Table VIII.7. Mammography X-Ray Beam-Quality Parameters
Beam
Code |
Tube
Voltage
(kV) |
Added
Filter
(mm) |
Half-Value
Layer
(mm Al) |
Homogeneity
Coefficient
(Al) |
| Mo Anode |
| Mo/Mo23 |
23 |
0.032 Mo |
0.271 |
0.702 |
| Mo/Mo25 |
25 |
0.032 Mo |
0.296 |
0.719 |
| Mo/Mo28 |
28 |
0.032 Mo |
0.332 |
0.743 |
| Mo/Mo30 |
30 |
0.032 Mo |
0.351 |
0.752 |
| Mo/Mo35 |
35 |
0.032 Mo |
0.392 |
0.784 |
| Mo/Rh28 |
28 |
0.029 Rh |
0.408 |
0.796 |
| Mo/Rh32 |
32 |
0.029 Rh |
0.445 |
0.821 |
| Mo/Mo25x |
25 |
0.030 Mo + 2.0 Al |
0.566 |
0.91 |
| Mo/Mo28x |
28 |
0.030 Mo + 2.0 Al |
0.626 |
0.964 |
| Mo/Mo30x |
30 |
0.030 Mo + 2.0 Al |
0.660 |
0.947 |
| Mo/Mo35x |
35 |
0.030 Mo + 2.0 Al |
0.748 |
0.902 |
| Rh Anode |
| Rh/Rh25 |
25 |
0.029 Rh |
0.351 |
0.755 |
| Rh/Rh30 |
30 |
0.029 Rh |
0.438 |
0.812 |
| Rh/Rh35 |
35 |
0.029 Rh |
0.512 |
0.858 |
| Rh/Rh40 |
40 |
0.029 Rh |
0.559 |
0.895 |
| Rh/Rh30x |
30 |
0.029 Rh + 2.0 Al |
0.814 |
0.964 |
| Rh/Rh35x |
35 |
0.029 Rh + 2.0 Al |
0.898 |
0.945 |
The beam codes are a combination of the chemical symbol of the anode and the
filter, respectively, followed by the constant potential in kilovolts. The
letter "x" ends the beam codes which denote "exit" beams. The exit
beam qualities, which are intended to represent the transmission of the x-rays
through the breast, are generated by an additional filtration of 2.0 mm
of aluminum.
The inherent filtration is 1 mm Be for all beam qualties. The calibration
distance is 1 m. The half-value layers were determined through direct
measurements with the primary standard free-air ionization chamber. The air
kerma rates for the entrance beams are between 0.5 mGy/s, and less than
0.2 mGy/s for the exit beams.
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Inquiries or comments:
michelle.obrien@nist.gov
(301) 975-2014
Online: July 1996 - Reviewed: June 2003
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