Image Formation and Differential Absorption (RAD 1102) Flashcards | Quizlet

Differential Absorption

The difference between X-ray photons absorbed photoelectrically in tissue and those transmitted through the patient to the image receptor.

Photoelectric Effect

An interaction where an incident X-ray photon transfers all of its energy to an inner-shell electron, completely absorbing the photon and producing a photoelectron.

Compton Scattering

An interaction between an X-ray photon and a loosely bound outer-shell electron, resulting in a scattered photon of lower energy and a recoil electron.

Attenuation

The reduction in the total number of X-ray photons in the primary beam as it passes through a specified thickness of tissue.

Radiopaque Structures

Anatomical tissues with high atomic numbers or mass density, such as bone, that absorb high proportions of X-rays and appear light or white on a radiograph.

Radiolucent Structures

Anatomical tissues with low atomic numbers or mass density, such as air or lung tissue, that allow X-rays to transmit easily and appear dark on a radiograph.

Remnant Beam

The X-ray beam that emerges from the back of the patient containing transmitted and scattered photons, which forms the image on the image receptor.

Primary Beam

The useful X-ray beam emitted directly from the X-ray tube target prior to interacting with patient tissue.

Image Receptor (IR)

The hardware device, such as a digital detector panel or photostimulable phosphor plate, that captures the remnant X-ray beam to create an image.

Subject Contrast

The inherent variation in X-ray attenuation among different tissue types within a patient, influencing image grayscale differences.

Atomic Number ($Z$) and Photoelectric Absorption

The probability of photoelectric absorption is directly proportional to the cube of the atomic number ($Z^3$) of the absorbing material.

X-ray Energy ($E$) and Photoelectric Absorption

The probability of photoelectric absorption is inversely proportional to the cube of the X-ray energy ($1/E^3$).

Compton Scattering Probability

Compton scattering probability depends on mass density and is inversely proportional to X-ray energy ($1/E$), remaining independent of atomic number ($Z$).

Coherent Scattering

A low-energy interaction ($<10\,\text{keV}$) in which an X-ray photon changes direction without losing energy or causing ionization.

Contrast Agents

High atomic number media (such as barium, $Z=56$, or iodine, $Z=53$) administered to accentuate differential absorption in soft tissue structures.

Scatter Radiation Fog

Unwanted uniform exposure on an image receptor caused by Compton scattered photons, resulting in a loss of overall image contrast.

Exponential Attenuation

The mathematical process where X-rays are reduced by a constant percentage per unit thickness of absorber rather than a fixed total number.

Half-Value Layer (HVL)

The thickness of a specified absorbing material required to reduce the intensity of an X-ray beam to half its original value.

Effect of $kVp$ on Differential Absorption

Decreasing $kVp$ increases differential absorption and subject contrast, but requires a higher patient radiation dose.

Effective Atomic Number of Bone

The effective atomic number ($Z$) of compact bone is approximately $13.8$, causing it to absorb significantly more X-rays than soft tissue.

Effective Atomic Number of Soft Tissue

The effective atomic number ($Z$) of human soft tissue is approximately $7.4$, resulting in higher X-ray transmission compared to bone.

Transmission Photons

X-ray photons that pass straight through tissue without undergoing absorption or scattering, exposing the image receptor to produce dark regions.

Mass Density Effect on Attenuation

Doubling the mass density of a tissue doubles the probability of both photoelectric and Compton interactions occurring in that tissue.

Pair Production

An interaction requiring minimum photon energy of $1.02\,\text{MeV}$, where an X-ray interacts with the nuclear field to create a positron and an electron.

Photodisintegration

A high-energy interaction ($>10\,\text{MeV}$) where a photon is absorbed by a nucleus, causing emission of a nuclear fragment.