Radiologic Physics Practice Flashcards

Basic Concepts of Matter and Atomic Structure

• Matter: Defined as anything that has mass and takes up space.

• Atom: The smallest unit of matter.

Parts of the Atom

• Nucleus: The central core containing:

  • Protons ($+$): These identify the element (analogous to a person’s name).

  • Neutrons ($0$): These contribute to the atomic mass.

• Electron ($-$): Particles orbiting the nucleus within specific shells.

• Analogy: Think of an atom as a solar system where the nucleus is the sun and the electrons are the planets orbiting it.

Historical Atomic Models

• Democritus: Proposed "Atomos," meaning indivisible.

• Dalton: Introduced the "Hook & Eye" model.

• Thomson: Proposed the "Plum Pudding" model and discovered electrons.

• Rutherford: Introduced the "Nuclear model," identifying a positive center.

• Bohr: Developed the "Planetary model," where electrons reside in specific shells.

Quantum Numbers and Shells

• Electrons are organized into shells labeled K, L, M, N, O, P, Q (Mnemonic: KLMNOPQ for 7 shells).

• Maximum Electrons Per Shell Formula: $2n^2$, where $n$ is the shell number.

  • Example: K shell ($n=1$) provides space for $2(1)^2 = 2$ electrons.

Units of Measurement and Mechanics

Fundamental Units

• Length: measured in meters ($m$); the distance from one point to another.

• Mass: measured in kilograms ($kg$); the amount of matter in an object.

• Time: measured in seconds ($s$); the duration of an event.

Derived Units and Formulas

• Force ($N$): $F = \text{Mass} \times \text{Acceleration}$

• Work (Joules): $W = \text{Force} \times \text{Distance}$

• Power (Watt): $P = \frac{\text{Work}}{\text{Time}}$

Gravity, Mass, and Weight

• Gravity: An invisible force pulling objects toward a larger mass.

  • Gravity on Earth: $9.81 / s^2$

  • Gravity on Moon: $1.61 / s^2$

• Mass: The amount of matter in an object ($kg$). Think of this as "how much stuff" is in a backpack.

• Weight: The force exerted by gravity on mass. Think of this as how heavy that backpack feels.

• Formula: $\text{Weight} = \text{Mass} \times \text{Gravity}$ (Units: Newtons or lbs).

Newton’s Laws of Motion

1. Inertia: An object at rest or in motion stays in that state unless acted upon by an external force.

2. Force: $F = \text{Mass} \times \text{Acceleration}$.

3. Action-Reaction: For every action, there is an equal and opposite reaction.

Energy and the Electromagnetic Spectrum

Forms of Energy

• Energy: Defined as the ability to do work.

• Kinetic (KE): Energy in motion. Formula: $KE = 0.5 \times \text{Mass} \times \text{Velocity}^2$

• Potential (PE): Stored energy. Formula: $PE = \text{Mass} \times \text{Gravity} \times \text{Height}$

• Chemical: Derived from chemical reactions (e.g., digestion).

• Electrical: Resulting from moving electrons (e.g., appliances).

• Thermal: Heat energy (e.g., boiling water).

• Nuclear: Energy contained within atomic nuclei (e.g., nuclear reactors).

• Electromagnetic (EM): Used in diagnostic imaging and X-ray systems.

The Electromagnetic Spectrum

Organized from strongest (highest energy) to weakest (lowest energy):

1. Gamma Ray: High energy; interacts at the Nucleus level.

2. X-ray: Interacts within Electron shells.

3. Ultraviolet: Interacts at the Molecular level.

4. Visible Light: Interacts at the Cell level.

5. Infrared: Interacts with Tissues.

6. Microwave: Interacts with centimeter-scale objects.

7. Radio Wave: Interacts with meter-scale objects.

Mnemonics:

• For the Spectrum: "Great Xylophones Use Violins In Making Rock"

• For Visible Light: VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red)

Radiation Concepts and Ionization

• Radiation: The transfer of energy through space.

• Ionization: The process of adding or removing electrons from an atom.

• Analogy: Ionizing radiation is like a billiard ball strong enough to knock others off the table.

Types of Radiation

• Ionizing: Possesses enough energy to knock out electrons (e.g., X-rays, Gamma rays).

• Non-ionizing: Only excites atoms without removing electrons (e.g., visible light, microwaves).

Sources of Ionizing Radiation

• Natural Sources: Cosmic rays, Radon gas, Earth materials (Uranium), and Internal body elements.

• Man-made Sources: X-rays, Nuclear medicine, Industrial sources, and Consumer products.

• Mnemonic for Sources: CRIP (Cosmic, Radon, Internal, Products).

Radioactivity and Decay

• Radioactive Decay: The process where unstable atoms release energy to reach stability.

• Half-life: The time required for a radioactive substance to reduce its activity by half.

Radiation Measurement Units

• Exposure: Roentgen ($R$) → Modern: Gray in Air ($Gy_a$)

• Absorbed Dose: Rad → Modern: Gray in Tissue ($Gy_t$)

• Effective Dose: Rem → Modern: Sievert ($Sv$)

• Radioactivity: Curie ($Ci$) → Modern: Becquerel ($Bq$)

• Mnemonic: RAGeS (Roentgen-Air, Gray-Energy, Sievert-Effect).

Decay Modes

• Alpha ($\alpha$): Releases 2 protons and 2 neutrons; heavy, stops quickly, but dangerous if inhaled.

• Beta Minus ($\beta^-$): A neutron changes to a proton, emitting an electron and an anti-neutrino.

• Beta Plus ($\beta^+$): A proton changes to a neutron, emitting a positron and a neutrino (utilized in PET Scans).

• Gamma ($\gamma$): The nucleus releases pure energy (highly penetrating; like tension being released).

• K-Capture: An atom absorbs an inner-shell electron, resulting in the release of characteristic X-rays.

• Mnemonic: "Always Be Good at Keeping Gamma safe!"

Electricity, Magnetism, and Transformers

Electricity Basics

• Voltage ($V$): Electrical pressure pushing electrons.

• Current ($I$): The flow of electrons, measured in Amperes.

• Resistance ($R$): Opposition to electron flow, measured in Ohms.

• Ohm’s Law: $V = I \times R$ (Mnemonic: VIR).

• Types of Current:

  • DC (Direct Current): One-way flow, like a battery.

  • AC (Alternating Current): Back and forth flow, used in households.

Magnetism and Induction

• Electromagnetism: Moving electrons create magnetism.

• Faraday’s Law: Moving magnets near wires generates electricity.

• Lenz’s Law: An induced current creates a field that opposes the change that caused it.

• Analogy: Like pushing against a revolving door—it pushes back against you.

Transformers in Radiology

Transformers change voltage using coils and induction.

• Step-Up Transformer: Increases voltage (more turns in the secondary coil).

• Step-Down Transformer: Decreases voltage (fewer turns in the secondary coil).

• Transformer Law Formula: $\frac{V_p}{V_s} = \frac{N_p}{N_s}$ (Voltage ratio equals the turn ratio).

• Analogy: A transformer is like a gear shifter for voltage.

Circuits

• Series Circuit: Single path where current is shared.

• Parallel Circuit: Multiple paths where voltage is shared.

X-ray Production and Equipment

X-ray Tube Components

• Cathode ($-$): The negative side; contains the filament that heats up to emit electrons via Thermionic Emission.

• Anode ($+$): The positive side; a rotating Tungsten target where electrons hit to produce X-rays.

• Glass Envelope: Maintains a vacuum environment.

• Important Stat: 99% of electron energy is converted to heat; only 1% becomes X-rays.

X-ray Production Processes

• Bremsstrahlung: An electron slows down or deviates near the nucleus, losing energy that is emitted as an X-ray.

  • Analogy: Like a car swerving near a cliff (nucleus) and losing energy as radiation.

• Characteristic X-ray: A high-speed electron hits and ejects a K-shell electron, causing an outer-shell electron to drop in and release a specific energy X-ray.

Heat Units (HU)

• Used to monitor tube heat loading.

• Formula: $HU = kVp \times mA \times \text{time} \times \text{correction factor}$

Radiation Interactions with Matter

Mnemonic: "Can Cool Photons Produce Destruction?"

Filtration and Safety

Filtration

Removes weak, low-energy X-rays to reduce patient dose.

• Inherent Filtration: Built-in (glass window, tube housing).

• Added Filtration: Aluminum sheets added externally to the tube port.

• Total Filtration: $\text{Inherent} + \text{Added}$

Minimum Total Filtration Requirements

• < 50\,kVp: $0.5\,mm\,Al$

• $50-70\,kVp$: $1.5\,mm\,Al$

• > 70\,kVp: $2.5\,mm\,Al$

Safety and Quality Control

• Leakage Limit: Radiation leakage from the tube housing must not exceed $1\,mGy/hr$ at a distance of $1\,meter$.

• Spinning Top Test: A specific test used to check the accuracy of the X-ray timer.