Contrast and dose with molybdenum, molybdenum-rhodium, and rhodium-rhodium target-filter combinations in mammography

Conference · Sat Mar 01 04:00:00 EST 1997

OSTI ID:526031

Gingold, E L; Wu, Xizeng; Barnes, G T ^[1]

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1. 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--
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
56 BIOLOGY AND MEDICINE
APPLIED STUDIES
BIOMEDICAL RADIOGRAPHY
ENERGY SPECTRA
MAMMARY GLANDS
RADIATION DOSES
SIGNAL-TO-NOISE RATIO
X-RAY EQUIPMENT