Current research projects

Imaging systems

Low-dose, real-time x-ray imaging system

We have developed a low-dose, real time x-ray imager for applications in interventional cardiology and for low cost chest X-ray imaging. The research results are now being commercialised by a 2015 Waterloo spin-off company, KA Imaging

Multispectral (Color) Digital X-Ray Imager

X-ray procedures are time and cost efficient, hence clinicians and administrators often request X-rays before an MRI or CT is recommended. Our research improves the quality and accuracy of chest X-rays by creating multi-spectral (sometimes called dual-energy) X-ray imagers to help reduce the demand for CT cancer diagnostics. Although CT offers better visualization than a traditional chest X-ray, CT throughput is a fraction of that of chest X-rays and the amount of radiation that patients receive can be upto 100X more, increasing the now well-acknowledged risk of cancer. Dual energy chest X-ray imagers differentiate between tissues by using discrete X-ray energies for visualizing e.g., bone and soft tissue and to date, there is increasing evidence that dual energy can highlight small calcifications that are indicators of cancer effectively. 

Circuit technology

Photon counting circuits for biomedical imaging

Using a novel pixel sensor architecture and avalanche-enabled amorphous selenium photodetectors, we are developing a small x-ray pixel array in CMOS (Complementary metal oxide semiconductor) technology. With fast circuitry and very high light sensitivity, this circuit is designed for very low-dose x-ray modalities.

 Semiconductor devices

Low cost x-ray detectors in amorphous silicon technology

In order to make x-ray sensors more compatible with other large-area deposition processes, like liquid-crystal-display television (LCD-TV) display manufacturing processes, the conventional PIN photodiode can be replaced with a lateral metal-semiconductor-metal (MSM) sensor, which can be built above the pixel, giving essentially 100% fill factor, which increases the electrical sensitivity to light. We have shown a lateral MSM sensor with competitive pixel performance to the conventional PIN photodetectors on the market. The previous demonstration used a direct-detection photodetector based on amorphous selenium. Current efforts are to reproduce the technology using widely used amorphous silicon.

Amorphous selenium lateral metal-semiconductor-metal photo sensor

S. Abbaszadeh, N. Allec, and K.S. Karim, "Characterization of low dark-current lateral amorphous-selenium metal-semiconductor-metal photodetectors", Institute of Electrical and Electronics Engineering (IEEE) Sensors Journal, Vol. 13(5), pp. 1452-1458, May 2013.

Amorphous selenium and CMOS-based high resolution x-ray detector

We have developed a high resolution amorphous selenium (a-Se) direct detection imager using a large-area compatible back-end fabrication process on top of a CMOS active pixel sensor with 25 micron pixel pitch. The detector structure is comprised of a polyimide (PI) buffer layer, the a-Se layer, and a gold (Au) top electrode. The PI layer is applied by spin-coating and is patterned using dry etching to open the backplane bond pads for wire bonding. Thermal evaporation is used to deposit the a-Se and Au layers, and the detector is operated in hole collection mode (i.e. a positive bias on the Au top electrode).

This work constitutes the first report of a 25-micron pixel pitch direct detection x-ray imager using an a-Se detector integrated with a CMOS backplane. As such, to the best of our knowledge, it stands as one of the highest, if not the highest spatial resolution x-ray detector reported to date for diagnostic x-ray energies.

Preliminary images demonstrating high spatial resolution have been obtained from a first prototype imager.

An x-ray image of an aorta stent with 25-50 micron thick wires

An x-ray image of an aorta stent with 25-50 micron thick wires