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Flashcards in Week 1 & 2 - Notes Deck (52)
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1
Q

Define collimated beam

A

Collimated light is light whose rays are parallel, and therefore will spread minimally as it propagates. The word is related to “collinear” and implies light that does not disperse with distance (ideally), or that will disperse minimally (in reality).

2
Q

Technician’s role in imaging

A
  • get imaging info on patients as efficiently as possible
  • consistent exposure and processing standards
  • protecting all involved from x-ray scatter
  • other imaging modalities in addition to radiography (e.g. ultrasonography, endoscopy, clinical photography)
3
Q

Other aspects to consider with imaging

A
  • keeping images as legal docs
  • appreciating digital revolution
  • radiology is a patient service and profit center, requiring mgmt
4
Q

What is an X-ray?

A

A short wavelength portion of the EM (electromagnetic) spectrum having an ability to penetrate/pass through biological tissue.

5
Q

What does an X-ray do?

A
  1. Hits the target
  2. Penetrates the target
  3. Emerges from the target
  4. Emergent radiation is “captured” by a recording media
  5. The media is processed to reveal the image
6
Q

Physical aspects of x-rays

Energy on the EMS

A
7
Q

Generating X-rays

A
8
Q

Inside the x-ray tube

A
9
Q

X-ray tube basics

A

Outside: Lead housing

Inside: X-ray tube

  • heat mgmt of tube is critically important (check tube rotating chart, how much heat can it take?)
  • larger machines have rotating anode, smaller machines have fixed anode (heat mgmt strategy)
  • anode + is red
  • cathode - is green
  • voltage comes across wire (like light switch)
  • filament creates boiling electrons, generated of off wire, sent to collision w/anode made of tungsten (hard metal), heat & x-ray are produced (instantaneously)
10
Q

Define focusing cup

A

Directs electrons to tungsten target creating heat and x-ray

11
Q

Define effective focal spot size

A

A reflection from anode’s surface

  • smaller than actual
  • larger focal spots create more image penumbra (soft image around focal point)
12
Q

Define anode brake

A

It slows down motor to a complete stop, once exposure has been made (heat mgmt strategy)

13
Q

Anode heat

A

99% of energy is heat

1% of converted energy are x-rays

14
Q

Define anode

A

Tungsten target in copper

15
Q

Define mAs

A

Milliamperage at filament (amount of current applied accross film) x exposure time

or

Amount of current x length of exposure

***Quantity of x-rays***

  • controls electron “boil” from cathode and quantity of x-rays emanating off of the anode
  • big knob in center of machine
  • timer needs to be set (choice is 100, 200, 300 mAs)
16
Q

Define Kvp

A

Peak kilovoltage

Thousands of volts applied to “drive” electrons from cathode to anode

***Quality of x-rays***

  • changes EMR wavelength of x-rays to affect the penetrant quality of x-rays
  • “65” setting means 65,000 Kvp potential energy controlled by tech to make electrons move from cathode to anode
17
Q

Film-focal distance

A

In vet med usually 40”

  • set and forget for consistency
  • Inverse square law (as we change distance between film focal distance, make exposure compensations)
18
Q

Technique chart

A

Each machine needs its own technique chart

  • ensure you get a reliable film
  • Santees law
19
Q

Formation of primary beam

A
  • x-radiation is filtered through thin sheet of aluminum upon departure from tube head (removes/absorbs “softer” irradiation to “harden” beam)
  • after leaving tube head beam is collimated via movable lead shutters to control vertical & lateral dimensions
20
Q

Latent image

A

Potential image on film

21
Q

Attenuation of x-ray passage creates an image

A

Attenuation = “slowing down”

Variation of passed vs absorbed x-rays yields an image

  • film has emulsion on/in it
  • x-rays hit emulsion layer (silver halide crystals) and change/sensitize it; now they’re susecptible to chemical developer
22
Q

Subject density vs radiographic density

A
  • increasing thickness attenuates x-ray absorption
  • the more penetration of x-rays, the greater the exposure
  • bone has great stopping power
  • lots of sensitized crystals, turn film black
  • lots of attenuation, turns film white
  • Thickness x what it is = subject density
  • All shades of colors = radiographic density
  • Density = how black is film?
23
Q

Image capture …DR

A

True DR = Digital radiography

  • pixel sized sensor arrays detec the intensity and frequency of transmitted x-rays
  • froms image directly from sensor output
  • digital means 1’s and 0’s (sensor hit = 1; sensor not hit = 0)
  • many options for post processing enhancements
24
Q

Image capture …CR

A

CR = Computerized radiography

  • not a direct process, but results in digitized image
  • special cassettes have storage phosphor capturing latent image for later retrieval and processing through scanning
  • place CR cassette in reader, latent image gets taken off phosphor and turned into digital image
  • laser process erases image so cassette may be reused
25
Q

Film (analog) image capture

A
26
Q

How is an image developed?

A

Via conversion of silver halide salt into elemental silver

  • dense black where there is much, tightly packed silver
  • no image (clear film base) where no silver halide was exposed (never sensitized)
  • shades of varying grays between black and clear (actual image, various densities of silver)
27
Q

Film processing

A
  1. Develop
    - developer solution is a reducer that works best at alkaline pH
    - reduces exposed silver halides to “grains” of opaque silver
  2. Stop
    - removes developer from emulsion to terminate development process
  3. Fix
    - thiosulfate fixer chemical dissolves unexposed silver to remove non-black portion of image to create clear and gray areas
  4. Wash & Dry (w/plain water)
28
Q

Processing Time/Temperature

A

To keep film’s image consistent:

  • chemical quality, time and temperature of processing are critical (major benefit of automatic processors w/100*F @ 35secs vs. dip tanks w/68*F @ 5 min)
  • care in handling film is critical to prevent artifacts
  • use special screen cleaners and lint free wipes

**The longer it stays, the warmer the temp, the greater the density of the film!**

29
Q

Reasons Digital is “nice to have”

A

More forgiving w/mistakes

No need for developing chemicals

30
Q

Anode “Heel” Effect

A

Due to the geometry of the angled anode target, the radiation intensity is greater on the cathode side.

Digital or analog

Theoretical and practical effects

Practice = Always point thicker side of anatomy toward cathode (-)

CAVT’s cathode is on left, therefore always have head of animal pointed to left

Very important in canine abdominal films especially in deep chested dogs

31
Q

X-Ray Scatter

A

Ricochets and reflections of the primary beam as they interact with tissue on their way through the target

Scatter exposes the media but cannot contribute to image

  • creates film fog
  • reduces contrast
  • degrades sharp edge effects
  • lateral scatter and backscatter expose patient and techs
  • useless to image formation and harmful to everything else
  • the thicker the tissue, the worse the scatter

PPE only protects against scatter, NOT the primary beam!

32
Q

Grids to control scatter

A

Grid factors include:

  • lines per inch
  • grid ratio or spacing ratio

Grid does what:

  • reduces scatter
  • improves film
  • absorbs some of primary radiation (need to compensate for this)
  • cut off is 10 cm:

Subject is less than 10cm = table top

Subject is greater than 10cm = shoot w/grid

(in the latter case, the order would be: subject, table, lead grid instrument, cassette)

33
Q

Focused grids

A

Progressively angled lead plates

Positioned at angles, allows more of radiation to come through

Factory set to 40” distance for focused grid

If subject is moved out of focus, you will lose some of image

34
Q

What is Sante’s rule?

A

Calculation for determining approximate kVp for given exposure, based on patient measurement in cm and grid being used. Used as a starting point for new technique chart.

kVp = Tissue thickness in cm times 2 plus SID in inches plus grid factor

Most veterinary grid ratios are 8 : 1

35
Q

Stationary vs. Moving grids

A

Stationary grids may show fine grid lines on the image

Potter-Bucky Grid & Diaphragm (“Bucky”) is a mechanical system to put the under-table grid into motion at exposure, thus blurring the grid lines

Film tray is stationary and is NOT the bucky

Grid movement is via motor or spring

Frequently used in veterinary radiography

Downside of bucky use: the sound/vibration may startle your patient

36
Q

Summary of grids

A

Is a grid present?

  • if shooting table top = no grid!
  • Equine extremeties = no grid!
  • shooting under table (larger animal, e.g. beagle), better w/grid

Generally begin using grid at >10cm patient thickness

Increased x-rays are needed to penetrate grids (therefore, different technique charts are needed for table-top vs under-table use)

Grids and bucky are precision instruments (require little care but lots of protection from damage)

37
Q

Safety w/ionizing radiation

A

Rapidly dividing cells are most at risk (somatic and genetic cells equally sensitive)

Young cells more vulnerable than older

Animals & humans equally sensitive

Blood or GI cells are more sensitive than skin or fat cells

X-ray energy can damage DNA (disrupt code, create mutation)

Ionizing radiation is mutogenic in low doses

In high doses it can destroy completely

38
Q

SIEVERT

A

Dose equivalent of absorbed radiation in biological tissue

Also reported as Millirems

Exposure is cummulative

39
Q

MPD

A

Maximum Permissible Dose

40
Q

ALARA

A

As Low As Reasonably Achievable

(objective to keep accumulation of radiation as low as possible)

41
Q

Do CTs and MRIs use radiation?

A

CT uses radiation

MRI does not use radiation

42
Q

Key Items to Work Safely

“The Big Three”

A

Time

Distance

Shielding

  • get a diagnostic exposure the first time
  • get as much distance as possible between yourself and the primary beam (inverse square law)
  • use proper PPE (thyroid shield, apron, gloves = inspect q6 months, radiograph annually to check for holes)
43
Q

Radiographic Density

A

Quantity

Degree of blackness in the film emulsion = exposed silver halides

Density is mostly controlled by mAs

Limits to achieving maximum blackness?

  • not enough mAs (# of x-rays/quantity)
  • not enough kVp (quality of x-rays)
  • compromised developer strength & activity
44
Q

Radiographic Contrast

A

Quality

The degree of perceptible difference between two adjacent gray “tones”

High contrast = large differences between adjacent densities/grays

Low contrast = small differences between adjacent densities/grays

Major controlling factor is kVp

Difference between shades of gray

45
Q

Short Scale of Contrast

A

Considerable differences between densities and a minimal number of total densities

  • this is achieved by using a lower kVp
  • usually selected for orthopedics and extremities
46
Q

Long Scale of Contrast

A

Image having only slight differences between adjacent densities and having a larger total number of densities

  • this is achieved by using a higher kVp
  • usually selected for abdomen & thorax
47
Q

Contrast Scale Differences

A

Fewer gray shades

Called “Higher Contrast”

Called “Shorter Scale”

Use Lower kVp

App = Orthopedics

Vs.

More gray shades

Called “Lower Contrast”

Called “Longer Scale”

Use Higher kVp

App = Soft Tissue

48
Q

Digital = “Noise”

Film = “Grain”

A

Noise is graininess mottling or a textured appearance

  • in film radiography the amount of grain is mostly set by the film/screen combination
  • in digital radiography the amount of noise increases due to underexposure
49
Q

Exposure changes for digital

A

To decrease noise, technician may increase mAs to keep DVM happy, however, …

  • upward “exposure creep” increases scatter for all involved
  • digital systems need a technique chart as much as analog systems
  • digital systems should not be considered “magic”
50
Q

Grids, Grid Lines, Collimation in Digital

A

Some true DR digital systems are able to process away fog and artifact from scatter and backscatter (grids not needed)

Tight collimation (as typical for film radiography to reduce scatter) is less necessary for digital systems

51
Q

Computer resources in digital

A

New systems come onto the market every 5-7 yrs

Image back up required

Acquire high quality, high latitude, gray scale monitor

Technical concerns:

  • brightness (lumens)
  • resolution
  • gray scale
  • contrast ratio
  • viewing conditions
  • scheduled recalibration
52
Q

DICOM

&

PACS

A

DICOM = Digital Imaging & Communications in Medicine

  • embeds signalment and exposure information
  • a universal technical standard for file transmission from computer to computer

PACS = Picture Archival Computing Systems

  • electronic film file management
  • uses DICOM and displays and “files” film locally
  • may help manage the on-site/off-site back-up