Cluster 2 IPE

X-ray Tube

What Is Tube Housing?

Material: Lead Lined

Description: Protective Device Prevents leaking

X-ray Tube

What is Glass Envelope?

Material: Pyrex

Description: Located in Tube Housing, Window of Glass envelope which is a small area made in thinner so X-ray Photons can pass easily

X-ray Tube parts

what are the two Electrons?

Positive Anode

Negative Cathode

Cathode Negative Parts

A filament is a source of electron what is it made off?

small coils of tungsten wire about 1 to 2 cm in length

Cathode:

2 Types of Filament

Small filament or small focus directs electrons to a smaller area on the target Large filament or large focus directs electrons to a larger area on the target

Cathode:

What is Thermionic Emission?

occurs when the negatively charged electrons break away from the hot filament to form a space charge

Cathode:

What is Space Charge?

a cloud of electrons around the filament which becomes the source of electrons in xray production

Cathode:

What is Space Charge Effect?

phenomena where further thermionic emission is halted by the space charge itself

Cathode:

what is Focusing Cup?

encases the two filaments and focuses the space charge on a target area on the anode

What are the Two Types of Anode?

Rotating (Mostly), Stationary (Outdated)

Anode:

What is a Rotor?

Material: shaft-like structure made of copper

Description: rotation device that turns the stem and target area

Anode:

What is a Stem:

Material: Copper

Description: attaches rotating target area to rotor

Anode:

What is a Rotating Target?

circular, disk-like structure with a beveled edge o receives electrons as they move from cathode to anode

Anode:

Rotating Target What is the Material made off?

tungsten

Anode:

Angle of Rotating Target and its no. of Rotation?

8 to 20°/ 9 to 15°

3000 to 10,000 rpm

Anode:

Focal Spot?

area of focal track that is struck by electrons

Anode:

Focal Track?

runs the circumference of the anode disk

Actual Focal Spot?

area being struck by electrons

Effective Focal Spot?

area directly below the target projected towards the window

Stationary anode?

Usually in Dental X-ray Units made out of Copper and Tungsten Target

X-ray Productions:

On and Off Switch

to connect the electrical power to the x-ray generator

X-ray Production:

Exposure Timer

determine the length of time that x-rays will be produced

X-ray Production:

Mechanical Timer

similar to spring-set dial, shortest setting is 1/10 s

X-ray Production:

Synchronous Timer

motor driven, utilizes the 60-Hz AC, has intervals related to 1/60 s, shortest setting is 1/120 s

X-ray Production:

Electronic Timer

most common, accurate, and reliable, designed with complex circuitry, shortest setting is less than 120 s

Evaluation of Timers:

Spinning Top Test

1-ø, full-wave rectified x-ray generators

Evaluation of Timer: Spinning Top Test

1 Dot per

1/120 sec exposure

Evaluation of Timer: Spinning Top Test

2 Dot per

1/60 sec exposure

Evaluation of Timer: Spinning Top Test

4 Dots per

1/30 sec exposure

Evaluation of Timer: Spinning Top Test

12 Dots per

1/10 sec exposure

Evaluation of Timer:

Calibrated oscilloscope

3-ø x-ray generator

compared to the selected time to verify accuracy

Evaluation of Timer:

Pulse-counter device

1-ø and 3-ø x-ray generator

placed in the primary x-ray beam, where pulses are counted and evaluated

Milliampere selector

counts the amount of electrical current flowing through the cathode filament

Milliampere selector Ranges

25 to 2000 mA

low current

small focal spot

high current

large focal spot

mAs Formula:

milliampere × time (seconds)

Kilovoltage selection

determine the specific tap on the autotransformer

kV major

changes of ~10 kV per turn

kV minor

changes of 1 to 2 kV per turn

“prereading” volt meter

position of meter indicates the amount of PD or voltage that will move across the x-ray tube during exposure

X-ray Production

Rotor switch

initiates the rotation of the anode in preparation for the exposure o maximum anode rotation is accomplished in ~1 sec

X-Ray Production:

Exposure switch

activated when the maximum RPM of the anode is reached

results in the production of x-rays

X-ray Production:

Accessory Controls Include:

Potter-Bucky diaphragm selection

vertical or horizontal devices

line voltage adjustor

X-ray Production:

Automated Exposure Controls (AEC)

termination occurs when desired amount of exposure reaches the film

X-ray Production:

PhotoTimer

terminates exposure when a proper amount of light reaches the photomultiplier tube

Location: Behind Cassette

X-ray Production:

Ionization Chamber

terminates exposure once a preset charge is accumulated and detected

Location: B/W cassette Holder and Pt

X-ray Production:

Back-up timer selection

a manual timer switch (ex: 1 sec) that will terminate exposure if the AEC failed, thus protecting the patient and the x-ray tube from continuous exposure

X-ray production:

Machine Controls mAS while kVP is?

AEC preselected Fixed KVP

X-ray Production:

Overexposure or underexposure in AECs

caused by improper chamber selection and/or patient positioning errors

Proper Care of Radiographic Equipment:

Warm Up Procedure: Anode Target Area

preheated each morning before use

X-ray Warm Up:

Exposures are Made using?

Low mA (50-100 mA), large focal spot, low to moderate kVp (65 to 70 kV), long exposure time of 2 to 3 seconds

Switch precaution

prolonged rotation with the presence of a “hot” filament will shorten the life of the anode and the cathode filament

Characteristic of X-Radiation:

Image Forming X-rays also known as Remnant Beam

those that exit the patient and interact with the image receptor

Characteristic of X-ray Radiation:

Exit Beam

the x-rays that remain as the useful beam exits the patient

X-ray Film:

Biggest Size

35 × 43 cm. or 14 × 17 in.

X-ray Film:

Smallest Size

20 × 25 cm. or 8 × 10 in.

X-ray Film:

Thickness

150 to 300 μm

Film Composition:

Base Purposes

support that allows the film to maintain its shape, prevent bending and provide support for the emulsion

Skeletal Framework

Film Composition:

Base Characteristics:

1. lucency – must be nearly transparent to white light

2. dimensional stability – maintain size and shape to prevent distortion of image

3. superior physical stability – flexible and sturdy to prevent damage when handling and processing

blue tint what its purpose

decrease eye strain, decrease parallax effect, improve contrast, contributes to 0.15 OD

X-ray Film:

Base is made up of what?

polyester – a polymer matrix

• ethylene glycol

• dimethyl terephthalate

X-ray Film:

Adhesive Layer

substratum layer

coated on the base before adding the emulsion simply adheres the base to emulsion

provides maximum contact b/w the base and emulsion

X-ray Film:

Emulsion Layer

radiation sensitive and light sensitive layer of the film coated on both sides of the base (duplitized)

X-ray Film:

the spectral response of an emulsion is

absorption of visible light emitted by the phosphors

X-ray Film:

To increase Contrast Emulsion you need

small, uniform grain size

X-ray Film:

Emulsion: made up of

Silver Halided Crystal

X-ray Film:

Silver Halide Crystal is Suspended in?

Gelatin

X-ray Film:

Emulsion: Gelatin is made out of what

a colloid extracted from cattle hooves and hide, then rendered into a very pure, uncontaminated state

X-ray Film:

Gelatin during

processing so that chemicals can penetrate the silver halide crystals

X-ray Film:

Gelatin Rehardens when

the invisible image becomes visible

X-ray Film:

Silver Halided Crystals Size

1.0 to 1.5 μm

X-ray Films:

Silver Halide Crystals Functions

energy detectors

X-ray Film:

Sensitivity specks

imperfections in the crystal structure

X-ray Film:

Silver Halide Crystal is made out of?

silver bromide – ~98%

silver iodide – ~2%

X-ray Film:

SuperCoat Layer

topcoat or overcoat

a durable protective layer that is intended to prevent damage to the sensitive emulsion layer underneath it

Characteristic of X-ray Films:

Film Speed

degree to which the emulsion is sensitive to x-rays or to light

As Film Speed increases

Increases Sensitivity, Decreases Exposure

2 primary factors that affect the speed point

the number of silver halide crystals

the size of silver halide crystals

Film Speed: Fast Number

200, 300

Film Speed: Average Number

100

Film Speed: Slow Number

>50

IR Speed Formula

1 divided by exposure

Density Maintenance Formula

old speed/new speed = new mAs/old mAs

Film Latitude

margin of errors in technical factors that the film allows that will still produce an acceptable range of densities

As Film latitude Increases

Decrease Contrast

Narrow Film Latitude

High Contrast Emulsion, Short GRAY Scale, High Contrast, High wavelength, Low Kvp, Low Penetrability

Wide Film Latitude:

Low Contrast Emulsion, Long Gray Scale, high KVP, High Penetrability, Low Wavelength

Types of X-ray Film:

Screen Type Film

the most widely used radiographic film, general choice for diagnostic radiology

one or two intensifying screens

parallax effect

crossover, crosstalk or print-through, occurs when light forms an angle affecting a spot in the emulsion and travels through the other side striking a spot not exactly corresponding to the opposite layer, producing an effect similar to penumbra

Ways to Reduce Parallax Effect

1. tinting the film with blue dye

2. using a monochromatic film – blue light cannot crossover blue dye, orthochromatic films will always have parallax as green light can crossover the blue dye

3. adding an anti-crossover layer

4. using a thinner base

Advantages of Screen Type Film

↓ emulsion thickness = ↓ developing time

↓ patient dose

disadvantages of screen-type film

↑ parallax effect = ↓ decreased resolution

↑ quantum mottle

Types of X-ray Film:

Direct Exposure Film (Non Screen Film)

designed for use without the need of an intensifying screen

Direct Exposure Film is commonly used

low-risk or low-exposure examinations of thin areas of the body

intraoral dental radiography

Advantages of Direct Exposure Film

↓ parallax effect/crossover/blur

↓ quantum mottle = ↑ image quality

Disadvantages of Direct Exposure Film

↑ patient dose ↑ emulsion thickness = ↑ development time

Type of X-ray Film:

Single Emulsion Film

has emulsion coated on one side of the base only

no parallax effect

Type of X-ray Film: Single Emulsion Film:

Anti Halation backing

prevents halation of light as the screens fluoresce,

↑ sharpness of image o requires ↑ exposure

Types of film according to spectral sensitivity

Monochromatic film is Sensitive to what Color?

blue sensitive, sensitive to wavelength