When evaluating the quality and performance of a mammography grid, it is difficult to perform a quantitative analysis. As a general method, the first step is to measure and compare the difference in film density (or detector exposure) across the entire area. The second step is to check the x-ray quality with a mammography phantom of 4.2cm thickness which is made of poly(methyl methacrylate), also known as PMMA. The material is a close match to the adipose tissue and glands in the breast. The film density is standardized to 1.0 when x-raying. There are 16 patterns in the phantom for image evaluation. The standard criteria for acceptable is generally over 10 of these patterns can be identified.