X-ray Production and Properties

• Diagnostic X-rays are a type of electromagnetic radiation with short wavelengths (0.1-1 Å) with very high penetrating power
• They are useful in diagnosis and radiotherapy.
• Electromagnetic radiation transports energy through space as a combination of electric and magnetic fields.
• Includes radio waves, radiant heat, visible light, and gamma radiation.
• The energy carried by each photon depends on the frequency of radiation.
• Energy is defined by the equation E = hv = hc / λ,
• h is Planck's constant (6.6 x 10^-34 joule-sec)
• c is the velocity of light (3 x 10^8 m/sec),
• v is the frequency of radiation

X-ray Production

• X-rays are produced when high-energy electrons interact with matter
• Some of the kinetic energy is converted to electromagnetic radiation.
• Main components of the X-ray tube include:
• A source of electrons which is the cathode filament
• The number of electrons and the produced X-ray photons is controlled by the product of the tube current and time (mAs).
• An evacuated space where electrons are sped up in a glass envelope.
• A high positive potential accelerates negative electrons, controlling the energy of electrons and X-ray photons (kV).
• A target which the electrons strike which is the anode
• Up to 99% of accelerated electron energy is converted to heat with approximately 1% converted to X-ray photons.
• Intensity is strongly related to target (anode) construction materials and power settings applied
• Higher atomic number (Z) of the anode produces a more intense X-ray beam and that Z of tungsten is 74.
• Increasing current in the cathode circuit also increases the number of electrons.
• Increasing kV increases electron speed, photon energy, and resolution.

Target Properties for X-ray Production

• Anode material must have a high melting point (e.g., tungsten melts at 3400 °C).
• X-ray tubes have two filaments used to produce large or small focal spots.
• A focal spotis an area on the target struck by electrons.
• Small focal spots reduce image blurring but concentrate heat in a small area.
• The area struck by electrons can be increased without increasing image blurring by angling the anode by 10° to 20°, which is known as the line-focus principle.
• Rotating anode X-ray tubes can rotate at 3600 rotations per minute.

Types of X-ray

• Bremsstrahlung Spectrum (Continuous X-ray): Produced when accelerated electrons pass near an atomic nucleus within the target.
• Electrons are decelerated and change direction, losing kinetic energy emitted as an X-ray photon called bremsstrahlung radiation.
• The amount of bremsstrahlung depends on:
• Atomic number of the target: More protons in the nucleus cause greater acceleration of the electron.
• Kilovolt peak, kV peak: Faster electrons are more likely to penetrate the nucleus region
• Characteristic X-ray: Produced when a fast electron strikes a K-shell electron in a target atom
• The electron knocks it out of orbit
• As an outer shell electron fills the vacancy, it emits a characteristic K X-ray photon.
• The difference in energy levels of the orbits specifies the atom, resulting in characteristic radiation.
• Diagnostic X-rays typically have energies of 15 to 150 keV, while visible light photons have energies of 2 to 4 eV.
• The number of electrons accelerated toward the anode depends on the filament temperature.
• The maximum energy of X-ray photons produced is determined by the accelerating voltage-kilovolt (kVp).
• Bremsstrahlung creates broad smoothing with low energy curve in the spectrum
• Characteristic X-rays represent spikes within that bandwidth
• One kilo electron-volt (keV) is the energy an electron gains or loses across a potential difference of 1000V where 1keV=1.610^-9 erg = 1.610^-16 J.
• The kVp used for an x-ray study depends on the thickness of the patient and the type of study like mammography and chest studies.

Energy Settings

• Mammography: 25 to 50 kVp
• Chest: ≈ 350 kVp
• Electron current: 100 - 1000 mA
• X-ray energy produced is not monoenergetic; it is a spectrum of energies up to its maximum.
• Power P for x-ray (watt) equals current I (amp.) x voltage V (volt)
• I = 1A and V = 100kV the P = 100kW
• 99% appears as destructive heat resulting in damaged anodes

X-Ray Absorption

• Attenuation of an x-ray beam is its reduction due to the absorption and scattering of photons out of the beam.
• It is described by the equation I = I0 * e^(-μx),
• I0 represents initial beam ,
• I represents unattenuated (transmitted) beam intensity, x is the thickness of the attenuator,
• μ represents linear attenuation coefficient,
• e = 2.718.
• Linear attenuation Coefficient (μ) measures the probability that a photon interacts (absorbed or scattered) per unit length it travels in a material.
• It depends on:
• Energy of x-rays
• Atomic number (Z)
• Density (ρ) of material
• Half-value thickness HVT (X1/2) is the thickness of material that reduces the intensity of the radiation beam to one-half of its value (50%).
• (HVT) X1/2 = 0.693 / μ.

X-Ray Interactions

• Three methods of X-ray interaction with matter include:
• Photoelectric effect (P.E)
• Compton Effect (C.E)
• Pair Production
• Photoelectric effect: Incoming X-ray photon transfers all energy to an electron, which uses it to overcome binding energy and get away from the nucleus.
• The free photoelectron uses the remaining energy to ionize surrounding atoms.
• Photoelectric effect is more common in high-Z elements at low energies.
• At 30 keV, bone absorbs X-rays about 8 times better than tissue due to the photoelectric effect.
• Compton effect occurs when the X-ray photon collides with loosely outer shell electron
• The electron receives part of the photon energy, and the remainder goes to a Compton photon.
• Compton Effect is more likely in low-Z materials.
• Compton effects happen greatest at low Z materials such as:
• Water
• Soft tissue, C.E. is more probable than P.E effect at energy ≥ 30 KeV.
• In bone, C.E. is more probable than the P.E. effect at energy ≥ 100 KeV.
• Pair production is rare at diagnostic energy ranges.
• The minimum energy required for pair production is 1.02 MeV.
• In pair production, the high energy photon enters the electric field of the nucleus and converts into two particles (electron and positron), which vanish, and their mass-energy converted to two photons called annihilation radiation.

X-Ray Contrast Media

• A technique using the photoelectric effect, where Radiologists often inject high-Z material into the body as contrasting media.
• Barium and iodine compounds are the most commonly used contrast agents.
• Zbarium = 56, Ziodine = 53, Zsoft tissue = 7.42.
• Examples include:
• Iodine compounds are injected into the bloodstream to show arteries.
• An oily mist containing iodine is sprayed into the lungs to make airways visible.
• A barium compound is given orally to see parts of the upper gastrointestinal tract.
• Air used for pneumoencephalograms.
• Barium enemas for lower digestive system visualization.
• Air & barium are used separately in double-contrasting studies.

X-Ray Image Formation

• In basic production needs an X-ray source and an image receptor.
• Three types of image receptors or films include:
• Double-sided radiographic film: Light-sensitive crystals coated on both sides of a transparent base, used in plain film imaging.
• Single-sided camera film: One emulsion layer. Used in mammography.
• Non-screen film: X-ray photons directly expose film. Used in dental x-rays.

Making an X-ray image

• The radiographic image presents information in a relatively easy-to-understand visual form.
• Different body parts absorb x-rays in varying degrees.
• Dense bone absorbs much radiation, while soft tissue (muscle, fat, organs) allows more x-rays to pass.
• Bone appears white, soft tissue in shades of gray, and air appears black on the x-ray film.

Increasing Sharpness

• X-ray images image shadows cast on film of various structures, and need to be as sharp as possible.
• Done by:
• Reducing blurring with a small focal spot.
• Positioning the patient as close to the film as possible.
• Maximizing the distance between the X-ray tube and the film..
• Reducing scattered radiation with grids consisting of lead and plastic strips.
• Holding breath during chest x-rays to reduce motion.
• Radiographic Image Quality

Image Quality for X-Rays

• The main problem in obtaining good X-ray images is blurring
• The blurred object edge is called a penumbra which is calculated as:
• p = D/L * l, where p represents penumbra width and D represents focal spot sized
• L represents the focal-object distance and l represents the object film distance
• For better X-Ray quality, take steps such as these to avoid blurring:
• Small focal spot, small D, to reduce the penumbra and increase quality
• Positioning the patient as close to the film as possible, small l1, to reduce the blur
• Increasing the distance between the x-ray tube and the film as much as possible, large L.
• Reducing scattered radiation by using a grid consisting of lead and plastic strips,
• Avoiding motion during exposure.

Methods for reducing errors

• A grid is necessary to reduce scatter radiation reaching the film.
• Thicker body parts create more scatter radiation
• Use grids of lead and plastic strips to absorb scattered radiation
• The main disadvantage of grids is high dose due to absorption of some primary beam photons.
• X-ray beam Filtration

X-Ray Beam Filtration

• Low-energy X-rays don't penetrate the entire thickness of the body, increasing patient radiation dose without improving the image quality.
• Using filters, thin plates of aluminum, copper, remove most of this low-energy radiation.

Measuring Radiations

• The measure of X-rays ionizing ability is called the exposure.
• The unit used for radiation exposure is the roentgen (R), a measure of the amount of electric charge produced by ionization in air.
• 1 R = 2.58 x 10^-4 C/kg of air.
• Exposure to a large area is more hazardous than the same exposure to a small area.
• The exposure-area product (EAP) describes radiation to the patient.
• Exposure Area Product, EAP is a calculation of the total emissions
• Expressed as: EAP (rap or R cm²) = exposure (roentgen) × area (cm²), where 1 rap = 100 R cm².
• If one receives an exposure of 0.6 R to an area of 33 cm², he will receive 20 R cm² (or 0.2 rap).

Radiation Risk

• Radiation risk refers to damage produced by ionizing radiation due to energy deposition in tissues.
• This energy may result in ionization within:
• Direct ionization causes: Direct radiation energy transfer causes DNA structural changes.
• Indirect ionization causes radiation to be absorbed by water molecules: Forming free radicals damages DNA.
• Adverse health effects of radiation are classified into two groups:
• Deterministic effects follow high radiation doses and result in relatively immediate damage
• Stochastic effects follow low radiation doses and may result in cancer development (lag period of at least 5 years, may reach to 10 or 20).

Modalities

• Fluoroscopy refers to continuous X-ray acquisition of a sequence of X-ray images over time (real-time X-ray movie).
• Fluoroscopic systems are capable of producing images rapidly.
• Fluoroscopy is useful for positioning catheters, visualizing contrast agents, and therapeutic procedures.
• It is also used to make X-ray anatomical movies, such as of the heart or the esophagus.
• Computed tomography creates images by passing X-rays through the body at a large number of angles, and rotating the X-ray tube.
• Opposing the X-ray is a detector array that collects the transmission projection data.
• Synthesized by a computer, numerous tomographic images are created
• Tomography refers to a graph of a slice, where the CTs ability comes from that the bodies-three dimensional slices eliminates the need to look at the 2D super-imposition of anatomical structures.
• Magnetic Resonance Imaging (MRI)
• Involves utilizing the magnetic properties of the hydrogen atom found in water as a powerful means of medical imagery.
• The patient is positioned in line with strong magnetic field that orients the net magnetization.
• Pulses of radio waves are generated by coils positioned around the patient
• Affecting the orientation of the protons and thus the field
• Protons will absorb radio waves and subsequently emit them later in real time, creating imagery
• These returning radio waves produce a signal that’s collected by the machine
• X-rays detect fractures/deformities in bones, but fine details of soft tissues are not clear.
• CT scan provides detailed cross-sectional images of bones and soft tissues by combining several x-ray images.
• MRI images soft tissues like tendons and ligaments.

Explore X-ray properties, production, and practical applications. This content covers electromagnetic radiation, energy determination, and anode material characteristics. Learn about the role of high positive potential and evacuated space in X-ray tubes.