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Diagnostic Imaging > Physics 1 Lecture > Flashcards

Physics 1 Lecture Flashcards

1
Q

Filament

  • AKA
  • Wire used
  • Terminal
  • How does it work
A

Cathode

Tungsten wire

Negative terminal

Filament is heated and e- are produced. Focusing cup directs e- towards anode (positive terminal)

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2
Q

Positive terminal is…

-targeted by

A

Anode

Tungsten target (from cathode). Attracts e- from filament

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3
Q

2 types of anodes

-relationships with large volumes

A

Stationary
-problematic when large volumes of xrays required

Rotary
-allows for greater heat dissipation over larger area

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4
Q

Line focus principle

  • focal spot to get best resolution
  • anode angle
A

Smaller focal spot=better radiographic resolution

Anode is angled 6-20 to help direct/focus beam of e-
-Effective length gets smaller with smaller angles.

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5
Q

Line focus principle helps

A

Improve resolution

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6
Q

In the line focus principle,

effective focal length equals

A

Actual focal length X sin (theta)

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7
Q

Define actual focal spot

A

-Area of the target hit by e-

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8
Q

The smaller the actual focal spot is…

A

-Smaller the actual focal spot, the more heat produced

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9
Q

Define effective focal spot

A

The area of the patient/film hit by Xrays

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10
Q

In effective focal spot, the smaller it is…

A

The sharper the image

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11
Q

Explain x-ray production

A

Charge is applied to filament (negative terminal) and anode (positive terminal)

Heated filament results in e- cloud

e- focused by focusing cup and directed or attracted towards anode (positive terminal)

Actual focal spot determined by angle of target

99% of e- collide w/anode and dissipate as heat

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12
Q

Actual focal spot is determined by

A

Angle of the target

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13
Q

What % of xrays hits target

A

1%

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14
Q

2 types of anode- electron interaction

A

Bremsstrahlung

Characteristic

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15
Q

Explain Bremsstrahlung

-AKA

A

“braking radiation”

e- gets close to nucleus, will slow down due to (+) charge of nucleus

When e- ‘brake’ xray photon released

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16
Q

In bremsstrahlung, how can you get a stronger xray made?

A

Closer to nucleus e- gets, stronger xray made

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17
Q

What accounts for most of xrays made in a diagnostic x-ray machine?

A

Bremsstrahlung

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18
Q

Explain characteristic

-what is this process known as

A

e- from inner shell is released

Outer shell e- fills inner shell void and E is given off
-this process is known as e- cascade

19
Q

In Characteristic, xray E is dependent on

A

E difference btw shells

20
Q

Radiographic opacity depends on

A

density, e-/gram, atomic #

21
Q

What do less dense organs look like on radiograph?

  • photons
  • film
  • example
A

Absorb few photons

Greater # of xray photons reaching the film
Blacker on the film

Lung

22
Q

What do denser organs look like on radiographs?

  • photons
  • film
  • example
A

Absorb more photons

Less x-ray photons reached film
Whiter on film

Bone or metal

23
Q

Give top 5 adiographic opacities

A 
Gas-black
Fat-Dark grey
Soft tissue/fluid- medium grey
Bone-light grey
Metal-white
24
Q

kVp

A

kilovoltage peak (E used in Xray tube)

25
Q

mA

A

milliampere (current)

26
Q

Exposure time

A

Seconds (time)

27
Q

mAs

A

milliampere X exposure time

28
Q

kVp

  • measures
  • Increases
  • Produces
  • Higher kVp
A

Quality (E/strength)

Increases penetrating power

Produces contrast (black and whie)

Higher kVp=lower contrast
-partially contributes to image darkness

29
Q

mAs

  • measures
  • high mAs
  • low mAs
A
  • Measures quantity of photons
  • -># e- flowing in

High mAs= more black film
–>Doubling mAs doubles images darkness

Low mAs=white image

30
Q

How can you double darkness

A

Double mA

kVp + 15%

31
Q

Contrast vs latitude

A

Contrast=black/white

Latitude=shades of grey

32
Q

High kVp

  • contrast
  • latitude
A

Low contrast

High latitude

33
Q

Low Kvp

  • contrast
  • latitude
A

Short contrast

Very few shades of grey

34
Q

If image had:
high contrast/low latitude
Very few shades of grey
Short scale of contrast

what might kVp and mAs be?

A

low kVp

highmAs

35
Q

If image had:
high latitude
many shade of grey
Long scale of contrast

What might kVp and mAs be

A

High kVp

low mAs

36
Q

2 types of interaction with matter?

A

Compton scatter

Photoelectric effect

37
Q

Describe compton scatter

A

Scater radiation
-Xray photon frees an orbital (low E) e-

  • Photon and e- scatter in different directions
  • Higher energy photons-increased scatter
38
Q

When will compton scatter occur?

A

Increased density
Increased e- density
Increased E (high kVp)

Independent of atomic #

39
Q

Disadvantages of compton scatter

A

Scatter

-decreases film contrast and hazard to others

40
Q

Explain photoelectric effect

A

xray photon ejects e- leading to an e- cascade

E of xray is COMPLETELY ABSORBED

Produces good image contrast

41
Q

What is unique in photoelectric effect?

A

Xray is absorbed NOT SCATTERED

42
Q

When will photoelectric absorption occur

A

Using lower E, low kVp
HIGH atomic #

Will increase contrast and patient exposure

43
Q

Inverse square law

A

I(1)/I(2) = d(2)^2/d(1)^2

Diagnostic Imaging (2 decks)

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