TY  - JOUR
AU  - Roser, J.
AU  - Muñoz, E.
AU  - Barrientos, L.
AU  - Barrio, J.
AU  - Bernabeu, J.
AU  - Borja-Lloret, M.
AU  - Etxebeste, A.
AU  - Llosa, G.
AU  - Ros, A.
AU  - Viegas, R.
AU  - Oliver, J. F.
PY  - 2020
DA  - 2020//
TI  - Image reconstruction for a multi-layer Compton telescope: an analytical model for three interaction events
T2  - Phys. Med. Biol.
JO  - Physics in Medicine and Biology
SP  - 145005
EP  - 17pp
VL  - 65
IS  - 14
PB  - Iop Publishing Ltd
KW  - Compton camera
KW  - Compton imaging
KW  - hadron therapy
KW  - image reconstruction
KW  - lm-mlem
KW  - monte carlo simulations
KW  - multi-layer Compton telescope
AB  - Compton Cameras are electronically collimated photon imagers suitable for sub-MeV to few MeV gamma-ray detection. Such features are desirable to enablein vivorange verification in hadron therapy, through the detection of secondary Prompt Gammas. A major concern with this technique is the poor image quality obtained when the incoming gamma-ray energy is unknown. Compton Cameras with more than two detector planes (multi-layer Compton Cameras) have been proposed as a solution, given that these devices incorporate more signal sequences of interactions to the conventional two interaction events. In particular, three interaction events convey more spectral information as they allow inferring directly the incident gamma-ray energy. A three-layer Compton Telescope based on continuous Lanthanum (III) Bromide crystals coupled to Silicon Photomultipliers is being developed at the IRIS group of IFIC-Valencia. In a previous work we proposed a spectral reconstruction algorithm for two interaction events based on an analytical model for the formation of the signal. To fully exploit the capabilities of our prototype, we present here an extension of the model for three interaction events. Analytical expressions of the sensitivity and the System Matrix are derived and validated against Monte Carlo simulations. Implemented in a List Mode Maximum Likelihood Expectation Maximization algorithm, the proposed model allows us to obtain four-dimensional (energy and position) images by using exclusively three interaction events. We are able to recover the correct spectrum and spatial distribution of gamma-ray sources when ideal data are employed. However, the uncertainties associated to experimental measurements result in a degradation when real data from complex structures are employed. Incorrect estimation of the incident gamma-ray interaction positions, and missing deposited energy associated with escaping secondaries, have been identified as the causes of such degradation by means of a detailed Monte Carlo study. As expected, our current experimental resolution and efficiency to three interaction events prevents us from correctly recovering complex structures of radioactive sources. However, given the better spectral information conveyed by three interaction events, we expect an improvement of the image quality of conventional Compton imaging when including such events. In this regard, future development includes the incorporation of the model assessed in this work to the two interaction events model in order to allow using simultaneously two and three interaction events in the image reconstruction.
SN  - 0031-9155
UR  - https://doi.org/10.1088/1361-6560/ab8cd4
DO  - 10.1088/1361-6560/ab8cd4
LA  - English
N1  - WOS:000552701600001
ID  - Roser_etal2020
ER  -