PSI - Issue 33

Niki Martini et al. / Procedia Structural Integrity 33 (2021) 295–303 Martini/ Structural Integrity Procedia 00 (2021) 000–000

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2.2. Experimental Validation

2.2.1. Phantoms’ construction Hydroxyapatite (FLUKA 21223, ⩾ 90% purity) phantoms of 0.7, 1.0, 1.5 and 3.0 mm thickness, and the equivalent thicknesses for calcium oxalate (CAS Nr: 563-72-4, 99.99% purity) and calcium carbonate CAS Nr: 207-439-9, ⩾ 99% purity) with the same quantity of epoxy resin (C 19 H 23 CIO 4 ) (Martini et al. 2021, Resoltech) were constructed. The mixtures were placed in silicon tubes of 22.31 mm inner diameter and then a vacuum tube VACIOTEM-T (SELECTA, Barcelona, Spain) was used in order the remaining air in the phantoms to be diminished. A 20 x 20 x 25 cm 3 PMMA tank filled with double distilled water was used to simulate the torso. The height of the double distilled water, with the phantoms immersed, was equal to 20.8 cm.

Fig. 1. Hydroxyapatite, calcium oxalate and calcium carbonate constructed phantoms (left) and the PMMA tank (right).

2.2.2. Irradiation conditions The Del Medical Eureka (DEL MEDICAL, Harrison, NY and Bloomindale, IL, USA) with Tungsten anode was used for the validation of the method. Ten low energy images were acquired at 50 kVp 200mAs with 3 mm Aluminum (inherent filtration) and ten high energy images were acquired 90 kVp 400 mAs with 3 mm 99.99% pure Copper foil. A terbium-doped gadolinium oxysulfide (Gd 2 O 2 S:Tb) phosphor screen (Min-R 2190 with mass thickness 33.91 mg cm -2 ) coupled to an optical readout device including a complementary metal-oxide-semiconductor (CMOS) Remote RadEye HR (Rad-icon Imaging Corp, Santa Clara, CA, USA) photodiode array. The CMOS photodiode array haw a format of 1200 x 1600 pixels, an active area of 27 x 36 mm 2 and the pixel pitch is 22.5 μm. The source to detector distance was set at 66 cm. The detector response curves for the low-and high-energy were measured in order to convert the pixel values to dose and finally to photons using the known attenuated intensities, ���� and ���� (Martini et al. 2017, Martini et al. 2021). The pixel values were converted to photons since the modified analytical model uses number of photons in order to calculate effective �� � ⁄ and the CV mCa/mP (%) (Linardatos et al. 2021, Martini et al. 2015, Martini et al. 2017, Michail et al. 2011). The measurement of the filtered spectra was accomplished with the Cadmium Telluride AMPTEK XR-100T (Amptek, Inc., Bedford, USA). The total entrance surface dose was 8.38 mGy. The experimental results of the effective �� � ⁄ were assessed through the two-tailed Mann-Whitney U non-parametric statistical test (Martini et al. 2017, Martini et al. 2021, Milton 1964). For all tests, the significance level was set at 5%.