Recent efforts have also paved the way to apply these techniques to conventional x-ray tubes 21, 22, 23, 24. This feature in combination with dedicated post-processing algorithms permits the exploitation of contrast formation mechanisms based on x-ray refraction and ultra small angle scattering (in the order of some tenth of µrad) due to multiple refraction 18, 19, 20. Their angular sensitivity in the order of µrad is due to the intrinsic properties of their transmission functions. These methods have been developed and extensively applied at synchrotron radiation sources. Similar information can be retrieved utilizing grating interferometers (GI) through the Talbot effect 16 or by edge illumination (EI) 17 as non interferometric grating technique. It has been shown that analyzing the deviation angle of monoenergetic x-rays penetrating tissue by virtue of perfect crystal optics in analyzer based imaging (ABI) 11, 12, 13 increases the visibility of certain diagnostic features and pathologies in biomedical imaging 14, 15. In order to assess refraction angles in the µrad regime, scattering or dark field in general, it requires additional optical elements. Here typically edge enhancement is achieved by tuning the sample-to-detector distance. It has been even applied for mammography in clinical studies with synchrotron radiation 7 and also in clinical environment using dedicated systems 8, 9, 10.
#Idl gaussian free#
Free propagation (or in-line) phase contrast 5, 6 is the simplest implementation since it requires only a certain degree of spatial coherence of the x-ray source. To mention are here bright, dark and phase contrast schemes yielding a substantial improvement in image quality particularly for low absorbing features in soft tissue imaging. In the last decades different endeavors have been undertaken to translate optical imaging methods towards x-ray imaging. This explains why despite of some early pioneering work 2, 3, 4 advanced x-ray imaging methods exploiting phase contrast have been established only in the late 1990s. Physiologically, stagnation in x-ray imaging might be traced back to Roentgen 1 who doubted the feasibility of x-ray lenses due to (at that time) non-observable refraction. Physically this is due to the fact that the index of refraction for x-rays is very close to unity. The translation of well-known and commonly used contrast mechanism in optical imaging to similar x-ray modalities is not straightforward. Owing to its extended angular acceptance range the algorithm allows precise assessment of local scattering distributions at biocompatible radiation doses, which in turn might yield a quantitative characterization tool with sufficient structural sensitivity on a submicron length scale. After a validation of the algorithm with a simulation code, which demonstrated the potential of this highly sensitive method, we have applied this theoretical framework to experimental data on a phantom and biological tissues obtained with synchrotron radiation.
#Idl gaussian full#
This analytical approach is based on a simple Gaussian description of the analyzer transmission function and this method is capable of retrieving refraction and small angle scattering angles in the full angular range typical of biological samples. We report on a novel algorithm for the analyzer based x-ray phase contrast imaging modality, which allows the robust separation of absorption, refraction and scattering effects from three measured x-ray images. In particular the possibility to obtain information from small angle scattering about unresolvable structures with sub-pixel resolution sensitivity has drawn attention for both medical and material science applications.
Unlike conventional x-ray attenuation one of the advantages of phase contrast x-ray imaging is its capability of extracting useful physical properties of the sample.
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