X-ray Machine

Grid ratio.

( height vs space between ) e.g. 6:1

2 stages of the exposure switch:

1. heat filament and anode rotator 2. generation of e- cloud (cathode to anode) & x-ray beam

What are two labelling systems?

1. led tape (before radiograph taken) 2. photo imprint (after radiograph taken)

List the densities in the body from most dense to least: Fat, bone, metal, air, soft tissue

1. metal 2. bone 3. soft tissue (fluid included) 4. fat 5. air

2 types of anodes:

1. stationary 2. rotating

What is the target angle for focal spot?

15-20 degree, an ACUTE angle (acute angles are less than 20 degrees)

What is the effective spot size?

1x1mm

Sante rule (standard mA setting)

50-300 mA used It won't work below 50 mA.

The target in the anode is at an angle of?

6 to 20 degrees

Machines operating above 50 kVp, radiation should be contained in a circle having a diameter of no more than?

7 cm (2.75 in)

Intensifying screens.

95% of exposure recorded on film from screens. Luminescent phosphor crystals bound together mounted inside the cassette. When struck by rays, they fluoresce, converting x-rays into visible light. These screens decrease the amount of radiation exposure necessary to produce picture.

Screen Care.

A cleaning solution recommended by the manufacturer. 70% alcohol solution. Kimwhipes.

Fully describe UK household current

AC = Alternating Current 50 Cycles per second = 50 waves per second = 50Hz An average of 230v All of Europe is the same (230v and 50Hz) USA has AC 120v and 60 Hz

What filters out detrimental long wave x-rays?

Aluminium Disc.

Total Filtration.

Always equals to 2.5mm Al equivalent.

Exposure rate.

Amount of radiation per second (mA).

X-rays only receive half of the alternating current.

An x-ray tube can receive only positive pulses, because the current can only flow one way through the x-ray tube.

What is the voltage compensator that corrects for minor fluctuations in the electric current?

Autotransformer.

The 2 parts of an x-ray film .

Base: A transparent polyester that provides flexible support. Emulsion: A gelatin suspension of silver halide crystals that coat film.

X-rays make a film WHAT COLOR?

Black

The two different types of radiation produced in the X-Ray tube.

Bremsstrahlung and Characteristic Radiation

The thicker or fat end of the patient should be towards the anode or cathode? Why?

CATHODE Refer to the heel effect that results in weaker penetration on the anode side of the x-ray tube than on the cathode side.

Layers of cassette .

Cassette top. Top padding. Intensifying screen. Film. Intensifying screen. Bottom padding. Lead foil. Cassette bottom.

Causes of tube failure

Causes of radiographic tube failure/malfunction: 1. almost 95% of damaged tubes are a result of technical error 2. cathode failure: filament evaporation one of the most common causes of failure 3. anode bearing failure: unnecessarily holding switch in pre-exposure position 4. anode target failure: lower kVp settings produce more heat / usable x-ray a. shooting over the machine's capacity OR b. shooting a lot of x-rays in succession

Focusing Cup.

Clusters electrons to keep them bunched in an area around the cathode's filaments.

Tube current (kVp).

Controls quality of photons

Milliampere (mA) control.

Controls quantity of photons, frees electrons, attached to filament and loosens electron bonds.

Dissipates heat from the target.

Copper Stem. Oil bath contained within a glass envelope.

Parts of Anode

Copper stem and tungsten target

Parts of Anode.

Copper stem and target

kVp and mA

Current (mA) - Number of photons that control the quantity Tube Voltage (kVp) - Penetrating power of beam

Anode target failure

Damage due to excessive heat. Surface rough from damage causes beam to be ununiform = so exposures and film density will vary from use to use Higher kVp and lower mA help prevent anode target failure

Lead Collimator.

Determines beam shape.

Lead Bucky Diaphragm

Determines beam size

Lead Diaphragm.

Determines beam size .

full-wave rectification

Directs both halves of cycle (pos & neg) to pass across x-ray tube (doubles output of x-ray tube).

As the exposure time increases, the mean and max energies of the beams ______?

Don't change .

As the tube current increases, the mean energy and max energy of the beams ________?

Don't change .

Exposure Time.

Duration of radiation production. 1 pulse = 1/50 second. Newer machines report directly in milliseconds. Exposure time x mA (speed) = total radiation.

2 types of timer:

Electrical timer Deadman switch

Characteristic Radiation

Electrons hits inner target electrons . Electrons then drop down to take their place. Energy is given out as X-rays. As there are only specific jumps/transitions that electrons can make, these appear as peaks on a graph of intensity vs wavelength. An electron transition from n=3 to n=2 is L-alpha; n=4 to n=2 is L-beta; n=5 to n=2 is L-gamma; etc

Bremsstrahlung Radiation

Electrons interact with nucleus of tungsten/target atoms. The nearer it gets to the nucleus the more it is slowed down (decelerated) and the more energy it gives up as X-rays. The KE the electron loses is converted into a photon, thus satisfying the law of conservation of energy. A continuous spectrum of wavelengths of X-rays is radiated out. 0.01 nm - 10 nm DX : (0.01 - 0.1) nm

Vacuum

Eliminates electrons collision with gas molecules (prevents electron slow down). Prevents oxidation of the metals.

mA

Energy used to heat up filament. Creating more x-rays. Also associated with time to give mAs.

Where is the aluminium disc placed in the x-ray tube?

Exit of tube head

Parts of the Cathode.

Filament, focusing cup, mA control

Beam filters

Filters out the beams with longer wavelengths. Aluminium is used to filter out (0.1-10)nm x-rays. These would provide no useful information, but would harm the patient.

Step-up transformer

Found in the high voltage circuit (after the autotransformer) to hugely increase the voltage. Secondary coils many more turns than the primary coil.

Rare earth phosphor screens.

Greater x-ray to light conversion than calcium tungstate. 4 x the ability to convert x-rays to light. Can produce either green or blue light depending on the metal. Significantly reduces the required radiation dose.

Types of supports

Hand held Attached to table or floor/wall mount Attached to ceiling

Filament.

Heated by mA. Is made out of tungsten.

Cathode failure/ filament failure

If filament has melted/fused no electrons can be produces and there will be no movement of the mA If higher temperature is maintained for a longer time, there is more chance of the filament fusing No filament= no electrons can be produce= no exposure of radiographic film

Collimation.

Increased collimation decreases number of photons reaching film, influencing beam intensity. Reduces scattered radiation (limits primary beam).

High voltage circuit / step-up transformer

Increases 230V UK to needed Kilovoltage Typically 50 000 V - 90 000v i.e. 50kV - 90 kV

As the exposure time increases, the total number of photons _____?

Increases.

As the tube current increases the total number of photons _______?

Increases.

There is an increase in the mean energy of the beam, the total number of photons and maximal energy of the photons when the kVp __________?

Increases.

Calcium tungstate screens.

Invented in 1896 by Thomas Edison. Emissions of light is in the blue region. It doesn't convert x-rays efficiently.

Self/half-wave rectified generators.

Inverse voltage - Voltage across negative half-cycle (AC)

kVp stands for?

Kilovoltage Peak/Potential It determines the kinetic energy of the electrons accelerated in the X-ray tube and the peak energy of the X-ray emission spectrum. The actual voltage across the tube may fluctuate.

Collimator

Lead shutter that limits the x-ray beam's dimensions. Adjusts down to decrease the size of the beam.

Collimation advantages

Less radiation used on the patient. Provides better detail on the finished radiograph.

Half Value Layer (HVL) .

Material needed to cut intensity of beam in half.

Full-Wave rectified generators

Negative half-cycle is reversed so always positive, using full wave

Full-Wave rectified generators.

Negative half-cycle is reversed so always positive, using full wave to make x-rays

Radiography objective and purpose.

Objective: Produce a visible photographic image. From the passage of x-rays through a body, with the best diagnostic information, from the least amount of radiation. Purpose: To study inner structures, as an aid to diagnosis.

Low voltage circuit

One action - it heats the cathode's filament. A hotter filament produces more electrons. That means more photons produced. This circuit is measured in mA.

Leakage radiation .

Originates at focal spot, but leaves tube through barriers around the tube. Glass, oil, and metal enclosure minimize leakage .

Secondary scatter radiation.

Originates in tissues. Causes image noise.

Lead Casing

Prevents X-Ray leakage

Lead Casing.

Prevents X-Ray leakage

Vacuum.

Prevents collision of the moving electrons with gas molecules that would be present in air. Such collisions would reduce their speed of electrons. Also prevents oxidation and burnout of the filament?

Alternating Current (A/C)

Produces one positive pulse and then one matching negative pulse. Only the positive pulse produces X-rays! This is why a rectifier might be used to convert AC to DC

Low voltage circuit / filament circuit

Provides milliamperage / mA (electrical energy) to the filament to produce an electron cloud / beam. - called "Thermoionic Emission".

What is Ionizing Radiation ? Name the 5 critical body parts in regard to this.

Radiation capable of breaking down body molecules. gonads thyroid lens and cornea of eye skin and intestinal epithelium blood forming organs

half wave rectification

Rectifier stops flow of current in opposite direction

Why is the target in the anode at an angle?

Reduce effective focal spot size. Improves image quality. Spreads electron stream. Improves head capacity of the anode.

Light sensitive chemical in radiographic film emulsion.

Silver Bromide (AgBr). Note that 'faster film' is more sensitive as its silver bromide crystals are larger. However, it results in less detail on the radiographic image.

Cones

Slide on to the tube, underneath the filter, to limit the size of the x-ray beam.

High voltage circuit

Speeds up electrons. Sends electrons from filament to target on the anode. Measured in kVp. kVp is the driving force - the penetrating power in x-rays.

What heats the filament to produce electrons?

Step down transformer in the low voltage circuit.

Heel effect

Target angled 20 degrees from vertical variation in intensity of the primary beam intensity is greater on cathode side thicker side on cathode side

mAs

The higher the mA the less time needed. If the mA is lowered, the time must increase. (The shorter the time, the safer for all.)

Rectification

The process of changing alternating current (A/C) into direct current (D/C): Production of x-rays depends on D/C flowing in one direction across x-ray tube Normal A/C changes direction 100 times per second (50 cycles per second). Equivalent is 120 and 60 in the USA

Anode failure

The rotor rotates the anode disc. Noise of rotating disc will change when bearings are wearing out. There will be no noise when the pre-exposure button is pushed if the bearings cease to rotate.

Total Filtration

Total Filtration Always equals to 2.5mm Al eq

What material are the filaments on the cathode made of? Why?

Tungsten It has a super high melting point, so it will not melt during all these radiographs.

What material are the filaments on the cathode made of? Why?

Tungsten It can withstand high temperatures without melting.

What is the anodes bevelled target made of? What is this seated in? Why is it seated in this specific element?

Tungsten a copper base=reduces heat

Why do x-ray tubes use pyrex glass?

Unaltered by heat and less expansion than metal .

Three-Phase Generators

Use three phase currents to generate a nearly constant potential across x-ray tube at all times (allows very short exposure times).

3 main parts to an x-ray machine:

X-ray tube, table top, control panel

The ______focal spot is perpindicular to the surface of the target.

actual

Leaded Glass housing (together with the beryllium window) provides:

an envelope to maintain vacuum (together with the beryllium window)

A sign of ____failure, you will hear a change in sound pre-exposure.

anode bearing

A sign of _____ _____ failure includes variable film densities. Sometimes black, sometimes white. Unpredictable exposures.

anode target

2 things to dissipate heat from target tungsten

anode's copper stem oil

4 parts to an intensifying screen.

base/support reflective layer phosphor crystal layer protective coat

Lead Collimator determines

beam shape

A sign of ____failure is unexposed processing.

cathode filament

The _____ controls the size of the beam.

collimeter

What is the anodes base made of? Why?

copper to reduce heat

What type of radiograph machines do you see stationary anodes ?

dental, portable

Rotating anodes have higher powered x-rays. This rotating feature helps to do what to the high power/high heated beams?

dissipates heat

The _____focal spot is smaller due to angle of 15-20 degrees.

effective

The _______spot is where e- collides with anodes.

focal

The smaller the angle, the smaller the _______=better film.

focal spot

The ____effect is the result of a smaller angle than the target angle which results in less power of the anode.

heel

What does the cathodes focusing cup do?

helps direct the e- produced across the space between the cathode and anode

The glass envelope

holds oil

The maximum voltage across the x-ray tube causing acceleration of the electrons?

kVp

What controls the voltage between the anode and cathode?

kVp switch.

The energy acquired by any individual electron in the beam?

keV

The x-ray tube is a ____tube surrounded by a ____housing filled with oil. The x-ray tube is under a _______. The window through which the x-ray exit the tube is made from _____________ ____________

leaded pyrex glass, metal, vacuum beryllium foil

The larger the focal spot, the _____image clarity. This is causes a ______effect.

less penumbra (halo)

Stationary anodes have ______than rotating.

low power x-rays

What regulates the current (temperature) of the filament?

mA switch.

Filament is: heated (units in... made from....

mA, tungsten

The cathode is housed in a focusing cup made of what?

molybdenum

The shorter a wavelength, the _____penetrating it is.

more

Secondary rays

rays that don't have enough energy to pass into the body

Focal Spot

small area of target where electrons collide on anode 20 degrees from vertical in tube if too small - destroyed quicker if too big - image blurry 1-2 mm larger in stationary anodes

What part of the cathode produces heat?

the cathode filament

Central ray

the most central ray

Primary rays

the rays on either side of the central ray that make up the primary beam

If the focal point is too small, what can this cause?

too hot, burn through anode

Step-down transformer

used to reduce incoming voltage to approximately 10 volts Secondary coils has fewer turns than the primary coil.

A sign of the ______ damaged is variable densities in the film. Metal deposits from overheating or air bubbles.

vacuum/glass enveloped x-ray tube

Autotransformer

◦Pre-reading voltmeter and line voltage compensation. ◦Measures incoming voltage and allows adjustments on the autotransformer so that the incoming line voltage remains constant. ◦This compensates for fluctuations in National Grid. ◦Usually automatic on modern x-ray machines. ◦kV selector provides pre-determined voltage to primary turnings of the transformer.