A feasibility study of soft-tissue imaging based on x-ray wide-angle diffraction contrast has been performed at the medical beamline of the European Synchrotron Radiation Facility (ESRF). The technique employs computed-tomography algorithms to reconstruct from one data set the spatial distribution of several tissues differentiated by their diffraction properties. Radial diffraction profiles are measured in parallel projections from the sample and decomposed into material-selective weighting factors, which form the sinograms for the reconstructions. Attenuation effects--inherent in imaging techniques using scattered radiation--are efficiently corrected for by a ray-tracing method applied to the corresponding absorption image. Images of 7 cm diameter samples composed of fat, bone and muscle were generated at 60 and 80 keV x-ray energy. The highest surface-absorbed dose was 24 mGy, but substantial contrast could still be obtained at 7 mGy, indicating potential applicability in medical imaging. The dominant noise contribution in the images stems from the detection system, pointing to a possible decrease in the surface-absorbed dose for an optimized system of more than a factor of 2.

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A new optical system to perform tomography based on the Rayleigh-to-Compton (RC) method with high spatial and spectral resolution is presented. The RC technique allows the effective atomic number of a sample to be measured and finds application in bone mineral densitometry in medicine. It is particularly useful for the characterization of the distribution of biological materials which do not exhibit distinctive diffraction peaks. The system is based on the separation of the elastic line from the spectrum that is scattered by the sample by means of a bent Laue analyser crystal, and the subsequent independent detection of the elastic and inelastic parts of the spectrum with two large-area scintillation counters. The high energy resolution permits operation at low momentum transfer, where the RC method has its best contrast-to-noise ratio for low-Z materials. The geometrical and spectral requirements in terms of the incident beam and the conical analyser crystal are discussed. A first-generation tomographic imaging system (pencil beam, scanned sample) as implemented at the ESRF Compton-Scattering Station ID15B is described. A high-resolution tomographic reconstruction of a bone sample is presented.

We present a novel approach to perform Rayleigh-to-Compton (RC) measurements using a bent analyzer crystal in Lane geometry. The ratio of the elastically to the inelastically (Compton) scattered photons gives directly access to the effective atomic number of the sample by eliminating several side effects falsifying the scattered spectrum, eg. absorption in the sample. The use of the analyzer crystal, instead of an energy dispersive detector, enables us to measure in forward scattering geometry, where the method is optimized in respect to the contrast-to-noise ratio for low Z materials. The first generation (scanning the sample with a pencil like beam) computed tomography approach enables us to reconstruct the RC-value independently from the scattering geometry on a square image grid. We give this method the acronym RC-CT (Rayleigh-to-Compton computed tomography). The identity of values in the RC method and the RC-.CT method will be derived. The conical bent crystal is focused on the source line (focal distance 1 m) where the incident monochromatic beam traverses the sample. The analyzer crystal reflects the elastic line of the scatter spectrum into a scintillation detector. The inelastic part of the spectrum passes the crystal and is recorded in a second scintifiation detector. By rocking the analyzer, the whole energy distribution of the scatter spectrum can be obtained with an energy resolution dominated by the rocking curve width of the bent crystal. We will discuss the requirements and the constraints on the geometrical parameter of the experiment. From this, it is concluded that the method requires high flux sources like synchrotrons. Employing the contrast-to-noise ratio introduced by Harding et a!,1'2 the wavelength dispersive approach to the RC method is evaluated for a wide range of elements. Finally, we show a first reconstruction of a bone sample and discuss possible applications in medical and material science.