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In film, it is called density. On the computer, it is called __________.
Brightness
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Two photographic factors that allow detail to be seen:
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Typical OD range
.25 - 2.5
.25 is lower density; whiter
2.5 is higher density, darker
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Instrument used to measure density.
Densotometer
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What is density?
variations of darkness; the black and white
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What is the main controlling factor of density?
mAs (mass)
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3 Lightening techniques:
Bright "hot" lights - higher intensity; higher amps (higher numbers) means more light penetrating
- Digital optical scanner - adjust the settings
- Duplication (copying)
- an older machine reprints the film lighter/darker
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main elements of the body that the x-ray interacts with:
hydrogen (water component, body tissue, low atomic #)
oxygen (water component, body tissue, low atomic #)
calcium (bone, high atomic #)
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Does increasing mAs increase or decrease density?
Increasing mAs increases density.
Decreasing mAs decreases density.
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What is the "rule of thumb" when increasing mAs to change density?
Double it to increase, Half it to decrease
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How much of a change is needed, in mAs, before a change in density is discernible to the naked eye?
a 30% change.
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What type of radiation are we using? What is special about it?
We use x-ray radiation. It is an ionizing radiation.
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What is the main influencing factor of density?
kVp
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To change the density by changing the kVp, what is the generalized rule?
Change in 15% increments...the 15% rule
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generators, listed from weakest energy to strongest energy:
- single phase
- 3-phase, 6-pulse
- 3-phase, 12-pulse
- high frequency
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Changing the kVp changes the:
energy of the beam
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If you have good technique on a high frequency machine, what would you have to do if you changed to a single phase machine?
You would have to increase your technique since it's a weaker beam. It would need increased power to show the same image as well as a stronger machine.
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Define Blooming.
causing pixel size to become larger than the nominal or state size; a distortion
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Describe the expected influence of the focal spot on density when the unit has been properly calibrated.
There should be no difference between large and small focal spots.
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What is the anode heel affect?
An effect that alters the intensity of radiation (and therefore the density) between the anode and cathode ends of the x-ray tube.
up to 45% difference depending on the angle of the anode
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When your patient is laying on the table, his/her head is always to your ________ (direction).
left
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The patient's head is located on the ______ side, and the feel are located on the _______ side.
head: cathode
feet: anode
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Towards the cathode side, the density is ________.
Greater (up to 45%)
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SID is short for:
Source-to-image receptor distance
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Inverse Square Law
- The law affects exposure in inverse proportions to the square of the distance.
- Simply, if you step ****
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In this class...what will we always do with distance when it comes to formulas?
Square anything to do with distance!!
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When distance increases, density ____________.
decreases
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When collimation increases, density __________.
decreases
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When field size increases, density __________.
increases
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When beam restriction increases, density __________.
decreases
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Increased filtration will ____________ density.
decrease
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Filtration ___________ overall average energy of the beam.
increases
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As tissue thickness increases, film density __________.
decreases
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What happens as the atomic number of tissue gets higher?
The tissue absorbs more of the x-ray, allowing less x-ray to pass through to the film. Therefore, the film density is less where there is tissue with high atomic number. Bone is an example of tissue with a high atomic number.
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Where is the highest atomic number in the body?
the teeth (because of the enamel)
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Tissue type is affected by which 2 main factors?
- the average atomic number
- the density of the tissue
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You may have to __________the density when making large tube angles.
increase
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In pathology, an additive __________ density and creates an effect called __________.
additive: decreases density and is radiopaque.
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In pathology, a destructive _________ density and creates an effect called _________.
destructive: increases density and is radiolucent.
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Example of an Additive:
Fluid in the lungs (pneumonia)
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Example of a Destructive:
Emphysema
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When grid ratio increases, density ___________.
decreases
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Grid advantage/disadvantage
- advantage: absorbs scatter; less reaches film
- disadvantage: increases exposure to patient
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Grid Conversion Formula
- GCF1 mAs1
- ____ = ____
- GCF2 mAs2
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Consider using a grid once the part being x-rayed reaches _______ in size.
10cm
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When Relative Speed (RS) increases, density ________.
increases
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RS conversion formula:
- mAs1 RS2
- _____= ___
- mAs2 RS1
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When film processing time increases, density __________.
increases
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When film processing temperature increases, density __________.
increases
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When chemical activity increases, density __________.
increases
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