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Physics > Xray Production, Xray Tubes And Xray Generators > Flashcards

Xray Production, Xray Tubes And Xray Generators Flashcards

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1
Q

A device that produces xrays in diagnostic energy range typically contains

A
  • An electron source
  • Evacuated path for electron acceleration
  • target electrode
  • external power source
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2
Q

Contains electron source

A

Xray tube insert

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3
Q

Provides protective radiation shielding and cools the xray tube insert

A

Tube housing

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4
Q

Supplies the voltage to accelerate the electrons

A

Xray generator

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5
Q

Shapes the xray energy spectrum

A

Xray beam filters

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6
Q

Define the size and shape of the xray field incident on the patient

A

Collimators

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7
Q

Source of electrons

A

Cathode

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8
Q

Target of electrons

A

Anode

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9
Q

Vast majority of interactions are

A

Collisional

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10
Q

Amount of energy lost by the electron and thus the energy pf the resulting xray is determined by the

A

Distance between the incident electron and the target nucleus

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11
Q

With increasing distance from the nucleus, the circumference increases, therefore the probability of interaction _______ but the xray energy ________

A

Interaction increase

Xray energy decrease

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12
Q

As the interaction distance decreases, xray energy increases because of

A

Greater electron deceleration

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13
Q

Probability distribution of xray photons as a function of photon energy (keV)

A

Bremsstrahlung spectrum

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14
Q

Shows an inverse linear relationship between the number and the energy of the xrays produced, with the highest xray energy determined by the peak voltage applied across the xray tube

A

Unfiltered bremsstrahlung spectrum

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15
Q

A typical filtered bremsstrahlung spectrum has no xrays below about

A

10 keV

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16
Q

Major factors that affect xray production efficiency include

A

Atomic number of the target material

Kinetic energy of the incident electrons

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17
Q

Most common target material in xray is

A

Tungsten

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18
Q

Most common target material in mammography is

A

Molybdenum and rhodium

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19
Q

The innermost shell designated as the ____ shell has the highest electron binding energy

A

K shell

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20
Q

Xray tube voltages must be greater than ___ kV for tungsten
____ kV for moldybdenum
____ kV for rhodium

A

69.5 tungsten
20 molybdenum
23 rhodium

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21
Q

Xray tube voltage is set to values from ___ to _____ kV for diagnostic imaging

A

40 to 150 kV

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22
Q

Voltage for mammo is set typically to

A

25 to 40 kV

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23
Q

Xray tube current in projection radiography

A

50-1200 mA

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24
Q

Tube current in continuous flouroscopy

A

1-5 mA

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25
Q

In pulsed fluoroscopy, tube current is set to

A

10-50 mA

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26
Q

3 major selectable parameters on the xray generator control panel that determine the xray beam characteristics

A

kV, mA and exposure time

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27
Q

It has a focusing cup totally insulated from the filament wires so that its voltage is independent of the filament

A

Biased xray

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28
Q

Xray tube that has a capability of rapidly switching the xray beam on and off

A

Grid-biased xray tube

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29
Q

A metal target electrode that is maintained at a large positive potential difference relative to the cathode

A

Anode

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30
Q

Widely used anode material because of its high melting point and high atomic number

A

Tungsten

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31
Q

Mechanically supports the tungsten insert and efficiently conducts heat from the tungsten target

A

Copper

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32
Q

Heat insensitive parts in the rotor anode

A

Non-volatile lubricant
Molybdenum
Infrared radiation emission

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33
Q

Angle of target surface with respect to the central ray im the xray field

A

Anode angle

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34
Q

Anode angles in xray tubes typically range from

A

7-20 degrees

12-14 degrees most common

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35
Q

Foreshortening of the focal spot length at the central ray is called the

A

Line focus principle

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36
Q

A small anode angle (7-9 degrees) is desirable for_____ field of view devices

A

Small field

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37
Q

Larger anode angles (12-15 degrees) are necessary for

A

General radiography

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38
Q

Common tools for measuring focal spot size are the

A

Pinhole camera, slit camera, star pattern and resolution bar pattern

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39
Q

Uses very small circular aperture (10-30 um diameter) in a thin, attenuating metal disk to project a magnified image of the focal spot onto an image receptor

A

Pinhole camera

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40
Q

Consists of a highly attenuating metal plate with a thin slit

A

Slit camera

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41
Q

Contains a radial pattern of lead spokes of diminishing width and spacing on a thin plastic disk

A

Star pattern tool

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42
Q

A simple tool for evaluation of focal spot size. It demonstrates the effective resolution parallel and perpendicular to the A-C axis for a given magnification geometry, determined from the number of bar pattern that can be resolved

A

Resolution bar pattern

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43
Q

An increase in the size of the focal spot resulting from high tube current and is caused by electron repulsion in the electron beam between the cathode and anode

A

Focal spot “blooming”

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44
Q

Refers to reduction in the xray beam intensity toward the anode side of the xray field caused by greater attenuation of xrays directed toward the anode side of the field by the anode itself

A

Heel effect

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45
Q

Heel effect is less prominent with a ______ source to image distance

A

Longer

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46
Q

Results from electrons that scatter from the anode, and are reaccelerated back to the anode, outside of the focal spot area

A

Off-focal radiation

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47
Q

Can reduce off-focal radiation by intercepting xrays that are produced away from the focal spot

A

Small lead collimator

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48
Q

Contains the cathode, anode, rotor assembly and support structures sealed in a glass or metal enclosure under a high vacuum

A

Xray tube insert

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49
Q

Used to trap gas in the insert and to maintain the vacuum

A

“Getter” circuit

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50
Q

Adjusts the size and shape of the xray field emerging from the tube port

A

Collimators

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51
Q

Collimator that automatically limit the field size to the useful area of detector

A

Positive beam limitation collimators

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52
Q

Grid-biased tube is used in applications such as

A

Pulsed fluoroscopy and cine-angiography

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53
Q

The output port of mammogram is made of

A

Beryllium/glass/metal insert material

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54
Q

Dynamic steering of the electron beam within the tube is achieved by _______ to direct the electrons to distinct focal spots on the anode, which can produce slightly different projections and improve data sampling during the CT acquisition

A

External electromagnetic deflection coils

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55
Q

Recommendations to maximize xray tube life:

A
  • Minimize filament boost “prep” time especially when high mA is used
  • use lower tube current with longer exposure time to arrive at the desired mAs if possible
  • avoid extended or repeated operation of the xray tube with high technique factors (kV and mAs)
  • always follow the manufacturer’s recommended warm-up procedure
  • limit rotor start and stop operations; 30-40 sec delay should be used
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56
Q

Removal of xrays as the beam passes thru a layer of material

A

Filtration

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57
Q

Filtration includes

A

Inherent filtration of the xray

And added filtration

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58
Q

Includes the thickness (1-2 mm) of the glass or metal insert at the xray tube port

A

Inherent filtration

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59
Q

Glass used for filtration

A

Silicon dioxide

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60
Q

Inherent filtration include attenuation by

A

Housing oil and field light mirror in the collimator assembly

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61
Q

It refers to sheets of metal intentionally placed in the beam to change its effective energy

A

Added filtration

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62
Q

What element is the most commonly used added filter material

A

Aluminum

Others include copper and plastic

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63
Q

In mammography, thin filters of ____, _____ and ____ are used to transmit bremsstrahlung xrays in the intermediate energy range (15-25 keV)

A

Molybdenum
Rhodium
Silver

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64
Q

Filters that are used to change the spatial pattern of the xray intensity incident on the patient, so as to deliver a more uniform xray exposure to the detector

A

Compensation (equalization) filters

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65
Q

Filters that are useful for lateral projections in cervical-thoracic spine imaging, where the incident fluence is increased to match the increased tissue thickness encountered

A

Wedge filters

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66
Q

Filters that are used in ct to reduce dose to the periphery of the patient, where the xray paths are shorter and fewer xrays are required

A

“Bow-tie” filters

67
Q

Principal function of an xray generator is to provide current at _____ voltage to an xray tube

A

High

68
Q

Transformers convert low voltage into high voltage thru a process called

A

Electromagnetic induction

69
Q

Phenomenon in which a changing magnetic field induces an electrical potential difference (voltage) in a nearby conductor and also in which a voltage is induced in a conductor moving thru a stationary magnetic field

A

Electromagnetic induction

70
Q

Magnitude of the induced voltage is proportional/inversely proportional to the rate of change of the magnetic field strength

A

Proportional

71
Q

Electric current, such as the electrons flowing thru a wire,
Produces a magnetic field whose magnitude (strength ) is proportional/inversely proportional to the magnitude of the current

A

Proportional

72
Q

Uses the principle of electromagnetic induction to change the voltage of an electrical power source

A

Transformer

73
Q

Direction of the current is dependent on the

A

Direction of the magnetic field

74
Q

The polarity and magnetic field strength are determined by the

A

Amplitude and direction of the current

75
Q

A basic transformer consist of

A

Iron core
Primary winding circuit
Secondary winding circuit

76
Q

Allows current to flow in one direction only

A

Rectifier

77
Q

Can route the flow of electrons thru an AC circuit to create a direct current (DC) a unidirectional movement of electrons in which the voltage polarity never reverses

A

Bridge rectifier circuit

78
Q

A device with 2 terminals

A

Diode

79
Q

Rate of energy production or expenditure per unit time

A

Power

80
Q

Power is equal to the product of

A

Voltage and current

81
Q

SI unit for power

A

Watts- 1 joule/sec

82
Q

Defined as 1 joule per coulomb

A

Volt

83
Q

Defined as 1 coulomb/sec

A

Ampere

84
Q

The focal spot size is usually determined by what setting

A

mA setting

85
Q

Measures the actual amount of radiation incident in the image receptor and terminate xray production when the proper radiation exposure is obtained

A

Phototimer/ automatic exposure control

86
Q

Maximal power that an xray tube focal spot can accept or the generator can deliver

A

Power rating

87
Q

Traditional unit that provides a simple way of expressing the energy deposition on and dissipation from the anode of an xray tube

A

Heat unit

88
Q

Constant voltage that would deliver the same power as a varying voltage waveform

A

Root-mean-square voltage

89
Q

Describes the penetrability of an xray beam with a higher energy xray photons having a larger half value layer and higher quality

A

Quality

90
Q

Refers to number of photons comprising the beam

A

Quantity

91
Q

It is nearly proportional to the energy fluence of the xray beam

A

Exposure

92
Q

Xray production efficiency, exposure, quality and quantity are determined by 6 major factors

A 
Xray tube target material
Tube voltage
Tube current
Exposure time
Beam filtration
Generator waveform
93
Q

Affects the efficiency of bremsstrahlung radiation

A

Anode target material

94
Q

Affects the quality of output spectrum

A

Tube voltage

95
Q

It is proportional to the number of electrons flowing from the cathode to the anode per unit time

A

Tube current

96
Q

It modifies the quantity and quality of xray beam by preferentially removing the low energy photons in the spectrum. It reduces the number of photons (quantity) and increases the average energy, also increasing the quality

A

Beam filtration

97
Q

Affects the quality of the emitted xray spectrum

A

Generator waveform

98
Q

Xray quality depends on the

A

kV, generator waveform and tube filtration

99
Q

Compensation for changes in kV with radiographic techniques requires adjustments of mAs on the order of ___ to ____ power of the kV ratio

A

4th to 5th

100
Q

kV determines

A

Quantity, quality and transmission

101
Q

mAs determines

A

Quantity only

102
Q

Production of a 2 dimensional image from a 3 dimensional object

A

Radiography

103
Q

Magnification would always be greater than ____

A

1

104
Q

For most radiographic examinations, the source to image distance is fixed at 100cm, except for upright chest radiography where the SID is typically set to

A

183 cm or 72 inches

105
Q

Higher object magnification increases the width of the ____ and reduces the spatial resolution of the image

A

Edge gradient

106
Q

Film is composed of a thin plastic base coated on one or both sides with a layer of high-sensitive emulsion consisting of

A

Silver halide

107
Q

It is a protrusion of the positive charge that reaches the surface of the crystal, induced by the lattice defects by silver monosulfide (AgS)

A

Sensitivity speck

108
Q

Slight difference in film density depending on the exposure rate is called

A

Reciprocity law failure

109
Q

A grain of reduced metallic silver atoms appears as ____ on the film

A

Black speck

110
Q

The film developer contains the

A

Aqueous chemical bath containing reducing agent

111
Q

After the film has passed thru the developer, it passes thru a bath of an aqueous oxidizing solution called ______ that dissolves the remaining (inactivated) silver halide from the emulsion layer areas that were not exposed (or underexposed) to light

A

Fixer

112
Q

After rinsing the film with water and allowing to dry, _______ striking the film emulsion acts locally to cause film darkening

A

Visible light

113
Q

Refers to photostimulable phosphor detector system which are historically housed in a cassette similar to screen film cassette

A

Computed radiography

114
Q

Traditionally scintilators that emit light promptly (nearly instantaneously) when irradiated by an xray beam

A

Gadolinium sulfide oxide and cesium iodide

115
Q

Light that is emitted from the screen that has shorter wavelength and higher energy per photon than the stimulating red light

A

Blue light

116
Q

Typical imaging plates are composed of about 85% ____ and 15% _____ activated with a small quantity of europium

A

85% BaFBr

15% BaFI

117
Q

The activation procedure called _____, creates defects in the BaFBr crystals that allow electrons to be trapped more efficiently

A

Doping

118
Q

Used in commercial grade television cameras and in scientific applications such as astronomy, which form images from visible light

A

Charge-coupled device detectors

119
Q

Charge-coupled device chip itself is an integrated circuit made of

A

Crystalline silicon

120
Q

Xray photons, visible photons and electrons are all forms of _____

A

Quanta

121
Q

Refers to the stage where the number of quanta is the lowest and therefore where the statistical integrity of the signal is the worst

A

Quantum sink

122
Q

Alternative to charged-coupled device

A

Complementary metal-oxide semiconductor

123
Q

Pixelated discrete detector systems

A

Flat panel detector system

124
Q

The photons in this TFT Propagates laterally, compromising resolution

A

Indirect thin film transistor based xray detectors

125
Q

In this TFT, the ion pairs liberated by xray interaction follow the electric field likes (electron holes travel upwards, electrons travel downwards) and have negligible lateral spread. Here, the detected electronic signal from one x-ray photons interaction is collected almost entirely in one detector element, and therefore better spatial resolution is achieved

A

Direct detector TFT based xray detectors

126
Q

Defined as the amount of energy deposited in a specific location in the detector by scattered photons, divided by the amount of energy deposited by primary (non-scattered) photons in the same location

A

Scatter-to-primary ratio (SPR) or scatter fraction

127
Q

Scatter fraction increases as the field size _____ and as the thickness of the patient ____

A

Field size increases and thickness of patient increases

128
Q

Most widely used technology for reducing scatter in radiography, fluoroscopy and mammography

A

Anti-scatter grid

129
Q

Ratio of the height of the interspace material to its width-the septa dimensions do not affect the grid ratio metric

A

Grid ratio

130
Q

Number of grid septa per centimeter

A

Grid frequency

131
Q

Grid that moves with a reciprocating motion during the xray exposure, causing the grid bars to be blurred by this motion and not visible in the image. This motion is perpendicular to the long axis of the linear septa in the grid

A

Bucky grid

132
Q

Describes the relative increase in xray intensity or equivalently, mAs needed when a grid is used, compared to when a grid is not used

A

Bucky factor

133
Q

Typical values for bucky factor for abdominal radiography range from

A

3 to 8

134
Q

Refers to the reduction in contrast due to scattered radiation

A

Contrast degradation factor

135
Q

Method used in mammography to to reduce scatter

A

Scanning slit (or “slot-scan”) method

136
Q

Most ubiquituous tool for scatter reduction

A

Anti-scatter grid

137
Q

Refers to the actual anode angle plus the physical tube tilt

A

Effective anode angle

138
Q

In mammogram, the anode is placed in the _____, while the cathode is placed in the

A

Anode is on the Anterior portion (nipple)

Cathode is posterior over the chest wall

139
Q

Anode is kept at ground potential and cathode is set to highest negative voltage to reduce

A

Off focal radiation

140
Q

Focal spot nominal sizes for contact mammography

A

0.3 to 0.4 mm

141
Q

Focal spot nominal sizes for magnification imaging

A

0.10 to 0.15 mm

142
Q

In order to avoid exposure of patient’s torsos and maximize the amount of breast tissue near the chest wall that is imaged, all dedicated mammography systems utilize a _____ xray beam geometry which is achieved by fixed collimation at the xray tube head

A

Half field geometry

143
Q

Tube port window in mammogram is made of

A

Beryllium

144
Q

The ideal spectral energy range is at

A

15-25 keV

145
Q

The half value layer is highly dependent on ______ and the HVL if incident xray beam

A

Tissue composition

146
Q

Useful for calculating the free-in-air incident air kerma or exposure to the breast for a mammography system target and filter combination, kV, mAs and source-to-breast surface distance

A

Xray tube output values

147
Q

An xray exposure that is not stopped by the AEC circuit and exceeds a preset time is terminated by a

A

Back up timer

148
Q

Most mammographic techniques use phototiming and proper choice of kV is essential for a reasonable exposure time, defined as a range from approximately

A

0.5 to 2.0 sec

149
Q

Carries information regarding the attenuation characteristics of the breast and delivers the maximum possible subject contrast to the detector

A

Primary radiation

150
Q

An additive, gradually varying radiation distribution that degrades subject contrast and adds random noise

A

Scattered radiation

151
Q

Xray scatter increases with

A

Increasing breast thickness and breast area

152
Q

Bucky factor in mammography is ____ so the breast dose is doubled or tripled

A

2-3

153
Q

Most commonly used screen phosphor in mammogram

A

Terbium activated gadolinium oxysulfide

154
Q

Indication of the amount of incident radiation required to achieve a specified OD on the film

A

Film speed

155
Q

Rate of change of OD For a known difference in incident radiation

A

Film contrast

156
Q

Device that emulates a range of incident radiation exposures by using a constant light source and calibrated optical attenuation steps to expose a mammographic film to known relative light intensities

A

Sensitometer

157
Q

Device that measures the light transmission thru a small area kd the film and calculates the OD

A

Densitometer

158
Q

Luminance in diagnostic radiology is typically about

A

1,500 cd/m2

159
Q

Acceptable illuminance of room lighting for viewing and interpretation of mammograms

A

Subdued room lighting

160
Q

Phosphor that converts xray into light

A

Cesium iodide

161
Q

Describes absorption of cxrays im the cesium iodide, the production of secondary light photons directed to a photodiode and the generation of the charge, which is stored on the storage capacitor in that detector element

A

Indirect conversion

162
Q

Refers to direct generation of charge by xrays within the photoconductor and capture by the electrode within intermediate signals

A

Direct conversion

163
Q

Provide the capability to localize breast lesions in three dimensions and physically sample them with a targeted biopsy instrument

A

Stereotactic breast biopsy

164
Q

Used to measure the air kerma for a given kV, mAs and beam quality

A

Air ionization chamber

Physics (7 decks)

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