Photographic Principles 2014 PDF

Photographic Principles ❑ Reminder ❑ The Photographic Effect ❑ Producing the Latent Image ❑ Radiographic film structure , characteristics , and types ❑ Han...

Photographic Principles ❑ Reminder ❑ The Photographic Effect ❑ Producing the Latent Image ❑ Radiographic film structure , characteristics , and types ❑ Handling and Storage of Radiographic Film Department of Radiologic Technology Dr. Elbagir Hamza Manssor, Ph.D. College of Applied Medical Sciences Dr. Shrooq Al Dahery, Ph.D. Assistant Professor Assistant Professor University of Jeddah  Learning objectives By the end of this Lecture the student will be able to: Explain the construction and function of the x-ray film. Identify the different sizes of x-ray films. List the different types of x-ray films. Explain the characteristic of each film type. Identify film characteristics and explain the effect of each in the recorded image. Discus the proper handling and storage conditions of x-ray films.  Radiographic Film Base – History Initially x-ray were taken on glass plates. In 1918 cellulose nitrate bases film replaced glass due to World War I (WWI) and a shortage of glass. Cellulose Nitrate was flammable so x-ray film was a fire hazard. Several severe hospital fire were caused by the x-ray film. 1920 Cellulose triacetate or safety base was introduced. Not as flammable. Polyester base replaced Cellulose Triacetate in the 1960’s. Still used today. It is semi-rigid and about 150 to 300 µm thick.  Radiographic and Photographic film What is the difference? Radiographic film is similar in construction and characteristics to Photographic film. Its spectral response is different from photographic film but the mechanism of operation is the same.  Film groups X-ray films: 1. Direct exposure film: Films exposed to x-rays alone (non-screen type) – e.g. dental film. 2. Screen type film: Films exposed to x-rays and light – (these are usually of double sided emulsion) 3. Films exposed to light only. E.g. fluorographic films, duplicating films, cine films (these are of single sided emulsion) Radiographic film structure Cross-section through double/single emulsion film  Radiographic film structure For the practical use to silver halides in image recording material they must be available in a specific form known as photographic emulsion which is the photosensitive layer of an x-ray film. This photosensitive layer is a suspension of microscopic crystals of silver halide in gelatin in the x-ray film.  Emulsion The emulsion is the heart of the film. The x-rays or light from the intensifying screens interact with the emulsion and transfer information to the film. The emulsion consists of a very homogeneous mixture of gelatin and silver halide crystals about 5 to 10 µm thick.  Gelatin The gelatin is clear so it transmits the light to the silver halide crystals. It is permeable so the processing chemicals can penetrate to the silver halide crystals. The primary function of the gelatin is to provide a support medium for the silver halide crystals by holding them in place.  Base It is the foundation of the film. It provides support for the emulsion. Most film bases are composed of polyester. Polyester can withstand higher temperatures and is more fireproof. The base is usually tinted blue to reduce light glare. Amount of tint varies per specifications of different manufactures.  Film Construction Supercoat: Protective (overcoat) layer An adhesive layer: attaches the (outer surface). emulsion to the base. Emulsion layer: Sensitive layer (~10µ). Base material (transparency and Image layer, composed of gelatin and silver mechanical resistance) (~170µ). halide (br, I) crystals in ionic form. Provides relatively thick, semi-rigid structure Speed, contrast, resolution varied in to film, but still allowing flexibility. emulsion. Almost (but not completely) transparent.  Manufacture The manufacturers closely guard the mixture they use to manufacture their film. Radiographic film is Manufactured in total darkness with protection for radiation. From the time that the emulsion ingredients are brought together until the film is packaged, no light is present. Standard Screen-Film Sizes English Units (in) SI Units (cm) 8 x 10 20 x 25 10 x 12 24 x 30 12 x 15 30 x 35 14 x 14 18 x 43 7 x 17 35 x 43 14 x 17 14 x 36  Types of X-ray Film Main types: Screen film used with intensifying screens (exposed to x-ray and light). Single emulsion- emulsion on one side of base. Double emulsion used with two screens. Direct exposure film or non-screen film (exposed to x-ray only). Special purpose: Duplication, Cine, Dental (single sided emulsion).  Film Types Direct Exposure (non-screen) Used without intensifying screens. Used mainly for extremities and intra-oral radiography, previously for mammography. Requires 10 – 100 times more the exposure dose. The emulsion is thicker than screen film. Renders excellent detail.  Film Types Mammography Film Single emulsion film. Fine-grain film. Single intensifying screen. Video Film Single emulsion film. Exposes images displayed on a video monitor. Can format to present up to 16 images on one film.  Film Types Laser film Single emulsion film. Uses a laser printer, provides excellent image quality. Must be processed in complete darkness. Uses the digital electronic signal. The intensity of the laser beam is varied in direct proportion to the strength of the image signal = LASER BEAM MODULATION. The more intense the signal the darker the image. Most lasers only print on 14 X 17 regardless of initial Image.Printers can be linked to multiple users (CT, MRI, US & Computed Radiology).  Film Types Duplication film Single emulsion film. Used for producing copies of radiographs. Sensitive to UV or blue light. Never used in cassettes.  Film Types Subtraction film A type of single emulsion film. One type prepares a positive copy of the image. The other type enhances subject contrast and detail. Used in angiography to do subtraction where the bone is removed for better visualization of the arteries.  Film Types Cine film Produced in 16 and 35mm sizes. Used with cardiac catheterization. Used in coronary angiography. Also used for radiography of the oesophagus. Spot film Special roll film of 70 to 105 mm width. Used in fluoroscopy with a spot film camera. Can be processed in x-ray film processor.  Film Characteristics Spectral matching Matching color sensitive film to the screen that emits that color Speed The sensitivity of film to x-ray and light Influencing factors: Emulsion thickness Crystal size and dispersion Contrast The difference between two adjacent densities. Film displays high or low contrast characteristics. Crystal Size and Dispersion – Speed Comparison of Low and High Contrast  Film Characteristics Detail The sharpness of the image. The degree to which the smallest structural lines of anatomy can be recorded. Depends on grain size. The use of screens also affect detail. Latitude (mAs range producing density within acceptable range) The range of exposure techniques that will produce an acceptable image Inversely proportional to contrast. Crossover Light emitted from each screen crossing over the film base. Reduced by an anticrossover layer and tabular grain emulsions. Crossover  Safelights Lamps with coloured filters that do not expose the film but allow sufficient light for sight. A 15 watt bulb is used no closer than 5 feet from the work surface. An amber filter can be used for blue-sensitive film only. A red filter must be used for green-sensitive film Also can be used for blue-sensitive film.  Film Handling and Storage Each of the following can have a negative effect upon film contrast: Improper handling Light and radiation Causes artefacts. Exposure to each can fog film decreasing contrast. Heat and humidity Shelf life Too much humidity can cause the emulsion to swell. Film loses speed, contrast and begins to fog with age. Too little humidity can cause static to develop. Too much heat can fog film.  Handling and Storage of Radiographic Film 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.  Handling and Storage of Radiographic Film 1. Improper handling of the film will result in poor image quality due to artefacts. 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 artefacts. Artefacts must be avoided.  Handling and Storage of Radiographic Film 2. 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 20º C (68º F). Humidity should be between 40% and 60%.  Handling and Storage of Radiographic Film 3. Light will expose the film. Film must be handled and stored in the 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 4. Shelf life. All film is supplied in boxes with an expiration date. Most film is supplied in boxes of 100 sheets. The 14” x 36” size is supplies in 25 sheet boxes with each sheet interleaved with paper. The oldest film in stock should always be used first. Rotation is important. Expiration date will cause speed and contrast loss and have increased fog.