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Calibrating the most demanding professional displays




                  www.qubyx.com
Why calibrate
              medical displays?




  Hospitals and clinics have quality programs for medical
equipment. However, often the displays used for diagnostics and
reviewing are not part of those quality assurance programs.


 No monitor, including medical ones, displays images perfectly.
Poor image quality results in fatigue of the doctors, more time
DICOM calibration
        of displays in medical
            environment
•
•   What is light and how does it influence
    image?
•   What is DICOM GSDF Part14?
•   Why calibrate displays to DICOM?
•   How does calibration work?
•   What displays can be calibrated?
•   What are the required tools?
What is light?




Visible light is the electromagnetic radiation that can be seen by
the human eye.Light is visible in the wavelengths from 380 to
740 nm. When light is broken by a prism, different colors of the
white light become visible.
How do we see light?




  Rod and con cells in the retina of the human eye are sensible to
light and can distinguish up to 10 million different color and
luminance shades. These cells form the images.


 Non image building cells are the photosensitive ganglion cells,
What is DICOM Part14?

  The DICOM Standard is developed and published by
the US organisation NEMA (National Electrical
Manufacturers Association).

 The Part 14 of this standard discusses how pixel
values should be interpreted and displayed.

 Part 14 also specifies a function that relates pixel
values to displayed luminance values. This function is
called GSDF (Gray Scale Display Function).
GSDF




  Originally developed by the researcher Peter G.J. Barten and published as
"Contrast Sensitivity of the Human Eye and Its Effects on Image Quality".
Why calibrate
                   to DICOM GSDF?
•   Adapt display to human eye. Human eye is not an digital device like a
    computer is. The computer display, as the interface between the human and
    the digital machine, must be adapted to the characteristics of the human eye.


•   Re-calibrate over time. Computer displays tend to change over time, like
    any other light source. Backlight lamps and RGB filters change. That is why
    even a factory calibrated display needs to be re-calibrated over time to
    continue matching the sensibility of the human eye.


•   Make sure displays look the same. Consistency of images on various
    displays is important for diagnostics. Calibration iensures that an image looks
    the same in all services and on all workstation.


•   Standardise display outputs. Calibrated displays meet the key quality
    assurance standards in medical industry.


•   Safety and     quality.   Increase   diagnostic   safety   and   improve   quality
    assurance.
Why calibrate
color of a display?
              •   human      eye  perceives
                  various color shades in a
                  different way



              •   a diagnostic image on a
                  color display is influenced
                  by color hues: reddish
                  gray    shade will      look
                  different   from     blueish
                  gray,      so     adjusting
                  luminance is not enough



              •   color calibration ensures
                  the        same        color
                  temperature on all driving
                  levels    (different   gray
                  levels) of the display
Why calibrate a display
               regularly?
•
•   display white level degrades


•   display back light changes over
    time


•   display color filters change over
    time


•   regular      verification   and
    adjustment of the white level of
    the display is necessary
How does calibration work?




  1. Measurements taken.Reference colors and gray levels are
displayed on the monitor and measured with a colorimeter or luminance
meter.


  2. LUT generated. From the actual measured values and the known
Barten's formula target values a correction table called Look Up Table
(LUT) is generated.
What displays can be calibrated
        to DICOM GSDF?




Almost any LCD, LED, or OLED display can be calibrated to DICOM GSDF to
compete with traditional medical displays.
Standardised Quality Assurance
In some countries the legal bodies enforce acceptance testing of diagnostic
   and reviewing displays when they are installed, and constancy testing
   for quality assurance on a regular basis.



Major QA standards are AAPM TG18, DIN 6868-57, DIN 6868-157,
   JESRA X-0093 , IEC 62563-1



The tests performed within those standards consist of visual tests and
   measurement tests, which verify conformance to the requirements of
   the standards.
Controlled Environment




Apart from calibration and constant verification of the display it is important
   to control the working environment:
 •   ambient light must be stable and remain within the acceptable range



 •   no direct reflection on the display panel should occur
calibrates any display
to DICOM GSDF.
performs
acceptance and constancy tests
   to key medical standards
Download
A free 15-day trial of PerfectLum display calibration
  and quality assurance software is available at
  www.perfectlum.com/downloads

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Medical display calibration and qa

  • 1. Calibrating the most demanding professional displays www.qubyx.com
  • 2. Why calibrate medical displays? Hospitals and clinics have quality programs for medical equipment. However, often the displays used for diagnostics and reviewing are not part of those quality assurance programs. No monitor, including medical ones, displays images perfectly. Poor image quality results in fatigue of the doctors, more time
  • 3. DICOM calibration of displays in medical environment • • What is light and how does it influence image? • What is DICOM GSDF Part14? • Why calibrate displays to DICOM? • How does calibration work? • What displays can be calibrated? • What are the required tools?
  • 4. What is light? Visible light is the electromagnetic radiation that can be seen by the human eye.Light is visible in the wavelengths from 380 to 740 nm. When light is broken by a prism, different colors of the white light become visible.
  • 5. How do we see light? Rod and con cells in the retina of the human eye are sensible to light and can distinguish up to 10 million different color and luminance shades. These cells form the images. Non image building cells are the photosensitive ganglion cells,
  • 6. What is DICOM Part14? The DICOM Standard is developed and published by the US organisation NEMA (National Electrical Manufacturers Association). The Part 14 of this standard discusses how pixel values should be interpreted and displayed. Part 14 also specifies a function that relates pixel values to displayed luminance values. This function is called GSDF (Gray Scale Display Function).
  • 7. GSDF Originally developed by the researcher Peter G.J. Barten and published as "Contrast Sensitivity of the Human Eye and Its Effects on Image Quality".
  • 8. Why calibrate to DICOM GSDF? • Adapt display to human eye. Human eye is not an digital device like a computer is. The computer display, as the interface between the human and the digital machine, must be adapted to the characteristics of the human eye. • Re-calibrate over time. Computer displays tend to change over time, like any other light source. Backlight lamps and RGB filters change. That is why even a factory calibrated display needs to be re-calibrated over time to continue matching the sensibility of the human eye. • Make sure displays look the same. Consistency of images on various displays is important for diagnostics. Calibration iensures that an image looks the same in all services and on all workstation. • Standardise display outputs. Calibrated displays meet the key quality assurance standards in medical industry. • Safety and quality. Increase diagnostic safety and improve quality assurance.
  • 9. Why calibrate color of a display? • human eye perceives various color shades in a different way • a diagnostic image on a color display is influenced by color hues: reddish gray shade will look different from blueish gray, so adjusting luminance is not enough • color calibration ensures the same color temperature on all driving levels (different gray levels) of the display
  • 10. Why calibrate a display regularly? • • display white level degrades • display back light changes over time • display color filters change over time • regular verification and adjustment of the white level of the display is necessary
  • 11. How does calibration work? 1. Measurements taken.Reference colors and gray levels are displayed on the monitor and measured with a colorimeter or luminance meter. 2. LUT generated. From the actual measured values and the known Barten's formula target values a correction table called Look Up Table (LUT) is generated.
  • 12. What displays can be calibrated to DICOM GSDF? Almost any LCD, LED, or OLED display can be calibrated to DICOM GSDF to compete with traditional medical displays.
  • 13. Standardised Quality Assurance In some countries the legal bodies enforce acceptance testing of diagnostic and reviewing displays when they are installed, and constancy testing for quality assurance on a regular basis. Major QA standards are AAPM TG18, DIN 6868-57, DIN 6868-157, JESRA X-0093 , IEC 62563-1 The tests performed within those standards consist of visual tests and measurement tests, which verify conformance to the requirements of the standards.
  • 14. Controlled Environment Apart from calibration and constant verification of the display it is important to control the working environment: • ambient light must be stable and remain within the acceptable range • no direct reflection on the display panel should occur
  • 16. performs acceptance and constancy tests to key medical standards
  • 17. Download A free 15-day trial of PerfectLum display calibration and quality assurance software is available at www.perfectlum.com/downloads