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Clinical Pod Med Exam 1 > 7 - Radiation Physics and X-ray II > Flashcards

7 - Radiation Physics and X-ray II Flashcards

1
Q

Matching REVIEW

**KNOW THIS **

1 - Primarily controls optical (radiographic) density…
2 - Primarily controls contrast…
3 - Equal to doubling mAs
4 - To increase contrast…

A

1 - Primarily controls optical density… mAs

2 - Primarily controls contrast… kVp

3 - Equal to doubling mAs… increase kVp by 15% *** (both cause more blackening of the film)

4 - To increase contrast… TWO THINGS: decrease kVp by 15% AND increase mAs by 2 ***

There will be a question on HOW you manipulate contrast - have to manipulate kVp and mAs **

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2
Q

Spatial resolution

A

Refers to image detail, sharpness, definition and is the recorded accuracy of the structures imaged

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3
Q

What influences spatial resolution

A
  • geometry
  • material
  • film/screen contact
  • motion
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4
Q

Terms related to the geometry of x-ray

A
  • Focal spot size
  • Object to image distance (OID)
  • Source to image distance (SID)
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5
Q

Focal spot size

A

Large size leads to decreased detail

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6
Q

Object to image distance

A
  • OID (object to image distance) or the distance between foot and film
  • The greater the distance, the less detail or sharpness
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7
Q

Source to image distance

A
  • SID (source to image distance) or the distance from the tubehead to the film
  • The greater the distance, the sharper the image (but requires increased mAs to maintain the same radiographic density)
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8
Q

Describe the materials of films and screens

A
  • Slower speed produces sharper image (but requires more radiation)
  • Slower screens have smaller crystal size, thinner phosphor layer and greater detail
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9
Q

Describe the contact between film and screens

A

If contact between the film and the screen located inside the cassette is not uniform, an area of blurring will occur

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10
Q

What is the effect of motion in an x-ray

A
  • Causes blurring
  • To limit motion of a part (e.g. pediatric or Parkinson patient), decrease exposure time by ½ and increase kVp by 15% to produce the same radiographic density

* This you will use - Important*

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11
Q

Distortion of x-ray images

A

Misrepresentation of size, shape, or positional relationships of recorded structures

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12
Q

Size distortion

A
  • Known as magnification ***
  • Occurs as OID increases
  • Results in blurring
  • Unavoidable even if foot placed directly on image receptor
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13
Q

Shape distortion

A

Unequal magnification of structures, displacing structures from their actual position

  • Elongation occurs when tube head is angled to the foot or image receptor
  • Foreshortening occurs when part is improperly aligned with tube head and image receptor

Occurs by three mechanisms

  • Central beam not perpendicular to film and/or foot
  • Foot plane not parallel to film
  • X-ray beam not centered over middle of foot
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14
Q

Technique for fixed kVp

KNOW THIS ****

A
  • Typically 60kVp

- mAs is varied per part thickness

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15
Q

Technique for fixed mAs

KNOW THIS ****

A
  • kVp varies depending on part thickness and is typically lower than 60 kVp
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16
Q

Cast radiography

How to take an x-ray through a cast

A
  • Plaster cast: increase mAs 2x normal OR add 10 kVp

- Fiberglass cast: increase mAs 1.5x normal

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17
Q

How to x-ray for a soft tissue mass or foreign body

A

Decrease kVp 15% and double mAs

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18
Q

Matching REVIEW

** KNOW THIS **

1 - X-ray through plaster…
2 - X-ray through fiberglass…
3 - X-ray soft tissue mass…
4 - When using fixed mAs in x-ray, the correct kVp is…

A

1 - X-ray through plaster… Increase mAs by 2x

2 - X-ray through fiberglass… Increase mAs by 1.5x

3 - X-ray soft tissue mass… Decrease kVp by 15% AND increase mAs by 2x

4 - When using fixed mAs in x-ray, the correct kVp is… 50 kilovolt

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19
Q

Artifacts on the film

A
  • Static
  • Fog
  • Scratches
  • Stains
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20
Q

Static

A
  • Caused by discharge of electricity which exposes the film

- Minimize by using a humidifier

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21
Q

Fog

A
  • Unwanted density
  • Caused by radiation, exposure to white light, overexposure to safelights, age of film and chemical reaction
  • Keep cassettes out of exposure room and as far away from radiation as possible
22
Q

Scratch

A

You scratched it when you transferred it

Only with the old way

23
Q

Stain

A

Chemical drops on film prior to exposure

Only with old way

24
Q

Image receptors

A

X-rays, after passing through the body…
1 - Interact with an image receptor (e.g, x-ray film)
2 - A latent image (invisible change) forms in the film
3 - Processed with chemicals to produce a visible image
4 - Viewed on a light box

25
Q

Interaction of x-rays with film/screen

A
  • X-Rays will produce a pattern of varying depths of blackness on the film
  • The incident photons are attenuated to varying degrees by the patient’s tissues
  • The emerging pattern of photons of differing energies affect the film emulsion to produce the latent image
  • Developing the film allows this image to become visible
  • The film emulsion consists of gelatin containing finely dispersed grains of silver bromide or halide
  • The absorption of X-Rays by the silver bromide grains renders them developable
  • Silver bromide grains which have been exposed to X-Rays will be turned black by the developer
  • Unexposed grains are dissolved and removed and leave a white area on the film
  • Therefore, the denser the tissue, the lighter (whiter) it looks because it prevents x-rays from reaching the film
Thicker or denser (bone) = WHITE
Less dense (fat) = BLACK
26
Q

Cassettes

A

A cassette is a light-tight, robust container which will:

  • Hold the film and intensifying screens in close contact
  • Protect the film from visible light, since this will blacken the film as will X-rays
  • Protect the film and screen from damage during use
27
Q

Role of two screens within the cassettes

A
  • Screens contain materials which fluoresce when bombarded by X-rays
  • The radiographic film is sensitive to this visible light emitted by the screens as well as the X-rays themselves
  • The use of both visible light and X-ray photons allows the reduction of exposure times
  • However, film without screens or a cassette is used when very fine detail is required
28
Q

What can make x-ray imaging safer?

A

90% of the exposure on radiographic film comes from the light emitted by the intensifying screen - makes x-ray imaging safer

Composed of light emitting phosphors (calcium tungstate or rare earth)that fluoresce when exposed to x-rays

Because x-ray film is sensitive to light, fewer x-rays are needed to expose the film which reduces exposure time

29
Q

Radiographic film

A

Speed depends on the silver halide crystal size, structure and sensitivity (the larger the silver halide crystal, the faster the speed and the less exposure)

30
Q

Digital radiography

A
  • Does not use the film/intensifying screen as the image receptor, but still need to produce a high quality image while exposure dose is as low as reasonably achievable (ALARA)
  • Uses an electronic detector as the image receptor instead of x-ray film in a cassette
31
Q

Describe the process of electronic detector

A
  • X-rays converted into an electrical signal
  • The latent image formed on the detector is measured and converted into an analog electrical signal that is converted into a digital signal, which is then processed by a computer producing a digital image viewed on a monitor
32
Q

Difference between analog and digital technologies

A

Analog
- Analog technology, information is translated into electric pulses of varying amplitude

Digital
- Translation of information is into binary format (zero or one) where each bit is representative of two distinct amplitudes

33
Q

What is the primary type of digital x-ray detector system that is used?

A

PSP = photostimulable storage phosphor detector

OR

CR = computed radiography detector

34
Q

PSP

A
  • Capture element is barium fluorohalide with europium
  • Whereas x-ray film and intensifying screen is housed in a cassette, PSP screen housed in a imaging plate (IP)
  • Most commonly used in podiatry

Don’t need any of the developing materials and it only takes 1 minute

35
Q

Characteristics of a digital image

A
  • ADC converts the electrical (analog) signal from the digital radiographic detector into binary numbers (the digital signal)
  • Binary numbers are bits
  • Bits are 0’s or 1’s transformed into a two-dimensional array of rows and columns of numbers called a matrix
  • The smallest unit in an image is a pixel
36
Q

Pixels

A
  • Each pixel has three numbers; location along an x- and y-axis (two numbers) and intensity of the pixel at that location
  • A pixel is two-dimensional representation that corresponds to a three-dimensional volume of tissue known as a voxel
37
Q

Pixels and resolution

A
  • Spatial resolution (sharpness of image) directly related to pixel size (smaller the pixel, the higher the spatial resolution
  • Contrast resolution (gray scale) is the smallest density change seen between two tissues that is detectable
  • Number of shades of gray is called dynamic range
  • High-contrast image has fewer shades of gray and has short-scale contrast and vice versa
38
Q

Matching REVIEW

KNOW THIS

1 - Same as high contrast image…

2 - Most common digital x-ray detector system…

3 - Smallest unit of a digital image…

4 - Three-dimensional volume of tissue…

A

1 - Same as high contrast image… Short scale contrast

2 - Most common digital x-ray detector system… PSP

3 - Smallest unit of a digital image… Pixel

4 - Three-dimensional volume of tissue… Voxel

39
Q

Special studies

A

Molecular Imaging Modalities

  • PET scan
  • SPECT scan
  • Fluoroscopy
40
Q

PET scan

A

Positron Emission Tomography

  • Radioisotope carrier is FDG (18-fluorodeoxyglucose)
  • Used to determine sites of abnormal glucose metabolism; inflammatory cells increase uptake of FDG
  • PET tracer emits positrons via radioactive decay
  • Produces results in 2 hours of injection
  • Study requires 30 minutes and patient must remain completely still
  • Usually combined with CT scan (called a PET/CT) and radiation exposure may be substantial
41
Q

SPECT scan

A

Single photon emission computed tomography

  • IV injection of a gamma-emitting radionuclide such as Tech-99, In-111, or Tech-99-HMPAO
  • Gamma camera, in contrast to planar scintigraphy (bone scan), rotates 360° around patient and produces a 3-D image
  • Radiation dose similar to PET/CT
  • Uses include diabetic foot infection, diagnosis early stress fracture
42
Q

Fluoroscopy

** Important **

A

Uses x-ray to produce real-time moving images-most new units use digital technology

Utilizes x-ray image intensifier to reduce radiation

  • Does not use a separate fluorescent screen in a cassette
  • Cesium iodide phosphor is deposited directly on the photocathode of the image intensifier (different than cathode of x-ray tube)
  • Output image is 10,000 times brighter than the input image

This is what you used for Feilmeier & Dayton research

43
Q

“C-arm”

A

Nice for examining an extremity and shaped like a C

It is used a lot in podiatry surgery

Uses an image intensifier and is transmitted to a tv screen

Want to put the body part as close to the intensifier as possible and as far away from the x-ray source as possible - patient safety

44
Q

Factors influencing fluoroscopy exposure rate

A
  • Modern fluoroscopy units produce images with an image intensifier which brightens the image level sufficiently so that the image may be displayed on a TV screen. Fluoroscopy units are usually operated in an automatic brightness control (ABC) mode
  • These units will automatically adjust the brightness by first increasing the kVp to increase x-ray penetration and then adjusts the mA to increase intensity

NOTE: Therefore, exposure to a thick patient will be greater than to a thin patient ***

45
Q

Recommendation #1 for C-arm

A

Recommendation # 1: The image intensifier input should be positioned as close to the patient as practicable. This results in a lower patient dose and sharper image.

46
Q

Recommendation #2 for C-arm

A

Recommendation # 2: Use the exposure pedal as sparingly as possible.

Radiation exposure during fluoroscopy is also directly proportional to the length of time the unit is activated by the foot pedal. Depression of the foot pedal determines the length of exposure. The fluoroscopy time is an important determinant of patient and staff radiation dose. Fluoroscopy units are equipped with a timer and an alarm which sounds at the end of 5 minutes. The alarm serves as a reminder of the elapsed time.

47
Q

Recommendation #3 for C-arm

A

Recommendation # 3: Use “last-image” hold and pulsed fluoro whenever possible.

Most modern fluoro units are equipped with “last-image” hold, which stores the last fluoro image and allows viewing without having to expose the patient again. Many fluoro units also offer a “pulsed fluoro mode”, in which the x-ray beam is pulsed rapidly on and off and results in a lower radiation dose without significantly degrading the appearance of the image on the display.

STOP and look at your image and hold it so that you’re not doing continuous x-ray exposure

48
Q

Recommendation #4 for C-arm

A

Recommendation # 4: Use the smallest field of view practicable.

Radiation exposure also depends on x-ray field size and keeping the x-ray field as small as possible (by using collimators) which will decrease the dose to BOTH the patient and staff in the fluoroscopy suite. Restricting the field size not only decreases radiation dose but will also produce a better image. The contrast in the image between various tissue types will be greater for the smallest field of view that encompasses the desired anatomy.

49
Q

Recommendation #5 for C-arm

A

Recommendation # 5: High dose or detail modes should be used only sparingly.

Many fluoro units will have various dose modes, such as low dose, medium dose and high dose mode.

It is important to recognize that fluoroscopic image quality can be adversely affected by too few x-rays in the image; the image is noisy for low dose. More tissue contrast is produced by the “high dose” mode which will improve the image quality at the expense however of increased patient dose.

50
Q

Recommendation #6 for C-arm

A

Recommendation # 6: Magnification should be used only when necessary.

Fluoroscopy units are capable of using different magnification modes. Image resolution is improved with magnification but field size is reduced and patient radiation dose is increased. Patient dose is minimized by using the lowest magnification (largest field size) appropriate for the image procedure being performed.

51
Q

Recommendation #7 for C-arm

A

For C-arm type fluoroscopy units, the patient should be positioned as far from the x-ray tube as practicable to minimize patient entrance dose. To reduce personnel exposure the x-ray tube should be positioned beneath the patient.

52
Q

What do you need to know for the exam?

A
  • Know first couple of slides (rad, rem, Sv, Gy know terms)
  • Definitions of exposure, absorption, dose equivalent, effective dose equivalent
  • Know techniques – child, Parkinson’s, soft tissue, cast, pregnancy
  • Proper use of flouroscopy unit
  • Difference between quantity, quality, what units determine each, settings that are normal that you can control
  • How you manipulate radiographic contrast
  • Know the difference between the types of x-rays that are produced out of the machine (characteristic, Bremm) and the reactions of x-rays (scattering and photoelectric effect)
  • Know how x-rays are produced on the film and silver/calcium tungstate in the screens, so how that produces white and black on the visible image
  • Realize that after you take the x-ray, if you take out the film without a PSP film, it is black, you have to develop it
  • Understand the PSP laser and light developing, photo detector, etc.
  • Anything I said is not on the exam is not on the exam

Clinical Pod Med Exam 1 (17 decks)

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