Foundations of Radiography, Radiographic Equipment, and Radiation Safety

Learning Objectives Lesson 38.1: Radiation Physics, Parts of the Dental X-Ray Machine, and Production of X-ray Images (Slide 1 of 2)

• Pronounce, define, and spell the key terms.

• Describe uses of dental imaging.

• Discuss the discovery of x-radiation and the pioneers in the history of dental radiography.

• Discuss radiation physics, which includes:

  • What happens during ionization.

  • The properties of x-rays.

• Identify the parts of the dental x-ray machine and the x-ray tube.

Learning Objectives Lesson 38.1: Radiation Physics, Parts of the Dental X-Ray Machine, and Production of X-ray Images (Slide 2 of 2)

• Explain how x-rays are produced.

• Identify the types of radiation.

• Discuss the characteristics of the x-ray beam, which include:

  • Three characteristics of the x-ray beam.

  • How the kilovoltage affects the quality of the x-ray beam.

  • How the milliamperage affects the quality of the x-ray beam.

  • The difference between contrast and density.

Introduction (Slide 1 of 2)

• The dental assistant must have a thorough knowledge and understanding of the importance and uses of dental imaging.

• Dental imaging enables the dentist to see conditions that are not visible in the oral cavity.

• The dental assistant must understand the fundamental concepts of atomic and molecular structure and have a working knowledge of ionizing radiation and the properties of x-rays.

Introduction (Slide 2 of 2)

• Radiation used to produce dental radiographs has the capacity to cause damage to all types of living tissues.

• Any exposure to radiation, no matter how small, has the potential to cause biologic changes to the operator and the patient.

• The dental assistant must have a thorough understanding of the characteristics of radiation to minimize radiation exposure to both the dental patient and the operator.

Uses of Dental Images

• Detect dental caries in the early stages.

• Identify bone loss in the early stages.

• Locate abnormalities in surrounding hard and soft tissues.

• Evaluate growth and development.

• Provide information during dental procedures (such as root canal therapy).

• Document a patient’s condition at a specific time.

Discovery of X-Radiation

• Wilhelm Conrad Roentgen, a Bavarian physicist, discovered the x-ray on November 8, 1895.

• For many years x-rays were referred to as roentgen rays, radiology was referred to as roentgenology, and radiographs were known as roentgenographs.

• During his lifetime, Roentgen was awarded many honors and distinctions, including the first Nobel Prize ever awarded in physics, in 1901.

• First radiograph of the human body, showing the hand of Roentgen's wife.

Pioneers in Dental Radiography

• Otto Walkhoff made the first dental radiograph.

• Dr. C. Edmund Kells, a New Orleans dentist, is credited with the first practical use of radiographs in dentistry, in 1896.

• Dental radiography has progressed from these early discoveries to the science it is today.

• New technology continues to improve our diagnostic abilities.

Earlier Experimentation

• Heinrich Geissler – 1838 Built the first vacuum tube.

• Johann Hittorf – 1870 Used the vacuum tube to study fluorescence.

• William Crookes – Late 1870s Discovered that cathode rays were streams of charged particles.

• Philip Lenard – 1894 Discovered that cathode rays could penetrate a thin window of aluminum foil.

History of Dental X-Ray Equipment

• William Coolidge – 1913 Developed the first hot-cathode x-ray tube.

• Victor X-Ray Corporation – 1923 Oil immersion of the tubehead.

• 1957 Variable kVp machine.

• 1966 Recessed long-beam tubehead.

Radiation Physics

• All things in this world are composed of energy and matter.

• Atoms are the basic form of matter, and they contain energy.

• Energy is defined as the capacity to do work.

• Matter is anything that occupies space and has form or shape.

• Matter is made up of specific arrangements of atoms called molecules.

Atomic Structure

• An atom has two parts: Central nucleus and orbiting electrons.

• Identified by composition of nucleus and arrangement of orbiting electrons.

• Electrons remain stable in their orbit unless disturbed or moved.

• X-rays can disturb orbiting electrons.

Nucleus

• The nucleus, or dense core, of the atom is composed of particles known as protons and neutrons.

• Protons carry positive electrical charges; neutrons carry no electrical charge.

• Dental x-rays do not affect the tightly bound nucleus of the atom and are only changed in direction or scattered.

• Dental x-rays cannot make atoms radioactive; therefore patients do not give off x-rays after the x-ray machine stops producing x-rays.

Electrons

• Electrons are tiny, negatively charged particles with very little mass.

• Electrons orbit around the nucleus of an atom.

• The orbit path of an electron is called an electron shell.

• Each shell can contain only a specific number of electrons.

• The electrons are maintained in orbit by electron-binding energy, a force similar to the force of gravity on earth.

Ionization

• Electrons remain stable in their orbits around the nucleus until x-ray photons collide with them.

• A photon is a minute bundle of pure energy that has no weight or mass.

• Ions are atoms that gain or lose an electron and become electrically unbalanced.

• X-rays have enough energy to push an electron out of its orbit, producing an ion (an atom that gains or loses an electron and becomes electrically unbalanced) in a process called ionization. Damage can occur.

Bremsstrahlung Radiation

• Bremsstrahlung radiation (bremsstrahlung from the German word for “braking”) is the primary kind of radiation produced in the dental x-ray tubehead.

• This type of radiation is produced when an electron from the cathode directly hits the nucleus of a target atom, causing it to stop suddenly, or passes so close to the nucleus of a target atom that the negatively charged (–) electron is pulled off course by the positively charged (+) nucleus, slowing it down considerably.

• Energy lost by deceleration of the electron is emitted in the form of either heat or radiation.

Page 17: Properties of X-Rays

• X-rays are a form of energy that can penetrate matter.

• X-rays belong to a group called electromagnetic radiation.

• Electromagnetic radiation is made up of photons that travel through space at the speed of light in a straight line with a wavelike motion.

• The shorter the wavelength of the x-ray, the greater is its energy.

• Electromagnetic spectrum shows the various wavelengths of radiation typically used.

Page 18: Components of the Dental X-Ray Machine

• Dental x-ray machines have three primary components: the tubehead, an extension arm, and the control panel.

• NOMAD hand-held x-ray machine.

• Label x-ray machine.

Page 19: Tubehead

• The x-ray tubehead is tightly sealed and contains the x-ray tube that produces dental x-rays.

• Tube head manor.

Page 20: Components of the Tubehead (Slide 1 of 2)

• The metal body of the tubehead is called the metal housing, filled with insulating oil.

• The tubehead seal is made of leaded glass or aluminum and acts as a filter for the x-ray beam.

• The x-ray tube is where x-rays are produced.

• The transformer alters the voltage of incoming electrical current.

• The lead collimator controls the size and shape of the primary x-ray beam as it leaves the tubehead.

Page 21: Components of the Tubehead (Slide 2 of 2)

• The aluminum filter is an aluminum sheet 0.5 mm thick.

• The lead collimator controls the size and shape of the x-ray beam as it leaves the tubehead.

• The PID is the open-ended, lead-lined cylinder used to aim the x-ray beam.

Page 22: The X-Ray Tube

• The x-ray tube is the heart of the x-ray-generating system.

• It is made of glass and is about 6 inches long and 1 inch in diameter.

• The vacuum environment allows the electrons to flow with minimum resistance between the electrodes.

• The cathode and anode are the two electrodes.

Page 23: Cathode

• The cathode consists of a tungsten filament in a focusing cup made of molybdenum.

• The purpose of the cathode is to supply the electrons necessary to generate x-rays.

• Electrons are generated in the x-ray tube at the cathode.

• The hotter the filament becomes, the more electrons are produced.

Page 24: Anode

• The anode is the target for the electrons.

• It is composed of a tungsten target embedded in the larger copper stem.

• The copper around the target conducts heat away from the target.

• The tungsten target serves as a focal spot and converts the bombarding electrons into x-ray photons.

• The x-rays at the center of this beam are known as the central ray.

Page 25: Position Indicator Device (PID)

• The lead-lined PID is used to aim the x-ray beam at the film in the patient's mouth.

• The open end of the PID is placed against the patient's face during film exposure.

• The PID may be cylindrical or rectangular.

• Take out PID and point it towards the mannequin.

Page 26: Extension Arm

• The extension arm encloses the wire between the tubehead and the control panel.

• It has an important function in positioning the tubehead.

• The extension arm folds up and can be swiveled from side to side.

• The dental assistant or the patient must never hold the tubehead to keep it in place during exposure.

Page 27: Control Panel

• The control panel of an x-ray unit contains the master switch, indicator light, selector buttons, and exposure button.

• Control devices such as time, milliamperage (mA) selector, and kilovoltage (kVp) selector are present.

• A single, centrally located control panel may be used to operate several tubeheads located in separate treatment rooms.

Page 28: Master Switch and Indicator Lights

• The master switch is used to turn the machine on and off.

• The orange indicator light shows when the master switch is on.

• The red emission indicator light comes on only when the exposure button is being pushed and x-rays are being emitted.

Page 29: Exposure Button and Selector Buttons

• The exposure button controls the flow of electricity to generate the x-rays.

• Exposure time is measured in fractions of a second, called impulses.

• Milliamperage (mA) is a measure of electrical current passing through the tungsten filament.

• Kilovoltage peak (kVp) selector is used to control the penetrating power of the x-ray beam.

Page 30: X-Ray Production (Slide 1 of 3)

• The x-ray machine is plugged into the wall outlet, and when the machine is turned on, the electric current enters the control panel.

• Current travels from the control panel to the tubehead through electrical wires in the extension arm.

• Current travels through the step-down transformer to the filament of the cathode.

• The filament circuit uses 3 to 5 V to heat the tungsten filament in the cathode portion of the x-ray tube.

• Heating of the filament results in thermionic emission.

Page 31: X-Ray Production (Slide 2 of 3)

• When the exposure button is pushed, the high-voltage circuit is activated.

• The electrons in the cloud are accelerated across the x-ray tube to the anode.

• The molybdenum cup in the cathode directs the electrons to the tungsten target in the anode.

• The electrons travel from the cathode to the anode.

• When the electrons strike the tungsten target, their energy of motion is converted to x-ray energy and heat.

Page 32: X-Ray Production (Slide 3 of 3)

• Less than 1% of the energy is converted to x-rays; the remaining 99% is lost as heat.

• Heat is carried away from the copper stem and absorbed by the insulating oil in the tubehead.

• X-rays travel through the unleaded glass window, tubehead seal, and aluminum filter.

• The aluminum filter removes the longer-wavelength x-rays.

• The x-ray beam travels through the collimator.

• The x-ray beam then travels down the lead-lined PID and exits at the end of the PID.

Page 33: Interactions of X-Rays with Matter

• X-rays can have four interactions with matter:

  • No interaction

  • Photoelectric effect: charged particles are released from or within a material when it absorbs electromagnetic radiation

  • Compton scatter

  • Coherent scatter

Page 34: Types of Radiation

• Primary radiation: x-rays that come from the target of the x-ray tube

• Secondary radiation: x-radiation created when the primary beam interacts with matter

• Scatter radiation: secondary radiation that occurs when an x-ray beam is deflected from its path by interaction with matter

Page 35: Radiolucent and Radiopaque Characteristics

• Radiolucent structures allow x-rays to pass through them and appear dark or black on the radiograph

  • Examples: air spaces, soft tissues of the body, dental pulp

• Radiopaque structures do not allow x-rays to pass through them and appear white or light gray on the radiograph

  • Examples: metal, enamel, dense areas of bone

Page 36: Characteristics of the X-Ray Beam

• Three characteristics necessary for a good radiograph:

  • Quality: describes the energy or penetrating ability of the x-ray beam

  • Quantity: refers to the number of x-rays produced in the dental x-ray unit

  • Intensity: combination of the number of x-ray photons (quantity) and energy of each photon (quality)

Page 37: Contrast

• Ideal contrast of an image shows radiopaque white of a metal restoration, radiolucent black of air, and many shades of gray between

• Higher kilovoltage produces more penetrating x-rays and lower radiographic contrast

• A 90-kVp setting requires less exposure time and produces a radiograph with low contrast (more shades of gray)

• A 70-kVp setting requires a slightly longer exposure time and produces a radiograph with high contrast (fewer shades of gray)

Page 38: Density

• Density is the overall blackness or darkness of an image

• Correct density enables the dentist to view black areas (air spaces), white areas (enamel, dentin, and bone), and gray areas (soft tissues)

• Degree of density is determined by the milliampere seconds (mAs)

Page 39: Other Factors Influencing Density

• Distance from the x-ray tube to the patient can affect density

• Developing time and temperature can affect overall density

• Body size of the patient can affect the amount of radiation needed

Page 40: Geometric Characteristics

• Three geometric characteristics affect the quality of the radiograph:

  • Sharpness: detail, resolution, or definition

  • Distortion: disproportionate change in size of images caused by excessive or insufficient vertical angulation

  • Magnification: proportionate enlargement of a dental image

Page 41: Sharpness

• Refers to how well the radiograph reproduces the fine details or distinct outlines of an object

• Penumbra refers to the fuzzy or blurred area around an image

• Influenced by focal-spot size, film composition, and movement of the patient or image receptor

Page 42: Learning Objectives Lesson 38.2

• Effects of radiation, measuring radiation, and radiation safety

• Discuss the effects of radiation on the human body

• Discuss how radiation is measured

• Discuss radiation safety, including protecting the patient and operator and explaining the ALARA concept

Page 43: Radiation Effects

• All ionizing radiation is harmful and produces biologic changes in living tissues

• Dental radiography uses small amounts of x-radiation, but biologic changes can occur

• Dental assistants need to understand the harmful effects of radiation and how to discuss the risks with patients

Page 44: Tissue Damage: Ionization

• Ionization is the harmful effect of x-rays that can disrupt cellular metabolism and cause permanent damage to living cells and tissues

• Ionization occurs when electrons are removed from electrically stable atoms through collisions with x-ray photons

• Atoms that lose electrons become positive ions and can interact with and damage other atoms, tissues, or chemicals

Page 45: Biologic Effects of Radiation

• Exposure to radiation can bring about changes in body chemicals, cells, tissues, and organs

• Effects of radiation may not become evident for many years after x-ray exposure (latent period)

Page 46: Cumulative Effects

• Exposure to radiation has a cumulative effect over a lifetime

• Tissues can repair some damage, but they do not return to their original state

• Cumulative effect of radiation exposure can be compared to repeated exposure to the sun's rays

• Cataracts, leukemia, and cancer are effects of cumulative radiation exposure

Page 47: Acute and Chronic Radiation Exposure

• Acute radiation exposure occurs when a large dose of radiation is absorbed in a short period

• Chronic radiation exposure occurs when small amounts of radiation are absorbed repeatedly over a long period

• Effects of chronic radiation exposure may not be observed until years after the original exposure

Page 48: Genetic and Somatic Effects

• X-rays affect both genetic and somatic cells

• Genetic cells (sperm and ova) can pass on damage to succeeding generations

• Somatic tissue cells can be damaged by x-rays, but the damage is not passed on to future generations

Page 49: Critical Organs

• Certain organs are considered critical, including the skin, thyroid gland, lens of the eye, and bone marrow

• The level of effect on these organs can be categorized as high, fairly high, medium, fairly low, or low

Page 50: Radiation Measurement (Slide 1 of 2)

• Radiation can be measured similar to time, distance, and weight.

  • Two sets of systems are used to define the measurement of radiation.

    • The older system is the traditional or standard system.

    • The newer system is the metric equivalent known as the Système Internationale (SI).

Page 51: Radiation Measurement (Slide 2 of 2)

• Traditional units of radiation measurement:

  • Roentgen (R)

  • Radiation absorbed dose (rad)

  • Roentgen equivalent [in] man (rem)

• SI units:

  • Coulombs per kilogram (C/kg)

  • Gray (Gy)

  • Sievert (Sv)

Page 52: Maximum Permissible Dose

• Maximum permissible dose (MPD) of whole-body radiation for occupationally exposed individuals is 5000 mrem (5.0 rem) per year.

  • This amount of radiation carries very little chance of injury.

• For nonoccupationally exposed persons, the current MPD is 500 mrem (5 mSv) per year.

• Dental personnel should strive for an occupational dose of 0 by adhering to strict radiation-protection practices.

Page 53: Radiation Safety

• Background radiation comes from natural sources such as radioactive materials in the ground and cosmic radiation from space.

• Exposure from medical or dental sources is an additional radiation risk.

• The benefit of disease detection from dental radiographs outweighs the risk of biologic damage from receiving small doses of radiation.

Page 54: Dentist’s Responsibilities for Dental Imaging

• Prescribe only images required for diagnostic purposes.

• Ensure proper installation and maintenance of radiographic equipment.

• Provide appropriate shielding to protect staff and patients from radiation effects.

• Require proper training and supervision for anyone exposing radiographs.

• Obey state radiographic licensing requirements, rules, and regulations.

• Participate in obtaining informed consent.

Page 55: Protective Devices

• The dental tubehead must be equipped with certain appropriate components:

  • Aluminum filters 0.5 thick.

  • Lead collimators 2.75.

  • PIDs rectangular.

• Equipment should be regularly checked by state or federal regulating agencies.

• Faulty or malfunctioning equipment should be repaired immediately.

Page 56: Aluminum Filtration

• The purpose of the aluminum filter is to remove low-energy, long-wavelength, and least penetrating x-rays from the x-ray beam.

• X-ray machines operating at 70 kVp or higher must have aluminum filtration of 2.5 mm as a federal requirement.

Page 57: Collimator

• The collimator is used to restrict the size and shape of the x-ray beam to reduce patient exposure.

• A collimator may have either a round or rectangular opening.

• A rectangular collimator restricts the beam to an area slightly larger than a size 2 intraoral image and significantly reduces patient exposure.

Page 58: Position Indicator Device

• The PID appears as an extension of the x-ray tubehead.

• It is used to direct the x-ray beam.

• Round and rectangular PIDs are available in two lengths:

  • Short (8-inch)

  • Long (16-inch)

Page 59: Illustrations of PIDs on Radiation Exposure

• Illustrations show the effect of different types of PIDs on the amount of radiation exposure a patient would receive.

Page 60: Patient Protection

• Lead apron and thyroid collar must be used on all patients for all exposures.

  • The lead apron should cover the patient from the neck to the lap to protect reproductive and blood-forming tissues from scatter radiation.

• Many states mandate the use of a lead apron.

Page 61: Image Receptor-Holding Devices

• The use of a film/receptor-holding instrument keeps the patient’s hands and fingers from being exposed to x-radiation.

• These devices also keep the film or receptor in a stable position and help the operator properly position the film or sensor and the PID.

Page 62: Exposure Factor

• Using the proper exposure factors limits the amount of x-radiation to which the patient is exposed.

• Adjusting the kilovoltage peak, milliamperage, and time settings controls the exposure factors.

• A setting of 70 to 90 kVp keeps patient exposure to a minimum.

• On some dental units, the kilovoltage peak and milliamperage settings are preset by the manufacturer and cannot be adjusted.

Page 63: Proper Technique

• Proper technique is necessary to ensure diagnostic quality images and reduce patient exposure to radiation.

• Nondiagnostic images must be retaken, resulting in additional radiation exposure to the patient.

• Retakes are a major cause of unnecessary radiation exposure and must be avoided.

Page 64: X-Rays During Pregnancy

• Dental radiographic procedures do not need to be altered because of pregnancy according to the Guidelines for Prescribing Dental Radiographs.

• The use of a lead apron during radiographic procedures nearly eliminates radiation exposure in the pelvic region.

• There is no detectable exposure to the embryo or fetus with the use of a lead apron.

Page 65: Operator Protection and Monitoring

• Failure to follow radiation protection rules may result in chronic radiation exposure for dental assistants.

• By following the rules, dental personnel can keep their radiation exposure to zero.

Page 66: Radiation Monitoring

• Three types of monitoring devices are used to determine the amount of radiation exposure to personnel:

  • Film badge

  • Pocket dosimeter (pen style)

  • Thermoluminescent, or TLD

• Radiation monitoring badges must be removed when the wearer is having medical or dental x-ray films taken because they measure only occupational exposure.

• If the operator's film badge indicates exposure to small amounts of radiation, the office should evaluate their techniques and equipment.

Page 68: Rules of Radiation Protection

• Never stand in the direct line of the primary beam.

• Always stand behind a lead barrier or the proper thickness of drywall if available.

• If a lead barrier is not available, stand at right angles to the beam.

• Never stand closer than 6 feet to the x-ray unit during an exposure unless behind a barrier.

Page 69: Equipment Monitoring

• Dental x-ray machines must be monitored for radiation leakage

  • If a dental x-ray tubehead has a faulty tubehead seal, leakage results

• Dental x-ray equipment can be monitored through the use of a calibration device

  • Calibration device can be obtained from the manufacturer or from the state health department

Page 70: Pediatric Patients

• Child's first dental check-up with Dentist taking xrays on pedo

• If the patient is a child who is unable to cooperate, he or she is seated on the parent’s lap in the dental chair

• Both the parent and child are covered with the lead apron

• The parent holds the film or sensor in place

Page 71: ALARA Concept

• The ALARA concept states that all exposure to radiation must be kept to a minimum, or “as low as reasonably achievable”

• Every possible method of reducing exposure to radiation should be used to minimize risk

• Radiation protection measures detailed in this chapter should be used to minimize patient, operator, and staff exposure, keeping radiation exposure “ALARA”

Page 72: Patient Questions (Slide 1 of 2)

• Patients often have questions and concerns about radiation

• Dental assistant must be prepared to answer such questions and educate the dental patient about the importance of radiographs

Page 73: Patient Questions (Slide 2 of 2)

• Examples of comments to make to patients during informal discussions:

  • “The doctor orders x-rays on the basis of your individual needs”

  • “Our office takes every step possible to protect you from unnecessary radiation”

  • “We use a lead apron and thyroid collar to protect your body from stray radiation”

  • “We use a high-speed film or sensor that requires only minimal amounts of radiation”

  • “Do you have any questions before we begin?”