The principle of ultrasound

Question 1

87. In what planes can we investigate using ultrasound?

Answer 1

– Any plane

While in other modalities, we usually make pictures in given planes and projections, in ultrasound, we can take sections in various planes and in various body positions. The ultrasound picture changes not only with the place we put the probe on, but also by the inclination of the probe towards the body surface. This is why the best way to learn about ultrasound is by physically doing the examination and seeing the images for yourself.

Question 2

88. Ultrasound –

Answer 2

is a dynamic examination

Question 3

89. Ultrasound has -

Answer 3

a higher frequency than audible sound

What are the physical principles behind ultrasound imaging? Well, the thing we hear is sound. Ultrasound is physically the same thing, but it has a different – much higher – frequency usually between 2 and 15 MHz.

Question 4

90. Choose the correct statement about piezoelectric effect

Answer 4

• the voltage causes volume changes in the crytal resulting in the emission of ultrasonic waves

Question 5

91. What is the name of the physical phenomenon that generates an ultrasonic signal in the probe?

Answer 5

Piezoelectric effect

The main physical principle is called the piezoelectric effect. For this, we need a piezoelectric crystal – this crystal can increase in volume when exposed to an electric current – this change in volume is accompanied by emitting of a sound. This crystal can also do the same thing but in the opposite direction – that is – if the crystal receives an ultrasound wave, it changes volume and this can generate an electrical current. The probes work like this – first, the crystal emits the ultrasound wave and then it waits for the waves to get back from the tissues – this creates the image.

Question 6

92. What is the physical phenomenon that records the ultrasonic signal in the probe?

Answer 6

piezoelectric effect

Question 7

93. In which of these tissues does ultrasound spread the fastest? -

Answer 7

Bones

The ultrasound waves travels through tissues with different speeds depending on the density of the tissue (E.g. – in bone it travels faster than muscle tissue)

Question 8

94. The reflection of ultrasound happens

Answer 8

• in places with different acoustic impedance

The waves can reflect from the tissue, scatter, bend or be absorbed. Reflection is the most important feature – and if you think about it, reflection of sound is usually called an echo.

An important factor that determines the effect in tissues is called acoustic impedance – this shows us the resistance of the tissue towards the sound waves. You can determine this by the product of tissue density and sound velocity in given tissue. The greatest acoustic impedance is therefore in the bones. The most important effect in the tissues is reflection – since we need the sound waves to come back to the probe, and this reflection happens most often in places where the acoustic impedance changes rapidly.

Question 9

95. The acoustic impedance (Z) is -

Answer 9

the product of the density of an environment multiplied by the velocity of the ultrasound propagation in a given environment

Question 10

96. In ultrasound we use the so-called B-mode. The letter B means -

Answer 10

Brightness

The image we form is black and white, which we refer to as B mode (B stands for brightness). Reflection and scatter are the most improtant effects for making this image. As we mentioned on the previous slide, the reflection or echo happens in the places where the acoustic impedance changes rapidly. The greatest changes in the body are between soft tissues and bone or soft tissue and gas.

Question 11

97. The greatest reflection of the ultrasound signal arises between

Answer 11

– soft tissue and bone; soft tissues and air

Question 12

98. If the US signal is fully reflected, a hyperechogenic line is formed and behind it a phenomenon that we call -

Answer 12

Acoustic shadow

When the ultrasound hits an area with great acoustic impedance difference nearly all of the waves rebound from the surface or are decelerated greatly as in the case of air, thus there is an acoustic shadow under this area.

Question 13

99. Acoustic shadow occurs -

Answer 13

if all of the ultrasound signal is reflected (most of the time behind air, bone or calcification)

Question 14

100. White ultrasound structures are called -

Answer 14

hyperechogenic

In ultrasound we use term „echogenicity“. Structures that can reflect a lot of US waves are whiter than the surrounding tissues and therefore are called hyperechogenic. The more homogenous a tissue is the less US waves get reflected, so these structures became darker and are called hypoechogenic. The term isoechogenic is used to describe structures that have similar echogenicity to their surroundings.

Question 15

101. Darker (not entirely black) ultrasound structures are called -

Answer 15

hypoechogenic

In ultrasound we use term „echogenicity“. Structures that can reflect a lot of US waves are whiter than the surrounding tissues and therefore are called hyperechogenic. The more homogenous a tissue is the less US waves get reflected, so these structures became darker and are called hypoechogenic. The term isoechogenic is used to describe structures that have similar echogenicity to their surroundings.

Question 16

102. Fully black ultrasound structures are called -

Answer 16

anechogenic

Structures that do not reflect ultrasound waves appear anechogenic, and they apear as black. The signal from the tissues under such a structure is whiter than all the same tissues in the same depth – this is called acoustic enhancement and it is specific for fluid deposits within a structure.

Question 17

103. An isoechogenic structure

Answer 17

• has almost the same echogenicity as its surroundings

Question 18

104. Which of these structures is the most hyperechogenic? –

Answer 18

bone

Question 19

105. Which of these structures is the least echogenic? -

Answer 19

fluid

Question 20

106. Which structure is physiologically anechoic? –

Answer 20

Gall bladder and urinary bladder

Question 21

107. Foreign bodies on ultrasound are most often -

Answer 21

hyperechogenic

Question 22

108. Using doppler ultrasound examination -

Answer 22

we can measure blood flow in blood vessels

We use this principle in ultrasound to visualize blood flow in vessels. If the blood flows toward the probe, the frequency of ultrasound increases. The difference between emitted and accepted frequency is called the Doppler frequency shift. This shift is described as 2x emitted frequency multiplied by cosine of the angle of the probe, divided by ultrasound velocity in given tissue (2f x cos(angle of probe) / velocity of US). This difference in frequencies can be recognized by the USG machine and visualized as colors.

Question 23

109. What is the Doppler principle? -

Answer 23

If a source of constant pitch (i.e. constant frequency) is moving towards an observer, he perceives this sound as a higher frequency (increasing pitch)

Question 24

110. When a constant frequency sound source moves towards a listener, the pitch height -

Answer 24

rises

Question 25

111. When a constant frequency sound source moves from an observer, the pitch -

Answer 25

decreases

Question 26

112. The frequency shift of the Doppler effect on ultrasound is calculated by –

Answer 26

(2 x frequency transmitted x cosin of insonation angle) ÷ the propagation velocity of ultrasound in the given environment

Question 27

113. In Doppler ultrasound imaging when we produce the doppler curve, it is called -

Answer 27

Spectral doppler

• Spectral Doppler can show us dependence of blood flow velocity in time, we can see a Doppler curve.
• Color Doppler shows us a map of colors in a certain area, which gives us a rough idea about blood flow.
• Triplex mode is an image of all three combined – that is B-mode, Doppler curve and color Doppler.

Question 28

114. Colours in the colour doppler US imaging –

Answer 28

can be set as required

Question 29

115. The ultrasonic probe is -

Answer 29

both the transmitter and the ultrasonic signal receiver

Question 30

116. The most expensive part of the ultrasound machine is –

Answer 30

the probes

Question 31

117. Convex vs. Linear probes –

Answer 31

Both use the same physical principle.

There are several types of probes according to their shape and frequency.
*Convex probes (the left one in the picture) are ideal for abdominal imaging.
*Linear probes (the middle one) for vessels and soft *tissues.
Sector probe (left one) for echocardiography 

There are lot of special probes for special investigations – bioptic probes (seen below), endosonographic probes etc.

Question 32

118. Which statement is true about ultrasonic probes?

Answer 32

The lower the probe’s frequency, the better the tissue penetration, but the lower the resolution; the higher the frequency, the lower the penetration, but the better resolution.

The frequency of the probe determines how deep we can see with the probe, or where the best resolution of the picture is. The lower the fruequency is, the better the penetration is, but the resolution is worse. Higher frequencies have good resolution, but the penetration is bad, so we can use them for surface imaging. In pratice – linear probes have higher frequencies and they are great for surface imaging, but we cant see anything in deeper areas. For deeper areas convex probes are better but the resolution decreases with the distance from the probe

Question 33

119. A linear probe has higher frequencies, indicating that

Answer 33

• it has excellent resolution but only a few centimeters from the probe

Question 34

120. A convex probe has a lower frequency, indicating that

Answer 34

• it has good penetration and displays deeper structures

Question 35

121. With the distance from the probe -

Answer 35

the image resolution decreases

Question 36

122. Ultrasonic gel –

Answer 36

is used to eliminate air between the probe and the skin of the patient

Question 37

123. Preparation for ultrasound examination of the abdomen includes –

Answer 37

Fasting prior to examination

Question 38

124. Which of the following features in a patient limits ultrasound imaging? –

Answer 38

Obesity and bowel pneumatology