Motion Correction 21.2.2005 Riku Klén

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

What is list mode acquisition? Normal acquisition (or frame mode acquisition) scanner sinogram acquisition image reconstruction List mode acquisition scanner 8800 4515 1100 0000 8000 0000 1212 1000 8800 4515 1100 0000 8000 0000 1212 1000 8800 4515 1100 0000 8000 0000 1212 1000 8800 4515 1100 0000 8000 0000 1212 1000 8800 4515 1100 0000 8000 0000 1212 1000 list mode data acquisition sinogram binning

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.

List mode acquisition HR+ 8800 4515 1100 0000 8000 0000 1212 1000 8800 8625 1100 5400 8000 1167 1844 1000 8800 4515 1100 0000 8000 0000 1212 1000 8800 3215 1100 3577 8000 3212 1184 1000 Each annihilation detected is represented as a LOR. Information about LOR is stored in list mode file.

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.

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

Motion tracking Polaris 8800 4515 1100 0000 8000 0000 1212 1000 8800 3215 1100 3577 8000 3212 1184 1000 8800 8625 1100 5400 8000 1167 1844 1000 8000 0000 1100 5400 8000 0160 4232 1000 8000 0000 1307 0044 8000 1673 5334 1000 8000 0000 1103 0000 0031 1634 1212 1000 8800 3215 1100 3577 8000 3212 1184 1000 8800 8625 1100 5400 8000 1167 1844 1000 8800 4515 1100 0000 8000 0000 1212 1000 HR+ Acquisition computer 8800 3215 1100 3577 8000 3212 1184 1000 8800 8625 1100 5400 8000 1167 1844 1000 8800 4515 1100 0000 8000 0000 1212 1000 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

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

Motion correction Original list mode data Motion corrected list mode data motion data 8000 0000 … move LOR up 8800 4515 … 8800 3215 … 8800 8625 … 8000 0000 … 8800 4515 … 8800 3215 … 8800 8625 … 8800 4215 … 8800 3215 … 8800 9625 … 8800 9215 … 8800 5515 … 8800 4215 … motion data 8800 1215 … 8800 6625 … 8800 2515 … 8800 8625 …

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.

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

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