Test 2: lecture 9 Flashcards
benefit of ultrasound vs xray
can see slices (parts of the organ)
can see blood flow- real time
what is ultrasound
high frequency sound that is produced in cycles and creates waves
2-20 MHz (very high range)
different substances will have a different speed of ultrasound
Each propagation medium has specific characteristics in terms of its ability to ____
transmit ultrasound
speed through different materials is different
how is ultrasound produced?
piezoelectric effect
transduction from mechanical energy to electrical
pressure waves → electrical (+/-)
electric hits crystal causes release of pulse → goes into patient and is bounced back this hits crystal → electrical and is interpreted
the higher the frequency the ____ the pulse
shorter
a 3 cycle long pulse is shorter at 7 MHz than at 3 MHz
Any medium in which ultrasound can be propagated
is characterized by a quantity called ____
ACOUSTIC IMPEDANCE. → Z
4 things that can happen to an ultrasound wave
Perpendicular specular reflection
Non perpendicular specular reflection and
refraction
Scattering
Absorption (transformation in heat)
perpendicular specular reflection
beam hits a new Z at a 90 degree (acoustic impedance→ new tissue with different ability to bounce back)
small amount of beam is bounced back as the reflected echo
rest of beam continues through new substance as transmitted ultrasound
the bigger the difference between the 1st and 2nd substance the bigger the reflected echo
___ helps seeing the border of an organ
perpendicular specular reflection → image of interfaces
____ does not contribute to image formation
non perpendicular specular reflection and refraction
non perpendicular specular reflection and refraction
hits interface between two different Z at an angle → reflected echo bounced back at an angle away from probe → lost in space and does not contribute to image formation
when ultrasound hits a rough interface what happens
scattering
two ways to have scattering of the ultrasound
beam hits rough interface
beam hits internal structure (small part of the parenchyma)
if you increase the ultrasound frequency what happens to the depth of tissue you can see
increased frequency → decrease in depth
The distance D between the transducer and the location where the echo originates from is calculated based on the____using the mean velocity of US in soft tissue: 1540 m/sec
TIME OF FLIGHT (T)
D= (c x T)/2
B mode
brillance (2D)
gives 2D picture of that is absorbing or bouncing back
each image is the result of the juxtaposition of many contiguous lines and represents a cross section of the patient
M mode
single line of ultrasound
used to study motion
____ ability of the system to display separately scatterers that are close to each other
resolution
decrease in space between two = increased resolution
ability to tell the different between two points
axial resolution
the ability to recognize two different objects at slightly different depths from the transducer along the axis of the ultrasound beam
axial resolution= spatial pulse length (SPL)/2
increase SPL= decreased frequency = worse resolution but better depth
decreased SPL= increased frequency= better resolution but decreased depth
SPL and resolution
increase SPL= decreased frequency = worse resolution but better depth
decreased SPL= increased frequency= better resolution but decreased depth
____ the ability to distinguish objects that are side by side
lateral resolution
at focal distance what happens to lateral resolution
focal distance is where the beam becomes smaller (focuses in)
focal distance = increased lateral resolution (can tell the difference between side by side object)
doppler effect
the frequency of the echo will be different when you hit a moving structure
bounce back will be (original frequency + delta shift in frequency)
spectral doppler
artery → see flow
color coded doppler
see flow in an area → away or toward transducer → change in color
red= + = toward transducer
