Meaghan Piretti- Image production: Registry prep :)

Define receptor exposure?

The amount of radiation hitting the IR

Can you list factors that do not affect receptor exposure?

- OID

- Focal spot size

- Motion

- Angle of tube, part, or IR

Can you list factors that do control receptor exposure?

- mAs

- kVp

- SID

- Grids

- Tube filtration

- Beam restriction

- Anode heel effect

- Patient factors such as size & pathology

How does mAs affect receptor exposure?

ex.) If mAs was to increase, what would happen to receptor exposure...

This is a direct relationship, it would increase receptor exposure

If you set 200 mA, how many photons would that be?

200 photons

Is mAs considered quantity or quality?

Quantity

Will increasing your kVp affect receptor exposure?

Yes

Is kVp considered quantity or quality?

Quality

Will increasing kVp increase beam energy?

ex.) As kVp increases, beam energy...

Yes, it is a direct relationship. It would increase beam energy.

Will increasing kVp increase beam penetrability?

ex.) As kVp increases, beam penetrability...

Yes, it is a direct relationship. It would increase beam penetrability.

The relationship between kVp and receptor exposure is not direct because?

We use the 15% rule

If we increase kVp by 15%, it does what to receptor expsoure?

It doubles receptor exposure

If we decrease kVp by 15%, it does what to receptor exposure?

cuts it in half

15% is roughly how many kVp?

10

Can you describe what SID is?

Source to Image Distance

When talking about SID, the source is not the face of the collimator but is?

Where the focal spot is at

Can you describe SOD?

Source to Object Distance

How does SID affect receptor exposure?

ex.) If you increase SID, what happens to receptor exposure...

It is a inverse relationship, receptor exposure would decrease

What law controls how SID affects receptor exposure?

Inverse square law

If you see a math question that is talking about exposure, and is using units milli-gray or milli-sieverts what formula would you use?

Inverse square law

If you are talking about distance, SID, and mAs what formula would you use?

ex.) what mAs you would need for a certain distance...

Exposure matinence formula

If you increase you distance (SID), what does you mAs do to compensate?

increase (kVp would stay the same)

If you increase SID, what technical factor needs to change?

Increase mAs

(HINT- As you increase you distance there is less photons that will make the full distance to the IR, so you need more photons to make it the whole distance)

When you increase you SID, you in-turn have to increase you mAs. Why would you not change the kVp as well?

Messes with the contrast of the image

How do grids affect receptor exposure?

ex.) Adding a grid and not making any technical exposure factor change

decreases receptor exposure

If you remove a grid, what does that do to receptor exposure?

Increases receptor exposure

(Reasoning: we are getting rid of a lot of the lead strips that are absorbing radiation)

When using a grid, what technical factor must you change?

Increase the mAs so there is more photons hitting the IR

Will a higher grid ratio increase or decrease receptor exposure?

Decrease receptor exposure

Does tube filtration affect receptor exposure?

Yes

What is the purpose of tube filtration?

Gets rid of low energy photons that are so low energy they don't even make it into the body to create scatter. These low energy photons add to patient skin dose.

Does added (more) filtration increase or decrease patient dose?

Decreases

If you had less filtration would that increase or decrease patient dose?

Increase

Grid conversion factor 5:1 is what?

2

Grid conversion factor 6:1 is what?

3

Grid conversion factor 8:1 is what?

4

Grid conversion factor 16:1 is what?

6

What would happen to receptor exposure if you increase collimation?

Decrease receptor exposure

Can you describe the anode heel effect?

Where the x-ray beam comes out it diverges and they cathode end has more receptor exposure, and then the anode end has less receptor exposure.

When using the anode heel effect, what side would you put the thicker body part?

Cathode

What factors will increase the anode heel effect, in other words when are we going to see greater receptor exposure difference?

Decrease SID, and wide (big) IR

(Reasoning: the shorter the SID the more divergence of the beam to cover IR, and size of IR)

If you have a smaller anode angle, what does that do to the anode heel effect?

Increases the anode heel effect

If you have a larger anode angle, what does that do to the anode heel affect?

Decreases the anode heel effect

Does patient size affect receptor exposure?

Yes

How will having a bigger person, effect receptor exposure?

Decrease receptor exposure

In a thicker person, what happens with photons & scatter?

They absorb more photons & more scatter happens

What type of pathology will increase receptor exposure (subtractive diseases)?

Anything with air, or adds air to the body

Pathologies that increase receptor exposure would be considered additive or subtractive?

subtractive (destructive)

What type of pathology will decrease receptor exposure (additive diseases)?

Added fluid or tissue

Pathologies that decrease receptor exposure would be considered additive or subtractive?

additive

What are some subtractive diseases?

(you would decrease kVp & mAs)

- pneumothorax

- COPD

- emphysema

- bowel obstruction

- Osteoporosis

What are some additive diseases?

(you would increase kVp & mAs)

- cystic fibrosis

- ascites

- Gout

- Pleural effusion

- Edema

Can you define spatial resolution?

The amount of detail

Can you list factors that do not affect spatial resolution?

- mAs

- kVp

- Grids

- Tube filtration

- Beam restriction

- Anode heel effect

How is spatial resolution measured?

Line pairs per millimeter (lp/mm)

How does OID affect spatial resolution?

ex.) If you increase OID, what happens to spatial resolution...

Inversely related, it would decrease spatial resolution

Contrast resolution is different from spatial resolution because instead of looking at the detail in the image we are looking at what?

The number of shades of grays

If you increase OID, what kind of distortion do you have?

Magnification (also known as size distortion)

How does SID affect spatial resolution?

ex.) Increasing the SID, does what to spatial resolution...

Increase spatial resolution

Will the large or small focal spot improve spatial resolution?

Small focal spot

What body part would we use a small focal spot for?

- Hand

- Extremities

- Feet

Trade offs:

When using a small focal spot, it gives us better spatial resolution but what does it do to the amount of heat that is given off?

Heat is increased

What body part would we use a large focal spot for?

- Chest

- Abdomen

- Thicker body parts in the middle

Trade offs:

When using a large focal spot, it gives us not as good spatial resolution but what does it do to the amount of heat that is given off?

less heat is given off

The highest heat load has what type of focal spot, and does it have a low or high mAs?

Smallest focal spot with the highest mAs

Will motion increase or decrease spatial resolution?

Decrease spatial resolution

If you unintentionally angle the x-ray tube against the part or IR, how would that affect spatial resolution?

Decrease spatial resolution

Magnification is what type of distortion?

Size

What are two types of size distortion?

Elongation and foreshortening

What factors control distortion?

- OID

- SID

- Patient factors (size & pathologies)

- Angle (tube, part, or receptor)

Will decreasing SID, increase or decrease magnification?

Increase magnification

If you decrease OID will that increase or decrease magnification?

Decrease magnification

How would you foreshorten something?

angle body part against IR

(when becky showed finger of hand angled against the board)

How would be elongate something?

Tube and IR not line up

(HINT: TIRE)

ex.) when we perform a scaphoid, sacrum coccyx, townes, axial BE, or calcaneus

Can you describe anatomically programmed technique (APR)?

Whatever body part you want to do, you would tap on it and the technique is already set

What technical factor varies on a fixed kVp technique chart?

mAs

What technical factor is not adjusted on a variable kVp chart?

mAs

How would you adjust technical factors for a cast?

Increase kVp

For a fiberglass cast how much would you increase the kVp?

3-4

For a small plaster cast how much would you increase the kVp?

5-6

For a large plaster cast how much would you increase your kVp?

7-8

What kVp is recommended for iodinated contrast studies?

80-90 kVp

What kVp is recommended for single barium sulfate studies?

110-125 kVp

What kVp is recommended for double barium sulfate studies?

90-100 kVp

What kVp is recommended for water soluble iodinated?

80-90 kVp

How should technique be adjusted when a grid is used?

Increase mAs

How would you choose AEC detectors for optimal image quality?

The AEC detectors that you select depends of the body part that you are looking at

How should you align the anatomy for optimal image quality when using AEC?

You want the body part totally covering the detector.

(Example: If you are performing a shoulder and there is a lot of detector above the shoulder, The direct exposure to the AEC will make it shut off a lot faster)

Can you explain the RTB example of "filling a bucket", how does this relate to AEC?

As photons are entering the AEC chambers, it's comparable to buckets as they get full they shut off

What does pixel stand for?

Picture element

What is pixel pitch?

The distance from the center of one pixel, to the center of the pixel next to it

Do we want a large or small pixel pitch for improved spatial resolution?

Small

The number of pixels in an image depends on what?

The size of the matrix

Will a small or large matrix provide better spatial resolution?

Large

If the matrix gets larger, how does the pixel size change?

The pixel size gets smaller

Would small or large pixels improve spatial resolution?

Small

What happens to spatial resolution when mag mode is used?

Spatial resolution increases

Does mag mode affect patient dose?

Yes, it increases patient dose

What is a DEL?

Detector element

Can you give a brief description of what a DEL is?

A square on the detector that captures photons and works to convert the photons into an image

What is fill factor?

Amount of area on the DEL that contributes to image formation