QUIZLET Exposure Factors Quiz 3 Review

What is radiographic fog? What are the sources of radiographic fog?

- a veil of unwanted IR exposure

- main source is scatter radiation

What are two expectations for this class?

- to create radiographic images of diagnostic quality with emphasis on the student's ability to understand technical factors that contribute to the production of an optimum diagnostic image

- to critique a radiographic image for its diagnostic quality after creating the image

Creating diagnostic quality images requires what?

requires making the appropriate technical choice to create an image that has visibility and sharpness of all the AOI and procedural skill to position the AOI according to Merrill's Atlas

Critiquing for diagnostic quality encompasses?

- consists of the broadest and most complete critique of an image where you critique both the technical aspect and procedural aspect of the image

What is the first step in the analytical process for evaluating for Dx quality?

ask the broad questions:

1. what is the name of this radiographic exam to be critiqued

2. what is the radiographic position to be critiqued

What is the second step in the analytical process and what aspects are we looking at?

narrow the search field to the question of is this image of diagnostic quality by narrowing down the technical aspect and procedural aspect of the image

What are the two properties of the technical aspect and what do they determine?

- photographic property determines visibility of all AOI

- geometric property determines sharpness of all AOI

What is the third step in the analytical process?

evaluation process to critique the technical and procedural aspect of the image

What are the two factors of the technical aspect and what are the four things that they evaluate?

1. primary source of critique process where specific questions must be addressed after the image has been created

2. secondary source that references the framework for "creating radiographic quality"

a. proper IR exposure

b. sufficient contrast

c. maximum detail/spatial res

d. minimum distortion

What are three categories of the critique conclusion?

1. optimal: no changes needed to the technical and/or procedural aspect

2. acceptable: minor changes can be made to the technical and/or procedural aspect but not worth a secondary exposure

3. unacceptable: does not meet requirement for visibility and sharpness and needs to be repeated

What makes a prime factor a prime factor?

prime factors determine the x-ray emission and is under the direct control of the radiographer (kVp, mA, and exposure time)

Define visibility and sharpness. What properties to they pertain to?

- visibility is determined by the photographic properties which consists of proper IR exposure and sufficient contrast

- sharpness is determined by the geometric properties which consists of maximum detail/spatial res and minimum distortion

Define radiographic IR exposure. What does proper IR exposure mean?

- radiographic IR exposure is one of the two photographic properties that comprise the visibility of the AOI, it is the amount of x-ray photons that interact with the IR

- proper IR exposure is when the radiographer selects the appropriate technical factors to produce an image of optimal diagnostic quality with just enough IR exposure so that visibility of the AOI is present

How is IR exposure created?

when photons from the x-ray beam interact with the IR after it has passed through a body part (attenuates) creating a visible image of the AOI

Define attenuation and make the arrow chart diagram for attenuation

reduction of the x-ray photons remaining in the beam after passing through a given thickness material

↑Thickness = ↑ attenuation

↓Thickness = ↓ attenuation

↑ Tissue opacity = ↑attenuation

↓Tissue opacity = ↓attenuation`

Define influencing factors and list them

influencing factors are factors that influence a particular property

-IR exposure: patient factors, SID, kVp, anode heel effect, orthopedic casting materials

-contrast: subject contrast, radiographic fog

Define radiographic quality

refers ONLY to the technical aspect of the critique process

How do we evaluate the procedural aspect of the critique?

use Merrill's Atlas "evaluation criteria"

Draw the arrow diagram for exposure time and IR exposure

↑ exposure time = ↑ photon energy = ↑ IR exposure

↓ exposure time = ↓ photon energy = ↓ IR exposure

Draw the arrow diagram for attenuation and IR exposure

↑ Attenuation = ↓ IR Exposure

↓ Attenuation = ↑ IR Exposure

Make an arrow diagram for part thickness and attenuation

↑Thickness = ↑ attenuation

↓Thickness = ↓ attenuation

Make an arrow diagram for opacity of tissue and attenuation

↑ Tissue opacity = ↑attenuation

↓Tissue opacity = ↓attenuation

What is the inverse square law? Make an arrow diagram for it

inverse square law states the intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance

↑ SID = ↓ IR exposure

↓ SID = ↑ IR exposure

Define controlling factors and list them

controlling factor is the number one factor that controls a particular property

- IR exposure: mAs

- contrast: kVp and LUT

What is the exposure maintenance formula?

it is the direct square law used to compensate for IR exposure changes that occur when distance is changed

mAs2 = mAs1 x (New Distance)^2/

(Old Distance)^2

What is the anode heel effect and when can we use it?

-the difference in intensity of the beam when out in the peripheral area. Due to angulation of the anode, the cathode side of the x-ray tube produces more x-ray photons than the anode side. This is because the electrons hitting part of the angled target have to travel through more of the anode and are attenuated therefore allowing less x-ray photons to exit the tube

-we can use anode heel effect when the anatomical part varies in thickness and the part thickness is 30 cm or greater

What is the procedure for orthopedic casting material?

-wet plaster cast: measure similar unaffected body part, then double mAs and increase kVp by 10% because water attenuates the beam a lot

- dry plaster cast: assess similar unaffected body part and double mAs but keep the same kVp

-fiberglass cast: measure affected body part with cast as if it were part of the body part, with the determined thickness select the appropriate exposure factors on the chart

What is the photographic property and how is it controlled?

it determines the visibility of the AOI and it is controlled by IR exposure and contrast

Define radiographic contrast. What is the prerequisite?

- the difference b/t adjacent densities, you need sufficient contrast so that differences within and b/t structures can be seen

- before analyzing for contrast, one must determine that the radiograph has proper IR exposure

What are the controlling and influencing factors of sufficient contrast?

CF: kVp and LUT

IF: subject contrast and radiographic fog

What is contrast appreciated on an image?

when the AOI is:

1) made up of more than one density of tissue

2) varies in thickness

3) a combination of 1 and 2

What is involved in the evaluation of contrast?

- golden rule: before analyzing contrast, one must determine if the radiograph has proper IR exposure

- adequate radiographic contrast means being able to see differences b/t IR exposures of adjacent body structures in all AOI

- verification that all tissue densities that make up the part of interest are VISIBLE on the radiograph

What is subject contrast?

- range of IR exposures that range of tissue densities that make up the part of interest

- range of IR exposures that result from range, types, and amounts of tissue densities making up the AOI

How do subject contrast and kVp interplay?

kVp influences subject contrast in terms of how it penetrates and attenuates through the tissues and affects resulting ranges of radiographic IR exposures

Make an arrow diagram for kVp and IR exposure

↑kVp = ↓wavelength = ↓ attenuation = ↑ penetration = ↑ remnant radiation = ↑ IR exposure

↓kVp = ↑ wavelength = ↑ attenuation = ↓ penetration = ↓ remnant radiation = ↓ IR exposure

What are the three different ranges of kVP and what amounts?

- low: 55-65 kVp

- middle: 66-80 kVp

- high: 81-120 (140) kVP

Name the four properties of image critique

1. IR exposure

2. contrast

3. detail

4. distortion

What determines quality of the x-ray beam?

kVp

What determines quantity of the x-ray beam?

mA

What is the primary factor and 5 influencing factors of IR exposure?

PF: mAs

IF: patient factors, kVp, SID, anode heel effect, and orthopedic casting material

What prime factor(s) control the quality of the x-ray beam?

kVp

What prime factor(s) control the quantity of the x-ray beam

mA and exposure time

What is the difference b/t exposure maintenance formula and the inverse square law?

-inverse square law states the intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance

-exposure maintenance formula is the direct square law where distance is directly proportional to the square distance

What are the following tissue densities: muscle, air, fat, and bone in order from least tissue dense to most tissue dense? Indicate which has the least IR exposure and most IR exposure

Least tissue dense : Air (most IR exposure)

Fat (second most IR exposure)

Muscles (second least IR exposure)

Most tissue dense : Bone (least IR exposure)

What is the 15% rule and how can we use it?

the 15% rule states that increase in kVp by 15% will cause an approximate doubling of the exposure. To MAINTAIN Density/IR exposure if the kVp is increased by 15% mAs must be reduced by 50% of its original value. Therefore if the 15% rule is used, we can cut our mAs by 50% and decrease patient exposure

If a person comes in after 1 hour of having an arm casted and the original mA is 100 @ 20 ms and kVp is 68, what is the new technique?

increase kVp by 10% and double mAs

10% of 68 = 75%

double mAs = 4

What is the controlling factor(s) and influencing factor(s) for contrast?

CF: kVp and look up table (LUT)

IF: subject contrast and radiographic fog

Define sufficient contrast

when there are just enough differences in the adjacent IR exposure that represent the different tissue densities within the part of interest of the AOI

Why is it important to have quality assurance?

- quality assurance provides adequate confidence that the radiology service provides high quality images and services

- it assesses everything that affects patient care

What are the four steps of QA for Beam?

1. establishing criteria

2. performing monitoring

3. collecting data

4. analyzing and evaluating data

Why are quality assurance and quality control so important?

to ensure that equipment is reliable in providing the patient with highest quality and excellence of service

- quality assurance: all activities that provide adequate confidence that a radiology service will render consistently high-quality images and services

- quality control : the aspect of quality assurance that monitors technical equipment to maintain superior standards

What is dynamic range?

a term to describe a scale of contrast

-narrow dynamic range: high contrast. short scale

-long dynamic range: short contrast, high scale

What is window width and how does it differ from window level?

- window width accurately describes the digital processing that produces changes in the range of brightness

- window level changes the overall brightness of the entire image and widow width changes the subtle differences w/i the AOI

What is the CA law in regards to collimators?

the CA State Law for the Accuracy of the Collimation device states that a collimator device may not be used if there is an error + or - 2% of the SID used in any direction that the x-ray beam is collimated

Define scales of contrast and how they are used

- scales of contrast is a means of describing the number of useful IR exposures that lie adjacent to one another on a radiograph

- they are used to describe contrast on the radiograph, whether there are big differences (short scale) or subtle differences (long scale) between adjacent densities.

What are the guidelines and rule of thumb for selecting kVp?

- For low kVp range:

o For every 1cm of increase thickness, increase kVp by 2

o For range 55-59kvp, change kvp by 2 to see visible change

o For range 60-65 kvp, change kvp by 4 to see visible change

- For middle kVp range:

o Use 15% rule

o 6kVp change for visible change

- For high kVp range 6kvp change for visible change

What are the methods of creating radiographic fog?

- beam restriction devices (aperture diaphragm, cylinder cone [40/60% kVp increase] and collimator

- grid

What is scatter radiation? What causes it?

- scatter radiation is created with Compton's effect when the photons interact with the tissue. photons interact with the tissue with loosely bound electrons on the outer shell which then goes to different directions, thus creating unwanted IR exposures on the image

- ↑ part thickness, ↑ scatter radiation, ↑ radiographic fog, ↓ ability to asses contrast, ↓ visibility of AOI, ↓ quality of diagnostic quality

- ↓ part thickness, ↓ scatter radiation, ↓

radiographic fog, ↑ ability to asses contrast, ↑ visibility of AOI, ↑ quality of diagnostic quality

What are some of the pathology that increase attenuation?

a. abscess

b. edema

c. congestive heart failure

d. empyema

e. pleural effusion

f. ascites

g. pagets disease

What are some of the pathology that decrease attenuation?

a. atrophy

b. emphysema

c. pneumothorax

d. bowel obstruction

e. carcinoma

f. degenerative arthritis

g. osteoporosis

What is the purpose of a grid?

absorb scatter radiation before it reaches to decrease radiographic fog

What are the three characteristics of a grid?

1. grid ratio: height of lead strips/distance b/t adjacent lead strips (5:1, 6:1, 8:1, 10:1, and 12:1)

2. grid type: linear grid and focus grid

3. strip density (lines per inch or cm)

What are the effects of a grid on radiographic IR exposure?

improves contrast by creating those subtle differences b/t the adjacent IR exposures

What are the two grid conversion formulas and when can we use them?

- bucky factor: mAs with Grid/mAs without Grid

- when converting from one grid to another: mAs1/mAs2 = GCF1/GCF2

- easy method rations: no grid = 1, 5:1, 6:1 = 2, 8:1 = 3, 10:1 = 4, 12:1 = 5, and 16:1 = 6

What is grid ratio?

- the ratio of the height of the lead strips to the distance b/t the strips

- higher grid ratios allow less scatter radiation to pass through their interspace material to reach the IR

What are the factors that determine detail?

- motion: involuntary and voluntary

- detector and monitor: matrix size, pixel size, and bit depth

- geometric factors: focal spot, OID, and SID

What are the two types of motion?

- voluntary: under direct control of the patient

- involuntary: not under conscious control of the patient and is controlled by the autonomic nervous system

How can we reduce voluntary and involuntary motion?

- voluntary motion: immobilization devices and communication/instruction with the patient

- involuntary motion: decreasing exposure time (reciprocity law, followed by 15% rule, decrease SID)

How do you maximize detail with geometric factors?

- using a small focal spot

- smaller OID

- increasing SID

What are the two types of distortion?

size distortion (magnification caused by ↑ OID and↓ SID) and shape distortion (foreshortening and elongation)

How do you minimize size and shape distortion?

- size distortion: minimize OID and increase SID

- shape distortion: CR perp to AOI, CR perp to IR, and AOI parallel with IR

How do you maximize detail?

- reduce motion

- reduce SID ( only when decreasing mAs to decrease exp time)

- increase matrix size

- decrease pixel size

- increase bit depth

- smaller focal spot

- decrease OID

- increase SID

Who makes technique charts?

any radiographer can be responsible for putting one together

Why do we need technique charts?

to reduce the number of repeats due to exposure factor selection error and to provide method of consistency in radiographic quality

When do technique charts function best?

when the large number of variables can be held constant while a single factor is permitted to vary

What are the variables in terms of technique charts to consider? Which variables can be kept consistent?

- variable: grid ratio, kVp, mAs

- constant: SID

What are 5 important facts about using technique systems?

1. provide method of consistency in radiographic quality

2. radiographers should use exposure charts

3. not using exposure charts will result in increase of repeat rate which increases patient dose

4. technique charts must be created for each rad unit, they are not interchangeable with other rad units in a department

5. technique charts are part of a rad department quality control and are valuable tools for baseline exposure factor selection but are not the ultimate answer

What are the advantages of having an exposure chart?

provide a method of consistency in radiographic quality and reduce the number of repeat rates, therefore reducing patient dose

What are the factors for success of technique charts?

- equipment must be calibrated accurately so you can rely on settings

- consistency in performing the exam

- consistency processing

What are the factors to consider when designing a technique chart?

1. variety of part thickness for anatomical part for the chart being designed

2. part opacity

3. film/screen combination

4. grid/nongrid

5. SID

6. focal spot size

Why are fixed kVp charts more preferable?

- measurement of part thickness is not as critical

- highest kVp is used, mA is reduced which results in less heat production and extended tube life

- exposure time can be reduced to limit patient movement

What are the tests that x-ray generators should include?

1. kilovoltage accuracy

2. timer accuracy

3. mR/mA and milliamperage linearity

4. exposure reproductivity