Ultrasound Flashcards
What is sound?
A result of mechanical energy producing alternating compression and rarefaction of the conducting medium
What is the unit of frequency?
Hertz (Hz)
What range of frequencies can humans hear?
20 Hz to 20 kHz
What is the frequency of ultrasound waves?
Greater than 20kHz
How do diagnostic ultrasound machines work?
Uses short sound pulses that are transmitted into the body
These can be reflected, scattered, refracted or absorbed
The combine effects of this causes attenuation in the intensity of the sound pulse as it travels
This allows the machine to distinguish between different tissues and create an image
What are the advantages of ultrasound?
Ultrasound is safe
No ionizing radiation
Equipment is portable and inexpensive
What are the disadvantaged of ultrasound?
Highly operator dependent
Structures around bone do not give clinically useful images
The attenuation of the ultrasound signal at air/tissue boundaries means it is unsuitable for imaging structures obscured by gas
What are the different components of an ultrasound machine?
Monitor US unit- signals are processed Control panel Transducers Data storage device
What are the main parts of the transducer?
Electrodes applying an alternating potential difference Piezoelectric crystal Plastic nose Backing block Acoustic insulator
What are piezoelectric crystals?
Ceramic crystals that deform and vibrate when they are electronically stimulated
How do piezoelectric crystals work?
Echoes distort the crystals and generate an electric pulse to create an image
High-amplitude echoes produce greater crystal deformation and generate a larger electronic voltage
What are the different types of transducers?
Convex array
Micro-convex array
Linear array
Endovaginal and rectal array
Describe linear-array transducers
Images obtained with linear arrays always have a flat superficial surface
Often very high frequency so can only be used for superficial tissues
Describe curved-array transducers
The surface is curved creating a convex shape
Those with short radi can be used for endoluminal scanning
Those with larger radi can be used for abdomen scanning
Describe phased-array transducers
Every element in the array participates in the formation of the pulse
Because the sound beams are steered at varying angles from one side to the other, sector images are produced
Describe intraluminal probes
Small transducers that can be placed within body lumens
Can be positioned closer to the organ so a higher resolution image can be obtained
Very small transducers have been added to flexible endoscopes to scan and guide biopsies in the gastrointestinal tract
What is A-mode imaging?
A method of displaying echoes acquired in 1 dimension.
Depth is represented along 1 axis and the echo amplitude is displayed along a perpendicular axis
What is B-mode imaging?
Brightness is the most commonly US mode
The brightness of the dot represents the amplitude of the returning signal
The position of the dot represents the depth from which the signal is returning and depends on the round-trip time of the US signal
Multiple scan lines across a plane are combined to produce a 2D image
What do the colours black, white and grey represent in a B-mode US?
Black- anechoic fluid
Dark grey- pus in an abscess
White-bone
Grey- organs and tissue
What are the different types of Doppler US?
Colour
Power colour
Pulsed
Describe colour doppler US
Measures and colour codes the direction and magnitude of the mean doppler frequency shifts that occur in moving red blood cells and superimposes a colour depiction of these data on the gray-scale image
Describe power colour doppler US
Depicts the amplitude or power of the doppler signals. This allows better sensitivity for the visualisation of small vessels, but at the expense of directional information
Describe pulsed doppler US
Allows a sampling volume to be positioned in a vessel visualised on the gray-scale image and displays a spectrum of the full range of blood velocities within the gate plotted as a function of time
Describe M-mode US
Designed to document and analyze tissue motion
Uses a line from the 2D scan- reflections from this line are displayed in a graphic form
Motion on vertical axis, time on the horizontal axis
Important for studying cardiac valve
Describe 3D US
Data is accquired as a stack of parallel cross sections with the use of 2D scanner
Can be displayed as multiplanar reformatting, surface rendering, volume rendering and virtual endoscopy
What frequency setting is resolution?
Highest
What frequency setting is penetration?
Lowest
What frequency setting is general?
Intermediate frequency
What is the gain control?
Adjusts amplification of the returning acoustic signals
Too little produces a dark image
Too much produces a white image
What sort of presets would be present on a US machine?
Vascular, breast, nerve, muscoskeletal
Describe acoustic enhancment
Only a small amount of energy will be absorbed by some fluids, meaning the tissues behind will be shown in a greater depth
What are the 4 manipulation manoeuvers?
Pressure
Alignment
Rotation
Tilt
What angle would you position the transducer?
At 90 degrees to the structure of interest
What is ansiotropy?
An artefact encountered when the US incorrectly diagnoses a tendon tear
How does ansiotropy happen?
Changing the angle when examining the tendon will change the colour from hyperechoic to hypoechoic. When seeing hypoechoic it is easy to misdiagnose tendinosis
What is lithotripsy?
Stones present in the urinary system are crushed by the vibrating impulses of the ultrasound machine
What is cavitation?
When the US produces small pockets of gas in the tissue
What are the Thermal index (TI) and Mechanical Index (TI) used for?
Provides operator with an indication of the potential for ultrasound induced bio-effects
What is the acronym ALARA?
As Low As Reasonably Achievable
What value should you keep the TI and MI under?
1
What is point-of-care ultrasound (POCUS)?
Defined as a goal-directed, bedside US examination to answer a specific diagnostic question or to guide performance of an invasive procedure
How does US help vascular access?
Guides the needle/cannular allowing the health professional to see the object enter the patients vein, in both transverse and cranial planes
How does the angle of incidence effect the resolution of the image?
If perpendicular more waves will be reflected back to the transducer resulting in a better image
If the wave are more parallel the waves will be scattered and create a worse image
How can you assess the hip stability of newborns?
A transverse scan of the hip while in flexion
Describe a benign breast lump
Oval shaped Wider than deep SMooth Variable to hyperechogenicity Uniform homogeneity of internal echoes
Describe a malignant breast lump
Variable in shape Deeper than wide Irregular or spiculated Low-level echotexture Absent lateral shadowing Attentuation with obscured posterior margin Calcification Microlobulation Intraductal extension Infliltration across tissue planes
What does the acronym FAST stand for?
Focused Assessment with Sonography in Trauma
What is FAST used for?
Performed in the emergency department to assess patients admitted with blunt abdominal trauma
