Light detection for medical imaging

A digital light detection technology from Philips Electronics is promising to remove the use of analogue signals from medical imaging entirely.




Philips’ silicon photomultiplier technology digitally detects light and processes the signal all on one chip.



The developers believe such a chip could improve the performance of positron emission tomography (PET), a nuclear medicine imaging technique that produces a 3D image of functional processes in the body.



Carsten Degenhardt, research and development manager of Philips Digital Photon Counting, said most light detection technology outputs information through analogue signals, which are affected by noise interference.



Degenhardt said that the Philips chip would be unaffected by such interference and therefore it could improve sensitivity and imaging capabilities.



‘So a physician could see a tumour earlier and adjust the treatment to treat a patient earlier,’ he said,  adding that scan time could also be reduced because detection and processing of light is done on one chip. This would mean patients would be exposed to less radiation.



The chip contains thousands of diodes, each capable of collecting a single photon of light and converting it directly into an ultra-high-speed digital pulse that can be directly counted by on-chip counter circuitry.



Current silicon photomultiplier technology detects light digitally, but then information such as photon count and the time of arrival of the first photon is outputted through an analogue signal. The signal then must be processed by a separate, power-hungry readout ASIC (Application-Specific Integrated Circuit).



Degenhardt said the main challenge for the Philips developers was building the light detecting diodes and electronic CMOS readout device on one chip.



‘Those light sensing elements operate at 30V, which is quite high voltage,’ he said. ‘The challenge was combining CMOS, which operates at low voltage, next to light sensing elements on one chip without having interference or affecting the sensitivity or noise behaviour of the photo detector.’



The digital silicon photomultiplier is still in prototype stage but Degenhardt said the chip will theoretically be easy to mass manufacture because it can be fabricated using a conventional CMOS process technology.



Philips is looking for partners for a variety of applications requiring the detection of weak light signals.



Degenhardt said these applications could range from night-vision goggles to the detection of fluorescent signals in DNA sequences. Their first commercial applications, he said, will likely be in the medical imaging field.



Siobhan Wagner