Radiography Basics Quiz

Course Information

• Course title: Introduction to Medical Imaging
• Course code: HSMI 1211
• Department: Diagnostic Imaging and Radiotherapy
• Kulliyyah: Allied Health Sciences

Learning Outcomes

• Students will be able to list various image recording technologies.
• Students will be able to discuss film-screen technology (principles, advantages, limitations).
• Students will be able to discuss digital technology (principles, types, advantages, limitations).

Image Recording Methods

• Analog: Radiographic images are permanently recorded on film.
• Digital: Radiographic images are displayed on a monitor and can be manipulated. Methods for recording include film-screen technology, imaging plates, and flat panel detectors.

Analog Method: Film-Screen Technology

• Film-screen receptor: The component that receives the latent x-ray image and converts it to a visible image.
• Components: Cassette, film, intensifying screen.
• Cassette function: Acts as a protector to film, lightproof, prevents bending/scratching, ensures film and intensifying screen are in close contact.
• Cassette consistency: Front cover (radiolucent material like aluminum, carbon fiber, light weight), and back cover (heavier metal like lead foil to prevent/absorb backscatter radiation).
• Film consistency: Film base, film emulsion, protective coating; cellulose nitrate or triacetate base; flexible yet tough, stable, and rigid; uniformly lucent.
• Film emulsion: Composed of silver halide crystals suspended in gelatin; sensitive to radiation; forms latent image on film.

Film-screen Technology: Intensifying Screen

• Purpose: X-ray film is more sensitive to light than x-rays; converts x-ray energy to visible light (amplifies x-ray beam); converts each x-ray into many light photons; decrease x-ray dose to the patient; decrease motion blur or unsharpness.
• Characteristics: Phosphor crystal layer with protective coating; high level of x-ray absorption; high x-ray-to-light conversion; little or no "afterglow" following radiation.
• Base layer: Polyester is the preferred material because it is flexible, yet tough, rigid, chemically inert, and uniformly radiolucent. Magnesium oxide or titanium dioxide may be added to redirect light towards the film, and an absorptive layer (coloured dye) may absorb light moving away from the film.
• Phosphor layer: Active layer of intensifying screen; emits light (fluorescence) when stimulated by x-rays; calcium tungstate (CaWO4); rare earth elements (gadolinium, lanthanum, yttrium) are used in newer, faster screens.
• Luminescence: Certain materials emit light in response to excitation. Two types: fluorescence (instantaneous emission of light after excitation), and phosphorescence (delayed emission of light).

Film-screen Technology: Screen/Film Combination

• Design: Designed to complement each other to provide a quality image; intensifying screens to emit light at a specific wavelength; films with enhanced sensitivity to that wavelength.
• Speed: Speed of imaging system is inversely proportional to the dose; as speed increases, dose required decreases to obtain the desired optical density.
• Resolution: Recorded detail or sharpness. Ability of an imaging system to demonstrate detail varies depending on the purpose.
• Care of screens: Handle carefully to prevent scratches, place film inside cassette, don't dig out with fingernails, and keep cassette closed. Clean regularly using manufacturer-recommended preparations (often antistatic). Ensure screens are completely dry before reloading.

Film-screen Technology: General Principle

• X-ray beam strikes cassette and screens.
• Light produced in the screen corresponds to the beam intensity.
• Light acts on the film (latent image); processed to highlight the image.
• Modulated beam interacts with compounds in radiographic film to produce the latent image.
• An invisible image is formed on the film, later made visible by photographic development.
• The image needs to be processed to be visible.

Film-screen Technology: Film Processing

• Film processing methods: Manual (films put into different chemicals by radiographer), film processor (uses tanks with different chemicals).
• Steps in film processing:
  • Developing, rinsing (stop bath), fixing, washing, drying
• Chemical processing: X-ray exposure → invisible latent image → developer → fixer → wash → dry → visible image.
• Darkroom characteristics: Clean, Organized (dry & wet areas), Lightproof, Safelight.

Film-screen Technology: Film Identification

• Every radiograph should be labelled properly for easy identification.
• Information on film should be permanent (name/address of hospital, date, patient ID, methods of labelling (lead markers, lead-impregnated tape, photo-imprinting).

Film-screen Technology: Film Filing

• Radiographic film should be completely dry, labelled appropriately, placed in a film sleeve, and filed according to the hospital filing system for easy location.

Film-screen Technology: Limitations

• Chemical hazard.
• Image cannot be altered/manipulated/erased.
• Poor image results may require repetition/retake, increase radiation dose, and increase patient waiting times, leading to cost increase.
• Film used for one projection cannot be reused, and stored for a specific period.
• Retrieval of radiographic images can be time-consuming.

Digital Method: Computed Radiography (CR)

• Digital radiographic system uses a photostimulable storage imaging plate (PSP or IP).
• Introduced in the 1980s by Fuji.
• A CR reader processes the plate, creating an image; a two-step process.
• IP is a rigid sheet with several layers, designed to record and enhance image transmission. A protective layer, phosphor layer, conductor layer, support layer, light shielding layer, and backing layer. Protective layers insulate the IP from handling damage.
• The phosphor layer holds the phosphor active component of the IP.
• The support layer grounds the plate to eliminate electrostatic problems.
• The backing layer absorbs lights to increase sharpness.

Digital Method: Digital Radiography (DR)

• Digital detectors absorb x-ray energy.
• Converts x-ray energy to electrical charges; computer processes these signals using post-processing software.
• Results displayed on monitors before possible hard copy creation.
• Two types of detectors: direct (x-ray to electronic signal); indirect (x-ray → light → electronic signal).

Digital Method: Advantages & Disadvantages

• Advantages: Less radiation dose, archiving in less space, images can be viewed in softcopy/hardcopy, images can be manipulated, images can be transmitted, reusable detectors, no chemicals needed for processing, faster retrieval, less possibility of image loss.
• Disadvantages: Expensive to set up, overexposure of radiation may not be easily detected.

Digital Technology: Digital Images

• Images are viewed via softcopy monitors or via hardcopy (printed film).