Xray Tube ch5 Principle of imaging

What 4 things are needed to produce X-rays ?

-Source of free electrons
-A form of accelerating electrons
-A way to focus the electrons
-A means to decelerate these electrons

Thermionic emission is ?

filament heats up - mA / BOILING OFF OF E-

Cathode charge?

negative charged side of X-ray tube

What is a means of accelerating electrons from Cathode to Anode?

Potential difference ( EMF/Voltage) kVp =kilo-voltage peak

How to focus the electrons?

Focusing cup focuses the electrons toward anode and made of Molybdenum or nickle

How to decelerate these electrons

rapidly stopping sudden deceleration by smashing into Anode- positive side made of Tungsten-Rhenium

x-ray tube name? Uses what kinda of energy?

COOLIDGE TUBE / VACCUM TUBE
-Electrical device used for the generation of x-ray photons.
-The energy of the x-rays is dependent on the kinetic energy of the electrons.

Glass envelope made of what? Why?

Pyrex Glass - wont crack under high heat

Cathode 2 primary parts

Filament -Dual filament
Focusing cup -Along with associated electrical wiring

Filament is the source of what? Made of what?

-source of electrons.
- coils made of tungsten wire

thermionic emission

The release of E- from the filament, forming space charge(thermionic cloud) around the focusing cup.

caused by increased energy (mA) = increased heat

boiling off electrons

If you increase the mA, what happens?

you increase the filament current = which increases tube current = increased heat = more E- boiled off = leads to more x-ray photons being created

Space charge

Electrons in outer orbits are flung out forming an "electron cloud" or "space charge".
provides the electron source for x-ray production.

focusing cup holds what? Made of?

houses the filaments and associated wires
-Made of Molybdenum or Nickle

What is the focusing cups charge? And why?

Focusing cup = negativity charged
needs to be negative to make it easier for the E- clouds to travel to the anode

When the kVp is applied what happens to the focusing cup

electrons are focused into a narrow beam
Directed from the cathode toward the Anode to the area of the focal track

What is kVp? The higher the kVp the......?

kilovoltage peak
-forces the electrons across the tube giving them kinetic energy
-higher the kVp the more energy the accelerating electrons will have

Anode

Positively charged electrode

Two types of Anodes

Stationary anode - Dental X-rays
Rotating anode- Medical x-rays

Deceleration of Electrons

electrons decelerate when they strike the anode

Why do we use tungsten for the anode? (3)

has a high atomic number (74)
a high melting point,
great heat-conducting ability

E- Percentage of heat produced vs XRay photons produced

99% of electrons are absorbed as heat
1% of electrons are created into x-ray photons through target interactions.

What is mA?

Milliampere = current =flow of electrons

How do we accelerate electrons?

kVp = kilo voltage peak

Why is the envelope vacuum sealed?

Vacuum sealed so electrons wont interact with other molecules, this makes for greater image quality

A current (mA) passes through and heats up the filament.
increased energy releases E- from the filament through thermionic emission. T or F

True

Anode neck made of? Anode base made of?

Neck = Molybdenum

base= copper bar

Rotating anode heating capacity?

RPM 3,200- 10,000RPM

Benefits of a rotating anode?

-Provide greater target area and heat dissipation
-greater exposure loads by providing larger area for electron beam

What is an actual spot?

Is where the electrons interact with the anode
(smash into the anode) physical area
larger quantity

What is the effective spot?

Is what exits the tube and interacts with the patient
(X-ray beam)
Smaller quantity

Focal track

Portion of impact

What is Line focus principle?

The relationship between actual focal spot on the anode surface and the effective focal spot size

Does the anode angle affect the size of the effective focal spot?

Yes

Smaller Anode angle means?

Steeper
smaller effective focal spot

Larger anode angle means?

Tilted back more
larger effective focal spot

Anode heel effect refers to what?

To the lower field intensity towards the anode compared to the cathode due to x-ray emission

anode <=============================cathode
. . . . . . .. . . . . ...............................

FAT CAT

Put the thicker part under the "cat"hode

The anode surface is flat. T or F

False it is angled

Where is the anode heel? Heel acts as?

The lower back corner of the anode disc

acts as a form of inherent filtration

What is the advantage of the heel effect?

-Helps get ideal imaging when imaging anatomical parts that are unequal in thickness and densities
-helps avoid unbalanced exposure

Anode is on what side of the x-ray tube?

Left side

Examples of when to use the Anode heel effect

AP Chest
AP T-spine
AP femur
AP foot
AP humerus

What does the induction motor do? Consist of?

Responsible for driving the rotating anode using electromagnetic induction
- consists of rotor and stator

What does the Stator do? Location?

Develops a magnetic felid from the current flowing into it.
- causes the rotor to rotate -
(only part of the X-ray tube outside the glass envelope)

Rotor rotates what?

Anode

The glass envelope sits in an oil bath or contain cooling fans that helps cool the X-ray tube. T or F

True

X-rays are emitted isotropically meaning?

X-rays are emitted isotropically meaning in all direction with equal intensity

Useful beam is a ?

X-ray emitted throw the window

X-rays emitted from any other portion of the housing are called?

Leakage

Lead housing reduces radiation leakage to....

Less than 1 mGy/hr at 1m

Lead lining protective housing is for?

-Preventing excessive radiation exposure
-preventing electrical shock to everyone
-protects X-ray tube from damage

Tube rating chart indicates what?

Shows the maximum exposure values that may be made w/o damage to the X-ray tube
(show kVp and mA)

On a tube rating chart, the (x,y axis point) anything

SAFE mA line
.
Point on your axis
.
UNSAFE mA line

Calculate For a single phase unit

HU = 1 x kVp x mA x s

Calculate 3 phase 6 pulse unit

HU = 1.35 x kVp x mA x s

Calculate 3 phase 12 pulse unit

HU = 1.41 x kVp x mA x s

Calculate High frequency unit

HU = 1.44 x kVp x mA x s

Why should we warm-up?

It prevents cracking the anode

When should we warm up anode/Xray tube?

Should be done at least every two 2 without shooting

What is the number 1 reason for X-ray tube failure?

Tube Arcing - vaporizing tungsten collection on envelope (blurry grey film)

What is the average exposure lifecycle of an X-ray tube?

10,000 - 20,000 exposures

How to extend x-ray tube life? (6)

- warm up X-ray tube
- avoid frequent boosting (holding done button for too long)
- use low mA
- use low Speed on rotor
- avoid rough handling of X-ray tube
- listen for abnormal sounds