a. Place the radiographic film on the illuminator.

In the tomogram, the image on the long diagonal wire will appear as two

blurred triangles. The apex of each triangle will appear in sharp focus at the

level of cut.

b. Reconstruct the outline of the triangles on the film using a marking pencil and

ruler.

c. Select one triangle.

d. Draw a baseline to the triangle using the reference scale as a guide.

e. Determine the distance from the apex of the triangle to the drawn base using

scale markings.

f. Record the information on the data form.

g. Measure the width of the reconstructed triangle at the drawn baseline using a

centimeter ruler.

h. Record the information on the data form.

i. Call the distance from the apex to baseline, b. Call the baseline width, c.

j. Calculate the tomographic exposure angle using the appropriate formula and

chart.

The tomographic exposure angle, A, is then given by the relationship A = 2

tan (c/2b). Calculate the quantity (c/2b) and with the aid of the figure below

determine the value tan (c/2b) that corresponds to this quantity. Tan (c/2b)

corresponds to 1/2 the tomographic exposure angle A when the value of C is

used in the calculation and to the tomographic half angles A and A where C

and C are used in the calculation respectively.

The exposure angle should also be evaluated for symmetry about the midline

of the exposure. This may be done by constructing a perpendicular line for

the baseline of the reconstructed triangle through the apex of the triangle and

calculating the exposure half angles as:

A = 2 tan (c /2b) and A = 2 tan (C /2b)

where C and C are defined on the film.

MD0062

6-7