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Emily Imaging > Radiography > Flashcards

Radiography Flashcards

1
Q

What is the formula for Magnification of an image, in terms of the size of the object and image?

A

M=(Limage)/(Lobject)

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2
Q

What is the formula for Magnification of an image, in terms of the distance from source to object to the screen?

A

M=(a+b)/a where a is the dist from the x-ray tube to the object and b is the distance from the object to the image

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3
Q

Would increasing the distance from the object to the image increase of decrease magnification?

A

increase!

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4
Q

In screen-film radiography, would a thicker screen cause more or less interactions? More or Less blurring?

A

More Interactions, More Blurring!

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5
Q

What is the chemical process in screen-film?

A

You have Ag+ ions originally. When interacted with, they produce Ag. Then while developing, you wash away Ag+.

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6
Q

Formula for Optical Density

A

OD = -log(T), log is base 10 and T=I/Io (intensity after transmitted thru film/intensity with no film in the way

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7
Q

Describe the important features of the Film Characteristic Curve

A

x-axis is Kerma (log scale). Y-axis is Optical Density
It starts flat - this level is called the base+fog.

There is then a linear region.

Then there is a shoulder

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8
Q

In two overlayed film characteristic curves, how can you tell which one is “more sensitive” or “has a faster speed”?

A

It will be the one that starts increasing (has a higher optical density) at a lower Kerma

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9
Q

What does the latitude of a screen-film curve talk about?

A

The latitude is the region over which the film gives a linear response

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10
Q

Small (narrow) latitude means high or low contrast

A

high contrast! like when we talked about adjusting brightness windows on digital images…

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11
Q

What does FPTFTAD stand for?

A

Flat Panel Thin Film Transistor Array Detectors. I think he made the up. The TFT is real, though.

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12
Q

Describe the difference between and Direct and an Indirect TFT (thin film transistor) Array.

A

With indirect, you get photons scattering in the scintillator so you detect signal in a few pixels. With direct, instead of photons you can ion pairs in the scintillator, and an electric field is applied across the scintillator so you get singal in one pixel/

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13
Q

I should maybe add a question about Scintillators and Intensifying Screens?

A

maybe

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14
Q

What is a typical Absorption Efficiency of Scintillators?

A

50% of x-rays are absorbed

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15
Q

What is a typical Conversion Efficiency of Scintillators?

A

10% of energy of each photon is converted to light

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16
Q

What is the formula for scattered to primary ratio?

A

SPR=S/P

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17
Q

What is the formula for “fraction”?

A

F=S/(S+P), where S and P are Secondary and Primary

18
Q

Think about the Scatter-to-Primary Ratio Graph… Would a thicker person result in the curve be shifted up or down?

A

Shifted up. Thicker=more scatter.

19
Q

What is the Bucky Factor? What is a typical value?

A

the relative increase of x-ray intensity you need when you put a grid in the way to get the intensity you would have without a grid. Typical value is 3 - 8.

20
Q

What is a typical grid ratio value? Grid Ratio=Height of grid (or depth?) / width between bars of the grid.

A

GR=H/W is typically between 8 and 14. Usually around 10.

21
Q

What is a Bucky Grid?

A

Reciprocating Grid. One that moves.

22
Q

Define Exposure and its units

A

Electric charge per unit mass produced by ionizing radiation. Units are the Roentgen R=C/kg

23
Q

Define Dose and its units

A

energy absorbed per unit mass by ionizing radiation. Units are Gy=J/kg.

Dose is also = (W)(exposure)

24
Q

Define W and its units

A

energy deposited per ion pair. J/C or eV/ion pair. 33.97!

25
Q

What is a Z value for soft tissue?

A

about 7.4. H=1 and O=8

26
Q

What energy range is ideal for mammography and Why?

A

15-20 keV. Think about the Graph of linear attenuation as a function of energy. There is a larger separation between Fat, Glandular, and Infiltrating Ductial Carcinoma (tumor) at lower energies. Anything lower then 15 will just be delivered as dose… bad.

27
Q

What target is often used for mammography? What are the characteristic photon energies?

A

Molybdenum. 17.5 and 19.6 keV.

28
Q

DESCRIBE THE K-EDGE

A

the energy level of a photon which is enough to knock out k-shell (inner-most shell) electrons. If photon energies are greater than this, there are lots more opportunities to interact, so more attenuation!

29
Q

Describe the Heel Effect.

A

the photon intensity is affected on one side by the anode you you end up with a boob-shaped curve. Great for imaging breasts.

30
Q

Molybdenum. What are the values for Z, k-edge, and two characteristic X-rays

A

Z=42
K-edge=20 keV
x-rays are 17.9 and 19.5 keV.

31
Q

Rhodium is sometimes used as a target in mammography. What are the values for Z, k-edge, and two characteristic X-rays

A

Z=45
K-edge=23.2 keV
x-rays are 20.2 and 22.7 keV.

32
Q

What can Beryllium be used for in mammograpy?

A

as a window to minimize absorption. Beam hardening.

33
Q

What is the Z of Beryllium

A

4

34
Q

compressing breasts lowers or increases scatter-to-primary ratio

A

lowers it.

35
Q

What are typical focal spot sizes in mammography and radiography?

A

0.3mm and 1.2 mm.

36
Q

What are typical values for frames per second, number of images, and amount of radiation compared to a normal x-ray in fluoroscopy?

A

around 18000 images

30 frames per second

1/1000 of typical dose

37
Q

What kind of detectors do we need for fluoroscopy?

A

very sensitive, low noise

38
Q

What is an image intensifier in fluoroscopy?

A

basically a photomultiplier tube. curved, large input with an anti-scatter grid and a small, flat output.

39
Q

describe pincusion distortion

A

fallout in brightness at the periphery of a fluoroscopic imag

40
Q

What are typical input and output diameters in fluoroscopy?

A

Input 15-35 cm

Output 2.5cm

41
Q

What to things contribute to brightness gain in fluoroscopy?

A

Electronic Gain ~50 and Minification gain ~50-140

42
Q

Fluoroscopy? Would a larger field of view result in a bettwe or worse resolution?

A

worse

Emily Imaging (6 decks)

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