POCUS - General Flashcards
Increased gain deep to a hypoechoic area is called ___________.
posterior acoustic enhancement
How can you tell the difference between a curvilinear probe and a phased array probe?
Curvilinear has a wider footprint. The phased array is cone-shaped and narrow.
How can you tell the difference between phased array and curvilinear on the screen?
- Phased array: narrow top, wide bottom
* Curvilinear: wide top, wide bottom
FAST stands for ___________.
focused assessment with sonography in trauma
RUSH stands for ____________.
rapid ultrasound for shock and hypotension
The e-FAST also includes which views (in addition to the FAST exam)?
Bilateral thoracic views for PTX and hemothorax
Describe the spine sign.
In a normal RUQ view, you should not see the spine above the diaphragm. The diaphragm should curve up and behind it you will see only anechoic space. If you see the spine going above the diaphragm, then that is a sign that there is something in the thorax – potentially a pleural fluid or lung consolidation – that is allowing sound to transmit to the spine.
These two principles help you with orientation: ___________________.
1) the top of the screen is always where the probe touches skin and
2) the indicator dot on the screen is always where the raised bump on the indicator is
Review the history of US in medicine by adoption by different specialties.
- 1950s: radiology
- 1960s: cardiology
- 1970s: OB
- 1990s: EM (Chicago started first fellowship 1997, ACGME said EM residents must be proficient in 2010)
- 2000s: PEM
While manually optimizing your gain is often needed, don’t forget about the __________ function.
auto-optimize
On the large Sonosite machines that UNC has, this button is below the depth adjustment column.
You can adjust the resolution on the right side of the screen. What are the three settings and their abbreviations on screen?
- Res (resolution): high resolution, low penetration
- Pen (penetration): low resolution, high penetration
- Gen (general): middle resolution, middle penetration
The ________ feature allows you to drag a box over the area you’d like to focus on.
zoom (on the right next to the resolution icon)
The ___________ feature allows you to look for hyperemia.
color
What types of scans is the linear array probe used for?
- MSK
- Vasculature
- Ocular
- PTX
What types of scans is the curvilinear probe used for?
- Abdominal
- Obstetric
- Pulmonary (effusions, B lines)
If you don’t have an order in, you can save your scan by ______________.
manually entering patient data
Review these types of probe manipulation:
- Sweeping
- Rocking
- Dragging
- Rotation
- Sweeping: keeping the probe in place and tilting it over the long axis
- Rocking: keeping the probe in place and tilting it over the short axis
- Dragging: keeping the probe perpendicular to the surface and moving it like a lawnmower over the skin
- Rotation: keeping the probe in the same location and spinning it around
True or false: ultrasound waves are lower frequency than the range humans can hear.
False
It is in the range of 1-20 MHz (whereas humans can hear 20 Hz - 20 kHz).
To obtain higher resolution, probes emit ______________ frequency sound.
higher
The downside is it can’t go as far as low frequency sound.
The denser the medium, the faster/slower sound travels.
faster
US machines assume that sound travels at ____________ m/s through soft tissue.
1540
Describe the phenomenon of refraction.
When sound (or any wave) passes from one medium to another in a non-perpendicular angle and there is a difference in the transmission of sound waves, then the wave changes angle of direction (it is refracted).
In ultrasound, if a sound wave changes direction through two media then you will see an anechoic line where the refracted line would have been.
Refraction of a wave in multiple directions is called ______________.
scattering
What scans are in the RUSH exam?
Cardiac x5
FAST
Aorta x3
Lung sliding x2
Review the frequencies of different probes.
Curvilinear: 2-5 MHz
Cardiac: 2-8 MHz
Linear: 5-10 MHz
Why are probes called transducers?
They transduce electric signals to sound energy and vice versa.
Another related term is the piezoelectric effect. This is when mechanical energy is converted into electrical energy.
How many piezoelectric crystals are in a typical US transducer?
Up to 200-300
Increasing gain happens by what mechanical change?
Increasing the amplitude of the returning sound waves (the decibels). It does not increase the outgoing signals so there is no increased acoustical exposure to patients.
Describe time gain compensation.
Time gain compensation is a property of ultrasounds in which distant signals are boosted to compensate for the attenuation they have as they pass through tissues. You can also manually do this.
You may see this as digital slide bars on the touch screen or through a column of physical slide bars.
For seeing specific, discrete structures –such as an embryo –use __________ frequencies.
higher
How does compound imaging work?
It uses multiple lines of US beam to form a single image that can reduce artifact.
Review Dr. Robert Jones’ general approach to getting the best US images.
1) Select the appropriate transducer for the job. Usually this is obvious, but play around to see if you can use a higher frequency transducer to obtain images.
2) Select the right preset mode.
3) Get your patient in the right position and use lots of gel.
4) Do a broad scan to get a gestalt image of what you’re looking at.
5) Adjust the depth then adjust the gain
6) Make fine movements and have the patient adjust as needed.
7) Adjust the focal zone to your target structure
8) Add tissue harmonics if it makes your images better
One good way to know if you have too much gain is _____________.
if there are artifacts within vessels
Why do artifacts occur?
Ultrasound machines operate on two assumptoins:
- Sound travels at a consistent speed (1,540 m/s)
- Sound travels only straight forward and straight back to the transducer
In reality, US beams pass through different tissue densities that cause the beam to travel at different speeds, leading to artifacts such reverberation artifact. Sound can also reflect off in different planes, thus leading to reflection artifact.
Ring down artifact can be produced by _______________.
air or metal (the distortion that you see below a needle on US-guided procedures is actually ring-down artifact)
When sound beams hit a dense object such as bone or stone and there is darkness behind it, this is an artifact called ______________.
shadowing artifact
When you see shadowing, you need to look for what types of shadowing?
Clean (from bone or metal) or dirty (from gas)
Clean shadowing will have linear borders and appear nearly uniformly anechoic.
When a sound beam passes through an anechoic structure (such as something filled with fluid), the image beyond it can appear brighter than it otherwise would due to an artifact called _______________.
posterior acoustic enhancement
What artifact is commonly seen around the diaphragm?
Mirror image artifact
This occurs when sound hits a highly reflective surface (like the diaphragm). The intense reflection leads to a mirror image of whatever is proximal to the reflective surface showing up distal to the reflective surface.
If two structures are similar in their echogenicity, you can call them ___________.
isoechoic
Explain the BART mnemonic for doppler.
Blue away
Red towards
(The probe)
What is pulsed-wave doppler?
A continuous doppler that has a selectable range (like what you use to listen to babies heart)
True or false: curvilinear is the lowest frequency transducer.
False
Phased array is the lowest
Phased array: 2-4 MHz
Curvilinear: 2-6 MHz
Linear: 4-12 MHz
The optimal angle of reflection for an ultrasound beam is ________.
90 degrees
This leads to the most reflection.
Why are some posterior shadows gray and some are black?
Gray (“dirty shadows”) occur when there is some air in an otherwise dense object. Air causes US waves to scatter.
What causes posterior acoustic enhancement?
US machines have a feature that boosts the signal of deep objects (to account for attenuation). When there is an anechoic structure (like a cyst) then those soundwaves don’t get attenuated. The automatic feature of the machine then boosts a non-attenuated signal, leading to PAE.
What is edging?
It is an artifact that happens when you look through an anechoic structure that is circular. Some sound waves strike the structure in the same plane (like a tangent) and then bend along the tissue. This causes an anechoic wedge to be cast distal to it.
What causes A lines?
A sound wave bounces off of a plane of air. Some waves will then ricochet off the air of the skin-air interface. This gets interpreted by the US machine as a second plane at a distance of 2x the air interface.
What causes B lines?
When there are pockets of fluid next to pockets of air, some sound waves make it through the fluid and then reverberate around the air. They will exit randomly after a certain amount of bouncing and then return to the sensor. This gets translated as lots of horizontal bars at various distances (that looks like a vertical stripe on the US).
___________ are like a smaller form of B lines. They are not always from an air-fluid interface.
Comet tails
They can also happen from small metallic bits or crystals that cause internal reflections of sound.
What causes mirror artifact?
Same principle as A lines.
Air-fluid or air-tissue is highly reflective. Some sound gets reflected off that interface and to another object closer to the probe. If a little bit gets reflected back off that object and then to the air-tissue interface the machine thinks there is something distal to that reflective surface.
