JPI has developed high precision carbon-interspaced antiscatter grids to be suitable for Digital Radiography (DR) by adopting a precise sawing process. For systematic evaluation of the grid performance, we prepared several sample grids having different grid frequencies (4.0 to 8.5 lines/mm) and grid ratios (5:1 to 10:1) and established a well-controlled test condition based upon the IEC (International Electrotechnical Commission) standard.

The use of antiscatter grids in diagnostic x-ray imaging is the most widely applied and accepted method for reducing the amount of scattered radiation at the imager and improving the image contrast. The structure of the grid conventionally consists of an aluminum interspace and lead strips. However, aluminum as an interspace material is relatively inferior to organic materials for better image contrast, keeping dose as low as possible, due to the considerable absorption of primary radiation penetrating the aluminum interspace. In addition, the uniformity of the lead strips is typically rough due to the conventional fabrication process of the grid. Nonuniformity in the lead strips may cause a complicated grid line artifact, known as a moire pattern, which is easily observed as a wavy shadow of the lead strips in the x-ray image. The moire pattern may be the most critical problem to be solved for the successful use of the grid in digital x-ray imaging.

In order to overcome these difficulties, JPI improved our manufacturing standard by adopting a precise sawing process with a carbon-fiber plate to produce high precision grids of good performance characteristics. For systematic evaluation of the grid performance, we prepared several carbon-interspaced grid samples having different grid frequencies and grid ratios, and established a well-controlled test condition based on IEC standard.
We presented the performance characteristics of the carbon-interspaced grids in terms of the transmission of primary radiation (Tp), the transmission of scattered radiation (Ts), the transmission of total radiation (Tt), contrast improvement factor (Cif), Bucky factor (B), and signal-to-noise improvement factor (SNRif). For comparison, we also prepared additional aluminum interspaced grid samples fabricated by using the conventional method. We examined the factors that affect the moire pattern, particularly the grid frequency and the grid rotation angle, by integrating the sample grids with an amorphous selenium (a-Se) based flat panel detector.

We developed high precision carbon-interspaced antiscatter grids to be suitable for DR by adopting a precise sawing process. We performed the systematic evaluation of the grid performance by using the IEC standard fixture and the moire pattern analysis with some prepared sample grids. The carbon-interspaced grids showed better grid performance than conventional aluminum-interspaced ones mainly due to the less absorption of any primary x-rays penetrating the carbon interspace. A moire pattern may be the most critical problem to be solved for the successful grid for use in DR.

Through the theoretical and experimental analyses, we found the frequency of the moire pattern decreased with decreasing difference in frequency between the grid and the detector and, thus, a moire-free image could be produced after frequency synchronization, possibly by adjusting the magnification of the grid strips.