X-Ray Machine Vision: Making Sure the Cure Isn’t Worse than the Disease
| By: Winn Hardin, Contributing Editor
Some physicians praised the Radiology report; others predicted dire consequences. But in 2010, both sides were surprised to learn that computed tomography (CT) for human medical diagnosis grew by more than 16% per year, every year, from 1995 to 2007. Radiation exposure from CT is appreciable. A CT of the brain can provide as much a 5mSv (milli-Sieverts) radiation dose, which exceeds the maximum recommend yearly dose of 1mSv . In contrast a dental x-ray dose is very low, i.e. 0.005mSv and airline security scanner doses are less than 0.00025mSv.
“This increase is potentially concerning, given the questions about the safety of radiation exposure and increasing healthcare costs,” says David B. Larson, MD, a physician at Cincinnati Children’s Hospital Medical Center. Hospitals aren’t the only place the average person will encounter manmade x-ray radiation. New backscatter 3D x-ray systems are one of the newest, most wide-spread security measures used in US airports where backscatter airport x-ray doses are limited to less the 0.00025 mSv by ANSI and the FDA.
“Our products find their way into all three industries: medical, security, and reverse engineering,” explains Joe Sgro, CEO of Alacron, Inc. (Nashua, New Hampshire), designer and manufacturer of high-performance frame grabbers and vision processors. “Each of these x-ray systems can use all the processing power you can throw at them because they tend to be non-standard size images at high resolutions, high frame rates, and high data rates. And of course, x-rays are very low signal strength compared to the associated noise, so it takes a significant signal preprocessing to get a high-quality image.”
Whether it’s healthcare, security, or industrial, each customer segment wants to use lower doses of potentially dangerous x-ray radiation for a variety of reasons. In healthcare, as Dr. Larson’s response above illustrates, there is a growing concern that the increasing use of x-rays could result in higher rates of cancer through the cumulative effect of absorbed radiation over a person’s lifetime. Therefore, the lower the x-ray dose, the better off the patient is.
Of course, the lower the x-ray dose, the noisier the image is, which makes signal processing even tougher.
In security applications, x-ray doses are extremely low because they’re not meant to see through tissue, only through clothing. So while x-ray absorption for both low-energy-level human scanning and high-level baggage scanning is not as great a concern as it is with medical x-rays, speed is a major concern. Thus industry demands the highest resolution image possible at the lowest possible dose.
“If you can scan at higher rates, you can run more items through a baggage scanner, for instance,” adds Alacron’s Sgro. “Customers want higher frame rates, higher resolution, and higher dynamic range and more complex algorithms to convert x-ray image density information into information and alerts that a security officer can use.”
The dose/speed trend is also present in industrial reverse engineering and biological micro-CT scanners. SkyScan, a manufacturer of micro-CT systems, recently choose XIMEA GmbH (Münster, Germany)’s xiRAY11 camera for its new micro-CT system because of its higher frame rate (4 fps at full resolution, 12 fps with 4x4 binning), high-image quality and ability to transmit image data out to clusters of PCs to help researchers speed up CT scans and 3D renderings.
More Processing Power Please
Like other frame grabber manufactures, Alacron has responded to the need for more image processing power on its frame grabbers by offering boards with mega-gate field programmable gate arrays (FPGA) and high-speed microprocessors. “We have a very programmable front end,” adds Sgro. “We can accept Camera Link, digital or analog signals, and the pixels don’t have to be in sequential order, because some systems don’t use a raster scan output methodology anymore. All of this power and flexibility allows OEMs to match a frame grabber or vision processor’s capability to their unique needs and sensors.”
Alacron is also looking at the new class of accelerated processing unit (APU), such as AMD’s Fusion APU, which combines a central processing unit (CPU) core with a graphics processing unit (GPU) on the same die. “Tilera’s TILE-Gx-3100 APU with 100 cores is another example,” explains Sgro. “We expect to increase our floating point calculations by 4 to 10 times in the near future. That’s where we see the future of frame grabbers for x-ray and other demanding imaging applications.” Other future developments include a move from PCI to PCI-express and the use of GPU mezzanine cards to enhance the performance of a frame grabber PCIe cards. “These cards give you more flexibility and offer longer lifetime support so you’re not having to adopt to a new architecture every 6 months,” Sgro concludes.
Frame grabber and x-ray system designers can expect to continue to obtain support for improved sensor designs while striving to keep up with high dynamic range images with larger pixel counts. Next generation CMOS imagers with extremely low dark noise, and single-digit electron noise will make detecting a low-energy x-ray signal easier. But it will take the combined effort of sensors, processing power, and software designers to keep up with the growing utility and demands of x-ray imaging systems.