Chapter 6 The Xray Tube

All of the following are related except one. Which one is NOT related?

Thermionic emmision

The function of the cathode is to produce?

Thermionic cloud

All of the following are part of the cathode assembly except?

Stator

All of the following are preferred cathode filament materials EXCEPT?

Copper

Filament materials are chosen primarly for their?

High melting points

Which of the following would affect the production of a thermionic cloud?

Filament temperature

A filament may break due to?

Vaporization

Driving the thermionic cloud from the cathode to the anode requires?

A small amperage

In order to time the x-ray exposure with rapid inspiration on an infant?

Three phase generators are preferred

The focusing cup has a ______charge

Negative

As more and more electrons build up in the area of the filament, their negative charges oppose the emission of additional electrons. This phenomenon is known as?

Space charge effect

X-ray photon production occurs at the?

Anode

Tungsten is the metal of choice for the source of x-ray photons because of its?

High atomic number

Pitting of the anode commonly occurs?

With extended use

Melting of the anode commonly occurs?

When the stator fails and the rotor ceases to turn

Cracking of the anode typically occurs?

When a cold anode is hit with a high kVp exposure

The exact point on the anode where the x-ray beam emanates is the?

Focal spot

The physical area of a rotating anode focal track, affected by the cathode electron beam is the?

Actual focal spot

The area of the focal spot that is projected out of the tube toward the object being radiographed is the?

Effective focal spot

The actual focal spot is controlled by the?

Length of the filament

The most common diagnostic radiography target angle is?

12

As the actual focal spot size increases, the effective focal spot size?

Increases

As the angle of the anode increases and the incident electron beam size remains the same, the effective focal spot size?

Increases

The cover a 14 in. by 17ft field at 40ft, a ____degree target is required?

12

The use of the line-focus principle causes a problem known as the __________effect.

Anode heel

The only portion of the anode assembly placed outside the vacuum of the envelope is the?

Stator

The function of the stator and rotator assembly is to?

Rotate the anode

The rotor is located____the stator and_____the envelope.

Inside;inside

The protective housing controls leakage and scatter radiation through?

Absorption

Insulation of the high-voltage components of the tube and absorption of the heat produced by x-ray production is achieved through the use of?

Dielectric oil

What type of radiation is composed of photons not produced at the actual focal spot?

Off-focus

When radiographing a wedge-shaped anatomical structure such as the femur, the thicker portion of the anatomy should be positioned?

Under the cathode end of the tube

Leakage radiation from the lead-lined housing must not exceed?

100 mR/hr measured at 1 meter

The problem of off-focus radiation?

Is particularly important with digital detectors, distorts the digital histogram, may result in suboptimal digital images (all of the above)

To determine the allowable combination of exposures factors, thus preventing x-ray tube damage?

An x-ray tube rating chart is checked prior to exposure

List 3 functions of the filament?

Target surface for high voltage electrons from the filament, conducts high voltage from the cathode back to xray circuit generator, primary thermal conductor

List two other names for the anode target?

Focus, focal spot

List the three parts of the anode assembly?

Rotor, stator, anode

In which direction should the anode be placed for an AP projection of the femur?

Towards the knees/feet

List the three primary functions of the xray tube's protective housing?

Controls leakage and scatter radiation, isolates the high voltages, provides a means to cool the tube

The use of stress-relief anodes is effective at dealing with what inherent characteristic of xray production?

Heat

What is the function of the filament?

Provide sufficient resistance to the flow of electrons so that the heat produced will cause a thermionic emission

Why is a vacuum created in the x-ray tube?

To remove the air to permit electrons to flow from cathode to anode without encountering the gas atoms of the air

Metal envelope xray tubes are gaining in popularity. Explain some key advantages to a metal housing xray tube?

They prolong tube life because they eliminate the problem of tungsten vaporization

Technologists are cautioned about moving the xray tube assembly quickly and with jerking movements, why is this important to remember?

Because of the bearings

What is number 1 on the anode xray tube?

Armature

What is number 2 on the anode xray tube?

Stator electromagnets

What is number 3 on the anode xray tube?

Bearing

What is number 4 on the anode xray tube?

Tungsten anode

What is number 5 on the anode xray tube?

Envelope

What is number 6 on the anode xray tube?

Filament circuit

What is number 7 on the anode xray tube?

Filament

What is number 8 on the anode xray tube?

Electron beam

What is number 9 on the anode xray tube?

Xray beam

What is number 10 on the anode xray tube?

Molybdenum neck and base

What is number 11 on the anode xray tube?

Rotating portion