PSI - Issue 10

N. Martini et al. / Procedia Structural Integrity 10 (2018) 326–332 N. Martini et al. / Structural Integrity Procedia 00 (2018) 000 – 000

330

5

Fig.4 shows all the oversampled ESFs (Fig.4a) used to create the average ESF and then the Fermi-fitted ESF (Fig.4b), as well as, the resulted LSF (Fig.4c), following the IEC 2015 protocol. The variation in the ESF curves that can be depicted from figures 4a,b, can be attributed to a statistical noise component mostly prominent at the edge surface area. Fig.4d shows results for the modulation transfer function of the CMOS sensor combined with the 118.9 μ m CaWO 4 screen, under the RQA-5 (70 kVp) beam quality, following both IEC 2003 and 2015 methods. MTF values, for both methodologies were found with close agreement in the low and medium spatial frequency ranges (spatial frequencies up to 5.7 cycles/mm). Thereafter, MTFs calculated following the 62220-1:2003 protocol, were found overestimated due to the noise components which are also averaged and transferred more efficiently than signal through the imaging chain, during the process of MTF averaging.

(a)

(b)

(c)

(d)

Fig. 4. ( a) ESFs of a 118.9 μm CaWO 4 /RadEyeHR CMOS combination, following the IEC 2015 method; (b) averaged and Fermi fitted ESF; (c) LSF; (d) Modulation transfer function comparison between IEC 2003 and IEC 2015 protocols, under the RQA-5 beam quality.

Table 1. Fitting values.

Configuration

Fermi-fitted values

a

b

c

d 0

RadEyeHR/ 118.9 um CaWO 4

7200

15

65500

4. Conclusions

Applications such as, non-destructive testing, medical imaging, particle astrophysics, etc. require efficient detectors, of high resolution. In this study the resolution properties of a non-destructive testing/industrial inspection CMOS sensor, in conjunction with a scintillating material that came to the spotlight once again (CaWO 4 ) was examined in order to further exploit and enhance the imaging capabilities of an integrated detector, incorporating these two modules. The influence of the calculation protocol on the resolution properties of a thin 118.9 μ m CaWO 4 scintillator screen, coupled to the CMOS digital imaging sensor, was investigated. Experiments were carried under X-ray radiography imaging conditions, following the IEC methods. Image resolution was investigated in terms of the modulation transfer function, in the general radiography energy range. MTF values of the CaWO 4 screen/CMOS combination were found in close agreement in the low and medium spatial frequency ranges (spatial frequencies up