Radiation/Imaging Flashcards
Conduction
• Direct transfer of energy through physical contact
Convection
• Indirect transfer of energy through a medium (ex. Heated air)
– Radiation
• Transfer/Emission of energy as electromagnetic waves or moving subatomic particles, especially high-energy particles that cause ionization.
Energy can be transferred from one object to
another in three ways
Conduction
Convection
Radiation
&Electromagnetic (EM) - photons
– Gamma rays
– X-rays
– UV
Particulate
– Alpha (He2+ nucleus)
– Beta (electron or positron)
Electromagnetic Radiation (EM)
• Composed of________
• Varying amounts of energy depending on_________
photons
wavelength (λ) & frequency (ƒ)
Isotopes –
two or more forms of the same element with an equal numbers of protons but different numbers of neutrons in their nuclei
differ in relative____________but not in ________
atomic mass but not in chemical
properties
________emit subatomic particles to decay down
to a stable state
• Unstable,
AS it loses protons, becomes less stable
also lose neutrons
Ex. of alpha decay – atom of Uranium 238
–
Emits an alpha particle (Helium nucleus)
β− decay (electron emission) –
n → p + e- + oῡe
neutron is converted into a proton, an electron, and an
antineutrino
Formula for B- decay
n → p + e- + oῡe
β+ decay (positron emission) –
proton is converted into a neutron, a positron, and a
neutrino
Formula for B+ decay
p → n + e+ + υe
Electron Capture Decay (“K-capture”) Define The neutrino is \_\_\_\_\_\_\_\_From the If the new nucleus is left in an excited state, \_\_\_\_\_\_\_\_will also be emitted formula?
• When an inner shell e- is drawn into the nucleus
and combines with a proton, forming a neutron and
a neutrino.
The neutrino is ejected from the atom’s nucleus.
• If the new nucleus is left in an excited state, gamma
rays (γ) will also be emitted.
p+ + e- → n + υe + γ
Half-Life (t1/2)
• The time it takes for the radioactivity of a specified
isotope to decay to half its original value.
• Example of Half life
• If we start with N0 atoms, after one half-life ½N0
remain.
• After two half-lives, ¼ N0 are left.
• After three half-lives 1/8 N0 are left and so forth.
• After seven half-lives, only (1/2)7 N0 remain.
Scatter Radiation
Occurs as a result of attenuation of the incident
beam to the patient’s body.
Three types of scatter radiation are
Coherent, Compton, Photoelectric
***Coherent scatter
• a.k.a.
“Thompson scatter”
– Occurs when an incident photon collides with an atom.
– The atom momentarily absorbs the energy and moves
into an excited states.
– The atom then releases the same energy as another
photon traveling in a different direction as scatter rad.
***Compton Scatter
Occurs when incident photon collides with outer
orbital e-. The e- is ejected from its orbit. The
photon is deflected from its original path and
continues with decreased energy in a new direction
as a scatter radiation.
*****Photoelectric scatter
• Occurs when an incident photon collides with an
inner shell orbital e-. The e- is ejected. When an
outer orbital e- moves to the inner orbit to fill the
vacated space, the difference in binding energy
between the 2 electron shells is emitted in the form of a new scatter photon.
Ionizing vs. Non-ionizing
• Ionizing radiation carries enough energy to free
electrons from atoms or molecules, thereby ionizing
them.
• Ionization of cell structures, organelles and DNA cause
severe cellular damage.
Penetrating energies are measured in electron volts
eV
- a unit of energy ~ equal to 1.6×10^-19 joules
Alpha particles can be stop by
paper or skin
Beta particles can be pass ______And stop by _____
Human tissue: thin aluminum
Gamma rays particles and xray
thick sheet of iron and lead can stop it
Neutrons
thick wall containing hydrogen can stop
Boundary of ionizing photon energy is
between 10eV and 33 eV in the UV range.
Non ionizing
Radio
Microwave
Infrared
Visible
Ionizing
mid ultraviolet
Xray
Gamma
2 types of cell interactions from ionizing radiation:
– Direct hit
– Indirect hit
• Direct hit:
breakage of a DNA molecule as a result of
being struck directly by EM or Particulate radiation.
• Indirect hit:
H2O breakage into H+ + OH- free radicals,
which then chemically damage DNA.
Cells may mutate and die
Somatic effects
– Short-term
– Long-term (“latent”)
Short term effects
Heme
GI
CNS
Further categorized according to body system
affected:
– Hematologic (dysplastic anemia)
– GI (“radiation sickness” damaged mucosal lining w/ infx)
– CNS (seizures, coma, death)
Short term effects occurs
3 months after exposure
Involve very high doses (
Long-term Effects
• Observed at_______Avg________
5 – 30 years, avg. at 10 – 15 years
• Latent effects of long term low dose ionizing radiation
–
Cataracts (with extensive fluoroscopy)
– Cancer (skin, thyroid, breast & leukemia)
– Shortened Life span
Genetic effects
• Occurs with radiation exposure to reproductive
organs (testes & ovaries)
• Involve mutations to the genes of the reproductive
cells
• Mutations carried over to progeny
Two systems used to measure radiation dose:
conventional and SI units
Conventional units
Roentgen
Rad
Rem
Roentgen (R) is a
unit of Exposure
1 R =
2.58 x 10^-4 C/kg
Rad (rad) is a unit of
• Absorbed Dose =
• Rad stands for “
Absorbed Dose (D)
the amt. of energy per unit mass
absorbed by tissue.
Radiation absorbed dose”
1 roentgen ~ 1Rad
• Corresponding SI unit is the
• 1 Gy = rad
• 1 rad =
of absorbed dose in muscle tissue
Gray (Gy)
100
0.01 Gy
Rem (rem) is a unit of
• Biologic effects of radiation vary according to the_________
• Rem stands for_________
• Corresponding SI unit is the Corresponding SI unit is the
Equivalent Dose (EqD) type of radiation involved. “radiation equivalent man” Sievert Sievert (Sv)
- To calc. occupational dose, a radiation_____________
* WR values are based on
weighting factor (WR) is assigned to each type of radiation. variation of biologic damaged produced by each type of radiation.
Equivalent dose (EqD) is calculated by multiplying absorbed dose by
D x W(r)R = EqD
• Ex. Worker receives 10rads alpha particles and
5rads x-rays. EqD =
• (10rads x 20 = 200) + (5rads x 1 = 5)
1 Sv = _____rem
• 1 rem = ______Sv
100
0.01
Doses are__________ in occupational exposure, devices (dosimeters) are worn to
cumulative
monitor doses received.
______of the common units are typically used
1/1000
Dosimeter “film badges”
- Common types include thermoluminescent-type
(TLD) - optically stimulated luminescence-type (OSL)
ALARA -acronym:
As Low As Reasonably Achievable
3 Factors of ALARA: –TDS
Time – Distance – Shielding
Shielding Equipment:
- Lead aprons
- Thyroid shields
Pb gloves
Leaded glasses
Ionizing Tests: examples
x-rays, CT, nuclear scans
Non-ionizing Tests:
US, MRI
______most common ordered imaging study (second
to________
CXR
dental films
PET – Positron Emission Tomography
• Pt. injected with beta emitter • FDG (fluorodeoxyglucose) • Fluorine -18 tagged to glucose • Sensors detect emissions from pt.
PET/CT
• Combines both tests in one machine, provides
highly detail information of anatomy and cell
physiology in one test.
SPECT scan
• Single-photon emission computed tomography
• Unlike PET/CT, Spect uses gamma emitting
radioisotope (ex. Galium111)
• 3D images for neurologic and cardiac studies
MRI
• Non-ionizing. Magnetic field aligns H2O molecules
• RF disturbs H2O, molecules reorient, sensors record
as image
ECHO 2 types
TEE vs. TTE
TEE Advantages: –
Heart rests on esophagus, only a few mm of tissue vs. chest wall (skin, fat, muscle, bone, lung tissues) – Better visualization of structures
TEE Disadvantages: –
Pt. must be NPO – Takes longer than TTE – Requires sedation or Gen. anesthesia
Ultrasound: Ionizing/nonionizing Transducer contain what? waves reflect? Receiver senses Used in \_\_\_\_\_\_\_\_\_ • For optimal visualization of structures, transducer must be
• Non-ionizing. Uses sound waves to image.
• Transducer contains piezoelectric crystal that
vibrates to generate high freq. sound waves.
• Waves reflect off internal structures.
Receiver senses reflected signal echo.
•Used in regional anesthesia.
manipulated.
Echogenic needles
Common needles used for regional blocks
• Smooth needles (A.) reflect sound energy away
from transducer.
