Module 7 test
Tungsten is used as a target material primarily because of which of the following? 1. Thermal capacity 2. Electrical capacity 3. Complex atoms a. 1 and 2 only b. 2 and 3 only c. 1 and 3 only d. 1, 2, and 3
1 and 3 only (Tungsten is primarily chosen for its thermal characteristics and because it has large complex atoms making for greater chances of interaction with filament electrons.)
According to the chart below, how long will it take for the anode to cool from 95,000 HU to 65,000 HU? a. 1.5 minutes b. 2 minutes c. 3.5 minutes d. 4 minutes
1.5 minutes (To determine the cooling time, first plot where the heat load currently stands and the desired heat load then count the number of blocks in-between, noting that each block is 30 seconds.)
How many heat units are produced using a high-frequency machine and the following factors for one exposure? 70kVp, 200mA, 0.5sec a. 7,000 b. 10,150 c. 14,000 d. 270.5
10,150 (Heat units are calculated by multiplying the kVp x mA x sec x c x number of exposures. The letter "c" represents a correction factor unique to each generator type. The c for high frequency = 1.45.)
Generally, an x-ray tube will have how many filaments? a. 1 b. 2 c. 3 d. 4
2 (most general-purpose x-ray tubes have two filaments, referred to as a small and a large focal spot.)
ll of the following are within the normal dimensions of the x-ray tube filament except: a. 7 mm by 1 mm wide b. 10 mm by 2 mm wide c. 15 mm by 1.2 mm wide d. 20 mm by 3 mm wide
20 mm by 3 mm wide (The filament coil is usually 7-15 mm long and 1-2 mm wide.)
How many heat units are produced using a three-phase, 12-pulse machine and the following factors for 5 exposures: 90 kVp, 400 mA, .02 sec.? a. 5076 b. 1015.2 c. 36,000 d. 490.02
5076 (Heat units are calculated by multiplying the kVp x mA x sec x c x number of exposures. The letter "c" represents a correction factor unique to each generator type. The c for three-phase, 12-pulse is 1.41.)
Which target angle will produce the smallest effective focal spot? a. 17 b. 12 c. 10 d. 7
7 (The smaller the target angle, the smaller the effective focal spot will be; however, if we get too small, the field size will not be adequate to cover large image receptors at 40 inches.)
According to the chart below, how long will it take for the anode to cool from its maximum to zero? a. 8 minutes b. 7.5 minutes c. 6 minutes d. 5.5 minutes
7.5 minutes (To determine the cooling time, first plot where the heat load currently stands and the desired heat load, then count the number of blocks in between noting that each block is 30 seconds.)
Where does the filament section draw power? a. Autotransformer b. Step-up transformer c. Step-down transformer d. Main power supply
Autotransformer (The filament circuit draws power from a set of taps on the autotransformer.)
Which end of the beam has the most intense x-ray photons? a. Anode b.Cathode
Cathode (Because of the anode heel effect, the beam has a greater intensity on the cathode side.)
By angling the anode target face, we decrease the size of the: a. Actual focal spot b. Electron stream c. Effective focal spot
Effective focal spot (Angling the face of the target, we decrease the size of the effective focal spot; the smaller the angle, the smaller the effective focal spot.)
What is the problem with a glass envelope losing its vacuum? a. It also loses heat load capacity. b. Electrons from the air would cause arcing and damage. c. The sterile components of the tube would be contaminated. d. The filament would burn up and break.
Electrons from the air would cause arcing and damage. (The purpose of a vacuum is to remove atoms of air that would otherwise add to or interfere with the filament electron steam.)
The electrical cables entering the tube housing may be used as a handle to move the x-ray tube. a. True b. False
False (While the housing does have special electrical receptacles and serves as an electrical insulator, it is not advisable to use the cables as handles to move the tube.)
The stators of the anadoe induction motor are inside the glass envelope a. true b. false
False (stators are outside the glass envelope of the x-ray tube, and the rotor is inside)
One of the roles of the anode is to: a. Give filament electrons kinetic energy b. Provide a reservoir of electrons c. Hold a negative charge d. Cool the tube
Give filament electrons kinetic energy (Because the anode acquires a very large positive charge, the filament electrons, which are negatively charged, are very strongly attracted to the anode, thus acquiring kinetic energy.)
Most of the energy used to produce x-rays results in which of the following? a. X-rays b. Protons c. Electrons d. Heat
Heat (X-ray production is a very inefficient process and approximately 99% of the energy used for x-ray production is wasted as heat.)
The focusing cup is wired to which circuit section? a. High voltage primary b. High voltage secondary c. Filament circuit
High voltage secondary (In order to focus and corral the electron cloud, the focusing cup needs a large negative charge. It gets this from the high voltage secondary.)
What is the primary advantage of the rotating anode? a. Increased x-ray production b. Increased heat load capacity c. Less expensive d. Faster x-ray production
Increased heat load capacity (The primary advantage and purpose of this design is to spread the heat produced over a larger surface area.)
Higher techniques are better tolerated by which filament size? a. Small b. Large
Large (Larger filaments are "heavier" and better able to withstand the higher loads associated with higher techniques.)
Why do we limit the smaller filaments to the lower mA stations? a. Greater x-ray production b. Easier to design this way c. Less heat produced with smaller stations and techniques d.Faster exposures
Less heat produced with smaller stations and techniques (The smaller filaments are more limited in heat load capacity, and smaller mA stations produce lower heat loads than do larger ones.)
Leakage radiation is reduced by the housing to: a. Less than 10R/hr b. Less than 100R/hr c. Less than 1000 R/hr d. Less than 10,000R/hr
Less than 100R/hr (One of the functions of the x-ray tube housing is to reduce leakage radiation to less than 100R/hr.)
Arcing in the x-ray tube may be a result of which of the following? a. slow anode rotation b. technique too high c. overheating d. loss of a vacuum
Loss of a vacuum (as an x-ray tube ages, it starts to lose its vacuum resulting in atmospheric electrons adding to and interfering with filament electrons which leads to arcing and tube failure)
The housing serves to do all of the following except: a. Thermal cushion b. Electrical insulator c. Maintain vacuum d. Mechanical support
Maintain vacuum (It is the role of the glass envelope to maintain a vacuum. All of the other functions listed are roles of the housing.)
What is the purpose of the target window of the glass envelope? a. Minimize interference with x-rays leaving the tube b. Help cool the tube c. Remove undesirable x-rays from the beam d. Add electrons to filament stream
Minimize interference with x-rays leaving the tube (The target window is made thinner than the rest of the glass envelope so as to minimize absorption of x-rays by the envelope.Objective: Explain the general purpose and function of each component of the x-ray tube.)
By what method is the rotor of the x-ray tube turned? a. Mutual induction b. Self-induction c. Mechanical rotation d. The rotor does not move.
Mutual induction (he rotor is a part of an induction motor and, as such, is based on the principle of mutual induction.Objective: Describe the stationary and rotating anode design and operation.)
What metal is added to the rotating anode disk to increase thermal capacity and tensile strength? a. tungsten b. copper c. molybdenum d. rhenium
Rhenium (rhenium has a very high melting point and is added to tungsten because of this and its tensile strength.)
Which part of the induction motor is inside the glass envelope? a. Rotor b. Stator
Rotor (The rotor is inside the glass envelope and is designed to be a part of the anode assembly's shaft.)
Rectifiers serve to do which of the following? a. Convert voltage to kilovoltage b. Protect tube from overload c. Route electricity through tube the same way d. Help cool the tube
Route electricity through tube the same way (Rectifiers are electronic "one-way gates" that route electricity through the x-ray tube the same way each time so that the anode is always positive an the cathode is always negative.)
Why is the beam less intense on the anode side? a. Too much heat produced which slows photons. b. Fewer electrons to produce x-rays c. Some photons have to penetrate the heel of the target. d. Some photons travel further and slow down.
Some photons have to penetrate the heel of the target. (Because x-rays are produced in all directions, those traveling towards the anode end of the tube must first penetrate the heel of the target before exiting, causing some to be absorbed and the beam be less intense overall.)
How does surrounding the x-ray tube with oil help cool it? a. as the oil burns, the tube cools b. the oil draws the heat away from the tube c. oil lubricates the tube d. oil insulates the tube from the "outside" world
The oil draws the heat away from the tube (by conduction, the oil draws heat away from the x-ray tube)
The effectiveness of the focusing cup depends on all of the following except: a. Size and shape of the cup b. Charge on the cup c. Size and shape of the filaments d. Thermal capacity of the cup
Thermal capacity of the cup (Thermal capacity of the cup is not a consideration or factor in the effectiveness of the focusing cup. The other factor not listed is the position of the filaments within the cup.)
What is added to the filament to increase thermionic emission? a. Thorium b. Molybdenum c. Rhenium d. Aluminum
Thorium (Thorium is a radioactive element added to the filament to increase thermionic emission.)
The force of attraction between the anode and filament electrons is so strong that the electrons reach ½ the speed of light. a. True b. False
True (Because of the huge positive charge acquired by the anode, filament electrons will reach speeds approaching ½ the speed of light in a distance of 1-3 centimeters.)
The two major components of the cathode are within the glass envelope. a. True b. False
True (Both the focusing cup and the filaments are within the glass envelope. It is the anode that has the stators of the induction motor outside the envelope.Objective: Describe the components of the x-ray tube.)
By rotating an anode disc, we are able to spread heat over a larger surface area. a. True b. False
True (By rotating an anode disc, the electron stream is interacting with the entire periphery of the disc rather than one small area. This spreads the heat over a larger surface area.)
Small changes in filament current will cause large changes in tube current. a. True b. False
True (Once the filament is hot enough for thermionic emission, small changes in filament current will boil off many more electrons and add greatly to the stream of electrons (tube current) flowing across the tube.)
There is a risk of burns from touching an x-ray tube housing. a. True b. False
True (One of the roles of the housing is to draw heat from the x-ray tube to keep it cool. In doing so, it can become rather hot.Objective: Discuss the importance of the protective housing.)
The protective housing serves as an electrical insulator. a. True b. False
True (With its specially designed high-voltage connectors, the protective housing effectively isolates the high-voltage connections from the outside and serves as an electrical insulator. Objective: Describe the importance of the protective housing.)
What metal do we use as the target because of its atomic complexity? a. Aluminum b. Lead c. Tungsten d. Copper
Tungsten (Tungsten has an atomic number of 74. While this number represents the number of protons in the nucleus, because tungsten is stable, the number indicates the number of electrons in orbit around this nucleus. This means that tungsten is a very large and complex atom.)
What is the problem with sun tanning of the x-ray tube? a. Ultimately results in arcing and tube failure b. Reduces heat load capacity of the anode c. Causes glare on the resultant x-ray image d. Requires a reduction in technique
Ultimately results in arcing and tube failure ("Sun tanning" of the tube is actually the depositing of vaporized tungsten on the inside of the glass envelope which eventually leads to arcing and failure.)
Using the chart below, is the following technique safe or unsafe? 150mA, .1 sec, 110 kVp a. Safe b. Unsafe
Unsafe (Using this chart, plot the mA and exposure time. The plotted point is below the given kVp line and is, therefore, unsafe. )
Sun tanning of the tube is a result of: a. Loss of a vacuum b. Arcing of the tube c. Vaporized tungsten d. Heat exposure
Vaporized tungsten (As tungsten from the filament vaporizes, it coats the inside of the tube causing a bronze discoloration, which leads to arcing and eventual tube failure.Objective: Explain the general purpose and function of each component of the x-ray tube.)
All of the following are needed to produce x-rays in the x-ray tube except: a. Source of electrons b. Large potential difference c. Place for electron interaction d. Way to cool electrons
Way to cool electrons (To produce x-rays, a source of electrons is needed, kinetic energy for the electrons, and a place for the electrons to interact.)
The glass envelope of the x-ray tube is made of Pyrex to: a. Withstand high temperatures b. Provide a source of electrons c. Help cool the tube d. Avoid easy breakage of glass
Withstand high temperatures (Pyrex is a special type of glass that is able to withstand high temperatures without damage.Objective: Explain the general purpose and function of each component of the x-ray tube.)
Why is it desirable to have a large actual focal spot? a. better image detail b. faster exposure times c. more x-rays produced d. better heat dissipation
better heat dissipation (a large actual focal spot is referring to the actual area on the anode disc where electrons interact. The larger this is, the better the heat dissipation.)
How does the focusing cup "focus" electrons on the anode? a. By emitting them one by one b. By focusing them through a narrow port c. By using a lens system d. By electrostatic repulsion
by electrostatic repulsion (During exposures, the focusing cup has a very large negative charge and repels the electrons into a group, overcoming their own smaller negative charge and tendency to repel each other.)
Why are stationary anodes impractical for general x-ray exams? a. cannot use large techniques b. too slow c. too many x-rays produced d. too large and bulky
cannot use large techniques (because of the tremendous heat produced by large techniques and the limited ability of the stationary anode to dissipate heat, they are not practical for general radiography.)
The housing serves as a thermal cushion by: a. Cooling the tube b. Stabilizing the tube c. Slowing rotation speed d. Maintaining a vacuum
cooling tube (The housing has two ways of cooling the x-ray tube: oil bath and cooling fans. Objective: Explain the general purpose and function of each component of the x-ray tube.)
Which metal is used in the design of the anode because it is a good conductor of both heat and electricity? a. tungsten b. aluminum c. lead d. copper
copper (copper is used because it is a good conductor of both heat and electricity)
The filaments are wired to which circuit section? a. high-voltage primary b. high-voltage secondary c. filament circuit
filament circuit (the filaments are very small coils of wires and receive a much lower voltage but higher current through the filament circuit section of the main x-ray circuit.)
How is the target window made for general x-ray tubes? a. air introduced into the glass b. hole made in the envelope c. glass ground thinner in that spot d. a shutter added to the envelopei
glass ground thinner in that spot (for general-purpose tubes, a 5x5 cm section of the glass envelope is ground thinner so as to minimize interference with x-rays exiting the tube
Most of the energy used to produce x-rays results is which of the following? a. x-rays b. protons c. electrons d. heat
heat (x-ray production is a very inefficient process and approximately 99% of the energy used for x-ray production is wasted as heat.)
What is the primary limitation of the stationary anode? a. Too large b. Heat capacity c. Too many x-rays produced d. Too slow
heat capacity (The stationary anode has a rather small surface area for interaction with the stream of electrons from the cathode. Because of the tremendous amount of heat produced during the creation of x-rays, this anode design is heat capacity limited.Objective: Describe the stationary and rotating anode design and operation.)
What determines which filament is selected? a. mA station selected b. tube size c. target rotation speed d. heel effect
mA station selected (the mA station, in part, determines the heat that will be produced during an exposure, and the filaments are tied to these. The smaller one to the lower stations and the larger one to the larger stations.)
What would happen to the filament electrons without the focusing cup? a. repel each other and scatter b. be attracted to each other c. would not boil off of the filament d. would overheat and melt away
repel each other and scatter (the natural tendency of like charges is to repel each other. The focusing cup has a greater "like" charge and forces the electrons to a group. Without this, the electrons would scatter.)
Iron bars are incorporated into which of the following? a. rotor b. anode disc c. glass envelope d. housing
rotor (the rotor is part of the induction motor, which operates based on mutual induction. For this reason, iron bars are used to help create a magnetic field as a part of the process.)
Is the following technique safe or unsafe? 100mA, .02 sec, 150 kVp. a. safe b. unsafe
safe
Using the chart below, is the following technique safe or unsafe? 100mA, .2 sec, 110 kVp? a. Safe b. Unsafe
safe (Using this chart, plot the mA and exposure time. The plotted point is below the given kVp line and is, therefore, safe.)
What does voltage become kilovoltage in the x-ray circuit? a. autotransformer b. step-up transformer c. step-down transformer d. x-ray tube
step-up transformer (voltage from the autotransformer will pass next to the step-up transformer where it is increased by about 500 times to become kilovoltage necessary for x-ray production.)
The boiling off of electrons is called: a. heat loaded b. electrical capacity c. thermionic emission d. ejection fraction
thermionic emission (the proper terms for boiling off electrons is thermionic emission.)
The filament electrons will physically penetrate the target a. true b. false
true (filament electrons penetrate about .5 mm into the target and will interact with many tungsten atoms along their path.)
The protective housing serves as an electrical insulator a. true b. false
true (one of the functions is to serve as an electrical insulator. the high-voltage connectors of the housing are specially designed receptacles to protect against electric shock)
