Fluke Biomedical 18-201 - Manual (Page 6)

Nuclear Associates 18-201 & 18-207
Operators Manual
1-2
3. Place the lead numbers corresponding to the number of the cassette on top of the mesh in the
image area.
4. Select a manual technique (at 28 kVp) that will produce a film density between 0.70 and 0.80 when
measured over the mesh near the chest wall side of the film.
5. The density of the film must be read with a densitometer using an aperture of 2.0 mm in diameter or
larger. The density is read directly over the image of the copper mesh.
6. Expose and process the film.
7. View the films at a distance of at least one meter on a mammographic viewbox. Areas of poor
contact will appear as dark areas in the image of the mesh (See Figure 1-1).
1.5 Problems and Pitfalls
1. It is essential to view the mesh images from at least one meter (3 feet) since the darker areas in the
image indicate poor contact. It is not necessary and extremely difficult to examine the images
closely looking for areas of sharpness.
2. Small pieces of dust or dirt can significantly reduce screen-film contact for distances up to 1 cm or
more away from the dust or dirt speck. If multiple areas of poor contact, about the size of a dime,
are present, thoroughly clean the screens using a screen cleaner recommended by the screen
manufacturer, allow them to dry, and retest the cassette.
3. Poor contact may also be caused by air entrapped between the intensifying screen and the film.
This is especially noticeable if the cassettes are exposed within 5 or 10 minutes after they are
loaded with film.
If this problem is evident, then it will be necessary
to wait at least 15 minutes after loading cassettes
with film for clinical studies in order to obtain
maximum contact. If less than optimum contact is
still evident after waiting 15 minutes, then the
cassette and screens should be replaced.
4. Poor contact can also result from damaged cassettes or screens, insufficient pressure from the
screens on the film, and from deterioration of the screen surface or foam in the cassette. In these
cases, the best solution is to replace the cassettes and screens providing less than optimum
contact.
1.6 Acceptance Limits
Areas of poor contact greater than 1 cm in diameter should not be tolerated. Areas of poor contact on the
chest wall side of the cassette should result in immediate replacement of the cassette and screens. Areas
of poor contact near the edge opposite the chest wall side, or near the two perpendicular edges will
probably not affect clinical images since areas of the breast are seldom, if ever, imaged in these areas.
More than two or three small areas of poor contact, especially in the primary mammographic image areas
of the cassette, should result in replacement of the cassette and screens. Cassettes with large areas of
poor contact should be removed immediately from use (see Section 1.5 regarding entrapped air).
NOTE