-
reciprocal
relationship btwn 2 numbers mutiplies together to equal one
-
pascal
unit of measurement for pressure
-
sound
is mechanical and longitudinal wave
-
y- axis
on a graph the vertical axis
-
x-axis
on a graph the horizontal axis
-
in-phase
if the rarefactions of 2 waves occur at the same time
-
destructive interferance
where the resultant wave is smaller then the one of its components
-
kg/cm cubed
proper unit to describe density
-
waves with different frequencies
type of wave will exhibit both constuctive and distructive interference
-
energys
what wave transfer from one location to another
-
all types of sound
mechanical energy transmitted by pressure waves in a medium
-
vaccum
sound waves can not travel through
-
they cause vibrations in the medium
properties common to all sound sources
-
medium
speed of sound depends on
-
commpressions
in sound wave, regions where the pressure is higher than normal
-
longitudinal wave
thype of sound wave that can propagate through soft tissue ( ultrasound waves)
-
wavelength
- dertemined by medium
- distance a wave travels one period of oscillation of the source
-
halves
frequency doubles, wavelength
-
Snell's Law
predicts the direction of the transmitted beam
-
-
period
- p=1/freq
- time it takes to complete a single cycle
-
frequency
- f= 1/period
- number of times the wave is repeated per second
- number of cycles per unit of time
- determined by source
-
amplitude
peak pressure or height of wave
-
when sound is traveling through same medium if frequency increases
- wavelength= decreases
- propagation= stays the same
- period= decreases
- amplitude= stays the sam
-
pulse duration
- pd=cycle# x period
- pd=cycle#/freq
- is the time that the pulse is acually on
-
duty factor (cycle) for continous wave ultrasound is
100%
-
spatial pulse length
space from start of pulse to the end of that pulse
-
typical freq range in medial ultrasound imaging
1 to 32 MHz
-
-
can sonographer adjust intensity of the US beam?
YES
-
speed of sound determined by
medium
-
can pulse duration be changed?
NO
-
when depth is adjusted, what parametes are affected
- PRP (
- PRF (pulse repetition frequency)
- Duty Factor
-
if image depth increases
PRF decreases
-
-
aspect of intensity refers to only the transmitted time
pulsed
-
sound intensity
directly proportional to transducer frequency
-
7 parameters
- period
- frequency
- amplitude
- power
- intensity
- wavelength
- speed
-
acoustic variables
- pressure (pa)
- intensity (kg/cm3)
- distance (unit: cm,ft,mile)
-
propagation speed
determined by density and stiffness
-
if density increases
speed of sound decreases
-
intensity doubled
amplitude quadrupled
-
power
- measured in watts
- rate at which work is done
-
ultrasound frequency
>20KHz
-
transducer
determines the initial amplitude of the sound wave
-
SPTP
the highest intensity
-
attenuation coefficient
the amount of attenuation per depth traveled
-
attenuation
- decreased power, amplitude and intensity
- determined by path length and freq
- measured in dB
-
amplitude and intensity
are directly related
-
spatial pulse length
are denoted by source and medium
-
can intensity be adjusted by sonographer
YES
-
rayleigh scatterer
a red blood cell
-
acoustic insulator
thickness is 1/4 wavelength
-
-
-
backing material
improves resolution by reducing ringing
-
order of impedance from large to small
-
low Q factor improved axial resolution and backing material
imaging transducer
-
characteristies of increased freq pulse wave transducer
- thinner PZT crystal
- faster speed in crystal
-
-
-
transducer diameter affect beam divergance
after focus, small diameter crystals diverge wider
-
how does frequency alter beam divergance in far field
decreased freq diverge more
-
-
-
-
-
actual speed in PZT crystal
influences freq
-
-
TGC & over all gain
brightening screen
-
ALARA
as low as reasonably achievable
-
demodualization
- use retofication to convert neg voltage to pos voltage
- uses smoothing to smooth out the bumps
-
reject
low level echos don't get into machine
-
-
28 shades of gray= ? bits
- 2x2x2x2=16 not enough need 28
- 2x2x2x2x2=32 enough
- then we count the 2's
- so 5 bits
-
binary numbers
1's and 0's
-
types of archieving and storage
- optical media (lazer, CD)
- magnetic media (floppy disk)
-
preprocessing vs postprocessing
- pre= manipulate TGC, zoom in without loss of resolution
- post= zoom in but looses detail
-
how do you find depth
time- round trip
-
transducer
detector of soundwaves by recieving the sound waves from the body
-
what sound parameter influences axial resolution?
pulse duration
-
2 parameters that influences speed of sound in medium
stifness and density
-
how to depolorize a PZT transducer
- curray point
- heat up to 365
-
-
-
what's focal depth affected by?
- transducer diameter
- freq of sound
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