A recent high-resolution fluoroscopic method for real-time diagnostic imaging has the resolution and sensitivity to detect conditions that previously went undetected. It also reduces patient exposure to radiation. The method can also include a small focal-spot (less than 50 microns) X-ray beam limited to just fill the input aperture of the fluoroscope.

“There are no satisfactory real-time fluoroscopes with the resolution to detect, for example, stent dislocation, restenosis, or other small details,” says Gil Zweig, president of Glenbrook Technologies, Randolph, N.J. (glenbrooktech.com). “What's worse, present diagnostic fluoroscopes expose patients to such high doses of radiation that they warrant a cautionary notice from the FDA.”

A fluoroscope works by converting X-ray images to visible-light images with a radioluminescent phosphor or scintillator. An image intensifier tube amplifies the light image and users see an intensified light image on video monitors.

To detect anomalies in an implant, with diagnostic quality, the original image must have the resolution to be magnified 10 to 40 times prior to display. This requires a minimum resolution at the intensifier output screen of 12 lp/mm (line pairs per millimeter). Conventional image intensifiers and flat panel detectors resolve to about 5 lp/mm, insufficient for small details.

Existing fluoroscopes don't have the resolution for magnification and high exposure rates. The high exposure rate required is partially due to the glass envelope. Digital flat-panel systems have neither a high enough video frame rate or resolution.

Conventional fluoroscopic detectors include a demagnifying CsI (Cesium Iodide) image intensifier, a flat panel imager, and the linear array detector. “The maximum resolution of the intensified or captured image in all three cases is 5 lp/mm,” says Zweig. In addition, flat panel and linear-array detectors do not have adequate frame rates (at least 20 frames/sec) for real-time fluoroscopy.

However, the following combination of components generates fluoroscopic images with resolutions of 12 lp/mm and greater:

• Radioluminescent phosphor coating employing the phosphor material Gd202S:Tb with resolutions greater than 12 lp/mm.

• Optically coupled phosphor coating to an input of an MCP (Microchannel Plate), 1:1 (non-demagnifying), Image Intensifier (MCP II).

• Viewing the intensified (1:1 or nondemagnified) output image of the MCP II with an Autofocus, Optically magnifying, CCD “Block” camera.