MRS110 Imaging

Two types of Anodes

1. Rotating 2. Stationary

What are transformers?

A device that transfers electrical energy from one circuit to another through inductively coupled conductors (the transformer's coils). They can be either step up or step down.

Photoelectric Absorption

Because of low atomic number most of the atoms in the body are secondary radiation.

Define Ionisation

Occurs when an x-ray passes very close to an orbital electron of an atom and transfers sufficient energy to the electric to remove it from the atom.

Film screen

Radiation exposure required to process a specific density

The ripple factor

The fuzziness of the x-ray. Aim to have zero ripple factors but is merely impossible

Filtration Defintion 2 types and effect

Used to improve beam profile. 1. Inherent 2. added The effect of filtration is to remove longer wave length radiation

High voltage transformer (3)

- Supplies voltages at necessary levels of x-ray production -mA meter measure tube current -Provides protection against electrical shocks.

three phase generators

-Industrial power -Expensive -4-13% ripple

Limitations of film screen radiography

-Limited contrast resolution -cannot show differences in tissue -Film can only display once -Film degrades overtime and is bulky.

Grid styles

-Parallel -Focused

The 4 layers of intensifying screens

-Protective Coat - Reflective Layer (incoming x-rays turned to light) -Phosphor layer (active layer of the intensifying screen) -Base

Layers of the image plate in computed radiography (6)

-Protective layer - CR phosphor layer -Electroconductive Layer -Support layer -Light shield layer -Rear protective layer

Advantages of medium frequency generators

-Provides near contrast, ripple free voltage -Does not require special power units - Units smaller and more manoeuvrable

Synonyms (2)

Photostimulable storage phosphor (PSP) Storage phosphor radiography (SPR)

Latent Image

Present but not visible

Rectification

x-ray tubes only produce radiation when the flow of electrons is from the cathode to the anode. Therefore when this process is reversed there is no radiation which is called rectification.

Advantages of the One phases generator

-Small business power -Inexpensive -100% ripple.

IP resolution (2)

-Standard- thicker phosphor layer, aborb more radiation -high- thinner phosphor layer, sharper images

Filament sub circuit consists of? (3)

-Step-down Transformer -mA selection - Cathode and wiring

What does the radiographer have control of?

-Tube voltage -Filament current -Duration of exposure

What does the autotransformer do? (4)

-Voltage for the x-ray tube filament circuit -voltage for the primary of the high voltage (HV) transformer -convient location for the kVp meter -A method of performing like voltage compensation

Tube requirements

-can only conduct in one direction because of thermionic emission. - need high voltage for x-ray production,

What are the three main components of the power source?

-incoming line -Circuit breaker -Line voltage compensator

Three Anode Assembly

1. Anode 2.Rotor 3. Stator

Coherent scatter (2)

1. Classical scattering 2. Thompson scattering- incident photon interacts with a single electron.

Four types of unsharpness

1. Geometric unsharpness 2. Motion unsharpness 3. Detector unsharpness 4. Digitisation unsharpness

What are the three types of exposure timer controls?

1. Mechanical 2. Electronic 3. Automatic

Evaluating film (2)

1. speed: response to film to radiation 2. latitude: films ability to display shades of gray

What causes x-ray tube failure?

1. thermal characteristics 2. temperature increases to rapidly causing the anode to crack. 3. melting is to serve resulting in tungsten to vaporise.

Six ways to attend tube life?

1. use lower mA when possible 2. do not prep unnecessarily 3. use low speed rotor when possible 4. warm up the anode according to manufactures recommendations. 5. Do not make repeated exposure near tube loading limits. 6. do not use a tube when you can hear loud rotor bearing.

Information about heat (2)

1.99% of all energy produced in a x-ray tube is heat. 2. heat is continusouly dissipated to the oil bath and the tube housing by conduction and radiation.

What are the Anode Functions?

1.Act as a target for the electrons from the filament. 2. Conduct high voltage from the cathode 3. serve as primary thermal conductor

What are the three elements of heat?

1.Radiation- transfer of heat in forms of waves. 2. convection-physical movement of the heated medium. 3.Conduction- transfer of heat as a result of direct contact of rapidly moving atoms through a medium.

Bucky Factor

A measure of how much an increase in exposure is needed to use a grid compared to an exposure without a grid.

What is the Stator

A wire coil outside of the x-ray tube that surrounds the rotor.

Grids advantages and disadvantages

A: improved visibility of detail D: Higher patient dose

Luminescence

Ability of material to emit light in response to excitation

Vrms

Allows you to compare one voltage source to another. It is the square root of the mean of the square of all samples.

What are Diodes?

Any device that blocks current in one direction while letting current flow in another direction is called a rectifier or diode.

Intenisty and mAs

As FFD changes you will need to compensate to make the intensity the same when it reaches the image plates, This will maintain the X-ray intensity reaching the imaging plate.

Inverse square law

As FID increases there is a decrease in intensity and conversely as FID decreases there is an increase in I.

FID relationship to intensity

As the FFD increases the x-ray beam becomes more divergent hence the number of photons.

Automatic exposure control timers

Automatically terminate exposure when sufficient radiation levels are reached. It measure the quantity of radiation reaching the image receptor.

Moving grids

Back and forth motion of the grid is know as reciprocation

Where are the time controls located?

Between the secondary side of the autotransformer and the primary side of the High voltage sub circuit.

Phosphor layer

Consists of very small crystals. These are sensitive to photon in the x-ray energy range.

Grid Ratio

Defined as the radio of the height of the lead strips to the distance between them. Higher grid ratios allows less scatter to pass through their interspace material.

What is the stress relieve anode?

Design feature in newer tubes allows faster dissipation of heat and does not require warm up exposure.

Distortion Definition and 2 types

Differentiation magnification or distortion of the image is more of a problem. This can change the shape of the problem 1. elongated 2. Foreshortening

Spectrum & Generator info.

Generator wave form effects the quality of the emitted x-ray spectrum.

Smoothing of the generator

Greatly reduces ripple to obvious goal of 0%. The smoothing capacitor converts the full wave rippled output of the rectifier into a smooth direct current out put voltage.

What is the Rotor

Hollow cylinder with thermal heat distribution.

Image assessment

How black and white is it? is the bone under or over exposed? Is the image sharp are the edges smooth?

Subject contrast

Inherent difference within the patient that leads ti differing amount if attenuation and transmisson of the x-ray beam causing differences in the exit intensities that will reach the image receptor and form an image.

What does Oil do in the x-ray tube?

Inside the glass housing it is to help dissipate heat and provides electrical insulation.

12 pulse

It is possible to obtain more pulses than twice the number of phases in a rectifier circuit. Through creative us of transformers, sets of full wave rectifiers may be paralleled.

Photoelectric effect

Major type of interaction at diagnostic x-ray energies. A photoelectron is ejected and the photon is completely absorbed.

What does beam filtration do?

Modifies the quantity and quality of the x-ray beam by selectively removing low energy photons in the spectrum.

Cathode

Negatively charged electrode by which electrons enter an electrical device.

Grid frequency

Number of grid lines per cm

Quantity

Number of photons comprising the beam -number of photons in the beam (intensity, exposure) -Total exposure (time X rate)

what is attenuation?

Passes through the body with interaction with atomic structures.

Quality

Penetrability of an X-ray beam -Ability to penetrate matter -Energy of the beam

Compton scattering

Photon interacts with an outer shell electron. Electron is removed from the shell and is called a compton.

Ripple

Pluses in the voltage waveform are referred to as voltage ripple. The ripple factor is the maximum drop in voltage expressed as a percentage of the Vmax.

What is the advantage of diodes?

Prevent potential damage to filament.

Tube Housing

Provides housing, supports, insulates and protects.

If mA increases what else does?

Quantity

Reciprocity law and failure

Relationship between intensity and the exposure factors of mA and t.

Air Gap techniques

Scatter can be significantly reduced and magnification is increased.

Focusing Cup

Shallow depression in the cathode assembly designed to house the filament.

Direct current

The flow of the electrical charge is only in one direction. To big to travel and doesn't change its voltage very well

Intensifying screens

Used to amplify incoming x-ray beam and reduce patient dose.

Medium frequency generator

Uses a high frequency current to produce nearly contrast potential voltage to the x-ray tube.Current is rectified then smoothed.

What is the Anode Heel Effect

Variation in intensity of the x-ray beam.

What is x-ray production? and materials

When electrons with a high kinetic energy strike a target, losing there kinetic energy through three different materials. -excitation -ionisation -radiation

What is filament failure?

When the filaments heat is to high resulting in the tungsten atoms to slowly vaporises and plate the inside of the glass envelope. leading to arcing and tube failure.

ADC

analogue to digital converter. a device that converts a continous quantity to a discrete digital number.

Bremsstrahlung Interactions

breaking or decelerating radiation

Spatial resolution

descibes the levels of detail that can be seen on an image.

Radiographic contrast

is the difference in OD as seen on the film or displayed in a CR or DR image.

Define Radiation

is the transfer of energy

Alternating current

the movement of electric charge periodically reverses direction. it is easier to transmit and travel high voltages to power stations, therefore being cheaper and easier to produce.

Latent image formation

x-ray exposure of the PSP creates a latent image and laser scanning of the exposed IP produces PSL.