Finals

• Digital imaging


  The creation of a representation of the visual characteristics of an object, such as a physical scene or the interior structure of an object
• Image Acquisition

  • Includes processing, compression, storage, printing, and display of images
• Digital image


  • Advantage: Ability to make copies digitally indefinitely without any loss of image quality
• Image acquisition is the first point of data entry into a PACS, and errors here can adversely affect clinical operations
• General predictors for successful incorporation of image acquisition devices

  • Ease of device integration into established daily workflow routine, high reliability and fault tolerance, simplicity and intuitiveness of user interface, device speed
• Image formation


  Latent image exists on film after exposure but before chemical processing, manifest image exists after exposure and processing
• Gurney-Mott theory is widely believed to best explain latent image formation on film
• Exposure indicator

  Reflective of noise content and signal-to-noise ratio in the image, appropriate incident exposure is variable based on desired signal-to-noise ratio
• Image noise content will decrease and SNR will increase as radiation exposure to the detector increases
• Detector exposure indicator reflects noise levels present in image data, adequate exposure results in appropriate noise level in the image
• Due to the imperfection of measurements, several types of errors are induced in the process and the results of a spatial analysis are further degraded
• Histogram analysis

  1. Digital radiographic image histograms are important for digital image production

  2. Histogram is a plot of the frequency of appearance of a given object characteristic

  3. Storing and analyzing characteristic image histograms for each radiographic projection

  4. Producing a representative histogram by averaging the value of each frequency interval from stored PA chest image histograms

  5. Regularly updating the histogram from newer images
• If the x-ray exposure field is not properly collimated, sized, and positioned


  Exposure field recognition errors may occur, leading to histogram analysis errors because signal outside the exposure field is included in the histogram
• Alignment of the exposure field on the IP is important

  When not oriented with the size and dimensions of the IP, image artifacts can appear
• Background radiation comes from environmental sources including the earth's crust, the atmosphere, cosmic rays, and radioisotopes
• Natural sources of radiation account for the largest amount of radiation exposure received by most people each year
• Radon, a gas produced by radium decay within rock, is currently believed to be a source of radiation
• Medical diagnostic procedures are the greatest manmade source of ionizing radiation exposure to the general population
• Exposure to low radiation doses may pose a small risk of inducing cancer years to decades following the examination
• Scatter radiation primarily results from Compton interactions, where an incoming x-ray photon loses energy and changes direction
• Two major factors affecting scatter radiation exiting the patient

  Kilovoltage peak (kVp) and volume of irradiated tissue
• Beam restriction limits patient exposure and reduces the amount of scatter radiation produced within the patient
• Increasing collimation decreases the volume of tissue irradiated, the amount of scatter radiation produced, and the number of photons that strike the patient
• Types of beam-restricting devices include Aperture Diaphragms, Cones and Cylinders, Collimators, and Grids
• Types of beam-restricting devices

  • Aperture Diaphragms
  • Cones and Cylinders
  • Collimators
  • Grids
• Aperture Diaphragms


  • The simplest type of beam-restricting device, made of lead with a hole (aperture), easy to use
• Cones and Cylinders

  • Shaped differently, have extended flanges, limit unsharpness surrounding radiographic images more than aperture diaphragms
• Collimators


  • The most sophisticated, useful, and accepted beam-restricting device, considered the best for radiography, equipped with lead shutters for beam limitation
• Grids


  • Devices placed between the patient and the IR to absorb scatter radiation, allow transmitted radiation to pass through while absorbing scatter radiation
• Collimation is the restriction accomplished with the use of a collimator
• A collimator has two or three sets of lead shutters to limit the x-ray beam, adjustable to produce projected fields of varying sizes
• The field shape produced by a collimator is always rectangular or square unless an aperture diaphragm, cone, or cylinder is placed below it
• Grids in radiographic examinations result in fewer photons reaching the IR
• The use and type of a grid depend on the thickness of the part, kVp, patient dose, contrast improvement, and likelihood of grid errors
• A network consists of two or more computers linked to share resources, exchange files, or allow electronic communications
• Common types of networks

  • Local Area Network (LAN)
• A LAN is confined to a relatively small area, generally limited to a geographic area such as a writing lab, school, or building
• Servers in a network provide services to other computers, while workstations are used by human users directly
• Servers tend to be more powerful than workstations, and configurations are guided by needs
• Servers located in a secure area

  • Operate without a dedicated display or keyboard
  • Size and speed of the server's processor(s), hard drive, and main memory can dramatically add to the cost of the system