1.6 Beam Restriction

What are beam restriction devices made of?

Lead

Lead is a ____ of x-ray photons and doesn’t let x-ray pass through

blocker/absorber

What is the atomic number and symbol for lead?

Pb 82

What is the difference between Filtration devices and Beam restrictions?

Filtration devices allow some photons to go through easier than lead lined does

Any time the primary beam goes beyond the boundaries of the IR and the anatomy of interest it causes?

Unnecessary exposure to the patient

What is beam restriction often referred to as?

Collimation

What do Beam restriction or collimation do?

Essentially because they both mean they are decreasing (restricting) the size of the projected field of radiation

What do beam restrictor ideally do?

decrease the field size, thus reducing the amount of matter (tissue) being exposed, which leads to less scatter produced

What are the two main purposed of beam restriction?

Reduce the amount of scatter, limit patient dose

Using beam restriction devices helps the image in what two ways?

The scale of contrast: increased/shortened

Visibility of detail of the structure imaged: increased

What is low contrast?

Lots of grays and choices on scale, smaller difference between each scale step

What is high contrast?

not many differences, not a lot of gray choices, big differences between steps on the scale

When we increase the contrast , you are ____ the differences between structures, therefore, are you increasing or decreasing the amount of gray options?

increase, decreasing or taking away more of the gray options

When we decrease the contrast , you are ____ the differences between structures, therefore, are you increasing or decreasing the amount of gray options?

decrease , increasing or adding more gray options

What are the factors that contribute to scatter?

1. kVp/penetrability of the beam

2. volume of irradiated material

3. field size (FOV)

4. Patient/Part thickness

When you INCREASE your collimation, are you increasing or decreasing your field size or FOV?

Decreasing

When you DECREASE your collimation, are you increasing or decreasing your field size or FOV?

Increasing

Increased field size increases volume of tissue irradiated result in ?

Increase in scatter, low/longer scale/decrease of contrast in image

Decreased field size decreases beam quantity results in?

decrease in scatter, high/shorter scale/increase of contrast in image

When using beam restriction devices, what must you do to accompany a significant reduction in filed size to maintain image receptor exposure?

Increase in mAs

What is quality?

The distribution of x-rays as a function of energy. Controlled through filtration and beam restriction

What is Quantity?

The number of x-ray photons, changed through the mA