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43 Cards in this Set

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What happens when electrons strike the anode
Electrons striking the target, located in the anode, produce heat and x-rays
Why is tungsten the most common anode
Tungsten is the most common target material because of its high atomic number (Z
= 74) and melting point.
What is often added to a tungsten anode
Rhenium is often added to reduce the pitting and cracking caused by overheating.
What is the make up of the anode used for mamography
Molybdenum (Z = 42) and rhodium (Z = 45) are used for targets in mammography.
When are stationary anodes commonly used
Stationary anodes are used in some C-arm x-ray units
What makes up the anode of a stationary anode
A stationary anode usually consists of a tungsten target embedded in a copper
block.
Why do most anodes rotate
A rotating anode greatly increases the effective target area used during an expo-sure and therefore raises the heat capacity.
What is the focal spot
Th e focal spot is the apparent source of x-rays in the tube.
What determine the focal spot size
Focal spot size is a result of the filament shape, focusing cup, and electric field cre-ated between the cathode and anode.
What does a focal spot tract look like
Why do you want a small focal spot
small focal spots make sharper images
Why do you want a large focal spot
larger focal spots can tolerate larger amounts of heat without melting
What are 2 considerations when determing the size of a focal spot
Focal spots must be small to produce sharp images, but large enough to tolerate a
high heat loading without melting the target.
What happens to the size of a focal spot as the current increases
Th e focal spot size enlarges as milliamperes increase owing to the repulsion of ad-jacent electrons. This effect is called blooming.
What are the sizes of focal spots used in radiology
What is the difference between the focal spot and focal tract (last image misleading...correct)
What is the line focus principle
The line focus principle is used to permit larger heat loading while minimizing
the size of the focal spot by orienting the anode at a small angle to the direction of the x-ray beam irradiating the patient
What is the typical anode angle
7-20 degree
What happens to the radiations field coverage as the anode angle increases
Radiation field coverage increases with increased target angle.
What are typical focal spot sizes
Focal spot sizes, as quoted by manufacturers of x-ray tubes, range from about 0.1
to 1.2 mm.
How are focal spot sizes measured
Focal spot sizes can be measured using pinhole cameras, star or bar test patterns, or
slit cameras.
When are large and small focal spot sizes necessary
-A large focal spot is favored when a short exposure time is the priority.
-A small focal spot is preferred when spatial resolution is a priority.
What is the technique to measure the focal spot size with a pin hole
How does an anode angle change the focal spot size
What happens to the focal spot size if the electron beam size is increased
Heel effect
How does a single anode have different anode angles
like this anode
What 3 controls are determined by the operator
I n manual mode, the operator selects the x-ray tube voltage, x-ray tube current, and
exposure time on the generator control panel.
What controls are set by the operator when using the automatic exposure control
I n automatic exposure control (AEC) mode, the operator selects the x-ray voltage
and the desired film density, and the generator circuits control the exposure time
and current (mAs).
What to settings are controlled automaticaly with AEC
millamps
time of exposure
What to settings are controlled by the operator with AEC
voltage
density
What is the X-ray tube output directly proportional to
Th e x-ray tube output is directly proportional to the x-ray tube current.
What is a typical X-ray tube current
A typical current for radiography is 100 to 1,000 mA.
How long is a typical x-ray tube exposure time
Typical radiographic exposure times are between tens and hundreds of millisecond.
How many mAs is there in a given exposure time
Typical tube current exposure times in radiography are tens of mAs.
What is the current in typical flouroscopy
In fluoroscopy, tube currents are typically between 1 and 5 mA.
What is the kVp typically for smaller body parts
Fo r small body parts, such as the extremities, x-ray tube voltages are generally 55
to 65 kVp.
What is the kVp for the majority of plain film and flouro
Most radiographic and fluoroscopy imaging is performed at x-ray tube voltages be-tween 70 and 90 kVp.
Is there usually higher voltages for larger patients
Higher voltages may be used for larger patients.
What is the typical kVp for chest X-rays
Chest radiography is often performed at higher x-ray tube voltages of about 120
kVp.
When is higher kVp used for flouroscopic imaging
High voltages (>10 0 kVp) are also used in some fluoroscopy performed with bar-ium contrast agents to provide sufficient penetration.
What percent of energy is converted to X-rays
Onl y about 1 % of the electric energy supplied to the x-ray tube is converted to x-rays. The rest is converted to heat
What is tube loading
Th e amount of heat energy deposited during an x-ray exposure is known as the tube
loading