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Novel x‐ray attenuation mechanism: Role of interatomic distance
Author(s) -
Poelzing Steven,
Smoot Adam F.,
Veeraraghavan Rengasayee
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2975151
Subject(s) - absorbance , diiodomethane , attenuation , iodine , chemistry , wavelength , anharmonicity , photon energy , harmonic , analytical chemistry (journal) , molecular physics , optics , materials science , atomic physics , photon , optoelectronics , organic chemistry , physics , condensed matter physics , chromatography , surface energy , quantum mechanics
Little progress has been made over the last 30 years for improving attenuation by x‐ray contrast agents, in part because the mechanisms of x‐ray attenuation are thought to be well understood. We hypothesized that x‐ray absorbance can be modulated by altering the interatomic spacing between K‐edge attenuating atoms. Iodomethane, diiodomethane, 2,6‐diiodo‐4‐nitroanaline, and diiodobenzene isomers were dissolved in DMSO and imaged with an OEC Compact 7600 fluoroscope. At a tube voltage of 42 kVp , absorbance of equimolar diiodomethane ( 150 mM ) was significantly ( p < 0.01 ) greater than iodomethane ( 150 mM ) by 45%. Interestingly, 150 mM diiodomethane absorbance was significantly greater than 300 mM iodomethane (by 5%, p < 0.01 ) despite equal amounts of iodine in both solutions. 1,3‐diiodobenzene absorbance was significantly greater than 1,2‐ and 1,4‐diiodobenzene ( p < 0.01 ) . However, 2,6‐diiodo‐4‐nitroanaline absorbance was similar to 1,3‐diiodobenzene. When a linear model was fit for absorbance as a function of density and harmonic error (the fractional remainder of the inter‐iodine distance and the K‐shell ionizing wavelength) at different beam energies, a significant overall fit was obtained for both unfiltered and hardened beams ( p < 0.01 ) . While the slope of absorbance as a function of harmonic error was significant for all conditions ( p < 0.01 ) , the slope with respect to density was significant only when the beam was unfiltered ( p < 0.05 ) . Also harmonic error, but not density, displayed significant energy‐dependent effects on absorbance ( p < 0.01 ) . These data suggest that harmonic error is a strong determinant of absorbance, particularly when the beam energy is concentrated near the iodine K‐edge and is likely a descriptor of K‐characteristic photon interactions. Therefore, x‐ray absorbance may be modulated by the distance between covalently linked x‐ray K‐edge attenuating atoms. This finding has important implications for increasing contrast agent absorbance as well as for designing molecular transducers capable of modulating K‐edge attenuating atomic distances and thereby x‐ray absorbance.