| Recent
Advances in Medical Applications of Synchrotron Radiation Stanford Synchrotron Radiation Laboratory March 4-5, 2002 Program Director: Edward Rubenstein |
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Secondary
X-ray Imaging for Angiography and other Medical Imaging Applications
Paul L. Csonka Department of Physics and Institute of Theoretical Science University of Oregon |
| Secondary
X-ray imaging can serve either a complement to, or sometimes perhaps
an alternative to the elegant K-Edge Subtraction and Dual Photon Absorbtiometry
based imaging techniques. We intend to explore the improvements and
advantages it may offer in conjunction with those well established
methods, or by itself under certain conditions, as well as its drawbacks.
Human Angiography will be considered as an illustrative example. The method can benefit from primary X-rays generated in wigglers and undulators on electron storage rings, particularly those from small emittance and short wavelength undulators. Since the method does not rely on the sudden change in cross section near an absorption edge, it can accept a broad range of primary photons. Because the photons generating the image are not the primary ones, their energy can be decoupled from the primary photon energy, which in turn leads to a reduction primary photon absorption in the human body. Also, higher primary harmonics are of no real concern, so that monochromatization is not required, which further decreases the demands on intensity, and should save expense. Only one (not two) pictures are required per image. All these factors contribute to a reduction of the primary photon intensity needed to achieve adequate image quality. The shadowing effect of dense tissue is expected to be decreased, because of the wide area detection inh erent in the method. Furthermore, with this approach sharp imaging is compatible with (appropriately defined) " locally quantitative " measurements, and (depending on the detector) with a pixel by pixel elemental analysis. Drawbacks of the method are that the primary beam is to be rastered through the sample (e.g. the human heart) along both the x and y directions; the detector area has to be large (to c apture a high fraction of secondary X-rays), and if the primary photon energies are high, they will require reflectors operating at grazing incidence angles. An analysis of APS and PETRA II shows that both machines can produce significantly more photons than would be required for high quality Angiography imaging. |
