Fundamentals of Imaging

RAD 206

Image Production

Image production

In principle, What is the difference between Radiographic Imaging & Photographic Imaging

Parts associated

X-ray production

Object

Image Receptor

Result: a radiograph

Requirements for x-ray production

1.Vacuum2.Electrons3.Accelerations4.decelerations

What is the ratio of x-ray to heat produced

X-ray ProductionX-ray Production

X-ray Tube

High energy electrons, accelerated by thousands of kilovolts of potential, interact with a metal target in an x-x-ray tuberay tube.

99% 99% heatheat

1% X-1% X-rayray

X-ray ProductionX-ray Production

Cathode Heating

X-rays are produced when the electrons are suddenly decelerated upon collision with the metal target (bremsstrahlungbremsstrahlung) or "braking radiation".

If the bombarding electrons have sufficient energy, they can knock an electron out of an inner shell of the target metal atoms.

Then electrons from higher states drop down to fill the vacancy, emitting x-ray photons with precise energies determined by the electron energy levels (characteristic x-rayscharacteristic x-rays).

X-ray ProductionX-ray Production

Compare between Bremsstrahlung and Characteristics xrays

Bremsstrahlung Characteristics Created by slowing (breaking)

of incident electronCreated by ejection of inner

shell electron, then the outer shell electron fills its space

X-ray energy produced is variable (continuous emission

spectrum)

X-ray energy produced is specific (discrete emission

spectrum)

Depends on kVp Depends on type of target material

Prime Factors Prime Factors ( technique Factors)

1.1. mAsmAs

2.2. kVpkVp

3.3. SIDSID

•Focal Spot Size

•Beam configuration (Size, quality, & angle)

•Quantity & quality of scatter

•Speed of image receptor

•Thickness of the Object

•Relative atomic number of Tissue

•Atomic Number of Anode + Anode Angle

How can a condition or a pathology affect the prime factors

mAsmAs mA/s is a measure of electrical current and “s” is a measure of duration … in all, they control the amount of electrons emitted from the filament, hence the number of interactions with the anode, hence the number of x-ray photons produced.

(sometimes termed as the quantity of x-ray )

kVpkVp kVp is the measure of electrical pressure (or difference ) between the cathode and anode, that pushes the electron from cathode and attracts it towards the anode. This electrical energy is corresponding to the energy transferred to the x-ray photon during x-ray production, and in turn controls the penetration power of the x-ray photon produced, which is sometimes termed as the quality of x-ray beam

SIDSID Source to image distance, is the source between the x-ray emission and the image receptor. It affects two major things

1.The intensity of the beam ( quantity)

2.Geometry of the imageAnd in some cases, causes artifacts

Which formula is used for SID and Intensity of beam

Other factors•Focal Spot Size

•Beam configuration (Size, quality, & angle)

•Quantity & quality of scatter

•Speed of image receptor

•Thickness of the Object

•Relative atomic number of Tissue

•Atomic Number of Anode + Anode Angle

Primary

Attenuation

Remnant

What is attenuation, what factors controls it?

Differential Differential AttenuationAttenuation

Differential Absorption

Differential Differential AttenuationAttenuation

Differential Absorption What is differential attenuation?

when all factors are standardized, The x-ray beam is not uniformly attenuated, it is attenuated ( absorbed) according to the properties of different tissues ( anatomy, pathology, physiology, thickness, relative atomic number, cell density, etc..), this produces variable degrees of attenuation that is responsible for producing a radiographic imageWhich two types of interactions are important to produce and image?

Differential Absorption

SOFundamental for image formation

The difference in x-ray interactions

Occurs because of three interaction Compton Scattering, Photoelectric absorption, and X-ray transmission

Differential AbsorptionIncreases as the kVp is reducedApproximately 1% of photons that interact with the patient (primary beam) reach the IR. Only 0.5% Of the 1% may interact with the IR to form the image

Radiopaque and Radiolucent Different degrees of attenuation produces different levels of remnant photons, and hence produces different levels of brightness and/ or blackness on the image, which is replace by Radiopaque and Radiolucent terms, respectively.

What is the ISO reference used for radiopacity and radiolucency

Radiographic Image Radiographic Image receptor systemsreceptor systems

Conventional radiography ◦Film screen system

Digital radiography◦(CR) cassette systems or ◦(DR) cassette-less systems

Fluoroscopic Imaging system

•DR, DDR, CR are abbreviations for :

First Radiographic Films made from Silver Halide on Cellulose Nitrate / Cellulose Triacetate; Highly Flammable Emulsion would crack & peel away from base when chemicals were too hot

Now they Use Silver Halide Polyster

X-ray films for general radiography consist of an emulsion-gelatin containing radiation sensitive silver halide crystals, such as silver bromide or silver chloride, and a flexible, transparent, blue-tinted base.

Film screen system

? Duplit ized ?

Film SpeedAka the sensitivity

Film SpeedAka the sensitivity

determines the amount of exposure needed to produce an image.

Can be :

100, 200, 400, 800, 1600, 3200 (The typical speed for a rare earth film screen combination is 400).

High sensitivity: requires less exposure but produces more noise

Low sensitivity: requires more exposure used to reduce image noise

Intensifying Screen Film stops light really well

Phosphor Layer = calcium tungstate

~ 1,000 light photons per x-ray photon ( with 50 keV energy)

Reflective layer prevents light from going backwards

Never Clean Screens with alcohol

Intensification factor

◦Direct film requires around 34 times more exposure than screen film

so◦A 0.1 second exposure on

screen film would require 3.4 seconds on non-screen film

◦Larger crystal = faster screen = more grainy

◦Thicker phosphor layer = faster screen = decreased detail

Care of Screens

Clean the screens at least monthly.

Use only specially formulated screen cleaner with anti static properties.

Never use alcohol to clean screens.

Make sure they are dry before reloading with film.

Must be tested for screen-film contact (Wire mesh test)

Film screen system

90 seconds processing

Safe light

Lamps with colored filters that do not expose the film but allow sufficient light for sight

A 15 watt bulb is used no closer than 5 feet from the work surface

The Dark Room

Film Storage

x-ray flow chart

Digital radiography (CR) cassette systems or (DR) cassette-less

(CR) cassette systems

Or (DR) cassetteless

Photostimulable phosphor system

``

````

(CR) cassette system

Inside the reader(CR) cassette system

(DR) cassetteless system

Two types of Digital Casseteless systems

Direct Capturea-Se

Indirect CaptureCsI

What similar technology do they use? What is a-Se / CsI?

Direct Capture

(DR) cassetteless system

Remnant x-ray phones are absorbed directly by the coating material and immediately converted to electrical signal

Indirect Capture

(DR) cassetteless system

Indirect capture happens in two steps

1.First: Remnant x-ray photons are absorbed by the scintillator and converted into light

2.Secondly: the light is converted to electrical signal by the amorphous silicon

How many pixels do the DR have?

How many pixels do the CR have?

Which one of DR or CR can be bent

What are the disadvantages of DR?

What is TFT

differences between CR and DR Technology

CR DR

IR Plate Phosphor screen in cassette Amorphous silicon connected to computer

Weight of plate Less than 1 kg around 3 kg

Initial Cost From BD4,000 From BD20,000Processing Time ( the time it takes from exposure to viewing)

Around 1 minute around 3 seconds

Size Relatively Mobile or could be Portable.

Portable for any use in any field or area