X-ray Sensor Technology

Factors Affecting Image Quality in Digitized X-rays When Using
X-ray Sensor Technology


Pictured:
SUNI Sensor

  1. X-ray Sensor (solid state detector) type and manufacturer.  Each manufacturer may have unique characteristics and set-up requirements.  Sensor types:  CCD, CMOS, CMOS APS, etc.  All should function in a reasonably similar manner but each has its own features and benefits.
  1. X-ray Generator (head) needs to meet certain technical specifications. Each of the following is very important and could affect image quality:
    1. Age of x-ray generators (head):  Those which are 10+ years old may lack important features.
    2. Uses DC current.  AC is not ideal for sensor capture.
    3. Generator needs to have an accurately calibrated digital timer.  Exposure times:  .02-.12 depending on equipment and cone length-As a general rule, maxillary teeth require longer exposure, as do molars.  Typically, the farther back in the mouth, the more exposure time will be required. Adjustments related to patient age and gender are also important.
    4. Exposure kV:  Should be less than 70kV; 50-70kV is optimal.
    5. Exposure mA:  2-8mA; 5mA or less is ideal.
    6. Small focal point.
    7. Unique settings for different modes, i.e. film, plate or sensor.
  2. Type of video board/frame grabber installed in the capture PC.  This could be one of the most important elements.
    1. What does the sensor manufacturer recommend?
    2. Is a USB connection required?
  3. X-ray generator has a “long cone”.  In general, x-ray generators with a long cone used with the “paralleling exposure” technique produce a better image than using a short cone and the “bisecting” technique.
  4. Monitor (diagnosing x-rays requires good black and white contrasting.)  Monitors need to have a minimum contrast ratio of 600:1 and dpi of less than 0.27mm.  1000:1 contrast ratio should be used, if possible.
    1. LCD devices used for x-ray diagnosis should be designed to optimally view grayscale rather than colors.
    2. Laptop displays, if used, must also have the recommended contract ratios.
  5. Variables introduced by operator/user:
    1. Attitude: Is staff enthusiastic, and ready and able to learn new skills?
    2. Are the dentist(s) and staff familiar with basic Windows® functionality, i.e. do they know how to use a mouse to click and drag, know how to open, close and modify basic applications?
    3. Improper sensor placement in mouth resulting in:
      1. Overlapping of teeth
      2. Foreshortening
      3. Elongation
      4. Cone cuts
      5. Missing components, i.e., root tips
    4. X-ray head is not stable or steady and could move during capture causing a blurry image.
    5. Operator not adjusting x-ray generator settings to reflect patient age, gender and/or area of the mouth of image to be captured.
    6. Operator not using automatic setting of x-ray generator (if provided).
    7. Improper utilization of sensor holders, i.e. Rinn® kit, Snap-A-Ray®, Wingers, etc.
  6. Poor images due to sensor misuse or damage.
    1. Auto-firing as a result of improperly seated or damaged sensor cable.
    2. Sensors left in an operatory during capture of other x-rays.  This allows a sensor to accumulate “scatter” radiation.
    3. Damage to sensor case due to misuse or patients biting into sensor.
    4. Sensor not “flushing” properly and retaining double images.

Pictured:
SUNI pan image

  1. Proper use of image enhancement features for diagnosis and capture:
    1. Noise — increasing x-ray exposure (while staying within recommended dose limits) improves signal-to-noise ratio, thus reducing noise perception.
    2. Contrast — exaggerates both the light and dark spectrums, but can have a negative effect on display of alveolar bone.
    3. Smoothing auto correction — used to add greater definition to images.
    4. Definition — sharpens image characteristics.
    5. Calibration — must be calibrated before use to ensure proper measurements.
    6. Colorization — used to quickly discern different tissue densities.
    7. Gamma Correction — used to expand the gray scale in a non-linear pattern.  The poles of the gray range go from absolute black on the left to absolute white on the right and are evenly distributed in between.  The alteration of the extraction curve allows more shade of gray in the desired area.  The end effect is that the darker or more radiolucent areas will have a larger number of gray shades and appear darker, whereas the radiopaque areas will appear virtually unchanged.  The net result should be an overall improvement of the image contrast—with a single operation—without causing density saturation at either extremities of the gray scale.
    8. Filters — applied either pre- or post-capture to affect definition, contrast, brightness, gamma and other variables to produce a more diagnostic image.
    9. Image reversal — gives image a positive, rather than negative image of the area, which allows better viewing detection of root tips, dentin, enamel and increased bony detail or the visualization of a very fine endodontic file at the apex of a tooth.  Also beneficial for reviewing images with patients.
    10. Embossing — useful tool for diagnosing interproximal caries as the image has an overall 3-D appearance.  Can also be helpful for checking crown margins.
  1. Proper use of image enhancement features for diagnosis and capture:
    1. Noise — increasing x-ray exposure (while staying within recommended dose limits) improves signal-to-noise ratio, thus reducing noise perception.
    2. Contrast — exaggerates both the light and dark spectrums, but can have a negative effect on display of alveolar bone.
    3. Smoothing auto correction — used to add greater definition to images.
    4. Definition — sharpens image characteristics.
    5. Calibration — must be calibrated before use to assure proper measurements.
    6. Colorization — used to quickly discern different tissue densities.
    7. Gamma Correction — used to expand the gray scale in a non-linear pattern.  The poles of the gray range go from absolute black on the left to absolute white on the right and evenly distributed in between.  The alteration of the extraction curve allows there to be more shade of gray in the desired area.  The end effect is that the darker or more radiolucent areas will have a larger number of gray shades and appear darker, whereas the radiopaque areas will appear virtually unchanged.  The net result should be an overall improvement of the image contrast with a single operation without causing density saturation at either extremities of the gray scale.
    8. Filters — applied either pre- or post-capture to affect definition, contrast, brightness, gamma and other variables to produce a more diagnostic image.
    9. Image reversal — gives image a positive, rather than negative image of the area, which allows better viewing detection of root tips, dentin, enamel and increased bony detail or the visualization of a very fine endodontic file at the apex of a tooth.  Also beneficial for reviewing images with patients.
    10. Embossing — useful tool for diagnosing interproximal caries as the image has an overall 3-D appearance.  Can also be helpful for checking crown margins.
  2. Printing Requirements: Printer must be able to print 256 shades of gray
  3. Office/operatory requirements:
    1. PCs in each room for view and capture of x-rays.
    2. Monitors are easily viewed from chair side in standard operating positions.
    3. PCs need to be less than three years old and meet standard specifications recommended by the vendor.
    4. PCs need to be connected to a network with images stored on a server which has appropriate failover characteristics.
    5. Images on server need to be copied via standard "back-up" routine to site or source which is remote to main server.

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