Contrast and dose with molybdenum, molybdenum-rhodium, and rhodium-rhodium target-filter combinations in mammography
- Univ. of Alabama, Birmingham, AL (United States)
Molybdenum target-molybdenum filter (Mo-Mo) source assemblies are commonly used for screen-film mammography and produce spectra rich in bremsstrahlung between 15 and 20 keV, and molybdenum characteristic x-rays (K{sub {alpha}} = 17.5 keV and K{sub {beta}} = 19.6 keV) that are, optimal for imaging a large segment of patients. With the normal variability of breast size and tissue composition that occurs in the population, Mo-Mo spectra are not always optimal, however. Particularly for thick, fibroglandular breast tissue, higher energy spectra are required, and are achieved to a limited degree by operating Mo-Mo tubes at higher tube potentials. At these higher tube potentials (28-31 kVp), the spectrum exiting the breast has a large contribution from bremsstrahlung of more than 23 keV. Most of the lower energy photons, including the molybdenum characteristic x-rays, are absorbed and result in a higher average tissue dose than is necessary. Incident spectra with x-ray energies in the 20-23 keV range are preferable. Such spectra have been realized with higher atomic number materials, such as rhodium (Rh), used for the anode or k-edge filter. The higher K-absorption edge of rhodium allows transmission of bremsstrahlung in the 20-23.2 keV range, and at a given kilovoltage the Rh-Rh combination results in a more penetrating beam than either Mo-Mo or Mo-Rh (molybdenum x-ray tube anode with rhodium K-edge filter) because of the difference in energy between the rhodium and molybdenum characteristic x-rays. The greater penetrating power of these spectra results in decreased entrance skin exposure and average glandular dose to the breast than with the conventional Mo-Mo spectra. However, associated with this can be a reduction in subject contrast in the mammogram. The objective of this study was to compare the contrast and dose produced with the three source assemblies as a function of x-ray tube potential, breast thickness, and breast parenchymal composition.
- Research Organization:
- National Council on Radiation Protection and Measurements, Bethesda, MD (United States)
- OSTI ID:
- 526031
- Report Number(s):
- CONF-960405-; TRN: 98:008256
- Resource Relation:
- Conference: 32. annual meeting of the National Council on Radiation Protection and Measurements, Arlington, VA (United States), 3-4 Apr 1996; Other Information: PBD: 1 Mar 1997; Related Information: Is Part Of Implications of new data on radiation cancer risk. Proceedings No. 18; Boice, J.D. Jr. [ed.]; PB: 320 p.
- Country of Publication:
- United States
- Language:
- English
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