Table of Contents
What is anode heel effect?
The anode heel effect in radiography is a well-described physical phenomenon,1,2 whereby radiation intensity varies along the anodeecathode axis of the X-ray tube, decreasing towards the anode. Photons emitted towards the tube’s anode side are attenu- ated more than those emitted towards the cathode.
Why tungsten is not used in mammography?
Tungsten anode x-ray tubes and aluminum filtration, the standard for all other types of radiography, is not used for mammography….
| Imaging Objectives | Rhodium Anode | Blurring and Visibility of Detail |
|---|---|---|
| Imaging Technique Factors | Film Contrast Transfer | Mean Glandular Dose |
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?
No substantial difference in contrast was seen between molybdenum and tungsten in the soft-tissue density. At fat density, tungsten showed slightly better contrast at low kilovoltage (20 kVp), but molybdenum showed progressively greater contrast as the kVp increased.
How do you overcome the anode heel effect?
Factors
- anode angle: by increasing the angle, the amount of target material perpendicular to the anode is decreased resulting in less resorption of x-rays produced.
- target-to-film distance: increase in distance reduces heel effect by allowing more divergence of the beam which produces a more uniform image.
How does the anode heel effect benefit the radiographer or radiologist?
Introduction: The anode heel effect can be used to optimize image quality and/or patient dose in digital radiography (DR). In film-screen radiography, the effect can equalize optical density in regions of varying attenuation.
What is the target material for mammograms?
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.
What kVp and mAs is used in mammography?
Variation of four mammography imaging parameters (mAs, time, HVL and AGD) with x-ray tube potential (25 and 28 kVp).
What is K edge in mammography?
The K-absorption edge (K-edge) refers to the abrupt increase in the photoelectric absorption of x-ray photons observed at an energy level just beyond the binding energy of the k-shell electrons of the absorbing atom.
What is AEC in mammography?
An automatic exposure control (AEC) is proposed for a scanning full field digital mammography system. It uses information from the leading part of the detector to vary the scan velocity dynamically, thus creating a nonuniform x-ray field in the scan direction.
How many protons does tungsten have?
74Tungsten / Atomic number
Tungsten contains exactly 74 protons in its nuclear makeup. This number of protons is unique to Tungsten as no other element shares this amount of protons. For this reason, tungsten has an atomic number or proton number of 74. An atom will have the same amount of electrons as it does protons.
What increases the anode heel effect?
anode angle: by increasing the angle, the amount of target material perpendicular to the anode is decreased resulting in less resorption of x-rays produced. target-to-film distance: increase in distance reduces heel effect by allowing more divergence of the beam which produces a more uniform image.
What is the visibility of anatomy and pathology in mammography?
Visibility of anatomy and pathology, the primary objective of mammography, can be affected by each of these individual characteristics, but in very different ways. The design of equipment, imaging protocols and techniques, and quality assurance procedures generally address each of these characteristics on an individual basis.
What is the perfect X-ray spectrum for mammography?
The ideal or “perfect” x-ray spectrum for mammography would be made up of photons all having the same energy (mono-energetic) and with the ability to adjust the energy for different breast conditions. That is represented by the vertical line shown here positioned at the optimum energy for this particular breast.
How does a compressed breast affect the exposure of a mammogram?
With the compressed breast and the resulting more uniform thickness, the range of exposure (exposure histogram) is reduced and hopefully will fit within the film latitude (dynamic range). Most mammograms are made using Automatic Exposure Control (AEC).
How is a mammography system evaluated for specific imaging protocols?
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. In this illustration (on the left) we see a diagram of the phantom interior showing the various objects that are included.