title: Anomalous Rayleigh scatter in dilute media.
abstract: Anomalous Rayleigh scatter is examined for dilute concentrations of the biomedically relevant element iodine in aqueous media including measurements with monochromatic synchrotron radiation in the vicinity of the iodine K-edge. The measurements agree with anomalous scatter-factor corrections to the form-factor approximation which has been shown to have good agreement with higher precision S-matrix calculations for small angle scatter over a wide range of energies but has not been adequately tested at the edge. Monte Carlo modelling, including the modelling of polarized Compton and Rayleigh scattered x-rays, is used to determine the relative contributions of the scatter and fluorescent components at the detector as well as the modelling of self-absorption and relative dose in the determination of detection limits. A Rayleigh scatter minimum of 28 barns/sr was observed at an energy 10 +/- 5 eV below the K-edge of iodine at a position predicted from an evaluation of the dispersion integral that includes bound-bound resonance contributions. Minimum detectable concentrations for observation of the anomalous Rayleigh scatter feature at an exposure of 10 mSv, predicted for iodine and iron, are 1 mg ml(-1) and 10 mg ml(-1), respectively. Upper limits to detection of the feature imposed by degradation of the signal by self-absorption are 0.021 g cm(-2) and 0.0029 g cm(-2) radiation lengths, respectively.
authors.affiliation: Imaging and Medical Physics Group, Queen Elizabeth Hospital, University Hospital NHS Trust, Birmingham, UK. richard.hugtenburg@uhb.nhs.uk
authors.forename: Richard P
authors.initials: RP
authors.lastname: Hugtenburg
authors.forename: P
authors.initials: P
authors.lastname: Muthuvelu
authors.forename: David A
authors.initials: DA
authors.lastname: Bradley
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D003287:Contrast Media / Q000494:pharmacology; D007455:Iodine / Q000494:pharmacology; D009010:Monte Carlo Method; D017785:Photons; D011859:Radiography / Q000295:instrumentation* / Q000379:methods*; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D014965:X-Rays
chemical_list: D003287:Contrast Media; D007455:Iodine