Equipment review (1)

X-ray machine

Introduction:

X-ray-department, location and lay out.

X-ray department should be easily accessed from ward

and casual, and in separate building, all protective

methods should be applied.

Types of X-ray machines

1-Portable X-ray machine

2-Mobile X-ray machine—(a) simple-(b) C-arm (c)

mammographic unit.

3-Dental (1) Simple self rectified (2) Othropantomography (OPG)

(3) Cephalostat.

4-Major or static X-ray machine.

Components of X-ray machine

1-Mains switch (Knife switch), manual or Electromagnetic circuit

breaker.

2-Control, disk or panel.

3-Auto-transformer

4-High tension tank (h.t.transformer, filament transformer, h.t

switch, rectifiers and oil).

5- High tension generators

6-X-ray tube assembley (insert, housing, collimator, handle of

brakes).

7-Types of X-ray exposure timers (Clock work, electronic,

automatic, guard, mAs, and synchronous timer).

8-High tension cables.

9-X-ray table (table top, potter Bucky, grid).

10-Stand Bucky.

11-Fluoroscopic attachment (tilting table, under couch tube, serial

changer, image intensifier tube, video camera and monitor).

12-Dark room accessories (safe lights, processing tanks, cassettes,

hungers, dry and wet bench).

X-ray machine

• The x-ray machine is divided into

four major components.

• The Tube

• The Operating Console

• The High Voltage Section

• The Film Holder , Grid Cabinet or

Table

X-ray Room

• Floor mounted x-ray

tube stand.

• Wall grid cabinet or

Bucky

• Mobile Table with

grid cabinet

• Film Holder

X-ray Room

• Control should

contain the operator

console and

technique charts and

space to store

cassettes.

• The wall between

the Control and X-

ray unit is shielded.

Chiropractic X-ray Room

• High Voltage

Section or

Generator used to

change incoming

power to levels

needed to produce

x-rays.

The X-Ray Tube Development

• Dr. Roentgen used a

Crookes-Hittorf tube

to make the first x-

ray image.

• There was no

shielding so x-rays

were emitted in all

directions.

The X-Ray Tube Development

• The Coolidge Hot

cathode tube was

a major

advancement in

tube Design. The

radiator at the

end of the anode

cool the anode.

The X-Ray Tube Development

• This is the variety

of tube designs

available in 1948.

• The Coolidge tube

was still available.

The X-Ray Tube Development

• Two major

hazards plagued

early radiography.

• Excessive

radiation exposure

• Electric Shock

The X-Ray Tube Development

• This is a modern

rotating anode x-

ray tube. It is

encased

completely in a

metal protective

housing.

The X-Ray Modern X-ray Tube

• There are two

principle parts:

• The rotating anode

• The cathode

• Any tube that has

two electrodes is

called a diode.

The X-Ray Modern X-ray Tube

Part of the X-ray Tube

Protective Housing

• The tube is housed in

a lead lines metal

protective housing.

• The x-ray photons

are generated in all

directions.

• The housing is

designed to limit the

beam to window.

Protective Housing

• The housing also

provide mechanical

support and

protection from

damage.

• On some tubes, the

housing also contains

oil that provides

more insulation and

a thermal cushion.

Protective Housing

• Never hold the

tube during an

exposure.

• Never use the

cables or

terminals as

handles.

The X-Ray Tube Glass Envelope• The glass envelope is

made of Pyrex to withstand the tremendous heat produced during x-ray.

• The window is a 5 cm square with a thin section of glass where the useful beam is emitted.

The Cathode

• The cathode is the

negative side of the

tube and contains

two primary parts:

• The filaments

• The focusing cup

The Cathode

The Filaments

• Most tube have

two filaments

which provide a

choice of quick

exposures or high

resolution.

• The filaments are

made of tungsten.

The Filaments

• Tungsten is used in x-

ray tube because of

it’s high melting

point of 3410°C.

• X-rays are produced

by thermionic

emission when a 4 A

or higher current is

applied.

Focusing Cup

• The focusing

cup has a

negative

charge so that

it can

condense the

electron beam

to a small area

of the anode.

Focusing Cup

Filament Current

• When the x-ray machine is turned on, a

low current flows through the filament

to warm it and prepare it for the big

thermal necessary for x-ray production.

Filament Current

• Once the current is high enough for

thermionic emission a small rise in

filament current will result in a

large rise in tube current.

Filament Current & Tube Current

• The x-ray tube

current is adjusted

by controlling the

filament current.

• The relationship

between tube and

filament current is

dependent upon the

tube voltage.

Space Charge

• When emitted by the

filament, the

electrons form a

cloud near the

filament

momentarily before

being accelerated to

the anode. This is

called a space

charge.

Saturation Current• When very high mA and

very low kVp, the

thermionic emission

can be space charge

limited.

• With high mA the cloud

makes it difficult for

subsequent electrons to

be emitted.

• Above 1000 mA space

charge limited exposure

can be a major problem.

The Anode• The anode is the

positive side of the

tube.

• X-ray tubes are

classified by the type

of anode:

–Stationary ( top)

–Rotating (bottom)

The Stationary Anode

• Stationary anodes

are used in dental

x-ray and some

portable x-ray

machine where

high tube current

and power are not

required.

The Rotating Anode

• The rotating anode

allows the electron

beam to interact with

a much larger target

area.

• The heat is not

confined to a small

area.

The Rotating Anode

• The anode serves three

functions:

– Receives the

electrons emitted

from the cathode.

– It is a electrical

conductor.

– Mechanical support

for the target.

The Rotating Anode

• The Anode must also

be a good thermal

conductor.

• When the electron

beam strikes the

anode more than

99% of the kinetic

energy is converted

to heat.

Tungsten is used as a target material, for the

following reasons:

(1) It has a high atomic number (74) and

efficiency of X-ray production increases with the

atomic number of the target.

( 2 ) It has a high melting point (3400°C) and is

thus able to withstand the high temperatures

reached by the target during an exposure.

(3) The characteristic radiation of tungsten

makes a useful contribution to the beam of X-rays.

Tungsten is used as a target material,

for the following reasons:

(4) It has reasonably good thermal

conductivity. This is important as heat must

be transferred from the focal areas to the

mass of the anode.

(5) It has reasonable thermal capacity.

(6) It has low vapor pressure at high

temperature which helps to preserve the

vacuum within the insert.

The Rotating Anode

• The rotor is an

electromagnetic

induction motor.

The Rotating Anode

• Even with the anode

rotating, the heat

must be rapidly

dissipated.

The Rotating Anode

• When the

exposure button is

depressed, current

is applied to the

tube that produces

a magnetic field

that starts the

rotation of the

anode.

The Rotating Anode• When the anode is

spinning at the

correct speed, the

exposure can be

made.

The production of x-ray

• The heart of an X-ray machine is an

electrode pair ion a cathode and an anode

ions that sits inside a glass vacuum tube.

• Cathode is a heated filament, like you

might find in an older fluorescent lamp.

2/4/201946

The production of x-ray

• The machine passes current through the

filament, heating it up. The heat sputters

electrons off of the filament surface.

• The positively-charged anode, a flat disc

made of tungsten, draws the electrons

across the tube

The production of x-ray

• The voltage difference between the cathodeand anode is extremely high, so theelectrons fly through the tube with a greatdeal of force.

• When a speeding electron collides with atungsten atom, it knocks loose an electron inone of the atom's lower orbital. An electronin a higher orbital immediately falls to thelower energy level, releasing its extraenergy in the form of a photon.

The production of x-ray

• Free electrons can also generate photonswithout hitting an atom.

• An atom's nucleus may attract a speedingelectron just enough to alter its course. theelectron slows down and changes directionas it speeds past the atom.

The production of x-ray

• This "braking" action causes the electron to

emit excess energy in the form of an X-ray

photon.

• In conventional x-ray only about 1% of the

electron energy converted to x-ray, the

remaining 99% appears as heat (that why

we use oil in tube housing)

The production of x-ray

The production of x-ray

• The high-impact collisions involved in X-

ray production generate a lot of heat.

• A motor rotates the anode to keep it from

melting (the electron beam isn't always

focused on the same area). A cool oil bath

surrounding the envelope also absorbs

heat.

The production of x-ray

• The entire mechanism is surrounded by a

thick lead shield. This keeps the X-rays

from escaping in all directions.

• A small window in the shield lets some of

the X-ray photons escape in a narrow

beam. The beam passes through a series of

filters on its way to the patient.2/4/201953

Types of X-ray

• Bremsstrahlung x-ray

• Characteristic x-ray

Bremsstrahlung x-ray

• produced the X-ray by the acceleration of

fast moving electron resulting in

conversion of some of its kinetic energy

into x-ray.

Characteristic x-ray

• The movement of an electron between

two inner shells in an atoms with

difference between the binding energies

of the two shells being radiated an x-ray

photon