diagnostic imaging

Question 0

If an x-ray has a short wavelength, what would the frequency be?
What does a high frequency mean?

Answer 0

It would have a high frequency. This means very energetic electromagnetic waves. Therefore, x-rays are potentially harmful due to the short wavelength and high frequency, therefore high energy.

Question 1

What are the 7 parts to the electromagnetic spectrum?

Answer 1

radio waves, microwaves, infra-red, visible light, x-ray, gamma-rays

Question 2

When x-rays interact with matter, what 3 things could happen?

Answer 2

penetrate, absorb, scatter

Question 3

what is the relationship between wavelength and energy?

Answer 3

energy is inversely proportional to wavelength. eg. short wavelength = high energy. and high frequency.

Question 4

What is it that x-rays do which cause damage? What do they cause damage to?

Answer 4

They produce ions in material that they penetrate. This causes biological DNA damage.

Question 5

What are the two types of damage that x-rays can cause?

Answer 5

They are ionizing - produce electron pairs in tissue.
Direct damage - destroys DNA
indirect damage - produce radicals by ionizing water.

Question 6

Once cells are damaged - what could happen?

Answer 6

They are either repaired or may mutate. Mutation leads to genetic changes, somatic changes, teratogenic changes, death.

Question 7

Which are the tissues most affected by x-rays? Give examples.

Answer 7

Tissues that divide regularly. For example, bone marrow, epithelial cells of GI tract, gonadal cells, embryonic cells (esp. at early stage.)

Question 8

Name the two biological effects of x-rays? Explain each one.

Answer 8

1. stochastic effect: probability of damage increases with dose - no known lower threshold.
2. deterministic effects: damage only over a threshold dose, severity increases with dose.

Question 9

What is the goal of radiation protection? name some of the principles.

Answer 9

Minimal exposure with maximal information gained. 
ALARA - as low as reasonably possible
justification - medical indication
high risk groups not involved
dose monitoring
dose limits
controlled and regulated areas.

Question 10

exposure units?

Answer 10

roentgen R

Question 11

Limited effective dose to whole body for employee?

Answer 11

20mSv/year - Sv (sieverts) is the effective dose to different body parts.

Question 12

What are the laws with regards to holding and restraining animals?

Answer 12

only permissable if there is a good clinical reason - small animals should be sedated and restrained with sandbags.

Question 13

name some methods of protection from x-rays?

Answer 13

indication, time kept low, distance (inverse square law) shielding (clothing), collimation, personnel monitoring.

Question 14

what is filtration of the X-ray tube?

Answer 14

built in metal plates to filter out low energy (harmful) radiation.

Question 15

explain the inverse square law of distance in x-rays?

Answer 15

as the distance from the primary source is doubled, the intensity decreases by a factor of 4.

Question 16

How could you increase distance from the X-ray tube? eg)horses?

Answer 16

use cassette holders, cords from the machine.

Question 17

protective clothing only protects you from what kind of radiation?

Answer 17

scatter only - not the main direct beams.

Question 18

what is collimation?

Answer 18

done from all four sides to reduce the area that is exposed to the x rays. Done using a built in collimator.

Question 19

explain dosimeters?

Answer 19

analyse every 3 months. any professional should wear one. wear under protective clothing. film badge or TLD.

Question 20

What happens within an x ray tube to produce x rays?

Answer 20

vacuum with an anode and a cathode inside. electrons fired from cathode to the anode. converted to EM radiation. they are produced, accelerated and decelerated. cathode made of tungsten. A lot of heat produced.

Question 21

What is mAs?

Answer 21

number of electrons. longer exposure = more x rays. so milli amps per second used. + longer exposure time = motion artefacts.

Question 22

what is kVp?

Answer 22

acceleration of electrons. faster they travel, more energy and more hit target.

Question 23

anode made of tungsten… why?

Answer 23

high melting point and can be rotating to avoid heating up. also can be angled to get a smaller focal point from a larger one.
smaller focal point = less blurry.

Question 24

what is it called when an image is more/less blurry?

Answer 24

penumbra

Question 25

what is the advantage of a larger focal point?

Answer 25

reduced detail but can use higher exposures.

Question 26

What happens if you increase the kVp? (energy electrons have)

Answer 26

increased velocity of electrons. increased number of x ray photons produced. increases the penetrating power and energy of electrons.

Question 27

what happens if you increase the mAs? (number of electrons) longer exposure = more electrons

Answer 27

increase filament heating. increased number of x rays produced.

Question 28

explain attenuation? 2 ways?

Answer 28

decreases intensity of an x ray beam as it passes through matter?

• absorption = photon removed
• transmission = photon changes direction

Question 29

explain transmission?

Answer 29

x ray passes through matter without interaction.

Question 30

What is the photoelectric affect?

Answer 30

complete absorption of x ray. = good image. atomic number dependant.

Question 31

what is the Compton effect?

Answer 31

depends on density. - scatter. depends on kVp. not good image. results if kVp too high.

Question 32

what do grids do?

Answer 32

they reduce scatter and produce a better contrast image. not a safety device.