Lecture 7 - Image Recording PDF

DEPARTMENT DIAGNOSTIC IMAGING AND RADIOTHERAPY KULLIYYAH OF ALLIED HEALTH SCIENCES HSMI 1211 Introduction to Medical Imaging IMAGE RECORDING TECHNOLOGY Learning Outcomes By the end of the session, the student shal...

DEPARTMENT DIAGNOSTIC IMAGING AND RADIOTHERAPY KULLIYYAH OF ALLIED HEALTH SCIENCES HSMI 1211 Introduction to Medical Imaging IMAGE RECORDING TECHNOLOGY Learning Outcomes By the end of the session, the student shall be able to: 1. List the various image recording technologies. 2. Discuss film-screen technology: principles, advantages and limitations. 3. Discuss digital technology: principles, types, advantages and limitations. Image Recording Methods IMAGE RECORDING Analog Digital Radiographic image is Radiographic image is displayed on permanently recorded in display monitor and can be film. manipulated. Film screen technology Imaging plate Flat panel ANALOG METHOD FILM SCREEN TECHNOLOGY Film-screen Receptor The receptor is the component that “receives” the invisible x-ray image coming from the patient’s body,known as the latent image and converts it into a visible image Components: Cassette Film Intensifying Screen Film-screen Technology: X-ray cassette FUNCTION Act as protector to film; lightproof Exposure to light Bending and scratching Ensure the film is in close contact with the intensifying screen. Film-screen Technology: X-ray cassette CONSIST OF Front cover; minimum attenuation Radiolucent material; aluminum, carbon fiber Easily penetrated by x-rays Light weight Back cover Heavier metal; Lead foil. To prevent/absorb backscatter radiation Film-screen Technology: X-ray film 3 important layers: Film base, Film emulsion, Protective Coating  Film-screen Technology: X-ray film Film base Cellulose nitrate & Cellulose Usually includes a blue dye to tint. triacetate base (currently).  Reducing eye strain To provide a support for the A special light-absorbing layer coating emulsion. the film bases to prevent crossover Desirable properties are: effect (prevent light from one screen  flexible yet tough crossing over to the other screen).  Stable  Rigid  uniformly lucent Adhesive layer: thin, to glue the emulsion to the base>prevent bubbles ir other distortion when the film is bent during handling Film-screen Technology: X-ray film Film emulsion Single or double-sided. Emulsion is composed of a Silver halide crystal: homogeneous mixture of:  Gelatin: The suspending medium sensitive to radiation. for silver (Ag) halide crystals or Experience changes to their grains.  Silver (Ag) halide crystals: The composition when acted by photosensitive agents. the light Forms the latent image on the film (foundation of the image). Film-screen Technology: X-ray film Handling and storage – Unexposed Film X-ray films are sensitive The optical density from the base material and film fog (B+F) to: must not exceed 0.30 OD.  Light  Heat Radiation exposure must be limited to 0.1 mGy.  Humidity  Chemical Film is sold in light-proof and moisture-proof packaging and contamination may be handled in dark safelight conditions (caution: ensure  Mechanical stress correct safelight filter).  X-ray radiation Boxes of film must be stored on edge (vertically; not horizontally flat) away from chemical fumes, at a temperature Storage conditions must range of 18⁰ C to 23⁰ C and humidity between 40% and 60%. protect unexposed film from stray radiation, Boxes of film must be used before their expiry date. chemical fumes and light. Loaded cassettes (with x-ray film) must be stored in a shielded area and must be limited to 0.5 μGy. Film-screen Technology: X-ray film Handling and storage – Exposed Film Conditions Duration of storage Adequate ventilation. Depending on the institution. Satisfactory illumination.  An original radiograph is stored is usually 5-8 years. Dust-free environment.  Obstetrical ultrasound are kept for 25 years. Smoke detectors and secure locks.  Pediatric radiographs are kept until the patient’s 25th birthday. Metal shelving units subdivided into compartments for easier  Unusual or rare pathology. storage of film file folders (containing patients x-rays). Film-screen Technology: Intensifying Screen Purposes Characteristics X-ray film is more sensitive to light Phosphor crystal layer with protective than x-rays. coating. Intensifying screen converts x-ray  High level of x-ray absorption. energy to visible light.  High x-ray-to-light conversion.  Little or no “afterglow” following radiation. Each x-ray is converted into many light photons.  To decrease x-ray dose to the patient.  To decrease motion blur or unsharpness.  Amplifies the effect of the x-ray beam. Film-screen Technology: Intensifying Screen Base Layer Provides mechanical support for the active phosphor layer. Polyester is the preferred material. flexible yet tough Rigid chemically inert uniformly radiolucent A reflective layer (magnesium oxide or titanium dioxide) may be added to redirect the light towards the film. An absorptive layer (coloured dye) may be added to absorb light going away from the film. Film-screen Technology: Intensifying Screen Phosphor layer Active layer of the radiographic intensifying screen. Emits light (fluorescence) when stimulated by x- rays. Phosphor; Phosphor (material): Calcium Tungstate (CaWO4); as an active component in the intensifying screen and works on the principle of the fluorescence rather than phosphorescence. Rare earth elements (gadolinium, lanthanum, and yttrium) are used in newer, faster screens. Film-screen Technology: Intensifying Screen Luminescence The ability of certain materials to emit light in response to an excitation. Emission of light by certain materials when they are relatively cool. 2 types: Fluorescence: an instantaneous emission of light following an excitation. Phosphorescence: a delayed emission of light Film-screen Technology: Screen/Film Combination Designed to complement each other to produce a quality image. Intensifying screens manufactured to emit a certain wavelength of light require films to have enhanced sensitivity to the same wavelength Characteristics Speed Resolution The speed of an imaging system is Recorded detail or sharpness. inversely proportional to the The ability of an imaging system to dose. demonstrate detail varies on its As the speed of a system Inverse purpose. increases, the dose required to relationship obtain the desired optical density decreases. Film-screen Technology: Screen/Film Combination Care of screens Should be handled carefully; rough handling may lead to scratches or damage resulting in radiographic artefacts. Place the film inside the cassette when loading. Do not dig the film out with fingernails when unloading. Do not leave the cassette open; susceptible to dust or darkroom chemicals. Cleaned regularly with manufacturer-recommended preparation, often containing an antistatic compound Screens must be completely dry before reloading. Film-screen Technology Latent image The radiographic film needs to be processed to show the image. DIGITAL METHOD COMPUTED RADIOGRAPHY DIGITAL RADIOGRAPHY Film-screen Technology: Film processing Film processing Manual Film processor Film processor contain tank with The radiographer different chemicals put the film in different chemicals. Dark room Day light Film-screen Technology: Dark Room Characteristics Clean Organized; dry & wet area Light proof Safelight Film-screen Technology: Film Processing Basic Steps Developing Rinsing (stop bath) Fixing Washing Drying Film-screen Technology: Film Processing Film-screen Technology: Film Processing Film-screen Technology: Film Processing Film-screen Technology: Film Identification Every radiograph should be properly labelled for easy identification. Information permanently recorded on film. Basic label information includes: Name and address of hospital Date Patient identification Methods of film labeling Lead markers Lead-impregnated tape Photo-imprinting Film-screen Technology: Film Filing Radiographic film should be filed so that they are easily located: Film should be completely dry. Labeled appropriately. Place in a film sleeve with ID information visible. Filed according to the hospital filing system. Film-screen Technology: Limitations Chemical hazard. Image cannot be altered or manipulated or erased. Poor image results → Repetition/Retake. Extra radiation dose to the patient Increases patient waiting times Extra cost to consumables (films, chemicals) and other associated costs Film cannot be used for another projection (permanent). Film can only be stored for a specific period of time. Retrieval of radiographic images can be time-consuming. Digital technology Digital Technology Benefits: Images can be immediately acquired, deleted, modified, and subsequently sent to a network of computers. Can make a radiological facility or department filmless → eliminates the chemical processing of films. The referring physician: Can view the requested image on a desktop or a personal computer Report in just a few minutes after the examination was performed The images are no longer held in a single location. The patient can have the x-ray images on a compact disk. Digital Technology: The general principle Digital detector absorb x-ray energy. Transferred into electrical charges. A computer then processes the electrical signals (raw data) using a post-processing software. The resultant images are displayed on monitors before a hard copy is made if indicated. Digital technology Digital Systems Computed radiography (CR) Digital radiography (DR) Photostimulable storage Detectors: Direct and indirect imaging plate (PSP or IP) Direct: Indirect: x-ray → electronic signals x-ray → light → Use a cassette electronic signals Amorphous selenium Charge-coupled device After exposure, read by a (CCD) reader. Amorphous silicon with a thin film transistor (TFT) Computed radiography Computed radiography: digital radiographic system that uses a photostimulable storage imaging plate (PSP or IP), typically inside a cassette. 1980s: introduced by Fuji. Require a CR reader to process the plate and create image: 2 step process.  Computed radiography IP: rigid sheet with several layers designed to record and enhance transmission of the image from a beam of ionising radiation. Insulates IP from handling damage Holds the photostimulable phosphor, active component in IP Grounds the plate to eliminate electrostatic problems and absorb lights to increase sharpness Prevent light from erasing the data, or leak through the backing layer A base to coat the other layer (decrease spatial resolution) Digital radiography (DR) Digital technology: Digital Images Can be viewed via: Softcopy using display monitors. Hardcopy (printed film) similar to analog x-ray images. Digital technology: Advantages & Disadvantages Advantages Disadvantages Less radiation dose. Expensive to set up. Archiving of images does not take up Overexposure of radiation much space. cannot be detected easily. Images can be: In softcopy or hardcopy Manipulated Transmitted through networking; PACS, HIS The detector to capture images can be used again for the next examination. No chemicals are needed for image processing. Less time to retrieve images. Possibility of image loss is reduced.