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GRAD Engineering LLC


Presented at AAPM July 26 2004

Automatic TG18 Testing

(What can be tested from the front side automatically)

R. Simpson & T. Furukawa

Key words for automatic TG-18 test

1. Why the front luminance meter is important

2. The background luminance changes by shipping vibration

3. Automatic TG-18 test

Front Luminance Meter is necessary for accuracy of medical image

1. Transmission (Gamma) of LCD panel changes over the time period.

2. Light output = Backlight + LCD transmission

3. It is necessary for the True Quality Control for Medical Image Displays

4. It is necessary for Consistent of Presentation of Image for the requirement.

Why photo sensor must be on the front ?

LCD panel transmission changes approx. 8% after 3,000hrs!  This can not be seen from a back side sensor.  It is true that 8% change in white level is not huge but....lets continue.

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Relative Change in Percent Verses Time

Factory-calibrated to the target curve must be done at the end users/Healthcare Facility

Factory-calibrated to the target curve is no longer usable (after shipment).
    Background will changed over 30% during shipping!

The following work must be done at the Healthcare Facility

    1) For manual calibration system  with external photo sensor:

calibration process must be done.

    2) For automatic calibration system with built-in front photo sensor:

a) Correlation process must be done:  A one time test that correlates the front side sensor with an external sensor.
b) Calibration process must be done:  White level, Black level and Gamma are set.   

The background brightness changes due to vibration test.  

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Black lever of a LCD monitor before shipment.  The right side is under 1fL.   The bottom left side is above 2fl.

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Black level of the monitor after a FedEx trip.  The bright corner dropped from 2.1 to 1.2fl.

        1. The background luminance changes after vibration test.
        2. Re-calibration is necessary. 
Data has been provided by  LCD Mfr.
The vibration test for existing 3M LCD monitor  
Change in % at high luminance(524cd/m2)- FedEx shipment test.

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One corner had a 4% change.

The vibration test for existing 3M LCD monitor  
Change in % at low luminance(0.97cd/m2)

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The center changed 9.2%. Over 30% change in two corners. 

A solution for the automatic TG-18 test  

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Attachable Front Luminance Meter
Measures Light from monitor (Color or B&W)and Room light
Connects to PC via USB or Serial 
Network Internet through PC  
Test Monitor 
Generates reports
Warning messages
(Single monitor) or (multiple sites)   
Diffuse Reflection Test  
Ambient Lighting Evaluation
QUESTION:Is the room light too bright?
Room Light Reflects Back Room light reflected back--must be less than 1/5 the black level. 
Measure room light and black level “Ambient Light is Acceptable.”   
Luminance Response Test  

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Test using 18 levels.  Measure and compare with DICOM standard.

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Question:Can the monitor meet brightness spec?
Aging of LCD back light Maximum light level drops with time.
Question: Can blacks be seen?  

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Can you see QUALITY CONTROL? Can you see all the information?
TG18QC pattern   

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If the room light is too bright, some black information is lost.

What color is WHITE? Normally used for color applications
Color matching of B&W monitors.   
Not all monitors are created equal.
Multi Monitor Installations....Why does monitor 3 look red?  
TG18QC modified  

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Test pattern for QC.