Radiology

Question 1

Best film for period disease>

Answer 1

BW, PA (Parallel)

Question 2

Ideal X-rays uses:

1. small or large focal spot?
2. long or short target-receptor distance?
3. long or short object-receptor distance?

Answer 2

1. smallest focal spot (image sharpness)
2. longest target-receptor (x-ray source and receptor) PID
3. shortest object-receptor (tooth and image receptor)

Question 3

Which results in more magnification:

1. shorter or longer PID?
2. shorter or longer object-receptor distance?

Answer 3

1. shorter PID (although long PID reduces exposure)

2. longer (although shorter is ideal to prevent distortion)

Question 4

increase exposure factor causes what to the density?

Answer 4

Increases it (darker it gets)

Higher kVp, mA, time
decreased thickness causes less exposure

Question 5

number of electrons flowing per second in the x-ray tube

Answer 5

mA (quantity) = TEMPERATURE of the filament = 7-15 mA

- Quality = penetrating power = kVp = speed and energy of electrons = 65 - 100 kVP

Question 6

Fractionalization

Answer 6

• means total radiation dose is delivered in smaller, but multiple doses
• Increases O2 tension –> Greater tumor destruction
• Has a larger chance for host cellular repair.

Question 7

Radiation effects to normal marrow

Answer 7

• replaced with fatty marrow and fibrous CT

- By end of Week 2 of therapy, loss o taste buds + mucositis –> pseudomembranes

Question 8

Osteoradionecrosis risk with ___ Greys of radiation

Answer 8

> 40 Gy

Hypocellular, hypovascular, Hypoxic

Question 9

Stochastic vs non-stochastic effects

Answer 9

stochastic = direct dose dependent = cancer
non-stochastic = have a threshold of radiation = hair loss, infertility

Question 10

most radiosensitive and radio resistant cells

Answer 10

radiosensitive = small lymphocyte
radioresistant = muscle, nerves

Question 11

X-ray properties

Answer 11

no mass
no charge
speed of light
travels in waves (short waves)
straight lines
can cause fluorescence (longer waves)
cannot be focused to a point

Question 12

Exposure time of digital vs F-film vs D speed

Answer 12

digital is 50% of F speed (Fast film)
F speed is 60% of D speed

Dental x-rays use 70kV or higher (higher doses lower patients exposure on skin)

Collimation is 2.5 inches max to reduce exposure

Question 13

most common digital image receptor?

Answer 13

CCD

• contains a silicon chip
• sensitive to light (x-rays)

Question 14

maximum permissible radiation dose

Answer 14

non-occupation = 0.001 Sv/yr (a pregnant occupation)
occupation = 0.05 sv/yr

• stand 6 feet, perpendicular (90 degrees) from source

Question 15

match high/low contrast with short/long scale contrast with black/grey/white scale with high/low kV

Answer 15

High contrast = black/white = short scale = low kV

Question 16

Process film by hand: developed –> fixer –> replenisher

Answer 16

1. Developer is needed to transform the latent image to a visible one. This removes the halide portion of the silver halide crystals. Silver halide crystals are reacted when touched with x-ray beam –> radiolucency.
2. Fixer is ammonium thiosulfate which clears unexposed/under-developed silver halide crystals and hardens it.

Note: the developer chemical is neutralized by an acidifier (acetic/sulfuric acid) that is part of the fixer solution. This is also done in the washing stage before the fixer.

3. Replenisher compensates for loss of volume from oxidation and maintains adequate amounts of chemicals for uniform processing

Fixing time (10 minutes) is twice as long as developer (5 minutes)

Question 17

1. There must be __ % of demineralization in teeth to be seen radiographically.
2. There must be ___% of bone alteration for PA breakdown to be seen radiographically.

Answer 17

1. 30-60%
2. 30-50%

PA radiolucency is only seen once cortical plate is perforated

Need only 0.5 - 1.0 mm needed through cortical bone

PA lesions will heal in 6-12 months post successful RCT

Question 18

SLOB rule angulation

Answer 18

Horizontally 10-15 degrees

Question 19

What is the most likely cause of a U shaped radiopacity covering the apex of the palatal root of the maxillary 1M?

Answer 19

zygomatic process of the maxilla

Question 20

Lateral ceph. growth reference point

Answer 20

Anterior cranial base

Lateral ceph magnification: 7-8% acceptable

Question 21

Hamulus (Hamular process)

Answer 21

• surved, hook shape of the medial pterygoid of the sphenoid bone
• superior attachment for the pterygoidmandibular raphe (a tendon between the buccinator and superior constrictor muscle)

Hamular notch is between the max tuberosity and hamulus

Question 22

Radiation types

Answer 22

kinetic enegery converts electrons to x-ray photons via:

1. General radiation = braking (sudden stop of photons due to Tungsten present = 70% of radiation) or Bremsstrahlung
2. Characteristic radiation = electrons dislodge an inner shell electron from tungsten, causing ionization. Other electrons fill it in and produce a photon = small % = occurs only at > 70kVp

Primary radiation = what leaves the tube head
Secondary radiation = formed after the primary beam hits matter.
Scatter radiation = type of secondary radiation where its deflected by matter
Compton scatter = type of scatter where ionization (high E interacts with OUTER ring) takes place (62% of scatter)
Coherent/unmodified scatter = lower E electron causes no interaction