Chapter 5 Power Point (Wednesday Lesson)

Information from PowerPoint (Wednesday Lesson)

Four things needed to produce x-rays

Source of free electrons

A means of accelerating electrons

A way to focus the electrons

A means to decelerate these electrons

Cathode side =

negative

Anode side =

positive

Anode is made of

Tungsten - Rhenium

X-ray tube is a vacuum tube with components contained in a glass or metal enclosure. What kind of glass?

Pyrex

Modern x-ray tubes, ________, is a vacuum tube.

Coolidge tube

2 primary parts of Cathode

Filament (dual filament)

Focusing Cup (associated electrical wiring)

Source of electrons is a _________ at the cathode end of the tube

filament

The filament consists of a

small coil of tungsten wire

Tungsten wire has

High heat capacity

High Atomic # 74

A _______ is passed through the tungsten filament and heats it up

current (mA)

As the tungsten filament is heated up, the increased energy enables electrons to be released from the filament through

thermionic emission (mA, current)

As tungsten is heated, electrons in the tungsten atoms orbits spin faster, moving farther from the nucleus. Electrons in the outer orbits are flung out of the atom, forming an

“electron cloud” or space charge

The _______ provides the electron source for x ray production

space charge

If you increase the mA, you increase the _______, which in turn increases the tube current

filament current

Increases in the mA, filament current, and tube current leads to more

x - ray photons being created

The focusing cup is made of

Molybdenum or Nickle

the focusing cup holds the ______ around the filament wires in a tiny cloud called a space charge until the exposure switch is engaged.

released electrons

When ______ is applied during the exposure the electrons are focused into a narrow beam

kVp

The narrow beam of electrons from the focusing cup are directed from the cathode toward the

Anode to the area of the focal track

kVp stands for

Kilovoltage peak

The higher the kVp the _______ the accelerating electrons will have

more energy

The free electrons must be _______ across the x-ray tube

accelerated

The free electrons must be accelerated across the x-ray tube from

cathode to anode

______, Kilovoltage peak (kVp) forces the electrons across the tube giving them kinetic energy

Voltage

Two types of Anodes

Stationary (dental, lower heat capacity)

Rotating (higher heat capacity)

Purpose of Anode

To decelerate electrons when they hit

The Anode is a _______ disk

Tungsten

__% of electrons are absorbed as heat

99

__% of electrons are created into x-ray photons through target interactions

1

The Anode Arm is made of

copper

How is the anode arm rotated?

Magnetism

The heating capacity of a rotating anode is further enhanced with an increased

RPM (3,200 - 10,000 RPM)

Higher RPM =

Higher heat dissipation

Line Focus Principle is

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

Actual focal spot is

where the electrons interact with anode (target)

Effective focal spot is

what exits the tube and interacts with the patient

Actual =

Larger

Effective =

Smaller

Electron beam size is related

to filament size

Smaller Anode angle =

steeper (smaller effective focal spot)

Larger Anode angle =

titled back more (Larger effective focal spot)

Best images are made from a

smaller effective focal spot

Common Anode angle

7’ - 12’

X-rays are emitted

isotropically

Isotropically =

in all directions with equal intensity (quantity)

X-rays from any other portion of housing is called

leakage

Useful beam x-rays emitted through the

window

____ housing reduces leakage radiation

Lead

Accepted level of leakage radiation

1mGy/hr // (0.88mGy/hr sometimes mentioned)

X-ray tube is always mounted inside a lead-lined protective housing that prevents leakage radiation and

prevents electric shock to the patient and operator (technologist)

mGy/hr represents

radiation emitted in air