Rad Tech 2 (Math)

what is sensitometry?

the relationship between the intensity of radiation exposure and amount of blackness produced after processing

what are the alternative names for the sensitometric curve?

-characteristic curve

-D log E

-Hurter and Driftfield curve

What are the parts of a sensitometric curve?

-Toe region

-Straight line region/slope

-Shoulder region

What is the range the toe region of the sensitometric curve?

-area of low IR exposure (below 0.25)

-underexposed

what is the range of the shoulder region of the sensitometric curve?

-max. IR exposure (above 2.5)

-overexposed

what is the range of the straight line region/slope of the sensitometric curve?

-the diagnostic or useful range of the IR exposures (0.25-2.5)

-the sweet spot

What is a penetrometer?

-produces a series of uniform densities/receptor exposures that resemble a step wedge using an x-ray source

-a test tool made form aluminum

-accurately calibrated filter strip that provides a stepped range of exposures

what is a densitometer?

a device used to numerically determine the amount of blackness

what is radiographic fog? and what causes it?

-unwanted receptor exposure on an image

-secondary/scatter radiation

-fog makes things harder to see

-contributes nothing good for the image

Contrast and fog are ___ factors.

opposing

What is the definition of scatter?

-radiation that changes direction after interaction

-shows up grey/hazy on images

what is the definition of secondary radiation?

-radiation transmitted by an atom

-stays in the same direction after interaction

What is the definition of image forming radiation?

(remnant) radiation that exits the patient and exposes the IR

As tissue thickness increases, what happens to fog?

increases

Hypersthenic patients produce ___ fog.

more

What is opacity?

film's ability to block light

less dense tissues produces ___ amounts of scatter/secondary radiation

greater

what does an increase in tissue density do to fog?

decreases

As opacity increases, fog ___.

increases

less dense tissues show up ___.

darker

what type of contrast would you have if scatter were present?

-low contrast

-long scale contrast

What is air gap technique?

-utilize the distance between the pt and IR to dissipate scatter/secondary radiation.

-increases magnification

-increased OID

-increase OID of entire body, decrease fog (not all scatter will hit the IR)

increase OID of a specific body part = ___ fog.

increase

What can be used if there's no grid?

air gap technique

air gap technique:

decrease in fog = ___ magnification

increase

what happens to scatter when you increase kVp?

-scatter increases

-gets a Compton interaction

fog levels are ___ when kVp is set according to penetration needs

minimal

what is another name for the photoelectric effect?

-true absorption

-photoelectric absorption

what kVp level does the photoelectric effect prevail?

40-140 kVp

what interaction is bad for the patient?

photoelectric effect

What interaction(s) are bad for the tech?

-compton scattering

-coherent effect

at what kVp level does the Compton effect prevail?

->100

-we see this with the x-ray effect

what is the x-ray effect?

refers to the phenomenon in which x-rays interact with matter, typically causing the emission of radiation or the absorption of energy

what kind of radiation is a result of the photoelectric effect?

secondary radiation

what happens with the photon during the photoelectric effect?

-the photon comes in contact with an inner shell electron

-the photon gives all it's energy to the electron and ejects from it's shell (true absorption)

-the electron is knows as a photoelectron

what happens with the photon during the Compton effect?

-the photon removes an outer shell electron while giving up parts of it's energy

what's another name for the Compton effect?

modified scatter

which effect only results in scatter?

coherent effect

what is another name for the coherent effect?

-unmodified scattering

-classical scattering

which effects produces contrast on an image?

photoelectric effect

in the Compton effect, what is the name of the electron ejected from the atom?

-recoil electron

in what type of radiographic procedure would you see the coherent effect?

mammography (below 40 kVp)

what interaction is not seen in diagnostic imaging?

coherent effect

what happens with the photon during the coherent effect?

-very low photon energy passes close to an orbital electron

-the photon does not dislodge the electron but changes direction without a loss of energy

what are ways of reducing fog?

-beam restriction

-use of grids

-air gap technique

-appropriate kVp

what Is the primary method used to reduce fog?

beam restriction (collimator)

photoelectric effect:

1. names

2. happens where?

3. what kVp does it occur?

4. scatter or no scatter?

5. bad for who?

6. results in?

1. true absorption/photoelectric absorption

2. inner shell

3. 40-140 kVp

4. no scatter

5. patient

6. secondary radiation and contrast in image

Compton effect:

1. names

2. happens where?

3. what kVp does it occur?

4. scatter or no scatter?

5. bad for who?

6. results in?

1. modified scatter

2. outer shell

3. 100+ kVp

4. scatter

5. tech

6. scatter and secondary radiation

coherent effect:

1. names

2. happens where?

3. what kVp does it occur?

4. scatter or no scatter?

5. bad for who?

6. results in?

1. classical/unmodified scatter

2. -40 kVp

3. scatter

4. tech

5. only excites the inner shell

6. only scatter

aperture diaphragm:

the ___ the cylinder and the ___ the diameter of the opening, the more restrictive the beam limitation

- longer

-smaller

what is an advantage of an aperture diaphragm?

can be designed with different shapes and sizes

what is PBL?

- positive beam limitation

-automatic collimation to the size of the cassette being used

what is a disadvantage of an aperture diaphragm?

-bulky

-have to manually be taken on and off

what you collimate what happens to contrast?

increases

what is an advantage of a collimator?

-beam size can be adjusted to the specific size and shape required with ease

-less scatter produced

-reduces patient dose

-decrease receptor exposure

What do lead blockers do?

-absorbs secondary radiation and scatter before it reaches the IR

-picks up scatter from the patient

-makes image better

what do the lead blockers NOT do?

-reduce patient dose/scatter

when you collimate, what happens to receptor exposure?

decreases

what is receptor exposure?

the amount of radiation striking the image receptor

what is the biggest producer of scatter?

patient

who invented the first grid?

Gustav Bucky

what year was the first grid invented?

1913

who invented the first moving grid?

Hollis E. Potter

what materials make up the interspace material of a grid?

-plastic

-aluminum

-radiolucent materials

what does radiolucent mean?

Transparent to X-rays—x-rays can penetrate easily through

in grids, the lead strips pick up ___ and ___ affect patient dose

-scatter

-doesn't

what designs do the grids come in?

-linear

-crosshatch

what does a linear grid look like?

-all lead strips lay side by side

-most grids are this type

what does a crosshatch grid look like?

2 grids perpendicular to each other

-limited use; cannot use a tube angle

what are the 2 types of grids?

-parallel

-focused

Parallel grids are best used at

-long SIDs; when the most perpendicular portion of the beam is being used

-36"-72"

Parallel grids are also called?

linear grids

what do parallel grids look like?

each lead strip is exactly parallel to the next

what does grid cutoff occur at with parallel grids?

<36"

what are parallel grids best used for?

mobile radiography

A focused grid's lead strips are angled to match

the angle of the x-rays in the primary beam

the table Bucky uses this type of grid:

focused grid

what is the most common and efficient type of grid?

focused grid

what is the point of convergence?

the point where the grid is most efficient

what is grid radius?

the distance from the convergence point to the center of the grid (focusing distance)

what grid remains stationary during the exposure?

stationary grid

what grid is where the motion blurs out the lead strips? (grid lines)

moving grid

increased ratio=

____ lead=

____ efficiency=

____ margin for error

-increases

-increases

-decreases

why do you increase technique when you use a grid?

to get more rays through

grid angles:

8:1 grid:

12:1 grid:

16:1 grid:

-7 degrees

-2.25 degrees

-3.5 degrees

what happens to the receptor exposure if grid ratio is increased?

decrease

define grid ratio

heigh of the lead strip compared to the distance between each strip

if a particular grid has lead strips 20cm wide, 120cm high, either an interspace width of 12cm, what is the grid ratio?

10

how many lines per inch is normal grid frequency?

60-200 lines/inch

what is the advantage of a focused grid?

more common and efficient

what are 2 physical characteristics of a grid?

-ratio

-frequency

what are the 2 functional characteristics of a grid?

-selectivity

-contrast improvement factor

what is the contrast improvement factor formula?

K = Contrast with grid / Contrast without grid

what is selectivity?

-percent of primary radiation transmitted to IR compared to the percentage of scatter radiation transmitted to the IR

increased grid frequency=

____ efficiency

increased

what is contrast improvement factor?

a measurement of how much contrast is increased by using the grid

what is the most common contrast improvement factor range?

-1.5

-3.5

high K factor and high ratio grids have ____ contrast

improved

grids with higher lead content have ____ selectivity

greater

non grid technique:

chest:

____% primary

____% scatter

-50%

-50%