Basics of Ultrasound Lecture

Question 1

What is sound?

Answer 1

A vibration that produces a compression wave. Mechanical energy produces alternating compression and rarefaction through the conducting medium

Question 2

What is amplitude?

Answer 2

Maximal displacement from equilibrium. In longitudinal waves, this is the max change in pressure between areas of compression. Higher amplitude = louder noise.

Question 3

What is frequency?

Answer 3

Number of cycles per unit time. Standard unit is Hz (Hertz). Audible range for humans is around 20Hz to 20kHz. Ultrasound frequencies are around 20kHz and greater.

Question 4

What are the applications of ultrasound?

Answer 4

Animals use US for echolocation, e.g. bats. It’s used to determine location and distance of an object by the reflected sound waves. Similar principle to sonar.

Question 5

What is diagnostic ultrasound?

Answer 5

Short ultrasound pulses are transmitted into the body, where they are reflected, refracted, scattered or absorbed. Combination of all of these results in attenuation of the intensity of the wave, which limits the depth of US imaging.

Question 6

What are the advantages of diagnostic ultrasound?

Answer 6

Safe mode of imaging
No ionising radiation
Portable equipment
Relatively inexpensive

Question 7

What are the disadvantages of diagnostic ultrasound?

Answer 7

Highly user dependent
Unable to image organs deep to bone
Unsuitable for air filled structures
(Distended) bowel/lungs

Question 8

What is “knobology”?

Answer 8

Understanding the controls on the ultrasound machine.

Question 9

What is the piezoelectric effect?

Answer 9

Generation of electrical charge due to an applied stress. Reverse piezoelectric effect is the change in shape or a piezoelectric material when an electric voltage is applied to it.W

Question 10

What does the piezoelectric effect allow?

Answer 10

Detection of the reflected ultrasound waves

Question 11

What does the reverse piezoelectric effect allow?

Answer 11

The production of ultrasound waves.

Question 12

What are piezoelectric crystals?

Answer 12

Electric current is applied to these which produces the ultrasound wave → propagates through the body.

They are deformed by returning waves, which produces an electric signal → relayed to the US unit.

Question 13

What does a higher amplitude wave mean?

Answer 13

Greater crystal deformation, hence larger current, and larger signals are displayed as brighter pixels.

Question 14

What are transducers?

Answer 14

Probes

Question 15

What are linear-array probes?

Answer 15

High frequency, good image resolution, low depth of imaging, and flat flootprint produces undistorted images.

Question 16

What are curved-array probes?

Answer 16

Low frequency probes, low image resolution, good depth of imagine, slight distortion of images.

Question 17

What are phased array probes?

Answer 17

Low US wave generated from the centre of the footprint. Small probe, but large scanning area. Can scan in small/awkward areas.

Question 18

What are intraluminal probes?

Answer 18

Can be used in various lumens/orifices, and have several advantages. Overcomes poor imaging resulting from overlying structures, and allows use of higher frequency, so high resolution images.

Question 19

What is B-imaging mode?

Answer 19

Produces 2D images, a spike from a returning wave is represented as a pixel, and the brightness is determined by the amplitude of the signal.

Question 20

What are the different shades of gray in US?

Answer 20

Isoechoic, Hyperechoic, Hypoechoic and Anechoic.

Question 21

What is isoechoic?

Answer 21

A shade of gray that is of the same brightness or echogenicity as the surrounding tissues.

Question 22

What is hyperechoic?

Answer 22

A shade of gray that is bright white or brighter than the surrounding tissues. - more bone

Question 23

What is hypoechoic?

Answer 23

A shade of gray that is dark or less bright than the surrounding tissues. - pus or lymph nodes

Question 24

What is anechoic?

Answer 24

An absence of echoes, hence blackness. - fluid: blood, urine

Question 25

What is the doppler effect?

Answer 25

The phenomenon of the altering frequency of an emitted wave depending on the source’s movement relative to the observer.

Question 26

How can doppler ultrasound be used?

Answer 26

Colour doppler - direction and magnitude of blood flow

Power doppler - better visualisation of small vessels but no directional information

Pulsed doppler - Allows a sampling volume positioned in a vessel

Question 27

What is M-imaging mode?

Answer 27

Used to analyse tissue motion, useful in cardiac valve studies.

Question 28

How does 3D imaging work?

Answer 28

Stacks of parallel cross-sectional images are compiled to form a 3D image.

Question 29

What is gain? (Ultrasound: Basic Controls)

Answer 29

Refers to the amplification of returning signals, icnreasing will make images brighter and more saturated.

Question 30

What are presets used for?

Answer 30

They adjust parameters to permit optimal viewing of specific structures.

Question 31

How do you determine correct probe orientation?

Answer 31

Probes have a marker on their side, corresponding to a specific side of the screen.

Question 32

What are the probe manoeuvres?

Answer 32

P = (Vertical) Pressure
A = Alignment (Sliding)
R = Rotation
T = Tilt (along long axis).

Question 33

What is tilting the probe good for?

Answer 33

Rotation about the long axis of the probs allows US waves to be directed to give a true-cross sectional image of deep structures which are not parallel with the skin.

Question 34

What is an ultrasound artefact?

Answer 34

Artefact refers to the distortion of an image due to any number of factors.

Question 35

What is acoustic enhancement? (Ultrasound artefacts?)

Answer 35

Ultrasound passes through certain structures more easily and with minimal absorption; regions lying deep to a fluid filled structure receive greater energy, so the area will appear uniformly brighter.

Question 36

What is anisotropy? (Ultrasound artefacts)

Answer 36

Refers to the changes in echoic appearance depending on the relative orientation of the ultrasound wave, most commonly seen when observing tendons.