From Jonny Eser@21:1/5 to All on Wed Oct 21 05:50:01 2020
I was hoping to get some clarification to an topic that I have come across.
Setup: CC view, Tomo arc 15 degrees, increments 1 degree, CW movement
In the tomosynthesis BTO images under the sequence 0018, 9507 we have three dicom tags:
0018,9508 Primary Positioner Scan Arc
0018,9510 Primary Positioner Scan Start Angle
0018, 9514 Primary Positioner Increment
Further under the same sequence we have another sequence 0018,9538 Per Projection Acquisition Sequence, and under this sequence we have the following tag:
0018,1510 Positioner primary angle (this would be present for each projection that is acquired, in our scenario 15 times)
For the first the dicom tags, I would expect the the following values: 0018,9508 = 15
For the 0018,1510 I have little doubts as to what it should be. Is this an indicator for the tube angle? Which it would mean that the first projection would get -7.5, and the next projection would be -6.5, and next would -5.5 until the last projection
which would be 7.5. Assuming the detector does not rotate during the tomo sweep.
Is this an indicator of the detector position? Which would mean that every projection Positioner primary angle would be the same, in our case 0 degrees for the CC view. Assuming the detector does not rotate during the tomo sweep.
Per the standard:
Positioner Primary Angle (0018,1510) Position in degrees of the X-ray beam vector in the coronal plane as if the patient were standing where movement of the x-ray source from right to vertical is positive, and vertical is zero.
Section C.22.214.171.124.1 in figure C.8.11.7-1 it has an illustration of the vector pointing from the focal spot to the center of the chest wall line of the detector.
From these definitions I would expect the positioner primary angle to be an indication of the position of the tube, relative to the detector. So if the detector is fixed then the positioner primary angle should change for each projection. If the detector
rotates then the angle would remain the same for each projection.
We have several vendors doing it differently and the viewing software needs to accommodate each vendor and I am trying to figure out this topic.