Presentation on theme: "4/30/20151 Presenter:Jitendra Thakur Moderator:Mr.Lalit K Gupta B.Sc.MIT(2007) BPKIHS,Dharan."— Presentation transcript:
4/30/20151 Presenter:Jitendra Thakur Moderator:Mr.Lalit K Gupta B.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 2
Characteristics of Radiographic Quality 4/30/20155 Sharpness/Unsharpness Contrast Resolution Noise Size of image Artifacts
6 1.Geometric(G) a)Focal size b)Focus-object distance c)Focus-film distance 2.Object factor(O) 3.Intrinsic factor(I) a)Grain size of film b)Grain size of I. Screen 4.Movement (M) a)~ of tube b)~ of object c)~ of film 5.Total unsharpness =G+I+O+M Sharpness/Unsharpness (factors)
4/30/20157 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.
4/30/20158 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 Expoxure Can 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..
4/30/201513 Subject contrast Exposure Scattered Radiation Development Image-acquisition device Subjective contrast The observer Viewing conditions Radiographic Contrast Radiographic/Objective contrast 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 sc The 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 contrast Kv Kv<1/subject contrast 4/30/201514
2.subjective contrast The personal appreciation of the contrast in the image is called subjective contrast. It depends on: The observer :visual perception, fatigue etc Viewing 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. 4/30/201515
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 profound effect on contrast. 4/30/201516
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. Noise The 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 4/30/201517
Tools for improved radiographic quality RT 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 4/30/201518
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 4/30/201519
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 4/30/201521
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 4/30/201522
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 4/30/201524
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