Clinical Applications of Ultrasound Imaging Flashcards
What is used in US imaging?
What are the 3 fundamental points to consider about US waves?
- US uses high frequency sound waves
- the waves are not part of the electromagnetic spectrum
- they are mechanical energy created by vibrations
- they are propagated through a medium by exerting pressure on particles
How does the US probe generate US waves (a beam)?
- the US probe can generate US waves as it contains piezo-electric crystals
- these are able to convert electrical energy into sound waves (mechanical energy) and vice versa
How does the US beam travel through body tissues when the probe is applied to a body surface?
How does energy return to the probe?
- the beam travels through body tissues by acting as a pressure wave
- this pressure wave temporarily shifts the position of the particles in that medium (e.g. air, soft tissue, etc.)
- as the sound waves (US beam) travels through the tissues, they lose energy
- they are reflected from the tissues to different degrees and these reflected sound waves are detected by the probe
- the probe converts the returning sound waves into an electrical current, which can be used to construct an image
What is the velocity of travel of sound waves dependent on?
What is meant by attenuation and what does this depend on?
- the velocity of sound waves through tissues depends on the tissue density
- the sound waves lose some of their energy to the tissues as they travel through them (it is converted to heat)
- the loss of energy of sound waves is attenuation
- the degree to which sound waves are attenuated partly depends upon the frequency of the sound waves
How do high frequency sound waves travel through tissues?
When do these tend to be used for imaging?
- high frequency sound waves have a short wavelength and attenuate quickly
- this means they do not travel far into the tissues, so are used to image more superficial structures / tissues
- high frequency sound waves give good resolution so are used when high clarity images are needed
How do low frequency sound waves travel through tissues?
When do these tend to be used?
- low frequency sound waves have a long wavelength and attenuate slowly
- they can penetrate deeper into the tissues so are used to visualise deep structures
- the image resolution is compromised
What happens to sound waves when they meet tissues that are not dense and tissues that are dense?
How does this allow an image to be generated?
- when sound waves meet tissues that are not dense (e.g. fluid), the waves travel through** and are **not reflected back to the probe
- when sound waves meet tissues that are dense (e.g. bone / stones), they reflect most of the wave back to the probe
- image generation relies on the fact that it is not a uniform signal being reflected back to the probe
What is acoustic impedance?
What happens when US waves meet a boundary between 2 tissues with different acoustic impedance?
- how easily a sound wave can travel through a tissue depends on its acoustic impedance
- when US waves meet a boundary between 2 tissues with a different acoustic impedance, some of the wave energy is reflected
- the bigger the acoustic impedance between the 2 adjacent tissues, the more wave energy is reflected
How does fluid appear on US and why?
What type of artefact is associated with a simple fluid-filled cyst?
- fluid appears dark as the sound waves pass through it and are not reflected back to the probe
- simple fluid-filled cysts appear black - they are hypoechoic / anechoic
- they are associated with posterior acoustic enhancement - a bright shadow is seen behind / below them
How do dense structures appear on US and why?
What type of artefact are they associated with?
- dense structures appear bright as sound waves cannot pass through them, so are reflected back to the probe
- these structures are echogenic / hyperechoic
- they are associated with posterior acoustic shadowing - a dark shadow is cast behind/below them
Why is gel applied to the US probe?
to eliminate air between the probe and the skin
- although gas is not dense, it conducts sound waves poorly and reflects most of them back to the probe
What are the 4 major views used in cardiac echocardiography?
Where must the US probe be placed and why?
- parasternal long axis
- parasternal short axis
- apical 4 chamber
- subcostal
- the probe must be placed over the intercostal spaces as bone reflects US waves, making it impossible to see the underlying structures
Where is the probe placed for the parasternal long axis view?
- probe is placed in the left 4th or 5th intercostal space and angled towards the patient’s right shoulder
- this allows for a view of the long axis of the heart
What structures are visible on the parasternal long axis view?
- right ventricular outflow tract
- left atrium
- left ventricle
- mitral valve
- aortic valve (between left ventricle and aorta)
- descending aorta (not always visible)
- this allows for a view down the length of the heart from “front to back”
- the probe is closest to the RVOT and ascending aorta, so these are seen at the “top” of the image
- the atrium and descending aorta are furthest from the probe, so seen at the “bottom” of the image
What are the following structures in this parasternal long axis view?
Where is the US probe placed when looking at the parasternal short axis of the heart?
- it is kept in the same position as the parasternal long axis (left side, 4th - 5th intercostal space), but angled towards the patient’s left shoulder
- the probe can be moved up and down beween the base and apex of the heart, allowing structures at 4 different levels to be seen
How does the parasternal short axis view allow for structures to be visualised?
- it allows for a view across the heart, from “left to right”
- the probe is on the chest wall, so it is closest to the structures of the anterior part of the heart (RVOF and RV) - these appear at the “top” of the image
- the LA and LV are located more posteriorly, so are seen at the “bottom” of the image
What structures are visible at the level of the aortic valve on a parasternal short axis view?
- RVOT
- aortic valve (appears like Mercedes logo)
- tricuspid valve
- bicuspid valve
- right atrium
- left atrium
- pulmonary artery
What are the following features at the level of the aortic valve?
What is shown in these images?
- the closed aortic valve appears like a “Y” and is called the “inverted Mercedes-Benz sign”
what structures are visible at the level of the mitral valve in a parasternal short axis view?
- right ventricle
- anterior leaflet of mitral valve (AML)
- posterior leaflet of mitral valve (PML)
What are the following features visible at the level of the mitral valve?
What structures are visible at the mid-ventricular level on a parasternal short axis view?
- right ventricle
- left ventricle
- anterolateral papillary muscle (ALPM)
- posteromedial papillary muscle (PMPM)
What are the following structures at the mid-ventricular level?
What structures are visible at the apical level in a parasternal short axis view?
- right ventricle
- left ventricle
What are the following features present at the apical level?
Where is the probe placed in the apical 4 chamber view?
What does this view allow the visualisation of?
- the patient is positioned on their left side so that the heart is lying against the chest wall
- the probe is placed over the apex of the heart
- this can be palpated on the left side, in the 5th intercostal space in the midclavicular line
- it allows visualisation of all 4 chambers with the ventricles being closest to the probe and the atria being furthest away
What structures are visible in an apical 4 chamber view?
- right ventricle
- left ventricle
- right atrium
- left atrium
- tricuspid valve
- mitral valve
- descending aorta
- the ventricles (apex) is seen at the top of the image
What are the following features in this apical 4 chamber view?
Where is the US probe placed in a subcostal view?
What does this allow for visualisation of?
- the probe is placed inferior to the xiphoid process and angled up towards the head
- it allows for visualisation of all 4 chambers
- unlike the apical view, the interventricular and interatrial septa can be seen as they are perpendicular to the US beam
- they can be assessed for any defects
What structures are visible on a subcostal view?
- right atrium
- right ventricle
- left atrium
- left ventricle
- tricuspid valve
- mitral valve
- interatrial septum
- interventricular septum
What are the following features of the subcostal view?
