Ultrasound Flashcards
what is sound
it is the transfer of energy from one place to another via collisions between adjacent molecules. Vibrations pass through a transmission medium
what is a wavelength
peak to peak
what is the amplitude
wave displacement
ultrasound info
- no IR or EM radiation
- 20 kHz +
- no adverse side effects
- visualises ST
- artefacts are recognisable
- direct contact is needed
- discriminates small differences between the structures
what is frequency determined by?
rate of repetition of the original disturbance
what does attenuation depend on?
frequency, medium and distance travelled
what is a higher frequency linked to
higher attenuation
what happens as sound passes through a medium
it becomes attenuated (scattered)
what happens when the energy gets absorbed
intensity decreases
what is refraction
a change in direction as they pass from one medium to another, accompanied by a change in WL and speed
what is echolocation
it is the use of echoes to locate something, once it hits a material it is reflected back
what does the pulse speed depend on
tissue type
what is reflection
it is when a wave hits a medium boundary, the way is then reflected and transmitted. This is dependent on the dissimilarity of two media
what is the piezoelectric effect
it is when a piezoelectric crystal is used which changes shape when a current is applied across it. The electricity current changes its shape as it oscillates when it sends an US pulse. A short pulse is directed as a narrow beam into the body the pulse reaches different tissues which are then reflected.
how does US work
- transmits a sound wave into the body
- intensity of the reflected echoes are interpreted
- a handheld probe makes contact with the skin
- data is collected
what does a transducer do?
it changes the signal from one form to another, an electrical signal -> sound and vice versa
what does the transducer size and shape depend on?
accessibility
tissue depth
examined area
how is an image formed
the sound emitted from the transducer is reflected from the patient back to the transducer
what does a higher frequency result in
higher detail, less distance
where does compression and rarefaction take place
compression = high pressure
rarefaction = low pressure
how is the time taken for an echo to return determined
by the distance from the probe
when does an interface occur
when there is change in density composition at which the sound passes through. This is a change in tissue between the boundary of the organ or fluid/gas
what happens when the transducer receives a pulse
- crystal changes shape to the US wave
- an electrical current returns to the machine
- image produced by the returning sound waves
- produces the piezoelectric effect in reverse
what is anechoic
without internal echoes
- echo free/poor
- echolucent
what is echogenic
produces echoes
- echo rich
-hyperechoic
what is hyper echoic
increased echoes compared to surrounding tissues
- echo dense
what is isoechoic
same echogeneity as surrounding tissues
what is hypo echoic
decreased echoes compared to surrounding tissues
what is the scanning planes
-respect to the patient as well as the organ imaged
