Fluke Biomedical 07-644 - Manual (Page 5)

Introduction
Introduction
1
1-1
Section 1
Introduction
1.1 Introduction
The Model 07-644 Grid Alignment Test Tool is designed to test alignment of the radiograph grid with
respect to the central ray of the x-ray tube.
An upside-down focused grid or an incorrect tube to grid distance can be easily detected by exposing a
cassette in its tray and observing the density fall off toward opposite edges of the processed film (grid
cutoff). , However, lateral decentering or tilting of the grid cannot be detected in this manner: the grid
cutoff in these cases causes a uniform reduction of density across the film. The result of such a
misalignment is increased patient dose and reduced image contrast. It is in detecting this type of
"unobvious" grid cutoff that the Grid Alignment Test Tool is very useful.
1.2 Description
The test tool is an easily used device consisting of a plastic covered lead blocker 1/16" x 3 ½ x 9-1/8 (0.2
cm x 9 cm x 23 cm) containing several holes. The five larger holes have centers spaced 1" (2.5 cm) apart
and allow test exposures to a film cassette while the smaller holes provide marking exposures on the film
to show the tool orientation. When an exposure is made through one of the large holes, two small lead
blockers are used to block out the other four large holes. For longer exposure times copper strips (0.040"
thickness is recommended) can be placed
over the holes.
Figure 1-1. Model 07-644 Grid Alignment Test Tool, with Lead Blockers