Interaction of Radiation and Matter - Chapter 3
17 July 2008
Chapter 3 Lecture Objectives
Describe the various ways xx-rays interact with and are
attenuated in matter
Describe the energy dependence of these interactions
Describe and calculate the various quantitative
parameters used to characterize x-ray attenuation
Differentiate between radiographic exposure absorbed
dose and equivalent dose as well as use of correct
radiological units
Interaction of Radiation and Matter Chapter 3
Brent K. Stewart, PhD, DABMP
Professor, Radiology and Medical Education
Director, Diagnostic Physics
a copy of this lecture may be found at:
http://courses.washington.edu/radxphys/PhysicsCourse.html
UW and Brent K. Stewart PhD, DABMP
Cartoon of the Day
UW and Brent K. Stewart PhD, DABMP
Excitation, Ionization and Radiative Losses
Energetic charged particles
interact via electrical forces
Lose KE through excitation,
ionization and radiative losses
Excitation: imparted E < Eb
emits
(char. xx-ray) or
Auger e- (de(de-excitation)
Ionization: imparted E > Eb
sometimes e- with enough KE
to produce further ionizations
(secondary ionizations)
Such e- are called delta rays
rays
Approx. 70% of e- E deposition
leads to nonnon-ionizing excitation
c.f. www.physics.utah.edu/~mohit/Physics_Cartoons.html.
www.physics.utah.edu/~mohit/Physics_Cartoons.html. UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.32.
UW and Brent K. Stewart PhD, DABMP
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Charged Particle Tracks
Linear Energy Transfer (LET)
e- follow a tortuous path through matter as the result of multiple
Coulombic scattering processes
2+
An
, due to it
its higher mass follows a more linear trajectory
Path length = actual distance the particle travels in matter
Range = effective linear penetration depth of the particle in matter
matter
Range path length
Amount of energy deposited per unit length (eV/cm)
LET q2/KE
Describes the energy deposition density which largely
determines the biologic consequence of radiation
exposure
2+
High LET radiation:
, p+, and other heavy ions
Low LET radiation:
-
Electrons (e-, - and +)
radiation (x(x-rays or -rays)
High LET >> damaging than low LET radiation
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.34.
UW and Brent K. Stewart PhD, DABMP
Radiative Interactions - Bremsstrahlung
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
Neutron Interactions and Scattering
Neutrons: no external charge
no excitation or ionization
2+
Can interact with nuclei to eject charged particles (e.g., p+ or
)
+
In tissue (or water) neutrons eject p (recoil protons)
Scattering: deflection of particle or photon from original trajectory
trajectory
Elastic: scattering event in which the total KE is unchanged
Inelastic: scattering event with a loss of KE
Deceleration of an e- around a
nucleus causes it to emit
radiation or bremsstrahlung
(G.): breaking radiation
radiation
Probability of bremsstrahlung
emission Z2
Ratio of e- energy loss due to
bremsstrahlung vs. excitation
and ionization =
KE[MeV]
KE[MeV]Z/820
Thus, for an 100 keV e- and
tungsten (Z=74) 1%
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.35.
UW and Brent K. Stewart PhD, DABMP
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.36.
UW and Brent K. Stewart PhD, DABMP
Interaction of Radiation and Matter - Chapter 3
17 July 2008
X-ray Interactions with Matter
Classical (Rayleigh or elastic) Scattering
Excitation of the total
complement of atomic
electrons occurs as a result of
interaction with the incident
photon
No ionization takes place
The photon is scattered (re(reemitted) in a range of different
directions, but close to that of
the incident photon
No loss of E
Relatively infrequent
probability 5%
There are several means of xx-rays and gamma rays
being absorbed or scattered by matter
Four major interactions are of importance to diagnostic
radiology and nuclear medicine, each characterized by a
probability (or crosscross-section
section) of interaction
Classical (Rayleigh or elastic) scattering
Compton scattering
Photoelectric effect
Pair production
UW and Brent K. Stewart PhD, DABMP
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.37.
Compton Scattering
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
10
Compton Scattering
Dominant interaction of xx-rays
with soft tissue in the
diagnostic range and beyond
(approx. 30 keV - 30MeV)
Occurs between the photon
and a free
free e (outer shell e
considered free when E >>
binding energy, Eb of the e )
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.38.
UW and Brent K. Stewart PhD, DABMP
Encounter results in ionization
of the atom and probabilistic
distribution of the incident
photon E to that of the
scattered photon E and the
ejected e E
A probabilistic distribution
determines the angle of
deflection ( )
Original photon deflected
deflected
decreased subject contrast
11
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.38.
UW and Brent K. Stewart PhD, DABMP
12
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Compton Scattering (2)
Compton Scattering (3)
Esc as a function of E0 and angle ( ) Excel spreadsheet
Compton interaction probability is dependent on the total
3
no. of e in the absorber vol. (e
(e /cm = e /gm density)
1
With the exception of H, e /gm is fairly constant for
organic materials (Z/A 0.5), thus the probability of
Compton interaction proportional to material density ( )
Conservation of energy and momentum yield the
following equations:
Eo = Esc + Ee-
Esc =
E0
E0
1+
1- cos
m ec 2
, where mec2 = 511 keV
UW and Brent K. Stewart PhD, DABMP
13
Compton Scattering (4)
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
14
Compton Scattering (3)
Esc as a function of E0 and angle ( ) Excel spreadsheet
As incident E0 both photon
and e scattered in more
forward direction
At a given , the fraction of E
transferred to the scattered
photon decreases with E0
For high energy photons most
of the energy is transferred to
the electron
At diagnostic energies most
energy to the scattered photon
o
Max E to e at = 180 ; max E
scattered photon is 511 keV at
o
= 90
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.39.
UW and Brent K. Stewart PhD, DABMP
15
UW and Brent K. Stewart PhD, DABMP
16
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Photoelectric Effect
Photoelectric Effect (2)
Interaction of incident photon with inner shell e All E transferred to e (ejected photoelectron) as kinetic energy (Ee)
less the binding energy: Ee = E0 Eb
Empty shell immediately filled with e from outer orbitals resulting in
the emission of characteristic xx-rays (E = differences in Eb of
orbitals), for example, Iodine: EK = 34 keV, EL = 5 keV, EM = 0.6 keV
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.41.
UW and Brent K. Stewart PhD, DABMP
PhotoPhoto-e and cation
2
Rem.: Eb Z ; characteristic xx-rays and/or Auger e
3 3
Probability of photophoto-e absorption Z /E (Z = atomic no.)
Due to the absorption of the incident xx-ray without
scatter, maximum subject contrast arises with a photophoto-e
effect interaction
Explains why contrast as higher energy xx-rays are
used in the imaging process
Increased probability of photophoto-e absorption just above
the Eb of the inner shells cause discontinuities in the
attenuation profiles (e.g., K-edge)
edge)
17
Photoelectric Effect (3)
UW and Brent K. Stewart PhD, DABMP
18
Photoelectric Effect (4)
Edges become significant factors for higher Z materials
as the Eb are in the diagnostic energy range:
Contrast agents barium (Ba, Z=56) and iodine (I, Z=53)
Rare earth materials used for intensifying screens lanthanum
(La, Z=57) and gadolinium (Gd, Z=64)
Computed radiography (CR) and digital radiography (DR)
acquisition europium (Eu, Z=63) and cesium (Cs, Z=55)
Increased absorption probabilities improve subject contrast and
quantum detective efficiency
At photon E << 50 keV, the photoelectric effect plays an
important role in imaging soft tissue, amplifying small
differences in tissues of slightly different Z, thus
improving subject contrast (e.g., in mammography)
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.26.
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
19
UW and Brent K. Stewart PhD, DABMP
20
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Pair Production
Conversion of mass to E occurs upon the interaction of a high E
photon (> 1.02 MeV; rest mass of e- = 511 keV) in the vicinity of a
heavy nucleus
+
Creates a negatron ( ) - positron ( ) pair
+
The
annihilates with an e to create two 511 keV photons
o
separated at an of 180
c.f. http://www.ktfhttp://www.ktf-split.hr/periodni/en/index.html
UW and Brent K. Stewart PhD, DABMP
21
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.44.
You couldn
couldnt hit the broad side of a barn!
barn!
Cross Section Illustration
During wartime research on
the atomic bomb, American
physicists bouncing neutrons
off 235U nuclei described it as
big as a barn and adopted
the name barn for a unit equal
to 10-24 cm2, about the cross
section of the uranium nucleus
The Barn is a very large unit;
for most nuclear processes it is
so large that a target with a
cross section equal to a Barn
would be as easy to hit as the
broad side of a barn.
c.f. http://ed.fnal.gov/painless/pdfs/cross.pdf
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
22
UW and Brent K. Stewart PhD, DABMP
Na
Cs
Na
Cs
Na
Cs
Na
Cs
Na
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
Cs
Na
Cs
Na
Cs
Na
Cs
Na
Cs
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
Na
185.8 pm
Na
Cs
Na
Cs
Na
Cs
Na
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
Cs
Na
Cs
Na
Cs
Na
Cs
Na
Cs
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
Na
185.8 pm
23
Cs
265.5 pm
Cs
Na
Cs
Na
Cs
Na
Cs
Na
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
265.5 pm
185.8 pm
UW and Brent K. Stewart PhD, DABMP
24
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Linear Attenuation Coefficient
Attenuation of an XX-ray Beam
Cross section is a measure of the probability (
(apparent
-24
2
area
area) of interaction: (E) measured in barns (10 cm )
Interaction probability may also be related to the effect of
traversing a thickness of material
linear attenuation
-1
coefficient: (E) [cm ] = Z [e
[e /atom] Navg [atoms/mole]
3
2 1/A [moles/gm] [gm/cm ] (E) [cm /e ]
(E) as E , e.g., for soft tissue
-1
n = - x n (n = # photons)
Photon flux, or intensity (I)
(photons/cm2-sec): n/cm2-sec
I=- xI
= - ( I/I)/ x
I/I = - x
Integrating both sides:*
n(I) n(I0) = - (x(x-x0) = - x
n(I/I0) = - x
Applying the Napier e
constant of each side:
I/I0 = e- x; I = I0 e- x
-1
(30 keV) = 0.35 cm-1 and (100 keV) = 0.16 cm-1
(E) = fractional number of photons removed
(attenuated) from the beam by absorption or scattering
Multiply by 100% to get % removed from the beam/cm
*For more info on the natural logarithm function ( n), see - http://en.wikipedia.org/wiki/Natural_logarithm
UW and Brent K. Stewart PhD, DABMP
25
Linear Attenuation Coefficient (2)
c.f. Wolbarst. Physics of Radiology, p. 108.
UW and Brent K. Stewart PhD, DABMP
26
Linear Attenuation Coefficient (3)
An exponential relationship between the incident
radiation intensity (I0) and the transmitted intensity (I)
with respect to thickness:
- (E)x
I(E) = I0(E) e (E) (e: Napier
Napiers const., intro. logarithms)*
total(E) = PE(E) + CS(E) + RS(E) + PP(E)
3 3
At low xx-ray E:
E: PE(E) dominates and (E) Z /E
At high xx-ray E:
E: CS(E) dominates and (E)
Only at veryvery-high E (> 1MeV) does PP(E) contribute
The value of (E) is dependent on the phase state:
water vapor << ice < water
*For more info on the Napier constant e, see - http://en.wikipedia.org/wiki/E_%28mathematical_constant%29
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
27
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.46.
UW and Brent K. Stewart PhD, DABMP
28
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Mass Attenuation Coefficient
Linear and Mass Attenuation Coefficients
Mass attenuation coefficient
2
m(E) [cm /g] normalization
for : m(E) = (E)/
Independent of phase state ( )
and represents the fractional
number of photons attenuated
per gram of material
- (E) x
I(E) = I0(E) e m(E)
Represent thickness
thickness as g/cm2
- the effective thickness of 1
cm2 of material weighing a
specified amount ( x)
125 kVp Radiograph of
Scotch on the rocks
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.47.
UW and Brent K. Stewart PhD, DABMP
29
Effective Atomic Number (Zeff)
Z eff
a1Z1m
UW and Brent K Stewart, PhD, DABMP
30
Thickness of material required to reduce the intensity of
the incident beam by
- (E)HVL
= e (E)
or HVL = 0.693/ (E)
Units of HVL expressed in mm Al for a Dx xx-ray beam
For a monoenergetic incident photon beam (i.e., that
from a synchrotron), the HVL is easily calculated
Remember for any function where dN/dx N which
upon integrating provides an exponential function (e.g.,
I(E) = I0(E) ekw ), the doubling (or halving) value of w
is given by 69.3%/k% (e.g., 7% CD doubles in ~10 yrs)
For each HVL, I by : 5 HVL
I/I0 = 100%/32 = 3.1%
a2 Z 2 m ... an Z n m , m 3
UW and Brent K. Stewart PhD, DABMP
UW and Brent K. Stewart PhD, DABMP
Half Value Layer
ai fractional e-/gr belonging to each atomic material Zi
c.f. Johns, et al. The Physics of Radiology,
4th ed., p.142.
c.f. Wolbarst. Physics of Radiology, pp. 108, 110.
31
UW and Brent K. Stewart PhD, DABMP
32
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Homogeneity Coefficient and Effective Energy
Mean Free Path and Beam Hardening
The effective (avg.) E of an xx-ray beam is to the peak value
(kVp) and gives rise to an eff, the (E) that would be measured if
the xx-ray beam were monoenergetic at the effective E
Homogeneity coefficient = 1st HVL/2nd HVL
Mean free path (avg. path length of xx-ray) = 1/ = HVL/0.693
Beam hardening
The Bremsstrahlung process produces a wide spectrum of energies,
resulting in a polyenergetic (polychromatic) xx-ray beam
As lower E photons have a greater attenuation coefficient, they are
preferentially removed from the beam
Thus the mean energy of the resulting beam is shifted to higher E
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 1st ed., p.281.
UW and Brent K. Stewart PhD, DABMP
A summary description of the xx-ray beam polychromaticity
HVL1 < HVL2 < HVLn; so the homogeneity coefficient < 1
33
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.45.
UW and Brent K. Stewart PhD, DABMP
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.43.
Raphex 2000 Question: Inter. Rad. & Matter
Raphex 2000 Question: Inter. Rad. & Matter
D1.
D1. In comparison to 20 keV photons, the probability of
photoelectric interaction in bone at 60 keV is
approximately:
D2.
D2. Compared with an iodine IVP exam, a barium exam
produces better contrast resolution because:
A. The mass attenuation coefficient of barium is much greater
than that of iodine.
B. The KK-edge of barium is much greater than the KK-edge of
iodine.
C. The diameter of the bowel is bigger than the diameter of the
ureter.
D. The atomic number of barium is significantly greater than the
atomic number of iodine.
E. A higher concentration of barium can be achieved than with
iodine.
- (E)x
- (E) x
Remember: I(E) = I0(E) e (E) = I0(E) e m(E)
A. 27 times as great.
B. 3 times as great.
C. The same.
D. 3 times less.
E. 27 times less.
remember:
(60)/
(60)/ (20)
Z3/E3
3
3
3
(Z/60) /(Z/20) = (20/60) = (1/3) = 1/27
PE(E)
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
34
35
UW and Brent K. Stewart PhD, DABMP
36
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Raphex 2001 Question: Inter. Rad. & Matter
Raphex 2000 Question: Inter. Rad. & Matter
D3. Carbon dioxide can be used as an angiographic
contrast medium because:
G50.
G50. If the linear attenuation coefficient is 0.05 cm-1, the
HVL is:
A. The K absorption edges of CO2 are significantly higher than
tissue.
B. The K absorption edges of CO2 are significantly lower than
tissue.
C. The linear attenuation coefficient of CO2 is significantly higher
than tissue.
D. The linear attenuation coefficient of CO2 is significantly lower
than tissue.
E. Of differences between the mass attenuation coefficients.
- (E)
(E)x
Remember: I(E) = I0(E) e-
= I0(E) e-
A. 0.0347 cm
B. 0.05 cm
C. 0.693 cm
D. 1.386 cm
E. 13.86 cm
HVL = 0.693/ = 0.693/0.05 cm-1
0.7 x 20 cm = 14 cm
(E)
(E) x
UW and Brent K. Stewart PhD, DABMP
37
Raphex 2000 Question: Inter. Rad. & Matter
G57. The intensity of a beam is reduced by 50% after
passing through x cm of an absorber. Its attenuation
coefficient, , is:
1. Production of bremsstrahlung.
2. Photoelectric interactions.
3. Collisions with other electrons.
4. Production of delta rays.
A. (0.693)
(0.693)x
B. x/0.693
C. 0.693/x
D. 2x
E. (0.693)
(0.693)x2
A. 1 and 2
B. 3 and 4
C. 1, 3 and 4
D. 1, 2 and 3
E. All of the above.
UW and Brent K Stewart, PhD, DABMP
38
Raphex 2001 Question: Inter. Rad. & Matter
G64.
G64. Electrons lose energy when passing through matter
by:
UW and Brent K. Stewart PhD, DABMP
UW and Brent K. Stewart PhD, DABMP
HVL = 0.693/ , so
39
= 0.693/HVL = 0.693/x
UW and Brent K. Stewart PhD, DABMP
40
10
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Raphex 2003 Question: Inter. Rad. & Matter
Fluence, Flux and Energy Fluence
G56.
G56. If a technologist were to stand 2 meters away from
a patient during fluoroscopy (outside the primary beam)
the dose received by the technologist would be mainly
due to:
Fluence ( ) = number of photons/cross sectional area
[cm-2]
Flux (d /dt) = fluence rate = fluence/sec [cm-2-sec-1]
Energy fluence ( ) = (photons/area)
(photons/area)(energy/photon) =
E [keV[J-m-2]
[keV-cm-2] or [JEnergy flux (d /dt) = energy fluence rate = energy
fluence/sec [keV[keV-cm-2-sec-1 ]
A. Compton electrons.
B. Photoelectrons.
C. Compton scattered photons.
D. Characteristic xx-rays generated in the patient.
E. Coherent scatter.
UW and Brent K. Stewart PhD, DABMP
41
UW and Brent K. Stewart PhD, DABMP
Kerma
42
Kerma (2)
A beam of ionizing radiation deposits energy in the medium through
through
a twotwo-step process
Mass Energy Transfer Coefficient ( tr/ )
Discount attenuation coefficient (absorption only, no scattered )
Photon energy is transformed into KE of charged particles (PE, CS)
CS)
These particles deposit energy through excitation and ionization
Kerma [J[J-kg-1] = [J[J-m-2] ( tr/ ) [m2-kg-1]
Mass Energy Absorption Coefficient ( en/ )
Kerma = Kinetic Energy Released in MAtter
Discount mass energy transfer coefficient (no bremsstrahlung)
KE transferred to charged particles from xx-rays
c.f. Johns, et al. The Physics of Radiology,
4th ed., p.218.
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
43
c.f. Johns, et al. The Physics of Radiology,
4th ed., p.218.
UW and Brent K. Stewart PhD, DABMP
44
11
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Absorbed Dose
Exposure and Dose
Absorbed Dose = E/ m [J[J-kg-1]
SI units of absorbed dose =
gray (Gy); 1 Gy = 1 J/kg
Traditional dose unit:
rad = 10 mGy; 100 rads = 1 Gy
( en/ )
( tr/ ) since at
diagnostic E and low Z
bremsstrahlung production
probability is low)
Calculation of Dose:
D = ( en/ ) [Gy] Kerma
c.f. http://www.uic.com.au/ral.htm
UW and Brent K. Stewart PhD, DABMP
Exposure (X): the amount of
electrical charge ( Q) produced
by ionizing radiation per mass
( m) of air = Q/ m [C[C-kg-1]
C = 6 x 1018 e-
Traditional units: Roentgen (R)
= 2.58x10-4 C/kg
also mR = 10-3 R
Measured using an airair-filled
ionization chamber
Output intensity of an xx-ray tube
(I) = X/mAs [mR/mAs]
45
Exposure and Dose
Imparted Energy [J] = Dose [J[J-kg-1] mass [kg]
Equivalent Dose (H) [Sievert or Sv]
R to Gray conversion factor =
0.00876 for air (8.76 mGy/R)
R to Gray conversion factor
0.009 for muscle and water
R to Gray conversion factor
0.02 0.04 for bone (PE)
In general, high LET
LET radiation (e.g., alpha particles and protons)
are much more damaging than low LET
LET radiation, which include
electrons and ionizing radiation such as xx-rays and gamma rays
and thus are given different radiation weighting factors (w
(wR)
X-rays/gamma rays/electrons: LET 2 keV/ m; wR = 1
Protons (< 2MeV): LET 20 keV/ m; wR = 55-10
Neutrons (E dep.): LET 4-20 keV/ m; wR = 55-20
Alpha Particle: LET 40 keV/ m; wR = 20
As D = ( en/ ) and the Zeff
(air) Zeff (soft tissue)
We can use the ionization
chamber exposure reading to
provide dose (D) to patient
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
46
Imparted Energy and Equivalent Dose
Dose (Gy) = eXposure (R) (R
to Gray conversion factor)
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.55.
UW and Brent K. Stewart PhD, DABMP
H = D wR; 1 Sv = 100 rem (traditional unit), 1 rem = 10 mSv
Replaced the quantity formerly known as dose equivalent
47
UW and Brent K. Stewart PhD, DABMP
48
12
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Summary
Effective Dose
Not all tissues equally
radiosensitive
ICRP publication 60 (1991):
tissue weighting factors (w
(wT)
First calculate the equivalent
dose to each organ: (HT) [Sv]
Effective Dose (E) [Sv]
E = wT HT
Replaces the quantity formerly
known as effective dose
equivalent (H
(HE) using different
wT per ICRP publication 26
(1977)
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.58.
49
UW and Brent K. Stewart PhD, DABMP
Raphex 2002 Question:
50
G2G2-G4. Match the quality factor (Q) or radiation
weighting factor (wR) used in radiation protection with the
type of radiation:
A. Ionizing elementary particles
B. NonNon-ionizing elementary particles
C. Ionizing photons
D. NonNon-ionizing photons
E. Other
A. 10
B. 2
C. 1
D. 0.693
E. 20
G46.
G46. Betas
G47.
G47. Heat radiation
G48.
G48. Visible light
G49.
G49. XX-rays
G50.
G50. Ultrasound
UW and Brent K Stewart, PhD, DABMP
UW and Brent K. Stewart PhD, DABMP
Raphex 2000 Question: Radiological Units
Radiation
G46G46-G50.
G50. Match the type of radiation with its description.
UW and Brent K. Stewart PhD, DABMP
c.f. Bushberg, et al. The Essential Physics
of Medical Imaging, 2nd ed., p.59.
G2.
G2. 1.25 MeV gammas
G3.
G3. 100 keV xx-rays
G4.
G4. 200 keV neutrons
51
UW and Brent K. Stewart PhD, DABMP
52
13
Interaction of Radiation and Matter - Chapter 3
17 July 2008
Raphex 2001 Question: Radiological Units
Raphex 2003 Question: Radiological Units
G3G3-G6. Match the following units with the quantities
below:
G9. Equivalent Dose is greater than absorbed dose for
__________.
A. Bq
B. Sv
C. C/kg
D. Gy
E. J
A. XX-rays above 10 MeV
B. Kilovoltage xx-rays
C. Electrons
D. Neutrons
E. All charged particles
G3.
G3. Absorbed dose
G4.
G4. Activity
G5.
G5. Exposure
G6.
G6. Equivalent Dose
UW and Brent K. Stewart PhD, DABMP
Remember: H = D wR
X-rays/gamma rays/electrons: LET
53
2 keV/ m; wR = 1
UW and Brent K. Stewart PhD, DABMP
54
Raphex 2002 Question: Radiological Units
G2G2-G5. Match the unit with the quantity it measures.
(Answers may be used more than once or not at all.)
A. Frequency.
B. Wavelength.
C. Power.
D. Absorbed dose.
E. Energy.
G2.
G2. Electron volt
G3.
G3. Hertz
G4.
G4. Joule
G5.
G5. Gray
UW and Brent K. Stewart PhD, DABMP
UW and Brent K Stewart, PhD, DABMP
55
14
