Establishment and validation of the Channelized Hotelling Model Observer for image assessment in industrial radiography

Abstract

A B S T R A C TA new method for industrial radiography is presented to assess image quality objectively. The assessment is performed by a modelled observer developed to interpret radiographic images in order to rate the detectability of structural defects. For the purpose of qualifying radiographic NDE procedures, computational tools simulate the image, but should additionally automatically assess the associated image quality instead of relying on human interpretation. The Channelized Hotelling Model Observer (CHO) approach, originally developed for medical imaging, is here developed for industrial NDE applications to measure objectively the defect's detectability. A validation study based on a comparison of the model's efficiency of observing circular and elongated flaws shows that the CHO outperforms other detectability models used by industry. Furthermore, the model's reliability was verified by comparing it to psychophysical data.

Soft modes of the dielectric response in the twist–bend nematic phase and identification of the transition to a nematic splay bend phase in the CBC7CB dimer

“…This peak can be assigned to a collective fluctuation of the tilt angle of the coarse grained director N out of the pseudo-layers normal, similar what has been reported for bent-core molecules [25]. As a response to an electric field one can expect electro-optic effects similar to the in-plane flexoelectric switching in the N* phase.…”

“…Such nanoscale modulation of molecular orientation promises extremely short response times. Indeed the time of electrooptic switching reported for bent-core is about 1μs [25] and for CB7CB and CB11CB dimers even shorter times being in the sub-microsecond range have been detected, much shorter [3,4,7] when compared to the ms range for uniaxial nematics. The field-induced distortional effect in the N TB phase may be extremely useful for technological applications as this has similarity to the electro-clinic effect [4,35].…”

“…Additionally, the polarity and chirality of the N TB phase formed by the achiral molecules has been investigated by electro-optical [4][5][6][7]12,22], magneto-optical [23,25], dielectric [22,[25][26][27][28] and nuclear magnetic resonance studies (NMR) [29][30][31]. A number of theoretical models have attempted to describe the new nematic ground state and the anomalously low or negative bent elastic constants [32][33][34].…”

Realistic Film Noise Generation Based on Experimental Noise Spectra

“…Because of the expense of performing these tests, computational simulations are a vital tool in order to produce realistic images and hence establish the best testing approach [29]. These simulated images are afterwards assessed for the purpose of indirect, computer based test setup improvements or testing procedure qualification [30]. For that reason, the simulated X-ray images need to be as realistic as possible, which includes an appropriate modelling of film noise too.…”

Radiographic film system classification and noise characterisation by a camera-based digitisation procedure

“…Currently, the assessment of film granularity is performed by time-consuming pointwise microdensitometer measurements, which therefore provides a significant need for a technique which could evaluate the film more efficiently. This data can also be valuable in other areas, for example in realistic simulation of film noise, as required in the simulation process of radiographic testing applied in industry for improving test setups [2] which are based on accurate film noise characteristics from real film samples [3].…”