QUALITY CONTROL TEST IN FOCAL SPOT SIZE: A PREREQUISITE FOR A GOOD IMAGE QUALITY

Abstract

 Regular implementation of quality control in diagnostic x-ray facilities is essential to provide good quality images

which will lead to proper diagnoses with less hazard to patients. The Quality Control test to determine the focal

spot size of ten (10) x-ray machines were studied in Plateau state, Nigeria using a RMI model 112B focal spot test

tool, consisting of a metal target with twelve bar pattern groups mounted on top of the test tool. Each group

consisted of six slots with three slots perpendicular to the other three. These slots were resolved and used to

calculate the effective focal spot size. The result showed the groups diminishing in size from 0.18 line pairs/mm

to 1.00 line pairs/mm for each the x-ray machines. With H7 having the highest number of resolved groups of

twelve (12) followed by H2, H3 and H4 with eleven (11) while H1, H5, H8, and H10 had ten (10), H6 and H9

had the least nine and eight (9 and 8) resolved groups respectively. The effective focal spot size calculated ranged

from 1.13mm to 5.63mm for the ten studied x-ray machines. The linear relationship between the effective focal

spot size and the line pair show a good linearity for all the x-ray machines with regression square values, R2

 ranging from 0.808 to 0.916 hence showing a good correlation between the effective focal spot size and the line

pair. This implies the smaller the estimated focal spot, the higher the magnification and the sharper and higher the

number of resolved images.

Keywords : Quality Control test, Effective focal spot size, Line pair and X-ray machine.