Lecture 1 Flashcards
what is the doppler shift?
the frequency of a reflected wave is different than the transmitted beam
what is the doppler shift
the difference between the incident frequency and the reflected frequency
RBCs moving towards the transducer are?
compressed= higher frequency
RBCs moving away are
expanded=lower frequency
positive doppler shift
towards transducer
above baseline
negative doppler shift
away from transducer
below baseline
is doppler shift in the audible range?
yes!
what is the doppler shift dependent on?
direction of movement
speed at which the target is moving
angle of incidence
angle formed by the axis of the incident sound beam and the incident flow
incident frequency
emitted from the doppler transducer
reflected frequency
returning to the doppler transducer
what kind of info is derived from doppler investigation?
- direction of blood flow
- velocity
- range of velocities
- type of flow
PW doppler
listens at one gate
has great range resolution
precise locations
CW doppler
listening along entire beam
wide range of velocities
separate crystals send and receive
info obtained by spectral analysis
type of flow
PS velocity
ED velocity
range of velocities
spectral window
direction of flow
describe laminar flow
orderly flow, most RBC are the same velocities
describe turbulent flow
can be change of flow direction due to stenosis or tortuosity
what happens to the doppler shift when you increase the angle
decreases
when is maximum flow detected?
when the flow is moving directly toward or away the transducer
lateral resolution is determined by what?
the beam width
daxial dimension is determined by what?
the pulse length
PRF is limited by what?
depth
what is the nyqusit limit?
it is ½ PRF and if exceeded aliasing occurs
aliasing is caused by?
long travel time
high velocity
aliasing
an incorrect estimation of the frequency of a signal due to insufficient sampling of the signal
how can you correct aliasing
- increase PRF
- lower baseline
- decrease probe frequency
- increase angle
- decrease depth
doppler effect
doppler formula
Angle of Incidence:
Angle formed by the axis of the incident sound beam and the incident flow.