List-mode aquisition on PET tomograph ECAT EXACT HR+
Positron emission tomographs like the ECAT EXACT HR+ not only allow data aqcquisition in commonly used frame-mode but also in rare used list-mode. List-mode enables acquisition of single cooincidence events making amongst others things an event based correction of patient motion possible. Sorting of list-mode data into 2D/3D sinograms is stronlgy limited, even impossible when incorporating external motion data, by manufacturer of the ECAT EXACT HR+. Therefore an event based motion correction is impractical. By implementing new software we have the ability to flexible analyse and sort list-mode data acquired with the ECAT EXACT HR+ into 2D/3D sinograms.
Implementation was carried out in a modular way with C++. A graphical user interface (GUI) was realised in Tcl/Tk too. Furthermore a batch mode is supported which executes processing configurations created with the Tcl/Tk GUI.
Our software makes flexible sorting of list-mode data available. On the one hand one can create dynamical studies with free selectable frame schemas. On the other hand list-mode data can be sorted into different gates on the basis of external motion data (EKG, respiration) which allows analysis of cyclic heart or respiration motion. Furthermore a combination of framed and gated sorting is possible. So it was shown, the metabolic rate of FDG using an end systole dynamic sequence is up to 50% higher compared to a non-dynamic sequence.
|Fig.1: PET image of a bronchial carcinoma: Left: not gated; Center: inhaled state; Right: exhaled state|
|Fig.2: Maximum intensity projection of the gated data|
With our new software processing of list-mode data allows retrospective improvement of dynamic studies (reframing) and combination of framed and gated sorting which was till now unrealised. Application of arbitrary reframing makes subsequent correction of patient motions possible on the base of informations supplied by a motion tracking system.