Radiology Lecture 2: X-Ray Machine I

What are the three steps of the radiographic process?

1. Image acquisition

2. Image processing

3. Image display

What are the four conditions for x-ray production?

1. Vacuum tube

2. Electron source

3. Accelerating potential

4. Decelerating target

What provides the vacuum tube for x-ray production?

Glass envelope

What provides the electron source for x-ray production?

Filament

What provides the accelerating potential for x-ray production?

Voltage

What provides the decelerating target for x-ray production?

Anode

What is the purpose for the cathode assembly?

Controllable electron source

What are the two components of the cathode assembly?

1. Filament

2. Focusing cup

What is used as a filament in cathode assembly?

Tungsten wire

What two material can the focusing cup of cathode assembly be made of?

1. Molybdenum

2. Nickel

Is the focusing cup of cathode assembly positively or negatively charged?

Negatively

What two things do connecting wires supply the filament with?

1. Low voltage current

2. 5 - 7 amperage

What is the melting point of tungsten?

3370 degrees Celsius

What is the function of the focusing cup?

Make electron stream converge onto target anode in required size and shape

What is the escape of electrons from themetal due to absorption of thermal energy?

Thermionic emission

What is the cloud ofelectrons emitted from filament?

Space charge

What is the number of electrons proportional to in thermionic emission?

Filament current/temperature

What is the flow of electrons from cathode to anode?

Tube current

What does electron flow result from?

Potential difference

What two things is the quantity electrons in tube current controlled by?

1. Milliamperes

2. Time

What are the three purposes of the anode assembly?

1. X-ray production

2. Electrical conductor

3. Thermal conductor

What are the two components of anode assembly?

1. Rotor

2. Stator

How much of the electron kinetic energy become heat in anode assembly?

99%

How much of the electron kinetic energy produces X-rays in anode assembly?

1%

What is the target in anode assembly made of?

Tungsten

What component of the anode assembly gives good heat conductivity?

Copper stem

What two benefits do envelopes give when used as a vacuum tube?

1. X-ray production efficiency

2. Heat dissipation

What two things are envelopes made of?

1. Glass

2. Metal

What is the main function of x-ray tube housing?

Protection

What is the function of the steel housing of the tube in x-ray housing?

Prevent electrical shock

What are the two functions of the oil within the tube in x-ray housing?

1. Prevent electrical shock

2. Heat dissipation

In the line-focus principle, is the actual focal spot or the effective focal spot larger?

Actual focal spot

In the line-focus principle, what does a larger actual focal spot allow?

Withstand more heat per exposure

In the line-focus principle, what does a smaller effective focal spot allow?

Increase spatial resolution

What is the anode heel effect?

Intensity of beam depends on angle the X-rays are emitted from focal spot