Radiographic Imaging

Radiographic tube rating charts, anode cooling charts, housing cooling charts

3 types of heating charts to help radiographers avoid thermal damage to x-ray tubes:

Size and shape of focusing cup, charge, size and shape of filament, position of filament within the focusing cup

4 factors to determine the focusing cups effectiveness:

The focusing cup

A shallow depression in the cathode assembly to house the filament is

kVp, mA, time

All radiographic tube rating charts plot:

positive

Anode side of the x-ray tube is:

The target area

Area of the anode where the high voltage electron stream bombards the anode is:

space charge effect

As more and more electrons build up in the area of the filament, their negative charges oppose the emission of additional electron. This is known as: thermionic emission, biased cloud formation, space charge effect, current saturation

rotating

Because of their efficiency, ________ anodes are utilized for nearly all diagnostic radiography units

Filament, focusing cup and associated wiring

Cathode assemble consists of:

negative

Cathode side of x-ray tube is...

when the unit is not warmed up properly

Cracking of the anode occurs: when the kilovoltage is too high, when the anode is off-focus, with extended use, when the unit is not warmed up properly

Use an average kVp and mA station for 1 second exposure followed by 2 more 2 second exposures made 5-10 seconds apart

Describe a typical warm-up procedure of exposures:

A large potential difference

Driving the thermionic cloud from the cathode to the anode requires: a large potential difference, a small voltage, a large amperage, a small amperage

high melting points

Filament materials are chosen for their: high melting points, high boiling points, ability to vaporize easily

Produce a thermionic cloud, conduct the high voltage to the gap between the cathode and anode, focus the electron stream as it is directed toward the anode

Function of the cathode assembly

the heat capacity of the tube

Increase in the speed of the rotating anode increases:

molybdenum

Mammography units use ________ as the primary target material due to its ability to emit a more uniform range of lower energy photons

99

More than _____ % of the electron's kinetic energy is converted into heat

dual filaments or dual focus

Most x-ray tubes have:

roughened or pitting of the target track

Normal use of a rotating anode will lead to:

target, focus, focal point, focal spot, focal track

Other names for target area are:

due to thermal characteristics of x-ray production with the large amount of heat produced.

Primary reason for tube failure is:

cracking of the anode and destroying the tube

Proper anode warm-up procedures prevents

present a much larger target area than stationary anodes, disperses heat over a larger area

Rotating anodes target discs do 2 things:

performing radiography that requires fine detail

Smaller filaments should be used when...

45 degree angle end of a short copper rod or base

Stationary anode targets are embedded in a:

rhenium alloyed tungsten target

Stationary anodes are composed of:

dental units

Stationary anodes are used more for ________ due to their low-power functions

True

T of F: As the anode target angle increases, the primary beam field size increases.

False

T of F: Filament saturation occurs when the negative charge of the electron cloud opposes the emission of additional electrons from the filament.

False

T or F: Like the cathode, the anode comprises a single metal called, tungsten.

False

T or F: The entire cathode and anode assemblies are enclosed within the glass or metal envelope.

True

T or F: The faster the anode rotation, the better the heat dissipation.

False

T or F: The filament is set in the cathode assembly outside of the focusing cup.

False

T or F: The line focus principle is used to reduce the actual area of the focal spot.

True

T or F: The term focal spot size refers to the effective focal spot.

True

T or F: When the target angle is less than 45 degrees, the effective focal spot is smaller than the actual focal spot.

target area

The _________ provides the actual source of x-ray photons and serve as the primary thermal conducting device

length of the filament

The actual focal spot is controlled by the: size of the effective focal spot, length of the filament, anode target angle, all of above

anode, stator, rotor, associated wiring

The anode assembly consists of:

Target surface for the electrons coming from the filament, conducts high-voltage from the cathode back into x-ray circuitry, serves as the primary thermal conductor

The anode assembly has 3 functions:

focusing cup

The filament is located within an oval shaped depression in the...

thoriated tungsten wire

The filament is made of

increasing the size of the target area

The main advantage of rotating anodes is

Tungsten

The metal of choice to serve as the source of x-ray photons:

actual focal spot

The physical area of the focal track affected by the electron beam is the: effective focal spot, effective focal track, actual focal spot, all of above

narrow the thermionic cloud as it is "driven" toward the anode

The purpose of the focusing cup is to:

electrons are suddenly stopped and become the source of x-ray photons

The surface of the anode is where the:

depress the rotor for too long before an exposure

To prevent premature breaking of the filament, it is important to not:

its high melting point and because it does not vaporate easily

Tungsten is used because of:

its high atomic number

Tungsten is used for the target area because of:

Cathode and anode

What are the 2 main parts of the x-ray tube?

Source of free electron, a target for the electrons to hit, a force to accelerate the electrons to the target, all must take place within a vacuum

What are the 4 conditions necessary for the production of x-ray?

both

What type of radiation is composed of photons not produced at the focal spot: off-focus, extrafocal, both, neither

Thermionic emission

When outer shell electrons of the tungsten filament atoms are boiled off and ejected from the filament this is called

They provide a guide regarding the maximum technical exposure factor combinations that can be used without overloading the tube in a single exposure

Why are radiographic tube rating charts, sometimes called tube rating charts, the most valuable?

stationary and rotating

2 primary types of anodes:

Control scatter and leakage radiation, isolate high voltages, provide a means to cool the tube

3 primary functions of the x-ray tube's protective housing: