Physics 1 Lecture Flashcards by Mary Miller

Filament

AKA
Wire used
Terminal
How does it work

Cathode

Tungsten wire

Negative terminal

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

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Positive terminal is…

-targeted by

Anode

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

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2 types of anodes

-relationships with large volumes

Stationary
-problematic when large volumes of xrays required

Rotary
-allows for greater heat dissipation over larger area

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Line focus principle

focal spot to get best resolution
anode angle

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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Line focus principle helps

Improve resolution

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In the line focus principle,

effective focal length equals

Actual focal length X sin (theta)

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Define actual focal spot

-Area of the target hit by e-

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The smaller the actual focal spot is…

-Smaller the actual focal spot, the more heat produced

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Define effective focal spot

The area of the patient/film hit by Xrays

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In effective focal spot, the smaller it is…

The sharper the image

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Explain x-ray production

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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Actual focal spot is determined by

Angle of the target

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What % of xrays hits target

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2 types of anode- electron interaction

Bremsstrahlung

Characteristic

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Explain Bremsstrahlung

-AKA

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

Closer to nucleus e- gets, stronger xray made

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

Bremsstrahlung

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Explain characteristic

-what is this process known as

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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

In Characteristic, xray E is dependent on

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E difference btw shells

Radiographic opacity depends on

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density, e-/gram, atomic #

What do less dense organs look like on radiograph?

photons
film
example

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Absorb few photons

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

Lung

What do denser organs look like on radiographs?

photons
film
example

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Absorb more photons

Less x-ray photons reached film
Whiter on film

Bone or metal

Give top 5 adiographic opacities

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

kVp

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kilovoltage peak (E used in Xray tube)

milliampere (current)

Exposure time

Seconds (time)

mAs

milliampere X exposure time

kVp - measures - Increases - Produces - Higher kVp

Quality (E/strength) Increases penetrating power Produces contrast (black and whie) Higher kVp=lower contrast -partially contributes to image darkness

mAs - measures - high mAs - low mAs

- Measures quantity of photons - -># e- flowing in High mAs= more black film -->Doubling mAs doubles images darkness Low mAs=white image

How can you double darkness

Double mA kVp + 15%

Contrast vs latitude

Contrast=black/white Latitude=shades of grey

High kVp - contrast - latitude

Low contrast High latitude

Low Kvp - contrast - latitude

Short contrast Very few shades of grey

If image had: high contrast/low latitude Very few shades of grey Short scale of contrast what might kVp and mAs be?

low kVp | highmAs

If image had: high latitude many shade of grey Long scale of contrast What might kVp and mAs be

High kVp | low mAs

2 types of interaction with matter?

Compton scatter Photoelectric effect

Describe compton scatter

Scater radiation -Xray photon frees an orbital (low E) e- - Photon and e- scatter in different directions - Higher energy photons-increased scatter

When will compton scatter occur?

Increased density Increased e- density Increased E (high kVp) **Independent of atomic #**

Disadvantages of compton scatter

Scatter | -decreases film contrast and hazard to others

Explain photoelectric effect

xray photon ejects e- leading to an e- cascade E of xray is COMPLETELY ABSORBED Produces good image contrast

What is unique in photoelectric effect?

Xray is absorbed NOT SCATTERED

When will photoelectric absorption occur

Using lower E, low kVp HIGH atomic # Will increase contrast and patient exposure

Inverse square law

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

Physics 1 Lecture Flashcards

(43 cards)