J Korean Acad Oral Maxillofac Radiol.  1999 Aug;29(2):417-422.

The study of standard deviation of gray scale histogram in digital subtraction radiography as a test parameter for superimposition error

• Cho BH

Abstract

PURPOSE: The aim of this study was to assess the validity of standard deviation of gray scale histogram in digital subtraction radiography as a test parameter for superimposition error.
MATERIALS AND METHODS
Twenty periapical radiographs used baseline images were copied to exclude the influence of exposure geomety and contrast differences. These subsequent images were displaced by 0.1-0.5 mm in the x-, y- and xy-directions, rotated by 0.5-3o and distorted by angular contraction of 1-5o in x- and y-axis before subtraction. Pearson correlation coefficients(r) were calculated between the standard deviation of gray levels in the subtracted image and misplacement and paired t-tests were performed to compare standard deviations.
RESULTS
Linear displacement showed high correlation coefficients of 0.997, 0.997 and 0.995 in x-, y- and xy-axis respectively. Statistically significant different standard deviation existed among all linearly displaced groups(p<0.05). Relatively low correlation coefficients of 0.982 and 0.959 in x- and y-axis distortion were demonstrated. The standard deviations between the two distortion groups were statistically significantly different(p<0.05).
CONCLUSION
Standard deviation of gray level distribution in digital subtraction images is satisfactory but not perfect similarity measure to assess superimposition errors.

Keyword

radiography; dental; digital subtraction; computer-assisted; periodontal

MeSH Terms

Radiography*