X-Ray Tube Components & Focal Spot

The most widely used support structure for the x-ray tube is the _____.

a. C-arm

b. floor-to-ceiling mount

c. ceiling support system

d. floor support system

C. ceiling support system

pg. 105: the ceiling support system is probably the most frequently used.

The external structure of the x-ray tube includes the support structure, the protective housing, and the ______.

a. anode

b. cathode

c. glass envelope

d. focusing cup

c. glass envelope

pg. 105 - 106

As an x-ray tube ages, the inside can become coated with tungsten, which can cause _____in the tube.

a. convection

b. anode pitting

c. off-focus radiation

d. arcing

D. arcing

pg. 107: ultimately tungsten metal does vaporize and is deposited on internal components. This upsets some of the electrical characteristics of the tube and can cause arcing.

The negative side of the x-ray tube holds the _____.

a. filament

b. anode

c. target

d. rotor

A. filament

pg. 107: the cathode is the negative side of the X-ray tube; it has two primary parts, a filament and a focusing cup.

What is the most common cause of the tube failure?

a. cracked anode

b. loose bearings

c. pitted anode

d. tungsten vaporization

D. tungsten vaporization

pg. 107: tungsten does not vaporize easily, However, tungsten vaporization with deposition on the inside of the glass enclosure is the most common cause of tube failure.

The filament is made of _____

a. graphite

b. tungsten

c. copper

d. molybdenum

B. tungsten

pg. 107: Filaments are usually made of thoriated tungsten. Tungsten provides for higher thermionic emission than other metals. It's melting point is 3410 degrees C.

Thermionic emission at the filament creates a ______.

a. space charge

b. grid control

c. line focus

d. heel effect

A. space charge

pg. 108: When emitted from the filament, electrons repel one another and form a cloud around the filament. This cloud of electrons, called a space charge, makes it difficult fo subsequent electrons to be emitted by the filament because of electrostatic repulsion. This phenomenon is called the space charge effect.

The rotating anode is turned by a _______.

a. thermal cushion

b. rotating belt

c. magnetic field

d. mechanical pulley

C. magnetic field

pg. 112: the rotating anode is powered by an electromagnetic induction motor. Current in each stator winding induces a magnetic field that surrounds the rotor...this magnetic field interacts with the ferromagnetic rotor, causing it to rotate synchronously with the activated stator windings.

When electrons bombard the target, _____% of their kinetic energy is converted to heat.

a. 10

b. 25

c. 50

d. 99

D. 99

pg. 110: when the projectile electrons from the cathode interact with the anode, more than 99% of their kinetic energy is converted into heat.

The target of the rotating anode is usually coated with a _____ alloy.

a. molybdenum

b. graphite

c. tungsten

d. copper

C. tungsten

pg. 110: alloying the tungsten gives it added mechanical strength to withstand the stresses of high-speed rotation and the effects of repetitive thermal expansion and contraction.

The _____ is the source of radiation in the x-ray tube.

a. filament

b. focal spot

c. focusing cup

d. stator

A. focal spot

pg. 113: the focal spot is the area of the target from which x-rays are emitted.

Because of the line focus principal, the effective focal spot size decreases with decreasing _______ .

a. target angle

b. rotor speed

c. window thickness

d. space charge

A. target angle

pg. 113: by angling the target, one makes the effective area of the target much smaller than the actual area of electron interaction. When the target angle is made smaller, the effective focal spot size also is made smaller.

High capacity tube rotors revolve at _____ rpm.

a. 2000

b. 3600

c. 6000

d. 10,000

D. 10,000

pg. 111: Most rotating anodes revolve around 3400 rpm. The anodes of high capacity x-ay tubes rotate at 10,000 rpm.

The x-ray intensity is lower on the anode side of the tube because of the _____.

a. line focus principle

b. heel effect

c. focusing cup

d. filament length

B. heel effect

pg. 114: the radiation intensity at the cathode side of the x-ray field is greater than that on the anode side. The x-rays that constitute the useful beam emitted toward the anode side must traverse a greater thickness of target material than the x-rays emitted toward the cathode direction. The intensity of the x-rays that are emitted through the heel of the target is reduced because they have a longer path through the target and therefore increased absorption. This is the heel affect.

The cathode side of the tube should be directed toward the ____ part of the patient.

a. upper

b. lower

c. thicker

d. thinner

C. thicker

pg. 115: the heel effect is important when on is imaging anatomical structures that differ in greatly in thickness/density. The cathode side of the x-ray tube should be over the thicker part of the anatomy to provide a more uniform radiation exposure of the IR.

What is the formula for heat units for a 3-phase, 6-pulse x-ray machine?

a. kVp x mA x seconds

b. 1.35 x kVp x mA x seconds

c. 1.41 x kVp x mA x seconds

d. 1.66 x kVp x mA x seconds

C. 1.41 x kVp x mA x seconds

pg. 119-120:

Single Phase: 1 HU = kVp x mA x seconds

Three Phase/High Frequency: 1.4 x kVp x mA x seconds

Tube failure can occur from _____

a. extrafocal radiation

b. short exposure times

c. high kVp techniques

d. long exposure times

D. long exposure time

pg. 117: a second type of tube failure results from maintaining the anode at elevated temperatures for prolonged periods.

The filament in an x-ray tube is about ______ cm in length.

a. 1-2

b. 3-4

c. 8-10

d. 10-20

A. 1 - 2

pg. 107: The filament is approximately 2 mm in diameter and 1 or 2 cm long.

A dual focus tube has two _____.

a. anodes

b. filaments

c. rotors

d. stators

B. filaments

pg. 109: fig. 6-9, in a dual-focus x-ray tube, focal spot size is controlled by heating one of the two filaments.

Each tube has it own tube rating chart to show _______

a. housing cooling times

b. anode cooling times

c. maximum exposure times

d. maximum patient doses

C. maximum exposure times

pg. 118: 3 types of x-ray tube rating charts are particularly important

1. radiographic rating chart - conveys which techniques are safe and which are unsafe for X-ray tube operation

2. anode cooling chart

3. housing cooling chart

The ____ is/are outside the glass envelope.

a. stators

b. rotor

c. focal spot

d. filaments

A. stators

pg. 111: the part outside the glass or metal enclosure, called the stator, consists of a series of electromagnets equally spaced around the neck of the tube.

Extrafocal or off-focus radiation is produced from ______.

a. overheated anodes

b. scattered x-rays

c. rebounding electrons

d. dual focus cathodes

C. rebounding electrons

pg. 116: some of the electrons bounce off of the focal spot and then land on other areas of the target, causing x-rays to be produced from outside the focal spot.

The heel effect is caused by the ______

a. stator windings

b. anode angle

c. exposure times

d. induction motor

B. anode angle

pg. 114: the smaller the anode angle the larger the heel effect.

The effective focal spot size is _____ the actual focal spot size.

a. equal to

b. larger than

c. equal to or larger than

d. smaller than

D. smaller than

pg. 114: the line focus principle results in an effective focal spot size much less than the actual focal spot size.

Localized pitting or cracking on the anode can occur from ______.

a. filament vaporization

b. a single excessive exposure

c. long exposure times

d. high kVp and low mA

B. a single excessive exposure

pg. 117: when the temperature of the anode is excessive during a single exposure, localized surface melting and pitting of the anode can occur.