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In many cases, digital fluoroscopy eliminates which of the following?
postprocedure "overheads" films
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a photostimulable phosphor is the active component of what piece of equipment?
computed radiogrophy imaging plate
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in computed radiography, the image must be turned into digital form by what device?
analog-to-digital converter
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a mathematical formula used to reconstruct the image in digital imaging is called?
an algorithm
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picture elements in a digital image are called
pixels
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a digital image is composed of rowns and columns known as a
matrix
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direct digital radiography differs from computed radiography in what way?
the use of fixed detectors that communicate directly with the computer
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window width in CR and DR controls what image property?
contrast
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a graphic display that is constructed to show the radiographer the distribution of pixel values is called
a histogram
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the law stating that the outer shell of an atom can contain no more than eight electrons is called
octet rule
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electromagnetic radiation travels in bundles of energy called
photons
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x-rays travel at what speed?
- speed of light
- 186,000 miles per second
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waves of radiation are called
sine waves
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wavelength is defined as the distance from
peak to peak of the wave
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frequency is defined as the
number of waves passing a point per unit time
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wavelength and frequency have a what type of relationship?
inverse proportion
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the x-ray beam will change as it travels through the patient by a process called
attenuation
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what are the two types of electromagnetic induction?
- self-induction
- mutual induction
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self-induction is used in the operation of what device?
autotransformer
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electricity is supplied to the imaging department by a
generator
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the electricity provided to the radiology department is
60Hz AC
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the electricity provided to the radiology department operates at?
120 pulses per second
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high-frequency power
has almost no ripple
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the primary advantage of three-phase power is that
voltage never drops to zero
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a variable transformer that is used to select kVp for the x-ray circuit is the
autotransformer
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a transformer that has more turns in the secondary than in the primary coil is called a
step-up transformer
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voltage coming to the x-ray machine is kept constant through the use of a
line voltage compensator
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where does thermionic emission occur
cathode
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what device is prereading
kVp meter
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what device reduces voltage and provides current to produce an electron cloud or space charge at the filament?
step-down transformer
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what changes AC to DC?
rectifier
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what is surrounded by a negatively charged focusing cup?
filament
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what is composed of solid state, silicon-based diodes?
rectifier
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what measures tube current?
mA meter
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what device spins at 3,300 to 10,000 rpm?
anode
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what is the source of bremsstrahlung and chracteristic rays?
anode
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what is the most commonly used AEC?
ionization chamber
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activating the rotor will
reduce tube life
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the process of thermionic emission causes
electrons to boil off the filament
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the electron stream passes from the cathode to anode because of ______ passing through the x-ray tube
current
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heat is produced in the x-ray tube as
electrons interact with the target material
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most of the energy conversion in the x-ray tube produces
heat
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what percentage of energy in the x-ray tube is converted to x-rays?
1%
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the xray beam is homogenous or heterogenous?
- heterogeneous or polyenergetic
- consists of many different energies (wavelength)
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what is total filtration?
- not less than 2.5 mm aluminum equivalent
- inherent filtration- glass envelope, tube housing, oil
- added filtration - aluminum
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what type of chart may be consulted to determine the safety of a single x-ray exposure?
tube rating chart
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what type of chart may be consulted to determine the safety of a series of x-ray exposures?
anode cooling curve
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the portion of the image-intensifier tube that converts visible light to an electronic image is the
photocathode
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the input phospor of the image-intensifier tube converts
x-ray energy to visible light
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total brightness gain achieved using an image intensifier equals:
flux gain times minification gain
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single phase, full-wave rectification produces:
pulsating direct current with 120 pulses per second and 100% ripple
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three-phase, six pulse full-wave rectification produces:
direct current with 13% ripple
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three-phase, twelve pule full-wave rectification produces:
direct current with 4% ripple
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the increase in average photon energy when using three-phase, six pulse equipment compared with single-phase equipment is:
35%
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the increase in average photon energy when using three-phase, 12 pulse equipment compared with single-phase equipment is:
41%
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the collimator must be accurate to a level of:
2% of SID
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kVp must be accurate to within
4
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exposure linearity must be accurate to within
10%
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exposure reproducibility must be accurate to
5%
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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
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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
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the test that measures the accuracy of adjacent mA stations is
exposure linearity
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the test that measures the accuracy of successive exposures is
exposure reproducibility
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automatic exposure controls may be tested using:
phantoms
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the amount of mA used for fluoroscopy is
3 to 5
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marks on the focal track of the anode resulting from bombardment of electrons are called
pitting
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what is the shortest time with an AEC
1 ms = 0.001
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what does the falling load generator do?
calculates the most efficient method of obtaining the required mAs
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100% ripple results from which unit containing what type of rectification?
full-wave rectification for single-phase generator with 4 diodes
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13% ripple results from rectification of which unit?
three phase, six-pulse
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4% ripple results from rectification of which unit?
three phase, 12 pulse
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1% ripple results from rectification of which unit?
high-frequency unit
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where are the filaments located in the x-ray tube?
cathode side
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where are the electrons "boiled off" of during exposure?
filaments
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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
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what element are the filaments made up of?
- tungsten
- because of its high boiling point
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how fast does the anode rotate?
3300 to 10,000 rpm
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what controls the rotation of the anode?
induction motor located outside the x-ray tube
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what does the target angle of the anode accomplish?
allows for a larger actual focal spot while producting a smaller effective focal spot
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what is the actual focal spot?
area bombarded by electrons
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what is the effective focal spot?
area seen by the image receptor
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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
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how many degrees can a target angle of an anode be?
7 to 20 degrees depending on tube design
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what does the glass envelope contain?
- cathode and target
- vacuum
- tube window
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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
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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
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at diagnostic levels, most xrays are produced from what type of interaction? Bremsstrahlung or characteristic?
brems
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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
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what determines a characteristic xray's energy?
it is equal to the difference in the binding energies of the shells involve
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xrays produced from which shell of an atom are of sufficient energy to be used in radiography?
k shell
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at what kvp level are characteristic xrays produced?
- above 70
- only in small number
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what does the input phosphor do?
convert xray energy to visible light
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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
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what are the components of an image intensifier? name the parts in order starting from when xrays first hit it
- input phosphor
- photocathode
- focusing lens
- output phosphor
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what does the output phosphor do?
- convert electrons from the photocathode into visbile light 50 to 75 times greater
- known as flux gain
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what is minification gain?
the output phosphor is smaller than the input phosphor, resulting in an increase in brightness
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how do you calculate the total brightness gain?
minification gain x flux gain
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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
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how do you calculate the heat units for a single-phase, full-wave rectified equipment
kvp x mAs
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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
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how do you calculate the heat units for a three-phase, 12 pulse, full-wave rectified equipment?
kvp x mAs x 1.41
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