Kenneth Alan Fetterly MS, Presenter: Nothing to Disclose

Beth Ann Schueler PhD, Abstract Co-Author: Nothing to Disclose

The conversion from screen-film radiography to digital radiography requires a new approach to grid selection. The SNR improvement factor (Ksnr) is an appropriate descriptor of image quality improvements attributable to grid use with digital x-ray systems. This work will identify the relationships between grid ratio, line rate, phantom thickness, and Ksnr to identify optimum grids for use with a computed radiography (CR) detector and a moving grid.

A series of 15:1 ratio grids with line rates in the range 44-80 line per cm and a series of 40 line per cm grids with ratios in the range 8:1 to 14:1 were studied. The grids had fiber inter-space material and carbon fiber covers. This work used Solid Water scattering phantoms of thickness 10-40 cm. A RQN8 x-ray beam quality was used. The x-ray field of view was 30 cm x 30 cm. For each combination of grid and phantom thickness, Ksnr was calculated as Ksnr = Kc / B^0.5, where Kc is the contrast improvement factor and B is the Bucky factor. Calculation of Kc requires knowledge of the scatter to primary ratio (SPR), which was measured using a lead beam stop method.

Overall, Ksnr was found to increase with increasing phantom thickness, increasing grid ratio, and decreasing line rate. Relative differences between the Ksnr values of the various grids increased as the phantom thickness increased. Of the group of grids tested, the 14:1, 40 line per cm grid had the highest Ksnr values. With this grid, SPR was reduced from 2.4 to 0.3 for a 10 cm phantom and 16 to1.9 for a 40 cm phantom. The corresponding Bucky factors were 1.5 and 7, and the Ksnr values were 1.4 and 2.2 for the 10 cm and 40 cm phantoms, respectively.

Appropriate anti-scatter grid selection can help optimize digital x-ray image quality. Proper grid selection was found to be important for all phantom/patient thicknesses, but was found to increase in importance with increasing thickness. As a result, selecting an optimum grid for imaging large patients can also be expected to optimize the system for smaller patients. This work demonstrates that the best performing fiber inter-space grids for use with CR and a moving grid have a low line rate and high grid ratio.

K.A.F.,B.A.S.: Eqipment supplied by Smit Roentgen / Philips Medical Systems, The Netherlands.

Fetterly, K, Schueler, B, Search for the Optimum Anti-scatter Grid for Use with Digital X-ray Imaging Devices.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4414478.html