[IGSTK-Users] CT Dicom images with gantry tilt

[Fucang Jia]

Hi, Patrick,

Thank you for your help on the object disappering during tracking. I will try the code later.

Today I found another problem, here is a head phantom scanned with CT gantry tilt.
The angle is
(0018|1120) Gantry/Detector Tilt = 6.68

so IGSTK will not read this set of DICOM.

I see there is  several DICOM sets with gantry tilt in Sandbox\Testing\Data\CT_WITH_GANTRYTILT,
E000147_1, E000147_2, E000147_4 can be read by NeedleBiopsy app, whose angle is
-16.5, -6.5, -1.5 separately.
But E000147_3, E000147_5, E000147_6 can not be read, whose angle is
6.5, 10.5,  20.5 separately.

I do not know why the gantry tilt with positive angle can not be read, while the one with negative
angle can be read into IGSTK. It seems that the shear transform should be corrected in either positive
angle or negative angle. Is that a bug in igstkDICOMImageReader.txx around line 593-607 ?

  // Check if the gantry tilt is within an acceptable range
    double gantryTilt;
    double gantryTiltThreshold=0.01;
  
    std::stringstream sstr;
    sstr.str( m_GantryTilt );
    sstr >> gantryTilt;

    if( gantryTilt > gantryTiltThreshold )
      {
      this->m_ImageReadingErrorInformation = "Unacceptable gantry tilt";
      this->m_StateMachine.PushInput( this->m_ImageReadingErrorInput );
      this->m_StateMachine.ProcessInputs();
      return; 
      }

And due to affine transform is needed to correct gantry tilt, should the gantry tilted CT images
be read or not be read into IGSTK before correction?

Thank you very much!

Fucang
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