RAD-236 Chapter 7 Flashcards

The purpose of the x-ray tube is to permit the production of _______.

photons

What four conditions are needed for x-ray production?

- source of electrons.

- appropriate target material.

- high voltage.

- a vacuum tube.

What are the two primary internal parts of the x-ray tube?

cathode and anode

The cathode and anode are both electrodes, and these two electrodes in the x-ray tube together are called a _____.

diode

What are the three external parts of the x-ray tube?

- support structure.

- protective housing.

- glass/metal enclosure.

The most common type of support structure for the x-ray tube is a _______ support system which uses two sets of ceiling-mounted rails.

ceiling

When the x-ray tube is centered above the exam table at the standard SID, the tube is in a preferred _______ position.

detent

The _____ __ ________ x-ray tube support system has a single column with rollers at each end.

floor to ceiling

The _-___ support system is used in interventional radiology and is ceiling-mounted.

C-arm

When x-rays are produced, they are emitted ___________, which means with equal intensity in all directions.

isotropically

We only use x-rays emitted through the _______ section of the protective x-ray tube housing, and these x-rays are called the ______ ____.

window, useful beam

Protective x-ray tube housing is used to reduce _______ _______, and helps to absorb x-ray photons that do not make it through the window.

leakage radiation

Properly designed protective x-ray tube housing reduces the level of leakage radiation to ___ mGy(a)/hr at 1 m when operated at maximum conditions.

0.88

Protective x-ray tube housing guards against excessive radiation exposure and even ______ _____.

electric shock

The protective x-ray tube housing may contain ___ that insulates and protects from electric shock, as well as dissipates heat.

oil

Oil is in a ______ that allows it to expand when heated, or a ___ can be used to cool the x-ray tube.

bellow, fan

An x-ray tube is an electronic vacuum tube with components contained within a _____ or _____ enclosure.

glass, metal

The x-ray tube is a special vacuum tube that contains two electrodes; the _______ and ______.

cathode, anode

The glass enclosure is made of ______ glass to enable it to withstand the tremendous heat that is generated.

Pyrex

The function of a glass or metal x-ray enclosure is to maintain a _______ in the x-ray tube.

vacuum

The vacuum in an x-ray tube allows for an _______ in x-ray production and tube life.

increase

The vacuum in an x-ray tube prevents ___ from getting in the enclosure which can cause x-ray production to fail.

gas

As a glass enclosure in the x-ray tube ages, _______ vaporizes and coats the glass which causes tube current to interact with the glass enclosure. This causes tube failure.

tungsten

A _____ enclosure is an improvement from the glass enclosures, and allows for a longer tube life and are less likely to lead to tube failure.

metal

Which is the most common type of enclosure used in the x-ray tube?

metal enclosure

The _______ is the negative side of the x-ray tube.

cathode

A ____-_______ cathode has two filaments that supply seperate electron beams to produce two focal spots.

dual-filament

What are the two primary parts of the cathode?

filament and focusing cup

How long is the filament in cm and in mm?

1-2 cm and 10-20 mm

What material is the filament wire made out of?

thoriated tungsten

The x-ray tube filament emits ________ when it is heated.

electrons

When the current through the filament is sufficiently high, the outer shell electrons of the filament atoms are "boiled off" and ejected from the filament. This is known as ________ _________.

thermionic emission

Thoriated tungsten is used for the filament because it ________ thermionic emission and tube life when compared to other metals.

increases

Thoriated tungsten is also not easily _________, though some still occurs in the x-ray tube.

vaporized

Vaporization of tungsten turns it from a _____ into a ___.

solid, gas

Tungsten vaporization with deposition on the inside of the glass enclosure, is the most common cause of ____ _______.

tube failure

The filament is embedded in the _______ ___.

focusing cup

The focusing cup is _________ charged so that it electrostatically confines the electron beam to a small area of the anode.

negatively

A biased focusing cup _________ negative charge which allows for more narrowing of electrons, and it _________ the focal spot size.

increases, decreases

Certain types of tubes called ____-________ tubes or ____-_______ tubes are designed to be turned on and off very rapidly, and are good for exams that require multiple exposures for precise exposure time.

grid-controlled, grid-biased

The term "grid" in grid-biased tubes is borrowed from _______ ____ technology and refers to an element in the x-ray tube that acts as the switch.

vacuum tube

In a grid-biased x-ray tube, the ________ ___ is the "grid" and therefore the exposure switch.

focusing cup

When you select an mA on the control panel, the label responds to the resulting tube current, but you are actually selecting a much higher _______ _______.

filament current

The _____ _____ _____ occurs during thermionic emission and is when electrons build up due to the negative charges of the electrons opposing further emission.

space charge effect

The space charge effect limits maximum ___ of equipment during lower ___ settings.

mA, kVp

As kVp increases, the x-ray tube current also increases until it reaches a maximum value. A further increase in kVp does not result in higher mA because all of the available electrons have been used, and this is called _________ ______.

saturation current

When an x-ray tube is operated at the saturation current, it is said to be _______ ______.

emission limited

Saturation current is not reached at _____ kVp because of the space charge effect.

lower

Most diagnostic x-ray tubes have two focal spots, termed _____ and _____.

large, small

The small focal spot is used when better ______ ________ is required.

spatial resolution

The large focal spot is used when _____ body parts are imaged and when other techniques that produce ____ ____ are required.

large, high heat

Selection of focal spot size is made with the __ ______ ________ on the control panel.

mA station selector

Either filament (small or large) can be used with lower mA stations, such as ___ mA or less.

300

At approximately ___ mA or higher, only the large filament can be used because the heat capacity of the anode would be exceeded if the small filament were used.

400