Mod 1 BS II

What images are useful?

Diagnostic images!

In film-screen combinations, how is the image produced?

By visible light photons

What is the effect of faster screens on film-screen combinations?

Reduce dose but decrease image quality

What affects image quality in film-screen combinations?

Size and shape of phosphor crystals

Because film is double sided, how many screens are used in combination?

2

Describe standard screens

blue light-emitting, calcium tungstate

Describe rare earth screens

Green light-emitting gadolinium or lanthanum

What is the canthomeatal plane?

From the corner of the eye to the middle ear

What is the frankfort plane horizontal?

From base of eye to ear and hits the mid-point of nose

What is the coronal plane?

divides front and back

What is the sagittal plane?

divides left and right

What is the axial plane?

Cut horizontally above the eyebrows

What is the ala-tragus plane?

From the nostril to the middle of the ear

Describe the lateral cephalometric projection

Image receptor is parallel to pts side of interest with beam pointed perpendicular to the receptor

What does the submentovertex projection give insight to?

Skull base and condyle position as well as cheek bones and sinuses, looking down at the skull from above

What does the jug handle view of the submentovertex projection allow us to see?

The zygomatic arches

What is the Waters or Occipito-Menton projection?

canthomeatal plane forms 37 angle with image receptor, pt faces receptor

What does the waters projection give insight to?

Sinuses, cheek bones, septum and mandible

What is the towne's veiw of the skull?

The anterior-posterior view where pt facing away from receptor and chin tilted down -30 degrees

What is the reverse towne projection?

The pt is facing the receptor with mouth open and chin tilted down -30 degrees

What do MRIs help us study?

Soft tissues

Why would we use a panoramic image?

To see dentition, joints, cysts, trauma, can't get intraoral images

What are the advantages of panoramic images?

Broad coverage, low radiation dose, easy, quick

What are disadvantages of panoramic images?

Magnification of image, low resolution, ghost images, positioning errors, difficult to decipher

What happens when the mandible is at the center of the focal trough?

Minimal distortion of image

What happens if the mandible is posterior to focal trough?

Widening of image

What happens if the mandible is anterior (too front) to the focal trough?

Lengthening of image

Why do we use an upward projection of the beam in panoramic images?

So that the beam spreads out and we can see vertical relationships of mandible and maxilla

If pt is rotated upward for a pan, what happens?

Overlapping images and hard palate obscures roots of teeth

If the pt is rotated downward for a pan, what happens?

The anterior teeth are distorted and cutting off symphyseal region

What happens if the tongue is not placed on the roof of the mouth?

Air is present and you cant see roots of teeth

What is Wilhelm Roentgen's contribution to dentistry?

Discovered x-rays

What is Otto Walkhoff known for?

The first dental radiograph

What was W.J. Morton known for?

The first radiograph of a skull

What was C. Edmund Kells known for?

The first dental radiograph on a LIVE person

What was William Rollins known for?

The first paper on the dangers of x-radiation

Who is considered the father of dental radiology?

Dr. C Edmund Kells

What is Howard Raper known for?

The introduction of oral and maxillofacial radiology to dental school curriculum, inventor of the bitewing, textbook on dental radiology

What are electrons?

Tiny, negatively charged particles

How do electrons travel around the nucleus?

In orbits that are maintained by electrostatic forces with the nuclei

Would an electron closer or farther from the nucleus have high energy?

Closer

What determines the binding energy of an electron?

The distance from the nucleus

What shell has the highest binding energy?

K shell —> need ≥70 keV to knockout

How is binding energy measured?

By electron volts

What is ionization?

The production of ions by converting an atom to ions

How does an atom become an ion?

An electron is ejected and the atom becomes positively charged (positive ion) and the electron plays the negative ion role

What is particulate radiation?

Tiny particles of matter that possess mass and travel in straight lines at high speed

What are the four types of particulate radiation?

Electrons, alpha particles, protons, and neutrons

Describe electrons

Fast moving beta particles emitted from the nucleus of radioactive atoms

What are alpha particlees?

Emitted from nuclei of heavy metals and exist as two protons and neutrons without electrons

What are protons?

Accelerated hydrogen nuclei with a mass and charge of 1

What are neutrons?

Accelerated particles with a mass of 1 and no electrical charge

What is the particle concept?

It characterizes electromagnetic radiation in terms of discrete bundles of energy called photons or quanta

Do photons have mass or weight?

No

How do photons travel?

as waves at the speed of light and move through space in a straight line

What is velocity?

The speed of the wave

What is wavelength?

The distance between crests

What is frequency?

the number of wavelengths that pass a fixed point in a given time frame

What are the three parts of the x-ray machines?

Control panel, extension arm and tubehead

What does the extension arm house?

the electrical wires that extend from the control panel to the tubehead

What is in the tubehead?

tightly sealed, heavy metal housing that contains the x-ray tube that produces dental x-rays

What is the purpose of insulating oil?

to prevent overheating

What is the purpose of the tubehead seal?

To permit exit of x-rays, seals oils and filters x-ray beam

What do aluminum disks do in the tubehead?

Filter non-penetrating, longer wavelength x-rays

What does the lead collimator do in the tubehead?

Restricts size of x-ray beam

What does the PID do?

Aims and shapes the x-ray beam

Describe the x-ray tube

Glass vacuum tube that includes leaded glass housing, cathode and anode

Describe the cathode

Negative electrode that has tungsten filament that produces electrons, molybdenum cup focuses electrons to a beam towards the tungsten target

How do electrons travel from the cathode to the anode?

By repellent forces of negative cathode and attractive forces of positive anode

Describe the anode

Positive electrode with tungsten plate that converts energy from electrons into x-ray photons

What is the purpose of a copper stem in the anode?

To dissipate heat away from the tungsten target

Describe tungsten

Most efficient in producing x-rays, high melting point and thermal conductivity

Describe filament circuits

3-5 volts, regulates flow to the filament, controlled by mA

Describe high-voltage circuits

65000-100000 volts (65-100kV), provides high voltage needed for x-ray, controlled by kV

How much energy is converted to x-rays?

Less than 1%

What is bremsstrahlung radiation?

When an e- gets close to the nucleus and “brakes” or slows down and results in an x-ray photon with lower energy → this is a braking or general radiation

What constitutes most x-rays that are produced?

Bremsstrahlung radiation

What is characteristic radiation?

Produced when high speed electron dislodges an inner shell electron from tungsten and causes ionization, electrons rearrange themselves

When does characteristic radiation occur?

≥70 kV

Describe compton scattering

57% of x-rays, degrades imaging and exposes pts, electron ejected from orbit

Describe coherent scattering

7% of x-rays and is minimal contribution to scattering, no loss of energy

Describe photoelectric absorption

27% of x-rays, basis of radiographic image formation

What does wavelength determine?

The energy and penetrating power of radiation

What length of x-rays have a greater penetrating power?

Shorter wavelengths

What does kilovoltage impact?

Quality, the penetrating ability of the x-ray

If voltage is increased, how are electrons impacted?

Their speed is increased and they strike the target with greater force

What kV do we need for dental imaging?

65-100 kV

What is the density of a dental radiograph?

The darkness

If we increase kV, what happens to the density?

The image will appear darker

If we decrease kV, what happens to the density?

The image will appear lighter

What is contrast?

How sharply dark and light areas are differentiated on an image

What is the impact of low kV on contrast?

High contrast, few shades of gray, good for detecting caries

What is the impact of high kV on contast?

Low contrast, many shades of gray, good for detection of periodontal/periapical disease

What does miliamperage affect?

The temperature of the cathode filament

If the mA is increased, what happens?

The temperature of the cathode filament increases and more electrons are produced meaning more x-rays are emitted

If we increase mA, what happens to density of image?

The image will appear darker

What is the inverse square law rule?

The intensity of the radiation is inversely proportional to the square of the distance from the source of radiation

What is the purpose of filtration?

To remove low energy photons, reduce intensity, and increase mean energy of the beam

What is inherent filtration?

Materials in the path of the photon beam from focal spot to exit point

What inherent filtration is there in dental x-rays?

Glass wall of tube, insulating oil, and barrier surrounding oil