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Nondestructive measurement of the grid ratio using a single image
Author(s) -
Pasciak A. S.,
Jones A. Kyle
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3191245
Subject(s) - nondestructive testing , medical imaging , materials science , computer science , optics , artificial intelligence , medical physics , computer vision , physics , medicine , radiology
The antiscatter grid is an essential part of modern radiographic systems. Since the introduction of the antiscatter grid, however, there have been few methods proposed for acceptance testing and verification of manufacturer‐supplied grid specifications. The grid ratio ( r ) is an important parameter describing the antiscatter grid because it affects many other grid quality metrics, such as the contrast improvement ratio ( K ) , primary transmission ( T p ) , and scatter transmission ( T s ) . Also, the grid ratio in large part determines the primary clinical use of the grid. To this end, the authors present a technique for the nondestructive measurement of the grid ratio of antiscatter grids. They derived an equation that can be used to calculate the grid ratio from a single off‐focus flat field image by exploiting the relationship between grid cutoff and off‐focus distance. The calculation can be performed by hand or with included analysis software. They calculated the grid ratios of several different grids throughout the institution, and afterward they destructively measured the grid ratio of a nominal r 8 grid previously evaluated with the method. They also studied the sensitivity of the method to technical factors and choice of parameters. With one exception, the results for the grids found in the institution were in agreement with the manufacturer's specifications and international standards. The nondestructive evaluation of the r 8 grid indicated a ratio of 7.3, while the destructive measurement indicated a ratio of 7.53 ± 0.28 . Repeated evaluations of the same grid yielded consistent results. The technique provides the medical physicist with a new tool for quantitative evaluation of the grid ratio, an important grid performance criterion. The method is robust and repeatable when appropriate choices of technical factors and other parameters are made.