Types of X-RAY FILM

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Slide 1:

Types of X-Ray Films & Sensitometry PRESENTED BY ABHAY KUMAR SINGH MODERATOR MR. LALIT K. GUPTA Deptt. Of Radio Diagnosis And Imaging Post Graduate Institute Of Medical Education & Research

Slide 2:

X-Ray Films

Slide 3:

What Is X-ray Film? X-ray film is a photographic receptor consisting of photographically active or radiation sensitive emulsion coated on a thin sheet like material, which is responsible to record the physical impression of an object by which we can get detail about the object. 3

History:

History 4 Early in Photography Certain silver compounds react to light making image production possible This phenomenon was applied to x-ray procedures In 1812, silhouettes were recorded on glass plates In 1819, the solvent action of sodium thiosulfate on silver chloride was discovered In 1839, the phenomenon of development was discovered by Louis Daguerre.

contd:

contd 5 During WWI, nitrocelluose based film was found to be a more feasable choice for recording x-rays This film was single-emulsion It was later discovered that double-emulsion responded to x-rays faster The flaw with nitrocellulose-based film was its easy flammability In 1924, cellulose acetate replaced the nitrocellulose based film Now a days safety base of polytetrapathalate resin is used universally.

Classification of the film:

Classification of the film 6 General radiographic film Dental film Kidney surgery film Radiation monitoring film Mammographic film CRT film Copying film Laser film Subtraction film Drystar Flm Dryview film

Direct Exposure Film:

Direct Exposure Film 7 Used without intensifying screens Used mainly for extremities, previously for mammography Requires 10 – 100 times more the exposure dose The emulsion is thicker than screen film Renders excellent detail

Indirect Exposure Film:

Indirect Exposure Film 8 These films are used in conjunction with pairs of I.S. . The latent image being produced mainly by light emission from screen phosphors. A wide range of different films are available both the blue- sensitive and green - sensitive . These types of films are sometimes referred to as contrast amplifiers because their average gradient is >1

Slide 9:

CHARACTERISTICS DIRECT EXPOSURE FILM INDIRECT EXPOSURE FILM Exposed with Only by x-rays Mainly by vissible light Used Without Screen With screen Emulsion layer Thick Thin Image formation In deep superficialy Processing time more less Resolution more less Characteristic curve No apprent shoulder region in useful density range Shoulder region within useful density range Screen artifact no May possible Exposure dose more less Used in Orbit and extremities radiography. Also in Industrial Radiography General radiography Difference B/W Non Screen & Screen Film

Slide 10:

characteristic Photographic film Radiographic film Mode of image capture By reflected light By penetrated/ transmitted light Emulsion layer On one side Either On one side or b oth Speed Slow Fast Grain size Small Large Resolving power 1000 lines/mm 6-10 lines/mm Irradiation by Light only Light as well as x-ray Non curl back layer Always present Absent in double coated Difference In B/W Photographic Film And Radiographic Film 10

Type Of Direct Exposure Film :

Type Of Direct Exposure Film 11 Dental Film Kidney Surgery Film Radiation Monitoring Film Industrial Film

Dental Film:

Dental Film 12 Periapical Dental Film:Used for single or group of Teeth Occlusal Dental Fiim:Imaging mandibles or maxillae Bitewing Dental film:Demonstrating the crown

Kidney Surgery Film:

Kidney Surgery Film 13 This duplitized film non screen film is designed to enable to radiographic exposure of kidney . Each packet contains two films ,one with a fast emulsion, the other slow. 10 CM 13 CM FOR RENAL VESSELS

Laser Film:

Laser Film 14 A laser printer uses digital electronic signal from an imaging device. It is high-contrast single-emulsion film with extremely fine grain, also known as IR film. Laser film is a silver halide film sensitized red light (Panchromatic) or laser light, e.g., HN Laser Film, IR Laser Film.

Films Used With Cathode Ray Tube Or TV Monitor:

Films Used With Cathode Ray Tube Or TV Monitor 15 These films are used with cathode ray tube camera and multi-formatter. The emulsions are orthochromatic of medium to high contrast and made to match a wide variety of CRT phosphor. The film sizes commonly used are 8” x 10”, 11”x14” and 14”x17” .

contd...:

contd... 16 Used in following modalities: Ultrasound Computerized tomography Magnetic resonance imaging Nuclear medicine Digital subtraction imaging

Substraction film:

Substraction film 17 A type of single emulsion film used with angiography One type prepares a positive copy of the image The other type enhances subject contrast and detail Duplicating Film It is used to duplicate the pre-existing film. Duplicating film is a single emulsion film that is exposed to ultraviolet light or Visible light through existing radiograph to produce a copy.

Polaroid Film:

Polaroid Film 18 It is made up of positive and negative film sheets with a pod of jellified processing chemistry. Used particularly in ultrasound imaging. The latent image is formed in the silver halide emulsion of the negative sheet. And the positive image formed due to migration of Ag ions from the negative sheet.

The Dry View Film :

The Dry View Film 19 High quality silver based material coated. The heat /laser light sensitive layer contains silver halide /silver behnate crystal. DRYVIEW Film also a type of laser film having high-resolution, It is infra red sensitive photothermographic film that needs no wet film processor.

The Drystar Film:

The Drystar Film 20 Direct thermal printing Drystar dry imaging films are designed to produce the highest diagnostic grayscale hardcopies. These images can represent the same "look and feel" as conventional x-ray film. Blue base Maximum optical density > 3.5 Daylight film loading (films are insensitive to light) Shelf life: to be used min. 18 months from packaging date Storage temperature: 5 - 25 °C Relative humidity: 30 - 60% Extended term storage: minimum 20 years

TYPES OF DRYSTAR FILM:

TYPES OF DRYSTAR FILM 21 1. CURIX FILM : the CURIX films are ideal for use in digitizers where electrostatic charging is a problem. Variable Range Hopping (VRH) is a unique Agfa-patented anti-static feature used in the CURIX films In VRH, a special electrically conducting polymer coating remains on the film after processing. This polymer, structured in clusters, is a fiber-like substance that allows electrons to jump from one cluster to another under the influence of an external electric field. As a consequence of its anti-static characteristics, the film repels dirt and dust and remains clean under the most adverse conditions This technology simplifies the procedure of scanning the film and guarantees images free of artifacts.

contd…:

contd … 22 2. DRYSTAR TS 2 : This films use Thermo-Sublimation. A dry imaging technique that can be used in full daylight. Designed to provide brilliant, full-spectrum color imaging with a minimum of effort Thermo-Sublimation is a dual-component system that uses heat to transfer colored dyes from a donor sheet to an acceptor sheet. This state-of-the-art dry color imaging solution produces higher Dmax and contrast than any other thermal dye diffusion printing systems

contd…:

contd … 23 CURIX Ultra UV film: uses exclusive UV Light Focus Technology. Use with ultra Uv screen which have high-density Yttrium Tantalate phosphor that emits Ultraviolet light. Ultraviolet light reduces screen light diffusion by 90 percent compared with conventional rare earth phosphors. The resultant is formation of sharper image

contd…:

contd … 24 CURIX Ortho HT film : physical and chemical stability, allowing film processing to take place at higher temperatures. All CURIX Ortho HT films are designed for processing in 45 seconds, enabling greater film volumes to be processed in a shorter time. This technology was made possible by the development of techniques such as the Split Emulsion Layer technique and an anti-static layer. Used with CURIX intensifying screens & top coat of these screen are based on Electron Beam Cured (E.B.C.) process.

Slide 25:

25 Cine film Used with cardiac catheterization Produced in 16 and 35mm sizes Also used for radiography of the esophagus Photoflourographic Film This is the film used in cameras to take pictures of a fluoroscopic screen (barium study). It comes in rolls & is green or blue light sensitive. It has emulsion on only one side. It is used for mass screening as in the army.

Mammographic Film:

Mammographic Film 26 3 emulsion layers allow the contrast curve to be individually steered for each portion of the contrast curve Emulsion Layer 1 provides enhanced skin-line visualization and controls OD > 3.8 Emulsion Layer 2 maintains a steep curve throughout the entire diagnostic area Layer 2a controls OD <2.0 Layer 2b controls OD >1.5

Spectral Sensitivity:

Spectral Sensitivity Spectral sensitivity is the range of wavelength of the electromagnetic radiation that the film will respond. PEAK SENSITIVITY is the range of wavelength in which the film will exhibit its highest response CUT-OFF SENSITIVITY is the range of wavelength beyond which the film is no longer sensitive.

Types Of Film According To Sensitivity:

Types Of Film According To Sensitivity MONOCHROMATIC - blue sensitive films

Contd…:

Contd … ORTHOCHROMATIC - green sensitive film

Contd…:

Contd … PANCHROMATIC - sensitive to all colors of the visible spectrum

Layers Of Radiographic Film::

Layers Of Radiographic Film: 31 Base Subbing layer Emulsion layer Supercoat

Film Construction :

Film Construction 32 0.0004” 0.0005 ” 0.007 ” 0.008 TOTAL FILM THICKNESS =0.008 INCH Double –sided emulsion film

Contd…:

Contd … 33 33 0.0004” 0.0005 ” 0.007 ” 0.008 Anti –Halation /non curl backing Single –sided emulsion film

Slide 34:

Difference b/w Single Coated And Double Coated X-ray Film Characteristic Single coated Double coated Emulsion layer One side Both side Patient Radtation dose More Less Noncurl back layer Present Absent Radiographic detail More Less Average gradient (G) Very less more Parallax effect No yes Contrast Less more

Radiographic Film Base:

Radiographic Film Base 35 Initially X-RAY were taken on glass plates. In 1918 cellulose nitrate bases film replaced glass,but discarded because of highly inflammable . In 1920 cellulose tricetate or safety base was introduced. Polyester base replaced cellulose tricetate in the 1960”s, Now a days POLYETHYLENE TEREPHTHLATE RESIN are used. Film Base .007”

Character Of Good Base Material.:

Character Of Good Base Material. 36 structural support for fragile emulsion low light absorption flexible, thick, & strong processing handling viewbox insertion / removal abuse dimensional stability in processing For archival varying humidity NON -FLAMMABLE

Function Of Base:

Function Of Base 37 Provide support for emulsion layer. To transmit light.

Subbing Layer (Adhesive Layer):

Subbing Layer (Adhesive Layer) 38 Also called adhesive layer or Substratum layer. Made of mixture of gelatin solution and solvent of film base. It keeps emulsion layer and base adhered to each other during coating stage and processing. When dye is added , it counteracts cross over effect. Provides uniform surface over which the emulsion can be coated uniformly.

Emulsion Layer :

Emulsion Layer 39 Emulsion is the heart of radiographic film . The X-RAY or Light from I.S. interact with the emulsion and transfer information to the film. It consists of a very homogeneous mixture of gelatin and silver crystal. In typical emulsion 90 to 99% is AgBr and about 1 to 10% AgI . NOTE: The presence of AgI produce an emulsion of much sensitivity than a pure AgBr emulsion. It also contains traces of sulfur(ALLYLTHIOUREA). Emulsion Layers

contd…:

contd… 40 Silver halide in a emulsion is in the form of small crystals. Silver halide crystals may be tabular,globular,polyhedral,or irregular in shape. Crystal size might vary from 1.0 –1.5 microns in dimeter with about 6.3 x 10 10 grains per centimeter of emulsion.

Grain Technology:

Grain Technology 41 Globular Grain:spherical in shape and has a bigger volume.Use for blue sensitive film. Tabular Grain:Has a table –top like structure that provides bigger surface but smaller volume.

Advantages Of Tabular Grain:

Advantages Of Tabular Grain 42 Increased RESOLUTION due to reduction in cross- over. Reduction in silver coating weight. Suitable for 45 s processing.

Grain Size And Distribution:

Grain Size And Distribution 43 GRAIN SIZE and DISTRIBUTION affects the following: SPEED : The bigger the average grain size, the higher the speed of the film. CONTRAST : Affected by size distribution. The more available in the film, the lower the contrast. GRAININESS : Graininess is the apparent clumping of the crystal as seen on the radiograph. The bigger the crystal,the higher the graininess o f the film.

Binder:

Binder 44 A binder is an ingredient used to bind together two or more other materials in mixtures. There are two types of binders which we can use: Collodion Gelatin

contd:

contd 45 Collodion is a flammable, syrupy solution of pyroxylin in ether and alcohol. In 1851, the Englishman Frederick Scott Archer discovered that collodion could be used as an alternative to egg white (albumen) on glass plates This also reduced the exposure time when making the image This became known as the 'wet plate collodion ' or 'wet collodion ' method. Collodion was also grainless and colorless, and allowed for one of the first high quality duplication processes, also known as negatives.

Gelatin:

Gelatin 46 Gelatin is used as the suspending medium and binding agent for the silver halide particles. It comes collagen fiber in which primary source are the cartilage, skin and the protein matrix (ossein) of bone of animals.

Why We Use Gelatin As Binder?:

Why We Use Gelatin As Binder? 47 It is a medium in which SILVER NITRATE and SODIUM BROMIDE can react and the resulting AgBr get finely and evenly dispersed and remain suspended. In warm state it can be easily spread on the film base. On cooling, it sets firmly on the base as gel. It is flexible and does not crack easily on bending. It is optically transparent . Gelatin does not react chemically with the silver halide . It is porous so the processing chemicals can penetrate to the silver halide crystals. Some of the constituents in gelatin enhances the activity of Silver bromide and some act as antifoggant . ?

contd…:

contd… 48 It is the great advantage of the gelatin in which it can set its intermolecular space a/c to the condition of the environment, While processing, gelatin swells up in contact with water, allows processing chemicals to enter the layer and react with the grains of emulsion, & On drying it regains its former state. It is believed that gelatin reduces the tendency of reversal of reaction of Silver bromide after exposure

Making Of The Film Emulsion:

Making Of The Film Emulsion 49 The light sensitive layer of a film is termed the Emulsion. The preparation of emulsion is carried out in four stages: Emulsification Ripening Washing Digestion

Emulsification :

Emulsification 50 Aqueous solution of Silver nitrate and Potassium bromide is mixed with warm solution of gelatin. AgNO 3 + KBr AgBr + KNO 3 Insoluble Silver bromide (AgBr) remains suspended in viscous gelatin. More rapid process of mixing results small grain size, that results narrow grain size distribution hence there is low graininess & better resolution. Note: More bromide is used to increase the negative charge barrier that helps in development process.

Ripening :

Ripening 51 Emulsion is placed in certain temperature and more gelatin is mixed. Size of the grains and their even distribution is determined at this stage Slow mixing with long ripening at high temp. => Fast emulsion (with large grains) Rapid mixing with short ripening at low temp. => Slow emulsion (with fine grains) Slow mixing with NH 3 at low temp. => Fast emulsion (with large grains)

Washing:

Washing 52 After ripening, emulsion is chilled to form thick gel. This gel is shredded. It is washed with water that remove KNO 3 and excess KBr by diffusion process.

Digestion:

Digestion 53 Shredded and washed emulsion is re-heated to further increase its sensitivity. Re-heating also make the emulsion liquid and suitable to spread on the film base.

Supercoat (overcoat):

Supercoat (overcoat) 54 Protective layer of gelatin Provides sturdiness to unexposed radiographic film. Antistatic Reduces damage from scratches, pressure, or contamination during storage, handling and processing. Supercoating

Few Additives:

Few Additives 55 Preservative – Phenol as bacteriocide Silver iodide – To extend sensitivity towards blue range. Some dyes may extend Colour sensitivity further Glycerin to make the emulsion pliable Saponin – To make the emulsion receptive to the processing chemicals Alcohol – To prevent frothing during coating

Coating The Film:

Coating The Film 56 Different layers of film are coated on the base material with rollers and squeezers. The film lengths are then passed over chilled rollers so that liquefied gelatinous layers settle and harden. Then The film lengths are hung like festoons in an air conditioned room to dry. Mechanical cutters cut The film lengths in sheets of desirable sizes.

Anti- Halation Layer :

Anti- Halation Layer 57 Halation : it is a phenomenon characterized by formation of a diffuse image or halo around the proper image. This occurs mainly in the single sided film.

Methods To Prevent Halation:

Methods To Prevent Halation 58 Adding a dye to base Adding a dye to non-curling layer.

Non-curling Layer :

Non-curling Layer 59 Preferred for single sided emulsion film . This layer is not removed during development.

Adding A Dye To Base:

Adding A Dye To Base 60 These dyes cannot be removed during development. Dye introduced in the base is carefully controlled because it increase the density and may interrupt the transparency of the film. Note-dye used in this should be complementary to the exposing light . e.g.,red dye is used for greeen sensitive film,yellow dye is used for blue sensitive film .

Cross Over Effect:

Cross Over Effect 61 It is a type of halation which occurs when film is used with intensifying screen. Occurs only with double emulsion films and two screens. Light from one screen expands in the form of a cone as it passes through the screen and emulsion where a slightly enlarged, less sharp image is formed.

contd:

contd 62 Special dyes incorporated in the emulsion Colored subbing layer is used. Addition of magenta dye also reduces cross over effect.

Irradiation:

Irradiation 63 It is the sideway scattering of light within the crystal of emulsion. This contributes to unsharpness (blurring) of image.

Slide 64:

How Film Records An Image There are three steps formation of subject contrast (Optical image) Recording of latent image Conversion of latent image into permanent image (processing) 64

Slide 65:

The Latent Image The latent image is the invisible change in the silver halide crystals. The interaction between the photons and the silver halide crystals produces the latent image or manifest image on the emulsion layer. This interaction is sometimes referred to as the photographic effect. 65

Slide 66:

Formation Of Subject Contrast Subject contrast:-the variation in intensity of x-ray beam after passing the absorber. Subject contrast depends upon atomic No., density, thickness of absorber and the energy of the x-ray beam. Different intensity of beam react differently with the photographic material of the film. 66

Slide 67:

67 The shape and lattice structure of silver halide are not perfect. It causes some imperfection which results in imaging property of crystals. So the sensivity specks is that low energy centre of the crystal which acts as rest house for the 1 º electron and development centre for the 2 º electron. Sensitivity Speck

contd:

For the formation of sensitivity specks impurity, usually a Silver-gold Sulfide is introduced by chemical sensitization at or near the surface. contd 68

contd:

The image forming x-rays deposit energy by photoelectric interaction with atoms of silver halide crystals. Formation of latent image is given by Gurney-Mott theory contd 69

Slide 70:

Br Br Ag - Br Ag Br Ag + Ag Ag Ag SENSITIVITY SPECK LATENT IMAGE SILVER HALIDE CRYSTAL INTERSTITIAL Ag ION 1. Photon Absorption 6. Ag Ion Migration 3. Ag Ion Migration 2. Electron Trapping Ag Br Ag + - Br Ag 4. Photon Absorption - + Ag Br + 5. Electron Trapping - Ag Ag GURNEY MOTT THEORY

Producing the Latent Image:

Producing the Latent Image 71 Radiation interaction releases electrons. Electrons migrate to the sensitivity center. At the sensitivity center, atomic silver is formed by attracting an interstitial silver ion. The process is repeated many times resulting in the build up of silver atoms. The remaining silver halide is converted to silver during processing. The resulting silver grain is formed. Silver halide that is not irradiated remain inactive. The irradiated and non-irradiated silver halide produces the latent image.

Conversion Of Latent Image Into Visible Image:

Conversion Of Latent Image Into Visible Image 72 This step is also known as processing. There are 4 step in this processing: Development Fixing Washing Drying

Characteristics To Be Considered While Selecting Film: :

Characteristics To Be Considered While Selecting Film: 73 Contrast Speed Crossover Spectral matching Bulk of purchase Time of purchase

Slide 74:

Care And Protection Of Film Films should be protected from Physical damage Light High temperature High relative humidity Harmful gases and fumes X-rays and radioactive source Fire and theft 74

Resolving Power Of Films:

Resolving Power Of Films 75 Ability of a photographic emulsion to record fine details It is expressed as the number of line pairs per millimeter which can be distinguished in the image as separate entities Factors affecting the resolution of an image are – Grain size, Processing, Diffusion of light inside the emulsion layer and Modular transfer function

Line Pairs Per Millimeter:

Line Pairs Per Millimeter 76 A black and a white line make a line pair A test pattern of slits cut on a metal plate with gradual fineness is exposed, processed and evaluated under magnification. Radiographic emulsions show 8 – 20 LP/mm Photographic Fast emulsions show 40 – 50 LP/mm Medium emulsions show 70 – 100 LP/mm Slow emulsions show over 1000 LP/mm

Slide 77:

Storage Of Film STORAGE AREAS :- The hospital or x-ray department The dark room The imaging room 77

Handling And Storage Of Radiographic Film:

Handling And Storage Of Radiographic Film 78 X-ray film is a sensitive radiation detector and it must be handled in an area free of radiation. Film storage must be shielded. The darkroom adjacent to the x-ray room must be shielded. If film use is low more shielding may be required.

Handling And Storage Of Radiographic Film:

Handling And Storage Of Radiographic Film 79 Improper handling of the film will result in poor image quality due to artifacts. Avoid bending, creasing or otherwise rough handling the film. Avoid sharp objects contacting the film. Hands must be clean and dry. Avoid hand creams, lotions or water free hand cleaners. Static electricity or a dirty processor can cause artifacts. Artifacts must be avoided.

Handling And Storage Of Radiographic Film:

Handling And Storage Of Radiographic Film 80 Heat and Humidity must be controlled. Film is sensitive to heat and humidity from the time it is manufactured until the time it is viewed. Heat and humidity causes fog or a loss of contrast. Film should be stored at 20 º C (68º F). Humidity should be between 40% and 60%.

Handling And Storage Of Radiographic Film:

Handling And Storage Of Radiographic Film 81 Light will expose the film. Film must be handled and stored in dark. If low level diffuse light exposes the film, fog is increased. Luminous watches, cell phone and darkroom light leaks should be avoided. Bright light causes gross exposure.

Handling And Storage Of Radiographic Film:

Handling And Storage Of Radiographic Film 82 Shelf life. All film is supplied in boxes with an expiration date. Most film is supplied in boxes of 100 sheets. The oldest film in stock should always be used first. Rotation is important. Expired will loose speed and contrast and have increased fog.

Slide 83:

83 Sensitometry

Sensitometry:

Sensitometry 84 It is the science in which we Study the response of Photographic materials towards various exposure. In other words , it is the measurement of sensitivity of that material. The photographic material of film reacts differentially with differentially attenuated x-ray beam

Radiographic Density:

Radiographic Density 85 All radiographs have some Transparent, some Opaque and some Not-so-opaque areas, which make the pattern we call an Image Density refers level of blackness If we take a small area of that image, it’ll show three characteristics Transmission Opacity Density

Slide 86:

Transmission is how much of the light gets through the film. Transmission ratio = Tr. light / Inc. light = L t / L i This ratio usually expressed as Percentage Transmission ratio % Transmission ratio = (L t / L i ) x 100 Transmission If 100 lux of light is falling on one side of the film, but only 25 lux gets through, then the transmission is 0.25. Example: A perfectly opaque area of an image has 0 transmission ratio and 0 % transmission 86

Opacity:

Opacity 87 It is ability to stop the light by a certain part of an image. It is reciprocal of Transmission Opacity = L i / L t The previous example shows Opacity = 100 / 10 = 10 As incident light is always greater than Transmitted light, Opacity is always greater than 1 The blackest part of image has an OPACITY approaching 10000

Optical Density:

Optical Density 88 This is the common Logarithm of Opacity Density = Log 10 L i / L t If we continue with the same example Density = Log 10 100/10 = 1 Useful density range in Radiography is between 0.25 – 2.5 Density range commonly found in C X R is 0.3 – 1.5 (in the abdominal area) to 2.5 – 3.0 (in the lung field) Measured by densitometer . Density on film depends upon mAs that represents amount of Ag-atom on the film

Optical Density: examples:

Optical Density: examples 89 T OD Comment 1.0000 0 Perfectly clear (does not exist) 0.7760 0.11 Unexposed film (base + fog) 0.1000 1 Medium gray 0.0100 2 Dark 0.0010 3 Very dark; requires hot lamp 0.00025 3.6 Maximum OD used in medical radiography

Contd…:

Contd … 90 To relate the number of sensitized grains to the optical density D the absorption of the light in the film material of thickness t can be described as: Using this relation the optical density can be calculated to: This relation is known as Nuttings Law ! Maximum optical density for an area on the film is obtained when all grains are sensitized: g = G E.G.- Typically for X –RAY material the optical density D max ≈3, for a typical diameter of 2.5 µm for the developed grain,the number of grains per area correspondsto : 90 Where as g= sensetised grains per unit area δ =cross section area of silver speck where the grain is being sensetised G= no. of total grains per unit area

Why We Take Log:

Why We Take Log 91 We use density in log form for 3 purpose There is large difference in no. on a small scale is not possible because opacity varies from 10-1000 & by the use of log we can compress this into 1-3only. The physiological response of the eye to difference in light intensity is logarithmic. Addition & superimposition of density is logarithmic. We take log of relative exposure because. It allows very wide range of exposure variation on small scale. Analysis of curve becomes easier .

The Characteristic Curve:

The Characteristic Curve 92 The characteristic curve is a graph which illustrates the way in which a film or film – screen system responds to different levels of exposure. The characteristic curve a valuable tool for describing the sensitometric behavior of a recording. The characteristic curve is a plot of DENSITY(D) against LOG RELATIVE EXPOSURE (LOG E). The curve is sometimes known as a D log E curve and also called Hurter and Driffield curve.

Slide 93:

Relative Exposure Relative exposure plotted on the X-axis of the C.C. is not exact as given on the film it is relative to some unit exposure. e.g. suppose we use 48kvp with 2.0 mAs in first step and in the second step we use 48kvp and 4.0mAs and we assume first as unit exposure than second is relatively double than previous An increase in the log relative exposure with 0.3 always represents doubling the relative exposure that result double of density. 93

How Is A Characteristic Curve Produced:

How Is A Characteristic Curve Produced 94 There are three basic stage involved: Exposing and processing the film. Measuring the densities produced. Plotting the curve.

Tools Needed For Making The C.C:

Tools Needed For Making The C.C 95 Densitometer Sensitometer Step wedge X-ray film x-ray equipment Processing unit Graph paper

Exposing And Processing The Film:

Exposing And Processing The Film 96 TO generate a CHARACTERISTIC CURVE we need to irradiate the film or film screen system with a series of exposures . The exposure series can be achieved in one of two ways: 1. TIME –SCALE SENSITOMETRY 2. INTENSITY –SCALE SENSITOMETRY

Varying Exp (Mas).:

Varying Exp ( Mas ). 97 A series of exposures are made on an X ray film using a wedge factor If 2 is considered as the wedge factor and the first exposure is X mAs , then the second exposure’ll be 2 X mAs , third exposure’ll be 2x(2 X mAs )= 4 X mAs and so on

Slide 98:

Varying Exp Time To get same result as the previous one we make the first exposure ( X mAs ) through a slit or hole of a lead mask, then shift the spot and make two exposures, and go on exposing spots doubling it every time. Thus we get spots exposed by factors - X mAs,2 X mAs , 4 X mAs etc 98

Using Step Wedge:

Using Step Wedge 99 It is a simple device resembling a flight of stairs. It is actually a filter with gradually varying filtration. The variation is governed by a constant wedge factor In diagnostic range Aluminium Step wedge is used but plastic and steel are common in softer or harder range When a single exposure is given through this device, we get a film strip with varying densities

Measuring The Densities Produced. :

Measuring The Densities Produced. 100 The optical density of each exposed step on the film test must be measured using a densitometer. The values should be tabulated alongside the corresponding values of relative exposure.

Plotting The Curve:

Plotting The Curve 101

Features Of The Characteristic Curve:

Features Of The Characteristic Curve 102 There are 3 parts of C.C. The region to the left of the TOE basic density basic fog Threshold exposure Region b/w toe and shoulder Contrast Speed and sensitivity Gradient Film and Exposure Latitude Region to the right of the shoulder Solarisation or Reversal of film Max density

The region to the left of the toe : :

The region to the left of the toe : 103 This is sometimes referred of underexposure. 1.BASIC DENSITY- :due to the absorption of light as it is transmitted through the polyster film base. 2 FOG- : it is the density recorded on the film without exposure.It has several cause storage fog chemical fog safelight fog Age veil Note that density of base plus fog is often referred to as GROSS FOG or BASIC FOG. GROSS FOG(<.2) = fog +density

Contd…..:

Contd ….. 104 NET DENSITY : Gross density-Gross fog THRESHOLD EXPOSURE :- it is minimum exposure required that can produce any amount of net density on the film. Subphrenic region of the chest radiograph is lies in this level of density.

Region B/W Toe And Shoulder :

Region B/W Toe And Shoulder 105 This is often called the straight-line part of the curve. There are two major part of this 1: CONTRAST 2: LATITUDE

Contrast :

Contrast 106 The exposure variation that constitutes subject contrast generate differences in image therefore produce contrast in the radiographic image. STEEPER THE CURVE HIGHER THE CONTRAST. So the maximum contrast shown by the straight line part of the curve. We can calculate this by plotting slope on any point of C.C. Generally it calculated at the point of INFLECTION where the slope is maximum. Actually in the C.C. no any exact straight line part and the point of inflection refers the point from where the C.C. changes its curve from convexity to concavity.

Contd…:

Contd … 107

Slide 108:

The maximum slope of the characteristic curve of an X ray film. The film gamma is a measure of the maximum change of film density for a certain change of exposure. This corresponds to the part of the characteristic curve with the steepest slope, i.e. at the point where the maximum derivative is found Film Gamma 108

Contd…:

Contd … 109

Average Gradient :

Average Gradient 110 The slope of a straight line joining the useful density range(0.2 -2.5)on C.C. Average gradient depends upon film and the intensifying screen system not upon subject, or on KVp selected so that it is different from contrast. It is calculated by straight line slope that meets the lower density and the upper density range. Average gradient= Useful density range Film latitude

Contd…:

Contd … 111 Average gradientY = D b - D a LogE b -Log E a tanØ = useful density ange film latitude Ø 0.94 1.43 =

Latitude :

Latitude 112 Latitude refers to the range of log relative exposure that will produce density within the accepted range for diagnostic radiology. Also express the tolerance of the system to extreme condition of exposure. LATITUDE studies in two parts . film latitude Exposure latitude FILM LATITUDE :-this represent the difference b/w the upper and lower limits of relative exposure, which produce useful density range. Film latitude = Log E b –Log E a

Contd…:

Contd … 113 = EXPOSURE LATITUDE :-this represent the tolerance of the film or film screen system to error in selection of exposure factor(e.g.- kvp , mAs , time, FFD) EXPOSURE LATITUDE= film latitude- log exposure range If the film latitude and exposure latitude approach each other in magnitude than the selection of exposure factors by radiographers demands great accuracy and the exposure latitude is poor. USEFUL DENSITY RANGE:-it is the range of exposure within which the image gets formed. Film latitude 1.75 Average gradient Useful density range Average gradient = 1.75 Average gradient

Speed:

Speed 114 The speed system is defined as the reciprocal of the exposure in roentgens required to produce an density of 1.0. Nearer the C.C. with the density axis speeder the film or film screen system. Where G = average gradient A is a mathematical constant of straight-line intersection point with the horizontal axis.

Contd…:

115 Film A is faster than film B because the C.C. film A is closer to the density axis Contd … A1 A2

Region To The Right Of The Shoulder :

Region To The Right Of The Shoulder 116 Maximum density :-As the film or film-screen system is subjected to greater and greater exposure,a point is reached where all of the silver halide grains in the film emulsion are reduced during development. Further increase in exposure cannot then in any increase in density. Thus .the film achieves a maximum level of density known as Dmax . Log relative exposure Density Dmax

Contd…:

Contd … 117 Numerical value of Dmax depends on two major factors: 1-Silver coating weight-greater the amount of halide per unit area of film ,the higher is Dmax.A non screen direct –exposure film has a higher value of Dmax than screen –type film. 2-Processing conditions -changes in developer activity ,perhaps due to temp variations or exhaustion of developing agents can lead to achieve the optimum value oe D max.

Contd…:

Contd … 118 Solarisation /reversal of the film :-as we increase the exposure density increase up to Dmax . Beyond that exposure the film starts to respond in the opposite way to normal, producing a reduction in image density as a result of increase in exposure. Use of reversal properties is being seen in duplicating the film . Historically photographic film were exposed to bright sunlight in order to trigger image reversal such films are solarized . Reversal or region of solarization

Uses Of Ch. Curve:

Uses Of Ch. Curve 119 Comparison of films – Contrast, Speed, Latitude Comparison of Intensifying screens Comparison of Developers Determining the performance of developer over a period Determining the fog level of a film stock.

Slide 120:

120 Ouality control of x-ray - film The radiograph is the its self a important QA tool so that that the quality of the x-ray film should be assured, so that we can evaluate our equipment and performance of an technologist. Quality control programme includes the folllowing ……….. Safe storage and handling of the x-ray film Reject film analysis

Slide 121:

121 FILM STORAGE 121 Film packs must be placed in vertical position (date wise) & not horizontally to prevent static marks caused by discharge energy of static electricity due to pressure.

Slide 122:

122 122 The analysis of rejected images is a basic component of the quality assurance program Those images judged to be of inadequate quality are categorized according to cause of reject, which may be related to the competence of the technical personnel, to equipment problems or specific difficulties associated with the examination, or some combination of these elements Due to exposure 38.6 Due to patient movement 2.3% Due to wrong techniques 2.1 % Due to processing 27.4 Reject film analysis

Slide 123:

123 Artifact On Film 123 Quality of the equipment and the performance of the radiological technologist is assured by the quality of the radiograph & the quality of the radiograph assured by there should no any artifact on the radiograph so the study of film artifact is neccessory . How Are They Produced? Due to fault in following procedure Exposure Processing Handling & Storage What is film artifact ? Any irregularity on an image that is not caused by the proper shadowing of tissue by the primary An undesirable optical density on radiograph

Slide 124:

124 Film artifact 124 D ue to Handling & Storage Radiation and Light fog Rough Handling- kink marks Static Hypo retention Kinks Scratches Static =results due to Electron buildup on emulsion In dry &Low humidity, these are, crown tree smuldge Before or After processing Kink marks Scratches Fingerprints

CONTD:

23: Organizing a QA in Diagnostic Radiology CONTD 125 WATER STAIN FINGER MARKS STATIC HYPORETENTION Radiographic Artifacts

Slide 126:

126 Standards of acceptable image quality Prior to the initiation of a quality control program, standards of acceptable image quality should be established . Ideally these standards should be objective , for example “acceptability limits for parameters that characterize image quality”, but they may be subjective for example “the opinions of professional personnel” in cases where adequate objective standards cannot be defined.

Conclusion:

127 X -ray film is a type of receptor which is widely used in radiology & it is very important component of whole imaging procedure in radio diagnosis deptt. A good practice to handling & storage of x-ray film reduces unwanted density on film & artifacts on film , hence increases good diagnostic detail. Like other diagnostic tool it also needed good QA & QC. Intellectual knowledge of sensitometery also makes the technologist work perfect. No doubt, the emerging technology of receptor makes film less examination & easier as well as reduces waiting time but there is significant importance of x-ray film due to high spatial resolution of conventional radiograph as well as less economic. Conclusion

Slide 128:

128 REFERENCES Radiographic Equipments By Chesney Christensen’s Physics For Diagnostic Radiology www.xray2000.uk www.radiologyinfo.com

Slide 129:

THANKS