Lausanne, Switzerland--A new collaborative research project has been formed to develop a new generation of smart, CMOS-based large-area networked image sensors for photon-starved biomedical applications. Called "Fully Networked Digital Components for Photon-starved Biomedical Imaging Systems" and nicknamed SPADnet (a SPAD is a single-photon avalanche diode), the project is being funded by the European Union within the Information and Communication Technologies (ICT) Theme of its Seventh Research Framework Programme (FP7).
Launched on July 1st, 2010, SPADnet is being coordinated by the Ecole Polytechnique Federale de Lausanne (EPFL) and includes seven leading European experts in image sensors, medical imaging, and photonics. SPADnet was granted 3,700,000 EUR of funding over a 42 month period. The SPADnet consortium met on July 16th, 2010 in Budapest for its general kick-off meeting.
Targeting single-shot rare events
In addition to the large-area CMOS-based networked image sensors, SPADnet will develop 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 that often occur 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. In addition, the relatively 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 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).
Spatial oversampling reduces dead time
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. In space oversampling, many SPADs will detect the same event independently, thus reducing the dead time on average by a factor of 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 analog electrical pulses, whereas the photonic component proposed in this project will generate streams of precomputed digital data.
The current state of the art for interchip 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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John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.