RS&DR

Question 1

What is the heel effect?

Answer 1

Variation in x-ray intensity across the FoV due to absorption within the target

Question 2

What is the reason for the change in exponential at low depth?

Answer 2

Not a monoenergetic beam so lower energies preferentially attenuated
Not a narrow beam due to scatter from the irradiated volume

Question 3

(a) What is the attenuation equation?
(b) What assumptions are made in the attenuation equation?

Answer 3

(a) N(t) = N(0)exp(-μx)
(b) A narrow and monoenergetic beam

Question 4

In Compton scattering, what is the equation for the change in:
(a) wavelength of the photon?
(b) photon energy?

Answer 4

(a) Δλ = h/mc (1 - cosθ)
(b) ΔE = E(0) (α (1 - cosθ))/(1+ α (1 - cosθ))
where α = E(0)/0.511 (MeV)

Question 5

Order the different materials according to their density (highest to lowest):
Bone, Air, Fat, Lung, Soft tissue/Muscle

Answer 5

Bone, Soft tissue/Muscle, Fat, Lung, Air

Question 6

What is the equation for the total attenuation?

Answer 6

I = I(0)⋅exp-(ε/ρ)(ρ⋅x)⋅exp-(τ/ρ)(ρ⋅x)⋅exp-(σ/ρ)(ρ⋅x)⋅exp-(π/ρ)(ρ⋅x)

ε/ρ: Elastic Scattering
τ/ρ: Photoelectric Scattering
σ/ρ: Compton Scattering
π/ρ: Pair production

Question 7

How do the different interaction processes contribute to absorption and attenuation?

(a) Elastic Scattering
(b) Compton Scattering
(c) Photoelectric Scattering
(d) Pair production

Answer 7

(a) No; Yes
(b) Partial (higher proportion of energy absorbed at higher energies) ; Yes
(c) Partial (Due to characteristic radiation production); Yes
(d) Partial (All absorbed but 1.02 MeV); Yes

Question 8

(a) What are the protection quantities?
(b) What are the properties protection quantities?

Answer 8

(a) Equivalent Organ Dose (HT)
Effective Dose
(b) They are not directly measurable.
They are something we want to assess and relate back to risk/compare to dose limits

Question 9

What are the measured physical radiation dose quantities?

Answer 9

Exposure, KERMA, Absorbed Dose, DAP, Bq, DLD, MU

Question 10

What are the operational dose quantities?

Answer 10

Ambient dose equivalent H*(d) (Sv)
Personal Dose Equivalent Hp(d) (Sv)

Question 11

What are the practical dose quantities that can be measured?

Answer 11

Surface Dose
Organ Dose
DAP
CTDI
Effective Dose

Question 12

What is the Equivalent Dose?

Answer 12

Equivalent dose (H_T) = Absorbed Dose (D) x Radiation Weighting Factor (w_R)

Question 13

What is the Effective Dose?

Answer 13

Effective Dose (E) = Σ w_T⋅H_T ;
Equivalent Dose (H_T) = Σ w_R⋅D

Question 14

What are the guideline dose rates in mSv per year in:

(a) Controlled area?
(b) Supervised area?
(c) Unsupervised public area?

Answer 14

(a) 6 mSv per year
(b) 1 mSv per year
(c) 0.3 mSv per year

Question 15

What is a classified person?

Answer 15

Anyone who is likely to receive and annual effective dose > 6 mSv

Question 16

What dosimeters are used for:

(a) whole body
(b) extremities
(c) lens

Answer 16

(a) Hp(10) mSv
(b) Hp(0.07) mSv
(c) Hp(3) mSv

Question 17

What is the difference between the entrance and exit dose?

Answer 17

Fewer photons
Peak shifted to the right- greater mean energy
Characteristic k-line unchanged
More penetrating/harder beam

Question 18

What is the equation for the number of grey levels?

Answer 18

No. of grey levels = 2^(No. bits per pixel)

E.g. for a 12 bit per pixel image 2^12 = 4096 individual grey evels