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Diagnostic Imaging > X-Ray Production & Radiation Safety > Flashcards

X-Ray Production & Radiation Safety Flashcards

1
Q

What are 4 helpful uses of diagnostic imaging?

A
  1. screening test
  2. disease localization
  3. disease progression - stable vs. progressed
  4. evaluation of therapy - pulmonary edema improvement, aboral progression of GI foreign material, therapeutic failure
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2
Q

How does radiography work?

A

x-rays are used to generate an image of specific body areas based on attenuation of x-rays by different organs and structures —> those rays that pass through are detected by a digital radiography detector

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3
Q

How many dimensional images are produced by radiography?

A

TWO-dimensional images of a 3-dimensional patient, displayed in shades of gray

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4
Q

What is fluoroscopy? In what situations are they commonly used?

A

use of X-rays to create real-time images of the patient (cineloops), typically to assess function

  • swallowing studies
  • dynamic assessments of respiratory tract to assess tracheal and bronchial collapse
  • evaluation of the urinary tract
  • placement of stents, coils, and other occluder devices
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5
Q

What is computed tomography (CT)? In what 2 ways does it compare to radiography?

A

use of X-rays emitted from a fan in a round gantry through which the patient is translated, producing thin, cross-sectional images

  1. lacks superimposition
  2. calculated attenuation of X-rays improves contrast resolution —> hemorrhage vs fluid, white vs gray matter, fluid vs soft tissue
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6
Q

What is magnetic resonance imaging (MRI)? What concept is used?

A

magnetic manipulation of the hydrogen atom (strong magnetic momentum) generates a current in a coil of wire abe to generate images based on the different environments and chemical bonds of hydrogen atoms

Faraday’s Law

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7
Q

How do ultrasounds work?

A

use sonic waves generated by piezoelectric crystals to create cross-sectional images

  • crystals create sound pulses that travel through a patient and are reflected at different tissue interfaces as pixels on the monitor with grayscale representing amplitude
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8
Q

What affects echogenicity of tissues on an ultrasound?

A

different tissue densities affect propagation and reflection of sounds, which dictates the visibility of the tissue interfaces

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9
Q

What is nuclear medicine?

A

radiation from radioactive elements (active radiopharmaceuticals) are used to target a specific physiologic process, like bone turnover or thyroid function

  • patients are the source of radiation energy used for imaging with cameras or radiation detectors
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10
Q

How are X-rays produced?

A
  • a current is applied to a cathode, allowing electrons to generate in a filament via thermionic emission
  • electrons dissociate from the filament into an electron cloud, which is accelerated toward a positive anode by applying kilovoltage potential
  • electrons hit the rotating tungsten target and decelerate, releasing heat and x-rays
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11
Q

How are the number and energy of X-rays controlled?

A

INCREASE NUMBER = increase tube current (mA) from cathode

INCREASE ENERGY = increase kilovoltage potential

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12
Q

How are the energy and wavelength of a wave related?

A

inversely proportional

higher energy = shorted wavelenth

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13
Q

What waves have low frequencies? High?

A

LOW = radio waves, long wavelength, travels great distances

HIGH = x-rays, gamma rays (diagnostic imaging), short wavelength, travel short distances

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14
Q

When is radiation considered ionizing? What is the threshold?

A

if it contains enough energy to eject an electron from an atom, creating an ion (this is what makes radiation dangerous)

15 electron-volts (eV)

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15
Q

What is transmitted radiation from x-rays? What dictates its opacification? What does the location that the x-rays strike determine?

A

contains information about the patient —> what is exposed on the detector

number of x-rays and relative energy of their waves

information about organ/lesion location, assuming it has not been scattered

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16
Q

What happens when x-ray energy is absorbed by the patient?

A

creates contrast in the resultant radiographic image

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17
Q

What is x-ray scatter? Why is it so significant?

A

radiation enters the patient, strikes body parts, and scatters in a new direction

degrades image quality and creates a source for personnel exposure (lead gloves, gowns, and thyroid protectors)

18
Q

In what 2 ways can scatter be mitigated?

A
  1. collimate appropriately (accurately parallel beams)
  2. use of a grid can degrade an image, but it will reduce scatter reaching the detector
19
Q

What is important to note about the use of lead gloves/equipment?

A
  • will NOT protect from primary beams, only scatter radiation
  • should NOT be in the image
  • will NOT protect from scatter radiation that passes through the animal where they are being held
20
Q

What are the 3 possible outcomes for x-rays used on a patient?

A
  1. absorbed by the patient’s tissues
  2. sent through the patent and to the detector - contributes to image formation
  3. scattered by patient’s tissues - fogs image and creates radiation hazard
21
Q

How are images on radiographs formed? What 2 things affect the image?

A

differential absorption of x-ray photons within a patient

  1. thickness of tissue
  2. tissue type (density)
22
Q

How does the number of x-rays hitting a detector alter an image?

A

HIGH NUMBER = darker, radiolucent

LOW NUMBER (more absorbed by patient) = white, radiopaque

23
Q

What structure is causing this opaque line? Why does it appear more opaque than the surrounding bone?

A

spine of the scapula

it is thicker than the surrounding bone, meaning more x-rays are absorbed

24
Q

What are the 5 tissue opacities seen on radiographs?

A
  1. air/gas - least dense, more x-rays pass through, most lucent (black)
  2. fat
  3. soft tissue/fluid
  4. bone
  5. metal - extremely dense, very little radiation passes through, white (radiopaque)
25
Q

Where is the most lucent (darkest) portion of air/gas seen on an x-ray?

A
  • portion around the patient* (x-rays freely pass through room air)
  • gas within organs (more opaque than the gas around the patient)

(pulmonary alveoli are gas-filled, but the x-ray is also passing through the body wall and parenchyma)

26
Q

Radiographic opacities:

A

A = air
B = bone
M = metal (ingested nail, microchip)
W = water, soft tissue (spleen)
F = fat (more lucent than fluid)

27
Q

What are the 2 mechanisms of radiation damage?

A

ionizing radiation dislodges an (outer shell) electron from an atom, causing biological damage to cell structures (15 eV)

  1. direct damage: release of energy damages DNA, proteins, cell walls, and other cell components (30%)
  2. indirect damage: produces free radicals, like ionized water and peroxides (H2O2) (70%)
28
Q

What are the 2 types of effects of radiation?

A
  1. deterministic effects - predictable adverse effects where incidence and severity increase as a function of dose after a threshold
  2. stochastic effects - occur by change where probability is proportional to the dose and severity is independent to the dose
29
Q

What affects the threshold dose of different tissues?

A

radiosensitivity, where rapidly dividing cells (intestinal epithelium, skin) are more susceptible than slowly dividing cells (muscle, kidneys, CNS)

30
Q

What can and cannot be calculated in stochastic effects?

A

probability (proportional to dose)

occurrence of the event in an individual

31
Q

What are 2 types of stochastic effects?

A
  1. genetic effects - most concerning in pregnancy, where they increase the probability of a random mutation that can affect fetal development, but are not carried forward
  2. somatic effects - relate to the probability of developing cancer (increased exposure increases probability, but there is no definitive outcome or threshold dose)
32
Q

What acronym is used for radiation protection?

A

As
Low
As
Reasonable
Achievable

33
Q

In what 3 ways is ALARA implemented?

A
  1. TIME - minimize the amount of times one is exposed (minimize retakes to protect the patient and staff and time one is exposed to radioactive patients and their excrements)
  2. DISTANCE - far away as possible, outside of the room at minimum 6 feet
  3. SHIELDING - lead aprons, gloves, thyroid shields, lead walls/shields, equipment maintenance of collimator and tube shielding
34
Q

What is the inverse square law?

A

quantity of radiation decreases inversely with the square of the distance from the source

35
Q

Should patients be held for radiographic examinations?

A

no —> use positioning devices, like sandbags, tape, troughs, chemical restraint

36
Q

How thick should lead safety equipment be? How should they be maintained?

A

5 mm lead equivalent

  • hung up to prevent cracks from forming in the shielding
  • every 6 months, radiographs of shields should be taken to ensure that no cracks have developed
37
Q

What organization creates recommendations for monitoring radiation? What are 3 important rules?

A

National Council on Radiation Protection and Measurements (NCRP)

  1. radiation badges must be provided by an employer and are required in radiation areas and must be submitted for readings to ensure exposure limits are not exceeded (National Voluntary Laboratory Accreditation Program for Personnel Dosimetry Processors)
  2. individuals under 18 are not allowed in the radiology suite (<18 = 1 mSv/yr)
  3. pregnant women should declare their pregnancy and should not be working in the radiology suite (500 mRem = 5 mSv/month)
38
Q

What can be provided if the presence of a pregnant woman is necessary in the radiology suite?

A

fetal dosimeters

39
Q

Why is radiographing large animals especially challenging?

A
  • typically standing and sedating
  • hard to be outside of the room during x-ray exposure

(STEP AWAY FROM TUBE DURING EXPOSURE)

40
Q

What are 2 major radiation safety violations seen in the radiograph?

A
  1. human digits are seen - even if they are wearing lead gloves, they are not protected from the primary beam
  2. entirely black background suggests there is no collimation, which would reduce scatter

Diagnostic Imaging (27 decks)

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