the increase in average photon energy when using three-phase, six pulse equipment compared with single-phase equipment is:
the increase in average photon energy when using three-phase, 12 pulse equipment compared with single-phase equipment is:
the collimator must be accurate to a level of:
2% of SID
kVp must be accurate to within
exposure linearity must be accurate to within
exposure reproducibility must be accurate to
when a spinning top test is performed on single-phase equipment, a radiograph exhibiting four dots would indicate:
an accurate timer, if set on 1/30sec
when a spinning top test is performed on three-phase equipment, a timer setting of 1/60sec should indicate the following on the resultant radiograph:
a 6-degree arc
the test that measures the accuracy of adjacent mA stations is
the test that measures the accuracy of successive exposures is
automatic exposure controls may be tested using:
the amount of mA used for fluoroscopy is
3 to 5
marks on the focal track of the anode resulting from bombardment of electrons are called
what is the shortest time with an AEC
1 ms = 0.001
what does the falling load generator do?
calculates the most efficient method of obtaining the required mAs
100% ripple results from which unit containing what type of rectification?
full-wave rectification for single-phase generator with 4 diodes
13% ripple results from rectification of which unit?
three phase, six-pulse
4% ripple results from rectification of which unit?
three phase, 12 pulse
1% ripple results from rectification of which unit?
where are the filaments located in the x-ray tube?
where are the electrons "boiled off" of during exposure?
what does the focusing cup do?
surrounds the filaments on three sides
has negative charge
concentrate electrons boiling off the filaments into a narrower stream and repels them toward the anode
what element are the filaments made up of?
because of its high boiling point
how fast does the anode rotate?
3300 to 10,000 rpm
what controls the rotation of the anode?
induction motor located outside the x-ray tube
what does the target angle of the anode accomplish?
allows for a larger actual focal spot while producting a smaller effective focal spot
what is the actual focal spot?
area bombarded by electrons
what is the effective focal spot?
area seen by the image receptor
what is the "line focus principle"?
the larger the actual spot, the greater the heat capacity
the smaller the effective focal spot, the greater the radiographic image sharpness
how many degrees can a target angle of an anode be?
7 to 20 degrees depending on tube design
what does the glass envelope contain?
cathode and target
Describe how x-rays are created step by step
the x-ray machine is turned on, and a small amount of current is sent to the filament to warm it and ready it for much higher current
radiographer takes equipment through warm up exposures to further warm the filament and the anode
radiographer chooses exposure factors on control console for the exam to be performed
electricity coming into the the radiology department is adjusted by the line voltage compensator in the x-ray equipment to maintain it at a constant level
when making the exposure, the radiographer presses the rotor switch and exposure switch in one continuous motion
the induction motor begins spinning the anode as the filament gets hotter
when the eposure switch is closed, the voltage selected by the mA control flows from the autotransformer, through the variable resistors, and into the step-down transformer in the filament circuit
the filament heats considerably, boils off electrons (thermionic emission), and creates a space charge or electron cloud aroud the filament
at the same time, the alternating current and voltage the radiographer selects by choosing taps off the autotransformer are sent to the primary coils of the high-voltage step-up transformer, where they are boosted to kilovoltage levels
after leaving the secondary coils of the step-up transformer, the voltage and alternating current are sent through the rectifier, which changes the alternating current to pulsating direct current
the kilovoltage creates a high potential difference in the x-ray circuit, making the anode less negative (relatively positive) and the cathode highly negative
this high potential difference causes the electrons to move at very high speed (approximately half the speed of light) from the cathode to the anode
the collision of these projectile electrons with the atoms of the target material causes a conversion of the electrons' kinetic energy (100%) to heat (99.8%) and xrays (0.2%)
heat is produced when the projectile electrons strike the outer shell electrons of the target material and place them in an excited state, which causes them to emit infrared radiation
the production of x-rays comes from two interactions with the anode
what are bremsstrahlung xrays?
xrays formed by a projectile electron missing an outer shell electron in the target and moves in close to the nucleus where it is slowed down (braking) due to repulsion (nucleus is positive and the electron is negative) thus releasing energy in the form of xrays
at diagnostic levels, most xrays are produced from what type of interaction? Bremsstrahlung or characteristic?
what are characteristic xrays?
a projectile electron collides with an inner shell electron of a target atom
it removes that electron from orbit and ionizes the atom
a hole exists in the inner shell from the vacated electron
an electron from an outer shell falls in to fill the hole and releases energy
what determines a characteristic xray's energy?
it is equal to the difference in the binding energies of the shells involve
xrays produced from which shell of an atom are of sufficient energy to be used in radiography?
at what kvp level are characteristic xrays produced?
only in small number
what does the input phosphor do?
convert xray energy to visible light
what does the photocathode do?
converts visbile light, converted by the input phosphor, into electrons
it releases electrons in amounts directly proportional to the visbile light striking it
what are the components of an image intensifier? name the parts in order starting from when xrays first hit it
what does the output phosphor do?
convert electrons from the photocathode into visbile light 50 to 75 times greater
known as flux gain
what is minification gain?
the output phosphor is smaller than the input phosphor, resulting in an increase in brightness
how do you calculate the total brightness gain?
minification gain x flux gain
how is magnification made possible in fluoroscopy?
by varying the voltage flowing through the image-intensifier tube, this changes the size of the area on the input phosphor/photocathode being used
how do you calculate the heat units for a single-phase, full-wave rectified equipment
kvp x mAs
how do you calculate the heat units for a three-phase, six pulse, full-wave rectified equipment?
kvp x mAs x 1.35
(remember this equipment produces x-ray photons with 35% higher average photon energy
how do you calculate the heat units for a three-phase, 12 pulse, full-wave rectified equipment?