Positron Emission Tomographs (PET) are the most commonly used functional imaging devices in medicine. Therefore, there is a need for transparent demonstrators where principles of the different modalities and their functions are presented. The aim of the developments was to demonstrate the major building blocks of PET for undergraduate students at Royal Institute of Technology, Stockholm, Sweden.

A small PET (called KTH-miniPET) have been developed to serve as demonstrators for educational purposes. The system is based on small (2x2x10 mm3) LSO crystals. The scintillator light is detected by position sensitive photomultiplier tubes (PSPMT) connected to FPGA based digital data acquisition systems. Unified data acquisition electronics and software platform were developed to serve the modularity and transparency of the systems (see KTH-spiralCT). Both demonstrators are built using similar type of gantry with computer controlled stepper motors for manipulating the detectors and the phantom.

The KTH-miniPET scanner contains two stationary detector modules placed on both sides of the rotating phantom. The phantom, a plastic doll is loaded with positron emitting 22Na radiation sources. The annihilation photons are detected by the two opposite detector modules, which consists of 64 LSO crystals in a 8x8 configuration array and a PSPMT.

Data acquisition electronics - In both demonstrators the same type of data acquisition cards (DAQ) is used. The DAQ consists of the Analogue Front End Electronics and the Digital Front End Electronics (DFEE) modules. The DFEE is based on a Memec Mini Module with a Xilinx Virtex-4 FPGA and Ethernet interface. The analogue corner signals of the PSPMT are digitized using a 12 bit, 50 MHz, 4 channel ADC. The digital signal processor core in the FPGA determines the energy and the X, Y coordinates of the incoming photons. These parameters are transferred to the data acquisition computer via Ethernet network. Data is acquired in list mode therefore full post processing of the data (such as energy and position discrimination) is performed in the PC.

Data acquisition, image reconstruction and presentation software - Both demonstrators use the same software components, such as DAQ and stepper motor controlling, image reconstruction and image presentation. Position and energy discrimination of the incoming events is also performed in the data acquisition PC. Coincidence sorting with different time windows and the sinogram generation in both demonstrators are performed in the data acquisition program. Filtered back projection and ML-EM (Maximum Likelihood Expectation Maximization) iterative methods have been implemented for the demonstration of the quality and the performance of the different image reconstruction algorithms.


Course website at Royal Institute of Technology

Laboratory instruction for the KTH-miniPET


Photos from the KTH-miniPET demonstrator.
Reconstruction of the two Na radiation sources. The sources were placed in Ken's head.