Basic principles

Question 1

Amplitude

Answer 1

Refers to the maximum variation of particle displacement, particle density or acoustic pressure of a sound wave.

The units of measure are dependant on Pascals, the units for displacement (or distance) are expressed as mm, cm, or m and the unit for density is expressed as g/cm3

Question 2

Wave length

Answer 2

Refers to the distance occupied by one complete cycle

when the amplitude is plotted against distance, that is, wavelength is the distance between two compression zones or between two rarefraction zones

Wvelength is expressed in units of distance such as m, cm, mm

Question 3

Frame rate

Answer 3

Number of frames per second

Question 4

Frequency

Answer 4

Number of cycles passing a given point per second (Hz)

Question 5

Acoustic impedence

Answer 5

Resistance of a medium to transmission of sound waves

Question 6

Attenuation

Answer 6

Reduction in signal strength as it transverses through a medium

Question 7

Temporal resolution

Answer 7

Ability tpo accurately display position of moving structures at a particular instant in time

Question 8

Period

Answer 8

Time taken for one complete wave cycle to occur

Question 9

Propagation speed is determined by

Answer 9

Density of the medium and compressability of that medium

Question 10

What assumption is violated to create a side lobe or grating lobe artifact?What causes side lobe and grating lobe artifact

Answer 10

the
assumption that the ultrasound waves are infinitely thin is
violated

Side and grating lobes are secondary beams around the central ultrasound beam and are produced by nonaxial vibrations of the piezoelectric elements

Side and grating lobe artifacts result in the blurring of the
edges of a displayed object (reduce lateral resolution)

Question 11

Use of high frequencies increases attenuation. Yes or no?

Answer 11

Yes

Question 12

-At shallower depths the frame rate is higher because the signal can return to the transducer faster.
-The least number of scan lines / smaller FOV & Decreasing the depth

Question 13

Write zoom

Answer 13

Increases frame rate (Improves temporal resolution)
Improves spatial resolution and measurement accuracy

Question 14

Are there an increased number of pixels in write zoom or read zoom? Which one improves resolution and what type of resolution does it improve?

Answer 14

Write zoom has an increased number of pixels per unit area
Therefore Write zoom improves spatial resolution

Question 15

What is dynamic range?

Answer 15

The range between the strongest to weakest echoes

Question 16

Colour hue/ brightness colour

Answer 16

Human eye can see more shades of colour and limited shades of grey. Therefore may improve visuals and perception of image

Question 17

What is the reject control

Answer 17

Filter that sets the minimum echo level that will be displayed. Therefore it reduces electronic and acoustic noise. Doewnside is it can also remove low amplitude tissue echo.

Question 18

What are imaging artefacts defined as?

Answer 18

False or misleading information introduced by the ultrasound machine.

Question 19

Artefacts can be catergorised/ caused by

Answer 19

Interaction between the beam and tissue
Faulty or damaged instrumentation
Sonographer related vaiables e.g improper use of equipment

Question 20

What are the five key assumptions that U.S machines use to produce 2D images?

Answer 20

1. There is a constant rate of attenuation
2. All echoes arise from the centre of a razor thin beam
3. The propagation speed in soft tisue is 1540m/s
4. The round trip time of a given echo is directly related to the depth of a reflector from the transducer
5. The U.S beam travels in a straight line and reflects just once

Question 21

Therefore… 2d imaging artefacts can be catergorised based on the violation of these assumptions, these four major catergories include

Answer 21

attenuation artefacts
Beam dimension artefacts
Depth of origin artefacts
Beam path artefacts

Question 22

The u.s machine assumes there is a constant rate of attenuation. What is this rate?

Answer 22

1dB/CM/MHz

Question 23

Acoustic enhancement artefact

Answer 23

Occurs when the beam passes through a structure that has low level of attenuation relative to the adjacent structures. As a result the structures beyond the low attenuating structure will appear brighter

Question 24

Acoustic shadowing occurs due to attenuation. The weakening of the beam occurs when the beam…

Answer 24

-Encounters an interface where high acoustic mismatch exits
- Encounters a structure that has high absorption properties
- Diverges
-Is refracted

Question 25

Name two attenuation artefacts

Answer 25

Acoustic shadowing
Acoustic enhancement

Question 26

Name 3 Beam dimension artefacts

Answer 26

Beamwidth artefact

Question 27

Depth of origin artifacts occur when what assumptions are violated?

Answer 27

propagation speed 1540 m/s ,
round trip time directly related to depth
U.S beam travelling in a straight line

Question 28

Two types of depth of origin artefacts?

Answer 28

-Propagation speed artefacts-speed propagation means calculation is wrong and echo is therefore placed in the wrong area
-Range ambiguity artefacts-second pulse emitted before the first has arrived (high prf). thinks the 2nd echo is the 1st

Question 29

Beam path artifacts occur when what assumptions are violated?

Answer 29

-the beam doesnt travel in a straight line and reflects more than once
-the propagation speed of 1540m/s in tissue is broken

Question 30

common types of beam path artefacts?

Answer 30

-reverberation-acoustic mismatch between two close interfaces, perpendicular to the beam
-refraction -speeds different in different media create bending look
-mirror image-large variance in acoustic impedance

Question 31

Why doesnt aliasing occur with CWD?

Answer 31

Aliasing does not occur with CWD because separate elements on the probe transmit while others simultaneously
“listen.” This eliminates the limitation set by the pulse repetition frequencies (i.e., pulses emitted per second).

Question 32

what imaging is used to record velocities within the myocardium?

Answer 32

Tissue doppler imaging (TDI) / DTI)

Question 33

PW picks up low amplitude and higher velocity, but TDI picks up?

Answer 33

DTI picks up high amplitude and low velocity

Question 34

How to tell the difference between a PW and CW trace

Answer 34

PW has a spectral windowand a spectral width