rad13

• Histogram


  Reference histograms for body parts, developed using appropriate exposure techniques, positioning, and collimation
• Histogram analysis


  Computer uses shape of histogram and algorithm to locate the VOI (value of interest) and determine the exposure indicator
• Image does not fit parameters used for reference histogram

  Histogram analysis error occurs
• When a histogram analysis error occurs, the image will not display appropriately</b>
• Appropriate density and contrast will not be displayed because the computer does not recognize the data
• Histogram analysis error can also give an incorrect exposure indicator number
• Exposure field recognition


  Process by which the imaging system identifies and selects the correct exposure field for an imaging study
• Exposure field


  Specific area of the patient's body that is targeted for imaging, determined by anatomic region and imaging modality
• Exposure field recognition errors can occur when the imaging system fails to recognize the correct exposure field, resulting in an image that is over or underexposed
• Types of exposure field recognition errors

  • Collimator border recognition errors
  • Exposure field distribution errors
• Collimator border recognition errors

  Imaging system fails to detect the correct collimation border, resulting in an image that includes areas not relevant to the targeted anatomic region
• Collimator border recognition errors

  • Lumbar spine with too much collimation
  • Abrupt straight line of tissue density when there are prosthetic devices or other parts with large density differences
• Exposure field distribution errors

  Imaging system fails to detect multiple exposure fields or plates, resulting in an image that combines multiple areas and images into a single image
• Exposure field distribution errors can lead to confusion and inaccuracies in diagnosis, as multiple images may be needed to accurately represent the targeted anatomic region
• To avoid exposure field distribution errors, imaging technicians should be trained to use the appropriate number and location of exposure fields or plates for each imaging study
• Imaging equipment can be equipped with automatic exposure field recognition software to help reduce the likelihood of these errors
• Incorrect anatomic menu selection

  Selecting the wrong anatomic menu during imaging acquisition, resulting in incorrect image parameters and an inaccurate image
• Incorrect anatomic menu selection can lead to misdiagnosis and improper treatment
• To avoid this error, it is important for imaging technicians to be trained in the correct selection of the anatomic menu, and to double-check their selections before taking the image
• Imaging equipment can be equipped with automatic anatomic recognition software to help reduce the likelihood of this error
• Another histogram analysis error will occur when an area of increased or decreased attenuation is located in the body where it is not normally located
• Areas of increased or decreased attenuation

  • Barium in the stomach on a chest
  • Uneven border of a lead shield
• The exposure field recognition portion of the software will not function correctly and the area corresponding to the lead or barium will be included in the histogram, resulting in a rescaling error that produces a dark image
• Photostimulable phosphor (PSP) plate


  Used in medical imaging to capture images of the body using x-rays, stores energy in the form of trapped electrons
• Advantages of PSP imaging systems

  • Ability to capture high-quality images using low-intensity radiation
  • More flexible and easier to use than traditional film-based x-rays
• Low-intensity radiation exposure in PSP imaging

  Can result in reduced signal-to-noise ratio, lower contrast and spatial resolution, and increased likelihood of motion artifacts
• Background radiation


  Constantly present in the environment, can come from natural or human-made sources, and can interfere with the accuracy of images produced by PSP plates
• The background radiation is usually about 40 μR/day to 80 μR/day, and the PSP plate can detect radiation levels that are only slightly higher than the background radiation
• PSP plates that have been unused for more than 48 hours should be erased before being used again to avoid interference from residual trapped electrons
• Scatter radiation


  Radiation produced when x-rays interact with matter, can cause interference and artifacts in images produced by PSP plates
• To minimize the effects of scatter radiation, it is recommended that PSP plates not be stored in the examination room where x-rays are being used
• Beam limitation


  Restricting the size of the x-ray beam to the area of interest, helps to reduce the amount of scattered radiation produced during a radiographic procedure
• Positive beam limitation (PBL)


  Accessory on most collimators that automatically collimates the beam to the size of the cassette
• Automatic collimators should leave a small unexposed border on all four sides of the exposed image, but it is possible to override the PBL devices
• Optimal exposure


  Carefully selecting exposure factors such as kVp, mA, and exposure time to achieve high-quality images while minimizing radiation exposure to the patient
• kVp


  Primary exposure factor that affects image contrast and radiation dose, increasing kVp increases beam penetration and reduces scatter radiation but also increases patient dose
• mA and exposure time


  Exposure factors that affect radiation dose and image quality, increasing mA or exposure time increases the amount of radiation reaching the image receptor but also increases patient dose
• Radiographic grids


  Carefully fabricated section of radiopaque (lead) and radioluscent material positioned between the patient and image receptor to reduce the level of scatter radiation reaching the image receptor
• mA


  Tube current - the number of electrons crossing the tube from cathode to anode per second
• Exposure time


  Length of time the tube is energized