Digital Signal and Image Processing in Jagiellonian Positron Emission Tomography

Positron Emission Tomography (PET) is a key technique in the medical  imaging area, which allows to diagnose the organism functions and to  track the tumor changes. In PET measurement the patient is injected with  radiotracer, containing a large number of metastable atoms of  radionuclide, that emmits positrons. As the result of positron  annihilation, the two photons travelling off with nearly opposite  directions are produced and registered by detection system positioned so  that it surrounds the patient body. State-of-the-art PET scanners use  scintillation crystals which are characterized by high detection  efficiency of annihilation photons.
In this context, it is worth to  mention that the Jagiellonian PET (J-PET) Collaboration developed a  novel whole-body PET scanner based on plastic scintillators. They are  much cheaper than crystal scintillators, which gives the opportunity to  reduce the high cost of PET scanners and make them more affordable.  However, plastic scintillators have much lower detection efficiency of  gamma quanta compared to inorganic scintillation crystals. This can be  compensated by increasing the scanner field of view and improving the  time resolution in the measurement of the time of flight of gamma  quanta. The J-PET scanner consists of plastic scintillator strips read  out at both ends by a pair of photomultipliers and arranged axially  around a cylindrical tomograph tunnel. The axial coordinate of the  annihilation photon interaction point in the scintillator strip is  derived from the difference of the light propagation time measured with  the pair of photomultipliers.

The operational principles of the  J-PET scanner are similar to conventional tomographs, except that the  highly accurate time information is of paramount importance. Therefore,  the J-PET scanner demands a preparation of novel methods on each step of  the data processing. The goal of the work presented in this  dissertation is a development of the signal and image processing  algorithms taking into account uniqueness of the J-PET detector. The  proposed methods include: signal recovery based on samples of a waveform  registered on photomultiplier output, reconstruction of position and  time of interaction of annihilation photon in the scintillator strip,  classification of PET events types and image reconstruction that  operates exclusively in the image space. Due to the dissimilarity from  the conventional PET scanners, majority of the methods presented in this  dissertation are innovative solutions in digital signal and image  processing in tomography.