Performance for obtaining maximal gain from a program for digital subtraction radiography

Noise in subtraction images made from pairs of intraoral radiographs: a comparison between four methods of geometric alignment

OBJECTIVES

To compare noise levels in subtraction images produced by four methods of geometric alignment.

METHODS

50 pairs of intraoral radiographs (Digora Optime; Soredex, Tuusula, Finland) were used in this study. Two programs were used to correct geometric differences: ToothVis 1.4 (TV) and DentalStudio 2.0 (DS). Three reference points were manually positioned in both programs (methods 1 and 2); four (method 3) and ten (method 4) reference points were positioned within TV in each of the 50 pairs of images. The standard deviation (SD) of the histogram defining the distribution of grey shades in the subtraction image was used as the statistical parameter for evaluation of homogeneity, i.e. the noise in the subtracted images.

RESULTS

The mean and median shade of grey values were lower for images after geometric correction in TV (126.6\126.8, 126.9\126.8 and 126.1\126.7, for three- four- and ten-point alignment, respectively) than those performed with the positioning module of DS (128.7\127.5) (P<0.05). For the SD, the mean values were significantly lower with TV (4.6, 4.0 and 3.3 for three-, four- and ten-point alignment, respectively) than with DS (6.8). The range of SD values was the largest for four-point alignment with TV (0.7-15.4), smaller for three-point alignment with DS (1.5-15.4) and three-point alignment with TV (0.5-13), and the smallest with ten-point alignment in TV (0.5-8.7).

CONCLUSIONS

The SD of the grey-shade histogram showed that subtraction images produced with ToothVis 1.4 software were statistically less noisy than images produced with Dental Studio 2.0 software. There is a relationship between the number of reference points chosen and the noise in the subtraction images.

Noise in subtraction images made from pairs of bitewing radiographs: a comparison between two subtraction programs

OBJECTIVES

To compare noise in subtraction images produced by two subtraction programs.

METHODS

Twenty-five pairs of bitewing radiographs exposed under clinical conditions were subtracted using two digital subtraction programs: X-PoseIt (XP) software and EMAGO/Advanced 3.43 (EM) software. Four reference points were located between the mesial surface of the upper first premolar and the distal surface of the upper first molar (the region of interest) on the same anatomical structures using XP and EM. The standard deviation (SD) of the histogram defining the distribution of the shades of grey in the region of interest was used as the statistical parameter for comparing noise in the subtraction images created by the two subtraction programs.

RESULTS

The mean and median grey shade value was lower with EM software (126.9, 126) than with XP software (128.3, 128) (P < 0.05). For the SD, the mean value was significantly lower with XP (6.2) than with EM (7.8) (P < 0.05). The range of the SD values was larger for EM (3.6-12.8) than XP (3.3-9.9).

CONCLUSIONS

The standard deviation of the grey shade histogram showed that subtraction images produced with X-PoseIt software were statistically less noisy than images produced with EMAGO/Advanced 3.43 software.