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Presenter:Jitendra Thakur Moderator:Mr.Lalit K GuptaB.Sc.MIT(2007)BPKIHS,Dharan

QUALITY OF RADIOGRAPH Is the exactness of representation of the patient’s anatomy on the radiograph The most important characteristics of radiographic quality are sharpness/unsharpness,contrast,resolution,noise,size of image(magnification and distortion) and artifacts.High spatial and contrast resolution require low noise and slow image receptors

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Characteristics of Radiographic Quality

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Sharpness/Unsharpness

Contrast

Resolution

Noise

Size of image

Artifacts

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1. Geometric(G)a) Focal sizeb) Focus-object distancec) Focus-film distance

2. Object factor(O)3. Intrinsic factor(I)

a) Grain size of filmb) Grain size of I. Screen

4. Movement (M)a) ~ of tubeb) ~ of objectc) ~ of film

5. Total unsharpness=G+I+O+M

Sharpness/Unsharpness(factors)

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1.Geometric unsharpness

As penumbra(partial shadows) increases with an increased focal spot size,increased object- to- film distance and decreased focus-to-film distance;the degree of geometric unsharpness increases.

Geometric unsharoness=FOD/FFD×Focal spot size

2.Object factor(o)

X-ray absorption vary across the object due to the shape of the structures in the body.As most structures in the body have a round edge,the gradual fall-off in absorption towards edge leads to the absorption unsharpness.

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3.Intrinsic factor(I)

a. Duplitized film produce more unsharpness than single-sided emulsion due to crossing over effect.

b. Spread of light will be greater with larger crystals of screen(regular/fast screen) and will be greater with increasing distance between crystals and film(poor film/screen contact) which increases unsharpness.

4.Movement unsharpness(M)

Is due to patient,equipment or film movement during the ExpoxureCan be minimized by using short-expoxure time,small FOD and particularly by immobilization(using various accessories i.e. pads,sand bags,binders,velero staps).

…cont..

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•Subject contrast•Exposure•Scattered Radiation•Development•Image-acquisition device

Subjective contrast

•The observer•Viewing conditions•Radiographic Contrast

Radiographic/Objective contrast

Factors Factors

•Region of body under examination•Contrast media•Pathology•KV[α 1/sbj contrast]

Subject Contrast

Factors

Contrast

Subject contrast Is a feature of the object(subject) under examination. The different irradiation intensities emerging from the spatial distribution of linear attenuation coefficients within the object.Factors affecting scThe region the body under examination Contrast media Pathology –if the density of a structure is changed due to pathology then there will be a change in subject contrastKv Kv<1/subject contrast

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2.subjective contrast The personal appreciation of the contrast in the image is called subjective contrast. It depends on:The observer :visual perception, fatigue etcViewing conditions: e.g. ambient lighting

3.Radiographic contrast(objective)Is the difference in OD on different parts of processed film or diff. in computer screen brightness recorded as a result of the range of emergent beam intensities.

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Factors affecting RC

• Subject contrast•Exposure – if too much or too little radiation is used ,there may be a

reduced range of densities visible on the image , thus radiographic contrast will be reduced or non-existent.

•Scattered radiation reaching the image receptor –the use of grid lead –backed cassette , lead rubber under cassette ,air gap technique ;may

reduce scatter radiation reaching IR which improve radiographic contrast.

•Development – to achieve optimum RC ,careful control of factors such as developer temperature, development time and processing chemical

activity is needed.•Image acquisition device – the design and function of the device used

to acquire the image such as certain types of film emulsion ,intensifying screen and phosphor plate ,software in digital system can have

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Resolution The ability to demonstrate closely spaced structures in the subject as separate entities on the image .It depend on contrast ,unsharpness , noise and speed .

NoiseThe random fluctuation in the OD of the image 3 kinds of image noise •Fog-due to the presence of scattered radiation •Quantum noise –due to quantum nature of x-ray beam •Electric noise –due to limitations in electronic processing of the image 04/21/23 17

Tools for improved radiographic qualityRT normally has the tools available to produce high –

quality radiograph For any given radiographic examination , a proper interpretation and application of following factors must be available :•Patient positioning The anatomical structure under examination must be close to IR CR should be incident on the centre of the structure The patient must be effectively immobilized to minimize motion blur

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Image receptors•In general ,extremity and soft tissue ,a fine detail screen film combination is used •Most other radiographs use double emulsion film with screens•The new ,structured- grain x-ray films used with high resolution intensifying screens produce exquisite images with limited patient dose

Selection of technical factors •Before any examination ,RT must select the optimum radiographic technique factors :KVp, mAs and exposure time•Image quality is improved with short exposure with the use of three-phase and high frequency generators as result of reduced motion blur•Adding filtration reduces the beam intensity but increases the quality•Different types of grids are used to improve image contrast

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Image artifacts Are undesirable optical densities or blemishes on a radiograph or any

other medical image Can interference with anatomical structures and lead to misdiagnose

Processing artifacts • Emulsion pickoff• Gelatin build up • Curtain effect • Chemical fog • Guide shoe marks • Pi-lines• Wet pressure sensitization • Diachronic stain

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Exposure artifacts •Motion •Improper pt positioning •Wrong screen film match •Poor screen contact •Double exposure •Warped cassette •Improper grid positioning

Handling and storage artifacts •Light fog •Radiation fog •Static •Kink marks •Hypo retention stain •Scratches

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Size of image Magnification • If FOD is increased ,FFD should increase to reduce

magnification • Magnification =image size /object size =FFD/FOD

Image distortion • A distorted image will produced if not all parts of

the image are magnified by the same amount

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References•Clark’posotioning in radiography •Radiological science for technologists•Encyclopedia of radiographic positioning•internet

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Thank you……….

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