LECTURE 1: X-RAY IMAGING SYSTEMS 1

Question 1

Are imaging systems serial or parallel type?

Answer 1

Serial - if one part is not working, the rest of the machine won’t work

Question 2

Can x-rays be deflected by electric or magnetic field?

Answer 2

NO! because they carry no charge (remember x-rays are photons)

Question 3

What does “heterogenous” mean (energy of x-rays)

Answer 3

Means that x-rays can have a whole range of energy

Question 4

What voltages are x-rays operated at?

Answer 4

25-150kVp - Think of what you do in labs!

Question 5

What currents are x-rays operated at? (mA)

Answer 5

100-1200 mA [Note that it is not mAs]

Question 6

Where is the High-Voltage Generator located and why?

Answer 6

Always close/inside the examination room - so voltage has less travelling distance, so less resistance

Question 7

What does mAs and kVp control?

Answer 7

mAs is the number of x-rays, kVp controls their penetrability

Question 8

AEC uses an ionisation chamber; T or F

Answer 8

T

Question 9

What does APR stand for? What is it?

Answer 9

Anatomically Programmed Radiography - buttons with already set kVp and mAs for certain projections

Question 10

What are the 3 main components of an x-ray system?

Answer 10

X-ray tube, operating console, high voltage generator

Question 11

How many transformers do you often have in an x-ray tube?

Answer 11

3: autotransformer, step-up and step-down

Question 12

What is an autotransformer?

Answer 12

Calculates how much step up or step down is needed

Question 13

What is “V.eff”?

Answer 13

the voltage that would produce an effective current so that a DC current of the same magnitude would generate heat in a resistor at the same rate as the AC current

Question 14

What is a “line voltage”?

Answer 14

the voltage supplied to the x-ray imaging room by the power company

Question 15

Most imaging systems are designed to operate at what voltage?

Answer 15

220V

Question 16

What is a Line Compensator?

Answer 16

It is a type of autotransformer! steps up or down the voltage supplied by the LINE - electricity from company

Question 17

Why is a Line Compensator needed?

Answer 17

To compensate for the fluctuation of the VOLTAGE supplied by the LINE

Question 18

What is a voltmeter, what does it do and where is it located?

Answer 18

Measures voltage - located BEFORE the autotransformer (line compensator). Tells us if there are enough windings on the primary coil

Question 19

How does an autotransformer work?

Answer 19

It has a core, with windings around it, then has tabs at different windings where you can choose how many coils you want - step up or step down

Question 20

The increase in voltage is directly related to the number of turns in the autotransformer- True or False?

Answer 20

True

Question 21

What is the Autotransformer Law?

Answer 21

Vs/Vp = Ns/Np
V = voltage
N = windings

Question 22

What is the difference between major and minor kVp selector?

Answer 22

Major and minor kVp selector: Taps on the autotransformer select major kV changes in increments of ten, or minor increments of one kV.

Question 23

Does filament current have high or low voltage?

Answer 23

LOW voltage, HIGH current

Question 24

The number of exposure is determined by the temperature of the filament. Why?

Answer 24

The hotter the filament, the more e- are ready (bullets) to be fired

Question 25

What is “current”?

Answer 25

The number of e- passing per unit time

Question 26

At what current do filaments operate at?

Answer 26

3-6 AMPERES

Question 27

Where are exposure timers/timer circuit located in an x-ray circuit?

Answer 27

On the primary side

Question 28

What does a timer circuit do?

Answer 28

They “make” or “break” the high voltage across the x-ray tube

Question 29

Where is the mAs timer located - what does it do?

Answer 29

On the secondary side of the high voltage transformer - since actual TUBE current must be monitored

Question 30

What are the two types of AEC?

Answer 30

Ionisation chamber and photodiode/photomultiplier

Question 31

AEC - what is it set at?

Answer 31

1.5 times the expected exposure time

Question 32

Difference between AEC (Photodiode+chamber) - Location?

Answer 32

Chamber = patient and IR
Photo = behind IR

Question 33

Difference between AEC (Photodiode+chamber) - Detection

Answer 33

Chamber = ionisation in the chamber creates a charge and this is measured
Photodiode = turns photons into light and this is detected