Medical Equipment Section4

1. Cairo University
Faculty of Engineering
Systems and Biomedical Engineering Department
Fall Semester, 2017
SBE 405 Medical Instrumentation IV: Ultrasound Imaging–Section 04
Ghaidaa Eldeeb
Chapter 4
 Q1) Compare the effects on a B-mode image of adjusting the overall gain and the
transmit power. How should the operator optimize the settings of each and what risks
should be taken onto account?
Transmit Power Control & Overall Gain
Problems of increasing Amplitude of Transmitted Pulse
1.
2.
When increase Overall Gain = have same effect of Transmit Power, but each one
has its problems
1.
2.
 Q2) A 5 MHz transducer is used to image a region of tissue which attenuates at a
rate of 0.7 dB cm-1 MHz-1 Explain how the scanning system compensates for the
attenuation and how the operator sets the TGC. At what rate in dB µs-1 will the
system increase the gain when the TGC is correctly applied?
Problem:
Solution:

2. For Operator:
Example:
 Q3) Explain what is meant by the dynamic range of echoes received at the
transducer. Why is it necessary to be able to display a wide dynamic range of
echoes?
 Mean: the ratio of the largest echo amplitude to the smallest that can be
distinguished from noise. The dynamic range is expressed in decibels.
 It is necessary to display a wide dynamic range of echoes
Because :
 Q4) Why is it necessary to compress the dynamic range of echoes and how is this
achieved by the scanning system? How does the dynamic range setting affect the
B-mode image and how should the operator choose the optimum value of
compression?
Problem:
How to compress:

3. Effect:
For Operator:
 Example for DR:
A component of ultrasound system can properly process voltages from 1mV to 1V what
is DR?!
 What is Wide DR and narrow DR
 An uncompressed signal has DR 85 dB , signal undergoes 30 dB compression ,
what is DR of compressed signal

4. Doppler Ultrasound
 Q1&Q2 Explain the Doppler effect as used in ultrasound assessment of blood
velocities and What are the two main types of display for Doppler ultrasound data?
Two Types of Doppler:
1- Continuous wave (CW) Doppler
2- Pulsed Wave (PW) Doppler

5. Q3) what is the purpose of the high-pass filter in the Doppler signal-processor?
Q8) To estimate blood velocity what two pieces of information must be measured from the patient?
- This is done automatically by machine
- C = 1540 m/ses & calculate t1 & t2
Problem 1:
Consider Doppler imaging of a vessel at depth d1=5 cm. derive the maximum detectible
velocity if the transmitted signal frequency was 6 MHz and Doppler angle was 45o.
Problem 2 :
Consider Doppler blood flow velocity estimation in a vessel at depth of 5 cm and angle of 60. Find out
whether aliasing will occur when estimating blood velocity if the actual velocity in that vessel is 50
cm/s. Let the transmitted signal frequency be 7 MHz.