.

Cirrhosis also has different stages. In the early stage, an enlargement of the liver and the spleen may appear clearly, and ascites surround the liver. In more advanced stages, the liver appears smaller while the caudate and the left lobe appear enlarged relative to the right lobe. Liver hypoechoic nodules with a diameter of less than 1 cm may be visible, as well as dysplastic nodules with variable echogenicity.

Infectious Diseases

Pus-filled masses caused by localized infections within the liver parenchyma are called liver abscesses. These abscesses are caused by certain types of bacteria diffusing from adjacent organs that affect the portal vein or hepatic artery. They present with different fluids, ranging from solid and hypoechoic for new abscesses to cystic anechoic for mature abscesses. In some cases, if abscesses are not treated immediately, they can be fatal.

What is hepatic candidiasis? Fungal infection is another type of infectious disease which usually occurs in individuals with compromised immune system function.

In detecting candidiasis using ultrasound, the most common finding is the presence of multiple hypoechoic nodules with discrete margins having a “wheel-within-a-wheel” shape.

Candidiasis can also manifest in multiple hypoechoic lesions with a strongly echogenic center known as a “bull’s eye.” The first stages of active candidiasis appear in the wheel-within-a-wheel and bull’s eye patterns. Other presentations typically occur later in the disease and reflect that the infection is subsiding.

Metabolic and Vascular Diseases

Metabolic and vascular diseases are divided into fatty liver and portal vein thrombosis.

What are the characteristics of a fatty liver? There are two types of fatty liver: diffuse fatty liver and focal fatty liver.

Diffuse fatty liver is characterized by:

  • Homogeneously increased echogenicity
  • An increase in liver brightness and echogenicity
  • Poor penetration of the posterior liver
  • Decreased portal vein wall visualization
  • Hepatomegaly

Focal fatty liver is characterized by:

  • Focal fat deposits superimposed on a normal background
  • Focal fatty sparing regions, which appear as hypoechoic masses within a dense, fat-infiltrated liver

Now, let’s discuss the portal vein thrombosis.

Portal vein thrombosis is a blockage or narrowing of the portal vein by a blood clot caused by:

  • Slow blood flow
  • Increased blood clotting
  • Inflammation, cancers, or other conditions

Ultrasonography findings may include a hypoechoic thrombus within the vessel. B-mode sonography visualizes an acute thrombus, either hypoechoic or anechoic, and color Doppler sonography shows portal vein flow and thrombus formation.

Liver Tumors

There are three different types of liver tumors: benign tumors, inflammatory pseudotumors, and malignant tumors.

Benign liver tumors are non-cancerous tumors. They are common but typically asymptomatic. Often these tumors are detected incidentally while scanning a patient to diagnose another condition. Two types of benign liver lesions typically have clinical relevance:

  • Solid lesions, including hemangiomas, focal nodular hyperplasia, and adenomas;
  • And Liver cysts

Liver hemangiomas are congenital tumors consisting of blood-filled cystic spaces. They are the most widespread and may occur in 20% of the general population.

A hemangioma is caused by a proliferation of vascular endothelial cells, which produces a mass of abnormally tangled blood vessels. The patient can have pain due to necrosis, infarction, or thrombosis. When a hemangioma becomes larger than approximately 10 cm, it can cause complications such as anemia and cytopenia.

Ultrasonography is often the first study applied to diagnose a hemangioma, and it is also used to monitor the tumor over time once it has been diagnosed. Typical features of a hemangioma as seen on ultrasound include:

  • A size less than 3 cm
  • Homogenous and hyperechoic appearance and acoustic enhancement
  • Hemangiomas may also exhibit a heterogeneous central area containing hypoechoic portions with a thin or thick echogenic border
  • Larger lesions may have a more mixed echogenicity due to the presence of necrosis

How to detect a hemangioma using the CEUS technique

Contrast-enhanced ultrasound findings typically include peripheral nodular enhancement in the arterial phase, with complete or incomplete centripetal filling in the portal venous and late phases.

The process takes approximately 1 minute. To prevent microbubble destruction during delayed lesion filling, it may be useful to stop scanning after 1 minute and then return every 30 seconds to observe the slow infilling of the lesion.

The second type of benign liver tumor is the focal nodular hyperplasia (FNH) anechoic.

Focal nodular hyperplasia is the second most common solid benign liver tumor, which occurs in approximately 3% of the population. It is a congenital arteriovenous malformation, described by abundant arterial vessels within a fibrotic star-shaped scar. In general, women 20 and 30 years of age are more often affected. As a benign tumor, FNH has no potential to become malignant.

FNH lesions have many features:

  • Solitary mass
  • Central stellate (star-shaped) scar
  • Fibrous septa emanate from the center, dividing the lesion into many nodules
  • Lesions may be multifocal accompanied by hemangiomas

What are the phases of FNH?

FNH is typically well-defined using ultrasound diagnosis and is hyperechoic or isoechoic relative to the liver. There are three phases to a contrast-enhanced ultrasound examination for FNH:

  • The arterial phase may show central tumor filling of the circulatory bed
  • The portal venous phase presents a complete enhancement; the center of the lesion becomes hyperechoic, enhancing the tumor scar, and the spoke wheel shape appears
  • In the late phase, the tumor becomes isoechoic to the liver

The last type of solid lesion is the hepatocellular adenoma.

Hepatocellular adenoma is a benign hepatic tumor. It is a rare and well-defined solitary lesion. It is related to estrogen exposure and occurs primarily in women of childbearing age. If not treated early, it can lead to other complications, such as spontaneous rupture and bleeding. In some cases, hepatocellular adenoma may undergo malignant transformation into hepatocellular carcinoma (HCC). For this reason, surgical removal of the lesion is recommended.

If the tumor size is greater than 6.5 cm, a rupture of hepatocellular adenoma may manifest, especially in pregnant women. Ruptured lesions may exhibit a clear fluid component within or around the tumor. The ultrasound images of an intact adenoma may be nonspecific with variable echogenicity.

Doppler and contrast-enhanced ultrasound are used to detect these lesions.

A Doppler examination may show no circulatory signal in some cases, but it may reveal peripheral peritumoral vessels and intratumoral vessels exhibiting a flat, continuous, or, less commonly, triphasic waveform. These signals are very helpful to distinguish hepatocellular adenoma from focal nodular hyperplasia.

Contrast-enhanced ultrasound may be also ambiguous. This issue is caused by the rapidity and large degree of enhancement during the arterial phase, with centripetal filling from the periphery toward the center. In this case, additional computer-based perfusion analysis and slow-motion video sequences are sometimes necessary to enhance the visualization. Initial enhancement is followed by moderate washout during the portal venous phase.

Liver cysts are another type of benign liver tumor.

Simple hepatic cysts occur among women between 50 and 60 years old. They appear in approximately 7% of the general population. They are often asymptomatic, but larger cysts may result in different complications, such as:

  • Hemorrhage within the cyst
  • Compression of the biliary tree or the vasculature
  • Rupture, infection, or cholangiocarcinoma

In some cases, cysts occur in groups and are detected incidentally in patients having other diseases. These cysts are anechoic, well-defined inside a thin wall with a presence of a fluid mass indicated by a posterior acoustic enhancement, and without a circulatory signal when viewed with Doppler or CEUS.

Less commonly, cysts may contain fine linear internal septa. Calcification may occur within the cyst, resulting in acoustic shadowing. As shown in this image, acoustic shadowing is caused by the calcifications that occur within the cyst.

Malignant Tumors

Hepatocellular carcinoma represents approximately 75% of all cases of liver cancer in the United States. As mentioned before, this type of malignant tumor often presents with liver cirrhosis caused by chronic alcohol abuse. Infections from the hepatitis B or hepatitis C virus also increase the risk of hepatocellular carcinoma.

Malignant tumors can develop in a healthy liver, metastasized from another part of the body. There are three types, which vary in shape and structure, and they are characterized by a very pronounced circulatory signal.

Liver cancer can be caused by metastases from other organs, such as the pancreas, breast, colon, lungs, and stomach. The liver can be affected by a single lesion, but, in most cases, multiple focal masses appear. These lesions may have different size and echogenicity, and they have different characteristics according to the primary cancer. For example, tumors from gastrointestinal cancer are hyperechoic, while those from lung cancer are hypoechoic.

A hypoechoic halo is the most important sign of malignancy, including for hepatocellular carcinoma (HCC) and liver metastases.

What are the three types of hepatocellular carcinoma and what are their characteristics?

Hepatocellular carcinoma (HCC) occurs in 3 primary forms: solitary, multiple nodules, and diffuse infiltrative disease.

These tumors may have different appearances. They may be highly echogenic or cystic masses. Most HCCs have a size of less than 3 cm, are hypoechoic, and may be limited by an echo-poor rim or halo.

However, some HCCs have an increased echogenicity due to hemorrhage, fibrosis, or necrosis. As consequence, it is difficult to distinguish them from hemangiomas using ultrasound alone. In addition, the presence of multiple compartments having different histologic characteristics within the tumor causes a “mosaic” pattern, which is also very difficult to detect.

Ultrasound is used in guided biopsy to detect increased vascularity, which is the most reliable characteristic for the identification and diagnosis of hepatocellular carcinoma.

In addition, dysplastic nodules produce abnormal new blood vessels having cellular characteristics that are not clearly cancerous. For this reason, ultrasound is used as part of a surveillance regimen for patients with cirrhosis. In fact, cirrhosis patients might undergo ultrasound imaging every 6 months, as well as blood testing for alpha fetoprotein, which is a serum marker of hepatocellular carcinoma.

Now, we will discuss inflammatory pseudotumors.

These lesions are caused by the infiltration and accumulation of inflammatory cells and are accompanied by varying degrees of fibrosis, necrosis, and other inflammatory reactions. They may produce clinical and imaging findings that resemble malignant tumors. Imaging findings are generally nonspecific. Lesions may manifest as a single or multifocal mass, which may appear hypoechoic or hyperechoic.

Abdominal Trauma

Why does liver trauma require ultrasonography?

In acute liver trauma, a fresh hemorrhage is highly echogenic. But after several days, the lesion becomes more hypoechoic and distinct. Septations and internal echoes may develop 2 to 4 weeks after trauma. Contrast-enhanced ultrasound is required for the examination of patients who have suffered liver trauma for many reasons, including:

  • To reduce population-level exposure to ionizing radiation; and
  • Contrast-enhanced ultrasound have increased sensitivity approaching that of contrast CT

CHAPTER 6
Summary

Ultrasonography techniques have increasingly been used to characterize a wide variety of liver lesions, including infectious processes, benign and malignant tumors, and traumatic injuries. Appropriate patient positioning is necessary to obtain high-quality ultrasound images of hepatic structures.

With the addition of newer ultrasound approaches, such as contrast-enhanced ultrasound (CEUS), the sensitivity of ultrasound for the detection of liver lesions may approach the sensitivity of CT or MRI imaging. A combination of B-mode ultrasound, Doppler imaging, and CEUS can provide a great deal of information about the structure and function of liver lesions.

Thank you for choosing Medical Professionals as your Continuing Education provider. We hope you found this course interesting and valuable. Before you take the post-test, please be sure to look over the module objectives to see if you need to review any of the information presented in the module.

Chapter selection