[Methods and Materials]

1.Computer simulation

• Computer-simulated X-ray projection with a very finite pixel pitch (5 μm), resembling analog images of the slit, edge and square-waves, were created.
• Simulated CR and FPD systems were constructed in our computer programs. The program can simulate the blurring at incident planes, data acquisition (sampling) and other signal processing. By using the program, the following data were analyzed : (a) Profiles and their spectra before and after the log conversion. (b) Comparison of resultant MTFs and true MTFs configured in the simulated CR and FPD.

2.Actual measurement

• The actual MTFs were measured in the horizontal (scan direction) and the vertical (sub-scan) directions by using a CR system.
  
  

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Method 1 - Computer simulation -

(1) Simulated X-ray projections

• The simulated X-ray projection data with a finite pixel pitch (5μm) were created to resemble analog signals for three test devices.
  

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• These projection data were processed and then sampled to create digital images with 175μm pixels by using the simulated CR and FPD system.

(2) Signal processing to simulate the CR system and configured true MTF

Fig.

Fig.

(Note)

Scan direction: the laser scanning direction.

Sub-scan direction: the direction perpendicular to the scan direction.

(3) Signal processing to simulate the FPD system and configured true MTF

Fig.

Method 2 - Actual measurements - ⁵⁾

The actual measurements by using the CR.
The presampled MTFs in scan direction and sub-scan direction were measured from the actual slit, edge and square wave images.

Fig.

MTF analysis procedures

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Fig.

Slit method^6)-8), Edge method^5),8)-11), Square-wave method¹²⁾