XRIM – Imaging

XRIM – Imagination

Learning aims

O Critique recorded item on assorted radiographic images.

o Differentiate between umbra and focal topographic point fuzz.

o Define border acuteness and border conspicuity.

O Analyze the relationships of factors impacting recorded item.

o Define deformation and differentiate between size and form deformation.

o Perform computations to find image magnification factor.

o Differentiate between magnification as deformation and macro-radiography.

o Summarize the relationship of factors impacting deformation.

o Formulate a program of action to diminish image deformation.

o Summarize the relationship of factors impacting exposure latitude.

o Discuss practical considerations in puting criterions for acceptable image quality.

o Assess radiographic density/brightness on radiographic images.

o Distinguish between acceptable and unacceptable image densities/brightness.

O Analyze the relationships of factors that control and affect image density/brightness.

O Critique the radiographic contrast within assorted radiographic images.

o Differentiate between capable contrast and image receptor contrast.

o Distinguish between acceptable and unacceptable contrast graduated tables.

o Compare long-scale/high spot depth and short-scale/low spot depth contrast images.

O Analyze the relationship of factors that control and affect radiographic contrast.

o Explain the principle for utilizing beam restricting devices.

O Describe the operation and applications for different types of beam-limiting devices.

o Evaluate beam-limiting devices for alliance and tolerance.

O Select the most appropriate beam-limiting device to be used for a given clinical state of affairs.

o Explain the impact beam filtration has on x-ray beam strength, beam quality and attendant patient exposure.

O Describe the alteration in the half value bed ( HVL ) when filtration is added or removed in the beam.

o Summarize the relationship of factors impacting scattered and secondary radiation.

o Evaluate the effects of scattered radiation on the image.

O Compare grid types.

o Articulate the advantages and disadvantages of grid usage.

O Describe grid care.

O Select the most appropriate grid for a given clinical state of affairs.

O Interpret grid efficiency in footings of grid ratio and frequence.

o Define grid cutoff.

o Summarize the factors that influence grid cutoff.

o Evaluate grid artefacts.

o Formulate a set of regulations for grid usage to forestall grid cutoff and artefacts.

o Explain the usage of standardised radiographic technique charts.

o Explain exposure factor considerations involved in choosing techniques.

Os Compare fixed kV ( kilovolt ) and variable kilovolt systems.

o Formulate a technique chart utilizing either a fixed kilovolt or variable kilovolt system.

o Apply mAs reciprocality to clinical simulations.

O Describe the effects of storage on image quality.

o Apply transition factors for alterations in the undermentioned countries: distance, grid, image receptors, mAs reciprocality and 15 per centum regulation.

Cardinal footings

Aperture stop

The aperture stop is a metal device that limits the country of the x-ray beam emerging from the x-ray tubing, it may be fixed or variable in size

Compton consequence

In the Compton consequence, single photons collide with individual negatrons that are free, or slackly bound in affair. The colliding photons transfer energy to the negatrons, and lose some of their impulse. At the minute of hit new photons are produced that spread at angles the size of which depends on the amout of energy lost. The Compton consequence was foremost observed by Arthur Compton in 1923.

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Compton Effect [ XRIM_001_compton_TW ]

Cones

Cones or cylinders are devices that can be connected to the x-ray tubing to parallel the x-ray beam. Cones and cylinders can be fixed or adjustable. In order to focus on the tubing for the x-ray the cone or cylinder must be removed and so replaced.

Contrast

Contrast is the difference in brightness between the visible radiation and dark countries of a radiogram

Contrast declaration

Contrast declaration is a step of the ability to separate between two next soft tissues. Contrast declaration is determined by spread radiation and other imaging noise.

Exposure clip

The exposure clip is the length of clip the exposure continues. This is normally measured in msecs.

Field size

The field size is the maximal country that will be exposed to radiation. The field size will change harmonizing to collimation

Grid

A grid is a level home base that contains lead strips interspaced with radiolucent stuff that are encased in aluminum to protect them. A grid is used between the patient and the image receptor to absorb spread radiation

kilovolt ( kilovoltage )

The kilovoltage ( kilovolt ) is set by the engineer harmonizing to the exposure chart, or required exposure for a radiogram. The kilovolt determines the quality of the xray beam. Some older x-ray consoles have accommodation controls for major and minor kilovolt

Milliampere ( ma )

The millampere is a step of the current across the tubing

Milliampere-second ( ma )

The milliampere-second ( ma ) is a step of the entire figure of negatrons produced as a merchandise of exposure clip and x-ray tubing current

Patient thickness

The patient thickness is that country of the patient that the radiation passes through to make the image receptor.

Penumbra

The penumbra is an country of changing denseness at the border of the image due to geometric factors. Penumbra is more evident with a larger focal topographic point.

Scatter radiation

Scatter radiation is radiation that interacts with the patient, losing energy, some spread is deflected back towards the incident beam while other spread will make the movie doing loss of contrast

Source-to-image receptor distance ( SID )

The SID is the distance from the focal topographic point of the x-ray tubing to the image receptor. The SID is of import due to the deformation that occurs. At a shorter SID there is more magnification than at a greater SID. This explains the importance of utilizing the right SID for each scrutiny.

A chest X ray is taken with a SID of 72” ( 180cm ) , this consequences in less magnification of the thoracic constructions.

More normally a SID of 40 – 48” ( 100-122 centimeter ) is used.

Spatial declaration

Spatial declaration is the ability to separate an object from its milieus and is a step of the acuteness of the image. Spatial declaration is determined by collimation, focal topographic point size and other factors the attention deficit disorder to image blurring

Umbra

The umbra part of the x-ray beginning is the homogenous part of the beam that is non blocked or partly blocked by the collimator.

1.0 Beam curtailing devices ( Chapter 14 )

1.1 Scatter radiation

Scatter radiation is produced by the interaction of X raies with the patient or another construction. Upon this interaction happening the scattered X raies change their way of travel and lose energy. As the sum of scattered radiation that reaches the image receptor increases the contrast of the image decreases.

1.1.1 kilovolt

As the kilovolt is increased ( this is the energy of the x-ray beam ) the sum of spread produced besides increases due to the Compton consequence. kV should be carefully selected taking into history patient size and necessary incursion. It is besides of import to guarantee that acceptable radiation protection patterns are adhered to ; utilizing higher ma will ensue in a higher patient dosage while still giving an equal radiogram. A balance between kilovolts and ma is necessary to accomplish high quality radiographs while maintaining patient dosage to a lower limit.

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Skull radiogram utilizing different exposures [ XRIM_002_skulls_TW ]

Collimators and grids are used to cut down the sum of scattered radiation making the image receptor

1.1.2 Field size

As field size additions, the sum of scattered radiation making the image receptor additions, this consequences in loss of contrast in the image.

Field size is controlled by the engineer utilizing collimators. When the field size in reduced, exposure factors may necessitate to be increased somewhat.

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Spine radiographs utilizing different collimation [ XRIM_003_spine_TW ]

1.1.3 Patient thickness

Imaging thicker parts of the organic structure, such as lumbar spinal column or pelvic girdle, will do more spread radiation than imaging thin organic structure parts such as the carpus. This is due to the sum of tissue available for the x-ray beam to interact with. This addition in scatter causes a lessening in the acuteness of the radiographic image.

Compaction devices can assist to cut down patient thickness thereby increasing spacial declaration. Compression besides helps to cut down patient radiation dosage and improves contrast declaration. This is peculiarly of import in mammography.

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manus radiogram [ XRIM_004_hand_TW ]

1.2 Control of spread

1.2.1 Effect of spread on image contrast

Scattered radiation consequences in reduced contrast in the image.

If merely primary X raies reached the image receptor the image would be really crisp with high contrast.

When merely scattered X raies reach the image receptor the image is really gray with no definition.

The correctly exposed image contains some primary x-ray and some scattered x-ray resulting in a combination of the contrast and Grey to bring forth a chiseled image with moderate contrast.

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Consequence of spread radiation on image contrast [ XRIM_005_scatter_TW ]

1.2.2 Beam restrictors

There are three basic types of beam restrictors, these are aperture stop, cylinder or cone, and collimator.

Aperture Diaphragm

The aperture stop is a metal device that limits the country of the beam emerging from the x-ray tubing, it may be fixed or adjustable. Some aperture stop are round, others are rectangular.

Typically the aperture stop is designed to cover somewhat less country than the image receptor used. In some systems the aperture stop is manually changed harmonizing to the image receptor size.

Aperture diaphragm [ XRIM_006_aperture_TW ]

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Cylinders and cones

Cylinders and cones are extensions of the stop and, as the name indicates, are either conelike or cylindrical in form. These cones/cylinders are used to cut down spread radiation and better contrast declaration for imagination of the facial castanetss, fistulas, etc.

X-ray cones/cylinders [ XRIM_007_cones_TW ]

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Collimator

The variable aperture collimator is the light placing collimator most normally used for beam limitation.

Not all X raies emitted from the x-ray tubing emerge exactly from the focal topographic point. This radiation is called off-focus radiation and it increases image fuzz.

The collimator controls this off-focus radiation with a first-stage entryway shuttering device that has multiple collimator blades. This first-stage shutter lies near the focal point.

The second-stage shutters are normally 3mm thick lead leaves that work in braces and are independently controlled utilizing boss on the front panel.

Light localisation is accomplished with a little lamp and a mirror that are adjusted so that the visible radiation projected coincides with the x-ray beam produced. The alliance of the visible radiation to the x-ray beam should be tested sporadically as portion of quality control.

Most collimators will automatically set to the size of the cassette loaded into the Bucky tray, the engineer should parallel farther if possible, utilizing the two collimator controls, to cut down patient radiation dosage and better the radiographic image.

Automatic variable-aperture Collimator [ XRIM_008_collimator_TW ]

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2.0 Radiographic grids

2.1 Grids

The x-ray grid was foremost used by Gustave Bucky in 1913 to cut down the sum of spread making the image receptor. The grid was stationary, which caused grid lines on the movies, but the decrease in the sum of spread making the movie greatly improved the contrast of the radiogram.

The grid is made utilizing strips of lead sandwiched between radiolucent stuff. The lead strips are angled in such a manner as to merely let X raies from the primary beam to go through through to the image receptor. The grid is placed between the patient and the image receptor.

These yearss the grid is built into the tabular array and unsloped Bucky system. However there are besides stationary grids, that are either built into the cassette or encased in a radiolucent stuff, available for usage on bed-ridden patients and for usage in trauma radiology.

Stationary grids [ XRIM_009_stationary_TW ]

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X raies and scattered radiation that strike the radio-opaque lead strips of the grid will non make the image receptor as they are absorbed. Some scattered radiation may go through through the radiolucent interspace stuff, but about 80 % to 90 % can be absorbed depending on the quality of the grid.

A grid should be used when the organic structure portion to be radiographed steps over 10 centimeters.

2.1.1 Grid ratio

Each grid is made taking three constituents into history:

* the thickness of the lead strip

* the breadth of the interspace stuff

* the tallness of the grid.

These three factors represent how good the grid will absorb spread radiation, and are called the grid ratio.

The grid ratio is defined as the tallness of the grid strip divided by the thickness of the interspace stuff. Grid ratio = H

Grid ratio [ XRIM_010_grid ratio_TW ]

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The higher the grid ratio the more effectual the grid is at taking spread radiation. However, owHo there are drawbacks:

* radiographic factors have to be increased to counterbalance for the losingss, ensuing in an increased patient radiation dosage

* the focus of the x-ray beam to the grid must be more precise

* and a narrower focal scope must be used.

The grids most frequently used scope between a grid ratio of 5:1 to 16:1. A 5:1 grid reduces spread radiation by about 85 % .

2.1.2 Grid frequence

Grid frequence is the figure of lead strips per inch. Most grids have a frequence of between 60 – 110 strips per inch.

Grids with a higher frequence show less distinguishable lines on the radiogram, but necessitate the usage of a higher exposure and are less effectual at absorbing high energy spread radiation.

2.1.3 Interspace stuff

The interspace stuff is used to keep the precise distance between the lead strips of the grid. The stuffs used for this are normally aluminium or fictile fibre.

2.1.4 Grid strip

The grid strip is by and large made of lead as it is easy shaped and cheap. Some other stuffs are used and gold, Pt, wolfram, and U have all been tried over clip.

2.2 Grid public presentation

2.2.1 Contrast betterment factor

The rule map of a grid is to take spread radiation, this will increase the contrast of the radiographic image. A contrast betterment factor of 1.5 to 2.5 is normal. A contrast betterment factor of 1 would bespeak no betterment.

The contrast betterment factor of a grid is able to be calculated utilizing the undermentioned equation:

The contrast betterment factor is higher for high-ratio grids.

2.2.2 Bucky factor

The Bucky factor, besides called the grid factor, is named for Gustave Bucky, the discoverer of the grid, and is a step of the addition in radiographic technique required when utilizing a grid to bring forth an image of the same optical denseness ( OD ) .

In general the higher the grid ratio, the higher the Bucky factor,

And the higher the kilovolt, the higher the Bucky factor.

As the Bucky factor additions, patient dosage besides increases.

2.3 Grid types

2.3.1 Parallel grid

This is the simplest type of grid. All the lead strips are parallel to each other.

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Parallel grid [ XRIM_011_parallel_ ( TW ) ]

The biggest advantage of the parallel grid is that the x-ray tubing can be angled along the grid length without grid cutoff happening.

The biggest job with this type of grid is that grid cutoff is common, this is most frequently due to a short beginning to image distance ( SID ) , or with a big image receptor ( IR ) .

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A short beginning to image distance ensuing in grid cutoff [ XRIM_012_cutoff_TW ]

Grid cutoff is the unwanted soaking up of primary X raies by the grid. It can be partial or complete. Cutoff will happen if the grid is improperly positioned.

2.3.2 Crossed grid

Crossed grids have lead strips that run parallel to the long and short axes of the grid. Crossed grids are more efficient than parallel grids at cleaning up spread radiation, as parallel grids merely clean up radiation in one way, along the axis of the grid. This becomes particularly noticeable at high kilovolt.

There are three disadvantages of crossed grids:

* The cardinal beam of the x-ray beam must match with the centre of the grid, therefore the grid must be positioned accurately.

* Tilt-table techniques are possible merely if the tubing and tabular array are aligned right

* The exposure technique requires the usage of higher radiation scene, ensuing in a higher radiation dosage to the patient

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Crossed grids [ XRIM_013_crossed_ ( TW ) ]

2.3.3 Focused grid

The focused grid is designed with the lead strips arranged in a radius around the centre of the grid. The xray tubing must be centered to the centre of the grid, and is merely able to be used at specified focal distances. This is because the lead strips are positioned so that they will co-occur with the divergent primary beam, positioned right there will non be any grid cutoff. If used at distances other than those specified grid cutoff will happen.

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Focused grids [ XRIM_014_focused_ ( TW ) ]

2.3.4 Traveling grid

The traveling grid was developed in the 1920s by Hollis E. Potter. This system is called a Potter-Bucky stop, most frequently shortened to ‘Bucky ‘ . This system is used to extinguish grid lines that appear on stationary grids.

The Bucky assembly consists of:

* A frame to keep the grid

* An anti-scatter grid

* A mechanism to travel the grid

* A steel cassette tray

The grid used within the Bucky is by and large a focussed grid that is mounted in a frame. The grid begins to travel merely before the x-ray exposure and Michigans after the exposure ends. The velocity and scope of grid motion must be sufficiently big to film over the grid lines, but non so big as to do grid cutoff.

The whole Bucky assembly is mounted on bearings to let smooth motion along a path the length of the tabular array

The two basic types of traveling grid mechanism are hovering and reciprocating.

Reciprocating grid – A reciprocating grid moves back and forth several times during the exposure. The entire distance moved by the grid is about 2 centimeters.

Hovering grid – An oscillatory grid is positioned within a frame with a 2 – 3 cm clearance on all sides. Delicate springs hold the grid centered. The grid is pulled to one side by a magnet during the prep stage of the exposure and is released at the beginning of the exposure.This allows the grid to hover for 20 to 30 seconds. The size of the oscillation reduces as the exposure continues.

There are multiple disadvantages to traveling grids:

* They are capable to failure as with any mechanical device

* The distance between the patient and image receptor is increased, increasing image magnification and fuzz.

* The traveling grid may present motion into the cassette doing extra image fuzz.

Fortunately the gesture fuzz is so minimum that it is virtually undetectable.

2.4 Grid jobs

2.4.1 Off-level grid

To work right a grid must lie perpendicular to the cardinal x-ray beam. Most instances of off-level grid are due to the x-ray tubing being improperly positioned, instead than the grid itself. This job can happen when the grid is tilted during horizontal beam skiagraphy. During nomadic skiagraphy, an off-level grid can happen when the image receptor sinks down into the patient ‘s bed.

The resulting image will be underexposed with grid cutoff across the image.

Off-level grid [ XRIM_015_off-level_TW ]

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2.4.2 Off-center grid

The grid must be centered to the cardinal x-ray beam to avoid grid cutoff. If the x-ray beam is perpendicular to the grid but off-centered the x-ray beam will be partly cutoff, an mistake of positioning known as sidelong decentering.

Off-center grid [ XRIM_016_off-center_TW ]

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2.4.3 Off-focus grid

A focused grid must be used at the specified SID. If the grid is used at the wrong SID, cutoff will happen as the divergency of the cardinal beam will non co-occur with the grid. The farther the grid is from the specified SID the worse the cutoff. Grid cutoff is more terrible at the borders of the image receptor than at the centre.

Off-focus grid [ XRIM_017_off-focus_TW ]

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2.4.4 Inverted grid

Care must be taken to guarantee that the stationary grid is placed confronting in the right way. If the grid is placed upside down there will be terrible grid cutoff on either side of the image.

It will be instantly obvious upon seeing a radiogram that the grid was upside down. The grid is labelled clearly by the maker to bespeak tube side and movie side.

Inverted grid [ XRIM_018_upside-down_TW ]

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2.5 Grid choice

2.5.1 Patient dosage

One major disadvantage of utilizing grids in skiagraphy is the addition in patient dosage. The needed radiation dosage to the patient additions by about 15 % when utilizing a traveling grid alternatively of a stationary grid.

In mammography, the usage of a low ratio grid greatly improves the contrast of the image with no loss of spacial declaration ; nevertheless, the patient dosage is increased.

As the grid ratio of the grid additions, the patient radiation dosage will besides increase. This is due to the addition in exposure factors required to bring forth a quality radiogram.

2.5.2 Air-gap technique

The air-gap technique is another method of cut downing spread radiation. This method does non utilize a grid.

The image receptor is moved 10 – 15 centimeter from the patient, thereby cut downing the sum of spread radiation that reaches the IR. Image contrast is enhanced utilizing this technique.

The exposure factors used are by and large the same as for an 8:1 ratio grid.

This technique has been utile in countries of thorax skiagraphy where the SID is increased from 180cm to 300cm ensuing in a sharper image with small magnification. Using this technique, the higher exposure factors do non bring forth a higher patient dosage.

The air-gap technique is by and large non used at higher kilovolt because the x-ray spread at higher kilovolt has a more forward motion due to the increased energy of the beam, cut downing the benefits of the air-gap.

3.0 Radiographic exposure

Radiographic exposure factors are the agencies used to bring forth a diagnostic radiogram of high quality.

The four premier exposure factors are kV, mA, exposure clip, and source-to-image receptor distance ( SID ) . These factors are under the control of the engineer, it is hence necessary for the engineer to understand how altering the factors will impact the image produced.

Focal topographic point size and filtration are secondary factors that require consideration.

3.1 kilovolt

kilovolt is used to increase or diminish the sum of incursion of the x-ray beam.

An addition in kilovolt will increase the sum of X raies emitted by the x-ray tubing, and those X raies will hold a higher energy and higher incursion. A farther merchandise of higher kilovolt is increased spread radiation due to the increased interaction by Compton consequence ; this addition in spread decreases the contrast of the image.

The kilovolt selected determines the optical denseness ( OD ) of the image, and the graduated table of contrast. An addition in kV consequences in a decrease in image contrast due to a decrease in differential soaking up.

3.2 ma

The ma determines the strength of radiation, or radiation measure, produced by the x-ray tubing.

If exposure clip remains changeless, an addition in the figure of negatrons going through the x-ray tubing will ensue in a relative addition in the figure of X raies produced. For illustration, an addition from 200mA to 400mA would duplicate the sum of X raies produced, and duplicate the dosage of radiation to the patient.

A alteration in ma will non ensue in a alteration to the quality of an x-ray image.

3.3 Exposure clip

Exposure clip is by and large kept every bit short as possible to cut down gesture fuzz caused by patient motion.

When exposure clip is decreased, mA must be increased proportionally to accomplish the needed x-ray strength.

Exposure clip on the x-ray console may be expressed as fractions ( 1/20, ? , 1.0 ) , milliseconds ( 50, 500, 1000 ) , or seconds ( 0.05, 0.5, 1.0 ) .

In some x-ray consoles, ma and exposure clip are combined and expressed as ma ( mAs=mA x s ) . The ma is responsible for finding the figure of X raies in the beam, and hence controls radiation measure. The ma scene is the chief determiner of commanding the optical denseness of the x-ray image.

3.4 Distance

The source-to-image distance ( SID ) does non consequence the quality or measure of the x-ray beam, it does nevertheless impact the strength of the x-ray beam at the image receptor.

Standard SIDs of 100cm and 180cm are most normally used, . Larger SIDs of 120cm for tabletop and up to 300cm for thorax skiagraphy are used in some centres.

The usage of longer SID reduces image magnification and focal topographic point fuzz, and increases spacial declaration. The longer SID requires a higher ma to be used.

3.5 Imaging system features

3.5.1 Focal-spot size

The bulk of x-ray tubings have two foca-spot sizes, normally referred to as little or big.

The big focal topographic point is used for imagination of dense or thick organic structure parts, therefore enabling sufficient ma to be used. The big focal topographic point enables a shorter exposure clip, which helps to forestall gesture fuzz.

The little focal topographic point is used for skiagraphy that requires a greater sum of all right item, such as for the appendages, where the measure of X ray required is comparatively low. A little focal topographic point is ever used for magnification positions.

3.5.2 Filtration

Three signifiers of filtration are used in x-ray beams: inherent, added, and compensating.

Built-in filtration

Built-in filtration is filtration of the x-ray beam that occurs within the x-ray tubing. The parts of the tubing that contribute to built-in filtration are the glass envelope, and the oil coolant within it.

The built-in filtration value is tantamount to about 0.5mm of aluminum ( Al ) .

Built-in Filtration [ XRUR_019_inherent_TW ]

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The variable collimator normally adds about 1.0mm Al tantamount filtration, due chiefly to the mirror within it. A farther 1.0mm Al filter is added between the collimator and the x-ray tubing lodging to run into the needed 2.5mm Al tantamount filtration. This demand comes from the National Council on Radiation Protection and Measurements ( NCRP ) .

The built-in filtration can non be altered by the engineer.

Added filtration

Added filtration is a thin sheet of aluminum placed between the x-ray tubing lodging and the x-ray beam collimator. The add-on of a filter consequences in an addition in the half value bed ( HVL ) of the x-ray beam. This addition in HVL increases the quality of the x-ray beam ensuing in a higher energy X ray.

Half value bed ( HVL ) is the thickness of absorptive stuff needed to diminish the strength of the x-ray beam by half.

It is non usual to add or alter the filtration, but some centres may utilize higher filtration for imagination of articulations, thoraxs and appendages.

When decently used, higher filtration can cut down patient radiation dosage.

Ensure that filtration is returned to its normal place before go forthing the x-ray room.

Compensating filters

Compensating filters are forms of aluminum mounted on a home base, which are added to the collimator when required.

Compensating filters are used to bring forth a more unvarying x-ray exposure at the image receptor by counterbalancing for the differences in organic structure thickness, or tissue densenesss.

The most normally used counterbalancing filters are the cuneus ; used for sidelong spinal column X raies, and the trough ; used for thorax skiagraphy to counterbalance for the difference in densenesss of the mediastinum and lungs.

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Types of aluminum counterbalancing filters [ BRAT_048_types_ ( TW ) ]

As added filtration is increased x-ray beam quality and perviousness additions. The ensuing image has more scattered radiation and hence decreased image contrast.

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Compensating filter on collimator [ BRAT_047_filter_ ( TW ) ]

Rubber counterbalancing filters are placed between the patient and the IR. This type of filter is used to rarefy extra radiation that may kill soft tissues.

The throwing stick counterbalancing filter is a curving gum elastic filter used to rarefy extra radiation that obliterates the humeral caput in shoulder radiogram. The filter is placed between the patient and the table/bucky. This filter is besides used for sidelong knee/patella, AP cervical spinal column, rhinal castanetss, soft tissue mentum, and oblique lower jaw.

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Boomerang counterbalancing filters [ BRAT_049_boomerang_ ( TW ) ]

Ingot counterbalancing filter

The metal bar counterbalancing filter is used to rarefy extra radiation to better visual image of C-7 or sidelong lumbar spinal column, particularly in patients with big hips and little waist. The filter is besides used for positions of the hip and greater trochanter, and in the axial position of calcaneum.

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Ingot counterbalancing filter [ BRAT_050_Ingot_ ( TW ) ]

The soft incline compensation filter

The soft incline is utile for radiogram of the custodies and pess where there is a thickness difference. The thicker portion of the filter is placed under the toes or fingers to take extra radiation with the dilutant portion under the thicker portion of the pes.

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Gentle incline counterbalancing filter [ BRAT_051_slope_ ( TW ) ]

3.5.3 High-voltage coevals

There are three types of high-voltage generator available for x-ray production, they are individual stage, three stage, and high frequence. The quality and measure of X ray produced in the x-ray tubing is straight influenced by the type of high-voltage generator used.

3.5.3.1 Single stage high-voltage generator

* Half-wave rectified generator

The half-wave rectified generator will merely bring forth and breathe x-rays half of the clip due to 100 % electromotive force rippling.

This system is inefficient as it produces no x-rays during half of the rhythm, the exposure clip has to be long to include a whole rhythm. However it is comparatively little and inexpensive and as such is used in dental x-ray units and some nomadic units.

The quality of radiation produced is the same as in the full-wave rectified generator, but the measure is halved.

* Full-wave rectified generators

Full-wave rectified generators are indistinguishable to the half-wave rectified generators except that the negative rhythms are inverted to duplicate the figure of positive rhythms, this causes a continual pulsation of X raies to be emitted thereby cut downing the exposure clip by half.

The quality of radiation produced is the same as for the half-wave rectification, but measure of radiation doubles.

3.5.3.2 Three-phase generator

Three-phase power is more efficient than single-phase power, bring forthing X raies of a higher quality and measure.

The 3-phase power uses 3 wires each holding a individual stage jumping current that is out of stage with the other two wires.

These generators are expensive and big, and have the possibility of more to travel incorrect.

* Three-phase, 6 pulsation

The 3-phase jumping current of each wire is rectified to bring forth two pulsations per line, ensuing in a sum of six pulsations. The rippling is reduced to 13 – 25 % .

* Three-phase, 12 pulsation

The 3-phase alternating current is rectified, utilizing a different constellation of transformers, to bring forth 12 pulsations per rhythm. The rippling is reduced to 3 – 10 %

3.5.3.3 High-frequency generators

The high frequence generator produces a about changeless electromotive force to the x-ray tubing, with a rippling of less than 1 % . The quality and measure of X ray produced is higher than any of the other generator types

The high-frequency generator is little plenty to be placed within the same enclosure as the x-ray tubing. These generators are used in dedicated mammography units, computed imaging systems and nomadic x-ray imaging systems.

4.0 Image quality ( Chapter 16 )

4.1 Definitions

4.1.1 Radiographic quality

Radiographic quality refers to the truth with which the organic structure portion being examined is imaged on the X ray. A radiogram that reproduces bone and soft tissue exactly is called a high-quality radiogram. The features that determine radiographic quality are spacial declaration, contrast declaration, noise, and artefacts.

4.1.2 Resolution

Resolution is the ability to separate between two separate objects and visually distinguish one from the other.

Spatial declaration is the ability to image little objects that have high capable contrast. Spatial declaration will better as screen fuzz, gesture fuzz and geometric fuzz lessening.

Contrast declaration is the ability to separate anatomical constructions of similar capable contrast, for illustration kidney and lien.

Some radiographic engineers use the term ‘detail ‘ in topographic point of ‘spatial declaration ‘ , and ‘recorded item ‘ in topographic point of ‘contrast declaration ‘ .

Optimization of image contrast and optical denseness ( OD ) better the ‘visibility of item ‘ or detail able to be seen on the radiogram.

4.1.3 Noise

Radiographic noise is random fluctuation of radiographic brightness that reduces the lucidity of little low contrast objects of the image

There are four radiographic mechanisms that contribute to the production of noise in skiagraphy, these are construction mottle, movie coarseness, quantum mottle, and spread radiation.

* Structure mottle is built-in within the escalating screen of the x-ray cassette, that is it is caused by a physical imperfectness in the screen, and relates to the distribution of the phosphor crystals. The engineer can non change construction mottle, and it is considered comparatively unimportant.

* Film coarseness is built-in to the movie emulsion, and relates to the size and spacing of the Ag halide grains within the emulsion. The engineer can non change movie coarseness and would necessitate a amplifying glass to be cognizant of the Ag grains.

* Quantum mottle is a major subscriber to radiographic noise. X-rays hitting theintensifying screen of the image receptor unevenly will bring forth quantum mottle. The engineer can change the sum of quantum mottle impacting the image by seting ma and kilovolt. Using a high ma and low kilovolt, combined with a slower image receptor will cut down quantum mottle.

4.1.4 Speed

* The velocity ( sensitiveness ) of an image receptor refers to the ability of the image receptor to bring forth a given image denseness. A high velocity escalating screen demands less x-ray exposure to bring forth a given denseness than a slower screen.

* Image receptors are either fast or slow.

* Slower image receptors have less noise than faster 1s, but they require more patient radiation dosage.

* Fast image receptors have more noise, but require lower patient dosage.

Fast image receptors have low spacial declaration and contrast declaration, with high noise.

Slow image receptors have low noise, and hence high spacial declaration and contrast declaration.

4.2 Film factors

Sensitometry is a survey of the relationship between the strength of exposure of a movie, and the inkiness of the movie following processing. Sensitometry is used for quality control within the radiographic section.

Film factors that may impact radiographic quality are characteristic curve, optical denseness and movie processing.

4.2.1 Characteristic curve ( H & A ; D curve )

The characteristic curve of a radiographic movie is a in writing representation of the relationship between optical denseness ( OD ) and radiation exposure. The characteristic curve is besides known as the H & A ; D curve.

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The characteristic curve of radiographic movie [ XRIM_020_curve_TW ]

To bring forth a characteristic curve a radiographic movie is exposed through a sensitometer. If a sensitometer is non available the movie can be exposed to radiation utilizing an aluminium measure cuneus.

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Sensitometer [ XRIM_000_sensitometer_TW ]

When the movie is processed an image is produced with increasing stairss of optical denseness that match the optical measure cuneus.

The processed movie is read utilizing a densitometer. The information should be recorded.

A densitometer is a device that has a little pin-hole visible radiation beginning on one side and a light detector on the other. The radiographic movie is positioned with a measure of the optical denseness cuneus between the detector and visible radiation. The densitometer measures the sum of light go throughing through the movie.

The recorded information is plotted to organize a characteristic curve. The information is presented as the alteration in OD at each measure. The x-axis uses a log comparative exposure ( LRE ) graduated table

Log comparative exposure -Due to the great scope of exposures making different countries of the film-screen image receptor a logarithm is used so that a scope 1 to 1000 becomes a scope of 0 to 3. This gives a dependable method of quantifying the exposure received by movies.

A typical characteristic curve is divided into three parts:

The portion to the left of the toe: this includes basal denseness of the movie, fog, and threshold. Base denseness of movie and fog are frequently referred to as Base fog, and should hold a value less than 0.2. Threshold is the portion of the the toe where denseness on the movie begins to lift above base fog.

The portion between the toe and the shoulder: this portion of the curve includes contrast, gradient, movie latitude, exposure latitude, velocity, and sensitiveness. Often referred to as the consecutive portion of the curve, this portion is most of import as it shows that a alteration in exposure causes a important alteration in denseness.

The portion to the right of the shoulder: includes maximal denseness, and reversal. This is besides called the part of over-exposure. There becomes a point at which the image can non increase denseness any farther ; this is maximal denseness. Reversal is an incident where the denseness of the movie has reached its maximal denseness and begins to cut down in denseness. Duplicating movie uses this phenomenon to make exact transcripts of radiogram

A decently exposed radiogram would look in the straight-line part of the characteristic curve.

Three parts of the characteristic curve [ XRIM_021_3 parts_TW ]

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4.2.2 Optical denseness

Optical denseness ( OD ) is a logarithmic map defined as:

The equation allows computation of the OD by mensurating the degree of light incident on a processed movie ( Io ) and the degree of visible radiation transmitted through the same movie ( It ) .

The scope of OD on a movie lies between 0 to 4. An OD of 4 would let merely 0.01 % of visible radiation to be transmitted to the X ray, ensuing in the blackest film.This would be maximal denseness on the characteristic curve.

Radiographic movie has base denseness and fog denseness. Built-in base denseness, due to the composing of the base and the shade that is added to the base, has a value of about 0.1. This allows between 50 % and 79 % light transmittal.

Fog is denseness produced by the development of Ag halide grains in the emulsion which have received no knowing exposure. Fog denseness should non transcend 0.1. Fog denseness can be caused by exposure of the radiographic movie during storage, chemical taint, and improper processing. As the grade of fog denseness additions, the contrast of the radiogram decreases.

The most utile scope of OD lies between 0.25 and 2.5 ; nevertheless, this scope may be altered by the form of the characteristic curve, viewbox light, and sing conditions.

* Reciprocity Law

The reciprocality jurisprudence states that the relationship between exposure and optical denseness ( OD ) should stay changeless regardless of the exposure rate. The optical denseness ( OD ) of the image will stay changeless as long as the ma is changeless, irrespective of whether exposure clip ( s ) is long or short.

The reciprocality jurisprudence merely applies for direct exposure with X raies, it does non keep for film/screen exposures less than 10ms, or greater than 2s. Reciprocity jurisprudence failure consequences in really short or really long exposures when movie is unable to efficaciously utilize incident visible radiation, doing OD to be lower than expected.

The reciprocality jurisprudence becomes of import when project processs that use really long or really short exposures as the ma may necessitate to be increased to counterbalance for reciprocality jurisprudence failure.

* Contrast

Radiographic contrast is the denseness difference between two countries of a radiogram. A high contrast radiogram shows a big alteration in optical denseness between the two countries of the radiogram.

High contrast radiogram [ XRIM_022_high_TW ]

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A low contrast radiogram shows a little alteration in optical denseness between the two countries

Low contrast radiogram [ XRIM_023_low_TW ]

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Radiographic contrast is determined by two factors ; Image receptor contrast, and capable contrast.

Image receptor contrast is built-in in the movie and escalating screen used, and is affected by movie processing. Different types of movie will hold different contrast, therefore it is of import for a section to standardise the film/screen combinations used to accomplish consistent radiogram. An image receptor with contrast of 1 has really low contrast.

kilovolt and ma choice for a given film/screen combination will be dependent on the contrast of the image receptor. The characteristic curve below demonstrates this with the steeper curve stand foring an image receptor with greater contrast.

Typical movie characteristic curve [ XRIM_024_film_TW ]

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Capable contrast is determined by the size, form and denseness of the organic structure portion being examined. X-ray energy ( kilovolt ) used will impact capable contrast ; usage of low kilovolts will bring forth a high contrast radiogram due to fading of the x-ray beam by the topic

Low kilovolt radiogram [ XRIM_025_low_kV_TW ]

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High kilovolt radiogram [ XRIM_026_high_kV_TW ]

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Control of kilovolt is the function of the radiographic engineer. By choosing an appropriate exposure the radiographic engineer can guarantee the OD of the image will lie in the utile scope.

The characteristic curve allows the radiographic engineer to measure the contrast degree by the abruptness of the consecutive line part of the curve, and by where their image contrast lies within the curve. The utile scope of the curve is the consecutive line part.

* Speed

The velocity ( sensitiveness ) of an image receptor refers to the ability of the image receptor to bring forth a given image denseness. A high velocity film/screen combination needs less x-ray exposure to bring forth a given denseness than a slower screen.

Characteristic curve for movie velocity [ XRIM_027_speed_TW ]

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The velocity of an image receptor is the reciprocal of the exposure, in Rs, needed to bring forth an optical denseness of 1.0 above base plus fog.

The characteristic curve shows the point at which the optical denseness of 1.0 plus basal fog is reached, this is the velocity point.

The radiation dosage to the patient is reciprocally relative to the velocity of the image receptor. This means that increasing the velocity of the image receptor by a factor of two ( ie traveling from 200-speed to 400-speed film/screen ) will cut down the patient radiation dosage by half.

* Latitude

Latitude is the scope of exposures that will bring forth densenesss in the diagnostic utile scope. This can besides be expressed as the border of mistake for exposure factors.

Latitude and contrast are reciprocally related. High contrast movies have narrow latitude while low contrast movies have wider latitude.

Characteristic curve demoing latitude and contrast [ XRIM_028_latitude_TW ]

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4.2.3 Film processing

Proper movie processing is important for obtaining an optimum image. If any of the development factors are wrong the image may be over or under- developed ensuing in an undiagnostic radiogram.

Tthe development of the image can be affected by many factors including:

* Concentration of processing chemicals

* Degree of chemical science agitation during development

* Development clip

* Developer temperature

The maker of a movie processor recommends a development clip that will give maximal contrast with low degrees of fog, at comparatively high velocity. Widening the processing clip will do a lessening to contrast while increasing fog degree and comparative velocity.

The maker will besides urge an appropriate developer temperature. Maximum contrast is reached utilizing the makers recommended developer temperature, utilizing a higher temperature will ensue in fog degree and image receptor velocity increasing.

4.3 Geometric factors

Geometric factors affect radiographic quality: magnification, deformation, focal-spot fuzz, and heel consequence.

4.3.1 Magnification

All radiographic images have a little sum of magnification. In most instances, this magnification should be kept to a lower limit ; nevertheless, some probes may necessitate magnification in order to better visualise a organic structure portion, for illustration in mammography.

Magnification is expressed quantitatively as magnification factor ( MF )

For images taken at the standard source-to-image receptor distance ( SID ) of 40” ( 100cm ) the MF = 1.1. At a SID of 71” ( 180cm ) the MF = 1.05. To maintain magnification at a minimal the SID should be every bit big as possible, and the object-to-image receptor distance ( OID ) should be every bit little as possible.

Fortunes may originate when the engineer needs to cipher the object size from the magnified image size. This is calculated utilizing the equation:

Or

The magnification for objects in the cardinal beam ( CR ) will be the same for objects positioned off the cardinal beam ( CR ) every bit long as they lie on the same plane. ( that is no farther off from and no closer to the image receptor ) .

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Magnification of objects off from the cardinal x-ray beam but in the same plane [ XRIM_029_mag_TW ]

Magnification skiagraphy is a technique used in mammography, neurology and vascular scrutinies to heighten and better visual image of little constructions. To accomplish a quality magnification view the OID is increased and the SID is kept the same as for normal skiagraphy. A little focal point is used to diminish focal-spot fuzz.

4.3.2 Distortion

Distortion of the organic structure portion under scrutiny can interfere with diagnosing. Distortion is caused when magnification is unequal over the organic structure portion.

Three factors cause deformation: object thickness, object form, and object place.

* Object thickness

Thicker objects or organic structure parts are distorted more than thinner objects because the object-to-image receptor distance ( OID ) changes across the thickness of the object.

If the thicker object lies laterally in the x-ray beam there is more deformation than in the cardinal x-ray beam.

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Object thickness deformation [ XRIM_030_thickness_TW ]

· Object form

Object form is peculiarly distorted when the form of the object is irregular. The object within the cardinal beam will demo little deformation, while object parts in the sidelong part of the x-ray beam will demo important deformation.

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Object form deformation [ XRIM_031_shape_TW ]

* Object place

Any object that is non parallel to the image receptor will be distorted by abridging or elongation.

Foreshorten – To abridge an object is to stand for the object shorter than it truly is due to the angle at which it is visualized

Elongate – To stretch an object is to stand for the object longer than it truly is due to the angle at which it is visualized

When multiple objects are positioned at different OIDs, spacial deformation can happen, beliing where an object lies in relation to the other objects.

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Object place deformation [ XRIM_032_position_TW ]

4.3.3 Focal-spot fuzz

Focal-spot fuzz is an unwanted consequence that causes a a bleary part on the radiographic image. This blurring causes ‘softening ‘ of the borders of big objects but their contrast remains the same. Smaller objects will hold contrast reduced by focal topographic point blurring.

In order to cut down focal-spot fuzz a little focal topographic point should be used, and the patient should be positioned so that the portion being examined is closest to the image receptor ( IR ) ( ie cut down the object-to-image receptor distance ( OID ) .

The source-to-image receptor distance ( SID ) should be every bit big as possible within the scope suitable for the organic structure portion being examined.

Focal topographic point fuzz [ XRIM_033_focal_TW ]

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Focal-spot fuzz can be calculated utilizing the equation:

4.3.4 Heel Effect

The ( anode ) heel consequence is the fluctuation of strength across the utile x-ray beam caused by the angle at which the X raies emerge from the surface of the focal topographic point.

The utile beam of the x-ray field can change in strength by up to 45 % due to the heel consequence. This is highly of import to retrieve as the x-ray beam at the cathode terminal of the tubing may hold radiation strength every bit high as 120 % while the anode side of the tubing may hold a radiation strength reduced to 75 % .

The heel consequence becomes particularly of import when imaging organic structure countries that differ in thickness or denseness. The thicker organic structure portion is best positioned at the cathode terminal of the x-ray tubing to better the uniformity of the x-ray image.

4.4 Capable factors

Capable factors are factors that relate to the patient such as the patients ‘ size, form, and tissue denseness, that affect radiographic quality.

4.4.1 Capable contrast

Capable contrast is the discrepancy in x-ray strength transmitted through immediate parts of the organic structure. Factors that affect fading of the x-ray beam, and hence the strength of the familial x-rays include: patient thickness, tissue mass denseness, effectual atomic figure, object form, and kilovolt.

* Patient thickness

If the x-ray beam is directed through two different thicknesses of tissue, the dilutant tissue will convey a greater figure of X raies than the thicker tissue. This is an of import factor for capable contrast.

Capable contrast is straight relative to the comparative figure of X raies transmitted through the organic structure portion.

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Anatomic thickness and capable contrast [ XRIM_034_thickness_TW ]

* Tissue Mass Density

Tissue mass denseness is a step of the measure of affair in tissue. The fluctuation in the mass denseness of tissues in the human organic structure will lend to capable contrast.

Tissues such as bone have a high mass denseness and will rarefy more of the x-ray beam than musculus that has a lower mass denseness.

* Effective atomic figure

Effective atomic figure is obtained from a leaden norm of the atomic components of different compounds and is used to foretell how x-rays will interact with different tissues. Compton interactions occur independant of atomic figure, while the photoelectric consequence interactions vary in proportion to the regular hexahedron of the atomic figure, and hence do an of import part to capable contrast.

When bordering tissues have a really different effectual atomic figure the capable contrast will be enhanced.

The usage of contrast media greatly enhances capable contrast due to the highly high effectual atomic figure of I and Ba.

Type of substance

Effective atomic figure

Bone

13.8

Soft tissue

7.4

lung

7.4

fat

6.3

air

7.6

I

53

Ba

56

Lead

82

* Object form

The form of the object or organic structure portion being examined will impact the topic contrast due to object fuzz ( sometimes called soaking up fuzz ) that occurs when the form of the portion does non fit the form of the x-ray beam. If the object is the same form as the x-ray beam so x-rays base on balls through the full thickness bring forthing a crisp boundary.

Object fuzz reduces the spacial and contrast declaration of the anatomic constructions thereby cut downing capable contrast. The sum of object fuzz that occurs is dependent on the form of the object and the distance over which denseness falls off.

* kilovolt

kilovolt controls capable contrast. This is the lone capable factor the radiographic engineer has control over.

As a regulation low kilovolt consequences in high capable contrast, besides called short grey graduated table contrast, with the x-ray image looking black and white with few sunglassess of grey.

The usage of high kilovolt gives a low topic contrast image with many sunglassess of grey between black and white ( long grey graduated table contrast ) .

It is of import for the engineer to understand that the usage of low kilovolt means a decrease in the incursion value of the x-ray beam, which will necessitate a higher patient dosage, that is achieved by increasing ma, to attainan acceptable image. It is of import to carefully choose the right kilovolt for the organic structure portion to be examined.

4.4.2 Motion fuzz

Motion fuzz is caused by motion of the either the x-ray tubing or the patient during the x-ray exposure. Patient motion is kept to a lower limit by reenforcing the demand to stay still during the exposure, or by usage of keeping devices. Gesture of the patients bosom and lungs during exposure is reduced by utilizing short exposure times and breath keeping techniques.

The usage of x-ray tubing motion for imaging is a deliberate usage of gesture fuzz to befog constructions on either side of the country of involvement.

Motion fuzz is reduced by utilizing a big source-to-image receptor distance, and a short object-to-image receptor distance.

4.5 Tools for bettering radiographic quality

4.5.1 Patient place

Correct patient placement is important to accomplishing quality radiogram.

The organic structure portion to be examined should be placed as near to the image receptor as possible with the axis of the organic structure portion aligned parallel to the image receptor. The cardinal beam of the x-ray tubing is centered to the organic structure portion.

The organic structure portion should be immobilized to minimise gesture fuzz.

4.5.2 Image receptors

Conventional skiagraphy uses fine-detail screen/film combinations for scrutiny of appendages and soft tissues. General skiagraphy uses movie with double-sided emulsion and a high-resolution intensifying screen.

4.5.3 Choice of technique factors

The engineer should choose exposure factors suited for the organic structure portion to be examined. The exposure clip is normally kept to a lower limit to forestall gesture fuzz. kilovolt is selected harmonizing to the sum of incursion required, whilst keeping good radiographic contrast.

ma is set at a value that will give optimal optical denseness ( OD ) and lower radiographic noise, while maintaining patient dosage at a lower limit to accomplish a quality radiogram.

5.0 Radiographic technique

5.1 Patient factors

The engineer must take into history patient size, form and physical status when sing the exposure factors for a organic structure portion.

There are 4 basic organic structure forms used in skiagraphy to depict patient organic structure habitus ; that is the size and form of the organic structure, these are: sthenic, hyposthenic, hypersthenic and adynamic

Recognition of organic structure habitus is indispensable, most exposure charts are designed for the sthenic patient, the engineer must be able to modify exposure factors consequently.

5.1.1 Thickness

The engineer should utilize calipers to mensurate organic structure portion thickness accurately. The thicker the organic structure portion, the more radiation required to bring forth a diagnostic quality radiogram.

5.1.2 Composition

The engineer must be able to measure whether a organic structure portion is radiodense or radiolucent. For illustration a patients ‘ thorax may be the same thickness as their hip, but the r