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. 2012 Jul;41(5):361-6.
doi: 10.1259/dmfr/94751012. Epub 2012 Jan 26.

Alternative X-ray filters for an intra-oral digital radiographic system

J Stecke  1 , A D Cruz, S M Almeida, F N Bóscolo
Affiliations

Alternative X-ray filters for an intra-oral digital radiographic system

J Stecke et al. Dentomaxillofac Radiol. 2012 Jul.

Abstract

Objective: The aim of this study was to evaluate the effect of the modulation of the radiation spectrum with the use of alternative X-ray filters in the quality of intra-oral digital images from storage phosphor plates.

Methods: The radiographic exposures were performed in a GE 1000 X-ray machine (General Electric Co., Milwaukee, WI), operating at 65 kVp, 10 mA, 40 cm focus receptor distance using three different exposure times: 0.05 s, 0.16 s and 0.35 s. The control filter (GC) was 100% aluminium (Al) with a thickness of 1.5 mm. The tested filters were: G1, 97% Al and 3% copper (Cu) with 1.47 mm thickness; G2, 96% Al and 4% Cu with 1.53 mm thickness; G3, 95% Al and 5% zinc (Zn) with 1.56 mm thickness; G4, 98% Al and 2% Zn with 1.5 mm thickness; and G5, 95% Cu and 5% Zn with 1.6 mm thickness. For formation of the image, a 12-step Al wedge (each step with increments of 1 mm in thickness) was radiographed 10 times. Pixel values measured in digital images were converted into optical density (OD).

Results: All replicates showed OD with high reproducibility (r > 0.95) for all exposure times and tested filters. In comparison between filters, statistically significant differences in density (p < 0.05) were observed. The OD curve of the G5 filter in all exposure times and G3 filter in an exposure time of 0.05 s showed changes in shape (p < 0.05).

Conclusions: Excluding the G5 filter, all others tested filters can be used as a substitute for GC without losses in image quality.

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Figures

Figure 1
Figure 1
Optical density curves of all filters in the exposure time of 0.05 s and regression analysis of the standard filter including a prediction limit of 5%. Al, aluminium; G1, 97% Al and 3% copper (Cu) with 1.47 mm thickness; G2, 96% Al and 4% Cu with 1.53 mm thickness; G3, 95% Al and 5% zinc (Zn) with 1.56 mm thickness; G4, 98% Al and 2% Zn with 1.5 mm thickness; G5, 95% Cu and 5% Zn with 1.6 mm thickness. GC, control filter
Figure 2
Figure 2
Optical density curves of all filters in the exposure time of 0.16 s and regression analysis of the standard filter including a prediction limit of 5%. Al, aluminium; G1, 97% Al and 3% copper (Cu) with 1.47 mm thickness; G2, 96% Al and 4% Cu with 1.53 mm thickness; G3, 95% Al and 5% zinc (Zn) with 1.56 mm thickness; G4, 98% Al and 2% Zn with 1.5 mm thickness; G5, 95% Cu and 5% Zn with 1.6 mm thickness. GC, control filter
Figure 3
Figure 3
Optical density curves of all filters in the exposure time of 0.32 s and regression analysis of the standard filter including a prediction limit of 5%. Al, aluminium; G1, 97% Al and 3% copper (Cu) with 1.47 mm thickness; G2, 96% Al and 4% Cu with 1.53 mm thickness; G3, 95% Al and 5% zinc (Zn) with 1.56 mm thickness; G4, 98% Al and 2% Zn with 1.5 mm thickness; G5, 95% Cu and 5% Zn with 1.6 mm thickness. GC, control filter
Figure 4
Figure 4
Example of images obtained during the study. (a) Control filter (GC)—0.05 s, (b) G1 [97% aluminium (Al) and 3% copper (Cu) with 1.47 mm thickness]—0.05 s, (c) G2 (96% Al and 4% Cu with 1.53 mm thickness)—0.05 s, (d) G3 [95% Al and 5% zinc (Zn) with 1.56 mm thickness]—0.05 s, (e) G4 (98% Al and 2% Zn with 1.5 mm thickness)—0.05 s, (f) G5 (95% Cu and 5% Zn with 1.6 mm thickness)—0.05 s, (g) GC—0.16 s, (h) G1—0.16 s, (i) G2—0.16 s, (j) G3—0.16 s, (k) G4—0.16 s, (l) G5—0.16 s, (m) GC—0.32 s, (n) G1—0.32 s, (o) G2—0.32 s, (p) G3—0.32 s, (q) G4—0.32 s, (r) G5—0.32 s
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