Daily system check in tomosynthesis mode
This test is an extension of the existing 2D daily system test, and the two would be most easily carried out together.
Use the same PMMA block and compression paddle as are used for the daily 2D system test. Place the PMMA on the breast support table.
This test should always be carried out with the paddle in the fixed position or carried out with the paddle in the flexible position.
Compress to 100 N (or as near to as possible, 95–105 N is acceptable) Set the AEC sensor to position 2.
In addition to the conventional 2D Autofilter flatfield image, take a tomosynthesis Autofilter image of the block. These two images may be taken as a combo exposure.
Record the following:
l compressed breast thickness
l kV
l mAs.
View the reconstructed image slices (not the projections) on the X-ray unit. While scrolling through the tomosynthesis slices, look for any abnormal artefacts in the image, and record whether or not any abnormality has been observed.
Enter all the recorded information onto the form/spreadsheet provided, and compare the mAs against the remedial level. Where any remedial levels are exceeded, repeat the test to ensure that a mistake has not been made.
If remedial levels are exceeded or abnormal artefacts are observed then contact the TOMMY physicist for advice before continuing to use the equipment for patients in the trial. Any image containing abnormal artefacts must be saved for investigation and a copy should also be sent to NCCPM.
(It is not possible to measure pixel values within a region of interest [ROI] in a reconstructed tomosynthesis slice on the Dimensions AWS, so the calculation SNR or CNR values for tomosynthesis images is not required for Radiographer QC.)
Weekly remote quality control images
Image of test object containing 1-mm aluminium ball in tomosynthesis mode
Place the 5-mm sheet of PMMA containing the 1-mm aluminium ball between the two 22.5-mm thick sheets of PMMA on the breast support table. The aluminium ball is located on the midline 6 cm from one
of the long edges of the sheet– this long edge should be aligned with the chest wall edge of the table.
Use the large 24 × 29 compression paddle (in fixed mode). Compress to 100 N (or as near as possible,
95–100 N is acceptable) Set the AEC sensor to position 2.
Take a flatfield tomosynthesis image with the AEC in Autofilter mode. APPENDIX 17
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View the reconstructed image slices (not the projections) on the acquisition workstation in the X-ray room.
Press the‘Actual pixels’ button to bring the image into full resolution, and using the wheel scroll through
the image. The aluminium ball should be visible as a spot somewhere between slice numbers 20 and 30. Find the slice at which the image of the ball appears sharpest and least distorted and record that slice
number. The ball may appear fairly sharp over a range of 3 to 5 slices– record a slice number
in the middle of the range.
Check that the ball appears sharp and circular in this slice. Record whether or not this is so.
Above and below the slice in which the ball appears sharpest the ball will appear to become elongated in the vertical direction (parallel to chest wall edge). Check that the appearance of this line is as normal with no broadening, twisting, or otherwise abnormal appearance. Record whether or not the appearance is as normal.
If any abnormalities are seen in the appearance of the ball in the reconstructed tomo image, contact the TOMMY physicist for advice before continuing to use the equipment for patients in the trial. Two dimensional and tomosythesis images of large plain PMMA block.
Place the two 22.5-mm thick sheets of PMMA on the breast support table. Use the large 24 × 29 compression paddle (in flexible mode).
Compress to 100 N (or as near as possible, 95–100 N is acceptable) Set the AEC sensor to position 2.
Take a flatfield combo image with the AEC in Autofilter mode. Display the 2D image on the monitor and check carefully for artefacts.
Display the reconstructed tomo image on the monitor and scroll through the slices, checking carefully for artefacts.
Record whether or not any abnormalities are seen. If any abnormalities are seen in either the 2D or the tomo image, contact the TOMMY physicist for advice before continuing to use the equipment for patients in the trial.
Send the three weekly images and QA spreadsheet to NCCPM.
Every week, send a copy of the aluminium ball tomosynthesis image, and the 2D and tomosynthesis images from the Combo exposure to NCCPM for further analysis.
Also send a copy of the Radiographer QA spreadsheet to NCCPM by e-mail. Monthly thickness check in tomosynthesis mode
This test is an extension of the existing 2D monthly thickness test, and the two would be most easily carried out together.
Use the same PMMA blocks, compression paddle and thicknesses as are used for the 2D thickness test. (Record the details of the method used when setting the baseline so that it can be reproduced for future measurements.) In addition to the conventional 2D Autofilter image, take a tomosynthesis Autofilter image for each thickness.
Record the kV and mAs for the tomosynthesis exposure on the form/spreadsheet provided and compare against remedial levels. Where any remedial levels are exceeded, repeat the test to ensure that a mistake has not been made.
If remedial levels are exceeded or abnormal artefacts are observed then contact the TOMMY physicist for advice before continuing to use the equipment for patients in the trial.