By
exploiting the spatial coherence of X-ray beams coming from synchrotron
light sources one can study several phenomena having a possible impact
on diagnostic radiology. Conventional absorption radiology is based on
the different X-ray absorption properties of different materials. A severe
limitation of this method is the fact that low density biological samples
having low X-ray absorption produce low values of the image contrast and
a scarce visibility of the details. This is typically the case of mammography,
where one wishes to examine soft tissue. An alternative approach to absorption
is the so-called "phase contrast radiology" where, besides absorption differences,
one detects the phase shifts undergone by the electromagnetic wave after
traversing a given detail.
This
is equivalent to saying that image contrast is produced using the real
part of the refractive index, which determines phase shift properties,
rather than its imaginary part, which determines absorption properties:
hence the name "phase contrast imaging". The picture shows the comparison
between a conventional absorption radiography of a mimosa flower (A) and
a phase contrast image of the same object (B).
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