Image Processing Reference
Figure4.11 X-ray shadowgram of a lily. (CourtesyofSteveMeyers)
develops a serum that enables him to see through objects. This ability becomes
uncontrollable and makes his life a nightmare.
Superman was equipped with x-ray vision that could only be stopped by lead
barriers. Figure 4.13 shows an image from Destination Moon, a comic book in
the Tintin adventure series. Two detectives (named Thomson and Thompson) are
trying to find a skulking skeleton, not realizing that they have been seeing each
other imaged with x rays in a fluoroscope screen.
Just as infrared energy can penetrate materials used in artwork to reveal
information about hidden material, so x rays are often used to examine old
paintings and other works of art. Figure 4.14 shows two views of an oil painting
called An Old Man in Military Costume, by Rembrandt. The radiograph shows
that there is only one painting on the canvas. Any other oil painting underneath
would almost certainly be revealed in the radiograph, since many oil-based
pigments contain lead and other metals that absorb x rays and cast shadows in
diagnostic radiographs. The x-ray diagnosis of paintings is often used to verify their
authenticity, since many art forgers paint forgeries over paintings on old canvases.
Art conservationists and archaeologists also use a variety of other x-ray imaging
systems originally developed for medical applications. Conventional medical and
industrial radiography only yields 2D information about the interior of objects. The
x-ray CAT scan is a method of capturing 3D x-ray images that has been applied
in some interesting non-medical applications. CAT scanning technology has been
a boon to modern medicine since its invention by Sir Godfrey Hounsfield in 1972.
CAT stands for computer-aided tomography, the process of building an image up
from many small “slices” through an object. The slices are made by measuring the
absorption of a thin beam of x rays projected through the object along a particular
path. The amount of x-ray absorption is a measure of “column density” along
that path. The CAT scan machine measures the column density along thousands
of paths through the body, paths that intersect each other in defined ways. The
computer determines the x-ray density of each intersecting point in space within the