Transcript Interactions of X-rays with matter

Patient Interactions
2011
FINAL
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Patient Interactions
1. ______________
2. ______________
3. ______________
4. ______________
5. ______________
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Interaction in the body
begin at the atomic
level
1. _______________
2. _______________
3. _______________
4. _______________
5. _______________
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X-ray photons can change
cells
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Some radiations are energetic enough to
rearrange atoms in materials through which
they pass, and can therefore he hazardous to
living tissue.
1913
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EM Interactions with Matter
General interactions with matter include:
1. ______________
– With or without partial absorption
2. ______________
– Full attenuation
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Interactions of X-rays with matter
1. ________________:
X-ray passes
completely and get
to film
2. ________________:
no x-rays get to film
3. ________________
________________
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Photoelectric effect
1.
Low energy (low kVp) x-ray photon ejects inner shell
electron (energy absorbed)
2.
Leaving an orbital vacancy. As vacancy is filled a
photon is produced
3.
More likely to occur in absorbers of high atomic
number (eg, bone, positive contrast media)
4.
Contributes significantly to patient dose,
5.
As all the photon energy is absorbed by the patient
(and for the latter reason, is responsible for the
production of short-scale contrast).
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FIG. 9–3 Photoelectric absorption interaction.
(Modified from Carlton RC, Adler AM: Principles of radiographic imaging, an art and a science, ed 4, Thomson Delmar Learning,
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2006, Albany, NY. Reprinted with permission of Delmar Learning, a division of Thomson Learning: http://www.thomsonrights.com. Fax
800-730-2215.)
CASCADE
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• PHOTOELECTRIC
ABSORBTION
IS WHAT GIVES US
THE CONTRAST
ON THE FILM
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CLASSICAL SCATTER IN
PATIENT
8 p+ + 8e- = neutral atom
1. Incoming
photons form
tube
2. Pass by the
electrons in
the patient
3. Do not
interact with
e–
4. Causes them
to vibratereleasing
small
amounts of
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heat
Classical
(Coherent) Scattering
1.
Excitation of the total
complement of atomic
electrons occurs as a
result of interaction with
the incident photon
2.
No ionization takes place
3.
Electrons in shells
“vibrate”
4.
Small heat is released
5.
The photon is scattered in
different directions
6.
Energies below 10K keV
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FIG. 9–2 Classic coherent scatter interaction.
(Modified from Carlton RC, Adler AM: Principles of radiographic imaging, an art and a science, ed 4, Thomson Delmar Learning,
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2006, Albany, NY. Reprinted with permission of Delmar Learning, a division of Thomson Learning: http://www.thomsonrights.com. Fax
800-730-2215.)
Compton scatter
1. High energy (high kVp) x-ray photon ejects an
outer shell electron.
2. Energy is divided between scattered photon
and the compton electron (ejected e-)
3. Scattered photon has sufficient energy to exit
body.
4. Since the scattered photon exits the body, it
does not pose a radiation hazard to the
patient.
5. Can increase film fog (reduces contrast)
6. Radiation hazard to personnel
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FIG. 9–4 Compton scatter interaction.
(Modified from Carlton RC, Adler AM: Principles of radiographic imaging, an art and a science, ed 4, Thomson Delmar Learning,
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2006, Albany, NY. Reprinted with permission of Delmar Learning, a division of Thomson Learning: http://www.thomsonrights.com. Fax
800-730-2215.)
COMPTON
SCATTERING
1. ______ shell
electron in
body
2. Interacts with
x-ray photon
from the
_________
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During Fluoro – the patient is the
largest scattering object
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XXXXX
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Differential Absorbtion
•
Results from the differences between xrays being absorbed and those
transmitted to the image receptor
1. ____________________________
2. ____________________________
3. ____________________________
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Compton and Differential
Absorbtion
1. Provides ____ useful info to the image
2. Produces image ________
•
•
dulling of the image
NOT representing ___________ information
3. At ____________ energies
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Photoelectric and Differential
Absorbtion
1. Provides _________________ information
2. X-rays do not reach film because they are
__________________
3. ______ energies (more differential absorbtion)
4. Gives us the ______________ on our image
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No interactions with Image
Receptor and Differential
Absorbtion
1.
2.
3.
4.
5.
No interaction
Usually ____________ kVp
Goes ______________ body
Hits ____________ ________________
Usually represents areas of __________
•
_____atomic numbers
6. Results in __________ areas on the film
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1. The probability of radiation interaction is a
function of tissue electron density, tissue
thickness, and X-ray energy (kVp).
2. Dense material like bone and contrast dye
attenuates more X-rays from the beam than
less dense material (muscle, fat, air).
3. The differential rate of attenuation provides
the contrast necessary to form an image.
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FIG. 9–5 Pair production interaction.
(Modified from Carlton RC, Adler AM: Principles of radiographic imaging, an art and a science, ed 4, Thomson Delmar Learning,
30
2006, Albany, NY. Reprinted with permission of Delmar Learning, a division of Thomson Learning: http://www.thomsonrights.com. Fax
800-730-2215.)
FIG. 9–6 Photodisintegration interaction.
(Modified from Carlton RC, Adler AM: Principles of radiographic imaging, an art and a science, ed 4, Thomson Delmar Learning,
31
2006, Albany, NY. Reprinted with permission of Delmar Learning, a division of Thomson Learning: http://www.thomsonrights.com. Fax
800-730-2215.)
Remember….
When reviewing diagrams
What is coming in (e or photon?
Where is it occurring (the tube or body?)
Keep practicing – you will get it
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