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Radiation biology > Radiation Physics + Biology > Flashcards

Radiation Physics + Biology Flashcards

1
Q

X-ray generation steps

A
  1. Form electron cloud
  2. accelerate electrons into tungsetn target
  3. interaction with tungsten electrons produces x-rays
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2
Q

what percent of energy created is lost as heat?

A

99%

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3
Q

focal spot is where? effective focal spot size?

A

in anode

changing angle to about 20 degrees so we can get a smaller focal spot as smaller = more sharpness

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4
Q

why use tungsten?

A

element that has several characteristics of an ideal target material, including the following: •High atomic number (74) •High melting point (3422°C) •High thermal conductivity (173 W · m−1 · K −1 ) •Low vapor pressure at the working temperatures of an x-ray tube

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5
Q

what interactions occur in the PATIENT

A
  • Photoelectric absorption

- Compton scattering

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6
Q

what attenuates more bone or soft tissues?

A

BONE

- more dense will attenuate more (like vs. tissues)

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7
Q

Definition of Attenuation

A

– reduction in intensity of the x ray beam by interactions with matter

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8
Q

Definition of Absorption

A

photon ionizes an atom, converts its energy to the kinetic energy of an electron, and the photon ceases to exist

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9
Q

Definition of Scatter

A

– photon interacts with an atom and moves off in a different direction

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10
Q

interaction in which photon ceases to exist?

A

Absorption

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11
Q

which interaction contributes the most to beam attenuation?

A

Compton Scattering

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12
Q

Breakdown of PERCENTAGES in

A

No interaction - 9% goes right through

Coherent scattering - 7%

Photoelectric Absorption - 27%

Compton Scattering -57%

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13
Q

Primary contributor to the image formation

A

Photoelectric Absorption

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14
Q

Photoelectric Absorption

A

Primary in image

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15
Q

what two interactions contribute to most x-ray beam attenuation?

A

PE (photoelectric absorption and Compton scattering)

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16
Q

Factors controlling the X-ray beam

A
  1. tube current (mA)
  2. Energy (kVp)
  3. Timer (s)
  4. Shape (collimation)
  5. Intensity (distance)
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17
Q

energy of the photons is referred to as

A

beam quality

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18
Q

Increasing kVp increases..

A

the number of photons generated

the mean energy of the photons and the maximum energy of the photons

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19
Q

exposure time and tube current mA are referred to as

A

beam quantity or beam intensity

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20
Q

Intensity formula

A

o I1/12=d2^2/D1^2
The intensity is inversly proportional to the square of the distance from the source

if move 3 x away
intensity becomes 1/9th

if move 4x as far away it becomes 1/16th of the intensity

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21
Q

exposure definitino

A

potential of a source of radiation to ionize

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22
Q

T/F absorbed dose is the same as equivalent dose

A

TRUE - for our circumstances

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23
Q

what accounts for 2/3 of radiation induced biological damage

A

INDIRECT effects of radiation

- free radicals

24
Q

deterministic effects occur when?

A

when radiation exceeds a THRESHOLD

  • does NOT occur below threshold levels
  • severity is proprotional to dose

vs. stochastic which there is NO minumum threshold for causation

25
can stoachastic (x-ray radiation) effects cause cancer?
Yes we assume it can | they cannot cause deterministic because they do not reach that threshold
26
dental radiographs can cause?
stochastic effects | but this is an ASSUMPTION
27
can dental x-rays cause congenital malformations in an embryo or fetus?
NO - this is a deterministic effect
28
natural background dose of radiation annually?
3.1 mSv (micro)
29
daily average background radiation dose?
8.5 UsV
30
DENTAL effective dose of ionizing radiation?
0.007
31
dose from medical, consumer products and other annually? importance?
3.1 msV which is equivalent to natural background radiation dose
32
the optimal operating potential of dental x-ray units is between?
60 and 70 kVp
33
patient dose is reduced or increased with higher kVp?
reduced | - we would get better contrast with low kVp - but the patient dose is reduced with higher kVp exposures
34
what is the TOTAL average radiation dose in the US from medical and consumer products?
3.1 MICRO severts | mSv
35
full mouth with CCD sensor | effective dose in uSv and equivalent background exposure in days
85 (5 each) 10 days
36
Bitewing effective dose in microSv and equivalent background exposure in days
5 with 0.6 days | so four bitewings would be roughly 2-3 days
37
dose from natural background
3.1 mSv Same as from medical in a year
38
dose from all radiation in a year
6.2 mSv
39
- Daily average background dose
8.5 MICROmSv
40
dose mSv from dental
0.007 mSv
41
what units are used to describe dose
1. Seivert -- effective dose | 2. Grey -- absorbed dose
42
how much is dose reduced by rectangular collimation compared to round collimation?
80%
43
Radiation protection laws and guidelines are made based upon what hypothesis?
Linear NON-threshold theory
44
the suspected dose to a fetus wearing a lead apron when getting FMX
.25 micro Gy or .25 micro seivert
45
what is the optimal potential of dental x-ray units
60-80 kVp
46
filtration minimum
aluminum with equivalent half value layer of 1.5mm | w/ filtration of 3mm aluminum the surface exposure is reduced by about 20% of the exposure with no filtration
47
filtration defintion and importance
Low energy photons are mostly absorbed by the patient and contributing to the patient dose but not the image *so if we remove these photons we can reduce the dose without any loss in the radio-graphic information
48
lead aprons vs thyroid collars
lead aprons are still required - however seem to be unnecessary *reducing exposure in the main beam is more necessary thyroid collars should be used whenever possible as this tissue is more suscpetible to radiation exposure and children are more at risk every precaution should be made so thyroid collars should be used whenever possible
49
kVp relationship b/w dose and contrast | ideal kVp?
- Should be used within 60-70 kVp - Even though lowering the kVp may make image contrast better, the dose to the patient would increase - The patient dose is reduced with a higher kVp exposures
50
color if over-exposure? under-exposed?
too dark if over-exposed too light = under-exposed
51
Milliampere-Seconds
- Amperage and time settings for exposure should be set for optimal quality - Should be of diagnostic density – so neither too dark (over-exposed) or too light (under-exposed) - Correct density should show  faint soft tissue outlines
52
position and distance rule
- At least 6ft (2m) away and at an angle of 90 to 135 degrees to the central ray of the x-ray beam
53
personal dosimeters
Recommended for workers who may receive more than 1 mSv and for pregnant workers. Required by law in certain states Optically Stimulated Luminescence Dosimeter Strip of Al2O3 – radiosensitive crystal Sensitive to 10µSv
54
personal dosimeters recommended for?
workers who may recieve more than 1 mSv and for pregnant workers
55
sensitivity of personal dosimeters
10 MICROSv
56
what is a typical anode target made from?
Tungsten and the stuff around it is copper
57
units for measuring effective dose
SEIVERTS (it is a 1:1 conversion with gray but this is the one we will focus on)

Radiation biology (19 decks)

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