Discovery of X-rays X-rays were discovered on November 8, 1895, by Dr. Wilhelm Conrad - PowerPoint Presentation

Slide1

Discovery of X-rays

X-rays were discovered on November 8, 1895, by Dr. Wilhelm Conrad Roentgen.

Accidental discovery

First radiograph of Mrs. Roentgen's hand

Roentgen received the first Nobel Prize presented for physics in 1901.

Public viewed discovery as a novelty

Radiographic imaging and therapy important to the medical sciences

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X-rays as Energy

A form of electromagnetic radiationBehave both like waves and like particlesMove in waves that have wavelength and frequencyWavelength and frequency are inversely relatedX-rays also behave like particles and move as photons

Slide3

Properties of X-rays

X-rays are invisible.

X-rays are electrically neutral.

X-rays have no mass.

X-rays travel at the speed of light in a vacuum.

X-rays cannot be optically focused.

X-rays form a polyenergetic or heterogeneous beam.

X-rays can be produced in a range of energies.

X-rays travel in straight lines.

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Properties of X-rays (cont.)

X-rays can cause some substances to fluoresce.

X-rays cause chemical changes to occur in radiographic and photographic film.

X-rays can penetrate the human body.

X-rays can be absorbed or scattered by tissues in the human body.

X-rays can produce secondary radiation.

X-rays can cause chemical and biologic damage to living tissue.

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Birth of Radiology

Dry plate- used to record x-ray images

exposure required were extremely long.

Glass plate easily broken.

Thomas Edison developed the first intensifying screen

WWI x-ray film was produced

the cellulose nitrate film base and was highly flammable and a fire hazard

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X-ray Production

The production of x-rays requires a rapidly moving stream of electrons that are suddenly decelerated or stopped.

The negative electrode (cathode) is heated, and electrons are emitted (thermionic emission).

The electrons are attracted to the anode, move rapidly towards the positive electrode, and are stopped or decelerated.

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X-ray Tube Housing

Metal or glass envelopeNegatively charged electrodePositively charged electrode

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Cathode

FilamentSource of electronsFilament currentThermionic emissionCoiled tungsten wireLarge and smallFocusing cupSpace charge effect

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Anode

Rotating anodeRequires a stator and rotor to rotateTungsten metalHigh melting pointEfficient x-ray production TargetDecelerates and stops electronsEnergy converted to heat and x-raysBremsstrahlung and characteristic interactions

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Target Interactions

Bremsstrahlung interactions

Braking or slowing down radiation

85% of x-ray beam

Characteristic interactions

Projectile electron energy at least 69.5 keV

Inner shell electron ionized

15% of x-ray beam

X-ray properties the same

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Bremsstrahlung- electrons interacts with the atomic nucleus, more energy is lost and a stronger x-ray is produced; account for the majority of the x-ray beam.Characteristic Radiation - electrons interact with an orbital electron from the atom, the pulling down of another electron from an outer shell causes an x-ray to be produced; account for a small majority of the x-ray beam

Review of Interactions in the x-ray tube

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Target Interactions (cont.)

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Contains low energy rays which will be absorbed by the x-ray tubeAverage energy of the beam is 1/3 of the maximum energyX-rays are an inefficient process99% heat, 1% converted to x-rays

Heterogeneous Beam

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Primary Radiation (PR)- portion of beam from tube to the patient; radiation before it enters the patientRemnant Radiation (RR)- radiation emerging from patient’s body to expose the film; image forming radiation

X-ray Beam

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5% of primary beam passes through the patient without any interactions15% of the primary beam interacts with atoms and produce secondary radiation, they make it out of the patient and expose the film.80% will be totally absorbed by patient

Primary Beam Distribution

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20% or 1/5 of the intensity of the original beam exposes the filmWith remnant radiation about 75% to 80% of the beam is made up of secondary radiation

Distribution of Remnant Radiation

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mA- milliampereS- seconds timekVp- kilovoltage peakSID- source to image distanceThese are all controlled by the technologist

Prime Factors of Radiography

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X-ray Emission Spectrum

The range and intensity of x-rays emitted changes with different exposure technique settings on the control panel.

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Kilovoltage

Creates potential differenceDetermines the speed of the electrons in tube currentGreater speed results in greater quantity and quality of primary beamIncreasing electron speed will increase x-ray beam penetrability

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Milliamperage

Unit to measure tube current or number of electrons flowing per unit timemA directly proportional to quantity of x-rays producedDouble the mA will double the number of x-ray photons produced

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Milliamperage and Time

Exposure time determines the length of time x-rays are produced.

Increasing time will increase the total number of x-rays produced.

Exposure time and x-ray quantity are directly proportional.

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Beam Filtration

Aluminum filtration added to x-ray beam to absorb low-energy photonsTotal filtrationInherentAddedReduces patient exposure

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Compensating Filtration

Added to primary beam to alter its intensityWedge filterTrough filterUsed to image non-uniform anatomic areasThicker part of filter lined up with thinner part allowing fewer x-ray photons to reach anatomic area

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Image Formation

Differential absorption

Anatomic tissues absorb and transmit x-rays differently based on their composition (atomic number and tissue density).

Bone absorbs more x-rays than muscle.

Attenuation: the primary x-ray beam loses some of its energy (number of photons) as it interacts with anatomic tissue.

Absorption

Scattering

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Differential Absorption

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X-ray Beam Absorption

During absorption, the energy of the primary beam is deposited within the atoms comprising the tissue.

Photoelectric effect: complete absorption of the incoming photon

X-ray ionizes atom

Low energy secondary x-ray photon created

Probability of photoelectric effect dependent on the energy of the incoming x-ray photon and tissue atomic number

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Determining Attenuation of the Beam

Three essential aspects of tissues will determine their attenuation properties and the resulting subject contrast:

Tissue Thickness

Tissue density

Tissue atomic number

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X-ray interaction with matter

When the primary x-ray beam interacts with anatomic tissues. Three processes occur during attenuation of the x-ray beam:

Absorption

Scattering

Transmission

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Transmission

If the incoming x-ray photon passes through the anatomic part without any interaction with the atomic structures, it is called transmission.

The combination of absorption and transmission of the x-ray beam will provide an image that represents the anatomic part.

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Scattering

The Compton effect occurs when an incoming photon loses some but not all of its energy, then changes its direction.

It can occur within all diagnostic x-ray energies and is dependent only on the energy of the incoming photon, not the atomic number of the tissue.

Higher kVp reduces the number of interactions overall, but the number of Compton interactions increases in comparison to the number of photoelectric interactions.

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Absorption versus Scattering

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Photoelectric Effect

The secondary x-ray photon does not reach the film.

The photoelectric effect is crucial to the formation of the radiographic image.

The photoelectric effect is responsible for the production of contrast on the radiographic image.

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Photoelectric Effect

During attenuation of the x-ray beam, the photoelectric effect is responsible for total absorption of the incoming x-ray photon.

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Scattering/ Compton Effect

The Compton photon may be scattered in any direction.

Scatter refers to any x-ray photon which has changed direction from the direction of the primary beam.

The Compton Effect may be considered as scatter, since 99% of all scattered x-ray photons originate from Compton interactions in the patient.

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Where do interactions occur

Compton interactions occur only in the outer shells of an atom.

Photoelectric interactions occur only in the inner most shell of an atom.

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Factors Affecting Beam Attenuation

Tissue thickness

X-rays are attenuated exponentially and generally reduced by ~ 50% for each 4 to 5 cm (1.6" to 2") of tissue thickness.

Type of tissue

Tissues composed of a higher atomic number will increase beam attenuation.

Tissue density

Increasing the compactness of the atomic particles will increase beam attenuation.

X-ray beam quality

Higher kVp increases the energy of the x-ray beam and will decrease beam attenuation.

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Exit Radiation

Remnant or exit radiation is composed of transmitted and scattered radiation.The varying amounts of transmitted and absorbed radiation create an image that structurally represents the anatomic area of interest.Scatter radiation reaching the image receptor creates unwanted exposure called fog.

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Secondary Radiation vs. Scatter Radiation

Secondary Radiation refers to any radiation resulting from interactions within the patient.

Scatter radiation refers only to that secondary radiation which has been emitted in a direction different than the original x-ray beam.

Most secondary radiation is scattered.

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Radiographic Quality

A quality radiographic image accurately represents the anatomic area of interest, and its information is well visualized for diagnosis.

Visibility of anatomic structures

Density

Contrast

Accuracy of structural lines (sharpness)

Resolution or recorded detail

Distortion

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Density

A film image is evaluated by the amount of density or overall blackness after processing.

A radiographic image must have sufficient brightness or density to visualize the anatomic structures of interest.

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Image Contrast

The radiograph must exhibit differences in the brightness levels or densities (image contrast) in order to differentiate among the anatomic tissues.

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Subject Contrast

Subject contrast is a result of the absorption characteristics of the anatomic tissue radiographed and the quality of the x-ray beam.

The ability to distinguish among types of tissues is determined by the differences in brightness levels or densities in the image or contrast.

Contrast resolution describes an imaging receptor's ability to distinguish between objects similar in subject contrast.

Gray scale: number of different shades of gray that can be stored and displayed in a digital image

Scale of contrast: the range of densities visible on film

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Scale of Contrast

Short scale or high contrast

Long scale or low contrast

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Recorded Detail

Anatomic details must be recorded accurately and with the greatest amount of sharpness.

Recorded detail

refers to the distinctness or sharpness of the structural lines that make up the recorded film image.

All radiographic images have some degree of

unsharpness

.

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Distortion

Radiographic misrepresentation of either the size or shape of the anatomic part

Size distortion or magnification is an increase in the object's image size compared to its true or actual size.

SID and OID affect magnification.

Shape distortion is a misrepresentation of an object's image shape.

Elongation and foreshortening

Central ray (CR) alignment of the x-ray tube, part, and image receptor affect distortion.

Slide46

Scatter

Unwanted exposure to the image receptor resulting in fog

A result of Compton interactions

Provides no useful information

Scatter or fog decreases image contrast.

Slide47

Radiographic film is composed of two main partsBaseEmulsion

Modern x-ray film

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Consists of emulsion of finely precipitated silver bromide crystals Crystals are suspended in a gelatin and is coated on both sides with a transparent blue tinted polyester support called the base

Film Construction

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Visible image you see when the film is processedWhat you see as your final radiograph

Manifest Image

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Film-screen Image Characteristics

Film used as medium for acquiring, processing, and displaying the radiographic image

Film emulsion: active layer of film that contains the crystals that serve as latent imaging centers

Intensifying screens: used to convert exit radiation intensities to visible light and expose the emulsion crystals

Film is chemically processed to display the range of densities created as a result of the x-ray attenuation characteristics of anatomic structures.

Slide51

Primary Exposure Factors

Milliamperage (mA)

Directly proportional to radiation quantity

Inversely related to exposure time to maintain exposure to image receptor (IR)

Exposure time (time)

Directly proportional to radiation quantity

Inversely related to mA to maintain exposure to IR

mA × time (seconds) = mAs

Kilovoltage (kVp)

Directly related to radiation quality and quantity

Inversely related to radiographic contrast

Slide52

Beam Attenuation

As the primary beam passes through the patient it will loose some of its’ original energy.

This reduction in the energy of the primary beam is known as attenuation.

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Image Receptor Exposure

To increase exposure to image receptor, increase mA, exposure time, or kVp.

To decrease exposure to image receptor, decrease mA, exposure time, or kVp.

To maintain exposure to image receptor

Increase mA and proportionally decrease time

Increase time and proportionally decrease mA

Increase kVp 15% and decrease mAs by half

Decrease kVp 15% and increase mAs by two times

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Changing Kilovoltage

Kilovoltage affects

X-ray beam quality and quantity

X-ray beam penetration and absorption in anatomic tissues

Increasing kVp increases penetration and decreases absorption.

Decreasing kVp decreases penetration and increases absorption.

Subject contrast

Increasing kVp decreases subject contrast.

Decreasing kVp increases subject contrast.

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kVp and Wavelength

KVP increases, wavelength gets shorter; penetrating ability increases.

KVP increases, wavelength decreases, indirect relationship

KVP increases, penetration increases, direct relationship

Slide56

kVp and Wavelength

shorter the wavelength, stronger the penetration, higher the kVp

Higher the kVp, shorter the wavelength

Lower the kVp, longer the wavelength

Slide57

Primary Factors: Film-screen

Kilovoltage and mAs have a direct effect on radiographic density for film-screen imaging.

Repeating a radiograph for a density error requires a change in mAs by a factor of 2 or a change in kVp by 15%.

For insufficient density multiple the mAs by 2 or increase kVp by 15%.

For excessive density divide the mAs by 2 or decrease kVp by 15%.

The best factor to change for density errors is mAs, because kVp also affects radiographic contrast.

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OID

Distance between the anatomic part and image receptor will affect

Radiation intensity reaching the image receptor

Amount of scatter radiation reaching the image receptor

Magnification

Recorded detail/spatial resolution

Slide59

OID (cont.)

An air gap will decrease the intensity of radiation and scatter reaching the image receptor.

Increasing the OID will decrease the exposure to the image receptor, increase contrast and magnification, and decrease recorded detail/spatial resolution.

Decreasing the OID will increase the exposure to the image receptor, decrease contrast and magnification, and increase recorded detail/spatial resolution.

Slide60

OID (cont.)

Distance created between the object and image receptor will reduce the amount of scatter radiation reaching the image receptor.

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Magnification Factor

Magnification Factor (MF) = SID . SODSOD = SID – OIDObject size = image size MF

Source-to-object distance is the distance between the source of the x-ray and the object radiographed.

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Shape Distortion

Any misalignment of the CR among these three factors—tube, part, or image receptor—will alter the shape of the part recorded on the image receptor.

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Grids

Limiting the amount of scatter radiation that reaches the image receptor improves the quality of the radiograph. The effect of less scatter or unwanted exposure on the image is to increase the radiographic contrast.

Much of the scatter radiation toward the image receptor will be absorbed when a grid is used.

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Grids (cont.)

Grids also absorb some of the transmitted radiation exiting the patient and therefore reduce the amount of radiation reaching the image receptor. Grid conversion formula mAs1 = grid ratio1 mAs2 grid ratio2

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Beam Restriction

A larger field size (decreasing collimation) increases the amount of tissue irradiated, causing more scatter radiation to be produced and increasing the amount of radiation reaching the image receptor. The increased amount of scatter reaching the image receptor results in less radiographic contrast.

A smaller field size (increasing collimation) reduces the amount of tissue irradiated and reduces both the amount of scatter radiation produced and the amount of radiation reaching the image receptor. The decreased amount of scatter radiation reaching the image receptor results in higher radiographic contrast, but it requires an increase in mAs.

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Generator Output

Generators with more efficient output, such as three-phase units or high frequency, require lower exposure technique settings to produce an image comparable to those of single-phase units.

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Patient Factors

Body habitus

Hypersthenic, sthenic, hyposthenic, asthenic

Part thickness affects

Beam attenuation

Exposure reaching image receptor

Scatter production and image contrast

Pediatric patients

Small size may require a reduction in exposure

Quicker exposure times may be necessary

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Body Habitus

Hypersthenic: The hypersthenic body is of massive build with a broad and deep thorax. The diaphragm is high and the stomach and gallbladder also occupy high positions. An extreme body type, the hypersthenic classification accounts for only about 5% of all people (large- stocky build).

Sthenic: Means active or strong. The sthenic body is the one we usually associate with the athletic type. The body is rather heavy with large bones. The sthenic body type is the predominant type, with about 50% all people falling into this classification( normal or average build).

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Body Habitus

Hyposthenic: Slender and light in weight with the stomach and gallbladder situated high in the abdomen. About 35 %of all people fall into this classification( slender, taller build).

Asthenic: Extremely slender, light build, with a narrow, shallow thorax, and the gallbladder and stomach situated low in the abdomen. An extreme type, the asthenic classification accounts for only about 10% of all people.

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Special Considerations

Projections and positions

Casts and splints

Pathology

Soft tissue imaging

Contrast media

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The 5 X-ray densities

Low density material such as air is represented as black on the final radiograph. Very dense material such as metal or contrast material is represented as white. Bodily tissues are varying degrees of grey, depending on density, and thickness.

Air –fat-soft tissue-bone-metal

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Positive Contrast Agents

Iodine or barium

Because of their high atomic number(ability to attenuate the beam) not there density, viscosity, or weight

Iodine is 53

Barium 56

Slide73

Rules to Remember

Changes in the average thickness of your patient still exist, and the changes in part thickness affects the x-ray absorption of photons in an exponential way.

For every 4 centimeter change in patient thickness, change the mAs by a factor of 2.

Scatter radiation exists in every radiograph, it increases as patient thickness increases

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Diseases which affect Radiographs

Degenerative disease

This disease breaks bone down; you need less kvp to penetrate it

Arthritis, emphysema

Additive disease

With this disease, you may need more kvp to penetrate it.

pneumonia, pleural effusion- fluid retention

Slide75

exposure latitude

With higher kvp’s you have greater exposure latitude.

With larger body parts there is greater exposure latitude.

thicker the body part, the greater the kvp

As kvp decreases, the exposure latitude decreases making it narrow latitude.

Slide76

Scatter Radiation

Scatter radiation is detrimental to radiographic quality, because it adds unwanted exposure (fog) to the image without adding any patient information.

Radiographic contrast for both film-screen and digital images will be decreased.

Increased scatter radiation either produced within the patient or higher energy scatter exiting the patient will affect the exposure to the patient and anyone within close proximity.

Slide77

Scatter Production

Increasing the volume of tissue irradiated results in increased scatter production.

Patient thickness

Increased thickness will increase the volume of tissue.

X-ray beam field size

Increased field size will increase the volume of tissue.

Higher kVp increases the energy of scatter radiation exiting the patient.

Slide78

Scatter Control

Beam restriction

Beam-restricting devices decrease the x-ray beam field size and the amount of tissue irradiated, thereby reducing the amount of scatter radiation produced.

Grids

Radiographic grids are used to improve radiographic image quality by absorbing scatter radiation that exits the patient, reducing the amount of scatter reaching the image receptor.

Slide79

Beam Restriction

Limits patient exposure

Reduces the amount of scatter radiation produced within the patient.

A beam-restricting device changes the shape and size of the primary beam.

Collimation

Increasing collimation means decreasing field size, and decreasing collimation means increasing field size.

Less scatter radiation is produced within the patient, and less scatter radiation reaches the image receptor.

To maintain exposure to the image receptor, mAs must be increased.

Slide80

Types of Beam Restrictors

Aperture diaphragm

A flat piece of lead (diaphragm) that has a hole (aperture) in it and is placed directly below the x-ray tube window

Cones and cylinders

An aperture diaphragm that has an extended flange attached that varies in length and shape

Collimator

Located immediately below the tube window, has two or three sets of lead shutters that limit the x-ray beam

Slide81

Radiographic Grids

A device that has very thin lead strips with radiolucent interspaces, intended to absorb scatter radiation emitted from the patient

Construction

Radiolucent interspace material

Grid frequency

Grid ratio

Grid ratio = h/D

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Grid Pattern

Linear grid pattern

Crossed/cross-hatched grid pattern

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Grid Focus

Comparison of transmitted photons passing through A, a parallel grid and B, a focused grid

Slide84

Grid Focus (cont.)

Imaginary lines drawn above a linear focused grid from each lead strip meet to form a convergent point. The points form a convergent line along the length of the grid.

The convergent line or point of a focused grid falls within a focal range.

Slide85

Reciprocating Grids

Stationary grids produce visible grid lines on the radiography.

Slightly moving the grid during the x-ray exposure will blur the grid lines, which will therefore be less visible.

Reciprocating grids are a part of the Potter-Bucky diaphragm.

Grid motion is controlled electronically.

Slide86

Grid Conversion

Grid conversion factor (GCF) = mAs with grid . mAs without grid mAs1 = GCF1 mAs2 GCF2

Slide87

Grid Cutoff

A decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the grid

Upside-down focused grid

Off-level grid

Off-center grid

Off-focus grid

Slide88

Grid Selection

Used for anatomic parts 10 cm (4") or larger

Examinations requiring higher than 60 -70kVp

Higher ratio grids will

Increase scatter absorption

Increase patient exposure

Increase potential for grid cutoff

Slide89

Film-screen Image Receptors

Radiographic film serves as the medium for image acquisition, processing, and display.

Double emulsion screen film is placed between two intensifying screens, which will allow patient exposure to decrease.

Sensitivity specks within the film's emulsion serve as the focal point for the development of the latent image centers. These latent image centers appear as radiographic density on the manifest image after processing.

Slide90

Film Characteristics

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

The greater the film speed, the more sensitive it is.

Increased film speed will require less exposure to produce a given density.

Film contrast: the ability of radiographic film to provide a level of contrast (density differences)

Film can be manufactured to display low, medium, or high contrast

Exposure latitude: the range of exposure needed to produce diagnostic densities

Films manufactured to display high contrast have a narrow exposure latitude compared to low-contrast films having a wider exposure latitude.

Slide91

Film-screen Imaging

Radiographic film must be sensitive to the light emission of the intensifying screen.

Spectral matching: correctly matching the color sensitivity of the film to the color emission of the intensifying screen

Spectral sensitivity: the color of light to which a particular film is most sensitive

Spectral emission: the color of light produced by a particular intensifying screen

Slide92

Intensifying Screens

A device found in radiographic cassettes that contains phosphors to convert x-ray energy into visible light, which exposes the film

Phosphor layer: active layer that absorbs the transmitted x-rays and converts them to visible light

Luminescence: the emission of light from the screen when stimulated by radiation

Fluorescence: the ability of phosphors to emit visible light only while exposed to x-rays

Purpose is to intensify the action of the x-rays and permit lower patient radiation exposure

Slide93

Intensifying Screen Speed

Intensifying screens can be manufactured at different speeds (their capability to intensify the action of the x-rays).

Faster speed screens emit more light for the same x-ray intensity.

Patient exposures will decrease.

Recorded detail decreases.

Slide94

Intensifying Screen Speed (cont.)

Factors

Absorption efficiency

Conversion efficiency

Thickness of phosphor layer

Size of phosphor crystal

Presence or absence of a reflecting layer, an absorbing layer, or dye in the phosphor layer

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Slide96

Slide97

FILM-SCREEN Image Quality

Slide98

Variables affecting quality

Electrical

Geometrical

Patient status

IR system

Processing variable

Viewing conditions

Slide99

3 cardinal rules

Time

Distance

shielding

Slide100

Image Instensification Tube

Slide101

Conventional Fluoroscopy

Allows imaging of the movement of internal structures

Uses a continuous beam of x-rays to create images of moving internal structures

Uses a low mA (0.5 to 5)

Deadman type switch

5-minute timer

Fluoroscopic images viewed on a monitor

Slide102

Fluoroscopy/tomography

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