Ultrasound Flashcards
What is sound?
A pressure wave (a form of mechanical energy) that travels in a longitudinal wave.
A sound wave is created when a vibrating object sets molecules of a medium (air) into motion.
What is compression?
High pressure
(Peak)
What is rarefaction?
Low pressure
(Trough)
Where is pressure measured? (On a graph)
Y-axis
Where is time measured? On a graph
X axis
What does frequency measure?
Pitch
(How many cycles occur in a given period of time)
What is wavelength?
Distance b/t two identical points in adjacent cycles.
Inversely related to frequency.
What is amplitude?
A sound’s loudness. Determined by the degree of pressure fluctuations.
What is the sound velocity through air?
343 m/sec
What is the sound velocity through soft tissue?
1540 m/sec
What is the sound velocity through bone?
3,000-5,000 m/sec
What do modern transducers employ?
A piezoelectric material called zirconate titanate
What is a piezoelectric material?
Can transducer electrical energy to mechanical energy and vice versa
What determines the vertical placement of each dot in an ultrasound image?
Vertical placement = time delay (how long it takes the echo to return)
What determines the horizontal placement of each dot in a ultrasound image?
Determined by the particular crystal that receives the returned echo.
What is the brightness of each dot determined by?
Amplitude of the returning signal.
(Echogenicity describes a tissues ability to transmit or reflect sound waves)
What are hyperechoic structures?
Produce strong amplitude echos (these tissues have high impedance)
**BONE
What is a hypoechoic structure?
Darker shade of grey
Produce weak (low amplitude) echoes (these tissues have a lower impedance)
**solid organs, skin, adipose tissues, and cartilage
What is an anechoic structure?
Don’t produce an echo.
(Vascular structures, cysts, ascites)
How do nerves appear on ultrasound?
It depends on echogenicity of the surrounding structures. (Anechoic ~ Roots of the brachial plexus)
Or (hyperechoic ~ honeycomb appearance like distal nerves)
What is axial resolution?
Beam depth
The ability to differentiate structures that exist along the length of the ultrasound beam
What is lateral resolution?
(Beam width)
The ability to differentiate structures that exist in the width of the ultrasound beam.
Position the sonoanatomy of interest in the focal zone
What is elevational resolution?
Beam thickness
The ability to differentiate structures that exist in the thickness of the ultrasound beam.
(Fixed value)
What are the three zones of the ultrasound beam?
Focal zone: region where the beam is narrowest and thinnest
Near zone: the region b/t the transducer and the focal zone
Far zone: the region beyond the focal zone
Where is the image resolution the best?
Focal zone
What is attenuation?
Reduction in image quality d/t the natural decrease in a sound’s strength and the fact that some sound waves never return.
(Bone produces the greatest amount of attenuation)
Absorption?
Sound waves are lost to the body as heat.
It’s an important determinant of the depth of tissue penetration (high frequencies experience a greater degree of attenuation as a function of absorption)
What is reflection?
It is the process where a sound bounces off a tissue boundary of differing acoustic impedance.
Applying gel b/t the ultrasound transducer and the patients skin reduces reflection.
What is scatter?
Occurs when the ultrasound wave encounters an object smaller than the wave
This explains why fluid filled objects appear anechoic
What is refraction?
Bending of the ultrasound wave that encounters a tissue boundary at an oblique angle.
Based on snell’s law.
What is short-axis view?
Cross section
What is long axis view?
Looks at a structure along its length
Which frequencies allow us to see deeper inside the body, but with a loss of resolution?
Lower-frequencies
Which frequencies produce the best resolution at the expense of being unable to visualize deep structures?
High-frequencies
What is the frequency (MHz) of high frequency transducers? What depth? And what is this good for?
> 10 Hz
For depths <3 cms below skin
For: interscalene, supraclavicular, axillary, wrist, ankle, femoral, superficial blood vessels
What is the frequency (Hz) of medium frequency transducers? What depth? What is it best used for?
Freq: 5-10 Hz
Depth: 3-6 cms
For: popliteal, sciatic, deeper blood vessels
What is the frequency (Hz) of low frequency transducers? What depth? What is it best used for?
Hz: < 5
Depth: > 6cm
For: lumbar plexus, celiac plexus, neuraxial, high BMIs
How is a linear array transducer configured?
Piezoelectric crystals are arranged in parallel
Operate in a high frequency
How is a curvilinear array transducer configured?
Convex footprint ~ piezoelectric crystals follow suit ~ fanlike image
Lower freq
How is a phased array transducer configured?
Very narrow in the near field and fans out with increasing depth
Best for small acoustic windows at a deeper level (I.e. looking b/t ribs)
Typically operate on low freq
What does gain adjust in the ultrasound?
The strength of the returning echoes
What does depth on a ultrasound determine?
How dee you can see into the body
What does the B-mode on the ultrasound machine mean?
Stands for the brightness of the pixels on the screen. Produces real-time imagery of the sonoanatomy.
What does the M-Mode on the ultrasound machine stand for?
Stands for motion. It’s a time lapse photo that illustrates the relative movement of the structures over time.
Used frequently in echocardiography (also useful in fluid responsiveness or diagnosing a pneumo)
Where should you focus your image?
Adjust the focus so the target sonoanatomy resides in the focal zone.
What does the y axis of the m-mode represent?
Degree of movement
What does the x-axis in m-mode represent?
Time
What is the Doppler effect?
Describes the change in the perceived frequency of a sound wave when there’s relative motion between the sound’s source and an observer.
If the sound source becomes closer to the observer ~ decrease in wavelength and increase in frequency (POSITIVE Doppler shift)
If the sound source becomes farther away from the observer ~ increase in wavelength and a decrease in frequency (NEGATIVE Doppler shift)
What are the three things that determine the degree of Doppler shift?
Frequency of the ultrasound beam
Blood flow velocity
Angle of insinuation
(Shift is greatest is beam is parallel)
(Shift is zero if US beam is perpendicular to flow)
What are the three factors that determine the degree of Doppler shift?
Frequency
Angle of Insonation
Blood flow velocity
What is the degree of insonation when the ultrasound beam is perpendicular to blood flow?
Zero. The cosine of 90 degrees = 0
According to the standard convention, the orientation marker on the ultrasound probe should point towards the patient’s what?
Right (usually in short axis view ~I.e arterial line)
head (long axis view)
What is the correct way to hold a transducer?
Like a pencil
Which technique improves image resolution by reducing the distance b/t the transducer and your anatomical target?
Compression
What does tilting the transducer do?
Helps orient the ultrasound beam perpendicular to an underlying structure ~ improves image quality by reducing signal loss.
Changes the angle of incidence
What does rocking on the transducer do?
Moves from side to side (while staying in the long axis)
Promotes better contact b/t the patient and the transducer ~ helpful for imagining inside a narrow acoustic window.
What is sliding the transducer?
Moving the short axis of the transducer up or down while maintaining the same angle of incidence
What does rotation on the transducer do?
Moving the transducer in a clockwise or counterclockwise direction.
Useful when going from short to long axis or vice versa
What is air artifact?
It happens when part of the transducer’s footprint fails to contact the skin, air pockets develops
Solved by applying more gel or applying more pressure
What is shadow artifact?
This happens when acoustic energy encounters a medium which doesn’t allow penetration( I.e bone)
Because of this, you’ll observe an acoustic shadow deep to the hyperechoic border
What is acoustic enhancement?
Opposite of shadow artifact
When the ultrasound wave reaches the interface of a fluid-filled structure (femoral artery) and the underlying tissue, the difference in acoustic impedance accentuates the brightness in this region
Wha this mirror image?
Occurs when the ultrasound beam gets trapped between two highly reflective tissue ~ this causes a time delay in some of the returning echoes
What is reverberation?
Similar to mirror image. Occurs when sound waves bounce between two strong parallel reflecting surfaces
**occurs during imaging of the pleura or an attenuating wide-bore needle
What is bayoneting?
The needles appears to bend as it penetrates a tissue boundary.
This occurs when the needle passes through adjective tissues of different acoustic impedance.
What are the three standard imaging windows?
Parasternal
Apical
Subcostal
What can you see in the Parasternal-Long Axis (PLAX)
Structures: LA, LV, MV, AV, aorta, pericardium
Interpretation: LV fx, mitral/aortic lesions, effusion
What can you see in the Parasternal-short axis (PSAX)
Structures: LV, papillary musc, RV, pericardium
(Looking from the apex up)
Interpretation: RV and LV fx, effusion
What can you see in the Apical 4-chamber (A4CH)
Structures: RA, RV, LA, LV, mV, AV, pericardium
Interpretation: LV and RV fx, AV lesions, pericardial effusion
What is the subcostal 4 chamber?
Structures: RA, RV, LA, LV l, MV, AV, pericardium
Interpretation: RV function/ pericardial effusion
What is the Subcostal IVC view?
Structures: Liver, RA, IVC
Interpretation: volume status
What do we assess to determine whether a patient is a full stomach?
Gastric antrum
What does the absence of lung sliding suggest?
Pneumo or endobronchial lntubation
What are a lines on a pulmonary ultrasound?
Horizontal lines from reverberation artifact
What are b lines on a pulmonary ultrasound?
Vertical lines (can be normal or pulmonary edema)
What position to do you place your patient for a gastric ultrasound?
Right lateral decubitus position
This allows air to rise and gastric contents to fall in the direction of the antrum
What does an empty stomach look like on ultrasound?
Target or a “bull’s eye”
What do clear liquids look like on gastric ultrasound?
Round and distended with an anechoic center.
What does particular matter look like in ultrasound?
Stomach will look round and distended
Fluids or food will appear grainy or as bright particular matter (more solid foods)
How do we calculate the volume of clear gastric fluid?
Gastric volume (mL) = 27 + 14.6 x CSA - [1.28 x age(years)]
What is considered a low risk gastric volume?
Volume < 1.5 mL/kg (GRADE 1)
What is considered a high risk gastric volume?
Volume > 1.5 mL/kg (GRADE 2)
