X-ray Imaging and Radiation Dose

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Questions and Answers

What percentage of x-rays incident on a patient reach the image receptor?

0.5%

1% (correct)

10%

What type of structures do x-rays that undergo photoelectric interaction represent?

Neither radiolucent nor radiopaque structures

Radiopaque structures (correct)

Both radiolucent and radiopaque structures

Radiolucent structures

What happens to x-rays that penetrate the body with no interaction?

They are scattered in different directions

They produce light areas on an x-ray image

They produce dark areas on an x-ray image (correct)

They are absorbed by radiopaque structures

What is the effect of reducing kVp on differential absorption?

It increases differential absorption Signup and view all the answers

What type of structures do x-rays that penetrate the body with no interaction represent?

Radiolucent structures Signup and view all the answers

What is the purpose of controlling and selecting the x-ray beam?

To produce high-quality x-ray images Signup and view all the answers

What is the result of Compton-scattered x-rays interacting with the image receptor?

They produce image noise Signup and view all the answers

What is the percentage of x-rays that interact to form an image?

0.5% Signup and view all the answers

Why does an image of the bone produce in x-ray imaging?

Because many more x-rays are absorbed photoelectrically in bone than in soft tissues. Signup and view all the answers

What is the relationship between the probability of an x-ray undergoing photoelectric effect and the atomic number of tissues?

It is proportional to the third power of the atomic number. Signup and view all the answers

What is the primary reason for using low KVP to image soft tissue?

To increase the differential absorption of x-rays Signup and view all the answers

What happens to the probability of Compton scattering when x-ray energy increases?

It decreases slowly. Signup and view all the answers

Why is low KVP used in mammography?

To increase the probability of photoelectric effect. Signup and view all the answers

What is the relationship between mass density and x-ray interaction?

X-ray interaction is directly proportional to mass density Signup and view all the answers

What type of x-ray beam contains rays that all have the same energy?

Monoenergetic Signup and view all the answers

What is the effect of increasing x-ray energy on the probability of an x-ray interaction with tissues?

It decreases the probability of interaction. Signup and view all the answers

Why is high KVP used for examination of barium studies and chest radiography?

To take advantage of the high intrinsic subject contrast Signup and view all the answers

What is the relationship between the probability of photoelectric effect and x-ray energy?

It is inversely proportional to the third power of x-ray energy. Signup and view all the answers

What is the effect of doubling the mass density of a tissue on x-ray interaction?

The chance for x-ray interaction is doubled Signup and view all the answers

What is the effect of increasing KVP on image quality?

It decreases image contrast. Signup and view all the answers

What is the unit of mass density?

Kilograms per cubic meter Signup and view all the answers

What is the difference between radiopaque and radiolucent structures?

Radiopaque structures absorb x-rays, while radiolucent structures transmit x-rays. Signup and view all the answers

What is the result of increasing the x-ray energy?

The relative frequency of Compton scattering is increased Signup and view all the answers

Why do bone structures absorb more x-rays than soft tissue?

Because bone has a higher mass density than soft tissue Signup and view all the answers

Study Notes

Image Contrast and Radiation Dose

Reducing kVp to increase differential absorption and image contrast results in increased patient radiation dose.
A compromise is necessary for each examination.

Dependence of Atomic Number

The probability of a photoelectric effect is proportional to the third power of the atomic number of tissues.
Bone has an atomic number of 13.8, while soft tissues have an atomic number of 7.4.
The probability of a photoelectric interaction is approximately 7 times greater in bone than in soft tissues.

X-ray Interactions

Photoelectric effect: X-rays that undergo photoelectric interaction provide diagnostic information to the image receptor.
Compton scattering: X-rays that undergo Compton scattering result in image noise.
Compton scattering is independent of atomic number of tissues.

Energy and Interaction

With higher x-ray energy, fewer interactions occur, and more x-rays are transmitted without interaction.
The probability of Compton scattering decreases with increasing energy.
The probability of photoelectric effect decreases with increasing energy (1/E³).

Image Receptor

The image receptor assumes that scattered x-rays came straight from the x-ray tube target.
Scattered x-rays result in image noise, a generalized dulling of the image.

Radiopaque and Radiolucent

Radiopaque: structures that absorb x-rays, such as bone.
Radiolucent: structures that transmit x-rays, such as air in the lungs.

Image Formation

Approximately 1% of the x-rays incident on a patient reach the image receptor.
Fewer than half of those that reach the image receptor interact to form an image.
The radiographic image results from approximately 0.5% of the x-rays emitted by the x-ray tube.

Relation between Differential Absorption and kVp

Differential absorption increases as kVp is reduced.
Producing a high-quality x-ray image requires the proper selection of kVp to result in maximum differential absorption.

Types of X-ray Beam

Monoenergetic: a beam containing x-rays with the same energy.
Polyenergetic: a beam containing x-rays with a range of energies (clinical x-rays).

Mass Density

Mass density is the quantity of matter per unit volume.
The unit of mass density is kilogram per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³).
Mass density is related to the mass of each atom and tells how tightly the atoms of a substance are packed.
The interaction of x-rays with tissue is proportional to the mass density of the tissue, regardless of the type of interaction.

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Description

Learn about the relationship between kVp, image contrast, and patient radiation dose in X-ray imaging, and how atomic number affects image production.