1. Reconstructions with TOF for in-beam PET
ENVISION WP2 Meeting
Feburary 2, 2010, CERN
Georgy Shakirin
Center for Radiation Research in Oncology – OncoRay
Medical Faculty C. G. Carus
Technische Universität Dresden

2. OncoRay experience with in-beam PET
Since 1997 – installation, technical and clinical support of the first in-beam PET scanner installed at GSI, Darmstadt
Complex simulations of ion interactions, production and transport of positron emitters, production and annihilation of positrons
Reconstruction algorithms for limited angle PET scanners
Routine evaluation of in-beam PET clinical data produced at GSI

3. Pricnciple of in-beam PET
Prescribed dose
Measurement
Application
Prediction:
Simulation +
Reconstruction
Expected β+-activity distribution
Reconstruction
Measured β+-activity distribution
Comparison

4. In-beam PET at GSI, Darmstadt
Properties of the scanner
8 × 4 position sensitive detectors per head (BGO)
Number of measured events: – 500 × 103
Effectivity: ~ 1.5 %
Spatial resolution: 5 – 10 mm g1
12C
Results of in-beam PET monitoring g2
: 440 patients monitored
Detection of density changes in irradiated volume or range changes (~ 15 %)
Detection of deviations in irradiation positioning (~ 10 %)

5. In-beam PET imaging Frontal Transversal Sagittal Reference image
Reconstruction

6. Evaluation of image quality
RMSE:
Contrast recovery for phantom: 1 4 ? 1 ?
11, 13
14, 18.5
Radiuses of cold inserts, mm
3, 5, 7, 9
5, 6.5, 8.5, 11
Radiuses of hot inserts, mm 45 90
Radius, mm
Height, mm
Eigenschaft
Standard 50
Small

7. Evaluation of image quality
Modification of maximum particle range
Normal range
Overrange
+ 6 mm in water
Underrange
- 6 mm in water

8. Simulation workflow

9. TOF simulation Simplified geometrical simulation d1 d2
No interaction in detectors
No scatter and attenuation
List mode data: [detector1_id, detector2_id, t]

10. Reconstruction algorithms with TOF
Time resolution lower than 0.2 ns (FWHM)
Integration of TOF in iterative algorithms
Shakirin et al., Proc. IEEE NSS MIC, Honolulu, USA, , 2007
Time resolution higher than 0.2 ns (FWHM)
Direct TOF method – reconstruction in real time
Crespo, Shakirin et al., Phys. Med. Biol. 52, , 2007

11. Reconstruction results
In-beam PET scanner geometry similar to GSI installation
OS-EM, no TOF
OS-EM, TOF 1.2 ns
DirektTOF 0.2 ns
DirektTOF 0.1ns

12. Reconstruction results
Reference image
Direct TOF reconstruction, 0.2 ns
OS-EM reconstruction, no TOF
OS-EM reconstruction, TOF 1.2 ns

13. Conclusions Plans within WP
TOF information increases the image quality for dual-head scanners even in case of low time resolution (1.2 ns)
If TOF resolution is better than 0.2 ns, the Direct TOF method can be applied and reconstruction can be performed in real time
Plans within WP
Precise TOF simulations easily applicable to different geometries / detector types / DAQs of in-beam PET scanner
Finding the best detector arrangement for TOF PET scanner
- Further development of reconstruction algorithms for TOF PET