Course Intro, Physics, Biology, and Safety Review

Lecture given 3/5/2026

What did Wilhelm Rontgen do?

Discovered X-rays in november, 1895

won nobel prize in physics in 1901

When were X-rays discovered ?

1895

Who is Otto Walkhoff?

Obtained first intraoral radiograph with exposure time of 25 mins

Wilhelm Koenig

obtained 14 radiographs of his own teeth using exposure time of 9 mins/tooth

Edmund C. Kells

took the first radiographs in the United states, 1896

Frank Harrison

first dentist to use radiology in england

published first adverse effects of radiation in 1896

William H. Rollins

among first to warn about adverse effects of radiation

1st commercial dental radiographic apparatus introduced in ____

Germany, 1905

Howard R. Raper

Introduced radiology into dental training in 1909, wrote first textbook abt dentistry in 1913

radiation

emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles which cause ionization

particulates

small fast-moving particles that have both energy and mass

particulate radiation is primarily produced by …

disintegration of an unstable atom and includes alpha and beta particles

t/f small, fast-moving particles that has only mass is called particulate radiation

false- has both energy and mass

electromagnetic

energy with no mass, vibrating or pulsating waves of electrical and magnetic energy

t/f radiation can be ionizing or non-ionizing

true

ionizing radiation changes the number of electrons of an atom

what are the types of ionizing radiation?

x-rays, ultraviolet radiation, alpha/beta/neutron particles, gamma rays

non-ionizing radiation / electromagnetic radiation

does not carry enough energy

visible light, microwaves, radio waves

t/f radio waves have the highest energy and shortest wavelength, while gamma rays have lowest energy and longest wavelength

false- opposite

R, M, IR, V, UV, X, G

what are the units of current?

measured in milliAmperes (mA)

what are the units of voltage?

measured in kiloVoltage (kV)

voltage as peak value/max voltage supplied (kVp)

what are the units of time?

measured in milliSeconds (s)

integrated exposure

product of mA and s: (mAs)

what are the components of an x ray machine?

cathode, anode, oil, power supply

what is this?

tube head

what is this?

xray tube

what is this?

cathode

what is this?

anode

focusing cup

focuses the electrons on to anode, cup is negatively charged, helps converge the electrons to the andode (target)

What charge is the focusing cup ?

negatively charge, helps to converge the electrons to the anode

what direction do electrons move- cathode to anode or anode to cathode?

cathode to anode

cathode

negative electrode, electrode source (aka filament of tungsten)

*what are the advantages of tungsten?

high atomic number (74), high melting point (3370C), good absorber and dissipater of heat, easily available, economical

what is the tungsten target (anode) bonded to?

large copper block- for better thermal distribution

which is an advantages of tungsten?

A.Low atomic number 55

B. Low Melting point 2270

C. Not easily available

D. Good absorber and distributer of heat

E. tungsten target (anode) bonded to large silver block for better thermal distribution

D. Good absorber and distributer of heat

electron production

filament is heated by allowing a current to flow through it

filament offers resistance, gets heated, then e- emission occurs (boils off)

filament current

current used to heat filament, controls # of electrons boiled off

tube current

electron flows from cathode to anode, uses mA units

filament transformer → voltage → heat → electrons emitted by cathode

electron flow from cathode to anode

quantity of electrons (mA)

increase in time increses the quantity of electrons and increases the number of x rays

beam quantity or beam intensity

what is the electron cloud/space charge?

cloud of electrons around filament from thermionic emission

fewer electrions being focused on the target

need to potential difference to pull these away from the cathode to the anode

anode

positive electrode at high potential difference, small tungsten plate (target) embedded in a large block of copper

major source of heat production

*stationary or rotating

what is major source of heat production ?

anode

*what are the characteristics of a stationary anode?

2-3 mm thick tungsten embedded in Cu, 1×1 cm dimensions

high atomic number/melting pt (3370 C), good heat absorber/dissipater, easily available, not very expensive

The wear and tear of a ____________ is less than half of the ____________

rotating anode / stationary anode

rotating anode

more heat tolerant/efficient, lesser cooling time/damage to anode, 3,600-10,000 rpm makes it more efficient at dissipating heat

*what are characteristics of an ideal material?

high atomic number, high melting point, high thermal conductivity, low vapor pressure

how are x-rays formed through electrons ?

e- accelerated from cathode to anode by high voltage (potential difference); e- strike anode, suddenly decelerated, energy lost is converted to x rays

what does the glass enclosure do?

provides a vacuum

if e- collide with gas molecules, lose energy, produce secondary e-, change #/energy of e-

is the goal to have a large or small focal spot?

small

*what is the line focus principle?

anode surface must be angled away from cathode, increased surface area presented to e- beam

apparent/effective focal spot size remains small, heat produced still distributed over same large area

effective focal spot

aka the x ray beam, want small

actual focal spot

electrode from cathode to anode, want big

the line focus principle is an area it the ___ of the anode

tilted

why is the tilt of the anode important in the line focus principle?

there is a better heat spread without compromising on resolution and maintaining smaller penumbra (shadow)

is the production of x-rays an energy effective proccess?

no

99% of energy converted to heat, only 1% to xray

why is heat dissipation needed?

prevent disruption of target surface: roughening, pitting, cracking etc.

what are the heat dissipation mechanisms?

radiation (though vacuum), convection (though surrounding oil and tube housing), conduction (through solid tube parts like copper)

what does the power supply do?

provides low voltage current to the filament, has high potential difference to accelerate the e-

tube voltage

increasing → kVp → electron energy → autotransformer

timer controls x ray exposure

what is the typical voltage of intra oral/ceph/pano x rays?

60-90 kVp

what is the typical voltage of CBCT?

90-120 kVp

bremsstrahlung radiation

electron passes by the nucleus, giving off photons of differing energies

electron collides with the nucleus, oblitering the electron

electron hitting target atom may be completely stopped (max energy x ray) OR deflected (lower energy photon)

continuous spectrum of photon energy ranging from near zero to a maximum

*energy is measured in keV

maximum energy will be equal to kVp

characteristic radiation

e- collides with an inner shell e-

photons with the same amount of energy

what are x-rays made of?

photons

what is the percentage of photon production and heat production?

1% photon, 99% heat- not an effective process

what factors affect controlling beam quality?

mA (tube current), kVp (energy), filtration (energy), exposure time, collimation (shape), distance (intensity)

what is the effect of current on x-ray production?

more current = more quantity of xrays, but energy stays the same

Define tube voltage peak (kVp)

increasing kVp- potential difference between cathode and anode

photon energy, number of photons generated

beam quality

how does energy of x ray vary with voltage?

increased voltage = high energy x rays (higher quality and density)

how does time relate to exposure?

increased time = increased exposure

filtration

the process of removing all photons that do not contribute significantly to image formation

removes most of the low energy photons that only add to the patient’s exposure, as well as some of the high energy photons

mean (average) energy of the beam goes up

*what are the benefits of filtration?

reduces patient dose, improves image contrast

inherent filtration

glass tube, oil, metal housing

equivalent of 0.5-2 mm aluminum

added filtration

aluminum disc placed over port to prevent low energy x-rays from exiting port

total filtration

inherent filtration + added filtration

*government regulations for x-ray machines 50-70 kVp are regulated to use ______ mm aluminum equiv

1.5mm

*government regulations for x-ray machines above 70 kVp are regulated to use ______ mm aluminum equiv

2.5 mm

collimation

process of shaping beam to make it no bigger than the size of receptor,

lead lined, focuses an x ray beam on the target

can be round or rectangular

protects a patient from non-diagnostic radiation

what are dental x ray beams collimated to?

a circle 2.75 inches (7cm) in diameter

what are the advantages of collimation?

less patient exposure, less operator exposure, less scatter generation and so improved contrast

*inverse square law

intensity of beam inversely proportional to the square of the distance between the source and target

what are the variables for the inverse square law?

I1- initial beam intensity

I2- beam intensity at a new location

D1- original distance from the source when intensity was I1

D2- distance of the new location from the source

if the intensity of beam at 2m from an x-ray source is ‘x’, what will the intensity be at a distance of 1m?

I2 = 4x

what percentage of x-ray beams have no interaction?

9%

what percentage of x-ray beams scatter coherently?

7%

what percentage of x-ray beams exhibit photoelectric absorption?

27%

what percentage of x-ray beams compton scatter?

57%

what type of beam attenuation is desired?

photoelectric absorption (27%)

what type of beam attenuation is unwanted?

compton scattering (57%)

what is coherent scattering?

incoming x ray photon is deflected by the electrostatic field of an outer orbital electron

resultant photon changes direction without loss of energy

only interaction where no energy loss occurs with change in direction

8% of all interactions

classical, rayleigh, or elastic scattering

compton scattering?

caused when an x ray photon scatters off an electrion, ejecting it from orbit

recoil electron, scattered photon (may exit tissue or interact with more material)

decreases contrast (62% of all interactions)

probability directly proportional to electron density

probability of occurance increases with energy of incident photon

attenuation of the beam is greater in bone than soft tissue

creates fog on the images

where do most interactions of photoelectric absorption take place?

k shell because the electron density is highest here

photoelectric absorption

gives the characteristic x-ray formation, most interactions take place in the k shell

approx 30% of all interactions

how does photoelectric absorption work?

x-ray photon strikes an electron near the nucleus with enough energy to knock it off its orbit, overcoming the binding energy

the photon is totally absorbed and its energy is transferred to the ejected / recoil electron

tldr how can a photon with e- interact with matter?

no interaction

coherent- causes vibration, photon with same energy but different direction, no information gained

compton- outer shell e-, creates fog

photoelectric- inner shell e-, characteristic radiation, photons with the same amount of energy, what we want!

beam attenuation

the reduction in the intensity of x-ray beams as it traverses matter by either absorption or deflection of photons from the beam

measured using the half value layer (HVL)

HVL

the thickness of any material required to reduce the intensity of the beam in half

beam hardening

mean energy of the beam is increase

what factors affect attenuation?

energy of radiation, atomic number (z) of material through which the beam passes, tissue density, electron density

differential attenuation

image contrast

different body parts attenuate the x ray beam to different extents depending on their density, thickness, energy of the beam, beam size, ect

exposure

ability of x rays or gamma rays to ionize air, measured as a charge per mass of air

traditional unit was roentgen (R) which was described as 1R = 2.58 × 10C/kg

measures the intensity of the radiation field

R replaced by the SI equivalent of air kerma

kerma

kinetic energy released in matter

measure of the energy transferred from photons to electrons

measured in gray (Gy)

1 gray = 1 J/kg