- Is a process whereby some of the x-ray beam is absorbed in the tissue and some passes through (transmits) the anatomic part
- The term differential is used because varying anatomic parts do not absorb the primary beam to the same degree
- Bone absorbs more x-ray than air
DIFFERENTIAL ABSORPTION
Creating a radiographic image by differential absorption requires several processes to occur:
- BEAM ATTENUATION
- ABSORPTION
- TRANSMISSION
- Primary x-ray loses some of its energy (intensity) beam as it passes through anatomic tissue
- Fewer x-ray photons remain in the beam after it interacts with anatomic tissue.
BEAM ATTENUATION
the reduction in the intensity or number of photons in the primary x-ray beam is known as
attenuation
Two distinct processes occur during beam attenuation:
- ABSORPTION
- SCATTERING
- X-ray photons are completely BLANK when the energy of the primary x-ray beam is deposited within the atoms comprising the tissue
- Complete BLANK of the incoming x-ray photon occurs when it has enough energy to remove (eject) an inner-shell electron.
ABSORPTION
The ejected electron is called a BLANK, and it quickly loses energy by interacting with nearby tissues.
photoelectron
responsible for total absorption of the incoming x-ray photon
photoelectric effect
- Happens incoming photons are not absorbed but instead lose energy during interactions with the atoms comprising the tiste
- When a higher kVp (kilovoltage peak) is used, the overall number of x-ray interactions with matter decrease because of increased photon transmission
- The percentage of photoelectric interactions generally decreases at higher kilovoltages within the diagnostic range, whereas the percentage of Compton interactions is likely to increase at higher kilovoltages within the diagnostic range
SCATERRING
controls scatter radiation
grid
total absorption
Photoelectric effect
- Increasing the thickness of a given anatomic tissue increases beam attenuation by either absorption or scattering
- X-rays are exponentially attenuated and are generally reduced by approximately 50% for each 4-5 cm (1.6-2 in) of tissue thickness
More xrays are needed to produce radiographic images for a thicker
anatomic part. - Fewer X-rays are needed to produce a radiographic image for a thinner anatomic part
Tissue Thickness
better to increase this, because of px dose
1 kVp
the compactness of atomic particles comprising the anatomic part, also affects the amount of beam attenuation
Tissue density (matter per unit volume)
- The quality of the X-ray beam or its penetrating ability affects its interaction with anatomic tissue.
- Higher-penetrating X-rays (shorter wavelength with higher frequency) are more likely to be transmitted through anatomic tissue without interacting with the tissues’ atomic structures.
- Lower-penetrating x-rays (longer wavelength with lower frequency) are more likely to interact with the atomic structures and be absorbed
- Lower kVp results in more absorption in the tissue; higher kVp results in more transmission through the tissue
X-ray Beam Quality
