Technology Overview of Digiray® Reverse Geometry X-ray® Imaging

Digiray® Corporation is the inventor and producer of Reverse Geometry X-ray® imaging, the world's only x-ray imaging system that virtually eliminates

• fogging due to x-ray scatter
• source/detector alignment difficulties

Combined with computerized image enhancement and other patented upgrades, Digiray direct-digital real-time systems provide

• the highest contrast sensitivity imaging on the market (up to ten times better than image intensifiers)
• higher throughput (up to 100 times better than film)
• easier access (freedom of alignment; small detectors)

Among the unique capabilites:

• real-time, fully-digitized, filmless radiography
• variable or multiple field(s) of view
• 3-D (stereo) imaging
• elimination of conflicting information: Motionless CT™ (laminography) slices without moving parts or multiple exposures

Digiray® RGX® systems have been used on aircraft (including the Space Shuttle) and oil pipelines to detect corrosion invisible to other systems. Baggage security applications are under evaluation.

Since 1895, when Wilhelm Roentgen discovered x rays, radiographers have employed a geometry in which the object to be imaged is placed between a point source of x rays and a relatively large-area detection medium, such as a film sheet. The object's absorption and deflection of x-rays produce a shadow on the detecting medium, placed directly behind it. The object must be placed far enough away from the small source to allow the x-rays to spread out; the object must be close enough to the detecting medium to remain in focus.

Many x-rays that should be blocked by the object of interest are merely deflected, and strike the detecting medium, but in the wrong place. This "scattering" of x-rays causes fogging. Fogging limits the quality (and contrast   sensitivity) of conventional x-rays.

Reverse Geometry virtually eliminates scatter-caused image degradation for clearer pictures and cleaner data

• The object of interest is moved away from the detecting medium (air gap), so most of the x-rays that it causes to deflect from their correct paths cannot create blurring in the image.
• The detector is reduced to a very small size, so it is too small to be struck by most of the stray x-rays.
• The x-ray tube source is physically large enough to illuminate an object placed very close to it. The raster scanning source resembles a television picture tube.

Advantages of Direct Digital Imaging

Television-type raster scanning, combined with computer-read digital data from the detector unit, constitute a fundamental change in the process of image production. Unlike a film sheet (or image intensifier screen), reverse geometry technology "reads and writes" first generation digital images.

The RGX® x-ray source ressembles the cathode-ray tube. Electrons sweep in a raster pattern across the dense target of a broad anode plate. X-rays originate from this moving point of impact.

The 1 microsecond-per-pixel readout rate of the detector unit is synchronized with the beam sweep of both the source and the CRT monitor.

The monitor displays images at various resolutions and frame times.

Because the first-generation image is directly digitized, RGX® imaging eliminates the need for film (and the time for developing it), image intensifiers, or vidicons. The advantage of high signal-to-noise ratio is augmented by the many classes of image-enhancement techniques in the digital tool kit. For detailed specifications see System Specifications.

Unique Capabilities

With Reverse Geometry X-ray® imaging, alignment of the x-ray source, object, and detector are no longer critical. X-rays are emitted over a wide angle, so there is great freedom in detector alignment (±45 degrees) and detector tilt. As long as x-rays can reach the detector, the computer can produce a radiograph correlating source/object space with raster time.

Real-time computer processing options include

• averaging (multiple frame integration modes)
• electronic zoom (raster shrink) and pan (raster deflection)

RGX® provides zoom magnification without any loss of resolution compressing the same number of pixels into a smaller area. The compressed raster can be moved about on the face of the source and thereby pan across the object of interest, without resorting to mechanical means. The operator sets instantaneous electronic controls to zoom and pan. (Close-ups can also be programmed in automatic sequence) to

• Selectively magnify a series of rivet or solder joints without spending time on regions of lesser interest.
• Speed up process control of welding: x-ray scanning can be limited to the critical area, that is, the welding pool.

To summarize Digiray® technology:

Setting of exposure is also easy because of the detector's wide dynamic range (greater than film). A scintillating crystal coupled with a photomultiplier tube permits 12 bits of gray scale latitude. The radiographer has access to 4096 shades of gray or 256 false-color hues that can be selected by "tint rolling" through trackball settings.

Other post-acquisition image enhancements of the digital signal include edge sharpening, field flattening, smoothing and histogram equalization. Multiple images may be displayed side by side for comparison on one or more screens. The operator can also add labels, arrows, lines, measurements, notations and radiographic parameters (kV, mA, exposure time) to the image data.

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