X-ray imaging systems

Question 1

What are the components of an x-ray imaging system?

Answer 1

1. x-ray tube
2. operating console
3. high voltage generator - which runs the tube

Question 2

How is the radiation exposure stopped?

Answer 2

1. Exposure time (mAs) in an x-ray tube is stopped by an electronic timer.
2. AEC (automatic exposure control) is a device that measures the quantity of radiation. When the image receptor has recieved the required amount of radiation, the exposure is automatically terminated.

Question 3

With the AEC, where does the radiation termination occur?

Answer 3

At the ion chambers, where the ion pairs are present.

Question 4

Full form of DAP meter

Answer 4

Dose area product

Question 5

SI unit of the dap meter

Answer 5

mGycm^2

Question 6

What does the DAP meter measure?

Answer 6

measures the dose in a plane, i.e. the photons passing through the a field to the patient.

Question 7

How many transformers are present in an xray generation circuit and what are their functions?

Answer 7

3 transformers
The primary transformer is for the mains input voltage and the secondary is the output voltage.
T1 = mains voltage
T2 = carries stepped up voltage
T3 = smaller transformer as it supplies the charge to the tube filament.

Question 8

What is a high voltage generator?

Answer 8

A high voltage generator increases the output voltage from a step up transformer to the required kVp for xray production.

Question 9

What are the components of an xray generator?

Answer 9

High voltage transformer, filament transformer and voltage rectifier.

Question 10

What type of current do transformers use?

Answer 10

AC

Question 11

SI unit of V and I used in primary and secondary coils

Answer 11

primary: V = volts, I = A
secondary: V = kilovolts, I = mA

Question 12

What does voltage rectification refer to?

Answer 12

The process of converting the AC to DC to ensure that current is flowing in one direction.

Question 13

What does a diode show?

Answer 13

A diode shows the direction of flow of conventional current (the arrow head direction).

Question 14

What happens when voltage is unrectified?

Answer 14

When voltage remains unrectified, current may flow back towards the cathode.

Question 15

How can unrectified voltage be fixed and which method is preferred?

Answer 15

Half-wave and full wave rectification, however, full wave rectification is preferred as it utilizes the power supply more effectively and results in less exposure time.

Question 16

What is a half wave rectifier?

Answer 16

This process involves removing the negative voltage power supply, so that for the negative portion of AC waveform, no current is conducted.

Question 17

Why is the half wave rectifier not beneficial?

Answer 17

As only half the wave is being used it is not an effective usage of power. By only using half the power, it requires double the exposure time.

Question 18

What is full wave rectification?

Answer 18

Allows for the negative cycle to be inverted in that it rectifies the negative component of the input voltage and converts it to DC.

Question 19

what type of power is half and full wave rectification?

Answer 19

single phase

Question 20

What are the phases of power?

Answer 20

Single phase and Three phase

Question 21

Describe single phase power

Answer 21

Has one distinct wave cycle and provides low energy, therefore offers low penetrability. Overall it provides less power - 2 pulses per 1/60s.

Question 22

Describe three phase power

Answer 22

Has 3 wave forms that are superimposed. So there is nearly always a high and constant voltage applied across the xray tube. Provides more power - 6 pulses per 1/60s.

Question 23

What is a high frequency generator?

Answer 23

They fully rectify AC and supply the tube with DC power. The frequency measured is very high.

Question 24

Why is a high freq generator preferred?

Answer 24

It produces a nearly constant voltage waveform, so the image quality is improved at a lower patient dose. The exposure time is also short.
It is also smaller, cheaper and more efficient than high volt generator.

Question 25

What is a voltage ripple?

Answer 25

the amount that the voltage varies between zero and the maximum value.

Question 26

The less the voltage ripple?

Answer 26

the more constant voltage is supplied to the xrayt tube and the more xray quality and quantity.

Question 27

Benefits of a rotating anode

Answer 27

1. promotes cooling between exposures as the xray beams are dispensed across the surface.
2. lasts longer
3. heat dissipation enables longer scans.

Question 28

How does the anode rotate?

Answer 28

Through an induction motor

Question 29

What are the 2 components of an induction motor and how do they work?

Answer 29

Rotor and stator.
The stator has numerous windings with current in them that create magnetic fields. The induced magentic flux as a result of this further induces eddy currents in the rotor. These eddy currents induce their own magnetic fields. So the mag field of the stator and the mag field of the rotor work interact with each other which creating a torque, and the rotor turns.