Ultrasounds Flashcards
What is ultrasound?
subtype of soundwave transmitted through air or soft tissues of patient - uses echolocation.
Why can’t we hear ultrasound?
frequency is above 20,000 Hz so it cannot be heard by the human ear
What is an echo?
sound that was reflected by a structure
What is the piezo electric effect?
the energy transfer that converts electric energy into mechanical energy - involves crystals and the production of soundwaves
What is transduction?
crystals become pressurized and this causes an energy change, which sends out a sound wave
What happens to the ultrasound pulse when the ultrasound frequency increases?
the higher the frequency, the shorter the pulse
Does ultrasound travel through different tissues at the same speed?
no
Does an ultrasound machine assume that ultrasound travels through all tissues at the same speed?
yes, it assumes 1540m/sec for soft tissue
What is the “time of flight?”
the time it takes for a signal to get from reflecting structure to receiver
What is specular reflection?
when the beam arrives at an interface which is smooth and or large dimension compared to ultrasound wavelength - part of beam is reflected, part is transmitted
What is ultrasound scattering?
multi-directional reflection that is produced either at an irregular interface between tissues or within a given tissue
- results from interaction between ultrasound and tiny reflecting objects that are comparable in size to or smaller than the ultrasound wavelength
What is ultrasound refraction?
change of direction by the beam due to an oblique angle that causes it to not return to the transducer
Does non-perpendicular reflection contribute to image formation?
no - it is a loss of signal
What contributes to the formation of the image of parenchyma?
multi-directional reflection caused by tiny objects that cause scattering
What contributes to the formation of the image of organ contours?
interface echoes due to specular reflection
When the difference in acoustic impedance between two tissues increases, what happens to the amount of reflection at the interface between these two tissues?
the proportion of ultrasound reflected is directly proportional to the difference in acousticimpedance(resistance), so reflection will increase
What is mostly responsible for attenuation of the ultrasound beam as it travels through tissues?
absorption is the dominant factor
When ultrasound frequency increases, what happens to attenuation?
the higher the frequency, the higher the attenuation
What is B mode ultrasonography?
“brilliance” - most common type of display in diagnostic ultrasound, it is two dimensional
Represents a slice of a patient using a grey-scale display. It is called a tomographic technique
What is M mode ultrasonography? What is its main area of application?
a single ultrasound line is studied continuously - continuous display of the variation in position and reflectivity of the structures along the line, as a function of time
main area of application: cardiology
What is axial resolution?
resolution in the direction of the ultrasound beam
- discerning objects on top of eachother
What happens to axial resolution when ultrasound frequency increases?
higher the frequency, higher the attenuation, so better axial resolution is achieved
- trade off: limited depth of exploration
What is lateral resolution?
direction perpendicular to the ultrasound beam
- depends on width of beam
- discerning objects next to eachother
Where is the lateral resolution the best along the path of the ultrasound beam?
the best resolution is where the ultrasound beam is the narrowest (focal distance)
What is the focal zone?
distance where the beam is the narrowest
What is the Doppler effect?
increase (or decrease) in frequency as sources move towards (or away from) each other
- if not moving, frequencies are equivalent
- sources are moving, so frequency plus delta F
Positive - moving towards transducer (red)
Negative - moving away from transducer (blue)
What is Doppler ultrasonography used for?
hemodynamics
What are the two principal types of Doppler display?
- Spectral doppler - analysis of flow is performed along a specific line of B-mode image
- Color-coded doppler - area of B-mode image is defined, and area is divided in multiple lines
What effect does frequency have on depth of exploration?
as frequency increases, depth of exploration decreases
What is the difference between a rectilinear, a curvilinear, and an annular-array transducer?
Rectilinear - a type of linear array transducer that consists of crystals aligned in a rectilinear fashion
Curvilinear - a type of linear array transducer that consists of crystals aligned in a curvilinear fashion
Annular array - consist of several crystals arranged in concentric circles
What is the shape of the image produced by rectilinear, a curvilinear, and an annular-array transducer?
Rectilinear - rectangular
Curvilinear - cone
Annular array - cone
Which of these three transducers is best suited to tendon ultrasonography?
Rectilinear array transducer
Which transducer is the one most used for abdominal ultrasonography?
Curvilinear array transducer
Which transducer is the one most used for echocardiography?
Annular array transducer
What is the general gain?
regulates echo amplitude from all depths equally
- changes brightness of ultrasound image
What is the TGC?
allows to amplify echoes depending on depth of reflector - provides an increasing amplification of the echoes with increasing depth to create a grey scale appearance through the image
What does TGC correct for?
increases amplification of echoes with increasing depth
What setting is used to make homogeneous organs like the liver look homogeneously bright on ultrasound?
TGC
The spleen is hyperechoic to the renal cortex in normal dogs: what does that mean?
brighter
Urine is anechoic in normal dogs: what does that mean?
echo-free, black
What artifact can be associated with gas in intestinal loops?
reverberation - 2 parallel echogenic interfaces are located on the path of a beam, and some of the waves are trapped and bouncing back and forth by the interfaces
What artifact can small gas bubbles create?
comet tail artifact - type of reverberation artifact
What artifact can a bladder stone create?
acoustic shadowing - echoes coming back to transducer are weak due to absorption of incident beam, so they are not strong enough to generate reverberations
What TWO artifacts can a normal gallbladder be associated with?
- edge shadowing - when beam reaches a border that separates two media, and a region deep to this does not receive any ultrasound, producing a shadow
- distal enhancement - when a fluid filled structure is encountered by beam
