1. Motion Correction 21.2.2005 Riku Klén

2. Motion correction List mode motion correction consists of
list mode acquisition
motion tracking
motion correction

3. What is list mode acquisition?
Normal acquisition (or frame mode acquisition)
scanner
sinogram
acquisition
image
reconstruction
List mode acquisition
scanner
list mode data
acquisition
sinogram
binning

4. Why list mode is needed? list mode data consists of events
every single event is stored
list mode data is binned into sinograms
framing and gating can be defined after acquisition
motion correction can be done inside each frame
Size of list mode file depends on number annihilations detected.
Amount of list mode data is gigabytes.
One frame of HR+ sinogram is 19 megabytes.
One frame of HR+ image is 2 megabytes.

5. List mode acquisition HR+ 8800 4515 1100 0000 8000 0000 1212 1000
Each annihilation detected is represented as a LOR. Information about LOR is stored in list mode file.

6. Why track motion? motion of the patient cannot be avoided
motion of head can be minimised, but motion of chest is essential
motion tracking gives more accurate information than mathematical modelling
head position is tracked with frequency of 20Hz
tracking accuracy is 0.5mm
We use optical tracking system Polaris.
It uses infrared cameras to detect motion.
Rotational accuracy of Polaris is 0.3 degrees.

7. Polaris system Polaris is a optical motion tracking system
It uses two infrared cameras to detect motion of a specified target
motion data
0 0 0
0 0 0
0 0 2

8. Motion tracking Polaris 8800 4515 1100 0000 8000 0000 1212 1000
HR+
Acquisition computer
Motion tracked by Polaris is stored to acquisition computer.
Information is send via pulse generator to the scanner.
Scanner adds the input information to the list mode stream.
Pulse generator

9. How motion is corrected?
motion correction is done for each event
each pair of detectors is transformed according to the motion
correction factors for attenuation and normalization are recalculated for corrected image

10. Motion correction Original list mode data
Motion corrected list mode data
motion data …
move LOR up … … … … … … … … … … … … …
motion data … … … …

11. Status of motion correction
list mode option for HR+ is ready and tested
new disk is installed
software for binning is written and tested
test reports are available in the new intranet
Polaris system has been set up and tested
pulse generator has been built and tested
calibration software is written
Calibration means finding spatial correspondence between HR+ coordinates and Polaris coordinates.

12. Future of motion correction
acquisition software from Hammersmith should be ready soon
motion correction software from Hammersmith is not yet finished
they have found problems in quantification

13. Thank you for your attention.
Questions
Thank you for your attention.