ch.5 P

Leakage radiation from the lead-lined housing must not exceed

100 mR/hr measured at 1 meter

the most common diagnostic radiography x-ray tube target angle is _______ degrees

12

to cover a 14 in. x 17 ft field at 40 ft, a _____ -degree target angle is required

12

a conscientious technologist will always handle the x-ray tube assembly with care, particularly when the x-ray tube has been used for high mAs and kVp exposures over a short period of time. technologist are cautioned about moving the x-ray tube assembly quickly and with "jerking" movements. explain why this is important to remember

Hot anodes assemblies are subject to metal fatigue and the stress placed upon them by gyroscopic inertia. Moving the tube quickly from one orientation to another places undue fatigue on the anode stem and disc and may cause it to become unbalanced or misaligned. many manufacturers will place an "anode brake" or reverse induction force on the stator to slow the anode in just a few seconds. this feature of extra technology will extend the life of the tube but does cost additional money in the x-ray tube purchase

How many heat units are generated when setting a technique of 70 kVp, 300 mA, 0.1 seconds on a 1f rectified unit?

2,100 HU

how many units are generated by na exposure of 70 kVp, 400 mAs, and 0.1 seconds on. a3f rectified unit?

3.780 HU

how many heat units are germinated by an exposure of 100 kVp, 400 mAs, and 0.1 seconds on a high frequency unit?

400 HU

all of the following are related except one. select the Choice that is NOT RELATED a. a source of electrons b. a vacuum c. thermionic emission d. a large potential difference

c. thermionic emission

the sue of the line-focus Principle causes a problem known as the ______ effect

code heel

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

focal spot

list three primary functions of the x-ray tube's protective housing

-controls scatter and leakage radiation -isolates the high voltages -provides a means to cool the tube

list the three function of the x-ray tube anode

-it serves as the target surface for the high voltage electrons from the filament -it conducts the high voltage from the cathode back into the x-ray generator circuitry - it serves as the primary thermal conductor

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

-off focus -extra focal

list other names for the anode target

-target -focus -focal point -focal spot -focal track

list the three parts of the anode assembly

-the anode -the stator -the rotor

how many heat units are generated by three exposure of 100 kVp, 400 mAs, and 0.01 seconds using a high frequency generator?

1,680 HU

using the following exposure factors on high frequency generator, how many joule sod electrical energy are being created? 400 mA 95 kVp 26 ms

1,773 J

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

three-phase, high frequency generators are preferred

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

Metal envelope times pace a ground on the metal casing. This feature minimizes the buildup of tungsten deposits on the inside of the envelope, as the envelope never builds up a positive chart to attract the electrons as they travel from cathode to anode. This is not possible with a glass envelope tube. Because of this feature, x-ray tube last longer and remain more efficient for the life of the tube. Additionally, metal envelopes tube prevent electrons form exiting the tube and striking the patient if the SID is extremely close

what is the function of the filament?

The function of the filament is to provide sufficient resistance to the flow of electrons so the heat produced will cause thermionic emission to occur.

why is a vacuum created in the X-ray tube?

The removal of the air permits electrons to flow from cathode to anode without encountering the gas atoms of air. this greatly increases the efficiency of the tubes operation and prevents tube arcing

cracking of the anode typically occurs

When a cold anode is hit with a high kVp exposure

driving the thermionic cloud from the cathode to the anode requires

a small amperage

the use of stress-relief anodes is effective at dealing with what inherent characteristics of x-ray production?

a stress relief anode is specially designed to permit rapid anode thermal expansion without anode cracking. these stress relief slits are similar to the stress lines in the disc brakes of motorcycles and automobiles. generally, stress relief anodes do not require an elaborate tube warm up procedure

the function of the cathode is to produce

a thermionic cloud

the protective housing controls leakage and scatter radiation through

absorption

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

actual focal spot

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

x-ray photo production occurs at the

anode

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

because the inferior upper leg is less dense, the anodes less-intense beam should be positioned toward the knee to help decrease the film density in that region

To increase the thermal loading capacity of the anode, x-ray tube manufacturers

bond graphite to the back of the anode

all of the following are preferred cathode filament materials except

copper

As the x-ray tube anode target angle increases from 10 degrees to 15 degrees: a. higher exposure values (mA, kVp) may be used b. the size of the actual focal spot increases c. image resolution decreases d. all of the above

d. all of the above

which of the following would affect the production of a thermionic cloud? a. filament diameter b. filament length c. filament temperature d. all of the above

d. all of the above

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

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

effective focal spot

an effective technology used in pulsed fluoroscopy to produce precise electrons steams from the cathode is

grid-biased x-ray tubes

tungsten is the material of choice for the source of x-ray photons primarily because of its

high atomic number

filament materials are chosen primarily for their

high melting point

as the actual focal spot size increase, 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 actual spot is controlled by the

length of the filament

the cathode focusing cup has a/an ____ charge

negative

the function of the stator and rotor assembly is to

rotate the anode

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

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

stator

all of the following are part of the cathode assembly except

stator

when radiograph 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

all for the following would lengthen x-ray tube life except

use high speed anode rotation on distal extremity studies

a filament may break due to

vaporization

melting of the anode commonly occurs

when the stator fails and the rotor ceases to turn

pitting of the anode commonly occurs

with extended use