Ultrasound 2017

Question 1

What type of wave is a sound wave?

Answer 1

Mechanical wave, longitudinal

Question 2

Write down the wave equation (which relates speed c, wavelength λ, and frequency f)

Answer 2

C=fλ

Question 3

Calculate the wavelength for US at 1540m/s at 1, 5, 10 and 20 MHz

Answer 3

1540/1000000 x 1000=1.54mm, 1540/5000 000 x 1000=0.308mm, 1540/10000000 x 1000=0.154mm, 1540/20000000 x 1000 =0.077mm

Question 4

Explain the terms compression and rarefaction

Answer 4

A region where the coils are spread apart, thus maximizing the distance between coils, is known as a rarefaction or a point on a medium through which a longitudinal wave is traveling which has the minimum density

Question 5

What tissue property affects impedance?

Answer 5

Resistance

Question 6

Why is the matching gel used in Ultrasound?

Answer 6

Reduce the acoustic impendance at air/skin interface to reduce reflection of sound beam and allow it to be transmitted into the body

Question 7

Give two examples of a tissue impedance mismatch which would result in a high amount of reflection.

Answer 7

Air/soft tissue and bone/soft tissue

Question 8

How does a US beam scatter when it encounters an interface about one wavelength in size?

Answer 8

Random scattering in all directions with all different energy amounts – Non-specular reflection

Question 9

What is the role of the matching layer on an US probe?

Answer 9

Matching layer minimises the energy lost due to an impedance mismatch between the transducer and the gel ; The impedance of the matching layer is chosen to be the geometric mean of the transducer impedance and the matching gel impedance.

Question 10

What effect does a backing layer have in an US probe?

Answer 10

Backing layer minimises the energy reflected off the back of the transducer ; made from a material with an acoustic impedance close or equal to the transducer impedance

Question 11

Sketch two pulses, one which will have good axial resolution and one which will have poor axial resolution and note the bandwidth of each

Answer 11

Short pulse, wide bandwidth, lower velocity/depth, increased axial resolution;
Long pulse, narrow bandwidth, higher velocity/depth, decreased axial resolution

Question 12

1. a) Sketch the beam shape for each transducer face

b) Indicate where the focal region is for the curved face transducer
2. What is the importance of beam width to image resolution?

and (

Answer 12

Beam width directly impacts lateral resolution – wider the beam the poorer the resolution

Question 13

What is the role of the matching layer on an US probe?

Answer 13

Matching layer minimises the energy lost due to an impedance mismatch between the transducer and the gel ; The impedance of the matching layer is chosen to be the geometric mean of the transducer impedance and the matching gel impedance.

Question 14

What effect does a backing layer have in an US probe?

Answer 14

Backing layer minimises the energy reflected off the back of the transducer ; made from a material with an acoustic impedance close or equal to the transducer impedance

Question 15

Sketch two pulses, one which will have good axial resolution and one which will have poor axial resolution and note the bandwidth of each

Answer 15

Short pulse, wide bandwidth, lower velocity/depth, increased axial resolution;
Long pulse, narrow bandwidth, higher velocity/depth, decreased axial resolution

Question 16

Describe

Detection

Answer 16

This received echo is collected by the transducer and converted into a small electrical signal

Question 17

Describe

Pre-amplification

Answer 17

This signal produced by the transducer is very small, and to prepare it for further analysis the signal is amplified

Question 18

Describe

Time Gain Compensation

Answer 18

TGC - Because the body is non-homogenous, the energy lost travelling though one part may not be the same as the energy lost travelling through another
This means the compensation required for collecting data in one area of the body may not be the same as is required for collecting a set of data
from a different area or patient

Question 19

Describe

Compression

Answer 19

This compression rate, that is the extent to which the small signals and large signals are made to look close together, is an operator specified
parameter

Question 20

Describe

Rectification and Envelope Detection

Answer 20

Rectification and Envelope Detection - To present the data so that we have a clear “spike” from each reflecting surface we take the signal which is below
zero and make it positive, Then we draw an envelope around the outside of the signal

Question 21

Describe

Rejection

Answer 21

Some signals are so small they are likely to be due to noise, These small signals are discarded or rejected

Question 22

Describe

Processed signal

Answer 22

• This data resulting from this analysis is then interpreted in terms of physiology and anatomy

Question 23

Briefly describe the phenomenon of aliasing

Answer 23

Sampling rate too low means inadequate representation of initial information

Question 24

What effect does it have on US data?

Answer 24

Means we can’t accurately represent velocities in a given sample

Question 25

How can an US machine be adjusted compensate for aliasing?

Answer 25

Increase PRF, shift baseline, reduce angle of incidence

Question 26

Why is aliasing not a problem in CW US?

Answer 26

No time waiting for echoes to return as 1 element of transducer solely for pulses and 1 solely for echoes and this happens continuously so sampling rate is as high as possible

Question 27

At what stage could you see this type of endometrium?

Answer 27

Basal layer endo at menstruation

Question 28

uterus anteverted or retroverted? How can you tell the difference?

Answer 28

fundus is at left of screen, if retroverted, fundus would be at right.
Also scan in trans – scanning superiorly should be fundus and inf should be cervix