Image Acquisition Unit 2 - Contrast

A radiographer that exhibits a long scale of contrast is one with what?

many shades of gray that have minimal differences

Which of the following will contribute to the production of a longer (low) scale of contrast?
-decrease in the grid ratio
-increase in kVp
-decrease in photon energy

increase in kVp

The available shades of gray in a digital imaging system is determined by the:

bit depth

Which of the following sets of exposure factors would produce the shortest (highest) scale of contrast?
-10 mAs, 70 kVp, 40 inch SID, 6 inch OID
-5 mAs, 90 kVp, 72 inch SID, 4 inch OID
-15 mAs, 80 kVp, 40 inch SID, 6 inch OID
-20 mAs, 100 kVp, 72 inch SID

10 mAs, 70 kVp, 40 inch SID, 6 inch OID

What is the primary function of contrast?

to make visible detail

If the field size is changed from an 8 X 10 to an 14 X 17 inch field size with no other changes in exposure factors, what would happen to contrast?

contrast would change to a longer scale of contrast

The reason contrast mediums result in a shorter scale of contrast in the body is:

the difference in atomic numbers between the contrast and tissue

What effect does increasing tube filtration have on the scale for contrast?

produces a longer scale of contrast

Increasing part thickness with compensation of exposure factors will:

increase Compton interactions and produce a longer scale of contrast

If a radiographic technique is originally 100 mA at 100 ms and then changed to 50 mA at 200 ms:

there will be no change in contrast

This is defined as the magnitude of the signal difference in the remnant beam as a result of the different absorption characteristics of the tissues and structures making up that part?

subject contrast

A term used to describe the mathematical formula used by the computer to reconstruct the image is referred to as:

algorithms

Which fo the following pixel bit depths would display a greater range of shades of gray to present anatomic tissues?
-10 bit
-12 bit
-14 bit
-16 bit

16 bit

If a radiographic technique designed for an 8:1 grid is changed to accommodate a 12:1 grid:

contrast will change to a shorter time

A 15% decrease in kVp accompanied by a 50% increase in mAs will result in a(an):

higher (shorter) scale of contrast

Which of the following would affect the production of scattered radiation?
-field size/collimation
-part thickness
-grids
-kVp

-field size/collimation
-grids
-kVp

Which of the following is (are) associated with subject contrast?
-tissue density
-kilovoltage (kVp)
-patient thickness

all 3 of them

Subject contrast varies by:
-tissue density
-tissue thickness
-atomic number

all 3

Decreasing part thickness with compensation of exposure factors will:

Decrease Compton interactions & produce a shorter scale of contrast

A 15% increase in kVp accompanied by a 50% decrease in mAs will result in a(n):

Longer (low) scale of contrast

A decrease from 90 to 77 kVp will result in:

shorter (high) scale of contrast

Radiographic contrast is the result of:

differential absorption

The reason contrast medias produce higher contrast (shorter scale) in the body is:

difference in atomic numbers between the contrast and tissue

Which combination will result in the most scattered radiation reaching the image receptor?

Using the same mAs and higher kVp

In which of the following ways can a shorter (high) scale of contrast be obtained?

by using a contrast medium

If the field size is changed from an 14x17 to a 8x10 inch field size, which statement about contrast is correct?

contrast would change to a shorter scale

If a radiographic technique designed for a 8:1 grid is changed to accommodate an 5:1 grid:

contrast would change to a long (low) scale of contrast

Remnant xrays are those that:

exit the patient and expose the image receptor

Beam limitation devices are used to help:

control the production of scattered radiation

This is defined as the visible difference between any two areas of brightness levels within the radiographic image:

contrast

The air-gap technique produces a shorter scale of contrast because:

the increased OID results in scattered radiation missing the IR

This is the magnitude of signal difference in the remnant beam due to various tissue characteristics:

subject contrast

As the amount of filtration is increased from 2.0 mm Al to 2.5 mm Al:

contrast would change to a lower contrast

Produced on an image when there is insufficient radiation hitting the image receptor

Quantum noise/mottle

Help to reduce the amount of scattered radiation reaching the IR

grids

As a general rule, grids are appropriate for anatomy ______ cm thick or more.

10 cm

What is the function of filtration?

remove low energy, long wavelength radiation

What type of bone is easier to penetrate?
Demineralized bone or healthy bone?

Demineralized bone, because it has less calcium and produces a longer/low scale of contrast. Healthy bone demonstrates a shorter/higher scale of contrast.

The use of contrast media increases contrast due to what in the body?

Photoelectric interaction