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

¹ Universidade Luterana do Brasil, Torres, RS, Brazil; ² Universidade Luterana do Brasil, Canoas, RS, Brazil; ³ Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

*Correspondence to: Aderson Gegler, Rua Cel. Jõo Correa, 97/307, CEP 91350-190, Porto Alegre, RS - Brazil; E-mail: adersongegler{at}hotmail.com

Received 9 December 2004; revised 9 May 2005; accepted 14 June 2005

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.

Keywords: diagnostic imaging;; subtraction technique;; image processing, computer-assisted;; image interpretation, computer-assisted