A very difficult problem for recent high-resolution digital x-ray detectors is that, as resolution goes up, so does the difficulty of eliminating grid artifacts from the image. This is a problem for mammography systems in particular, where resolutions are much higher than in general radiography. In this article, we will discuss mathematical methods for predicting what combination of grid and bucky movement are needed to avoid grid lines in the image.
Grids are normally used in two different applications—stationary and reciprocating (moving). In reciprocating applications, the grid is installed in a bucky tray that moves the grid side to side. When a grid is reciprocated, the grid lines are blurred so they are not visible on a film or a digital image.

Gustav P. Bucky invented the grid in 1913. For many years, grids have been used in conventional film-based x-ray and image intensifiers. Prior to 1990, the highest line rate available was 103 lines per inch. However, in stationary applications, grid lines were visible on the image. Until 1990, the reciprocating bucky was an essential in removing grid lines. Today, some systems still use reciprocating buckys to remove grid line visibility in low line grids.

When using a low line grid in a reciprocating bucky, the distance between the grid and film is 3 to 5cm. When the grid is moved, the grid lines becomes blurry due to the shadow of the grid line being moved across the image. In conventional film and Computed Radiography (CR) systems, the reciprocating cycle can also be set to an effective, consistent, optimal movement by setting exposure time and motor speed.

For several years a major question with digital imaging has been if is best to use a low line grid with a reciprocating bucky or use a highline stationary grid. To reduce dose, cost, and eliminate noise and image distortion, the current trend is to eliminate the reciprocating bucky and use a highline grid. Bucky trays require additional space, have construction and design costs, and create image distortion problems in Digital Radiography (DR) systems due to the electromagnetic interference and motor noise. Therefore, the higher line stationary grids have become very popular in general radiography. General radiography grids today often have a line of frequency of up to 270 lines per inch. JPI-2100 grid can be produced over 300 lines per inch with extremely high accuracy.

In mammography systems, grid line visibility remains a major problem. The MTF in mammography is very high compared to general radiography. Even with high line grids, fine grid lines are visible on a mammography image. Mammography system companies have a considerable challenge to identify solutions for removing grid line artifacts. Even with well-optimized reciprocating cycles, it is still extremely difficult to eliminate grid line visibility when working with high resolution direct detecting radiography (DDR) detectors.

There are four types of bucky devices

• Solenoid reciprocating, which uses flat spring;
• Cam reciprocating using DC motors:
• Reciprocating using linear lead screw; and
• Oscillating, causing vibration using a small motor.

The general movement of a bucky is a temporary movement from right to left during the exposure. In general radiography, the cam diameter is usually 2-3cm. In mammography, the cam is less than 1cm. While performing an exposure, the grid moves slowly a short distance across the exposed area. Once the exposure is complete, it returns to the home position.