Project Initiated for Advancement of New Biomedical Imaging Technology

The project launched on July 1, 2010, is coordinated by the Ecole Polytechnique Federale Lausanne (EPFL; Switzerland) and it includes seven leading European experts in image sensors, medical imaging, and photonics. SPADnet was granted 3.7 million EUR of funding over a 42-month period. The SPADnet consortium met on July 16, 2010 in Budapest, Hungary, for its general kick-off meeting.

SPADnet's goal is to build ring-assembly modules for positron emission tomography (PET) imaging, and carry out performance tests in a PET evaluation system. While suited to applications offering repetitive measurement techniques, existing sensors are not well adapted to single-shot, rare events often occurring in diagnostic tools based on specific radiation detection, PET, single photon emission computed tomography (SPECT), gamma cameras, and other minimally invasive point of care tools. Moreover, the comparatively small field-of-view of existing sensors is a limiting factor.

SPADnet's prime objective is to develop a scalable photonic component for large format, rare-event imaging. The core of the component will be a SPAD (single photon avalanche diode) array implemented in CMOS. Large formats will be achieved by tessellating several tens of dies in abutment style using innovative packaging techniques based on through-silicon vias (TSVs). The ability to stamp the time and position of each photon impingement in a burst event offers a second key advance. The concept of spatial oversampling is introduced, where a single measurement is partitioned into a myriad of submeasurements, occurring simultaneously. The difference is that in space oversampling many SPADs will detect the same event independently, thus reducing the dead time on average by the number of detectors involved. The decomposition of the large format imager to a network of independent arrays is key to managing massive data streams. In conventional photomultiplier tubes (PMTs) or silicon photomultipliers (SiPMs), the sensitive device produces a stream of analogue electrical pulses, whereas the photonic component proposed in this project will generate streams of precomputed digital data.

The current state-of-the-art on inter-chip data exchange will be the basis for efficient data communication, in a true network communication style. Data packets will be routed in the network and will be handled on-demand. For example, coincidence-mapping engines can be used in this context as snoopers on the data bus, thus considerably simplifying systems such as PET.

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