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Reproducibility of and file format effect on digital subtraction radiography of simulated external root resorptions.

OBJECTIVE
To evaluate, in simulated external root resorptions (ERR), two factors that may affect results of digital subtraction radiography (DSR): (1) intraobserver and interobserver reproducibility and (2) effects of digital file formats (TIFF, BMP and JPEG) on the estimation of mineral loss.


METHODS
Eleven incisors were radiographed three times (NR, no resorption; SR, small--#1/4 round bur; and LR, large--#2 round bur) on standardized projections. The resulting images were reproduced and saved as TIFF, JPEG and BMP file formats. The pairs of TIFF images (NR x SR and NR x LR) were subtracted three times at 1 week intervals by three observers. One observer subtracted pairs of images (NR x SR and NR x LR) for all file formats. For each subtraction the resorption area was selected and mean pixel density values were calculated.


RESULTS
Analysis of variance (ANOVA) (P = 0.05) showed no statistical differences for intraobserver and interobserver values. Mean pixel density values were: observer A, 121.60 +/- 2.56 (NR x SR) and 111.84 +/- 4.04 (NR x LR); observer B, 121.86 +/- 2.50 (NR x SR) and 110.92 +/- 3.36 (NR x LR); and observer C, 121.70 +/- 2.39 (NR x SR) and 111.10 +/- 2.67 (NR x LR). Also, no statistical differences were found between file formats for LR (TIFF, 110.88 +/- 2.79; JPEG, 111.35 +/- 3.35; BMP, 111.00 +/- 2.70) and for SR between TIFF (121.30 +/- 2.34) and JPEG (120.46 +/- 1.51) or BMP (121.67 +/- 2.18) file formats. Differences were found between the JPEG and BMP groups.


CONCLUSIONS
DSR is reproducible in simulated ERR, and JPEG or BMP file formats do not affect results.