The x-ray tube and housing assembly are quite heavy; what is required so the radiology tech can position them?
What support system is probably the most frequently used?
What is telescoping column attaches the x-ray tube housing to the rails?
source-to-image receptor distance (SID)
When the x-ray tube is centered above the examination table at the standard SID, the x-ray tube is in what position?
preferred detent position
Some ceiling-supported x-ray tubes have a single control that removes all locks, allowing the tube to ____.
Which support system have a single column with rollers at each end, one attached to a ceiling mounted rail and the other attached to the floor-mounted rail?
floor-to-ceiling support system
On which support system the x-ray tube slides up and down the column as the column rotates?
floor-to-ceiling support system
Which support system has the colum positioned with one or two floor-mounted rails?
Single floor support system
What system is ceiling mounted and provide for very flexible x-ray tube positioning and shaped like a C?
When x-rays are produced with equal intensity in all directions, how are they emitted?
We use only x-rays emitted through the special section of the x-ray tube called
The x-rays emitted through the window are called
X-rays that escape through the protective housing are called
What contribute nothing in the way of diagnostic information and result in unnecessary exposure of the patient and the rad tech?
Properly designed protective housing reduces the level of leakage radiation to less than ____ at 1 m when operated at max conditions
What does protective housing guard against (2)
excessive radiation exposure
What incorporates specially designed high-voltage receptacles to protect against accidental electric shock?
What protective housing support provide for the x-ray tube and protects the tube from damage caused by rough handling
The protective housing around some x-ray tubes contains oil that serves as both ____ and ____.
insulator (against electric shock)
thermal cushion (to dissipate heat)
An x-ray tube is an electronic vacuum tube with components contained within a ____ or ____
What is a special type of vacuum tube that contains two electrodes?
X-ray tubes contain two electrodes called
X-ray tubes are relatively large, perhaps ___ to ___ cm long and ____ cm in diameter.
30 to 50 cm
Which enclosure is made of Pyrex glass to enable it to withstand the tremendous heat generated?
Which enclosure maintains a vacuum inside the tube and allow for more efficient x-ray production and a longer tube life?
Which tube were not vacuum tubes but rather contained controlled quantities of gas within the enclosure?
Crookes tube (early x-ray tubes)
Which tube is a vacuum tube, if it becomes gassy, x-ray production falls, and the tube can fail?
Coolidge tube (modern x-ray tube)
As a glass enclosure tube ages, what vaporizes and coats the inside of the glass enclosure?
What is the result of the electrical properties of the tube allowing tube current to stray and interact with the glass enclosure? (2)
What tube maintain a constant electric potential between the electrons of the tube current and the enclosure. Therefore, they have a longer life and are less likely to fail.
Metal enclosure tubes
What are designed with a glass or a metal enclosure?
What is the negative side of the x-ray tube; it has two primary parts, a filament and a focusing cup?
What are the cathode 2 primary parts?
What is a coil of wire similar to that in a kitchen toaster, but it is much smaller?
An x-ray tube filament emits electrons when it is ____.
When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are ____ ____ and ____ from the filament.
When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are "boiled off and ejected from the filamemts. This phenomenon is known as what?
What are filaments usually made of?
What provides for higher thermionic emmission than other metals?
What vaporization with deposition on the inside of the glass enclosure is the most common cause of tube failure.
The filament is embedded in a metal shroud called
All of the electrons accelerated from cathode to anode are electrically (positive or negative)
Because all of the electrons accelerated from cathode to anode are electrically negative, the electron beam tends to spread out owing to what?
Some electrons can miss the ____ completely.
What is negatively charged so that it electrostatically confines the electron beam to a small area of the anode?
Effectiveness is determined by its size and shape, its charge, the filament size and shape, and the position of the filament in what?
Most rotating anode x-ray tubes have two filaments mounted in the cathode assemble "side by side" creating ____ and ____ focal spot sizes.
large and small
The x-ray tube current is adjusted by controlling what?
Because electrons carry (positive/negative) charges, they repel one another and tend to form a cloud around what?
What is the cloud of electrons called
What makes it difficult for subsequent electrons to be emitted by the filament because of electrostatic repulsion.
Cloud of electrons called a space charge, makes it difficult for subsequent electrons to be emitted by the filament because of electronstatic repulsion. This phenomenon is called
space charge effect
What emission at low kVp and high mA can be space charge limited?
What rises with increasing voltage to a maximum value?
x-ray tube current
The x-ray tube current rises with increasing voltage to a maximum value is ____ current
Most diagnostic x-ray tubes have two focal spots:
Which focal spot that is used when better spatial resolution is required?
small focal spot
Which focal spot is used when large body parts are imaged and when other techniques that produce high heat are required?
large focal spot
Normally, either fialment can be used with the lower mA station - approx 3-- mA or less. At approx 400 mA and up, only the larger focal spot is allowed because the heat capacity of the anode could be exceeded if the small focal spot were used.
Which focal spot range from 0.1 to 1 mm?
small focal spot
Which focal spot range from 0.3 to 2 mm?
large focal spot
What are the two types of anodes?
Which anode x-ray tubes are used in dental x-ray imaging systems, some portable imaging systems and other special-purpose units in which high tube current and power are not required?
Which anode are general-purpose x-ray tubes are capable of producing high-intensity x-ray beams in short time?
What is the positive side of the x-ray tube; it conducts electricity and radiates heat and contains the target?
The anode serves 3 functions in an x-ray tubes:
What recieves electrons emitted by the cathode and conducts them through thr tube to the connecting cables and back to the high voltage generator?
The anode that provides support for the target?
When the projectile electrons from the cathode interact with the anode, more than 99% of their kinetic energy is converted into heat is called
What is the area of the anode struck by the electrons from the cathode?
In stationary anode tubes, what consists of a tungsten alloy embedded in the copper anode?
In rotating anode tubes, the entire rotating disc is the ____.
What is the material of choice for the target for general radiography?
Tungsten is the material of choice for the target for general radiography for three main reason:
high melting point
Tungsten results in high-efficiency x-ray production and in high-energy x-rays
Atomic number, 74
Tungsten nearly equal to that of copper. It is therfore an efficient metal for dissipating the heat produced.
Any material, if heated sufficiently, will melt and become liquid
High melting point (3400 degrees C compared with 1100 degrees C)
X-ray tube allows the electron beam to interact with a much larger target area: therefore heating of the anode is not confined to one small spot, as in a stationary anode tube.
Higher tube currents and shorter exposure times are possible with which anode
What electromagnetic motor is used to turn the anode?
What is powered by an electromagnetic induction motor?
What is the area of the target from which x-rays are emitted
the focal spot
What spot is required in the Line-Focus Principle for the better spatial resolution of the image
small focal spots (because the smaller the focal spot, the better)
Unfortunately, as the size of the focal spot decreases, the heating of the target is concentrated onto a smaller area; This is the limiting factor to ____ ____ ____.
focal spot size
What is the actual x-ray source
Before the rotating anode was developed, another design was incorporated into x-ray tube targets to allow a large area for heating while maintaining a small focal spot; this design is known as
Diagnostic x-ray tubes have target angles that vary from approx ___ to ___ degrees.
5 to 20 degrees
What results in an effective focal spot size much less than the actual focal spot size?
What is one unfortunate consequence of the line-focus principle is that the radiation intensity on the cathode side of the x-ray field is greater than that on the anode side?
What interact with target atoms at various depths into the target?
The ____ the anode angle, the ____ the heel effect. (larger or smaller)
What effect results in reduced x-ray intensity on the anode side of the useful beam caused by absorption in the "heel" of the target?
The difference in radiation intensity across the useful beam of an x-ray field can vary by as much as ___ %
What is the useful beam is the imaginary line generated by the centermost x-ray in the beam?
If the radiation intensity along the central ray is designated as ____ %, than the intensity on the cathode side may be as high as ___ %, and that on the anode side may be as low as ___ %
What effect is important when one is imaging anatomical structures that differ greatly in thickness or mass density?
In general, positioning the cathode side of the x-ray tube over the thicker part of the anatomy provides more uniform radiation exposure of the image receptor
What effect results in smaller effective focal spot and less radiation intensity on the anode side of the x-ray beam?
X-ray tubes are designed so that projectile electrons from the cathode interact with the target only at the focal spot.
Some of the electrons bounce off the focal spot and then land on other areas of the target, causing x-rays to be proced frome outside of the ____ ____.
focal spot (called off-focus radiation)
What are the 3 ways heat can be dissipated?
What is the transfer of heat by the emission of infrared radiation. Heat lamps emit not only visible light but also infrared radiation?
What is the transfer of energy from one area of an object to another. The handle of a heated iron skillet becomes hot because of this?
What is the transfer of heat by the movement of a heated substance form one place to another. Many homes and offices are heated by this?
What results in reduced x-ray tube life?
Maximum radiographic techniques should never be applied to a cold anode
Example: just like your car has to warm up
A second type of x-ray tube failure results from maintaining the anode at elevated temperatures for prolonged periods.
A final cause of tube failure involved the ____.
The most frequent cause of abrupt tube failure is electron arcing from the filament to the enclosure beacuse of the ____ ____.
What is the primary support structure for the x-ray tube, which allows the greatest ease of movement and range of position?
ceiling support system
What covers the x-ray tube and provides the following 3 functions?
What are the 3 funcitons of protective housing?
reduces leakage radiation to less than 1 mGya/hr at 1 m
provides mechanical support, thereby protecting the tube from damage
serves as a way to conduct heat away from the x-ray tube target
What surrounds the cathode (-) and the anode (+), which are the electrodes of the vacuum tube?
glass or metal enclosure
What contains the tungsten filament, which is the source electrons?
What anode is the tungsten-rhenium disc, which serves as a target for electrons accelerated from the cathode?
What results from angled targets?
What is the variation in x-ray intensity across the x-ray beam that results from absorption of x-rays in the heel of the target?
Safe operation of the x-ray tube is the responsibilty of who?
Tube failure can be prevented. There are 3 caused of tube failure:
A single excessive exposure causes pitting or cracking of the anode.
Long exposure time causes excessive heating of the anode, resulting in damge to the bearing in the rotor assembly. bearing damage causes warping & rotational friction of the anode
Even with normal use, vaporization of the filament causes tungsten to coat the glass or metal enclosures; this eventually causes arcing