Basics of Ultrasound Lecture Flashcards
20/11/24
What is sound?
A vibration that produces a compression wave. Mechanical energy produces alternating compression and rarefaction through the conducting medium
What is amplitude?
Maximal displacement from equilibrium. In longitudinal waves, this is the max change in pressure between areas of compression. Higher amplitude = louder noise.
What is frequency?
Number of cycles per unit time. Standard unit is Hz (Hertz). Audible range for humans is around 20Hz to 20kHz. Ultrasound frequencies are around 20kHz and greater.
What are the applications of ultrasound?
Animals use US for echolocation, e.g. bats. It’s used to determine location and distance of an object by the reflected sound waves. Similar principle to sonar.
What is diagnostic ultrasound?
Short ultrasound pulses are transmitted into the body, where they are reflected, refracted, scattered or absorbed. Combination of all of these results in attenuation of the intensity of the wave, which limits the depth of US imaging.
What are the advantages of diagnostic ultrasound?
Safe mode of imaging
No ionising radiation
Portable equipment
Relatively inexpensive
What are the disadvantages of diagnostic ultrasound?
Highly user dependent
Unable to image organs deep to bone
Unsuitable for air filled structures
(Distended) bowel/lungs
What is “knobology”?
Understanding the controls on the ultrasound machine.
What is the piezoelectric effect?
Generation of electrical charge due to an applied stress. Reverse piezoelectric effect is the change in shape or a piezoelectric material when an electric voltage is applied to it.W
What does the piezoelectric effect allow?
Detection of the reflected ultrasound waves
What does the reverse piezoelectric effect allow?
The production of ultrasound waves.
What are piezoelectric crystals?
Electric current is applied to these which produces the ultrasound wave → propagates through the body.
They are deformed by returning waves, which produces an electric signal → relayed to the US unit.
What does a higher amplitude wave mean?
Greater crystal deformation, hence larger current, and larger signals are displayed as brighter pixels.
What are transducers?
Probes
What are linear-array probes?
High frequency, good image resolution, low depth of imaging, and flat flootprint produces undistorted images.
What are curved-array probes?
Low frequency probes, low image resolution, good depth of imagine, slight distortion of images.
What are phased array probes?
Low US wave generated from the centre of the footprint. Small probe, but large scanning area. Can scan in small/awkward areas.
What are intraluminal probes?
Can be used in various lumens/orifices, and have several advantages. Overcomes poor imaging resulting from overlying structures, and allows use of higher frequency, so high resolution images.
What is B-imaging mode?
Produces 2D images, a spike from a returning wave is represented as a pixel, and the brightness is determined by the amplitude of the signal.
What are the different shades of gray in US?
Isoechoic, Hyperechoic, Hypoechoic and Anechoic.
What is isoechoic?
A shade of gray that is of the same brightness or echogenicity as the surrounding tissues.
What is hyperechoic?
A shade of gray that is bright white or brighter than the surrounding tissues. - more bone
What is hypoechoic?
A shade of gray that is dark or less bright than the surrounding tissues. - pus or lymph nodes
What is anechoic?
An absence of echoes, hence blackness. - fluid: blood, urine
What is the doppler effect?
The phenomenon of the altering frequency of an emitted wave depending on the source’s movement relative to the observer.
How can doppler ultrasound be used?
Colour doppler - direction and magnitude of blood flow
Power doppler - better visualisation of small vessels but no directional information
Pulsed doppler - Allows a sampling volume positioned in a vessel
What is M-imaging mode?
Used to analyse tissue motion, useful in cardiac valve studies.
How does 3D imaging work?
Stacks of parallel cross-sectional images are compiled to form a 3D image.
What is gain? (Ultrasound: Basic Controls)
Refers to the amplification of returning signals, icnreasing will make images brighter and more saturated.
What are presets used for?
They adjust parameters to permit optimal viewing of specific structures.
How do you determine correct probe orientation?
Probes have a marker on their side, corresponding to a specific side of the screen.
What are the probe manoeuvres?
P = (Vertical) Pressure
A = Alignment (Sliding)
R = Rotation
T = Tilt (along long axis).
What is tilting the probe good for?
Rotation about the long axis of the probs allows US waves to be directed to give a true-cross sectional image of deep structures which are not parallel with the skin.
What is an ultrasound artefact?
Artefact refers to the distortion of an image due to any number of factors.
What is acoustic enhancement? (Ultrasound artefacts?)
Ultrasound passes through certain structures more easily and with minimal absorption; regions lying deep to a fluid filled structure receive greater energy, so the area will appear uniformly brighter.
What is anisotropy? (Ultrasound artefacts)
Refers to the changes in echoic appearance depending on the relative orientation of the ultrasound wave, most commonly seen when observing tendons.
