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Review Of Radiologic Physics > 3 Projection Radiography I > Flashcards

3 Projection Radiography I Flashcards

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1
Q

Analog radiography uses film to do what?

A

Capture, display, and store radiographic images.

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2
Q

Film consists of what?

A
  • ∼10-μm-thick emulsion supported by a 150- to 200-μm-thick polyester (Mylar) base.
  • Emulsion layer on both sides of the base.
  • Protective coating, antistatic, or anti-crossover layer.
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3
Q

What are the machines uses single emulsion films?

A

Laser and mammography.

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4
Q

What is the contains of the emulsion?

A

Silver halide (iodobromide) grains, which can be sensitized by radiation or light to hold a latent image.

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5
Q

What is the contains of Silver halide?

A

1 μm in diameter and contain between 10^6 and

10^7 silver atoms.

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6
Q

How many grains?

A

10^9 grains per cubic centimetre.

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7
Q

How the grain will be sensitized?

A
  • Several light photons must be absorbed to sensitize each grain.
  • A grain may also be sensitized by absorbing a single x-ray photon.
  • Can also be sensitized by thermal and chemical processes without photons (i.e., fogging).
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8
Q

Fading and fogging can be aggravated by what?

A

Environmental heat and humidity.

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9
Q

What are the steps of film processing?

A

Exposure, Developer, Fixer, Wash, and Dry.

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10
Q

What will happen after exposure?

A

After exposure, grains have a few neutral silver atoms in the speck along with millions of Ag+ ions.

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11
Q

What is the film development process?

A

Converts the invisible latent image to a permanent visible image.

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12
Q

How sensitized grains are reduced in the alkaline developer solution?

A

By the addition of electrons, which converts the positive silver ions to silver atoms.

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13
Q

What is the result of a developed step?

A
  • A developed grain results in a speck of silver that appears black on the film.
  • Unexposed grains with no latent image are developed at a much slower rate.
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14
Q

Film speed, contrast, and fog levels are all affected by what?

A

Developer chemistry and temperature.

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15
Q

What is the effect of increasing the developer temperature or developer time?

A

It can increase film contrast and density also increases the level of fogging on the processed film.

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16
Q

What is developer temperatures typically range?

A

From 31◦C to 35◦C.

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17
Q

What is (replenishment)?

A

The processor must supply fresh developer as more films are run.

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18
Q

What is the fixing solution contains? and what will do to the image?

A
  • The fixing solution contains acetic acid to inhibit further development and remove unexposed silver halide grains.
  • Fixing makes the image stable.
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19
Q

What is the result of poor or Inadequate fixation?

A

It can result in a milky appearance to the film.

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20
Q

Why washing the film again?

A
  • After fixing, the film is washed again to eliminate all chemicals and is then dried by heaters or infrared lamps.
  • Incomplete removal of the fixer causes the film to turn brown.
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21
Q

How long is the total processing time?

A

Typically 90 seconds (e.g., 25 seconds developer time, 21 seconds fixer time, 44 seconds washing and drying time).

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22
Q

What is the effect of dirty, uneven, or maladjusted rollers?

A

Can leave lines or other artifacts (e.g., π lines) on
the film.
Static electricity also causes severe film artifacts.

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23
Q

Processor QC involves what?

A

Measuring developer temperature and monitoring the density and contrast of film exposed to a light source in a sensitometer.

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24
Q

Film blackening is measured using what?

A 
Optical density (OD)  = log10(I_0/I_t), where I_0 is the light intensity incident on the film, and I_t is the light
transmitted through the film. OD can be measured using a densitometer.
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25
Q

What is the transmittance of the film?

A

Transmittance is the fraction of incident light passing through the film, where the transmittance = I_t/I_0. As OD increases, transmittance decreases.

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26
Q

What is the useful range of film ODs?

A

Is from∼0.3 (50% transmittance)to∼2 (1% transmittance). Densities greater than about 2 require the use of a hot (bright) light.

27
Q

What are characteristic curves are also known as H and D curves?

A
  • Represents the relation between radiation intensity (air kerma) and resultant film optical density.
  • The toe is the low-exposure region, and the shoulder is the high-exposure region of the curve.
  • Fog is the level of blackening due to a few grains being developed in the absence of any radiation exposure.
  • Base refers to the density of the film base alone, which will absorb a small fraction of any incident light.
  • Base plus fog levels are ∼0.2 OD units.
  • An unexposed film that is processed will thus have a film density of ∼0.2.
28
Q

What is the relationship between film time and radiation?

A

Fast films require less radiation to achieve a given film density. Slow films require more radiation.

29
Q

What are the Intensifying screens?

A
  • Contain phosphor crystals that absorb about 50 times more of the incident x-rays than a radiographic film.
  • For each x-ray absorbed in a screen, hundreds of visible light photons are produced that expose the film.
30
Q

What is the job of the Intensifying screen?

A

The screen converts the x-ray pattern to a light pattern, which is subsequently recorded on radiographic film.

31
Q

What are the advantages of the Intensifying screen?

A

The use of intensifying screens decreases the exposure time required for a given film density.

  • Shorter exposures result in a lower patient dose.
  • Shorter exposure times decrease x-ray tube loading.
  • Shorter exposures also decrease blur caused by patient motion.
32
Q

What are the contains of the Intensifying screen?

A

High atomic number materials to maximize the absorption of x-rays.

33
Q

What are the disadvantages of using calcium tungsten in the Intensifying screen?

A

Tungsten has a high K-shell binding energy (70 keV), which is higher than the mean photon energy levels normally used in diagnostic radiology.
*The high K-edge energy of tungsten (W) means that x-ray absorption is less than optimal.

34
Q

What is the common screen thickness?

A

A common screen thickness is ∼200 μm.

35
Q

What are the emitted colors of Lanthanum oxybromide and calcium tungstate?

A

*Lanthanum oxybromide (LaOBr) and calcium tungstate (CaWO4) emit mainly blue light.

36
Q

What are the emitted color of Gadolinium oxysulfide?

A

*Gadolinium oxysulfide (Gd2O2S) emits mainly green light.

37
Q

Define spectral matching?

A
  • The light color from a screen and the light sensitivity of the film must be matched.
  • Matching the light emitted by the screen with film sensitivity is known as spectral matching.
38
Q

Conventional film is sensitive to what?

A

Conventional film is sensitive to ultraviolet and blue light.

39
Q

Orthochromatic film is also sensitive to what?

A

Orthochromatic film is also sensitive to green light.

40
Q

What is absorption efficiency?

A

The percentage of x-ray photons absorbed in the screen.

41
Q

What is the intensification factor?

A

The ratio of exposures, without and with intensifying screens, required to obtain a given film density.

42
Q

The intensification factor depends on what?

A

The absorption and conversion efficiency of the screen.

43
Q

What are the typical intensification factors?

A

Typical intensification factors are 30 to 50.

44
Q

What is the name of the computer system?

A

Computers use the binary system (base two).

45
Q

Defined the bit?

A

A bit (binary digit) is the fundamental information element used by computers and can be assigned one of two discrete values.

46
Q

What are the types of detectors?

A
  • Gas detectors.
  • Solid state detectors (Semiconductor Radiation Detector).
  • Photostimulable phosphors.
  • Scintillators.
  • Photoconductors.
47
Q

Define Gas detectors?

A

*A high voltage across an air or gas chamber measures the electrons liberated by the
incident x-rays.
*Used to accurately measure
x-ray beam intensities and are calibrated in air kerma (Gy).

48
Q

For imaging, what is the type of gas detector?

A

Gas detectors must have a high x-ray absorption efficiency and would not use air. Therefore, high atomic number gases and/or high pressures.

49
Q

Example of imaging gas detector?

A

*Xenon is a high atomic number gas (Z = 54; K-edge energy 34.6 keV) and is an efficient x-ray detector at high pressure.

50
Q

Define solid-state detectors?

A

In solid-state crystals (e.g., NaCl), atoms are arranged in a regular three-dimensional structure.
In solid-state crystals, electrons occupy energy bands.

51
Q

Define Photostimulable phosphors detectors?

A

The release of stored energy within a phosphor by stimulation with visible light
Computed radiography (CR) uses photostimulable phosphor plates made of barium
fluorohalides.
X-ray photons interact with the electrons in the phosphor, creating a latent image.

52
Q

Define Scintillators detectors?

A

Scintillators are materials that emit light when exposed to radiation. Scintillators are also known as phosphors.

53
Q

Define photoconductor detectors?

A

A solid state device that detects x-rays directly.

Selenium (Z = 34; K edge energy 12.7 keV) is the most common photoconductor in use in digital radiography.

54
Q

Define Image window width?

A

Refers to the range of gray scale values displayed.

55
Q

Define Image contrast?

A

Within the window range is increased more as the window is narrowed.

56
Q

Define Windows level?

A

The center value of the window width and therefore overall image brightness.

57
Q

Define Histogram?

A

Equalization eliminates white and black pixels that contribute little diagnostic information, and expands the remaining data to the full display range.

58
Q

Define Low-pass spatial filtering?

A

A method of noise reduction in which a portion of the

averaged value of the surrounding pixels is added to each pixel.

59
Q

Define Unsharp masking?

A

Involves subtraction of a smoothed version from the original, which is then added to a replicate original.
Visibility of tubes, lines, and catheters is improved, but noise increases and artifacts may be introduced.

60
Q

Define Background subtraction?

A

It can digitally reduce the effect of x-ray scatter to increase image contrast.

61
Q

Define Energy subtraction?

A

Techniques are based on subtracting projection radiographs obtained at two x-ray generator settings (e.g., 60 and 110 kV).

62
Q

AEC is also known as phototiming

A

–Measures the actual amount of radiation incident on the screen–film and terminates the exposure when the correct amount has been received.
–To ensure the correct film density,

63
Q

Screen film speed

A

–As the speed increases, the air kerma required decreases.

64
Q

Screen speed increases with

A

–Increasing screen thickness, absorption efficiency, as well as conversion efficiency.

Review Of Radiologic Physics (11 decks)

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