Imaging board to target medical applications

In legacy medical imaging systems, proprietary display signals are often used to drive monitors at nonstandard resolution. One of the problems facing developers who wish to add networking or printing capabilities to such systems is obtaining a highly accurate representation of the displayed image from the display controller used in the system.

Imaging board to target medical applications

In legacy medical imaging systems, proprietary display signals are often used to drive monitors at nonstandard resolution. One of the problems facing developers who wish to add networking or printing capabilities to such systems is obtaining a highly accurate representation of the displayed image from the display controller used in the system.

In the GE CT/i CAT (computer-assisted tomography) scanner, for example, images are displayed at 1280 x 1024 resolution at either 72 or 76 Hz noninterlaced, depending on the version of the system. By capturing the RGB and horizontal and vertical syncs from the display-controller output, systems integrators can digitize, distribute, and even print images from the CAT system. But not any frame grabber is suitable.

"Typically, systems integrators demand a frame-capture device that will add as little degradation to the captured image as possible," says Al Meola, technical support manager at Imagraph (Chelmsford, MA). To meet these demands, Imagraph has developed its PCI-based Hi*Def Accura frame grabber. When used in conjunction with the company`s Hi*Def video splitter, the board and video-breakout box can transfer images from systems such as the CT/i into PCs for further networking, image analysis, or printing functions.

In a typical setup, RGB, Hsync, and Vsync signals are input to the Hi*Def video splitter, where they are simultaneously transferred to the system monitor and the Hi*Def Accura frame grabber. Once digitized by the frame grabber, they can be transferred across a network using a PCI-based network-interface card or to a film printer using the PC`s serial or parallel ports.

"Because several of our customers write film from the digitized images captured by our frame grabber," says Forrest Vatter, director of the Hi*Def program at Imagraph, "they required a board that could digitize images to at least 9-bit accuracy and one that was extremely stable in terms of gain, jitter, and phase."

To accomplish this, Vatter and his colleagues developed a method of stabilizing the temperature of both the analog front end and the phase-lock-loop (PLL) circuitry on the board.

In the design of the Hi*Def board, Vatter used the PIC16C54 8-bit microcontroller from Microchip Technology (San Jose, CA) as an on-board temperature regulator to stabilize four Ohmtek surface-mount resistors from Vishay Dale Electronics (Yankton, SD). "To keep both the analog front end and the PLL at this consistent temperature," says Vatter, "the analog-to-digital converters, microcontroller, and power resistors were covered in Therm-A-Gap A574 foam from Chromerics (Woburn, MA). "This allows the front end and PLL sections of the board to be maintained at a temperature of approximately 57°C and keeps temperature-dependent jitter and phase variations to a minimum. The result is a board that features a pixel jitter specification of ۪.5 ns and 10-bit accuracy and that can be used in demanding applications such as medical-image capture.

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