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Past Winner
2004 NSERC Doctoral Prize

Karim S. Karim

Biomedical Technology

University of Waterloo

New digital X-ray technology developed by a Canadian graduate student could soon be helping radiologists diagnose digestive tract problems, and surgeons guide catheters through veins with greater accuracy and lower doses of radiation than ever before.

The new diagnostic imaging technology also has the potential to improve mammography by providing much better tumour detection.

"Our digital X-ray fluoroscopy technology has very direct relevance right now. And it has great commercial potential," says Dr. Karim Karim, a recent University of Waterloo Ph.D. recipient, and winner of a 2004 NSERC Doctoral Prize – one of Canada's premier awards for new doctoral graduates.

Fluoroscopy is moving real-time X-ray imaging. With existing fluoroscopy technology, the X-ray image is projected onto a fluorescent plate coupled to the equivalent of a television camera. A radiologist watches the images on a TV screen. The technique is commonly used for diagnostic medical imaging of digestive tract problems; a patient swallows a barium mixture and the radiologist watches its progression through the gut.

"The technology used now for fluoroscopy is bulky and doesn't have the advantages that digital imaging offers," says Dr. Karim, who joined Simon Fraser University in February 2003 as an assistant professor of engineering and founder of the Biomedical Imaging Electronics research group.

Compared with traditional film radiographs, digital X-rays are immediate and can be easily stored and shared, reducing the need for large X-ray film archives. Digital X-rays also open the door for real-time tele-radiology.

Dr. Karim's doctoral research at the University of Waterloo, in close collaboration with his Ph.D. supervisor Dr. Arokia Nathan, a former NSERC Steacie Fellow, applied insights from recent advances in large, flat-screen liquid crystal display (LCD) panels, such as those used on laptops. LCD screens achieve their large size and thinness through the use of amorphous silicon. Unlike the highly-ordered crystalline silicon used in most digital electronics, amorphous silicon is a disordered jumble.

However, silicon crystals, while more efficient and yielding higher-performance electronics, are limited in size to about 30 square centimetres. Amorphous silicon can be applied onto inexpensive glass sheets of much larger sizes.

The challenge for the team of researchers developing these digital imagers for fluoroscopy, including Dr. John Rowlands, a senior scientist and medical physicist from Sunnybrook and Women's College Health Sciences Centre in Toronto, was in overcoming amorphous silicon's disadvantages. It requires a greater surface area for each pixel, or imaging sensor, and these pixels traditionally produce blurrier images.

The solution turned out to be a triple combination of stack, boost and stabilize.

To maximize the pixel area, and thus the resolution, Dr. Karim turned the traditional pixel architecture on its head.

"We put the sensor on top, rather than beside, the silicon readout electronics as has traditionally been done, thus maximizing the pixel surface area for X-ray detection," says Dr. Karim.

Fluoroscopy uses low-dose radiation to minimize exposure, and existing digital imaging technology provides poor image quality at the low X-ray levels. To improve on this, Dr. Karim and colleagues added a signal amplifier directly into the pixel readout circuit, creating the first "active pixel" – able to sense and amplify – in amorphous silicon.

The technology also incorporates a self-correcting feedback mechanism to ensure that the image quality and characteristics remain consistent over time.

Dr. Karim is presently extending the amorphous silicon imaging technology to dual-mode fluoroscopy, similar to a video camera that's able to switch from movie mode to taking high-resolution single pictures.

He's also experimenting with applying the technology to tomosynthesis, a way of producing localized 3-D digital X-rays. Applications for tomosynthesis include breast X-rays, but with much higher contrast and image quality than currently-used mammography techniques.

"The trend is to move towards digital X-ray imaging," says Dr. Karim. "It's inevitable."