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medical radiation sciences 2 > Equations > Flashcards

Equations Flashcards

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USMLE® Step 1 flashcards
1
Q

What does Io (I knot) stand for?

A

The inital intensity before passing through matter

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2
Q

What does x stand for in relation to photons passing through matter?

A

The thickness of the material

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3
Q

What does I stand for in relation to photons passing through matter?

A

The intensity after going through the material

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4
Q

What is the probability of the photoelectric?

A

Probability of PE=denisty (Z^3)/E^3

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5
Q

What is the probability of compton scatter?

A

Probability of CS=denisty/E

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6
Q

How do you find the kinetic energy of a photoelectron?

A

Incident x-ray photon E-BE of electron

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7
Q

How do you find the energy of the primary photon with the photoelectric effect?

A

EP=EBE+EKE
EP=energy of the primary photon
EBE=Binding energy of the orbial electron
EKE=kinetic energy of the photoelectron

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8
Q

How do you find the energy of the primary photon during a compton electron interaction?

A

EP=ES+EBE+EKE
EP=energy of the primary photon
EBE=Binding energy of the orbial electron
EKE=kinetic energy of the recoil electron (compton electron)
ES=Energy of the scattered photon

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9
Q

Within the patients body, a 30 kV x ray undergoes a photoelectric interaction with a k-shell electron in a calcium atom. IF the e- binding E of a K-shell e- in a calcium atom is 4kV, what will be the kinetic energy of the photoelectron speeding away from the atom?

A

EP=EBE+EKE
30=4+x
x=26 kEV

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10
Q

Within the patients body, a 40 kV x ray undergoes a CS interaction with an L-shell e- in a calcium atom. The absolute value for the binding E of the L shell is .5 KV. The compton (recoil) e-speeds away from the atom with 5kV of KE. What is the energy of the compton scattered photon?

A

EP=ES+EBE+EKE
40=x+.5+5
40-.5-5=34.5

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11
Q

What is the probability of an 80 keV x-ray interacting with fat (z=6.3) and barium (z=56) compared to soft tissue (7.4)?

A

Clarify with teacher

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12
Q

How much more likely is an x ray to interact with bone (z=13.8) than with muscle (z=7.4)

A

(13.8/7.4)^3=2628/405=6.5

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13
Q

How do you find the TMAC?

A

Divide total linear attenuation (u) by density (p)

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14
Q

What is the unit for PE absorption?

A

t

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15
Q

What is the unit for CS?

A

o (sigma)

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16
Q

How do you find the PEMAC?

A

t/p

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17
Q

How do you find the CEMAC?

A

o/p

18
Q

How do you find the probability of P.E. absorption when using PEMAC?

A

t/p (z^3)/E^3

19
Q

How do you find the probability of compton scatter when using CEMAC?

A

o/p(p)/E

20
Q

The HVL of a beam of radiation is 3mm of tin. What % of the beam will be transmitted though a tin sheet 9mm thick?

A

12.5 %

21
Q

What does e represent?

A

Base of the natural log

22
Q

What is the basic logarithmic function formula?

A

Logb(X)=Y
b^y=X

23
Q

What is log3(9)=?

A

3^x=9
x=2

24
Q

What is logx(1)=?y

A

X^y=1
y=0

25
Q

What is the base of the natural log?

A

e=2.718

26
Q

How do you calculate the intensity after passing though a material?

A

I(x)=(Io)e^-ux

27
Q

How do you find the attenuation coefficent?

A

u=-ln(Ix/Io)/x or u=-ln(0.5)/HVL

28
Q

How do you find the HVL?

A

I(x)/Io=.5

29
Q

How do you calculate the TVL?

A

TVL=2.303/u

30
Q

If 6x10^7 x ray photons enter a 2cm thick layer, what will be the number of x ray photons transmitted though the layer if u=1.42?

A

3.5x10^6

31
Q

What is the attenuation coefficient of a certian material if we know that 5cm of the material absorbs 80% of the gamma rays?

A

0.322 cm

32
Q

How do you calculate the PMT gain?

A

PMT gain=g^n
g=dynode gain
n=number of dynodes

33
Q

An 8 stage PMT (8 dynodes) has a dynode gain of 3. What is the PMT gain?

A

PMT gain=g^n
=6561

34
Q

How do you calculate flux gain?

A

Flux gain= # of output light photons/ # of input x ray photons

35
Q

How do you calculate minification gain?

A

Minification gain=d1^2/do^2
d1=Diameter of the IP
do=Diameter of the OP

36
Q

How do you calculate brightness gain?

A

Brightness gain=Flux gain x minification gain

37
Q

What is the brighness gain for a 17 cm II tube with a flux gain of 120 and a 2.5 output phosphor?

A

5548.8

38
Q

How do we find the electronic magnification factor?

A

MF=IP old size/IP new size

39
Q

How magnified is the image of a 25/17/12 II in the 17 cm mode compared with that produced in the 25 cm mode?

A

MF=1.47 times more magnififed in the 17 cm mode

40
Q

A 23/15/10 II tube is sued in the 10 cm mode. How much higher is the patient dose in this mode compared with the 23 cm mode

A

5.29 times higher in the 10 cm mode

41
Q

How do we find the patient dose factor?

A

Patient dose factor=(IP old size/IP new size)^2

medical radiation sciences 2 (13 decks)

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