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Physics - Test 4
Chapter 6
32
Anatomy
Undergraduate 1
11/02/2017

Additional Anatomy Flashcards

 


 

Cards

Term
Describe the space-charge effect
Definition
As electrons build, their charges begin to oppose the emission of additional electrons, limiting the mA range to 1000-1,200
Term
What is the atomic # of tungsten?
Definition

74 

 

Symbol of "W"

Term
What is the only part of the anode or cathode assembly that is located outside the vacuum of the glass envelope?
Definition
The Stator
Term
According to the NCRP, what is the maximum allowable radiation leakage from the tube?
Definition

Must not exceed 100 mR/hr

 

(at 1 meter from the tube)

Term
What is the primary purpose of the tube glass housing?
Definition

The envelope is the glass housing that protects the tube.

 

(Also, to provide a vacuum, permitting electrons to flow from cathode to anode without interacting with atoms in air.)

Term
Describe the anode-heel effect
Definition
Due to the geometry of the angled anode target, the radiation intensity is greater on the cathode side.
Term
Describe the Actual Focal Spot (AFS)
Definition
The physical area on the focal track that is impacted.
Term
Describe the Effective Focal Spot (EFS)
Definition
Area that is projected out of the tube
Term
How does the Line Focus Principle relate to EFS?
Definition

Used to reduce the EFS thus increasing resolution.

 

** permits the best resolution of detail while permitting as large as actual area as possible.

Term
Describe the focusing cup and what it does.
Definition

Shallow depression in the cathode assembly that houses the filaments - made of nickel.

 

Operates to narrow or focus the electron cloud during thermionic emission to be directed toward anode

 

Term
What is responsible for the noise during rotor acceleration?
Definition
Ball bearings inside the cuff of the rotor
Term
Describe what it means when the x-ray tube is gassy.
Definition
During thermionic emission, if vaporization occurs, you end up with a gassy tube which decreases the vacuum inside the glass envelope.
Term
What material commonly makes up the target for mammographic units?
Definition

Molybdenum (atomic # 42)

 

** because of it's ability to give a more uniform range

of lower energy photons.

Term

What material is used for the anode target area?

Why is it used?

Definition

Tungsten

 

  1. Higher x-ray production efficiency
  2. Thermal conductivity
  3. High melting point
Term
What happens if the stator malfunctions?
Definition

The rotor will not turn and a spot will melt on the anode.

 

(picture p. 119)

Term
What happens if the rotor malfunctions?
Definition
A malfunctioning bearing can prevent the rotor from turning and produce melting in one spot on the anode.
Term
Describe the filament
Definition
A coil of thin tungsten wire set within the focusing cup
Term
Why is the filament made of tungsten?
Definition
  1. High atomic # of 74 - has higher x-ray production efficiency
  2. Thermal conductivity
  3. High melting point
Term
Is the Cathode side of the tube negative or positive?
Definition
Negative
Term
Is the anode side of an x-ray tube negative or positive?
Definition
Positive
Term

Why is a rotating anode more desirable

than a stationary anode?

Definition

There is better heat dissipation from the rotating anodes, which permits bombardment of electrons from the filament to a given area in a short amount of time.

 

Stationary anodes are low-power and inefficient for heat dissipation.

Term
What is the Heat Units (HU) formula?
Definition
kVp x mA x time x rectification constant = HU
Term

What are the 4 main components of the

x-ray tube assembly?

Definition
  1. Cathode (the source of electrons)
  2. Anode (target)
  3. Glass envelope (vacuum)
  4. Protective housing (made of very heavy lead)
Term
What 3 things make the Cathode assembly?
Definition
  1. Filament(s)
  2. Focusing cup (located in the filament)
  3. Associated wiring
Term
What 3 things make up the anode assembly?
Definition
  1. Anode
  2. Stator
  3. Rotor
Term
What are the 3 functions of the Anode assembly?
Definition
  1. Serve as target surface for electrons from the filament, eventually becoming the source of x-ray photons
  2. Conducts high-voltage from the cathode back into the generator circuitry
  3. Serves as the primary thermal conductor

** x-ray photons are made at the anode **

Term
List other names for the 'Target Area'
Definition

Target

Focus

Focal point

Focal spot

Focal track

Term
Where do you measure the "source" when measuring for SID?
Definition

Target Area

(portion of the anode where focused electron stream impacts)

Term
Describe Thermionic Emission
Definition
The negative electrode (also called the cathode) is a wire filament that emits electrons when heated. This process is called thermionic emission and the wire filament is called an 'electron gun'.
Term
What are 'Tube Rating Charts'?
Definition
They provide a guide to the maximum technical factors that can be set without overheating the tube.
Term
What is an 'Anode Cooling Chart'?
Definition
Permits calculation of time necessary for anode to cool enough for additional exposures to be made.
Term
Describe 'Off focus radiation'
Definition

Composed of photons that were not

produced at the focal spot.

 

These photons are produced away from the focal spot and have sufficient

energy that when they strike another object in the tube, they

produce photons and can produce an image.

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