x-ray week 2

What are the 4 basic components of a X-ray room?

High voltage generator

Operating console

X-ray tube

Image receptor

In what way are x-rays emitted?

Isotropically

What are they x-rays emitted through the tube called?

Useful beam

Primary beam

What are the x-rays that leak through the protective housing called?

Leakage radiation

What is the protective housing made of?

Steel housing with lead lining

What must leakage radiation not exceed?

100 mR/hour at 1 meter

What are the basic internal components of a X-ray tube?

Cathode

Anode

Why does the X-ray tube have a vacuum?

More efficient X-ray production

What would gas in the tube result in?

Reduced electron flow

What is the most common cause of tube failure?

Tungsten vaporizes and coats the inside of the glass enclosure

What occurs at the cathode?

Thermionic emission

What occurs at the anode?

X-Ray production

What is thermionic emission?

Electric circuit sends electrons to filament and boils off a could of electrons

What is the filament made of?

Thoriated tungsten

What is the melting point of tungsten?

3419 C

What are the major products from the transfer of kinetic energy from cathode to anode?

99% heat

Electromagnetic energy

What is the charge of the focusing cup?

Negative

What is the purpose of the focusing cup?

Direct negatively charged electrons into smaller area on target

What is the purpose of the small focal spot/filament?

When better spatial resolution is required

What is the purpose of a large focal spot/ filament?

When large body parts are imaged

When are electrons created?

When electrons are shot over from cathode and slam into anode

What are the basic types of anodes?

Stationary

Rotating

When are stationary anodes used?

High tube current and power not required

What is the benefit of rotating anodes?

Produce higher energy x-rays and shorter exposure times

What makes a rotating anode more efficient?

More surface area

More heat dissipation

What is an induction motor?

Rotates anode with no mechanical connection to the outside

What powers the rotating anode?

Electromagnetic induction motor

What are the parts of the electromagnetic induction motor separated by the glass or metal?

Stator

Rotor

Which part of the electromagnetic induction motor is on the outside?

Stator

Which part of the electromagnetic induction motor is on the inside?

Rotor

What is the shaft of the rotor made of?

Copper/iron

What are the main functions of the anode in an X-ray tube?

Electrical conductor

Mechanical support for target

Thermal dissipator

What is the target?

Area of the anode strock by the electrons from the cathode

Where is the target in a stationary anode tube?

Embedded in the anode

Where is the target in a rotating anode tube?

Rotating disc

Why is the target made of tungsten?

Atomic number (#74)

Thermal conductivity

High melting point

What form of electrical current do x-rays require?

DC

What is a voltage rectifier?

Allows current to flow in one direction

Converts AC to DC

Uses diodes

What is the ripple in alternating current?

100%

What is the ripple in single phase half rectified?

100%

What is the ripple in single phase full rectified?

100%

What is the ripple in triple phase full rectified?

14%

What is the ripple in high frequency?

<1%

What is gained from a lower voltage % ripple?

Greater X-ray quantity and energy

What voltage are most X-ray systems designed for?

220

What does the line compensator do?

Measures the voltage provided to the X-ray machine

Adjusts that voltage to exactly 220v

What is radiation quantity?

Number of x-rays or intensity of X-ray beam

What determines the number of x-rays that reach the image receptor?

X-ray tube current (mA)

Time (s)

What is radiation energy?

Penetrability of X-ray beam

How is radiation energy expressed?

Kilovolt peak (kVp)

What is radiation quantity?

How many x-rays (# of photons) are made

What is the effective focal spot?

Area projected onto patient

What is actual focal spot?

Area on anode where X-ray photons are emitted

What determines the focal spot size?

Target angle

What happens to the effective area by angling the target?

Becomes smaller than actual focal spot

What is impacted by the size of the effective focal spot?

Resolution

What is the line-focus principle?

As the target angle decreases, so does size of effective focal spot

What is the range of varying target angles?

5-20

What is off-focus radiation?

Some electrons miss focal spot and make x-rays in other areas of target

Why is off-focus radiation undesirable?

It extends size of focal spot

Increases skin does

Reduce image contrast

What can be damaged on the anode from elevated temps for prolonged periods?

Bearings in rotor

What can be used to determine operational limits of X-ray tube?

Radiographic rating chart

Anode cooling chart

Housing cooling chart