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Innovative Software for Advanced PET Imaging

Final Report Summary - INSPET (Innovative Software for Advanced PET Imaging)

Positron emission tomography (PET) is the fastest growing nuclear medicine tool in terms of acceptance and applications. PET images biochemical reactions and physiological functions by measuring concentrations of radioactive chemicals that are partially metabolised in the body region of interest. PET exhibits a great potential in clinical oncology, neurology, cardiology, neuropsychology, psychiatry and pharmacology. In particular when dealing with patients with brain tumors, imaging techniques are required at every step, from diagnosis, staging, treatment planning to follow-up of the patient. Several design trends have been developed in the last years, as PET entered into clinical practice. At the moment, no PET system has the ideal physical characteristics required to make it the gold standard reference for clinical and research applications. A novel PET design named Axial-PET (AX-PET) and conceived to merge all the current requirements in nuclear imaging, is currently under development at CERN, the European centre for nuclear research. AX-PET, which is based on several layers of axially-oriented crystals combined with wave length shifter (WLS) strips, pursues this goal: AX-PET presents a high sensitivity powered by a three dimensional (3D) homogeneous spatial resolution.

INSPET was addressed at developing software supporting the optimisation and study of AX-PET, from data analysis to system modeling and reconstruction.

In the past two years AX-PET grew quickly (P. Beltrame, et al 'The AX-PET demonstrator design, construction and characterisation', Nucl. Inst. Meth. A, 2011, vol 654, 546-559). Two modules were fully assembled and set in coincidence, in order to acquire sources of different complexities, thus providing data sets of various natures, ideal for testing the software. The Marie Curie (MC) researcher was deeply involved in all the stages of the measurement campaigns: preparation, acquisition, analysis and reconstruction. The project went through three campaigns:
- April 2010: Radiopharmaceutical laboratory at ETH (Zurich, CH) http://www.pharma.ethz.ch/
- July 2010: Advanced accelerators applications - AAA (St. Genis Pouilly, FR) http://www.adacap.com/
- July 2011: Advanced accelerators applications - AAA (St. Genis Pouilly, FR)

The campaigns were tracking the evolution and improvements of the project, eventually providing very competitive images, with respect to already existing devices. The main features of the device were proved:
- Almost parallax-free geometry
- Good homogeneous spatial resolution and sensitivity
- Inter-crystal scatter recovery

The AX-PET was fully modeled: from the complex geometry to the no-trivial count-rate behavior ('Full modeling of AX-PET, a new PET device with axially oriented crystals, based on GEANT4 and GATE' P. Solevi, J.F. Oliver, J. Gillam, M. Rafecas, medical imaging 2011: Physics of medical Imaging (2011), 'Modeling AX-PET throughput: A Monte-Carlo based model and its experimental validation' P. Solevi, et al (2012), to be submitted), thus providing a solid platform for any further studies AX-PET related. The comparison with experimental data shows an excellent agreement and on the other way around the simulation provides precious feedbacks to better understand the behavior of the system that is still at the prototype testing stage.

The large fraction of inter-crystal scatter (ICS) events yielded by the peculiar granulated geometry of the device could be successfully processed and included in the reconstruction algorithms, by means of different recovery techniques. The inclusion of those events results in an increased accuracy once proper weights are applied, despite a small loss in resolution detected in small structures (J.E. Gillam, P. Solevi, J.F. Oliver, and M. Rafecas, 'Inclusion of ICS data in PET', accepted for presentation at the ISBI 2012 - International symposium on biomedical imaging).

AX-PET presents a continuous axial coordinate and discrete x and y. Dealing at level of image reconstruction with the different nature of the spatial coordinates is no-trivial, thus a new approach was suggested and tested (P. Solevi, J. F. Oliver, J. Gillam, and M. Rafecas 'Image reconstruction for AXPET: different approaches to histograming for semi-continuous data', Proceedings of the 11th international meeting on fully -3D image reconstruction in radiology and nuclear medicine, 2011, pp. 180-183).

The software developed in the INSPET project for this unique and demanding device, AX-PET, could be certainly extended and adapted to many other cases.

The aforementioned results of the INSPET project, presented at several congresses and seminars, help drawing the international attention to the AX-PET device and give the chance to the researcher to start enlarging her international scientific network.

During the MC fellowship the researcher could improve her leadership, communication, teaching and mentoring skills. Paola Solevi supervised a number of students, all working on projects related to software development for PET devices, in collaboration with the University of Cagliari (Italy), University of Rabat (Morocco) and Imperial College (UK), and got as well the chance to give advanced classes at the international school on medical physics (Bogotá, Colombia).

The experience in proposal writing gained through the MC network was a valuable knowledge the researcher will exploit for future projects.

The MC resulted then in the chance for Paola Solevi to boost her scientific career, placing herself as a mature and experienced scientist.