RAD 304 Radiographic Contrast

What is the definition of radiographic contrast?

The difference between adjacent density shades (or tones) across the radiographic image.

What are two primary functions of contrast?

Make recorded detail visible; distinguish different types of anatomic tissues.

What are the differences between high contrast and low contrast?

High: few densities with large differences. Low: many densities with small differences.

Long scale contrast refers to ______ contrast?

Low

Short scale contrast refers to ______ contrast?

High

What technical component (i.e. mA, seconds, kVp) is the primary controller of contrast?

kVp

A radiograph that exhibits many shades of gray, from white to black may be described as having ______ ______ contrast?

Long scale

How would an image with just a few wide density differences be described as?

Short-scale / high contrast

Contrast is a ______ property of the radiographic image?

Subjective

What does an increase in kVp do to radiographic contrast?

Decreases contrast; creates long-scale / low contrast

Increased mAs: what is the effect?

Increased density (recorded exposure)

Increased kVp: what is the effect on contrast?

Less contrast, longer scale of contrast

Decreased kVp: what is the effect on contrast?

Higher contrast, shorter scale of contrast

When kVp is increased and all other factors are unchanged, what happens to recorded exposure and contrast?

Recorded exposure increases; contrast decreases

In order to maintain density (recorded exposure), when one increases kVp from 70 to 80 kVp, one must?

Decrease mAs to 1/2 the original

The factor that alters beam penetration is:

kVp

Most gasses such as nitrogen, oxygen, and hydrogen, have a low attenuation for x-rays and are classified as:

Radiolucent

A radiograph is taken using 68 kVp @ 68 mAs. Using the 15% Rule, what technique will decrease contrast and maintain the same density?

78 kVp @ 34 mAs

An abdomen image is done using 66 kVp and 40 mAs. Image density is appropriate but the image has too high (short scale) contrast. Which exposure factors are the best change?

76 kVp and 20 mAs

Compton interactions will ______ when employing a long-scale of contrast.

Increase

What is the definition of OID?

The distance between the anatomical part being radiographed and the image receptor.

As OID increases, radiographic contrast will do:

Increase

A smaller field size irradiates ______ tissue and ______ the amount of scatter on the image.

Less; reduces/decreases

What type of relationship exists between beam restriction and radiographic contrast?

Direct: more beam restriction increases contrast

List two forms of positive contrast agents.

Barium and iodinated contrast (iodine)

Placing a grid between the anatomic part and the IR absorbs scatter. What will happen to the contrast of the image?

Increase

What is the definition of subject contrast?

Caused by differences in the composition of the patient's body parts.

List the tissues of the body in order of increasing absorption: (fat, muscle, water, teeth, bone, air)

Air → fat → water → muscle → teeth → bone

Solve the missing factors, Scene #1: 86 kVp, 100 mAs; increase kVp 15%, maintain recorded exposure.

98.9 kVp, 50 mAs

Solve the missing factors, Scene #2: 92 kVp, 65 mAs; decrease kVp 15%, maintain recorded exposure.

78.2 kVp, 130 mAs

Solve the missing factors, Scene #3: 65 kVp, 20 mAs; increase kVp 15%, maintain recorded exposure.

74.75 kVp, 10 mAs

Solve the missing factors, Scene #4: 75 kVp, 15 mAs; decrease kVp 15%, maintain recorded exposure.

63.75 kVp, 30 mAs

Solve the missing factors, Scene #5: 100 kVp, 64 mAs; increase kVp 15%, maintain recorded exposure.

115 kVp, 32 mAs

Long-scale contrast would be most correctly defined as:

Many shades of gray

Which of the following pertain to long-scale radiographic contrast?

I. It is produced by low kilovoltage

II. It produces many shades of gray

III. It produces small differences between adjacent densities.

2 & 3 only

The contrast between bone and soft tissue is due primarily to:

The difference in their atomic numbers

Increasing kVp and increasing photon energies:

Increases Compton interactions and decreases subject contrast

An exposure of 85 kVp and 200 mAs produces a correct recorded exposure, but too much contrast. What mAs should be used if the kVp is raised to 100 kVp?

100

Increasing the field size will ___ the amount of scatter.

Increase

Which of the following contribute to the radiographic (subject) contrast present on a radiograph?

I. Atomic number of the tissues radiographed

II. Any pathologic process

III. Degree of muscle development.

1, 2 and 3

To alter the technical factors so that a pediatric technique can be set, the technologist should:

Decrease mAs and decrease kVp

A patient is being radiographed as a follow-up for a wrist fracture wearing a fiberglass cast to stabilize the fracture. To optimally expose the radiograph, the radiographer should:

Use the same PA Projection of the Wrist technique for a patient without a cast

What is the atomic number of Barium and Iodine respectively?

56 and 53

Which two of the following do NOT affect subject contrast?

A) Grid ratio

B) kVp

C) mAs

D) Object shape

E) Object size

C) mAs; D) Object shape

Which of the following radiographic techniques is likely to produce the best visualization of low subject contrast structures?

107 kVp, 800 mA, 25 mS

In a radiographic examination of the lumbar spine, which of the following techniques would result in greatest exposure (greatest dose) to the patient?

70 kVp/200 mAs

An anteroposterior examination of the abdomen is taken at 80 kVp, 50 mAs, and 100 cm SID. If the scale of contrast is to be shortened, but there is satisfactory recorded exposure, the Radiologic Technologist must do which of the following?

Reduce kVp and increase mAs

Anatomic structures that readily transmit x-rays:

Are called radiolucent

Fill in blanks: Low kVp versus High kVp: scale contrast, contrast, wavelength

Low kVp: short-scale, high contrast, long wavelength. High kVp: long-scale, low contrast, short wavelength.

What will happen to contrast (increase, decrease, or remain the same): 8 x 10 light field to 14 x 17 light field?

Decrease

What will happen to contrast (increase, decrease, or remain the same): 100 mAs to 350 mAs?

Remain the same

What will happen to contrast (increase, decrease, or remain the same): SID from 40" to 20"?

Remain the same

What will happen to contrast (increase, decrease, or remain the same): kVp from 92 to 80?

Increase

What will happen to contrast (increase, decrease, or remain the same): 10:1 grid to 16:1 grid?

Increase

What will happen to contrast (increase, decrease, or remain the same): Collimate from 14 x 17 light field to 8 x 10 light field?

Increase

What will happen to contrast (increase, decrease, or remain the same): 2 feet to 10 inches OID?

Decrease

What will happen to contrast (increase, decrease, or remain the same): Normal bone to osteoporotic bone?

Decrease

What will happen to contrast (increase, decrease, or remain the same): 200 mAs to 225 mAs?

Remain the same

What will happen to contrast (increase, decrease, or remain the same): 12:1 grid to 8:1 grid?

Decrease

What will happen to contrast (increase, decrease, or remain the same): SID from 40" to 60"?

Remain the same

What will happen to contrast (increase, decrease, or remain the same): kVp from 46 to 42?

Increase

What will happen to contrast (increase, decrease, or remain the same): Removal of 1.5mm Aluminum filtration?

Increase

What will happen to contrast (increase, decrease, or remain the same): 100 small FSS to 100 large FSS?

Remain the same

What is contrast resolution?

The ability of a digital imaging system to distinguish small objects that attenuate the x-ray beam similarly.

What happens to contrast when the number of shades of gray increases?

It decreases.

What is grayscale in digital radiography?

The number of shades of gray that can be stored and displayed by a computer system.

What is differential absorption?

Different tissues absorb x-ray photons differently based on tissue density, atomic number, and compactness.

What do positive contrast agents do?

Increase attenuation; appear white. Examples: barium and iodine.

What do negative contrast agents do?

Decrease attenuation; appear darker. Example: air.

What kVp range do the slides specify for barium sulfate studies?

90 kVp and above.

What kVp range do the slides specify for iodinated solutions?

70-80 kVp.

What happens to contrast when kVp increases?

Contrast decreases; long-scale contrast and more shades of gray.

What happens to contrast when kVp decreases?

Contrast increases; short-scale contrast and fewer shades of gray.

Place these events in order: A current is applied to cathode, heating up the Tungsten filament, Rapid deceleration of electrons at the anode, Collimators restrict the primary beam, Remnant beam exits the patient.

Current to cathode → Deceleration at anode → Collimators restrict beam → Remnant beam exits

Arrange these tissues in descending order of radiolucency: (Air, Lung tissue, Blood, Barium Sulfate)

AIR → LUNG TISSUE → BLOOD → BARIUM SULFATE

Arrange these tissues from lowest atomic number to highest: (Air, Fat, Muscle, Bone)

AIR → FAT → MUSCLE → BONE

Which set of technical factors will produce the highest recorded exposure?

50 kVp @ 5 mAs

Decreasing Grid Ratio does what to RECORDED EXPOSURE?

increase

High kVp has a short wavelength. (True/False)

True

X-ray photons with shorter wavelengths have a higher penetrating power. (True/False)

True

Long scale of contrast needs what type of kVp?

high

Where does thermionic emission occur?

Cathode

Decreasing collimation does what to contrast?

Decreases

Plaster cast requires

increase in exposure factors (2x for dry) (3x for wet)

Fiberglass cast requires

no change in technique

pediatric patient 0-5 years old

25% (1/4) of mAs for adults

pediatric patient 6-12 years old

50% (1/2) mAs for adults

pediatric patient: premature

50 kvp minimum

pediatric patient: infant

55 kvp minimum

pediatric patient: child

60 kvp minimum