physics 2

The more attenuation for x-ray the more we need:

Atomic mass

As the energy of the x-ray beam increases, the linear attenuation coefficient generally:

Decreases

The more given structure, the more it attenuates radiation and appears dark on a finished radiographic film image (true/false)

False

higher attenuation coefficient indicates that materials have higher transparency (true/false)

False

The difference in attenuation coefficients between materials creates the contrast in

radiography. (true/false)

True

The materials have more attenuation when they have.

More atomic number, More electrons

What makes materials have higher transparency for X-ray photons?

Low atomic number (Z), low density, and small thickness.

How do we increase the intensity of X-ray photons? Write it down.

Increase the tube current (mA) or increase the exposure time (mAs).

As far as attenuation concerns, the more attenuation for X-ray quantities, the less thickness of the material increases. (true/false)

False

The lower density of material means:

The less probability of an X-ray photon to interact with atoms

The mass attenuation coefficient is dependent on material's physical state - different from the linear attenuation coefficient. (true/false)

True

What makes the bone have a much higher attenuation coefficient than soft tissue?

Bone has higher density and much higher effective atomic number (Z) due to calcium

(Z=20) and phosphorus (Z=15).

In any given sample of biological material, both density and atomic number are important in determining attenuation. (true/false)

True

Which of the following defines attenuation?

Absorption and scatter

X-ray incident on substance: final intensity = initial intensity. Density = 1.2 kg/cm3, thickness

= 1 cm. Find the mass absorption coefficient.

Mass attenuation coefficient (mu/rho) = 0, since I = I0 (no attenuation).

If we want to make sure that X-ray photons have no charge, what shall we do?

X-ray photons are inherently uncharged - no action is needed.

Which of the following influences attenuation? (1. Effective atomic number 2. Mass density 3.

Thickness)

1, 2, and 3

Which characteristic primarily differentiates the probability of the various X-ray interactions

with human tissue?

Energy of the incoming photon

The interactions of X-ray photons with atoms of biologic matter are:

Random - effects cannot be predicted with certainty

Exit, or image-formation, radiation is composed of which of the following?

Primary photons and Compton scattered photons

Which of the following contributes significantly to the exposure of the radiograph?

Compton-scattered photons

In the radiographic kilovoltage range, which structure undergoes the most photoelectric absorption?

Compact bone

In which X-ray interaction is the energy of the incident photon partially absorbed?

Compton

When a high-Z contrast agent is ingested/injected, which of the following occurs?

Photoelectric interaction significantly enhanced, leading to increased absorbed

dose in structures containing the contrast medium

Radiographic fog from unwanted exposure results from which interaction?

Compton scattering

What are the processes of X-ray interaction with matter? Which are important in diagnostic

radiology?

1) Coherent scattering, (2) Photoelectric absorption, (3) Compton

scattering, (4) Pair production, (5) Photodisintegration. Important in diagnostic radiology:

Photoelectric absorption and Compton scattering.

In which X-ray interaction is the energy of the incident photon partially absorbed?

Compton scattering (also called incoherent scattering

Coherent scattering - the photon loses kinetic energy when interacting with atoms of human

tissue. (True / False)

False

The process of coherent scattering is important in any diagnostic range. (True / False)

FALSE

Compton scattering reduces overall image:

- A. Quality B. Quantity C. None of them

Quality

In Compton interaction, lack of atomic number dependence implies it does not differentiate

between bone and soft tissue. (True / False)

TRUE

Contrast media attenuate X-rays primarily through:

Photoelectric effect

When a contrast agent fills an organ/vessel, it drastically decreases the density of lower-Z

atoms in that area. (True / False)

FALSE

Write the negative contrast media.

Air and carbon dioxide (CO2).

For optimal differential absorption and image contrast, we use:

Lower energy X-ray photons

To create image contrast, what area of the body must be covered?

Low absorption

How do we create the high contrast image necessary for diagnosis?

Through differential absorption - using natural differences in atomic number, density,

and thickness between tissues, or by introducing contrast media.

What does the contrast media (e.g., iodine and barium) do?

Contrast media fill cavities, vessels, or organs to increase the difference in X-ray

attenuation between those structures and surrounding tissues, making them visible on X-ray

images.

Barium sulfate contrast media is used specifically for imaging the:

GI tract (Gastrointestinal)

Barium coats the mucosal surface of the GI tract, making its outer contour and shape visible

on X-ray. (True / False)

True

For a contrast image, what is the result of a much higher attenuation coefficien?

Greater X-ray absorption in that region - appears brighter/whiter on the X-ray image, creating high positive contrast.

What materials can be used as contrast agents?

Positive contrast agents: Iodine-based compounds (for vessels/urinary tract) and

Barium sulfate (for GI tract). Negative contrast agents: Air and Carbon dioxide (CO2).

What is the advantage of using contrast media?

Contrast media allow visualization of structures that would otherwise be invisible on

plain X-ray because they have similar natural attenuation to surrounding tissues (e.g., blood

vessels, GI tract, urinary system).

In the radiographic kVp range, which structure undergoes the MOST photoelectric

absorption: air cavities, compact bone, fat, or soft tissue?

Compact bone

Quality assurance of exposure parameters is NOT essential in diagnostic radiology. (True /

False)

False

List the key exposure parameters and their QA tests.

1. Kilovoltage (kVp). 2. Timer accuracy. 3. mA settings (tube current). 4. Radiation

output reproducibility. 5. Automatic exposure control (AEC) consistency. 6. Cathode/filament

thickness

What is the process by which an X-ray beam is reduced in intensity as it passes through matter?

Attenuation

Why must radiographers understand the processes of interaction between radiation and

matter?

To optimize image quality, minimize patient radiation dose, select appropriate

exposure parameters, understand image artifacts, and apply radiation protection principles effectively.

How is an X-ray beam produced?

Electrons are emitted from a heated cathode filament (thermionic emission),

accelerated across a high voltage (kVp) toward the anode, and decelerated upon striking the

tungsten target - producing Bremsstrahlung radiation and characteristic X-rays.

Why is tungsten (or tungsten-rhenium) used in the X-ray tube target?

Tungsten has a very high atomic number (Z=74) for efficient X-ray production, the

highest melting point of any metal (3422 degrees C) to withstand heat, and high thermal

conductivity. Rhenium is added to improve ductility.

Describe the function of filtration in a diagnostic X-ray beam.

Filtration selectively removes low-energy (soft) X-ray photons using metal absorbers

(typically aluminum), reducing patient skin dose without significantly affecting the diagnostic

image - a process called beam hardening.

What is attenuation?

Attenuation is the reduction in intensity of an X-ray beam as it passes through matter,

caused by both absorption (photoelectric effect) and scattering (Compton and coherent

scattering).

Why do human bones appear white in a completed diagnostic image?

Bone has high effective atomic number (calcium, phosphorus) and high density,

causing high X-ray attenuation. Fewer photons reach the detector, producing less exposure - bones appear white/bright.

Describe X-radiation-matter interactions in the diagnostic radiology range.

Two dominant interactions in diagnostic kVp range (50-150 kVp): (1) Photoelectric

absorption - photon completely absorbed by inner-shell electron; responsible for subject

contrast. (2) Compton scattering - photon transfers part of its energy to an outer-shell

electron; reduces image contrast by producing scatter (fog)

In the expression E = mc2, what does c represent?

c represents the speed of light in a vacuum: approximately 3 x 108 m/s.

What type of radiation is used in positron emission tomography (PET)?

Gamma rays (annihilation radiation) - specifically 511 keV gamma photon pairs

produced when positrons (beta+) emitted from the radiotracer annihilate with electrons in tissue.

When a high-energy photon collides with a nucleus during photodisintegration, how much of

its energy is directly absorbed by the nucleus?

All of the photon's energy is absorbed by the nucleus (the photon is completely

absorbed)

What are the possible views on the interactions of ionizing radiation with matter?

1) No interaction - photon passes through unaffected. (2) Coherent

(classical) scattering. (3) Photoelectric absorption. (4) Compton (incoherent) scattering. (5)

Pair production. (6) Photodisintegration (at very high energies)

What are the sources of ionizing radiation? Write them down.

Natural sources: cosmic rays, terrestrial radiation (uranium, thorium, radon gas),

internal radionuclides (K-40, C-14). Artificial sources: X-ray machines, nuclear reactors,

particle accelerators, and radioisotopes used in nuclear medicine.

What are the forces that govern the nucleus components? Write them down.

1) Strong nuclear force - short-range force holding protons and neutrons (nucleons)

together, overcoming electromagnetic repulsion. (2) Electromagnetic (Coulomb) force -

repulsive force between positively charged protons. (3) Weak nuclear force - responsible for beta decay.

What happens when electrons in their orbit emit energy?

When an orbital electron emits energy, it drops to a lower energy shell (closer to

nucleus). The emitted energy appears as a photon of electromagnetic radiation - characteristic

X-rays (inner shell transitions) or visible/UV light (outer shell transitions).

As far as charge is concerned, what makes the atom stable?

An atom is electrically stable when the number of electrons (negative charges) equals

the number of protons (positive charges), resulting in a net charge of zero (electrically neutral

atom).

What is the advantage of rotating the anode?

The rotating anode distributes heat over a much larger focal track area (the entire

annular ring) rather than a single spot, allowing much higher tube currents and shorter exposure times without damaging the target.

What are image receptors (IR)? Write them down.

Devices that capture the X-ray beam to form a visible image. Types: (1) Film-screen

systems (traditional). (2) Computed Radiography (CR) - photostimulable phosphor plates. (3)

Digital Radiography (DR) - flat-panel detectors. (4) Fluoroscopic image intensifiers. (5) CT detectors.

What are the differences between ionizing and non-ionizing radiation?

Ionizing radiation has enough energy (12 eV or more) to remove electrons from

atoms, causing ionization - includes X-rays, gamma rays, alpha, beta, and neutron radiation.

Non-ionizing radiation lacks sufficient energy to ionize atoms - includes visible light, UV,

infrared, microwaves, and radio waves.

What are the reasons for the nucleus to emit beta+/-? Explain.

Beta- (negatron) emission: nucleus has too many neutrons - a neutron converts to a

proton + electron (beta-) + antineutrino. Beta+ (positron) emission: nucleus has too many protons - a proton converts to a neutron + positron (beta+) + neutrino.

Rules governing electrons in orbits and formula for number of electrons per orbit.

1) Pauli Exclusion Principle - no two electrons can have the same set of four quantum numbers.

(2) Electrons fill lowest energy shells first (Aufbau principle).

(3) Each shell n can hold a maximum of 2n2 electrons.

What happens when a much higher energy is absorbed by the atom?

If the absorbed energy exceeds the binding energy of an electron, the electron is completely ejected from the atom (ionization), leaving behind a positive ion. The ejected electron (photoelectron or Compton electron) carries the excess energy as kinetic energy.

Is there a process governing electron emission from the filament? What is it and why is it useful?

Thermionic emission. When the filament (cathode) is heated by electrical

current to ~2200 degrees C, electrons gain enough thermal energy to overcome the work function and escape the metal surface into the surrounding vacuum.

initial number of nuclei = surviving number after time t, what is the mean lifetime?

t=0