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RT 209 > 5. X-ray Machine and Tube > Flashcards

5. X-ray Machine and Tube Flashcards

1
Q

3 MAIN COMPONENTS OF AN X-RAY IMAGING SYSTEM

A
  • X-ray tube
  • Operating console
  • High voltage generator
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2
Q

a vacuum tube containing electrode that accelerate electrons and direct them to a metal anode, where their impacts produce x-rays

A

X-ray Tube

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3
Q

EXTERNAL COMPONENTS

A
  • Support structure
  • Protective housing
  • Glass or metal enclosure
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4
Q

consists of two perpendicular sets of ceiling-mounted rails

A

Ceiling Support System

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5
Q

has a single column with rollers at each end

A

Floor to Ceiling Support System

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6
Q

the image receptor is attach to the end of the C-arm from the x-ray tube

A

C-arm Support System

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7
Q

guards against excessive radiation exposure and electrical shock

A

Protective Housing

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8
Q

is made up of pyrex to withstand the tremendous heat generated

A

Glass or Metal Envelope

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9
Q

is the area of the glass or metal enclosure approximately 5 cm2, that is thin and through which the useful beam of x-rays is emitted

A

X-ray Tube Window

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10
Q

X-rays emitted through the window is called the

A

useful beam

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11
Q

X-rays that escaped through the tube housing are called

A

leakage radiation

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12
Q

Leakage radiation should not exceed ______ when operated at maximum condition

A

100 mR/hr at 1 m

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13
Q

INTERNAL COMPONENTS

A
  • Cathode

* Anode

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14
Q

is the negative side of the x-ray tube and had two primary parts: a filament and a focusing cup

A

Cathode

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15
Q

usually approximately 2mm in diameter and 1 or 2 cm long

A

Filament

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16
Q

when the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are “boiled off” and ejected from the filament

A

Thermionic Emission

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17
Q

Filaments are usually made of

A

thoriated tungsten

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18
Q

Filaments are usually made of thoriated tungsten because

A
  • Tungsten have high melting point (3410 C)
  • Does not vaporize easily
  • Addition of 1% to 2% thorium to tungsten increases the efficiency of thermionic emission
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19
Q

where the filaments are embedded

A

Focusing Cup

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20
Q

is used when better spatial resolution is required. Ranges from 0.1 to 1 mm

A

small focal spot

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21
Q

is used when large body parts are imaged and when other techniques that produce high are required

A

large focal spot

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22
Q

is the positive side of the x-ray tube

A

Anode

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23
Q

it conducts electricity and radiates heat and contains the target

A

Anode

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24
Q

FUNCTIONS OF ANODE ASSEMBLY

A
  • Electrical conductor
  • Mechanical support
  • Thermal dissipator
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25
area of the anode struck by the electrons from the cathode
Target
26
TYPES OF ANODE
* Stationary anode | * Rotating anode
27
are used in dental x-ray imaging systems, some portable imaging systems, and other-purpose units in which high tube current and power are not required
Stationary Anode
28
capable of producing high intensity x-ray beam
Rotating Anode
29
heat capacity can be further improved by increasing the speed of anode rotation
Rotating Anode
30
Rotating Anode rotates
3400 rpm and 10,000 rpm
31
the target is consists of tungsten alloy embedded in a copper anode
stationary anode tubes
32
stationary anode tubes size
About 4 mm^2
33
the entire rotating disc is the target
rotating anode tubes
34
rotating anode tubes size
About 3159 mm^2
35
Tungsten is the material of choice for the target for general radiography for 3 main reasons
* Atomic number * Thermal conductivity * High melting point
36
specialty x-ray tubes for mammography have ______ targets principally because of their low atomic number and low K characteristics x-ray energy
molybdenum or rhodium
37
is powered by an electromagnetic induction motor
rotating anode
38
an induction motor is consist of 2 parts:
the stator and the rotor
39
is the actual x-ray source
Focal Spot
40
results in an effective focal spot size much less than the actual focal spot size
Line-Focus Principle (Goetze Principle)
41
diagnostic x-ray tubes have target angles that vary from approximately ____ degrees
5 to 20
42
radiation intensity is greater on the cathode side of the x-ray field than that on the anode side
Heel Effect
43
the smaller the anode angle, the ____ is the heel effect
larger
44
greater anode angle _____ useful beam
wider
45
electrons bounce off the focal spot and then land on other areas of the target, causing x-rays to be produced from outside of the focal spot
Off Focus Radiation
46
WAYS HOW TO EXTEND X-RAY TUBE LIFE SPAN
* X-ray tube life may be extended by using minimum radiographic factors of ma, kVp, and exposure time appropriate for each examination * Use of faster image receptors * Excessive heat results in reduced x-ray tube life
47
3 WAYS TO DISSIPATE HEAT
* Radiation * Conduction * Convection
48
CAUSES OF X-RAY TUBE FAILURE
* Vaporized tungsten * Rotor bearings breakage * Anode pitting * Cracked anode
49
3 types of x-ray tube rating charts significant to radiologic technologist
* Radiographic rating chart * Anode cooling chart * Housing cooling chart
50
The capacity of the anode and the housing to store heat is measured in
Heat Units (HU)
51
One heat unit is equal to the product of
1 kVp, 1 mA, and 1s
52
SINGLE-PHASE Heat Unit
HU = kVp x mA x s
53
THREE-PHASE/HIGH-FREQUENCY Heat Units
HU = 1.4 x kVp x mA x s
54
1 HU =
1 HU = 1.4 J
55
1 J =
1 J = 0.7 HU
56
Radiographic x-ray tube housings usually have ______ heat capacities in the range of several million heat units
maximum
57
Complete cooling after maximum heat capacity requires from
1 to 2 hours
58
transfers heat from focal spot track to anode body
Conduction
59
transfers heat from focal spot track to tube housing
Radiation
60
transfers heat from tube housing to the atmosphere
Convection
61
atomic number of Niobium
41
62
atomic number of Silicon
14
63
atomic number of Germanium
32
64
atomic number of Titanium
22
65
atomic number of Molybdenum
42
66
atomic number of Rhodium
45
67
k-shell binding energy of Molybdenum
19 keV
68
k-shell binding energy of Rhodium
23 keV

RT 209 (11 decks)

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