6 - Radiation Physics and X-ray I Flashcards

Question

Describe the x-ray tube

Answer 1

- Enclosed in glass or metal and maintains a vacuum - Has area which allows for passage of the x-rays called the useful beam 2 basic components - Cathode - Anode

Answer 2

Negative electrode of the x-ray tube

Answer 3

- Filament: composed of tungsten and produces electrons when heated-the number of electrons produced is determined by the temperature of the filament and is measured in milliamperes - Focusing cup: directs the filament electrons to the anode

Answer 4

Positive electrode of the x-ray tube

Answer 5

- Target: area to which electrons produced by cathode are directed and made of tungsten - Focal spot: area on target from which x-rays are emitted

Answer 6

- Inherent: tube housing absorbs off-focus radiation that does not contribute to the useful x-ray beam - Added: filters the useful x-ray beam and absorbs low energy x-rays that cannot reach the image receptor-usually made of 1.5 to 2.5 mm thick aluminum Notes: Not every x-ray beam will be focused or used for diagnostics, so you want to filter out the x-ray beams that you don't need. The lead will absorb some of the scatter radiation (INHERENT) and then just before it leaves, there is another filter that absorbs low-energy radiation and this will then never reach the patient (ADDED)

Answer 7

Shape the dimensions of the useful x-ray beam so that only the area of interest is x-rayed, a process called collimation

Answer 8

- First step is to turn on a light source which shines on the dimensions of the part to be examined and will correspond to the area exposed by the useful beam - The center of the light source has crosshairs or a circle to accurately position the central beam Notes: Nothing more than a flashlight that allows you to control the length and width of the field you will expose the patient to - this field of exposure is called collimation

Answer 9

What we are asking here is what PRIMARILY controls quality Answer: Timer of 1/70 of a second This is because it is a conventional foot x-ray (correct range)

Answer 10

- Electrons generated at the cathode end at the filament - Focusing cup directs electrons toward the anode target - Electrons interact with the target where x-rays are produced

Answer 11

- Characteristic radiation | - Bremsstrahlung radiation

Answer 12

- Electron interacts with atom’s inner shell electron and removes the electron which causes ionization - X-ray photons produced as outer-shell electrons fill the inner shells

Answer 13

- Electron slows down or “brakes” as it passes by + charged nucleus - Changes course of electron which causes it to lose energy in the form of x-ray photons

Answer 14

X-ray quantity (output intensity, x-ray intensity, x-ray exposure) is the number of x-rays

Answer 15

X-ray quality is the penetrability of the x-ray or how much energy it has

Answer 16

- The more x-rays that strike the film, AND the more energy x-ray strikes the film, the blacker it makes the film and the less contrast there is (can’t tell white from black as well) - You WANT to have as much contrast as possible without exposing the patient to excess x-ray - More contrast means you can clearly tell white from balck

Answer 17

- X-ray emission spectrum is the range of x-rays energies present in a quantity of x-rays-influenced by mAs, kVp, and added filtration - Increasing mAs increases quantity but not quality - Increasing kVp increases both quality and quantity - Filtration decreases quantity, increases quality

Answer 18

- Increases quantity | - Does NOT increase quality

Answer 19

- Increases BOTH quality and quantity

Answer 20

- Decreases quantity | - Increases quality

Answer 21

- Useful x-ray beam has greater intensity on the cathode side than the anode side which is a result of the line-focus principle - Position the thicker portion of the part to be examined closer to the cathode The thicker part of the body part that you want to look at, put it closer to the cathode because it will be exposed to more x-rays

Answer 22

Listen for the rest of the answers 1 - X-rays are produced by this process... Bremsstralung radiation 2 - Place the thickest section of the object closest to the cathode... Heel effect 3 - X-ray emission spectrum... Range of energies in x-ray beam 4 - Affect quality of x-ray... kVp, filtration 5 - Affect quantity of x-ray... kVp, mA, filtration, time of exposure, BUT mA PRIMARILY controls quantity

Answer 23

Occurs in 3 ways which have application to podiatric radiography: - Coherent scattering - Compton scattering - Photoelectric effect

Answer 24

As x-ray photons excite the target atom, a secondary photon of equal energy is released in different direction which is absorbed by the patient but does not contribute to diagnostic image

Answer 25

- Occurs when x-ray photon interacting with matter ejects the outer-shell electron causing ionization - Original x-ray continues in different direction with decreased energy - This creates “fog” that impairs the image quality by reducing its contrast

Answer 26

- X-ray photon is totally absorbed and an inner-shell electron is ejected during ionization - This process causes beam attenuation and image formation - Also contributes to patient-absorbed dose

Answer 27

The diagnostic image is formed by the photoelectric effect and remnant radiation (x-rays that pass through patient and strike the image receptor)

Answer 28

Most x-rays interact with matter by Compton scattering which causes image fog Low kVp - Favors photoelectric effect, but increases dose of radiation (more radiation is absorbed by the body) High kVp - Favors Compton scattering (more radiation makes its way to the x-ray film)

Answer 29

- Differential absorption is manifested by attenuation which is the reduction in x-ray beam intensity as it is absorbed and scattered by matter - Bone absorbs x-rays to a greater degree (appears white) than fat and soft tissue (appear black)

Answer 30

1 - Forms the diagnostic image... Photoelectric effect 2 - Forms image fog... Compton scattering 3 - Favors photoelectric effect... Low kVp 4 - Favors Compton scattering... High kVp

Answer 31

- Sufficient radiographic density - Acceptable contrast - Optimal detail - Minimal distortion

Answer 32

Ability to separate and distinguish between two separate objects

Answer 33

- Ability to distinguish between two objects which are side by side and have different contrasts (bone vs. soft tissue) - High spatial resolution is able to distinguish between two objects that are aligned closely together

Answer 34

Ability to distinguish between differences in density or intensity

Answer 35

The about of "darkness" or "blackness" on the film AKA "optical density"

Answer 36

- Amount of darkening in a radiograph - Along with contrast (adequate differences in density), are required to give visibility to the structural detail of a subject

Answer 37

- mAs is the primary controlling factor and is the product of milliampere multiplied by exposure time in seconds (mA x seconds) - Can have the same mAs but different milliamperes and seconds

Answer 38

Film becomes DARKER Known as the law of reciprocity

Answer 39

- If you need to make an adjustment in density either increase the mAs by a factor of 2 (to increase darkness) or decrease by a factor of ½ (to increase lightness) - Change either mA or s, but not both Note that if you need to make an adjustment, you will need to increase or decrease mAs by at least 30% or the human eye cannot tell a difference

Answer 40

- Kilovoltage (kVp) - Distance (SID) - Film/screen combinations - Compensation filter - Film processing

Answer 41

- Governs penetrating power of electrons - Alters both quality (energy) of x-ray beam and quantity of photons produced - Abides by a 15% rule

Answer 42

- Low kVp produces high contrast (tissues appear black or white without much gray - High kVp produces low contrast (tissue appears uniformly gray)

Answer 43

Need a 4% to 8% change in kVp (3 to 7 kVp) for the human eye to see a visible difference in the x-ray

Answer 44

- A 15% increase in kVp will cause the same change in radiographic density (make image look darker) as doubling the mAs - A 15% decrease in kVP will cause image to look lighter to the same extent as will halving the mAs

Answer 45

Source-to-image distance (SID) will alter number of photons striking the film Inverse square law: - If tube is too far from film, too few photons strike film producing a lighter image - If too close to film, more photons produce a darker image

Answer 46

- Film/screen speed-sensitivity of intensifying screen in cassette to the x-ray photons - The higher the speed of the film/screen, the less radiation is necessary to produce an image, but the less image detail is produced

Answer 47

- Forefoot is thinner than rearfoot; as a result, radiographic density varies between toes and tarsus (toes are thinner than tarsus) - If exposure technique selected for toes, tarsus will be underexposed (look lighter) - If exposure technique selected for tarsus, toes will be overexposed (look darker) *** Need compensation filter to balance unequal radiographic density between forefoot and rearfoot

Answer 48

As temperature and immersion time of film in developer increase, radiographic density increases (image darker), and vice versa Don't need to worry about this because you will never have to do this

Answer 49

Allows visibility of detail Two types - Radiographic contrast - Subject contrast

Answer 50

- Result of difference in densities that allows viewer to discern between two adjacent densities within the same image - Affected by type of intensifying screen, film’s density, characteristic curve, and processing

Answer 51

- Result of attenuation differences as x-rays pass through body - Affected by tissue thickness, type, atomic number and density

Answer 52

- Short | - Long

Answer 53

- Used in foot and ankle imaging | - Distinguishes bone margins from adjacent soft tissues

Answer 54

- Used in abdomen | - Visualize different soft tissue structures that have more similar densities

Answer 55

- Higher kVp’s produce low contrast and vice versa - To produce shortened contrast, increase mAs by 2 and decrease kVp by 15% - To produce lengthened contrast, decrease mAs by ½ and increase kVp by 15% *** NOTE: need to adjust mAs to maintain the same radiographic density (degree of "blackness"), so if your contrast is off, you need to change TWO things, you can't just change the kVp *** If you don't manipulate the mA you will either get a too-dark or too-light image *** KNOW THIS ***

6 - Radiation Physics and X-ray I Flashcards

(80 cards)