Biomedical Imaging

6Phase contrast radiography

Despite the enormous success and widespread use of radiography for over 100 years, projection imaging based on differential absorption of x-rays in matter is subject to a number of severe limitations and shortcomings:

–The contrast of soft and weakly absorbing tissue is too low. As discussed in Chapter 3, the photoelectric effect is the dominant interaction for light elements in the diagnostic energy range up to ∼ 100 keV, resulting in a particular scaling of the linear absorption coefficient μ with elemental composition (atomic number Z), density ρ and photon energy E, approximately as

$\mu \propto \rho \frac{Z^4}{E^3}.\left(6.1\right)$

Hence, absorption of x-rays provides excellent contrast between bone (high content of Ca and ...