Ultrasounds

Question 1

What is ultrasound?

Answer 1

subtype of soundwave transmitted through air or soft tissues of patient - uses echolocation.

Question 2

Why can’t we hear ultrasound?

Answer 2

frequency is above 20,000 Hz so it cannot be heard by the human ear

Question 3

What is an echo?

Answer 3

sound that was reflected by a structure

Question 4

What is the piezo electric effect?

Answer 4

the energy transfer that converts electric energy into mechanical energy - involves crystals and the production of soundwaves

Question 5

What is transduction?

Answer 5

crystals become pressurized and this causes an energy change, which sends out a sound wave

Question 6

What happens to the ultrasound pulse when the ultrasound frequency increases?

Answer 6

the higher the frequency, the shorter the pulse

Question 7

Does ultrasound travel through different tissues at the same speed?

Answer 7

no

Question 8

Does an ultrasound machine assume that ultrasound travels through all tissues at the same speed?

Answer 8

yes, it assumes 1540m/sec for soft tissue

Question 9

What is the “time of flight?”

Answer 9

the time it takes for a signal to get from reflecting structure to receiver

Question 10

What is specular reflection?

Answer 10

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

Question 11

What is ultrasound scattering?

Answer 11

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

Question 12

What is ultrasound refraction?

Answer 12

change of direction by the beam due to an oblique angle that causes it to not return to the transducer

Question 13

Does non-perpendicular reflection contribute to image formation?

Answer 13

no - it is a loss of signal

Question 14

What contributes to the formation of the image of parenchyma?

Answer 14

multi-directional reflection caused by tiny objects that cause scattering

Question 15

What contributes to the formation of the image of organ contours?

Answer 15

interface echoes due to specular reflection

Question 16

When the difference in acoustic impedance between two tissues increases, what happens to the amount of reflection at the interface between these two tissues?

Answer 16

the proportion of ultrasound reflected is directly proportional to the difference in acousticimpedance(resistance), so reflection will increase

Question 17

What is mostly responsible for attenuation of the ultrasound beam as it travels through tissues?

Answer 17

absorption is the dominant factor

Question 18

When ultrasound frequency increases, what happens to attenuation?

Answer 18

the higher the frequency, the higher the attenuation

Question 19

What is B mode ultrasonography?

Answer 19

“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

Question 20

What is M mode ultrasonography? What is its main area of application?

Answer 20

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

Question 21

What is axial resolution?

Answer 21

resolution in the direction of the ultrasound beam
- discerning objects on top of eachother

Question 22

What happens to axial resolution when ultrasound frequency increases?

Answer 22

higher the frequency, higher the attenuation, so better axial resolution is achieved
- trade off: limited depth of exploration

Question 23

What is lateral resolution?

Answer 23

direction perpendicular to the ultrasound beam
- depends on width of beam
- discerning objects next to eachother

Question 24

Where is the lateral resolution the best along the path of the ultrasound beam?

Answer 24

the best resolution is where the ultrasound beam is the narrowest (focal distance)

Question 25

What is the focal zone?

Answer 25

distance where the beam is the narrowest

Question 26

What is the Doppler effect?

Answer 26

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)

Question 27

What is Doppler ultrasonography used for?

Answer 27

hemodynamics

Question 28

What are the two principal types of Doppler display?

Answer 28

1. Spectral doppler - analysis of flow is performed along a specific line of B-mode image 2. Color-coded doppler - area of B-mode image is defined, and area is divided in multiple lines

Question 29

What effect does frequency have on depth of exploration?

Answer 29

as frequency increases, depth of exploration decreases

Question 30

What is the difference between a rectilinear, a curvilinear, and an annular-array transducer?

Answer 30

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

Question 31

What is the shape of the image produced by rectilinear, a curvilinear, and an annular-array transducer?

Answer 31

Rectilinear - rectangular Curvilinear - cone Annular array - cone

Question 32

Which of these three transducers is best suited to tendon ultrasonography?

Answer 32

Rectilinear array transducer

Question 33

Which transducer is the one most used for abdominal ultrasonography?

Answer 33

Curvilinear array transducer

Question 34

Which transducer is the one most used for echocardiography?

Answer 34

Annular array transducer

Question 35

What is the general gain?

Answer 35

regulates echo amplitude from all depths equally - changes brightness of ultrasound image

Question 36

What is the TGC?

Answer 36

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

Question 37

What does TGC correct for?

Answer 37

increases amplification of echoes with increasing depth

Question 38

What setting is used to make homogeneous organs like the liver look homogeneously bright on ultrasound?

Answer 38

TGC

Question 39

The spleen is hyperechoic to the renal cortex in normal dogs: what does that mean?

Answer 39

brighter

Question 40

Urine is anechoic in normal dogs: what does that mean?

Answer 40

echo-free, black

Question 41

What artifact can be associated with gas in intestinal loops?

Answer 41

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

Question 42

What artifact can small gas bubbles create?

Answer 42

comet tail artifact - type of reverberation artifact

Question 43

What artifact can a bladder stone create?

Answer 43

acoustic shadowing - echoes coming back to transducer are weak due to absorption of incident beam, so they are not strong enough to generate reverberations

Question 44

What TWO artifacts can a normal gallbladder be associated with?

Answer 44

1. 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 2. distal enhancement - when a fluid filled structure is encountered by beam