assessment of bone age; however, during the first months of life, the feet are more
satisfactory for appraisal of bone age because more ossification centers appear at an
earlier age than in the hand. Associated radiographic views will be governed by the
established routine of various clinics. The procedure is always such that comparative
views of two similar areas are taken, that is, both hands, both feet, both forearms, etc.
a. Scanography is a radiographic procedure that provides an accurate
measurement of long bones. It consists of taking radiographs of the joints of long bones
using a special metal ruler taped to the table. This examination is done quite frequently
on children if the physical findings suggest a difference in the length of their extremities.
It may also be used to determine the length of the femur before the insertion of an
intermedullary pin in surgery. The method generally used is spot scanography.
b. In addition to the standard x-ray unit, a special radiopaque rule is needed to
accomplish the examination. The positions in this examination are standard AP
positions of the lower extremities. We will discuss both the use of the ruler and the
importance of the proper position.
4-33. SPOT SCANOGRAPHY
In spot scanography, two "spot" exposures are made at specific points on the
part. The film-object plane is parallel and CR is perpendicular to the film plane. The
part and film remain in the same position during both exposures. The film identification
is "burned-in" after completion of spot exposures. If the part under consideration is of
such length that it overrides the film, the film may be placed diagonally with the long
axis of the part. Measurements are made after the film is processed.
4-34. PRINCIPLES OF SCANOGRAPHY
The radiopaque ruler is a specially constructed ruler. It is evenly graduated,
usually at 1-cm intervals, up to 100 cm. This is a sufficient length to include the long
bones of the lower extremities. Its purpose is to show the magnification of the part in
relation to the ruler. A perpendicular central ray is used to reduce the magnification
caused by divergence of the beam. This provides for an accurate measurement. The
central ray must be restricted to the area of interest; this requires proper collimation.