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EM behavior when the wavelength is much smaller than the object
Published in James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney, Basic Introduction to Bioelectromagnetics, 2018
James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney
In this chapter, we discuss the case where the wavelength of the electromagnetic radiation is much smaller than the size of typical objects. Since details smaller than about 0.3 mm are difficult to resolve with the naked eye, this chapter is concerned with waves whose frequencies are high enough that their wavelengths are smaller than 0.3 mm. Since f = c/λ (Eq. 1.15), this means that the frequency will be in the range of 3 × 108 (m/s)/0.3 × 10−3 (m) = 1 × 1012 (Hz) = 1 THz and higher. The lowest end of this frequency range intersects with the millimeter-wave band, so named because its wavelengths are fractions of a millimeter up to a few millimeters (see Figure 1.31 for a graph of the various electromagnetic regions). At somewhat higher frequencies are the far-infrared waves, then the near-infrared waves whose wavelengths are on the order of micrometers, named far and near according to their relative closeness to visible light wavelengths. Higher in frequency (shorter in wavelength) is the very important visible wavelength range (between 400 and 700 nm), where many significant discoveries and devices such as lasers have been made, undoubtedly due to the significance of light in human vision. At slightly higher frequencies are the ultraviolet (UV) waves. At much higher frequencies are the soft, then hard, X-rays.
Dictionary
Published in Mario P. Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Hardness. (X-rays) A term referring to the penetrating power of X-rays. Soft X-rays, of lower frequency and hence lower energy, are less penetrating. Hard X-rays, having a higher frequency and greater energy, are more penetrating.
3D analysis of the myenteric plexus of the human bowel by X-ray phase-contrast tomography – a future method?
Published in Scandinavian Journal of Gastroenterology, 2020
Niccolò Peruzzi, Béla Veress, Lars B. Dahlin, Tim Salditt, Mariam Andersson, Marina Eckermann, Jasper Frohn, Anna-Lena Robisch, Martin Bech, Bodil Ohlsson
X-ray computed tomography (CT) provides volumetric information in a non-destructive way and is widely used for medical applications. Standard X-ray attenuation-based microtomography would normally not show any contrast between different cell types or soft tissues, because of their low and relatively homogenous X-ray attenuation coefficient. Aside from attenuation, however, an X-ray wave that interacts with a material is also subject to a shift in its phase. Novel X-ray imaging techniques can obtain contrast from this phenomenon, in what is commonly called X-ray phase-contrast imaging (PCI). For hard X-rays and low atomic number materials, such as biological tissues, PCI provides the possibility to significantly increase the contrast (or alternatively decrease the radiation dose while keeping a comparable contrast) compared with attenuation-based imaging [11,12]. PCI can be performed with a wide variety of modalities and setups. Until recently, state-of-the-art results would require highly coherent X-rays only produced at synchrotron facilities [13]. Laboratory setups, of easier accessibility, are, however, starting to show comparable results [14].