Molybdenum is also often used as the target material for anodes used in mammography because it has an intermediate atomic number (Z=42) and the produced characteristic x-rays are of energies suited for this purpose. Why do we use molybdenum and graphite for anode? The molybdenum conducts heat from the target.
Why is low kV used in mammography?
Lower kV values are used to enhance contrast but do not provide sufficient penetration through thick or dense breast tissue where the higher kV values are required. When the kV is reduced in a specific examination, the mAs (in the units of mAs) must be increased to produce the necessary receptor exposure.
Which is better target tungsten or molybdenum?
At fat density, tungsten showed slightly better contrast at low kilovoltage (20 kVp), but molybdenum showed progres- sively greater contrast as the kVp increased. At calcium density, molybdenum showed greater contrast at all kVp levels.
Why tungsten is used in mammography?
"Tungsten generates higher energy, which penetrates the breast better, so less radiation is absorbed in the breast and more goes to the imaging plate itself," said Jonny Eser, mammography product manager in the U.S. for Siemens.
What is target material for mammography?
Target. Need material that produces characteristic x-rays with energies of 17-20 keV (20-30 keV for larger breasts) to produce the best contrast. The commonly used material is Molybdenum (characteristic x-rays at 17.5 and 19.6 keV).
Why molybdenum is used in mammography and not tungsten?
In digital mammography, a molybdenum/molybdenum spectrum delivers the lowest dose for a 2 cm breast, but gives the highest dose for thicker breasts. Tungsten/rhodium or rhodium/aluminium spectra provide the lowest doses at greater thicknesses.
Why molybdenum target filter is used now in mammography machine?
Molybdenum is also often used as the target material for anodes used in mammography because it has an intermediate atomic number (Z=42) and the produced characteristic x-rays are of energies suited for this purpose.
Why Beryllium is used as tube port in mammography?
Beryllium is commonly used in mammography (which use low-energy photons) as it provides very little filtration. Other types of x-ray generally use aluminum, copper or tin. Filtration reduces x-ray intensity, but not the maximum energy of the x-ray beam spectrum.
What kVp and MAS is used in mammography?
Screen-film mammography Mammography also uses low x-ray tube voltages, typically 25 kV or so, x-ray tube currents of 100 mA, and exposure times of 1 second or more depending on the thickness of the compressed breast.
Why is tungsten used as anode material?
The anode converts the energy of incident electrons into x-rays dissipating heat as a byproduct. Most x-ray tube anodes are made of tungsten (the target material). Tungsten has a high atomic number (Z=74) and a high melting point of 3370°C with a correspondingly low rate of evaporation.
Which filter is used in mammography?
Commonly used x-ray beam filters are molybdenum (Mo), rhodium (Rh), silver (Ag) and aluminium (Al). The x-ray beam filter material and its thickness vary among current mammography and digital breast tomosynthesis (DBT) systems (Sechopoulos, 2013, Vedantham et al., 2015).
What are the three types of mammography?
In general, there are two main types of mammograms: Digital mammography in 2D. Digital mammography in 3D (digital breast tomosynthesis).
Why is mammogram gold standard?
Mammography remains the gold standard screening technique and offers an effective means to detect breast cancer early. It is noninvasive, relatively inexpensive, and has reasonable sensitivity (72–88%) that increases with age.
Why is tungsten preferred for target material?
Because of its properties such as high atomic number and high melting point (3,422 °C), tungsten is used as the target material in X-ray tubes [1].
Why is tungsten used for the anode target?
Most x-ray tube anodes are made of tungsten (the target material). Tungsten has a high atomic number (Z=74) and a high melting point of 3370°C with a correspondingly low rate of evaporation.
Is tungsten harder than molybdenum?
Molybdenum is a 5th period transition metal. The high-strength, tough and hard metal is a glossy, silvery white. It has the highest melting point of all 5th period elements. While it is a very hard metal, it is softer and more ductile than tungsten.
Is molybdenum similar to tungsten?
Silvery in color and with a brittle texture, molybdenum has a melting point of 4,753.4 degrees, a number exceeded by only five other naturally occurring elements. Like tungsten, molybdenum is classified as a heavy metal, although it has a lower density than tungsten.
Why is mammography important?
Mammography is an X-ray imaging examination of breast tissues, primarily for detecting breast cancers. Breast cancers have both high morbidity and high mortality rates in the female population around the world. By estimate, one in eight women worldwide are affected by breast cancer. Early detection of breast cancer is considered crucial because treatment outcomes are typically better for breast cancers at earlier stages. Mammography plays a key role in the screening of breast cancer among asymptotic women, for the following reasons:
Why do mammographic systems use X-rays?
For example, mammographic systems use X-ray beams of significantly lower energies than do standard X-ray equipment to increase the difference in attenuation between normal and cancerous tissues that would otherwise be too subtle for detection.
What material is used for anode target material?
Molybdenum (Mo) and rhodium (Rh) have long been used as anode target materials in screen-film and digital mammography. Characteristic X-rays, highly dependent on the electron-shell structure of the anode material, account for a large fraction of the X-ray photons produced by the X-ray tube; Mo and Rh both have an electron structure that results in abundant X-ray photons near 20 keV (17.5 and 19.6 keV for Mo, and 20.2 and 22.7 keV for Rh), the desired energy range for breast imaging.
What is the difference between mammography and radiography?
The difference between mammography and radiography in their X-ray beam quality can be seen in differences in their half-value layers (HVLs). HVLs of an X-ray beam, defined as the thickness of a reference material (aluminum is most often used) needed to attenuate the beam intensity by half, are commonly used to characterize its beam quality.
What is added X-ray tube filtration?
Added X-ray tube filtration further shapes the energy spectrum of the X-ray beam by selectively removing undesired X-ray photons with either too high or too low energies. It is often accomplished using materials that have K-edge energies that are slightly above the upper bound of the optimal energies for breast imaging. The K-edge of an element is the energy level at which X-ray photons have just enough energy to knock out atomic electrons on the K-orbit and a substantial increase in X-ray absorption results. Mo, Rh, and Ag are typical elements with suitable K-edge energies for providing added beam filtration for mammography (Figure 4.3). The added filter heavily absorbs both low-energy photons (<15 keV), due to high photoelectric absorption, and high energy ones (above the K-edge), due to dramatically increased absorption beyond the K-edge. The result is selective transmission of X-rays in a narrow band of energies from about 15 keV up to the K-absorption edge of the filter.
What is mammography for women?
Mammography is an X-ray imaging examination of breast tissues, primarily for detecting breast cancers. Breast cancers have both high morbidity and high mortality rates in the female population around the world. By estimate, one in eight women worldwide are affected by breast cancer. Early detection of breast cancer is considered crucial because treatment outcomes are typically better for breast cancers at earlier stages. Mammography plays a key role in the screening of breast cancer among asymptotic women, for the following reasons: 1 Mammography excels at detecting certain early signs of breast cancer, including microcalcifications, speculated masses, and distorted tissues. 2 Mammography demonstrates both high sensitivity and high specificity of cancer detection by clinical studies. 3 Mammography poses minimal risk to the subject with very low radiation dose. 4 Mammography is cost-effective and supports high throughput among a large population.
What is the energy level of X-rays?
At X-ray energies of 40 keV or higher (the mean energy level standard radiography uses), the difference between the two types of tissues becomes too subtle to detect; so low-energy X-rays are preferred.
What is the purpose of film in mammography?
With film based mammography, film serves as the media for recording within the receptor, transporting and storing images, and is the image display device . The significant characteristic is that the contrast of the image is "fixed" and cannot be changed after the film is exposed and chemically processed.
What are the large objects that are visible in mammography?
The large objects (masses, fibers, or specks ) will always be visible, even under inferior imaging conditions. A mammography system and a specific imaging protocol is evaluated by imaging the phantom and then counting the number of objects of each type that are visible.
What is the optimum photon energy for mammography?
The optimum photon energy (spectrum) for mammography depends on the size and density of the breast. With a thin compressed breast that is relatively easy to penetrate the optimum energy for the best contrast to dose relationship is relatively low as shown here.
What is the K edge principle of mammography?
The filters used in mammography are based on the "k edge" principle and attenuate or block the radiation above the k-edge energy of the specific filter material, either molybdenum or rhodium as illustrated in more detail later. 14. The Molybdenum Spectrum.
What material produces characteristic radiation?
It varies with the atomic number (Z) of the material. Molybdenum, and in some cases, rhodium, are materials that produce characteristic x-radiation that is near the optimum energy for mammography.
What is the requirement for mammography?
A major requirement for effective mammography is high contrast sensitivity . As illustrated here, contrast sensitivity is the characteristic of an imaging process that determines the visibility of objects in the body that have low physical contrast. That is the challenge we have in mammography.
What is the importance of compression in mammography?
Potential benefits derived from compression include: A more uniform breast thickness resulting in a better fit of the exposure into the film latitude or dynamic range.
Why is mammography green sensitive?
Mammography film is green sensitive to match the spectral characteristics of the green emitting screen. An object measures 9 cm on the film when a source-to-image distance of 60 inches is used. It is know that the object is 5 inches from the film.
Where should the radiographic intensifying screen be on a film?
a. The radiographic intensifying screen should be on the x-ray tube side of the film.
What are the units used in MRI?
The standardized units for tissue measurement in MRI are the Hounsfield units.
Can breast radiation double?
Radiation to the breast can double during magnification radiography.
