Chapter 3: Interaction of X-Radiation with Matter Flashcards
Highest energy level of photons in the x-ray beam, equal to the highest voltage established across the x-ray tube
Peak kilovoltage (kvp)
The product of electron tube current and the amount of time in seconds that the xray tube is activated
milliampere- seconds (mAs)
True or False:
No dose is a safe dose
True
controls the quality, or penetrating power, of the photons in the x-ray beam and to some degree also affects the quantity, or number of photons, in the beam.
Peak kilovoltage
If x-rays enter a material such as biologic tissue, they may:
- Interact with the atoms of the biologic material in the patient and be absorbed
- Interact with the atoms in the biologic material and be scattered, causing some indirect transmission
- Pass through without interaction
amount of energy absorbed per unit mass is referred to as the
absorbed dose (D).
what is patient dose
mas
what decreases patient dose
increased kvp and decreased mas
is your current and quantity
mas
is your penetration and quality
kvp
what are carriers of manmade electromagnetic energy
xrays
If an interaction occurs, electromagnetic energy is transferred from the x-rays to the atoms of the patient’s biologic tissue. This process is called
absorption
Selects technical exposure factors that control beam quality and quantity
Is actually responsible for the dose the patient receives during an imaging procedur
RADIOGRAPHER
what gives you the different shades of gray
absorption
what interaction is your absorptoion
photoelectric
True or False
Without absorption and the differences in the absorption properties of various body structures, it would not be possible to produce diagnostically useful images in which different anatomic structures could be perceived and distinguished
True
Reasons tungsten and tungsten rhenium are used as target materials
-high melting points
-high atomic numbers
Target (anode) composition used in general radiograph
Tungsten (a metal)Tungsten rhenium (a metal alloy)
where is xray produced
at the anode
atomic number of tungsten
74
What is produced when a stream of very energetic electrons bombards a positively charged target in a highly evacuated glass tube.
A diagnostic x-ray beam is produced
is the x-ray photon beam that emerges from the x-ray tube and is directed toward the image receptor
primary radiation
atomic number of rhenium
75
As the electrons interact with the atoms of the tube target, what is produced
xray photons are produced
are particles associated with electromagnetic radiation that have neither mass nor electric charge and travel at the speed of light
Photons
exit from the tube target with a broad range, or spectrum, of energies and leave the x-ray tube through a glass window.
xray photons
permits passage of all but the lowest-energy components of the x-ray spectrum. It therefore acts as a filter by removing diagnostically useless, very-low-energy x-rays. In addition to this, a certain thickness of added aluminum is placed within the collimator assembly to intercept the emerging x-rays before they reach the patient.
Glass window
what is the average energy
1/3 of the kvp
as a whole
kvp
individual
kev
In diagnostic radiology, the voltage is expressed in thousands of volts, or:
kilovolts (kv)
because the voltage across the tube fluctuates, it is usally charcterized by :
kilovolt peak value (kvp)
True or False:
Not all photons in a diagnostic xray bean have the same energy
True
True or False :
The most energetic photons in the beam can have no more energy than the electrons that bombard the target
True
Photons that strike the image receptor are called
Transmitted photons
are the photons that have undergone either absorption or scatter and do not strike the image receptor
attenuated photons
X-rays sometimes interact with atoms of a patient such that they give up all of their energy and cease to exist. These photons are said to be
absorbed
Other photons interact with atoms of the patient, but only surrender part of their energy. They will continue to exist but will emerge from the interaction at a different angle (somewhat like a billiard ball colliding with another billiard ball). These photons are said to be
Scattered
Some primary photons will traverse the patient without interacting.
These noninteracting x-ray photons reach the radiographic image receptor (e.g., phosphor plate or digital radiography receptor).
Direct Transmission
Direct and indirect transmission of x-ray photons
When an x-ray beam passes through a patient, it goes through a process called
Attenuation
Other primary photons can undergo Compton and/or coherent interactions and as a result may be scattered or deflected with a potential loss of energy. Such photons may still traverse the patient and strike the image receptor
Indirect Transmission
Decrease in amount of photons reaching IR
Attenuation
are photons that pass through the patient being radiographed and reach the radiographic image receptor
Exit, or image-formation, photons
are photons that have interacted with atoms of the patient’s biologic tissue and have been scattered or absorbed such that they do not reach the radiographic image receptor
Attenuated Photons
are photons that emerge from the x-ray source
Primary, exit, and attenuated photons
which characteristics are non diagnostic
coherent
which characteristics are diagnostic
photoelectric and compton
The two that miss the detector are
classified and attenuated
Coherent scattering is sometimes also called by the following names:
- Classical scattering
- Elastic scattering
- Unmodified scattering
When a low-energy (typically less than 10 keV) photon interacts with an atom, it may transfer its energy by causing some or all of the electrons of the atom to momentarily vibrate. This is analogous to the behavior of electrons in the antenna of a receiver intercepting a radio signal. Because they are charged particles, each of the atom’s now vibrating electrons radiates energy in the form of electromagnetic waves. These waves combine with one another, as multiple water waves would similarly merge, to form a resultant scattered wave, or photon. Because the wavelengths of both incident and scattered waves are the same, no net energy has been absorbed by the atom (see Appendix E). However, a small change in direction for the emitted photon is very likely. In general, this change in direction is less than 20 degrees with respect to the initial direction of the original photon. This is the net effect of coherent, or unmodified, scattering. Although coherent scattering is most likely to occur at less than 10 keV (energies that will be eliminated by the inherent filtration), some of this unmodified scattering occurs throughout the diagnostic energy range and can result in small amounts of radiographic fog (Fig. 3.5). This source of fog, however, is not significant in general diagnostic imaging.
coherent
Interaction of photons with biologic matter is
random
which interaction is diagnostic and therapeutic
Compton
A relatively simple process that results in no loss of energy as x-rays scatter
coherent scattering
It occurs with low-energy photons, typically less than 10 keV
coherent scattering
Because the wavelengths of both incident and scattered waves are the same, no net energy has been absorbed by the atom (see Appendix E in textbook).
Rayleigh and Thompson scattering play essentially no role in radiography
coherent Scattering
come in with same energy, leave with same energy
coherent
-form of scatter
-no loss of energy as xrays scatter
-unmodified
coherent
Diagnostic radiology energy range: 23 to 150 kVp
This is the most important mode of interaction between x-ray photons and the atoms of the patient’s body for producing useful images
Photoelectric Absorption
-Inner shell (kshell)
-Absorption
-biological damage , your pt. dose
-creating photoelectron
-one incoming and one leaving (photon coming in, photoelectron leaving)
Photoelectric Absorption
one incoming and one leaving
photoelectric
what comes in and what leaves in a photoelectric absorption
photon coming in, photoelectron leaving
is an interaction between an x-ray photon and an inner-shell electron (usually in the K or L shells
photoelectric absorption
Discovered by Pierre Victor Auger in 1925
Produces an Auger electron
Is a radiationless effect
Auger Effect
Probability of Occurrence of Photoelectric Absorption
Depends on
Energy (E) of the incident x-ray photons
Atomic number (Z) of the atoms comprising the irradiated object
Probability of Occurrence of Photoelectric Absorption
Increases markedly as the
E of the incident photon decreases
Z of irradiated atom increases
what is brighter and has more absorption, less transmission
bone
what has less absorption and more transmission
soft tissue
tightly packed
density
The less a structure attenuated radiation, the darker or lighter the image will be and vise versa
The less a structure attenuates radiation, the darker the image will be and vice versa
least dense to most
fat, muscle, bone, organs, metal, air
air
fat
muscle
organs
bone
metal
what is the binding number of tungsten
69.5
Compton scattering is also known by the following terms:
- Incoherent scattering
- Inelastic scattering
- Modified scattering
less attenuation, darker or lighter the image
darker the image
1 contrast agent
air
bone higher atomic number ,
more absorption
increase atomic number, increase absorption, what happens to tranmission
decrease
As absorption increases, so does the potential for
biologic damage
true or false
The greater the difference in the amount of photoelectric absorption, the greater the contrast in the radiographic image will be between adjacent structures of differing atomic numbers
true
Responsible for most of the scattered radiation produced during radiologic procedures
Compton
which interaction is your occupational dose
Compton
-occupational dose
-outershell
-modified
-1 incoming, 2 leaving
- decrease contrast
compton
before it loses energy, it can scatter up to
2times
every time xray photon scatters it leaves how much original intensity
0.1 percent
Radiation that has interacted with an atom and traveling in a new direction
scatter
Process: oIncident photon interacts with electrons in the atom and causes excitationoPhoton exits atom with no loss in energy, no ionizatio
coherent scattering
Also called classical scattering, unmodified scatter
Occurs at photon E of less than 10 keV
coherent scattering
Process: oIncident photon interacts with outer shell of the atom oElectron is ejected: termed a “Compton” or “recoil electron”oRemaining energy emitted as a photon (with lower E and longer wavelength) in a new direction; able to exit the patient)
compton
Responsible for the majority of scatter produced – occupational dose (stand at 90-degree angle)
Compton
Process: oIncident photon interacts with inner (K or L) shell of the atom oElectron is ejected: termed a “photoelectron”oVacancy filled with an outer shell electronoResults in a characteristic photon being emitted (very low energy; not able to exit the patie
Photoelectric Effect
Produces the lighter densities on conventional x-ray imagesResults in total absorption of the x-ray photonIncident photon E must be slightly greater than the binding energy of the electronResults in an ionized atomoName of ejected electron is termed a photoelectro
photoelectric effect
As tissue thickness increases what happens to attenuation, absorption, and transmission
Attenuation and absorption would increase as transmission would decrease
As the atomic number increases what happens to the attenuation, absorption and transmission
Attenuation and absorption increases and transmission decreases
As tissue density increases what happens to attenuation, absorption and transmission
Attenuation and absorption increases as transmission decreases
